In the Electrathon of Tampa Bay series in Florida, our advanced battery class has grown to five cars. It is lively and fun racing. For those of you thinking about trying Lithium, I have put together some Pros and Cons. I hope others will share their experiences and thoughts.
Pros
Equel intial cost: Rhino Lithium-Polymer pack rated at 972 Watt hours/tested at 1,100+ and less than 15 lbs cost around $350 delivered. This is around the same cost as a 840 normal/1008+ tested (Dave Cloud reported) Watt hour pack Optimas.
More races from a pack: Lithium-Polymer batteries can be fully discharged 300-400 times before their capacity is significantly diminished. Lead acid do not do well when fully discharged. Our Deka lead acid pack lasted around 24 full cycles (a season and a half) before it was non competitive. The maxium number of races I have ever heard of a lead acid pack doing is close to 80 races.
Faster: Faster acceleration from 58 pounds less weight. Faster average speed from slightly better usable capacity.
Safety advantages: Being 58 pounds lighter than lead acid car means possibly less kinetic energy in a crash. A spinning car will stop sooner and could do less damage. (See safety negatives as well)
Educational opertunity: Understanding proper operation, charging and maintenance of lithium-polymer batteries is a useful skill in today's world.
Variety: Number of voltage options broadens choices of controllers and motors espectially from the remote control and electric bicycle market.
Cons
Risk of damage to batteries: Lithium-Polymer is less tolerant of damage (such as improper charging and discharging) than lead acid so damage from accidental misuse could drive up costs.
Risk of damage to equipment and facilities: Over-charging and over-discharging create the possibility of fire.
Lack of institutional knowledge about Lithium-Polymer: Lead acid batteries can cause fires and can be damaged by improper charging and discharging but a wealth of experience minimises these dangers. Experience with Lithium-Polymer is less wide spread.
Safety disadvantages: Slightly higher speeds due to faster acceleration from lighter vehicle weights and higher average speeds from more usable capacity means possible increase of kinetic energy in a crash.
Requires additional equipment: Most teams will need to buy a Lithium specific charger. They cost around the same amount as a good three stage lead acid charger. Additional wiring is required to monitor individual cell voltages. Individual cell voltage monitors should be used but are very inexpensive ($4 to monitor 6 cells).
Institutional inertia: It can be difficult to convince funding organizations to approve purchase of components that do not have a long and proven history of use.
Lack of competition: Unless other teams in the region commit to switching over, a team runs the risk of being the only car in their class.
Unknowns
Calender life: Batteries lose capacity from aging. This is true for lead acid but is less of a problem in electrathon racing since lead acid cycle life is very short. Lithium-Polymer batteries have reported calender life ranging from 3 to 8 years.
Archer321 said
Apr 12, 2017
All good points.
My reason for sticking with lead acid is a little more fundamental.
The races I have participated in have never had more than a handful of open class cars and no experimental battery cars.
This means that the majority of what is on the track is high school lead acid cars.
I really enjoy talking with students about Electrathon so by staying with lead acid myself I can lead by example (or follow by example sometimes) and the conversations stay apples to apples.
I look forward to seeing an experimental battery car run in person sometime.
Brendan_Smith said
Apr 13, 2017
I did the same balancing act recently to decide what I was going to use in a few projects, including my Electrathon build that I'm aiming for in November.
Comparative to LiPo;
+ Improved shelf life (about 50%) , particularly at non-ideal parked charges
+ Improved cycle life (about 100%)
+ Best available explosivity, incendiary and puncture safety
- Between 15-35% increased capital cost (but cheaper life-cycle overall)
- About 40% increase in weight, 30% volume for the same capacity
Otherwise the two are quite comparable.
While not the highest potential performance, the gain in stability over time is brilliant and, in the age where there's discussion of regulation on chemical capacitive technology such as Tesla Powerwall in my home country, having dependable, safe tech in place is a great thing.
But, if going for outright performance, I'd have gone LiPo too!
ProEV said
Apr 14, 2017
Archer,
We ran lead acid for two season because we felt it was essential to understand the series. We were fortunate that there were a couple of Open class racers who were already pushing the technology in fun ways (espectially an unforgettable leaner design) and wanting to build an advanced battery class.
