Unique Application

[florida cracker]

Many 100 ah batteries can support 100 amps (or 50) but that's well outside your design limits.

Have you looked at ebike batteries? NMC can often do 5c or higher, that should ld easily fulfill your needs

I have been looking into ebike batteries and see that most of them have better discharge rates but they seem to want you to use their charger hookup rather than just use it like a regular battery with a + and - terminal.

Need to find out what happens when you use their discharge connector to charge through also

 

[ejfluhr]

Check EarthX for some high-power while low Ah batteries. They are aircraft-rated, where safety is a bit important. I'm not sure if they can be series-connected, though.

Follow-up: I looked them up and they have great specs but not the flexibility in size. At least it shows what is possible with lithium. Their ETX-1200-24 is 19.4Ah at 26.4v, which is only 510Wh. 150A disharge and 80A charge, though. They do have 11.7Ah and 15.6Ah varieties, which in parallel would be 27.3Ah, which at 26.4v is 720.72W...maybe that meets spec if they aren't sticklers?

Not cheap, but it would crush the competition:

24V Lithium Iron Phosphate Batteries | EarthX Batteries

Our powerful, long lasting, and lightweight lithium batteries are ideal for aircrafts and powersport vehicles. Browse our products.

earthxbatteries.com

 

[Vigo]

The very little I know about RC packs is that the smaller charge connector is also used for balancing. for purposes of a single race it will not be a problem to charge the pack in series through the ‘main’ connector because you won’t be able to do enough charging off of Solar in 20 minutes to have any single cell be going over its max voltage regardless of how imperfectly the cells are matched. At least, thats my thinking.

 

[Vigo]

So im in the middle of doing some testing on this idea of a 2ah ‘starter’ lifepo4 in parallel with an 18ah ‘normal’ lifepo4.

So far one thing ive tested is that with a 100a load, the 18ah battery bms trips almost instantly, BUT when loaded through some 12ga wire it did 75amps for as long as i cared to hold it, about 5-7 seconds. This supports my theory that a larger capacity battery in parallel with a smaller battery with a larger bms, would be able to support a fairly large total current from the pack without its bms tripping instantly because you can ‘throttle’ the current by adding resistance to the parallel connection. A light vehicle with a 36v 200+a drivetrain would accelerate very quickly and not be able to sustain that high current draw long enough to bother the pack BMS’s, is my theory.

The 2ah ‘starter’ battery (powersports/motorcycle) i am not impressed with yet, but i need to repeat some tests to make sure i can give accurate statements..

 

[zcskywire2]

A bit high on the voltage side but dead on the money in Wh is one of the greepower drone batteries. They are stacked lipo pouch batteries. We have a drone shop near my office that uses these and they kick ass

100A continual rated, 240amp peak 44.4v nominal

Product Details

Tattu Plus 1.0 Compact Version is a UAV Smart Battery developed by Grepow Battery mainly used in agriculture plant protection, security mapping, logistics and other medium and large drones. Grepow team has effectively solved the current problems of smart drone batteries after years of technical...

www.grepow.com

Edit: pack datasheet now attached
Edit 2: switching to the drone battery would also save you over 30lbs of weight vs the sla batteries

 

[Hedges]

So im in the middle of doing some testing on this idea of a 2ah ‘starter’ lifepo4 in parallel with an 18ah ‘normal’ lifepo4.

So far one thing ive tested is that with a 100a load, the 18ah battery bms trips almost instantly, BUT when loaded through some 12ga wire it did 75amps for as long as i cared to hold it, about 5-7 seconds. This supports my theory that a larger capacity battery in parallel with a smaller battery with a larger bms, would be able to support a fairly large total current from the pack without its bms tripping instantly because you can ‘throttle’ the current by adding resistance to the parallel connection.

The 2ah ‘starter’ battery (powersports/motorcycle) i am not impressed with yet, but i need to repeat some tests to make sure i can give accurate statements..

I do wonder how much different the "starter" LiFePO4 cells really are. Used at much higher "C" rates than we see for most, but briefly. Maybe there is a tradeoff of excess current vs. cycle life rather than different construction.

Makes sense that the two different batteries are each capable of supplying what you want them to, but the difficulty is getting the load sharing to be as desired. That problem shows up in a number of situations.

If each fed a different inverter or DC/DC converter, those could be configured to stay within specs. Like LG RESU-H "HV" battery" with is really (one or more?) 48V batteries with boost converter to 400V. The boost converter could obey current limits.

My idea for similar load sharing is AGM on Sunny Island to handle surges, and a lithium battery AC coupled (e.g. feeding PV inputs of GT PV inverter, or rather a commercially available AC coupled battery inverter.) The lithium battery would never be asked to deliver more than its rated current, but it would deliver kWh to recharge and float the AGM battery. Trick is getting it to also absorb surplus PV.

