Inexpensive Lithium Batteries?

GoldenMotor.com

jdcburg

New Member
Jul 9, 2009
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Hi folks - I can’t vouch for the company but if you’re willing to gamble a little you can get single 3.2v nominal 20 ah Yesa LiFePO4 cells for 9.99USD ea. The site is Refurbished Electric Bike motors, Store Demos, Yard Sale, Bargains, One-of-a-kind They are in Texas, so US shipping should be quick and reasonable. They say these were ordered by a scooter manufacturer but were not up to the task so they have “thousands” to sell. I don’t know but I think these might be the cells: LiFePO4 Battery,LiFePO4, the best choice to replace Lead acid battery! If so, they are 2C continuous 4C burst, so they’re good for 40 amps continuous. Burst usually means no more than 5 seconds every 30 seconds. Both terminals are on top and look like they are threaded, so it would be easy to hook them up in series. Just stand them upright in a box and connect + to – with drilled bars or wires and terminals. 4 in series is 12.8 nominal so these are essentially $40 for a 12 volt 20 ah lithium battery, if all the cells are good. They clearly state there are no guarantees. LiFePO4 are 14.6V right off the charger but are usually in the 13 to 13.6 range during use. By my calculations a 12V battery (4 cells) would be under 6x3x6 inches and weigh 6.25 lbs.

LiFePO4 are the “safe” lithium cells that are very stable and unlikely to catch fire or explode if charged or discharged too quickly (like by short-circuit). These special deal cells are sold without a BMS (battery management system). The BMS keeps all cells in balance and prevents overcharge or overdischarge, which can be a problem with lithium batteries. There are separate BMS systems available but some people (including me) believe that you can watch your cell voltages and balance the cells manually, especially if you don’t draw too heavily or discharge too deeply. I am running similar 20 ah LiFePO4s that I got from ElitePowerSolutions.com. I am still collecting data but as an example my 24V 350W shift kit mtb used about 9ah on a hilly 13 mile ride with moderate pedal assist. The maximum amps was under 28, so I was well under the limit for 20ah 2C batteries. I find the individual cells are usually within 0.1 volt of each other off the charger and nearly dead even after some use. For instance after that 13 mile ride each cell was 3.27V. The total was 26.17V so the 24V motor still had plenty of pep. By extrapolation, I should be able to go 25 miles on a charge. Not bad for a 13 lb battery - jd

ps - in re-reading the specs on the site, these are 1C continuous/2C burst, so they're not the Yesa's I found. Still might be worth a try. Also, look into a LiFePO4 charger for best charge/longest battery life with lithium batteries
 
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zabac70

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Mar 17, 2010
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Belgrade , Serbia
Some stuff looks OK , but , as you said - it is a gamble with batteries( I disagree for BMS - very smart thing for all kinds of batts). It looks like deacon's next project...:)
 

deacon

minor bike philosopher
Jan 15, 2008
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"not I," said the fat boy.

the 1c sounds alot like the nimh I am working with now. The batteries are getting easier to charge actually. Here is the trick to charging the kind of batteries you are talking about.

This is from what I have read and what I see with the pack I am working with.

The problem is not the batteries in series. Unless you have a bad cell in the string, Which will show up with the multimeter, they will all charge the same. The problem is the strings to make the proper voltage being different charges after use. But with a 20ah cell you would only have three strings so jut charge each one till it is full. Or buy three smart chargers and charge each one individually. I don't have a problem with that any more. It just takes checking them to make sure they are close and none is over charged.

I did make one test yesterday that was interesting. I ran the chain bike with no charger on full nimh from the house. It seemed to run at about half power. But the intersting part was when I stopped on the side of the road and unplugged half the battery pack. It ran much much slower, so their are a couple of things I learned from that.

1. with the batteries I am working for they are no more than 1c maybe less.

