# small high current battery advice sought



## lkcl (Sep 16, 2011)

hi folks,

i'm building a "heavy quadricycle" (350kg) hybrid electric vehicle (on-board generator) so i need only a small battery pack - 2.5kWh would suffice - and have chosen to go with a light-weight 48v DC motor (the PMG226).

peak power is about 10kW; peak ampage about 200A, but the average operating current is going to be about 125amps. the battery pack being 2.5kWh, that's 50Ah at 48v.

the problem is this: most batteries - almost all the ones i have found so far, if they're small, they only supply small current. a 50Ah battery pack typically has an operating current of say 20 amps *not* 125 amps: you have to go up to a 200Ah battery pack which is 10x heavier (400kg), 10x more expensive and 900% of such a battery pack is completely unnecessary for a hybrid vehicle anyway.

no, ultracapacitors are *not* an option: they're 1/10th the capacity and 10x the price.

so, my question is simple: has anyone encountered, anywhere, a battery pack or any batteries that are small but also have a high operating current, of around 100 to 125 amps?

thanks in advance,

l.


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## rwaudio (May 22, 2008)

No the easiest to use but A123 20Ah pouches or even Headway cells would probably do the trick.


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## lkcl (Sep 16, 2011)

hallo rwaudio, thanks for the recommendations. just looking up e.g. 48v 20Ah headway batteries:

http://stores.headway-headquarters....0Ah-BATTERY/Detail.bok?category=Battery+packs

maximum discharge current is rated at 40A which is unfortunately 1/5th of what's needed. this is quite common, when investigating these batteries, to find this!

the A123 20Ah on the other hand looks much more promising. not bad pricing, either. silly people don't however state what the maximum current is.... or maybe they do, it's hard to tell from the datasheet (www.a123systems.com/prismatic-cell-amp20.htm)

it says discharge power 1200 watt, and if the voltage is 3.3v, that's wow - 363 amps! if that's correct then bloody hell that's damn good. at about 500g per pack, 48v would be 15 packs, which would be about 7.5kg - also damn good.

yeah, i think this might be exactly what i'm looking for. super!


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## jeremyjs (Sep 22, 2010)

lkcl said:


> hi folks,
> 
> i'm building a "heavy quadricycle" (350kg) hybrid electric vehicle (on-board generator) so i need only a small battery pack - 2.5kWh would suffice - and have chosen to go with a light-weight 48v DC motor (the PMG226).
> 
> ...



Why not get 60 ah calbs, thundersky or GBS batteries? They're rated 3c continuous and 10C for 10 seconds....


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## rwaudio (May 22, 2008)

lkcl said:


> hallo rwaudio, thanks for the recommendations. just looking up e.g. 48v 20Ah headway batteries:
> 
> http://stores.headway-headquarters....0Ah-BATTERY/Detail.bok?category=Battery+packs
> 
> ...


The headways you linked to are current limited by the BMS (they are e-bike batteries)

If you look at the raw cells the 8Ah "power" cells can do 200A peaks
http://www.manzanitamicro.com/products?page=shop.product_details&flypage=flypage.tpl&product_id=61&category_id=29

I'm using the A123's and yes they can put out the current!!
Headways would be easier to connect though and with the small pack you require could actually be a simpler/cheaper option.


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## lkcl (Sep 16, 2011)

http://www.ebay.com/itm/16-A123-20a...US_Rechargeable_Batteries&hash=item3a6a1df080

right. found something. according to some of the photos on that ebay page the A120 20Ah is a "3C" continuous which i understand to mean that it can do "3x what the Ah rating is", in this case 20Ah, meaning it can do 60amps continuously.

but.. hmmm... http://www.diyelectriccar.com/forum...a123-amp20m1hd-cells-charged-4ci-56862p3.html shows that these cells have been discussed before, contradicting what mr ebay above is saying. argh - need to find out more...


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## rwaudio (May 22, 2008)

lkcl said:


> http://www.ebay.com/itm/16-A123-20a...US_Rechargeable_Batteries&hash=item3a6a1df080
> 
> right. found something. according to some of the photos on that ebay page the A120 20Ah is a "3C" continuous which i understand to mean that it can do "3x what the Ah rating is", in this case 20Ah, meaning it can do 60amps continuously.
> 
> but.. hmmm... http://www.diyelectriccar.com/forum...a123-amp20m1hd-cells-charged-4ci-56862p3.html shows that these cells have been discussed before, contradicting what mr ebay above is saying. argh - need to find out more...


