Is my new battery charger over-volting my Headways Batteries

[e-beach]

Is my new battery charger over-volting my Headways Batteries?

My Kingpan KP3612EL LiFePO4 battery charger stopped working. It cost about $200.00 shipped and only lasted 1 year! I will be doing a repair post or a post mortem post later on that one, but having read that ping uses 45 volt chargers I bought a cheapish V-Power 45 volt 6 amp charger on eBay that stated it was suitable for LiFePO4 batteries. (Actually the price was right, $42.90 including shipping.)

The charger charges up to 44.9 volts on my multi-meter then the green light comes on. But, once the pack voltage of 44.9v is reached the charger holds it at that voltage. When the chargers green light comes on and is connected to my battery pack the cell voltages read like this.
1 – 3.73
2 – 3.73
3 – 3.77
4 – 3.7
5 – 3.75
6 – 3.76
7 – 3.74
8 – 3.73
9 – 3.72
10 – 3.74
11 – 3.74
12 – 3.76


But when I take it off the charger and wait 10 minutes the voltages read like this.

1 – 3.54
2 – 3.52
3 – 3.56
4 – 3.56
5 – 3.56
6 – 3.53
7 – 3.52
8 – 3.53
9 – 3.53
10 – 3.53
11 – 3.52
12 – 3.54


The second set of numbers makes me think that everything is working fine, but because my Kingpan charger was set to 43.6 volts, and stopped charging when the voltage was reached, only to turn on and off as the pack balanced, makes me wonder if my new charger is ok for my Headways batteries. I guess my questions are:

Do the voltages look OK?
Is the 44.9 volts safe to leave connected to my pack over night without harming my batteries?

Any help would be appreciated.

Below are the specs of what my components are.

Thanks

 

[wb9k]

The Voltages look OK to me. If your cells were coming to rest above 3.60 Volts, that would be a concern. I would expect that to happen if you left this charger on this battery all night. To leave a charger on that long, you want one that will not deliver more Voltage than needed to hold each cell at 3.60 Volts. In this case, the ideal charger for extended plug-in times would max out at 43.2 Volts. It's OK to charge to higher Voltages (the higher the charge current, the higher you can go--within reason), but you don't want to stay there long enough for the cells to come to rest above 3.60. If you stay too high long enough, the cells will charge to that full Voltage, unless you have balancers that can absorb all extra charge current above that level, effectively holding the cells at 3.60 and dissipating all power from the charger that would otherwise take them higher.

Overcharging LFP causes Li to plate on the cathode, trapping it there forever. This means capacity loss and impedance rise, and it's permanent.

 

[999zip999]

I would put a timer on the cheap charger. I could take a couple of cycles to understand it better.

 

[wb9k]

I would put a timer on the cheap charger. I could take a couple of cycles to understand it better.

Any new setup (or existing setup with a new component added) should be baby-sat through a complete cycle or two just to establish what the behavior of the system will be--BEFORE regular use begins. That, and applied knowledge of what is appropriate for the cells are the keys to success. That said, I am not comfortable charging any Li pack completely unattended unless the cells are LFP, and the charger setup has redundant mechanisms for avoiding overcharging. Thorough fusing of the pack is also a must--preferably down to the cell level. Safety first.

 

[arkmundi]

I'd reinvest in a new charger that has the intelligence to shut itself off. I too have a 12S LiFePO4 battery pack and am charging it with this Smart Charger (6 A) for 38.4V ( 12 cells ) LiFePO4 Battery Pack. I like the fast 6A charge rate, that its smart enough to turn itself off at the right voltage, and its quality construction. Preserve your investment in a quality battery.

 

[dnmun]

but you have no BMS to protect the battery.

 

[scoot]

e-beach... if that was my Headway pack & charger, I would be very happy with how it is charging... perfectly balance charged and for Headways, the "surface charge" seems to be draining off evenly across the board for all of the cells. Even if they drop below 3.4 after a few hours, I'd say there is no evidence yet of anything irregular going on. That's my perspective anyway. :wink:

Looks like your charger has a decent "balancing current" too... while not phenominal, more than a lot of chargers & BMSs I've seen.