ProEV said
Apr 14, 2017
Brendan,
I think in the long term, the HS class teams will want to migrate to more advanced batteries. For this to happen, there will need to be a proven standard 'plug and play' system. Reliability, robustness and long term costs will be more important than ultimate performance, so Lithium-Polymer might not be the best choice. What chemistry are you looking at?
meangreen said
Apr 15, 2017
I can add a little of my experience to the lead-acid story. First, when I started in Electrathon in 2002 there were no Experimental class cars in Florida. In fact, we were still running the old flooded cell lead-acid batteries. They didn't perform worth a hoot and half the cars never finished a race! I think it was 2005 when the rules were changed to require Gel-Cell or AGM leakproof batteries. Not only was this a huge step forward in safety, but the batteries performed much better. I was the mentor of a 3-car team (at Astronaut High School) back then and we bought 12 Optima red top batteries (two pair for each car; cost approx. $1800). Back then we only ran 3 or 4 races per season. The red tops lasted two seasons and started losing performance dramatically after that. When I retired from teaching I built two new cars for myself and I bought 8 new Optima yellow top batteries ($1450). That was the Spring of 2010. I ran those batteries until January of 2016 when I sold them with my cars. They were showing no loss of performance and the team that bought them continued racing with those 6-year-old batteries. In February of 2016 I built another new car and bought 4 new Optima yellow tops ($800).
The points of my story: (1) If you are going to run lead-acid batteries, Optima yellow tops are expensive initially, but amortized over 6-year life expectancy cost isn't bad. They require proper care to make them live that long - fast charging them at high amperage will kill them in just over a year. Yellow tops are supposed to be good for 300 cycles; red tops are only good for about 30 cycles (as are a lot of other AGM batteries) making their true cost higher because of more frequent replacement.(2) To take proper care of them you need a charger that brings them up in stages. The charger I use was $322. (3) The initial cost of running Lithium-Polymer may actually be less expensive.
If I was just starting out now I would probably go with Lithium. To change over now is cost prohibitive to me. Also, I'm a mechanic not an electronics wizard; I can fabricate most anything and have designed a very successful and competitive car. Unfortunately, I know nothing about the idiosyncrasies of using Lithium. When someone comes up with a "plug and play" Lithium system maybe my batteries will need replacing again and I'll look into it,.. but I may be re-retired by then.
Archer321 said
Apr 16, 2017
Why would anyone re-retire from Electrathon???
Brendan_Smith said
Apr 17, 2017
Hi Cliff,
Only after reading your post did I realise I didn't even end up placing the chemistry selected on the message!
I have a pair of LiFePO4 batteries sitting in the cart at BlueMySky (bmsbattery.com) ready for purchase for when I hit the "go" button.
The critical mass of users appears to have been reached that there's a good number of shelf batteries available for a comparable cost, and with outputs that match well to Electrathon requirements, particularly if experimenting with higher voltages and/or brushless motors.
dmorgan said
Apr 28, 2017
A lot of the GA cars have gone to small wheelchair batteries and 36 volts. I did this simply because of cost. I bought 6 Duracell batteries for less that $400. A pair of yellow top Optimas cost more than that. The 36 volt gives a little more umph climbing the North Ga mountains too. My only experience with Li-ion batteries has been reading the news about them exploding in flames. I've seen lead acid explode but never a fire.
ProEV said
Oct 9, 2017
Hi fellow Electrathoners,
I thought I would update everyone on what I have learned so far from the Rhino pack. The headline news is that I made an error calculating pack capacity when doing my discharge test. I did the calculations in note pad and thought that my manufactured rated 972 Watt hours pack was delivering over 1,100 Whrs. No such luck. I had an embarrassing race or two where I tried to run the higher rate and ran out of power
I copied my data into Excel and re-did the calculation. At the one hour rate (1C), on the third charge discharge cycle, I got 928 Whrs. I did another discharge test at the 15 cycle and got 912 Whrs. Unlike lead acid, lithium batteries seem to have their highest capacity right away and slowly get worse, so 928 Whrs is the best I expect from this set up.
Interestingly, cycle 6, I did a 25 minute discharge test (2C) and got 911 Whrs which hints that capacity holds up well despite higher discharge rates.
My next idea is to disassemble the pack and test capacity of each of the 9 battery packs. The packs are set up three in series and three in parallel. Then re-assemble the pack so that the total capacity of each paralleled threesome is the same (i.e. weak packs with stronger packs). If I can get a 5% improvement, I will be close to the 972 Whrs rated capacity.
This requires getting out the more accurate battery capacity tester that I built for another project and writing new software for it, so I doubt I will get to it soon. When I do, I will post the results.
Attached is an Excel sheet with the first 20 cycles data. Most cycles occur at races and are not full discharges because other bits and pieces broke. This is all done with a meter and a stop watch, so I am not sure what my margin of error is.
Hmmm...I can't figure out how to attach the Excel file. Anyone have a clue?
-- Edited by ProEV on Monday 9th of October 2017 08:09:47 PM
Zaine Stapleton said
Dec 30, 2018
I can see a big benefit to moving over to lithium powered cars. Had a few questions to ask in regards to this because I've now been flying FPV mini quad copters for around a year and a half now to understand how they work. Yes, they are smaller batteries, but they get the point across.