Mavizen is the only authorized reseller of these cells (that I know of), if I was going to trust someones ratings I would trust theirs.
http://www.mavizen.com/A123.html

Mavizen is insanely expensive though so it might not be your first choice to buy from. And the cells found on the grey market may or may not live up to those specs. It's a tough call, but many people have tested them (including myself) and they live up to their specs. Even capacity as Mavizen states 18.5-20Ah.


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## lkcl (Sep 16, 2011)

rwaudio said:


> Mavizen is the only authorized reseller of these cells (that I know of), if I was going to trust someones ratings I would trust theirs.
> http://www.mavizen.com/A123.html
> 
> Mavizen is insanely expensive though so it might not be your first choice to buy from. And the cells found on the grey market may or may not live up to those specs. It's a tough call, but many people have tested them (including myself) and they live up to their specs. Even capacity as Mavizen states 18.5-20Ah.


http://www.mavizen.com/A123/Special_Notice.html - some ebayers / alibabaers / taobaoers are likely to be intercepting quality-controlled *failed* items that are for recycling and passing them off as new, potentially placing recipients at risk due to catastrophic failure. mavizen is an authorised reseller.

ok. well - if the ones people on here have got are ok, and actually deliver and don't blow up, i'm happy with that


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## rwaudio (May 22, 2008)

lkcl said:


> http://www.mavizen.com/A123/Special_Notice.html - some ebayers / alibabaers / taobaoers are likely to be intercepting quality-controlled *failed* items that are for recycling and passing them off as new, potentially placing recipients at risk due to catastrophic failure. mavizen is an authorised reseller.
> 
> ok. well - if the ones people on here have got are ok, and actually deliver and don't blow up, i'm happy with that


If you were the one legit reseller of these cells but they could be had all over the place for 1/5 - 1/3 the price wouldn't you try to scare people away from buying them?
No guarantee the cells are perfect, but for the price it's worth the risk to some people.


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## lkcl (Sep 16, 2011)

rwaudio said:


> The headways you linked to are current limited by the BMS (they are e-bike batteries)


ahhh, i understand.



> If you look at the raw cells the 8Ah "power" cells can do 200A peaks
> http://www.manzanitamicro.com/produ...page=flypage.tpl&product_id=61&category_id=29


*whistles*



> I'm using the A123's and yes they can put out the current!!
> Headways would be easier to connect though and with the small pack you require could actually be a simpler/cheaper option.


 ehh, i'm all for simple


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## winzeracer (Apr 3, 2012)

rwaudio said:


> If you were the one legit reseller of these cells but they could be had all over the place for 1/5 - 1/3 the price wouldn't you try to scare people away from buying them?
> No guarantee the cells are perfect, but for the price it's worth the risk to some people.


Jack Rikard on evtv.me has done lots of testing with the "grey market" A123 Amp20's he has several rather long videos on testing these cells. He says they are good for 375 amps (23C) and he is selling them http://evtvshop.projectooc.com/products.php?cat=10

I was contemplating using these for my high current eKart build, but I needed a little more so I will be going with the Haiyin 6ah 3.7v calls which claim 50C ( voltage drops to 3.3v) constant draw. http://www.ecedra.com/thebatteryshop.html
These are what Lithuimmanics Drag racer runs \, but you have to be comfortable making you own pack. Make sure when you are taking voltage drop into account when calculating your max Kw rating. There are TONS of threads about this so I will not go into it here.

Happy Hunting.


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## Ziggythewiz (May 16, 2010)

With most smaller cells you'll need a series-parallel pack, so if you see a headway that only does 1/5 what you need, you just need 5-6 in series. I think some do up to 30C though, so you shouldn't need that many.


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## frodus (Apr 12, 2008)

If you built a pack of Headway batteries with 16s5p for a 48V 50Ah pack with the 10Ah batteries, you'll have absolutely no problem getting 200A. That's only 40A per cell or ~4C. That barely gets these cells warm. 125A would be around 25A a cell, or right about 2.5C, which they'll readily do.

US distributors with warranty, they're affordable and easy to replace.....

not that A123 is bad, they're just more risky, and assembly can be a PITA.


