Please help! LiFePo4 from China to fit in triangle?

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GCinDC's picture
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El cheapo, here. Want the best but not to pay for it.... Finally, after 9 months of research, I decided I needed a crystalyte 400 series, but then bought for cheaper on eBay a rear wheel kit 48V 500W. When it arrived I saw that it's from Golden Motors... No documentation, and lots of wires. Well, first I need a battery! The seller recommended a 48V 10AH LiFePo4 battery. I'd like to spend under $400, but will go as high as $500, and I'd like it under 11 lbs. This is so my wife or I can commute up some big hills with at least one kid on the rear rack child seat, and maybe another in a trailer. Here are my questions:

> By choosing the 48V kit, have I made it necessary to buy a bigger battery?

> How can I fit a child seat and a boxy LiFePo4 battery on the bike? (It's an old Hybrid, but I'm toying with the idea of buying a cheap Wal-mart bike w/ some suspension...

> What's the best battery size/shape to mount in the triangle, NOT on the rear rack? (child seat is there) I'd wanted a case that mounted like a BionX battery, but all the 48V LiFePo4 packs I'm finding on eBay are 5" to 7" wide or occasionally like 11" X 7" x 3"...

> Where can I buy cases or bags to hold the battery, or am I going to have fabricate something?

> Would a smaller (and even less powerful) battery work and fit better for my circumstances? (see background below) If so, what battery configurations would you recommend?

> Ping batteries have been recommended, but there are so many cheap 48V LiFePo4 batteries on eBay. Are all the rest junk?
http://shop.ebay.com/?_from=R40&_trksid=m38&_nkw=lifepo4+48v&_sacat=See-All-Categories

> They seem willing to build custom-size packs, which brings me back to the bag/case question.

Any thoughts?? Please help! Thanks, Greg

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dogman's picture
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Re: Please help! LiFePo4 from China to fit in triangle?

Ping can build you a pack in a funny shape to fit the triangle. If you want it to last though, you need the 20 ah sise, more than 500 bux. Smaller will stress the battery too much and die a lot quicker than 1000 cycles. If it runs the motor without cutouts that is. As for other sellers, so many new ones we have no non ebay feedback on. One seller changes identity pretty frequent and is known to sell junk. This guy has sold under several names, east united music, Jimmywu, There is some difficulty finding out who he is this week.

Many of the other sellers are selling cylidrical cell packs that can have a tendency to have problems simply because so many of em are needed to make a big battery. So an individual cell can die easier than packs like Pings that use a prismatic cell. Prismatic cells are 4 ah each so 6 of em make 20 ah 3.5v That is a lot less connections than with the round cells. Also the prismatic cell packs have soldered connections instead of spot welds like the round cells use. The spot welds can pop when you hit a pothole and repairing them is not easy I'm told.

Ping is the only seller I know is using prismatic cells that is known to deliver and do customer service when there is a problem. The other seller that sells hi-power brand prismatic packs is still in the we don't really know category at this time. Happy hunting!

Another thing, some folks with your requirements, triangle, lower cost, etc, are pretty happy with thier nicad packs. If your ride is short enough, maybe nicad till you can afford the big lifepo4 pack?

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GCinDC's picture
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Re: Please help! LiFePo4 from China to fit in triangle?

Thanks for the reply! I almost bought from mp3hk, but read more about him, and others...

Going w/ Ping or Nicad w/ triangluar packs sound like good suggestions. (48V nicad, right?)

But back to the question about battery voltage/amperage -- A 48V 10AH battery will get stressed and the motor might cut out? I've read so much about people running 48V on 36V systems, I figured I could run the 48V kit with a 36 volt battery! Faulty logic, huh? Would, for example, a 36V 10AH battery run a 48V motor as fast as a 36V motor?

I'd decided on the 48V system for the extra umphf on the hills, not nec speed, and I doubt we'll commute over 10 miles...

Any comments about shockley (sp?) battery packs for my system?

Thanks! -Greg

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Re: Please help! LiFePo4 from China to fit in triangle?

Good you didn't buy from mp3hk, he may be the bogus seller. I just read a new post about one of his batteries arriving nonfunctional.

The deal on Ah and lifepo4 is basically that the cheaper type is only good for so many amps per amp hour. So for the thing to last, you can't get more than about 1.5 amps per amp hour. So it takes a 20 ah pack to service a 30 amp draw for continuous use. If you pull much more than that, like 25 amps on a 10 ah duct tape battery, it will not last so long. A ping 20 ah can put out almost 60 amps for a few seconds, but needs to be limited to 30 amps while cruising. Some folks use a cycle analyst to limit amps, but I think you need to just buy a big enough pack for your motor.

The more expensive lifepo4, A123, for example can put out a lot more amps per amp hour than the cells in the duct tape packs.

With nicad, you can get away with a 10 ah pack and be OK.