But, and there is always a but; *you need to know what you are doing with lithium, be it Li-Ion or Li-PO to understand how to keep yourself and everyone around you safe.*
These batteries can be dangerous if not handled and taken care of properly. I've seen one too many fires happen when a FPV quad crashes and the electronics fail (mainly electronic speed controllers or ESCs for short) and those are not fun to see. I haven't seen a battery go off yet, but have heard horror stories. Least there isn't a person strapped onto the quad, but in electrathon racing there is hence the 20 second get out of the car rule.
Questions!!!
1. So, does anything special need to be done to the car besides put something in to monitor cell voltage if you're running a certain number of cells on your battery pack? Can you just wire it up like any normal battery. Currently most of our cars are build for lead acid, but since it's a battery the car's electrical system doesn't car what type of battery you have. As long as it has voltage right? If I were to do it, I'd probably do a 6s setup. Either two batteries in parallel to keep it 6s (25.2v) and keep the somewhat same gearing that I have right now. Or jump up the efficiency with lower current draw on 12s (50.4v). I'd be more inclined to go 12s since it means way less current draw than a 6s parallel setup. The higher the voltage the less current you need to pull the same amount of power out. Only draw back is I'd need to make a special sprocket for the drive wheel to make sure the motor is not getting bogged down by too small of a gearing causing the wheel to spin too fast. This is electrathon racing, not a drag race.
2. How are you putting your batteries in the car? Obviously we're strapping them in to keep them from moving around. But are you putting special padding around and in between the pack(s) to keep them protected from vibrating on the frame? I've had one too many lead acid batteries get worn down over the years due to them vibrating against the frame while driving for a hour around a track. In FPV racing with the quad copters, some people will print up TPU parts on a 3D printer to help protect the batteries in crashes since we tend to hit stuff pretty hard with them. Yeah they're small but they can easily get up to 80-120mph in a split second, granted we're only flying for around two minutes or so in a race. Little longer than that if going out to do freestyle flying around 3-5 minutes depending on throttle management. Or even ten minutes to close to thirty minutes with the long range efficiency quads.
3. What voltage are you charging your cells to and how much are you discharging your packs to? I know there are lithium batteries that are rated as high voltage (HV) that will charge each cell to 4.35 volts per cell which definetly can expand the capacity of the pack but is not recommended for long term use since the packs will degrad faster compared to charging to 4.20 volts per cell. Yes, HV from what I've read will help for the first minute of a race, but since FPV races are only two minutes per heat it's cheaper to just run the packs at a 4.20v charge since the packs will last longer. Speaking of longevity, are you running batteries to 80% discharge? I do know for a fact you cannot run LiPO lower than 3.50v, otherwise you risk the battery getting out of balance and having dead cells as a result of it. There are only a few batteries on the market that meet or almost meet the 15 pound rule that have a per battery watt hour rating of say 621.6. Times that by two you've got 1243.2wh total, BUUUUT you times that number by .8 (for 80% of the total capacity of the battery) and you get 994.56wh no matter if you run it in parallel or series. Current rules state advance/experiemental battery class cannot have a watt hour rating exceeding 1000wh. If you go past 1000, then it's on you to do whatever needs to be done to prevent the batteries from going out of control I guess.
4. Lithium-ion or lithium-polymer? I do know for a fact that lithium-ion can be discharged even lower than LiPO, but cannot charge nearly as fast (at only a .5c rate versus 1c or higher for LiPO) but cannot sustain a certian current draw compared to LiPO. So, what would you use? Li-Ion or LiPO? Personally I feel that LiPO would be more suited for electrathon racing since you'd be on and off the throttle constantly coming out of corners. Yeah little wasteful in power usage, but that's the name of the game. Plus Li-Ion cannot get to a certian tempreture since they are in cylinders they can't expand a little like LiPO does when being used. Plus Li-Ion doesn't like high temperature heat. Also you'd have to make a custom Li-Ion pack. (correct me if I'm wrong on this next part) Last I checked you have to have a manufactured battery with original labels etc. like the lead acid standard class does. No custom batteries. LiPO you can get and they are readily available with the manufacture labels on them, safety info, balance leads, discharge leads, etc. You'd just need to figure out how to get it mounted in the car and keep it from flying out and hitting stuff/make your own connections to hook the whole thing up.
I can't think of anything else since I already have a 6s capable charger to work with. I'd just need to look at getting two of them to test out and see what happens I suppose.
Thanks!