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## lkcl (Sep 16, 2011)

hi travis, thanks for the idea... let's think it through, though, from both a cost and a weight perspective. the Headway cells are £12 each (about $18) from a UK supplier, and they're 0.346kg each. whereas evassemble.com is doing Thundersky 40Ah 1.6kg packs for $52 each (ok excluding shipping and tax) - but still, to make up 40Ah with 8Ah Headway cells that's $18 x 5 x 16 = $1440! whereas Thundersky cells, $52 * 16 = $832.

weight-wise, it's a close call: .346 x 5 x 16 = 27.68kg, and the thunderskys are 1.6 x 16 = 25.6kg.

in some ways i would actually be better off with those A123 cells - 0.6kg (or so?) x 16 = 9.6kg but they're 20Ah so half the capacity, pricing $30 (or so) x 16 = $496 - double those numbers and they're good on weight and reasonable on price.

so, making it all 40Ah, it's


thundersky: 25.6kg, $832
A123: 20kg, $1000
headway: 27.68kg, $1400
looks to me like the thundersky cells are the best price/weight/performance option.


/peace


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## rwaudio (May 22, 2008)

lkcl said:


> hi travis, thanks for the idea... let's think it through, though, from both a cost and a weight perspective. the Headway cells are £12 each (about $18) from a UK supplier, and they're 0.346kg each. whereas evassemble.com is doing Thundersky 40Ah 1.6kg packs for $52 each (ok excluding shipping and tax) - but still, to make up 40Ah with 8Ah Headway cells that's $18 x 5 x 16 = $1440! whereas Thundersky cells, $52 * 16 = $832.
> 
> weight-wise, it's a close call: .346 x 5 x 16 = 27.68kg, and the thunderskys are 1.6 x 16 = 25.6kg.
> 
> ...


That is all correct, the thing to watch out for is continuous and peak currents, it will be much higher for the A123/Headway option (if you need those current levels) if you don't go thundersky. It's pretty much the same choices that EV builders make, if TS/CALB will give enough current go with them, they are so much easier to use. If that won't give enough current the choices move to a higher current cell like A123/Headway.

You need to add one more column to make it more relevant continuous and peak currents. That should help you make the final decision on the best cell for your application.
Given equal current loads the A123/Headway would have the lowest sag at a given current output vs TS, take that into account and see if the sag from a TS cell is acceptable.


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## winzeracer (Apr 3, 2012)

lkcl said:


> hi travis, thanks for the idea... let's think it through, though, from both a cost and a weight perspective. the Headway cells are £12 each (about $18) from a UK supplier, and they're 0.346kg each. whereas evassemble.com is doing Thundersky 40Ah 1.6kg packs for $52 each (ok excluding shipping and tax) - but still, to make up 40Ah with 8Ah Headway cells that's $18 x 5 x 16 = $1440! whereas Thundersky cells, $52 * 16 = $832.
> 
> weight-wise, it's a close call: .346 x 5 x 16 = 27.68kg, and the thunderskys are 1.6 x 16 = 25.6kg.
> 
> ...


Rw is correct you are not cimparing apples to apples. The TS cels will max at 5C burst and sag to ~2.7v underload so 2.7vX40ahX100vX5C=~50kw
The headways may sag to 2.5v under thier max 10C load
2.5vX40ahX100VX10C= 100kw
A123.amp 20 I guess sag to be down to atleast 2.5v at 23C
2.5X40X100X23=230kw

All.very different numbers. You.are also comparing 2 different chemistrys, and 3 different levels of difficultly for install. All things that must be entered into the equation.


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## frodus (Apr 12, 2008)

Agreed.... best to look at what power you need, and work that way. TS isn't a great choice for something that needs high C-ratings. If you do, consider double or even tripling the Ah rating (i.e. go with 100Ah TS cells).

Weight and price they may have others beat, but they've got a ways to go on performance.


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## skooler (Mar 26, 2011)

lkcl said:


> hi travis, thanks for the idea... let's think it through, though, from both a cost and a weight perspective. the Headway cells are £12 each (about $18) from a UK supplier, and they're 0.346kg each. whereas evassemble.com is doing Thundersky 40Ah 1.6kg packs for $52 each (ok excluding shipping and tax) - but still, to make up 40Ah with 8Ah Headway cells that's $18 x 5 x 16 = $1440! whereas Thundersky cells, $52 * 16 = $832.
> 
> weight-wise, it's a close call: .346 x 5 x 16 = 27.68kg, and the thunderskys are 1.6 x 16 = 25.6kg.
> 
> ...


Hi,

Who is the UK supplier of headway cells?

Cheers,

Mike


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## lkcl (Sep 16, 2011)

skooler said:


> Hi,
> 
> Who is the UK supplier of headway cells?
> 
> ...


http://eclipsebikes.com/headway-lifepo4-38120s-10ah-p-1011.html

seems like they sell electric bikes (and offer parts), some of the parts being those cells, it looks like they got a bunch in. good for them.

l.


