How do I rebalance LiFePo4 Headway pack

[e-beach]

].....Some of my cells do go a lot higher than the others and it is the ones that I had added and are not from the original batch. So until I get my new charger there will not be enough time for them to balance with the BMS, but with my current charger cutting from what I can tell it does not get high enough voltage to damage any of the high cells. I also tried putting large 10 ohm resistor in line with charger to lower current = which it did but charger still cuts off too early so that does me no good either.

OK, sounds like you are busy with work or life....but you will still need to determine a lot of different thing that are still a mystery to us on the other side of your posts, and post them so we know what they are

Your new charger might give you 58.4v but that is still no guarantee the cells will match in capacity even if your new charger works well with your old bms. Why would you want to lower the current of your charger?

We still need to know if your bms functions at 57.6v so do what dnmun has suggested to find that out.
We still need to know what your terminal cell voltages are after your charger turns off.
We still need to know what your cell voltages are after you left it on the charger over night.
We still need to know what your individual cell capacities are so you can build the bet pack possible with used cells.

We need you to post that info.





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[bikeelectric]

].....Some of my cells do go a lot higher than the others and it is the ones that I had added and are not from the original batch. So until I get my new charger there will not be enough time for them to balance with the BMS, but with my current charger cutting from what I can tell it does not get high enough voltage to damage any of the high cells. I also tried putting large 10 ohm resistor in line with charger to lower current = which it did but charger still cuts off too early so that does me no good either.

OK, sounds like you are busy with work or life....but you will still need to determine a lot of different thing that are still a mystery to us on the other side of your posts, and post them so we know what they are

Your new charger might give you 58.4v but that is still no guarantee the cells will match in capacity even if your new charger works well with your old bms. Why would you want to lower the current of your charger?

We still need to know if your bms functions at 57.6v so do what dnmun has suggested to find that out.
We still need to know what your terminal cell voltages are after your charger turns off.
We still need to know what your cell voltages are after you left it on the charger over night.
We still need to know what your individual cell capacities are so you can build the bet pack possible with used cells.

We need you to post that info.


.

true - I am a bit challenged by time I can put into this right now due to work. It is a bit of a chore for me to pull the battery out of the bike, unwrap it and check all those voltages. I should go to harbor freight and get 16 cheap multimeters to wire in ! As it is now I have been using a single DC clamp on multimeter and need to switch from amps to volts etc to see what is going on - then the charger clicks off so it is frustrating.
I was hoping to lower the current on the charger so that the cells would come up on voltage slower so the charger would not click off so soon and it would give me more time to take and log voltages and take measurements. The reason I put the old BMS back in is because I can actually get meter probes on the bypass resistors where I could not do that with the other BMS.

 

[999zip999]

Cellog or other cell checker. I think I talked about this before. I hook up a set of sense wires for access. For checking voltage a place to hook up a single cell charger to help balance.
In your case two 8s or four 4s. Yes you would have to connect one time. I love having cell access with the BMS also.

 

[bikeelectric]

Cellog or other cell checker. I think I talked about this before. I hook up a set of sense wires for access. For checking voltage a place to hook up a single cell charger to help balance.
In your case two 8s or four 4s. Yes you would have to connect one time. I love having cell access with the BMS also.

I ordered one of the wattmeters - just have to wait until it arrives .
I will have to set up a good test bench with everything needed - and some loads to put on.

 

[dnmun]

if your charger "clicks off" then it cannot balance your battery. how do you know that the charger turns off?

 

[bikeelectric]

if your charger "clicks off" then it cannot balance your battery. how do you know that the charger turns off?

I can see the LED light turn from yellow(charging) to green and also had the DC clamp meter on the charging circuit which show no current when it went to green LED - plus you can hear the relay click on it . So yes it just shuts off and will not turn back on to charging until you unplug the charger and re-power it.

 

[dmwahl]

if your charger "clicks off" then it cannot balance your battery. how do you know that the charger turns off?