There are some HV inverters with multiple battery connections; those would also limit each to what BMS says is allowed.

 

[Vigo]

I personally suspect the cells are NO different and there is simply a cost to longevity or even reliability. The cost of the ‘motorcycle’ starter battery i bought is within $15 or the cheapest SLA equivalent, and surely cheaper than some of the higher end SLA/AGM brands in same group size, so it would have to have a cycle life or reliability worse than lead acid (in a motorcycle, mind you!) to register as a problem. Im guessing sellers are simply betting ‘no way it gets the claimed 2000+ cycles but its not gonna be enough worse than lead acid to bite us’. ?‍

 

[florida cracker]

So im in the middle of doing some testing on this idea of a 2ah ‘starter’ lifepo4 in parallel with an 18ah ‘normal’ lifepo4.

So far one thing ive tested is that with a 100a load, the 18ah battery bms trips almost instantly, BUT when loaded through some 12ga wire it did 75amps for as long as i cared to hold it, about 5-7 seconds. This supports my theory that a larger capacity battery in parallel with a smaller battery with a larger bms, would be able to support a fairly large total current from the pack without its bms tripping instantly because you can ‘throttle’ the current by adding resistance to the parallel connection. A light vehicle with a 36v 200+a drivetrain would accelerate very quickly and not be able to sustain that high current draw long enough to bother the pack BMS’s, is my theory.

The 2ah ‘starter’ battery (powersports/motorcycle) i am not impressed with yet, but i need to repeat some tests to make sure i can give accurate statements..

We are back at school and I checked in with this thread, I have just discovered lithium starter batteries also. I found one that seems like it might do what we need. https://lithiumhub.com/product/lithium-12v-400cca-u1-lifepo4-starter-battery/

6 of these wired 3s2p should give me the ability to get the kart started with the higher amp rush and maintain speed while staying under BMS limitations. it also allows for relatively high amp charging also.

I do still need to get students out to test both 24v and 36v setups to see how many amps it pulls at both settings to attain and maintain speed we are shooting for (we'd like to get to 34-35 mph just for shits and giggles).

 

[Vigo]

I dont know if you happened to see the thread in which i tested this idea, here.

In my opinion its 100% viable. Just taking the combo I put in my tractor and putting 3 sets in series (3s2p) to make 36v nominal, it would support well over 200a (~10hp) for short bursts, and 50a+ for long periods, and thats with only one of the two parallel strings being made of starter batteries. If you made both strings out of starter batteries your ‘surge’ and continuous ampacity would be silly high, but it may be a relatively expensive way to hit your Wh cap vs mixing starter and non starter as i did in my thread.

Either way, 10hp is enough to get a ‘go kart’ to hit 30mph on a smooth surface, so you should be good to do that at least briefly as far as the battery end of things.

 

[florida cracker]

I dont know if you happened to see the thread in which i tested this idea, here.

In my opinion its 100% viable. Just taking the combo I put in my tractor and putting 3 sets in series (3s2p) to make 36v nominal, it would support well over 200a (~10hp) for short bursts, and 50a+ for long periods, and thats with only one of the two parallel strings being made of starter batteries. If you made both strings out of starter batteries your ‘surge’ and continuous ampacity would be silly high, but it may be a relatively expensive way to hit your Wh cap vs mixing starter and non starter as i did in my thread.

Either way, 10hp is enough to get a ‘go kart’ to hit 30mph on a smooth surface, so you should be good to do that at least briefly as far as the battery end of things.

How would this work with the charging system? I'm not an electrical engineering guy, just a Special Ed teacher who thought this thing looked interesting a couple years ago. From what I understand (limited) the charge controller needs the batteries being charged to be the same to properly charge them? Or am I mixing what I have learned about the panels into my thought process here

 

[Vigo]

As long as the two parallel strings are expecting the same charging voltages, its totaly possible to charge strings with differing capacity from the same charge source. I do this in my house and rv daily.

It is somewhat dependent on it being lifepo4 vs some other chemistry like lead acid. This is because lifepo4 has such low internal resistance that the resistance of the wiring between each battery and the charge source ends up being a much bigger factor in which batteries receive more of the charge current vs the difference in resistance between the larger and smaller capacity batteries.

So, conceptually its fine, but it is somewhat possible to booger the idea in execution depending on how you wire it. If I were to execute this plan i personally would wire each larger battery into parallel with the smaller (starter) battery individually through some smallish wire such as 12ga before wiring the 3 pairs into series. Your main positive and negatives and the large wires between each 12v pair would hook to the terminals of the smaller starting batteries, and the larger capacity batteries with smaller amp BMS’s would only hook to the starter batteries through the small connecting wires which would add enough resistance to keep them from flowing enough current to engage their BMS overcurrent protection features.

