# Lead acid charger doesn't charge LiFePO (not even a bit)



## Ziggythewiz (May 16, 2010)

Does it have any settings?

You can't safely complete the charge with your full pack charger (I assume that's what you're referring to). The highest you take the cells should be with them paralleled unless you have some means of stopping the charge when the first one gets full.


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## sabahtom (Mar 1, 2011)

It's got 6v and 12v only. Its a constant current charger.

I wasn't clear re completing the charge. I plan to do that as yourself/elithion suggested (if I understood properly):

1. charge in batches of 2s 4p with the lead acid charger until all the cells are at 3.5v. I will only do this while I'm watching.

2. After all are charged to 3.5v, connect the entire pack in parallel

3. Wait a day, then charge in series using 312v 10 amp LiFePO charger and BMS


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## Ziggythewiz (May 16, 2010)

If you're using a BMS anyway supposedly you don't have to bother balancing them anyway, that's the job of the BMS.

Have you tried charging 2 in series with the 6V setting? That will likely go to a higher VPC (and would definitely need watching). I've heard it common for the 6V setting to go up to 9V, and I use mine daily to charge an 8V GC batt.


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## sabahtom (Mar 1, 2011)

My reason for doing this was to save charging time and work for the bms if there was a large difference in SOC between the cells. They range from 3.22 to 3.28 when I measured a week ago. 

Per Elithion's website, it's a bad idea to connect cells in parallel when one is more than 80% charged, particularly if others are much lower. I don't have that issue so maybe the quickest and safest way to do this is to connect them all in parallel for a day, then connect them to the bms and 312v charger in series and let them charge as normal.


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## evmetro (Apr 9, 2012)

I just tried the same thing today with my gbs 200 gen3 cells. My auto lead charger took my four pack from 13.2 to 13.3 and stopped. Auto disply read 100%.


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## sabahtom (Mar 1, 2011)

6v setting on the lead acid charger with 2s LifePO cells also doesn't charge. The combined cell v is 6.51, no change with charger on or off. Guess I'll just have to let the BMS do the work.


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## sabahtom (Mar 1, 2011)

I just posted this on another thread in response to a question, but since everyone has kindly helped me out I guess I'll put the end of the story (I hope) here too.

I got an upgraded charger from the same manufacturer. It has two settigns, one 1.8amp and one 10amp. The 10amp gives higher v right from the start. 

This model is a constant V, current controlled model, and seems to follow a soft start and gradual increase in V. Only let it run for 25 min because I wanted to check the individual cell v after a bit of charging. Seems like the charger will keep going up past 13.7v if I let it run longer.


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## Ziggythewiz (May 16, 2010)

That's still rather low, but should be good enough to get them up, then tie em in parallel to balance, then string em in series and let the BMS do it's job.


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## GizmoEV (Nov 28, 2009)

sabahtom said:


> Per Elithion's website, it's a bad idea to connect cells in parallel when one is more than 80% charged, particularly if others are much lower.


Has he actually tested doing that? When I connected two TS-LFP40AHA cells together in parallel, one at near 0%SOC and the other at near 100%SOC the current between them peaked at only ~29A as measured with a 50A 50mV shunt. The current very quickly dropped to below 10A after that. If you subsequently charge the parallel cells until they go up the knee of the voltage curve a bit and hold them there at near zero current then all parallel cells will be in balance

If I was needing to take a pack of LiFePO4 cells at random SOC values I wouldn't worry at all what they were at. Even if the initial current was high it wouldn't be more than the cells could handle anyway so why worry about it?


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## Elithion (Oct 6, 2009)

Paralleling the typical Li-ion cells, whose SOC is not far off, is not a problem, especially for LiFePO4. So, paralleling Thundersky-type cells for balancing is fine. That's what we do here as well.