I can see the LED light turn from yellow(charging) to green and also had the DC clamp meter on the charging circuit which show no current when it went to green LED - plus you can hear the relay click on it . So yes it just shuts off and will not turn back on to charging until you unplug the charger and re-power it.

The charger may be shutting off once the current drops below a certain level (?). If so, try adding a single 1k/5W resistor (or multiple)across the charger output to increase the current the charger sees. The resistor will get fairly hot, but you'll only be at about 2.5-3W. Might not work, but it's what I would try.

 

[dnmun]

show a picture of the charger. open the charger and show a close up picture inside in the back end. measure the charging current with an accurate meter like your DVM on 10A scale or use a wattmeter like everyone else.

do not put resistors in the charging leads.

 

[bikeelectric]

if your charger "clicks off" then it cannot balance your battery. how do you know that the charger turns off?

I can see the LED light turn from yellow(charging) to green and also had the DC clamp meter on the charging circuit which show no current when it went to green LED - plus you can hear the relay click on it . So yes it just shuts off and will not turn back on to charging until you unplug the charger and re-power it.

The charger may be shutting off once the current drops below a certain level (?). If so, try adding a single 1k/5W resistor (or multiple)across the charger output to increase the current the charger sees. The resistor will get fairly hot, but you'll only be at about 2.5-3W. Might not work, but it's what I would try.

When I turned the adjustable pot on the right it would change the current but never made the charger kick off. The adjustable pot on the left changed the voltage seen on the charger with no battery connected and that would be the voltage the charger kicked off at when charging battery.

But I can give the 1K resistor a try too - always worth a try.

 

[dmwahl]

do not put resistors in the charging leads.

Why not? I was suggesting in parallel with the charger output, not series.

 

[bikeelectric]

show a picture of the charger. open the charger and show a close up picture inside in the back end. measure the charging current with an accurate meter like your DVM on 10A scale or use a wattmeter like everyone else.

do not put resistors in the charging leads.

I had posted a close up photo of the charger on first page of this thread. Here is photo again .
I use a DC clamp on meter which is quite accurate.

 

[dnmun]

then verify with the ammeter on your DVM to see if it is actually turned off. i cannot see any circuitry in the back end that would shut off the charger output. but something may turn off that relay and if it does then you will have to rewire the relay so it does not turn off or buy another charger made for charging lifepo4 packs.

 

[bikeelectric]

then verify with the ammeter on your DVM to see if it is actually turned off. i cannot see any circuitry in the back end that would shut off the charger output. but something may turn off that relay and if it does then you will have to rewire the relay so it does not turn off or buy another charger made for charging lifepo4 packs.

Yes the relay switches( latches) off when the voltage setpoint is reached. I did not think of jumping across the relay - though not sure I want to do that and take chance of destroying charger somehow. I have ordered a new LifePo4 rated charger and hope it get here soon !

 

[bikeelectric]

Here is follow up to my original post and taking some time to analyze everyone's comments and suggestions.
Yesterday I received my new 6 amp LiFePo4 16s charger . It goes up to 60v which seems a little high. I have monitored the cell voltages along with the BMS.
This new charger does shut off and will come back on automatically as the voltage drops. Unfortunate is that it does not have a low current balance stage from what I can tell and only surges to 6 amps , then cuts off. My original charger did cut back current from it's bulk to a lower amount.

I do have some cells that are out of balance and I have been trying to put resistors on the high ones so that the others can catch up. I also notice that the BMS resistors are turning on and trying to do their thing but the out of balance of the cells is a bit too much for them to catch up.

Last night I was single cell charging one low cell with an Accucell charger and though maybe I could connect my old charger that had failed to bulk charge - thought it might put out a little current and help balance. As soon as I plugged it in - it made the Accucell charger release a might nice puff of smoke. Accucell still lights up display and seems to function but will not charge. Have not had time to open it up yet and see what smoked. The old charger does not put out any current but must have some electrical short in it or grounding issue.

So live and learn !

My conclusion - which is as others have stated from the beginning - I need to try to find 16 cells that share similiar patterns so they will match and charge and discharge together more evenly.