Zaine (BikeGuy)
Also I have a youtube channel and instagram account, look up BikeGuy or BikeGuy_FPV to see awesome flights and racing footage that I've been doing for the past couple of months as of recently and photos/short clips for the last year and a half. I recently got a movie editing program to work with which is super nice to have hence the increase in YT videos.
1 & 3, can be solved with a BMS which you absolutely should have racing, i have used battery buzzers but, they often either come loose and beep early, or some of the pins end up breaking and having to replace them ( although that just may be my experience ), you can buy a BMS based on how may cells your pack have and then it will use the industry standard to limit overdraw and overcharging.
2. we currently put the battery's in an ammo case ( with some holes in the back to ventilate away from the driver in case of an explosion ), it was already a tight fit, we just put 2-3 bungee chords just in case.
4. in the end im not sure if it really matters that much, since all packs are balanced to 1kwh, its going to be up to you if you want a slightly easier time going with lion vs lipos can easily reach 1kwh in 12lbs or less, so its up to you if the 3-5 lbs you save makes a difference to you.
ProEV said
Jan 1, 2019
Zaine Stapleton wrote:
I can see a big benefit to moving over to lithium powered cars. Had a few questions to ask in regards to this because I've now been flying FPV mini quad copters for around a year and a half now to understand how they work. Yes, they are smaller batteries, but they get the point across.
But, and there is always a but; *you need to know what you are doing with lithium, be it Li-Ion or Li-PO to understand how to keep yourself and everyone around you safe.*
These batteries can be dangerous if not handled and taken care of properly. I've seen one too many fires happen when a FPV quad crashes and the electronics fail (mainly electronic speed controllers or ESCs for short) and those are not fun to see. I haven't seen a battery go off yet, but have heard horror stories. Least there isn't a person strapped onto the quad, but in electrathon racing there is hence the 20 second get out of the car rule.
Questions!!!
1. So, does anything special need to be done to the car besides put something in to monitor cell voltage if you're running a certain number of cells on your battery pack? Can you just wire it up like any normal battery. Currently most of our cars are build for lead acid, but since it's a battery the car's electrical system doesn't car what type of battery you have. As long as it has voltage right? If I were to do it, I'd probably do a 6s setup. Either two batteries in parallel to keep it 6s (25.2v) and keep the somewhat same gearing that I have right now. Or jump up the efficiency with lower current draw on 12s (50.4v). I'd be more inclined to go 12s since it means way less current draw than a 6s parallel setup. The higher the voltage the less current you need to pull the same amount of power out. Only draw back is I'd need to make a special sprocket for the drive wheel to make sure the motor is not getting bogged down by too small of a gearing causing the wheel to spin too fast. This is electrathon racing, not a drag race.
The biggest thing is to make sure your controller will work with the new voltage. If your controller is for 24 volts, doubling the voltage to 50 might let the smoke out. Also check minimum voltage. Your six cells in series will range from 18 volts empty to 25.2 full.
Yes, you do need to track each cells voltage. I have had the same experience as 4Trident4 with the battery buzzers. Something comes a little loose and the buzzer goes off prematurely. A nice feature on a controller is a 'soft' voltage cutoff. You set a minimum voltage and the contoller cuts back the current when the voltage sags to the minimum. That gives you both the loss of power and the battery buzzer to protect the batteries.
2. How are you putting your batteries in the car? Obviously we're strapping them in to keep them from moving around. But are you putting special padding around and in between the pack(s) to keep them protected from vibrating on the frame? I've had one too many lead acid batteries get worn down over the years due to them vibrating against the frame while driving for a hour around a track. In FPV racing with the quad copters, some people will print up TPU parts on a 3D printer to help protect the batteries in crashes since we tend to hit stuff pretty hard with them. Yeah they're small but they can easily get up to 80-120mph in a split second, granted we're only flying for around two minutes or so in a race. Little longer than that if going out to do freestyle flying around 3-5 minutes depending on throttle management. Or even ten minutes to close to thirty minutes with the long range efficiency quads.
We pad them with foam as well. It makes sense to put something fire resistant between the driver and the cells. 4TRIDENT4 solution sounds good. Protection but not a sealed container. Vents to direct the energy away from the driver.
3. What voltage are you charging your cells to and how much are you discharging your packs to? I know there are lithium batteries that are rated as high voltage (HV) that will charge each cell to 4.35 volts per cell which definetly can expand the capacity of the pack but is not recommended for long term use since the packs will degrad faster compared to charging to 4.20 volts per cell. Yes, HV from what I've read will help for the first minute of a race, but since FPV races are only two minutes per heat it's cheaper to just run the packs at a 4.20v charge since the packs will last longer. Speaking of longevity, are you running batteries to 80% discharge? I do know for a fact you cannot run LiPO lower than 3.50v, otherwise you risk the battery getting out of balance and having dead cells as a result of it. There are only a few batteries on the market that meet or almost meet the 15 pound rule that have a per battery watt hour rating of say 621.6. Times that by two you've got 1243.2wh total, BUUUUT you times that number by .8 (for 80% of the total capacity of the battery) and you get 994.56wh no matter if you run it in parallel or series. Current rules state advance/experiemental battery class cannot have a watt hour rating exceeding 1000wh. If you go past 1000, then it's on you to do whatever needs to be done to prevent the batteries from going out of control I guess.
