Battery concern.

Paderolis

100 W
Joined
Dec 14, 2013
Messages
108
Location
Las Vegas NV. USA
Hello all! I have a question concerning a battery I just received from an eBay purchase. It is a 48V 12AH Lithium-ion battery. I didn't know until I got it that it is rated for a 500W MAX motor, as it wasn't in the description text. It is on the actual battery label, but you don't see that unless you zoom in on one of the photos. Honestly I never realized it mattered, I thought as long as the voltage rating was the same, you were good. Okay, so my system is a 48V 1000W system that I use 99% of the time as a pedalic only. My throttle is installed but not connected. If I use this battery, will I damage my motor? The battery? Both?

I have been using LIPO batteries until now, 3 18.5V 5,500mAH in series. Thank you for your advise.

http://www.ebay.com/itm/New-48V-12ah-Electric-Bike-Battery-Kit-Comes-with-Charger-FREE-SHIPPING-/253058973271?hash=item3aeb7d7e57:g:dncAAOSwrhBZAjgU
 
potentially you can damage the battery or the BMS you could always get a 2nd battery and run in parallel for double the power change the BMS if the cells can take it

if your willing it might be worth talking a look at the internals and seeing what cells it has inside
 
Controllers have Max Amp ratings and that rating does not change according to the voltage you put it.. it's a fixed number... ie : 20 or 25 amp controller... or 35 etc...

example.. a 10 amp controller will draw 10 amps from either a 36v ( 360w )... or 48v ( 480w ) battery.
 
Thank you for your input guys! I contacted the seller about it, he runs an electric bike shop in California. He said the battery will work fine, I just wont get as many miles between charges as a larger AH battery with the same voltage. The 500 Max motor thing threw me off. He did say he would try to update the description for the future.
 
Paderolis said:
Thank you for your input guys! I contacted the seller about it, he runs an electric bike shop in California. He said the battery will work fine, I just wont get as many miles between charges as a larger AH battery with the same voltage. The 500 Max motor thing threw me off. He did say he would try to update the description for the future.

just be careful when you try it just to be on the safe side the BMS "should" cut it off if you go over speck but you never know for sure
 
The battery will work - but the problem is, you don't know if you're going to get 3 years or 3 months out of it.

As another poster calculated, towards the end, you'll be pulling 2C. I've got some cells which I draw 10C from every day, and they've lasted years. I've got some cells that from the day I bought them, (and I knew they were cheap/bad), a 1C draw caused big voltage and within 30 cycles, the cells started puffing, despite no over-discharge.

If I were you, and it might not be possible on your bike, I would insert a voltameter into the circuit, then go to a small hill. Note the resting voltage of the bike, then go full throttle up the hill. Check what the lowest voltage you see is. If it drops much more than 10-15%, your battery is going to have a fairly short life.
 
Sunder said:
The battery will work - but the problem is, you don't know if you're going to get 3 years or 3 months out of it.

As another poster calculated, towards the end, you'll be pulling 2C. I've got some cells which I draw 10C from every day, and they've lasted years. I've got some cells that from the day I bought them, (and I knew they were cheap/bad), a 1C draw caused big voltage and within 30 cycles, the cells started puffing, despite no over-discharge.

If I were you, and it might not be possible on your bike, I would insert a voltameter into the circuit, then go to a small hill. Note the resting voltage of the bike, then go full throttle up the hill. Check what the lowest voltage you see is. If it drops much more than 10-15%, your battery is going to have a fairly short life.

just so anyone that reads this know this only works well for low power bikes as big bikes at high powers will have a bit more sag
 
Yeah, not sure I 100% agree with that...

Sure, high powered bikes will pull the same battery down a lot more than a low powered bike. That part I agree with.

BUT, the cathode erosion occurs at an accelerated rate when high discharge rates are used. The cathode doesn't pop out and check whether you have a high powered bike or low powered bike. If the rate of discharge is faster than the cathode is designed for, it will wear prematurely.
 
Sunder said:
Yeah, not sure I 100% agree with that...

Sure, high powered bikes will pull the same battery down a lot more than a low powered bike. That part I agree with.

BUT, the cathode erosion occurs at an accelerated rate when high discharge rates are used. The cathode doesn't pop out and check whether you have a high powered bike or low powered bike. If the rate of discharge is faster than the cathode is designed for, it will wear prematurely.

most of us with high power bikes will see 10% drops on big hills but its only for a few a sec ( i am pulling 20c peaks on my offroad bike and thats with a very good battery and i still see 10-15% v drop at times depending on what the SOC is but i am pushing the power far more than 90% of the people on here )
 
zackclark70 said:
most of us with high power bikes will see 10% drops on big hills but its only for a few a sec ( i am pulling 20c peaks on my offroad bike and thats with a very good battery and i still see 10-15% v drop at times depending on what the SOC is but i am pushing the power far more than 90% of the people on here )

From what you described, I would say your battery is fine, but close to the limits of design for a full life. It doesn't really fall into the case that I described (10-15% on a small hill, you're on the lower end of that on a big hill.).

But you do bring up a good point, which I hesitated to because I didn't want to confuse the matter. SOC does matter, because internal resistance is dependant on SOC. It's less noticeable in LiIon/LiPo, because the discharge curve is more of an even slope, but doing the test on a full LiFePo4, where there's like 5% capacity between 3.65v and 3.3v (10% voltage drop right there), would give you erroneous results.

Either way, there's no "magical line" where your battery will get a long and full life on one side and will die a short and fiery death on the other. But from my reading and personal experience, 10-15% sag is where things start to get concerning.
 
It will work, but likely not last 4 years. The more you pedal, or rather, the more you limit the amps on the steepest hills, and on starts, the more the battery will be under 500w continuous. and like he said,, when its nearing empty, that's when to really slow down and go easy on it.

Into some wind, up slight hills, etc, 20 mph will take about 600w. That is about 12.5 amps, or 1c more or less for your battery. I see no problem with you riding your bike 20 mph all you want.

It will draw close to double that at 30 mph,, into some wind, up a slight hill. Wind and your back, or downhill, haul ass all you want.

One thing you can do that will help you monitor how your battery is doing is install a digital voltmeter, or watt meter on the bike. You will then be able to judge how hard your battery is being run by the sag under load. 2v sag is excellent, but you won't see that. 4-6v sag under heavy load is what I think you will see. Try to ride so at cruise, you have 2-4v of sag.

The other way to judge it, is even simpler. If after a ride, your battery is really hot, you pulled too hard on it. Sure, its within factory spec, but it did not like it. The battery will always get very warm. I mean it gets so hot its uncomfortable to hold it in a bare hand. try to avoid that.
 
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