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## lkcl (Sep 16, 2011)

okok sorry they have the 10Ah, 12Ah and 16Ah versions, their system says they have 180 of the 16Ah cells in stock, they're not the higher current 8Ah ones though.


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## frodus (Apr 12, 2008)

Just realise, the 16Ah cells are no longer being produced... so they'd be hard to source later.


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## dreamer (Feb 28, 2009)

Those 10AH Headway cells are much at EV Assemble, but shipping, VAT, etc. could wipe out the savings I suppose. $15.50 vs. $19 at eclipse.

http://www.evassemble.com/index.php?main_page=product_info&cPath=2&products_id=18

Even $15.50 seems high to me as I swear I used to see them at other vendors for $13. Of course, maybe that's why those vendors don't exist anymore, eh ;-)


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## frodus (Apr 12, 2008)

Why not order them direct from Headway?


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## dreamer (Feb 28, 2009)

frodus said:


> Why not order them direct from Headway?


For the samall qty he needs, would it be worth it ? What is the current price direct from Headway ?


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## frodus (Apr 12, 2008)

Email them, I'm not sure.

It's worth it going direct if you're ok with money transfer.


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## lkcl (Sep 16, 2011)

dreamer said:


> For the samall qty he needs, would it be worth it ? What is the current price direct from Headway ?


http://stores.headway-headquarters....-batteries,-EV,/Detail.bok?category=BATTERIES

bless 'em it's $18 and that's excluding shipping and then (when it gets into the UK) 12% customs duty (on top of the total price - 64*18+shipping), 20% VAT on top of the customs duty *and* the shipping *and* the tax *and* the product!

so all told that works out at somewhere around $1682 whereas if i got the cells already in the country from that shop it'd be around $1312.

so i don't understand. even buying in bulk from headway-headquarters.com they still don't give a large enough discount to match up the discrepancy between those two costs.


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## lkcl (Sep 16, 2011)

ok, so i've chosen to go with those headway 10Ah cells, in a 16s4p arrangement. at a maximum continuous discharge current of 100 amps, a parallel set of 4 should handle 400 amps easily, which is over three times the nominal continuous current required for the vehicle to sustain a speed of 60mph on the flat.

in the end i went with evassemble.com because they had good advice and a decent rate on the BMS system required to look after the cells. i will let people know how it goes - thank you for everyone's advice.


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## frodus (Apr 12, 2008)

Just remember, at 10C, you will NOT get 10Ah out of the cell, expect maybe 5-6Ah or so out of the cell at that kind of discharge rate.


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## lkcl (Sep 16, 2011)

frodus said:


> Just remember, at 10C, you will NOT get 10Ah out of the cell, expect maybe 5-6Ah or so out of the cell at that kind of discharge rate.


hi travis, thanks for the heads-up - i believe i will get away with it.

the expected power consumption at a steady speed of 60mph on the flat is around 6kW. that works out to be 31 amps per cell (3C).

however i will not be using the vehicle to travel even at 60mph for prolonged periods: where we presently live, which is in a remote area, it's a 10 mile trip to town mostly on single-track roads, where it's sometimes safe to do 75mph but for the most part speeds above 30mph are about the absolute maximum limit, and on some stretches the safe limit drops to 20mph.

expected power consumption for the majority of journeys is therefore only around 2kW peak (41amp) which works out at 10amp per cell (1C).

for the whole round-trip journey this would work out to be about 0.8kWh, and the whole battery pack is rated, when 100% charged, at 1.92kWh.

so... i believe we're good. of course, i could have entirely got my design and the maths completely and utterly wrong, but we will find out soon enough, eh?


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## frodus (Apr 12, 2008)

As long as you know that anything over 1C discharge won't get you 10Ah, then you're fine. I just like to make sure people know because it's not obvious at first. Sometimes it's only a 10% drop in Ah capacity, sometimes it's quite more, but it all depends on the C-rate.

Good luck on things, sounds like you're mostly on the right track..... but real-world is sometimes different than mathematical models.


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## lkcl (Sep 16, 2011)

yehh... my mum's got a car with a towbar, and i bought an a-frame towing dolly juuust in case. the first few major test journeys will definitely not be unaccompanied: the population density in the area i'm in is waaay too low to do otherwise. http://goo.gl/maps/9At6

/peace.


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