2. when building a battery pack forget about the motor size. It's about total available watts from the battery pack. I learned that from switching the pack from 36v to 24v and got exactly the same performance (within reason) The total amps in the pack is what you are dealing with not the amps of each battery within the pack. You can configure a total of 60amps worth of batteries anyway you want you still have the same power. The flood gate kick of sla hides that simple lesson.

3. I proved yet again that they will work given enough batteries in the pack. Also that the amp hours of the pack effects how much total current is available at any given time on these batteries. Not true Sla.

On charging what I do is charge the complete battery (each 12v section) at one time. I charge them for one hour, then I let them rest an hour before I read them. The individual strings inside the battery are usually very close by that time. Each battery might require a little difference in the total time to get them close. By letting them rest, I think they co-mingle the volts and come together (as the beatles said)

I have not been able to test range since I can't get the batteries to run the bike enough yet. My guess is the manufacturers have way over rated the ah of the batteries or they are draining less than 1c.



The 1c lithium batteries proved unacceptable for the bike manufacturer for a reason guys. they would have had to use twice as many to make a pack to drive a high performance bike, I think.

DO NOT charge at over two amps though. I burned a few batteries at 6amps.

I had to throw out one of my old sla batteries yesterday, So I have a decision to make. I have one viable set of sla batteries 17ah. I also have managed to put together one experimental set of old 7ah batteries. The decision to be made is this. Do I keep adding nimh batteries until I get enough to run the bikes or do I buy more sla batteries. Since I have a working set of Sla batteries and my need is small I think I will continue to add to the nimh pack a little at a time.
 

jdcburg

New Member
Jul 9, 2009
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massachusetts
I'd love to see a few more people here try lithium. When I ended up pushing my SLA powered bike up the last hill of a 6 mile ride early this spring, I knew I had to change. These only had 25-30 charges in them. They used to go 12 miles. I almost went with NiMH but I'm glad I didn't after reading about Deacon's experience, although I have read about honestly rated NiMH that can handle 10C discharge.

I've already put more miles on my lithiums than I did on the SLAs. So far they have way more power and less sag. I don’t think I’ve come close to seeing how far they’ll go. The farthest I have been is a little over 15 miles round trip. That's to work, where they sit there all day and then take me home. I had to take a charger and charge the SLAs whenever I did that - I don't think they take well to sitting all day half-charged and they probably wouldn’t have gone the full distance anyway.

I agree, the cheap lithiums might not be a good choice for first timers, although I suspect they are underrated, not overrated like the NiMH. If they didn’t work out, it might sour a lot of others on lithium. I’ll probably get a set. I have a B&D battery lawn mower that will need a new battery soon. The 24V SLA replacement is $130 and weighs probably 25 lbs. I’m willing to try an $80 lithium replacement that weighs half as much. Once I get them I’ll surely try them on the bike just for grins - jd.
 

deacon

minor bike philosopher
Jan 15, 2008
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let us know how it works out. My only problem with lithium is the high buy in price. I will wind uip with probably as much money in the nimh pack and may still have a crap pack when I'm finished. Only time will tell.
 

jdcburg

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Jul 9, 2009
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massachusetts
My 24V 20ah lithium (not these cheapies) was $240. Shipping was under $20 and they arrived in a week to Massachusetts. They are rated 2C continuous/10C impulse. I've had them up to 1.4C and they've never sagged or felt even warm. They don't have a BMS. That would have been $70 more. So far I haven't felt the need but I watch them pretty closely. If I can get 5x the use of SLAs out of them (1000 cycles vs 200 for SLAs) then that brings them down to less than $50/SLA pack. They are rated for 1500 cycles at 80% DOD (depth of discharge). By the time these are shot there will probably be better batteries out there and maybe even cheaper - jd
 

deacon

minor bike philosopher
Jan 15, 2008
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Thats a good price... I have seen the 36v 20ah go for as much as 600 bucks with the bms and charger... Thats too heavy for me.