 

[bikeelectric]

I found what smoked
Looks fixable - and others have had same problem
http://www.rcgroups.com/forums/showthread.php?t=1980332

 

[dnmun]

that mosfet is connected to the output i suspect, just cannot see the layout of the circuit from your picture. it is turned off until you make the connections with the balancing charger first. i did not realize you had a balancing charger, thought it was a bulk charger.

are you intending to repair it? you can use other mosfets to replace it. should be an nchannel mosfet on the ground leg of the charger.

i have several imaX B6 charger with similar mosfets and all blown up by accident in use.

your lifepo4 charger has to have a balancing current to allow the BMS to balance the pack at the end of charging.

 

[bikeelectric]

that mosfet is connected to the output i suspect, just cannot see the layout of the circuit from your picture. it is turned off until you make the connections with the balancing charger first. i did not realize you had a balancing charger, thought it was a bulk charger.

are you intending to repair it? you can use other mosfets to replace it. should be an nchannel mosfet on the ground leg of the charger.

i have several imaX B6 charger with similar mosfets and all blown up by accident in use.

your lifepo4 charger has to have a balancing current to allow the BMS to balance the pack at the end of charging.

I just ordered replacement mosfets from Digikey for the Accucell charger
http://www.digikey.com/product-detail/en/0/IRF7413PBFCT-ND
Yes I thought the new charger would have trickle balancing charge - and that is what the description says but I have not seen it doing this - only cycling on and off at full current
http://www.ebay.com/itm/281183088331

 

[dnmun]

then you need to open the charger and adjust the output voltage so it will push a balancing charge at the final voltage. do not use anything but a wattmeter or ammeter on your DVM to measure the charging current. it is the mA range.

 

[e-beach]

How do you know that your new charger is not switching to a low current constant voltage state? Do you have a volt meter and amp meter connected inline?

 

[bikeelectric]

How do you know that your new charger is not switching to a low current constant voltage state? Do you have a volt meter and amp meter connected inline?

Yes I have a wattmeter inline - the kind that tells all the watts, amps , voltage , etc that was suggested earlier . After leaving it on over night and letting it do it's thing I now see that the new charger is operating properly and putting out small current to do proper balancing.
I think the reason I noticed strange behavior initially is because one cell was too far off so voltage climbed up high too quickly. As the cell became more in balance and the pack voltage could stabilize near the cutoff setpoint then it gave the charger a chance to roll back it's current to balancing level so the BMS could properly do it's job.

Cycle Analyst says I used 1.81 amps
Wattmeter says I just put in 1.960 amps
Pretty close considering they are probably not in exact calibration with each other

So all is well now - thanks again for all the advice so now I have a very good understanding of what the BMS, charger, and cells are supposed to do when they are balancing .

 

[dnmun]

the charge does not 'roll back' the charging current. when the pack voltage climbs high enuff to closely match the full charge voltage then there is more resistance to the flow of current into the cell. this causes the current flowing from the charger to the cell to be reduced towards a minimal point.

your charger has a circuit designed to tell the charger when this charging current has dropped to about 5-10% of the full charging current level. when this happens then the charger will switch from the CC mode to CV mode and the green light appears on the charger but it is still pushing current, and this small current is now called the balancing current.

when i asked for you to measure the cell voltages while charging it was with the intent to find the one cell which had reached the HVC level so you could drain the charge off that cell to allow the charger to shift back into a high current CC mode again until the entire pack could reach a high enuff voltage to allow the charger to switch over to CV mode and provide the balancing current to allow the pack to balance.

 

[riba2233]

your charger has a circuit designed to tell the charger when this charging current has dropped to about 5-10% of the full charging current level. when this happens then the charger will switch from the CC mode to CV mode and the green light appears on the charger but it is still pushing current, and this small current is now called the balancing current.

Wrong! CV phase starts earlier, while current is still maximum. After that, it starts lowering while the voltage stays the same. What you're talking about, is just a point when the charger turns on the LED which indicates that the charging is over.