My understanding is LIPO cells should not be charged above 4.23 volts. For long life, 4.1 is recommended. I use 4.1 for testing. 4.15 for race. I set my buzzers to go off at 2.9 but my minimum controller voltage is around 3.5 per cell.
The rules state that the manufacture rating can not be above 1,000 Watt hours no matter the weight. From the enforcement side, we can not say people are only going to discharge to 80%, so a 1,243 WHR pack is legal because we do not have an easy way to check that. We can see what the manufacturer says and everyone has the same constraints. Learning how far you can go and not hurt your batteries is going to be part of the challenge.
I would love to see a sealed tracking device that could be issued to teams that would read power used and then cut off power at a set number like 1,000 watts. That way every team could run a slightly bigger pack and not worry about damage. Different classes might have different limits. Lead Acid batteries suffer being discharged to dead so it would be good for that class as well, allowing packs to be competetive for more races. I would make it WiFi so everone could see real time power usage.
4. Lithium-ion or lithium-polymer? I do know for a fact that lithium-ion can be discharged even lower than LiPO, but cannot charge nearly as fast (at only a .5c rate versus 1c or higher for LiPO) but cannot sustain a certian current draw compared to LiPO. So, what would you use? Li-Ion or LiPO? Personally I feel that LiPO would be more suited for electrathon racing since you'd be on and off the throttle constantly coming out of corners. Yeah little wasteful in power usage, but that's the name of the game. Plus Li-Ion cannot get to a certian tempreture since they are in cylinders they can't expand a little like LiPO does when being used. Plus Li-Ion doesn't like high temperature heat. Also you'd have to make a custom Li-Ion pack. (correct me if I'm wrong on this next part) Last I checked you have to have a manufactured battery with original labels etc. like the lead acid standard class does. No custom batteries. LiPO you can get and they are readily available with the manufacture labels on them, safety info, balance leads, discharge leads, etc. You'd just need to figure out how to get it mounted in the car and keep it from flying out and hitting stuff/make your own connections to hook the whole thing up.
There is a lot of confusion here about terms. As far as I know, there are no Lithium Polymer batteries commercially available anymore. Lithium Ion batteries are available both in a starved liquid and polymer form. So what many people call LiPo are actually Lithium Ion Polymer.
Lithium ion batteries have other materials in them. These additives modify the characteristics of the battery. Some batteries have better cycle life, some can deliver higher current. There are a number of different polymers that can be used as well. So all lithium ion batteries are not the same.
Battery manufacturers are often a little vague about what makes up their batteries since this is their propriety edge.
My reading of the rules is that you can not make your own cells or use cells that are not commercial available. My understanding of the rules is that you can use individual commercially available cells and wire them together to create a pack. This is basically what we are doing with lead acid batteries. We wire two batteries together to create a 24 volt pack or three for a 36 volt pack or four for 48. People have also wired together Cyclon lead acid single cell batteries to create a pack.
I can't think of anything else since I already have a 6s capable charger to work with. I'd just need to look at getting two of them to test out and see what happens I suppose.
Thanks!
Zaine (BikeGuy)
Also I have a youtube channel and instagram account, look up BikeGuy or BikeGuy_FPV to see awesome flights and racing footage that I've been doing for the past couple of months as of recently and photos/short clips for the last year and a half. I recently got a movie editing program to work with which is super nice to have hence the increase in YT videos.
"I would love to see a sealed tracking device that could be issued to teams that would read power used and then cut off power at a set number like 1,000 watts. That way every team could run a slightly bigger pack and not worry about damage. Different classes might have different limits. Lead Acid batteries suffer being discharged to dead so it would be good for that class as well, allowing packs to be competetive for more races. I would make it WiFi so everone could see real time power usage."
That sounds awesome!
Getting to watch everyone's real time usage would add a whole new side to the race.
Someone should build that.
Zaine Stapleton said
Apr 2, 2019
So, maybe there could be an exception to the rule. Maybe change it to 15.5 pounds or 16.5 pounds to allow slightly heavier batteries but the correct watt hour rated ones to be used so you can get the best life out of them. Currently there are several packs that could be used if the weight limit was raised by half a pound to one pound. For instance, you could run four 6s 14000mAh Tattu packs in either parallel or series-parallel to up the voltage, but these weigh in around 1882g, times that by four and convert grams to pounds and you get 16.5 pounds. The watt hours still comes in at under 1000wH since it would only be sblebto generate 994wh if following the 80% rule.