But like dnmun eluded to, might want ensure you have some sort of LV (low voltage) protection employed... individual cell based LVC is best if you ever use most of the packs capacity during your rides.

 

[e-beach]

but you have no BMS to protect the battery.

I don't understand....my BMS specs are listed above.

 

[frodus]

Do you have the charger wired into the BMS? or is it just connected straight to the battery?

 

[chilledoutuk]

In my opinion your cells are being charged to too high a voltage for my liking but then that seems to be how there bms works anyways.

To me though i don't see the point in a BMS that lets the cells be charged higher than there ideal CV.

I would much rather balance charge a pack and then just bulk charge it whilst periodically keeping an eye on cell balance.

 

[e-beach]

Do you have the charger wired into the BMS? or is it just connected straight to the battery?

Yes, the charger is wired into the bms.

 

[999zip999]

The bms will charge the cells to 3.7-3.8v the cells don't keep that level of charge. the bms will bring them down. 3.6v is full with a bms but full is 3.5v. Meaning there is not much above 3.45v- 3.5v so most people without bms don't go there and no reason to. Yes a bms can go to 3.8v or some can even hit 3.9v. to bleed down and balance. They don't stay there as they bleed down.
Do a couple light cycles just don't find the bottom of the pack. right now.

 

[frodus]

Do you have the charger wired into the BMS? or is it just connected straight to the battery?

Yes, the charger is wired into the bms.

It looks like it should be protected against any cells going too high then.

Where did you get the BMS to begin with?

Lifepo4 should tolerate 3.7V charges just fine, but it would be better to charge to a lower voltage so you're not right on the edge of the manufacturer recomendations.

 

[e-beach]

It looks like it should be protected against any cells going too high then. Where did you get the BMS to begin with?

Lifepo4 should tolerate 3.7V charges just fine, but it would be better to charge to a lower voltage so you're not right on the edge of the manufacturer recomendations.

Got the BMS from Headway-Headquarters http://headway-headquarters.com/xji-12s-36v-50a-100a-bms/

I bought it from them along with the batteries and now dead 12ah charger. I emailed them about a charger question, but they never got back to me.

So far it is sounding like I am OK, with the "caveat" of charging right at the edge of manufacturer recommendations. Now I am wondering if I can tweek the new charger to get the voltage down just a bit?......This is a cheap charger, so it has no variable resistors to adjust, so something else would have to happen to get the voltage down under 45 volts.

 

[Spacey]

43.8v should be the correct voltage for Headway 12S pack. I would maybe lower down to 43v. Once the BMS has balanced them all there is next to nothing useful above 3.4v.

 

[e-beach]

Problem solved!

I isolated a resistor that could be replaced with a variable resistor. I happened to have a potentiometer in my parts box that would work, soldered it in and was able to adjust the voltage down to 43.8. 8)

I will post a small build thread soon.

 

[dnmun]

can you show picture of what you decided to replace? why did you not just adjust the voltage down with the trimpot? do you know how the charger works and where the resistor you removed is in that circuit?

 

[e-beach]

can you show picture of what you decided to replace?

Yes, Resistor "R15. I will be posting a build thread tomorrow.

why did you not just adjust the voltage down with the trimpot?

This unit didn't come with a trim-pot.

do you know how the charger works and where the resistor you removed is in that circuit?

Vaguely..it was the only small (1/4w?) resister on the positive DC side that was going to a step up coil or voltage regulator.
(at least the only one I could figure out :lol
It metered at 37.8v without load so I figured that I could sneak a variable resister in there and trim from there.

 

[999zip999]

Thanks good pic's can you put an arrow on the pic's ? Please.

 

[e-beach]

Thanks good pic's can you put an arrow on the pic's ? Please.

I will do it on the next round of posts on this little mod. Please let me know what you want me to point to and I will do my best to accommodate. If you mean the resistor I removed and replaced, the R15 I removed is next to the LED's. I will shoot a better picture of that area of the PCB later.

 

[e-beach]

The build thread can be viewed here:

http://endless-sphere.com/forums/viewtopic.php?f=2&t=52980&p=787292#p787292