The problem may occur for very low resistance cells, and especially for the non-LiFePO4 chemistries:


EiG F007 cells
Kokam 4 to 5 AH cells
Eberdell HEV 16 AH cells

I gave a talk on Tuesday at the Battery Power Conference about this very topic. If you're interested, you can find the presentation here.
Here is a slide form it.
In the worst case, connecting an empty EiG cell directly in parallel with a bunch of charged cells will result in a peak discharge of more that 100 C!










But, again, this is not an issue with the kind of cells that DIYers use.


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## major (Apr 4, 2008)

Elithion said:


> I gave a talk on Tuesday at the Battery Power Conference about this very topic. If you're interested, you can find the presentation here..........
> But, again, this is not an issue with the kind of cells that DIYers use.


Thanks Davide,

Very interesting and well done. And we do have a number of DIYers using A123, Kokam, EnerDel and cells where it is an issue.

major


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## Elithion (Oct 6, 2009)

major said:


> we do have a number of DIYers using A123, Kokam, EnerDel and cells where it is an issue.


Most Kokam cells have a sufficiently high resistance, so that's not an issue.
It's only the SLPB....H5 cells, 4, 4.5 and 5 Ah that have an excellent resistance and you have to be careful with. But they cost A LOT, so I don't see DYIers using those.

Enerdel has an EV and an HEV cell. All DIYers I watched got the EV cell, which has mediocre resistance. It's only the HEV cell that has an excellent resistance and you have to be careful with.

A123 20 Ah pouch cells are mostly hype: their resistance is better than Thundersky, yes, but it is really not that impressive. So, no worries with A123 pouch cells. The old 26650 "M1" are far better, and you do have to be somewhat careful with those, but nothing compared to EiG, Enerdel and Kokam low resistance cells.


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## sabahtom (Mar 1, 2011)

Davide thanks for the link, the slideshow is very informative. 

I've now tried the 10amp lead acid charger with 
4s, 
4s 2p and 
4s 3p cells. 

Seems the charger treats 4s 3p almost like a lead acid battery, per the attachment.

At the end of the charge 4s 3p: charger supplied (13.9v-13.35)/ 4 amps = 0.137ohm total resistance. 

I guess 4s 5p will go to 14.1v and 3.6amps. I'll try it next week.


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## dtbaker (Jan 5, 2008)

GizmoEV said:


> If I was needing to take a pack of LiFePO4 cells at random SOC values I wouldn't worry at all what they were at. Even if the initial current was high it wouldn't be more than the cells could handle anyway so why worry about it?



I would worry.... most of the active shunting system BMS cannot handle more than an amp or two of shunting current. If you have one cell way above the rest, the charger is chugging along at full output in CA mode, and the BMS board cannot shunt at that load and turns off the charge before finishing the rest, so they never get balanced.

MUCH better to do a reasonably close top-balance so that the pack is at least all in CV stage when the shunts start kicking in.

10 amp Mastech power supplies are less than $200, and a good way to do initial balance... not speedy, but settable!


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## Ziggythewiz (May 16, 2010)

I did a final top-up on mine last weekend at 4S10P before connecting in parallel. My cheapo 6/12V charger continued to do well, but only went to 14.16 (I was shooting for 14.6, but close enough for me) instead of the 14.2 it cut out at every time with 4S.


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## joamanya89 (Feb 13, 2012)

Hi, what's really the diference between lead acid's charger and lipo4 charger?

And is it posible to get a lipo4 charger to then cut the positive and negative charger wires that goes to the batteries, reassemble it in the number of cells you got (if you have 20 cell, get 20 wires from positive and 20 for negative) and then charge it one by one all in paralell?

Of course,I'll be testing each cell voltage to be sure it doesn't pass the 3.5v


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## Ziggythewiz (May 16, 2010)

joamanya89 said:


> Hi, what's really the diference between lead acid's charger and lipo4 charger?
> 
> And is it posible to get a lipo4 charger to then cut the positive and negative charger wires that goes to the batteries, reassemble it in the number of cells you got (if you have 20 cell, get 20 wires from positive and 20 for negative) and then charge it one by one all in paralell?
> 
> Of course,I'll be testing each cell voltage to be sure it doesn't pass the 3.5v


The charge profiles are different, and lead may include a gassing cycle which LiFePO4 doesn't.

