# ME1003 Motor on Go Kart - 40Ah batteries ok?



## winzeracer (Apr 3, 2012)

What I found is that though these cells are "rated" for 12C, the basic design and chemistry of these cells are really only meant for 5C max if you want more than 100 cycles. You can check out some of my other threads where some senior members validate this over and over. This is the reason I sold my CALB cells. They just are not meant to be pushed that hard. Also a 72-84v pack is too heavy for the kart, if you like to turn. Check these 2 threads out.

http://www.diyelectriccar.com/forums/showthread.php?t=74588

http://www.diyelectriccar.com/forums/showthread.php?t=74323


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## lostinspacebar (Mar 4, 2011)

I chose the 40Ah mostly because of the C ratings. Ideally, I'd rather have 20Ah batteries and have 2 sets of them at the track that I can swap out so I get both racing time and lower weight. But the 20Ah LiFePO4s don't seem to do the C ratings I need. 

I checked out your page again, maybe I should consider LiPo too. LiPo is very very expensive though. Although more research may change that.

Any other opinions? experience?


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## Ziggythewiz (May 16, 2010)

If you want higher C's with lower weight you could look at the headway 8ah cells. A 24 ah pack of those would happily put out over double what the CALBs would.


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## lostinspacebar (Mar 4, 2011)

The headways look interesting but mounting them seems like a custom job? 

I found some other LiPo stuff at hobbyking: http://www.hobbyking.com/hobbyking/..._5300mah_2S2P_50_100C_Hardcase_Lipo_Pack.html

If I got like 40 of those (in a 10s4p configuration) I should get 74V with 2.2Ah. And with a C rating of 50C-100C, I should be able to do about 265A continuous (5.3Ah * 50) and 530A burst (5.3Ah * 100). I this math right? Cause 40 of these is ~$1300. My only problem then would be to figure out how to freaking charge a battery pack of them...

EDIT: Was mixing up links and specs for battery


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## Ziggythewiz (May 16, 2010)

Headways are the most customizable in terms of pack shape, but with the holders and busbars they come with they're probably better /cell than any other option, more cells means more time though.

Those LiPos should be able to dish it, though double the $/ah compared to headways.


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## winzeracer (Apr 3, 2012)

lostinspacebar said:


> The headways look interesting but mounting them seems like a custom job?
> 
> I found some other LiPo stuff at hobbyking: http://www.hobbyking.com/hobbyking/..._5600mah_1S2P_65_130C_Hardcase_Lipo_Pack.html
> 
> If I got like 40 of those (in a 10s4p configuration) I should get 74V with 22.4Ah. And with a C rating of 65C-130C, I should be able to do about 380A continuous (5.6Ah * 65) and 625A burst (5.6Ah * 130). I this math right? Cause 40 of these is ~$1000. My only problem then would be to figure out how to freaking charge a battery pack of them...


Math is a bit off 22.4ah*65 C= 1400+amps you probably dont need that large of C rates, I was looking at biulding a test pack of the 45C turnigy lipos, bms and charging is a bit different, I have not fully researched it yet. But charging times will be wayyy better than lifepo4. Should be able to have charge time equal drive time.


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## lostinspacebar (Mar 4, 2011)

Ziggythewiz:
The cheapest of the 8Ah headways I've seen so far are $15. And for a 72V @ at least 20Ah I'd need like 60 of them in 20s3p. So about $900. That's not bad. But that's from EvAssemble. I think those guys are china. Not sure what the shipping deal is there. Some US based places have it for $20. So thats about $1200. Still not bad. Do you know if the mounting stuff will add much to that cost?

winzeracer:
Thanks for catching that. Forgot I was putting stuff in parallel. That brings down price quite a lot. Now a pack of 14.8V 20C batteries in 5s4p would be $500 and give me more than I need... The charge time is definitely nice too. If I can figure out some insane charging setup that can charge like 30-40 battery packs lol.


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## frodus (Apr 12, 2008)

40Ah may be ok. You'll be putting 400A peak to the motor, but I seriously doubt you'll be getting 400A battery side.

Power in is roughly equal to power out of the controller (minus losses). 400A might occur only at really low RPM, like 0-10% throttle. With 10% throttle, you'd only be doing 10% of pack voltage (unless there's an algorithm inside the controller, it'll be somewhat similar). So that's like 7V on a 72V pack, lots of torque, but low RPM.