Any time they werent under a heavy load, or when charging, the resistance would still be low enough that they would ‘distribute’ the charge adequately well for the purpose youre trying to achieve. As i said before, there’s no way you’re going to accomplish enough charging DURING the race to worry much about imbalance in the pack, and any imbalance created by the differing capacities and wiring paths would be rectified by a perfectly normal full charge before and after. The batteries can transfer charge to each other faster than you can charge them, basically. If you hold the pack at full charge voltage until it stops accepting much current, the batteries will ‘self-balance’ between each other, and internally their BMS’s will balance between their internal cells.

 

[florida cracker]

As long as the two parallel strings are expecting the same charging voltages, its totaly possible to charge strings with differing capacity from the same charge source. I do this in my house and rv daily.

It is somewhat dependent on it being lifepo4 vs some other chemistry like lead acid. This is because lifepo4 has such low internal resistance that the resistance of the wiring between each battery and the charge source ends up being a much bigger factor in which batteries receive more of the charge current vs the difference in resistance between the larger and smaller capacity batteries.

So, conceptually its fine, but it is somewhat possible to booger the idea in execution depending on how you wire it. If I were to execute this plan i personally would wire each larger battery into parallel with the smaller (starter) battery individually through some smallish wire such as 12ga before wiring the 3 pairs into series. Your main positive and negatives and the large wires between each 12v pair would hook to the terminals of the smaller starting batteries, and the larger capacity batteries with smaller amp BMS’s would only hook to the starter batteries through the small connecting wires which would add enough resistance to keep them from flowing enough current to engage their BMS overcurrent protection features.

Any time they werent under a heavy load, or when charging, the resistance would still be low enough that they would ‘distribute’ the charge adequately well for the purpose youre trying to achieve. As i said before, there’s no way you’re going to accomplish enough charging DURING the race to worry much about imbalance in the pack, and any imbalance created by the differing capacities and wiring paths would be rectified by a perfectly normal full charge before and after. The batteries can transfer charge to each other faster than you can charge them, basically. If you hold the pack at full charge voltage until it stops accepting much current, the batteries will ‘self-balance’ between each other, and internally their BMS’s will balance between their internal cells.

Would the lower "max charge current" of the 14ah batteries allow them to accept the charge coming from my SCC through the starting batteries??

I'm not understanding how I can recharge them after each heat. I understand the starter batteries handle the initial draw of the motor as it starts from a dead stop, the deep cycle batteries will flow through them to power the kart once it is at speed, and the SCC will be providing power all of the time. I also understand that the starter batteries will accept the high current to recharge but I can't wrap my head around how the lower amp charge limit on deep cycle batteries will allow them to properly recharge.

My solar charger has put out roughly 30 amps in full sun historically. If I had that hooked up to a 36v system, would each bank get roughly 10 amp charge??

I realize I am looking at this like I was dealing with amounts of water, is that a completely wrong way to visualize what is happening here??

 

[Vigo]

No, so far you are pretty spot on.

So, each part of a series circuit gets the same current. In this case it would be each PAIR of batteries would receive 30 amps. How the 30 amps is distributed between the two is up to the resistance of A. the battery and B. the path to the charge source. If you wired it as i said then the starter batteries, while smaller which generally means higher internal resistance, would be more directly connected to the charge source. The larger, lower resistance battery would be have an extra section of say 12ga leads between it and the charge source. I cant say exactly how the 30amps would distribute but i DO expect that it would split evenly enough to stay under the ‘continuous amp rating’ of the larger battery which is all that matters. In reality what would likely happen is that if one battery in the pair were to rise a tenth or two of a volt higher than the other due to greater charge acceptance, that would shift the balance of which got more in favor of the other one. In any case 30 amps is only mildly harsh even if it ALL went to one or the other (it wouldnt..) so its the discharge that is the priority to handle, conceptually. Thus the smallish 12ga leads (some experimentation may be required to ‘tune that in’).

I dont want to oversell it, but my understanding and my testing of the concept shows it to be viable. I just dont want to give the impression im trying to dominate the discourse with this particular idea. Its possible people who know more than me are just waiting for me to say something they can poke holes in before weighing back in.. ?

 

[florida cracker]

No, so far you are pretty spot on.