Just a thought...
Also those 6s 14000mAh Tattu packs are like $170 each, so not too bad of a price if you ask me.
Zaine (BikeGuy)
Archer321 said
Apr 2, 2019
Zaine Stapleton wrote:
The watt hours still comes in at under 1000wH since it would only be able to generate 994wh if following the 80% rule. Just a thought...
What 80% rule?
Zaine Stapleton said
Apr 2, 2019
For Lipo lacks you discharge to 80% capacity is what I meant to say.
Hello fellow racers,
In the Electrathon of Tampa Bay series in Florida, our advanced battery class has grown to five cars. It is lively and fun racing. For those of you thinking about trying Lithium, I have put together some Pros and Cons. I hope others will share their experiences and thoughts.
Pros
Equel intial cost: Rhino Lithium-Polymer pack rated at 972 Watt hours/tested at 1,100+ and less than 15 lbs cost around $350 delivered. This is around the same cost as a 840 normal/1008+ tested (Dave Cloud reported) Watt hour pack Optimas.
More races from a pack: Lithium-Polymer batteries can be fully discharged 300-400 times before their capacity is significantly diminished. Lead acid do not do well when fully discharged. Our Deka lead acid pack lasted around 24 full cycles (a season and a half) before it was non competitive. The maxium number of races I have ever heard of a lead acid pack doing is close to 80 races.
Faster: Faster acceleration from 58 pounds less weight. Faster average speed from slightly better usable capacity.
Safety advantages: Being 58 pounds lighter than lead acid car means possibly less kinetic energy in a crash. A spinning car will stop sooner and could do less damage. (See safety negatives as well)
Educational opertunity: Understanding proper operation, charging and maintenance of lithium-polymer batteries is a useful skill in today's world.
Variety: Number of voltage options broadens choices of controllers and motors espectially from the remote control and electric bicycle market.
Cons
Risk of damage to batteries: Lithium-Polymer is less tolerant of damage (such as improper charging and discharging) than lead acid so damage from accidental misuse could drive up costs.
Risk of damage to equipment and facilities: Over-charging and over-discharging create the possibility of fire.
Lack of institutional knowledge about Lithium-Polymer: Lead acid batteries can cause fires and can be damaged by improper charging and discharging but a wealth of experience minimises these dangers. Experience with Lithium-Polymer is less wide spread.
Safety disadvantages: Slightly higher speeds due to faster acceleration from lighter vehicle weights and higher average speeds from more usable capacity means possible increase of kinetic energy in a crash.
Requires additional equipment: Most teams will need to buy a Lithium specific charger. They cost around the same amount as a good three stage lead acid charger. Additional wiring is required to monitor individual cell voltages. Individual cell voltage monitors should be used but are very inexpensive ($4 to monitor 6 cells).
Institutional inertia: It can be difficult to convince funding organizations to approve purchase of components that do not have a long and proven history of use.
Lack of competition: Unless other teams in the region commit to switching over, a team runs the risk of being the only car in their class.
Unknowns
Calender life: Batteries lose capacity from aging. This is true for lead acid but is less of a problem in electrathon racing since lead acid cycle life is very short. Lithium-Polymer batteries have reported calender life ranging from 3 to 8 years.
Comparative to LiPo;
+ Improved shelf life (about 50%) , particularly at non-ideal parked charges
+ Improved cycle life (about 100%)
+ Best available explosivity, incendiary and puncture safety
- Between 15-35% increased capital cost (but cheaper life-cycle overall)
- About 40% increase in weight, 30% volume for the same capacity
Otherwise the two are quite comparable.
While not the highest potential performance, the gain in stability over time is brilliant and, in the age where there's discussion of regulation on chemical capacitive technology such as Tesla Powerwall in my home country, having dependable, safe tech in place is a great thing.
But, if going for outright performance, I'd have gone LiPo too!
Archer,
We ran lead acid for two season because we felt it was essential to understand the series. We were fortunate that there were a couple of Open class racers who were already pushing the technology in fun ways (espectially an unforgettable leaner design) and wanting to build an advanced battery class.
Brendan,
I think in the long term, the HS class teams will want to migrate to more advanced batteries. For this to happen, there will need to be a proven standard 'plug and play' system. Reliability, robustness and long term costs will be more important than ultimate performance, so Lithium-Polymer might not be the best choice. What chemistry are you looking at?
