Need help converting bike from NiMH to lithium...

[unclejemima]

I'm converting a NiMH bike to Lithium. My ebike had a 3.6AH 24V NiMH battery and I had a ebay seller from China make me a 24V 8AH battery with the same dimensions.

Anyway, I figured it would be a plug and play scenario, but it was not.

After hooking up everything like it was before with the NiMH, the LED meter shows only 1 bar (empty) with the new lithium battery.

I tried taking the bike for a spin, it worked for only about 5 seconds before it quit. I checked the LED meter on the battery and now it showed 0 led's.

My question, will the LED meter read different with NiMH vs the Lithium unit? Does it not just read voltage? If not, the perhaps my battery is just not charging properly?

Here is some photos of the setup. Perhaps you guys can suggest why this is not working?


the battery shell with the new lithium setup inside.


specs of the old battery what now houses a 8AH lithium unit.


LED meter only showing 1 LED (blinking)


Ghetto cord? Whats with green wire?


charger specs. It uses what appears to be a XLR cable (same as microphone) for the charging port from the battery to charger. I thought this was supposed to be 24V, whats the deal with 29V?

 

[lbz5mc12]

Is there an on off key/switch on your battery? If so make sure it's turned off before you charge it. Did you charge the battery before you tried to use it?

 

[dogman dan]

Sounds like for some reason, the new battery did not fully charge. Bike should show more bars if it got 29v. How many volts did the old battery charge to?

 

[skeetab5780]

Should get a $5 multi-meter and grab some voltage readings so this is a little more clear. Your little "ghetto wire" is a ground pigtail since the line side of your charger is only 2 prong, it just adds some protection to the circuit if you may desire to ground it to the system(the buildings ground) I wouldn't worry about it tbh.

now your old SLA pack ran 2x 12v batteries in series probably around 15.2v each fully charged so assume around 30.4v fully charged.

Your new pack is probably 18650 lithium cells and is configured in a 7s5p configuration probably. So that is 7 cells in series. the nominal voltage of these cell is typically 3.7 volts

So 3.7 x 7pieces = 25.9v nominal (normally)

and when the cells are fully charged they are 4.2v

so 4.2 x 7pieces = 29.4v full charge

Dogman is right that it seems more of the lights on the gauge should be lit up since the topped off voltage of each pack are within 1-2v

The battery cutting out seems odd(not sure if theres a BMS), but everything we say here is speculation until we see a voltage reading or a fully charged battery light somewhere.

 

[Tommy L]

And you cant trust the LED anymore and if the pack is LiFePO4, it has a flat voltage drain curve.
You will need LVC protection or a Watt Meter to ensure you won't over discharge your
new investment. If you use LVC then you will be doing 100% or more depth of discharge.
I recommend using a watt meter. 24v x 8ah = 192 watt hours and only use 80%
of that so approx 150 watt hours available. If you are using 20 watt hour per km,
you can only go 7 or 8 km.

Tommy L sends....

 

[Tommy L]

Also, to answer your question of:

"whats with 29v for this charger" ?

You now have what I believe to be LiFePO4 chemistry. If you divide your charger voltage by 8S, that is 3.675v per cell.


So let's not assume...... how many cells are in series?

and you always need more voltage (which is pressure) than the nominal voltage of the pack in order to charge it

Tommy L sends.....

 

[to the beach]

I would EMAIL the EBAY seller and ask how many cells are in series, and if there is a battery management system.

 

[arkmundi]

multimeter and test! work forwards from battery towards motor. there may be a fault in the circuit which you'll discover. Or, as previously stated, the new battery pack is not charging up as expected. Sometimes a pack can leave the factory just fine, but after a long ship from China, arrive DOD. Only one connection in series popping loose will lead to failure. If this latter, send it back to the manufacturer for either a refund or replacement. If not forthcoming, reverse the charges using your credit card company.

 

[unclejemima]

Thanks guys. I will get more info from the seller on the battery spec.

The battery does have external BMS wired to it. I was very certain to make sure I got a battery with BMS for that exact reason.

The battery was removed from the bike to charge (as you can see, its portable. It clips into and out-of the bike)

I will test the battery with a voltage with a multi-meter and let you know guys know the specs.

I hope the battery is not DOD!

The charger is odd. It would at first be solid red for about 1hr, then it would start blinking red/green, but it would not be constantly blinking (sometimes 1 blink ever second, then 1 blink every 3 seconds, sometimes it would blink many times in a row). Then after about 4 hours the green was solid on, though it was a dim green.

The thing is, the green LED lights up on the charger as soon as I plug it into the wall...even before I plug the battery into it, and its a dim green. Not sure if its supposed to be a brighter green or not?

I'm thinking I may try getting a quality charger from a RC shop, the ones that auto calibrate (for correct voltage and amperage). I'm hoping its just a poopy charger.

I'll keep you posted,

 

[unclejemima]

photo of charger showing green LED. Same green LED that shows when I plug the charger into the wall (before plugging the battery in)

 

[999zip999]

That is just a baby of a battery. How far do you want these battery to go. Miles ?

 

[arkmundi]

photo of charger showing green LED. Same green LED that shows when I plug the charger into the wall (before plugging the battery in)

Same thing - with your trusty multimeter, check the voltage and current output of the charger. Probably just fine. You need to find the actual fault and not guess. Sometimes it can be something simple, like a wire that knocked loose, or a bad solder job. If its something simple like that, you can save yourself a lot time and aggravation by fixing it yourself rather than going back to the manufacturer.