So, each part of a series circuit gets the same current. In this case it would be each PAIR of batteries would receive 30 amps. How the 30 amps is distributed between the two is up to the resistance of A. the battery and B. the path to the charge source. If you wired it as i said then the starter batteries, while smaller which generally means higher internal resistance, would be more directly connected to the charge source. The larger, lower resistance battery would be have an extra section of say 12ga leads between it and the charge source. I cant say exactly how the 30amps would distribute but i DO expect that it would split evenly enough to stay under the ‘continuous amp rating’ of the larger battery which is all that matters. In reality what would likely happen is that if one battery in the pair were to rise a tenth or two of a volt higher than the other due to greater charge acceptance, that would shift the balance of which got more in favor of the other one. In any case 30 amps is only mildly harsh even if it ALL went to one or the other (it wouldnt..) so its the discharge that is the priority to handle, conceptually. Thus the smallish 12ga leads (some experimentation may be required to ‘tune that in’).

I dont want to oversell it, but my understanding and my testing of the concept shows it to be viable. I just dont want to give the impression im trying to dominate the discourse with this particular idea. Its possible people who know more than me are just waiting for me to say something they can poke holes in before weighing back in.. ?

Its an interesting idea that I don't believe I have seen on any other kart up there in the past two years I have been doing this. Most still run the SLA batteries because of the simplicity (no BMS to deal with and high rates of charge/discharge). This would be new and different and possibly be the solution nobody else has wandered into.

To make sure I am understanding this properly, the 30 amps coming out of SCC would send 10 amps to each pair of batteries, being wired to the starter batteries in parallel. This would also be charging the deep cycle batteries at the same time

My other option was stringing several starter batteries together that was going to be expensive. This will still require 6 batteries but they are much lower priced than 6 of these: https://lithiumhub.com/product/lithium-12v-400cca-u1-lifepo4-starter-battery/ at $169 each

I am curious as to whether anyone else can/will speak up about how or why this wouldn't work

 

[Vigo]

To make sure I am understanding this properly, the 30 amps coming out of SCC would send 10 amps to each pair of batteries, being wired to the starter batteries in parallel. This would also be charging the deep cycle batteries at the same time.

So in series current is the same everywhere. If you put 3 12v batteries in series and push 30 amps of charge, each battery will receive the same 30 amps.

Now take each battery and split it into two. 30 amps will come in, some will go left and some will go right based on resistance and voltage, but coming OUT of that pair of batteries it will recombine and still be 30 amps going to the next pair.

 

[ejfluhr]

If I understand what Vigo is suggesting, it is the same as using 6 Ionic batteries in a 3s2p config. However, instead of using 2 identical batteries for symmetric behavior, you marry 1 high-current-low-capacity battery with a high-capacity-low-current battery. That asymmetric design may offer better performance for kart racing, depends on the motor draw w.r.t. time. Also might be cheaper than other options?

It's a cool idea but I suspect keeping it simple (K.I.S.S.) with the 6 Ionic batteries would work just fine for you.

 

[florida cracker]

If I understand what Vigo is suggesting, it is the same as using 6 Ionic batteries in a 3s2p config. However, instead of using 2 identical batteries for symmetric behavior, you marry 1 high-current-low-capacity battery with a high-capacity-low-current battery. That asymmetric design may offer better performance for kart racing, depends on the motor draw w.r.t. time. Also might be cheaper than other options?

It's a cool idea but I suspect keeping it simple (K.I.S.S.) with the 6 Ionic batteries would work just fine for you.

If I can get the school to pay for the Ionic batteries, I will likely go that route but I will say the asymmetrical setup is intriguing

I'm gonna find out today how many amps it pulls at speed with 24v setup and would run it at 36 to see what it does but extra batteries have crapped out on me. Only have two SLA batteries to run

 

[florida cracker]

Got in our batteries
https://www.amazon.com/EBL-Motorcyc...C1VN5HS/ref=psdc_404722011_t5_B091NYZMDP?th=1
https://www.amazon.com/gp/product/B0B7MBRC69/ref=ewc_pr_img_1?smid=A2NKEN9O69YXYL&th=1

had them hooked up in parallel the in series to get 36v, ran it on our track around the football field, and promptly dumped it over on its side. Too fast for a turn that sharp.

It now does 30 mph and those batteries work together to get it off the line and allowed it to recharge and start again.

 

[ejfluhr]

So you went with Vigo's idea for asymmetric batteries? Nice!

It will be exciting to hear how well that works, particularly w.r.t. charge & discharge management. I hope y'all win!

 

[florida cracker]

So you went with Vigo's idea for asymmetric batteries? Nice!

It will be exciting to hear how well that works, particularly w.r.t. charge & discharge management. I hope y'all win!

I think they worked but we really didn't get a chance to run it for as long as we're going to need it to run. Also didn't have a good sun to see how it charges at full strength. Now we have to wait for repairs (actually refitting another schools kart that doesn't want to participate in this) to really know

Fingers crossed, lol