The points of my story: (1) If you are going to run lead-acid batteries, Optima yellow tops are expensive initially, but amortized over 6-year life expectancy cost isn't bad. They require proper care to make them live that long - fast charging them at high amperage will kill them in just over a year. Yellow tops are supposed to be good for 300 cycles; red tops are only good for about 30 cycles (as are a lot of other AGM batteries) making their true cost higher because of more frequent replacement.(2) To take proper care of them you need a charger that brings them up in stages. The charger I use was $322. (3) The initial cost of running Lithium-Polymer may actually be less expensive.
If I was just starting out now I would probably go with Lithium. To change over now is cost prohibitive to me. Also, I'm a mechanic not an electronics wizard; I can fabricate most anything and have designed a very successful and competitive car. Unfortunately, I know nothing about the idiosyncrasies of using Lithium. When someone comes up with a "plug and play" Lithium system maybe my batteries will need replacing again and I'll look into it,.. but I may be re-retired by then.
Only after reading your post did I realise I didn't even end up placing the chemistry selected on the message!
I have a pair of LiFePO4 batteries sitting in the cart at BlueMySky (bmsbattery.com) ready for purchase for when I hit the "go" button.
The critical mass of users appears to have been reached that there's a good number of shelf batteries available for a comparable cost, and with outputs that match well to Electrathon requirements, particularly if experimenting with higher voltages and/or brushless motors.
Hi fellow Electrathoners,
I thought I would update everyone on what I have learned so far from the Rhino pack. The headline news is that I made an error calculating pack capacity when doing my discharge test. I did the calculations in note pad and thought that my manufactured rated 972 Watt hours pack was delivering over 1,100 Whrs. No such luck. I had an embarrassing race or two where I tried to run the higher rate and ran out of power
I copied my data into Excel and re-did the calculation. At the one hour rate (1C), on the third charge discharge cycle, I got 928 Whrs. I did another discharge test at the 15 cycle and got 912 Whrs. Unlike lead acid, lithium batteries seem to have their highest capacity right away and slowly get worse, so 928 Whrs is the best I expect from this set up.
Interestingly, cycle 6, I did a 25 minute discharge test (2C) and got 911 Whrs which hints that capacity holds up well despite higher discharge rates.
My next idea is to disassemble the pack and test capacity of each of the 9 battery packs. The packs are set up three in series and three in parallel. Then re-assemble the pack so that the total capacity of each paralleled threesome is the same (i.e. weak packs with stronger packs). If I can get a 5% improvement, I will be close to the 972 Whrs rated capacity.
This requires getting out the more accurate battery capacity tester that I built for another project and writing new software for it, so I doubt I will get to it soon. When I do, I will post the results.
Attached is an Excel sheet with the first 20 cycles data. Most cycles occur at races and are not full discharges because other bits and pieces broke. This is all done with a meter and a stop watch, so I am not sure what my margin of error is.
Hmmm...I can't figure out how to attach the Excel file. Anyone have a clue?
-- Edited by ProEV on Monday 9th of October 2017 08:09:47 PM
I can see a big benefit to moving over to lithium powered cars. Had a few questions to ask in regards to this because I've now been flying FPV mini quad copters for around a year and a half now to understand how they work. Yes, they are smaller batteries, but they get the point across.
But, and there is always a but; *you need to know what you are doing with lithium, be it Li-Ion or Li-PO to understand how to keep yourself and everyone around you safe.*
These batteries can be dangerous if not handled and taken care of properly. I've seen one too many fires happen when a FPV quad crashes and the electronics fail (mainly electronic speed controllers or ESCs for short) and those are not fun to see. I haven't seen a battery go off yet, but have heard horror stories. Least there isn't a person strapped onto the quad, but in electrathon racing there is hence the 20 second get out of the car rule.
Questions!!!
1. So, does anything special need to be done to the car besides put something in to monitor cell voltage if you're running a certain number of cells on your battery pack? Can you just wire it up like any normal battery. Currently most of our cars are build for lead acid, but since it's a battery the car's electrical system doesn't car what type of battery you have. As long as it has voltage right? If I were to do it, I'd probably do a 6s setup. Either two batteries in parallel to keep it 6s (25.2v) and keep the somewhat same gearing that I have right now. Or jump up the efficiency with lower current draw on 12s (50.4v). I'd be more inclined to go 12s since it means way less current draw than a 6s parallel setup. The higher the voltage the less current you need to pull the same amount of power out. Only draw back is I'd need to make a special sprocket for the drive wheel to make sure the motor is not getting bogged down by too small of a gearing causing the wheel to spin too fast. This is electrathon racing, not a drag race.