I have my hopes penned to a sla with a lead allow to cut the weight. At half the weight and increased life they would be fine for me. I don't like the bulk of them but they still seem to pack the most punch for the buck.... Still who knows what will come alone now that people are finally looking into battery technology. Automobiles will set the pace and standards I expect.
 

SANGESF

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Feb 23, 2009
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Lake Worth
My 24V 20ah lithium (not these cheapies) was $240. Shipping was under $20 and they arrived in a week to Massachusetts. They are rated 2C continuous/10C impulse. I've had them up to 1.4C and they've never sagged or felt even warm. They don't have a BMS. That would have been $70 more. So far I haven't felt the need but I watch them pretty closely. If I can get 5x the use of SLAs out of them (1000 cycles vs 200 for SLAs) then that brings them down to less than $50/SLA pack. They are rated for 1500 cycles at 80% DOD (depth of discharge). By the time these are shot there will probably be better batteries out there and maybe even cheaper - jd
On the one's you're talking about, I've heard good and bad...

it's the luck of the draw.....
$240 is just the pack. So if you already have a way to charge 'em and they're all VERY close in AH, then That'll work....

But just like the other's have said, that kind of pack (2-12v 20ah packs) is not really for the beginners....

Even the one's that theOP spoke of, on their website, they say, that there is prolly a 50% bad battery rate, and that they didn't test them.

(FYI... that means that most of them (80%) are around 17AH , 15% are around 12-14 and 5% are less than 10) (At least that's how my last sample went, out of the 40 i got last time from that kind of vendor.. 32 were abot 17AH (NOT 20), 6 were from 12-14AH and the last two were just pure useless..)
 

jdcburg

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Jul 9, 2009
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massachusetts
I agree 20 ah lithiums w/o BMS are not for rank beginners. But if you can design and build an ebike and wire a battery, controller and throttle, you're not really a beginner anymore. Most hub motor kits are sold with a lithium battery pack and I think most people do well with them. I'm sure there are notable exceptions. I bought a single cell lithium charger that I can use to top the cells up if I want to or to balance them if I need to. So far they self-balance with use. The last time I charged them 2 cells were higher than the others but after a half mile they were all within 0.01v of each other. So far after every ride, long or short, they have been within a few hundredths. They also seem to self-balance overnight if I leave the controller plugged in. ymmv - jd
 

deacon

minor bike philosopher
Jan 15, 2008
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north carolina
all my nimh cells in parallel usually self balance to each other. I only have to balance the series ones to each other. At one tenth of a volt I call them balanced and move on. Usually I try to have them run about 13.5 after an hours rest.

Right now they work best as a secondary parallel battery pack. They seem to extend the charge on the sla pack but I'm not exactly sure how much. much more testing to be done. The only real problem i had with the charging issue was the 6amp burnout of some strings.
 

SANGESF

New Member
Feb 23, 2009
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Lake Worth
I agree 20 ah lithiums w/o BMS are not for rank beginners. But if you can design and build an ebike and wire a battery, controller and throttle, you're not really a beginner anymore. Most hub motor kits are sold with a lithium battery pack and I think most people do well with them. I'm sure there are notable exceptions. I bought a single cell lithium charger that I can use to top the cells up if I want to or to balance them if I need to. So far they self-balance with use. The last time I charged them 2 cells were higher than the others but after a half mile they were all within 0.01v of each other. So far after every ride, long or short, they have been within a few hundredths. They also seem to self-balance overnight if I leave the controller plugged in. ymmv - jd
Anyone know a good place to find an inexpensive single cell LiFePO4 charger?
 

deacon

minor bike philosopher
Jan 15, 2008
8,114
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north carolina
now that is a deal... I have one of those nicad/nimh battery chargers that accepts aa aaa c or d cells. But would not do for lithium because it charges to just under 1.5 max. I use it now and then when I need to charge a single cell nimh for some reason.