Then when RPM increases, current drops off, so torque ends up being less.


Lets say 23kw and 400A, that's ~57A on the motor side. Battery side, that's ~319A. But you have voltage sag, so it'd be a little more amperage. But it'd be about 8.5C or so peak... and not for very long periods of time. The CALB say they can do pulses of 10C for less than 10 seconds, so I don't really see an issue. MAYBE consider 60Ah batteries, or higher C-rates.... but you could always turn down the controller if you had issues with the 40Ah batteries.


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## lostinspacebar (Mar 4, 2011)

frodus:
Thanks for the analysis. I think the 400A is going to be maybe for 5-10 secs at most probably. The LiPo solution looks more and more tempting now. Do you have any experience with that?

There are a few threads on the forums for smaller electric bikes. Seems interesting.


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## frodus (Apr 12, 2008)

Just make sure you have a good cell-level BMS installed with Lipo and a balance charger and that the batteries are not mounted in an area where they'd hurt the rider if they went up in flames. They're more volitile than Lifepo4 cells, so be sure you want to take that extra risk.


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## Yabert (Feb 7, 2010)

lostinspacebar said:


> Thanks for the analysis. I think the 400A is going to be maybe for 5-10 secs at most probably.


On motor side maybe, but not on battery side.
Like Frodus try to explain to you, the current on battery side will be lower on battery side except at peak power.

But anyway, I don't think Calb 40Ah is your best choise (easiest yes!). 
My best suggestion is to use A123 AMP20, but they can be complex to assemble.
The red Headway 38120HP powerfull with an impedance of only 3 mohm. A 26S 2P battery pack (83v 16Ah (38 lbs)) can be really fun in a small kart.
If not, the TURNIGY nano-tech (lipo) are sold in 10S configuration with different power capability (50C to 130C). Two 5Ah 10S pack (7 lbs only) can be really fun for few sec. If no, add some pack in parallel (exemple, 20S 3P = 74v 15Ah).


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## lostinspacebar (Mar 4, 2011)

Yeah the lipos are starting to look better and better. Not sure how sturdy these hard case lipos really are though. Need to find out more about them.

The a123 stuff seems kind of a pain to assemble and cost isn't better. At least for a smaller battery pack like mine.


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## winzeracer (Apr 3, 2012)

lostinspacebar said:


> Yeah the lipos are starting to look better and better. Not sure how sturdy these hard case lipos really are though. Need to find out more about them.
> 
> The a123 stuff seems kind of a pain to assemble and cost isn't better. At least for a smaller battery pack like mine.


Ya I looked at the hard case ones too but with Lipo, you really need to proctect yourself better, I spoke with an EV guy that had not used them in EV's but had lots of helicopter Lipo experience and he said that at home he stores his in a metal safe because he has seen them spontaneously combust. I personally will have them in a metal box something like this http://www.automationdirect.com/adc/Overview/Catalog/Enclosures/Metal/NEMA_3R There are lots of different sizes, you can get them at Electrical Distributors or maybe even home depot. It is a little more mass but worth it if you have a little extra time to get away from it if it catches fire from a crash or some other malfunction.

Edit: Also check out these bussbars if you do not want to make your own
http://www.jozztek.com/shop/7-busbars-wiring


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## winzeracer (Apr 3, 2012)

Check out Jozzer's huge Turnigy pack

http://www.diyelectriccar.com/garage/cars/338

EDIT: Here is another REALLY good thread I just found where Jozzer talks a bit more about his Lipo's

http://www.diyelectriccar.com/forum...-s-mx-motorcycle-66006.html?highlight=turnigy


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## lostinspacebar (Mar 4, 2011)

winzeracer: NEMA enclosure sounds pretty good. Yeah I'm probably going to also take the extra weight hit and put a fire extinguisher on here


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## winzeracer (Apr 3, 2012)

lostinspacebar said:


> winzeracer: NEMA enclosure sounds pretty good. Yeah I'm probably going to also take the extra weight hit and put a fire extinguisher on here


Haha, I think you need Halon system, I dont think an ordinary extinguisher will do anything.


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## winzeracer (Apr 3, 2012)

just found this it would make things alot easier.

http://www.methtek.com/2012/02/05/complete-hobby-king-lipo-protection-kit/

http://www.methtek.com/docs/MethTek_LVC_HVC_Parallel_Manual.htm


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