2. How are you putting your batteries in the car? Obviously we're strapping them in to keep them from moving around. But are you putting special padding around and in between the pack(s) to keep them protected from vibrating on the frame? I've had one too many lead acid batteries get worn down over the years due to them vibrating against the frame while driving for a hour around a track. In FPV racing with the quad copters, some people will print up TPU parts on a 3D printer to help protect the batteries in crashes since we tend to hit stuff pretty hard with them. Yeah they're small but they can easily get up to 80-120mph in a split second, granted we're only flying for around two minutes or so in a race. Little longer than that if going out to do freestyle flying around 3-5 minutes depending on throttle management. Or even ten minutes to close to thirty minutes with the long range efficiency quads.
3. What voltage are you charging your cells to and how much are you discharging your packs to? I know there are lithium batteries that are rated as high voltage (HV) that will charge each cell to 4.35 volts per cell which definetly can expand the capacity of the pack but is not recommended for long term use since the packs will degrad faster compared to charging to 4.20 volts per cell. Yes, HV from what I've read will help for the first minute of a race, but since FPV races are only two minutes per heat it's cheaper to just run the packs at a 4.20v charge since the packs will last longer. Speaking of longevity, are you running batteries to 80% discharge? I do know for a fact you cannot run LiPO lower than 3.50v, otherwise you risk the battery getting out of balance and having dead cells as a result of it. There are only a few batteries on the market that meet or almost meet the 15 pound rule that have a per battery watt hour rating of say 621.6. Times that by two you've got 1243.2wh total, BUUUUT you times that number by .8 (for 80% of the total capacity of the battery) and you get 994.56wh no matter if you run it in parallel or series. Current rules state advance/experiemental battery class cannot have a watt hour rating exceeding 1000wh. If you go past 1000, then it's on you to do whatever needs to be done to prevent the batteries from going out of control I guess.
4. Lithium-ion or lithium-polymer? I do know for a fact that lithium-ion can be discharged even lower than LiPO, but cannot charge nearly as fast (at only a .5c rate versus 1c or higher for LiPO) but cannot sustain a certian current draw compared to LiPO. So, what would you use? Li-Ion or LiPO? Personally I feel that LiPO would be more suited for electrathon racing since you'd be on and off the throttle constantly coming out of corners. Yeah little wasteful in power usage, but that's the name of the game. Plus Li-Ion cannot get to a certian tempreture since they are in cylinders they can't expand a little like LiPO does when being used. Plus Li-Ion doesn't like high temperature heat. Also you'd have to make a custom Li-Ion pack. (correct me if I'm wrong on this next part) Last I checked you have to have a manufactured battery with original labels etc. like the lead acid standard class does. No custom batteries. LiPO you can get and they are readily available with the manufacture labels on them, safety info, balance leads, discharge leads, etc. You'd just need to figure out how to get it mounted in the car and keep it from flying out and hitting stuff/make your own connections to hook the whole thing up.
I can't think of anything else since I already have a 6s capable charger to work with. I'd just need to look at getting two of them to test out and see what happens I suppose.
Thanks!
Zaine (BikeGuy)
Also I have a youtube channel and instagram account, look up BikeGuy or BikeGuy_FPV to see awesome flights and racing footage that I've been doing for the past couple of months as of recently and photos/short clips for the last year and a half. I recently got a movie editing program to work with which is super nice to have hence the increase in YT videos.
https://www.youtube.com/channel/UClnNk1zwapYRrWUN4jDeykg?view_as=subscriber
https://www.instagram.com/bikeguy_fpv/?hl=en
1 & 3, can be solved with a BMS which you absolutely should have racing, i have used battery buzzers but, they often either come loose and beep early, or some of the pins end up breaking and having to replace them ( although that just may be my experience ), you can buy a BMS based on how may cells your pack have and then it will use the industry standard to limit overdraw and overcharging.
2. we currently put the battery's in an ammo case ( with some holes in the back to ventilate away from the driver in case of an explosion ), it was already a tight fit, we just put 2-3 bungee chords just in case.
4. in the end im not sure if it really matters that much, since all packs are balanced to 1kwh, its going to be up to you if you want a slightly easier time going with lion vs lipos can easily reach 1kwh in 12lbs or less, so its up to you if the 3-5 lbs you save makes a difference to you.
"I would love to see a sealed tracking device that could be issued to teams that would read power used and then cut off power at a set number like 1,000 watts. That way every team could run a slightly bigger pack and not worry about damage. Different classes might have different limits. Lead Acid batteries suffer being discharged to dead so it would be good for that class as well, allowing packs to be competetive for more races. I would make it WiFi so everone could see real time power usage."
That sounds awesome!
Getting to watch everyone's real time usage would add a whole new side to the race.
Someone should build that.
What 80% rule?