And on the case, bags can be bought for the triangle nicad packs, but with the ebay, duct tape packs people just have to get fabricating.

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GCinDC's picture
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Re: Please help! LiFePo4 from China to fit in triangle?

FYI, correspondence from Ping: (I hope he won't mind me sharing; I just hope it helps someone else out there.)

Hi Greg, For 500w kit, I recommend our 48v12ah at least. It can be made in size 160x75x320mm. Is it thin enough?
We don’t have battery cases or bags. If you want, we can search one in the local market for you. Best regards, Ping

Hi Greg, Price of 48v12ah pack is 398usd + 85usd shipping fee. Lead time is about one week. Shipping time is 7-10 days. We cannot make it in a triangle, because our cells are rectangular. But we can build the pack like 2 building blocks like this attached picture. (picture of L rotated 90 degrees). Best regards, Ping

So there it is. Price is great, now I have to commit to a 12Ah pack, which I now have doubts about. And decide if I can fabricate a waterproof triangle to fit building blocks that will hang nicely from tubes... ;-/ Or get a 'notebook' shape that will be easier to protect and mount... It probably wouldn't be good to mount it on the back of the child seat, would it??? The children will only use the child seat for a couple years anyway, and hopefully I'll use the kit for longer... I'm just typing to try to make up my mind....

I searched this site for "child seat" and only got another hit... weird.

Thanks for any feedback. I feel good going w/ Ping though... -Greg

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Re: Please help! LiFePo4 from China to fit in triangle?

Hi, I saw a triangle shaped battery bag for sale so thought I'd post the link if you're interested :)

http://www.ebikes.ca/store/store_batteries.php

good luck

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Re: Please help! LiFePo4 from China to fit in triangle?

36V_life_pack.jpg
this is a triangle LiFe pack courtesy falconEV

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Re: Please help! LiFePo4 from China to fit in triangle?

GCinDC, the voltage rating for a motor is based on its ability to dissipate heat on a constant load that is about 20% of its absolute maximum instantaneous power. If used at its rated power and voltage (and also bear in mind many manufacturers are knowingly too optimistic in their labelled ratings) a motor can run for days and never overheat under a normal load.

If over-volting, the RPM's of the motor will increase, and it will run warmer. If you take an over-volted motor up a hill, the motor and controller will get noticeably hot, and hopefully cool off rolling down the other side of the hill. A motor that provides 20 MPH at 36V, might provide 24 MPH at 48V.

If the hill is very long, and you + cargo are very heavy, and the ambient air temp is a hot summer...something may fry halfway up the hill. So, why do it?

The Crystalyte 5-series can easily provide 25 MPH and climb hard hills without overheating, all while using its rated voltage. Its also heavier and more expensive, and will have a shorter range as it draws more amps from the battery pack even when just cruising.

If you use a lower voltage on a higher-voltage rated motor, it will spin slower than its rated speed.

If the battery is too small, I "think" it may sag, and the controller will think the battery is low and activate a "Low Voltage Cutout" (LVC)

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Re: Please help! LiFePo4 from China to fit in triangle?

does anyone know if the weight rule of thumb applies to LifePO4 battery packs...

i.e. that if a battery feels much lighter then it usually has much less power density regardless of the printed capacity (when comparing like chemistries)

i've seen some LifePO4 48V 20AH packs on ebay which weigh 9KG and others with the same AH which weigh 14KG.. is it relatively safe to assume that the heavier pack is more likely to have a capacity a closer to the printed AH ?..

as for the triangle battery pack (pictured above) i dont believe triangle is a very stable shape for stacking cylinders.. i cant help but feel that if you do a fair amount of offroad riding that there would be a higher risk of the battery contacts breaking than compared to an upright square block of battery cells.

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Re: Please help! LiFePo4 from China to fit in triangle?

custom bike-rt.jpg

here's your frame battery pack from www.falconev.com

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Re: Please help! LiFePo4 from China to fit in triangle?

I've had two ebikes where the batteries were in the center triangle. I think it's a very good location for batteries, down low for good center of gravity etc. But I do agree the battery block needs to be solid. The picture proton shows with the batteries held ONLY by the metal connection plates just does not look like a good idea. I doubt battery cell designers had in mind those mounting points would see serious stress.

I've put together a pack using Headway cells and the matching battery holders. These are plastic pieces shaped correctly for the Headway LFP38120 cells, they snap together in rectangular blocks, and they feel very rigid. They're built so the connection plates can easily connect cells together, but the connection plates do not contribute to the rigidity.

I imagine you could use those holders to construct a semi-triangle pack.

Once you've done that the bag and mounting system proton shows might be sufficient. But I dunno if I'd want to trust velcro straps to hold a 20+ lb block of batteries in place.

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Re: Please help! LiFePo4 from China to fit in triangle?

Maybe reikman should order a frame bag so he can report from direct experience.

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