You could hack up your charger cables, but why? Just hook the cells in parallel and use the regular charger leads.


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> I would worry.... most of the active shunting system BMS cannot handle more than an amp or two of shunting current. If you have one cell way above the rest, the charger is chugging along at full output in CA mode, and the BMS board cannot shunt at that load and turns off the charge before finishing the rest, so they never get balanced.
> 
> MUCH better to do a reasonably close top-balance so that the pack is at least all in CV stage when the shunts start kicking in.
> 
> 10 amp Mastech power supplies are less than $200, and a good way to do initial balance... not speedy, but settable!


Why would you use a BMS? If you read the entire post you will see the topic was *paralleling* cells at different SOC. They will self balance and be all matched up at the top after charging to above the knee. No shunting BMS since there is really only one "cell" now.


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## dtbaker (Jan 5, 2008)

GizmoEV said:


> Why would you use a BMS? If you read the entire post you will see the topic was *paralleling* cells at different SOC. They will self balance and be all matched up at the top after charging to above the knee. No shunting BMS since there is really only one "cell" now.


I don't use a BMS, but the OP was asking 'why balance if you are going to use a BMS'. Answer is that you still should do a top balance in parallel with a power supply to some voltage at or near your intended average end-of-charge vpc whether you intend to use a BMS, or not.

putting cells in parallel at resting voltage doesn't cut it as the resting voltage may not reflect the SOC very well since it is so flat below the knee.


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## GizmoEV (Nov 28, 2009)

dtbaker said:


> I don't use a BMS, but the OP was asking 'why balance if you are going to use a BMS'. Answer is that you still should do a top balance in parallel with a power supply to some voltage at or near your intended average end-of-charge vpc whether you intend to use a BMS, or not.
> 
> putting cells in parallel at resting voltage doesn't cut it as the resting voltage may not reflect the SOC very well since it is so flat below the knee.


Go back and re-read my post #10. You quoted me out of context and are trying to make what I said apply to something that I wasn't talking about. Also, I did say to CHARGE the parallel set up into the knee of the voltage curve. I'm not sure what you are trying to do. You imply what I said was wrong and then proceed to say what should be done when it is exactly what I said in the first place.


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## joamanya89 (Feb 13, 2012)

Going back a few posts, is it possible to stop the lipo charger every 10min, for something like 20 seconds, so my uController will be able to test the real voltage and then if it is under the limit start back charging?

Because it is not possible to read the real voltage while is being charged, because the voltage it shows is the charger voltage not the cell one.


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## Ziggythewiz (May 16, 2010)

Yes it's possible, but difficult and unnecessary. It you charge a cell using the recommended specs you won't overcharge.


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## joamanya89 (Feb 13, 2012)

Yes? if I got it well balanced, does the charger stop at determined voltage?
Does it use to get un balanced too frequently?


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## GizmoEV (Nov 28, 2009)

joamanya89 said:


> Yes? if I got it well balanced, does the charger stop at determined voltage?
> Does it use to get un balanced too frequently?


I'm charging a 200Ah LiFePO4 pack with a Zivan NG1 (and NG3) which does not stop until the timer shuts it off. It just cuts back current based on voltage. I have balanced my cells at the top of the voltage range for LiFePO4 (3.6V would be fine). I have my charger set to not charge above 3.455volts per cell since the current tapers down to nearly 0A before timing out. Based on the resting voltage several hours later the cells generally do not get overcharged.

Over the past 15 months or so, the cells do not appear to be drifting apart from each other. This is with no further balancing.

Ideally the charger will turn off at a set voltage AND current level. The standard charge procedure is to charge to something like 3.6V and hold that voltage until the current drops to 0.05C or 5% of the Ah capacity of the battery.


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