 

[dnmun]

you need to open the battery case and show a picture of the battery inside so we can inspect and then you need to show the BMS so we can show you where to measure the individual cell voltages. once you do that then we may have enuff info to at least direct you in what and how to test it. sounds like the battery is severely imbalanced and the BMS is not charging because one cell is full already, but we don't know what the voltage is yet.

 

[unclejemima]

I checked and it 29.2V out of the battery.

I'll post pics later tonight of the battery

 

[unclejemima]

I spoke with the battery vendor, and he said 29.2V is correct. Though he did not tell me what the battery composition was, the best I can guess is Lifepo4 and 8 cells...? So this would make 3.65V per cell? Does that sound about par?

I'm worried if I crack the skin off the battery, then the seller won't let me return if it is actually broken.

Let me know what you guys think about the 29.2V and perhaps you can better explain it to me

 

[unclejemima]

Did some quick reaseach, and it appears 3.65v per cell for a 8v lifepo4 is about perfect...so, there must be something else up.

Here is a photo of my rig (ok, someone elses, but mine is the same.) You can see where the tiny battery goes. The stock one was claimed at 30km in eco mode for 3.6AH unit...obvious BS, so my tiny 8AH Lifepo4 unit is more than 2x better than stock!

Any suggestions where to start looking to solve my problem? Not sure if its the BMS stopping the battery from giving out power or the bike cutting power off.

Let me know what you guys figure,

 

[dogman dan]

8 ah is very small, and you may have a bike too big for it. It could just be the bms is set to protect the battery, at an amps limit too weak for the bike. For example, if the bms on that tiny battery pops at 20 amps, and your bike pulls 25 amps.

It all depends on the type of cell in that battery. If it's 2c cells, 16 amps max. If it's 5c, 40 amps max. Your nimh might have been as much as 5c. Cheap lifepo4 won't be better than 2c.

But chances are, it's also out of balance. Leave it on that charger 24-7 and see if it improves. The charger going from red to green to red is the bms working to balance it. But, it's also possible that there is a problem with that charger, like a simple bad solder on the wire to the battery.

Re reading,,, you asked for an 8 ah battery. Maybe he made you an 8 amps battery?

 

[unclejemima]

Did some testing last night...I'm really not sure what is going on, but I think the bike might be somehow cutting power?

Here is what I did. I insert the battery, turn the key and it work. It works for about 15-30 second, then shuts off. At this point I can turn the key on/off multiple times, and it will not work again....unless I remove the battery (even just 1/4") and then re-insert it, it will work again for 20-30 seconds.

Something is happening when I'm re-moving and re-installing the battery. I'm not sure if the bike is re-setting, or the battery?

I thought 24V NiMH, and 24V Lithium would provide the same results...but obviously not. What is different about the power the NiMH created vs what the lithium produces? Why should the motor care? Is there perhaps a protection module in the bikes motor or electronic system that could prevent this? Its obviously not a fuse, or it would be as simple as changing it...something else in the line.

I might rip the engine case apart and see if I can direct wire this bad boy. Perhaps I can solve this problem another way.

My analogy goes to AA size batteries. I can buy regular AA batteries, and I can buy AA lithium batteries. The latter costing more and lasting longer, and can be used in all the same devices as the regular AA. Get my drift?

Let me know guys, not sure where to go from here.

 

[dnmun]

if you refuse to open the pack so we can tell you where to measure on the BMS there is nothing else to do. you can send the battery back and demand your money back if you won't work on it and see how that goes. you can hook it up to a dummy load and see how many amp hours it can push through your watt meter.

 

[unclejemima]

Hi Guys. Got another update from the battery seller last night.

The battery is a Li(NiCoMn)O2 pouch cells, 3.7v per cell

So not sure if my 29.2V is sufficient then.

Let me know what you guys figure with the above info. What the heck type of lithium is this and is it any good?

 

[unclejemima]

if you refuse to open the pack so we can tell you where to measure on the BMS there is nothing else to do. you can send the battery back and demand your money back if you won't work on it and see how that goes. you can hook it up to a dummy load and see how many amp hours it can push through your watt meter.

Ok. I will open it tonight. Can I source some type of heat shrink to wrap the battery again like it is now?

 

[dnmun]

it appears to be in a grey plastic case. i did not see any shrink wrap. as i said we need to have picture of the BMS so we can tell you where to measure, you don't have to cut any shrink wrap. we just have no way to help you if there is not any information to use to work from. we have nothing so far.

 

[ambroseliao]

Many older NiMH battery setups had a temperature probe built into the packs which would signal when there was an overtemp condition (NiMH batteries rise in temperature as they approach full charge). If the temp sensor isn't attached and the controller was smart enough, it could shut the system down with an error. Perhaps that is what the green wire in the picture above is connected to...

 

[dnmun]

this is a good point. the controller may use the same temperature probe that the charger uses in order to supervise the discharge. do you still have the original battery pack and can you show a picture of it and all the wires coming out of it?

 

[unclejemima]

Many older NiMH battery setups had a temperature probe built into the packs which would signal when there was an overtemp condition (NiMH batteries rise in temperature as they approach full charge). If the temp sensor isn't attached and the controller was smart enough, it could shut the system down with an error. Perhaps that is what the green wire in the picture above is connected to...

Bang. You are correct. There was what appear to be a temp probe in old NiMH pack, sandwiched between the cells. I figured it would only be used for charging, and not have anything to do with driving.

I'll really try and get some good photos tonight for you guys...and I'll try re-installing the temp probe as well.

Thanks for all the help guys,