Battery charger voltage question : Correct voltage?

[onemorejoltwarden]

I just got a battery charger sold as a Lithium 42 volt bulk charger for my 36v 10s LiPo pack

My VOM shows it as 43.8 volts output

My impression is that this is a LiFe charger and this is too high and will damage Lipo.
Is this correct and it should go back? or is that within spec?

RIch

 

[dogman dan]

If your pack is limn, or lico, then for sure you do not want to charge a 10s pack to 43.8v. That would be 4.38v per cell. It does seem to be set for 12s lifepo4, at 3.5v per cell.

It might be possible to open the charger and adjust the voltage. Look for a small trim pot near the DC output wire. If not, it should be possible to lower the voltage another way.

It could also be that your meter is off. How old is the battery in it?

 

[dnmun]

yep, they sold you a lifepo4 charger.

send them a message telling them they sent you the wrong one and see if they will send you another one to replace it. take a picture of the voltmeter reading from the charger and include it in the email so they can confirm it without you shipping the charger back.

then after you do that, go modify the output voltage like dogman says.

if they send you a second charger it may or may not be 42V but at least you will have a backup charger.

if they tell you to pay shipping then that would be a deal worth doing too.

 

[onemorejoltwarden]

Thanks to you both
Sounds like good approach

Rich

 

[onemorejoltwarden]

I got a very promppt reply from the vendor after responding as it was recommended and will include it below
I need some help confirming his information
He has a done a lot of internet business and seems to have a good reputation on Ebay.
I have no reason to doubt him , but haven't seen his numbers in the things I have read.

I suspect I have dead cell in my battery pack , so under load figures will not be available to me



QUOTE FROM HIS REPLY :
Yes, with no load on the charger it should be above 43.3 volts but after it starts charging for a few minutes it will adjust under its charging load to about 42.8 volts which is totally normal. LifoPo4 chargers without any load will be at 45.8 volts and then drop down to about 43.8 under load after about 10 minutes of charging. ----- So, this is NOT a LifePo4 charger.

About 98% of lithium batteries for e-bikes will also regulate this charge voltage thru the Battery BMS not allow it to charge past 42.2 volts.
Also, this charger will self--shut down once your battery reaches 42.00 volts. (give or take 1/10 of a volt)
Chargers are supposed to charge at about 1.0 volt above the final FULL voltage level.

YOU will see that after your battery is fully charged with this charger---- you can do a reading and your battery will be between 41.6 ---- 42.2 V which is fine for LIPO batteries and chargers. This is the proper charger for LIPO batteries We have been using this same charger on our LiPo batteries for over 3 years. and we have used literally thousands of these chargers on our e-bikes.

You will see after one charge cycle that it will not charge your battery beyond 42.2 volts. If it goes beyond that please tell us. (But it won't)

Even if it did charge your battery to 43 volts it would not hurt your battery just one time. You would need to over charge it 7---8 times to begin to damage your batttery. Thanks, Apar

Thanks to all and I appreciate Apar's response

rich

 

[dnmun]

some of the lithium battery chargers do turn off when they reach final voltage. it is not too hard to defeat that but if you wanna have the BMS balance the pack then it helps to have a the charger continue in CV mode to supply the balancing current.

i have figured out how to defeat these latching output chargers on two different types of chargers so we should be able to fix this one too.

 

[dogman dan]

Hmm, I suppose you could rely on the bms to prevent any overcharge. But that does sound to me a lot like what a lifepo4 battery charger does. Charges each cell to 3.65 or so, when full is 3.5v.

Test it and see. Indeed, when the pack is not fully charged, you will see a lower voltage. But I would not want it to charge my cells to 43v, even one time. I wouldn't want to bet my batteries life on the bms working every single charge. Much better to rely on the bms to balance the pack while never getting full pack voltage above 42v.

What will happen at 42v is, when it shuts off, one cell or another will be higher than the others, so cells can get over 4.2v per cell even when it shuts off at 42v. Having the charger at 43.8v will cause the current to be higher at that moment when you need it to be going slow so the bms stops it in time.

In an analogy, would you rather coast up to a red light, then apply brakes, or have somebodies foot on the gas as you try to stop?

Sounds like a refund is not in the offing, but if he is reading this, he sucks for selling it as a 42v charger. It runs to 43.8v dude. By his logic, you could just use a 72v charger, and rely on the bms. But is it a good idea? I don't think so.

Do you even have a bms?

Time to open it up, unless it's glued shut, and see if you can find a voltage adjustment pot inside.

 

[onemorejoltwarden]

Thanks
I have a BMS on my battery, but as I am getting a 0 volts from its big wires , I am assuming it has a shorted cell and I can't use it for load testing.
I get what dogman is saying. Good analogy and clear as to the mechanism of damage to unbalanced Lithium packs

I now have two projects, to get the battery up and adapt my new charger to protect any batteries I use it on, as needed.
I'll take pictures so if this comes up again ,I can forward it and see if I can adjust the output.
It is glued so if seller is adamant it is correct, I will see if he has advise on modifying it .

Charger is a SANS SSLCO84V42 if you have pictures or schematics

I have some knowledgeable support to dissect and evaluate my battery pack and the charger.
Battery has a 10 pole plug and board soldering of what I can decipher as the power and common leads visible
and have found basic battery testing resources through ES.

Sigh, may have to see if there are silverfish 36v 10Ahr batteries that I can use to get going, after I make sure the rest of the bike works

Thanks again
Rich

 

[dnmun]

you will have to show a picture of where you measure 0V on your BMS. we can show you how to test it to determine if it is functional. the BMS is an electronic switch in the ground lead of the battery. it has no voltage output.

 

[onemorejoltwarden]

dnmun, I appreciate presenting it. That process alone makes me catch stuff I need to know.

I carefully cut back a bit of the shrink wrap
I remeasured and got 1.24 volts on the thick wires, red and black going down the side of my battery pack
I can take off more , but wanted to go slow. the wires are covered by a hard wide layer (board like) that is inside the shrink wrap, and I cant feel them.

I have ten thin wires going to a 10pin connector on the BMS board and ,
two thin red wires going to the BMS board where they are soldered,
and two thick wires RED and BLACK, on going to a fuse
(F20AL250v) kept inside the top box (dumb idea, to be fixed later) that is intact by the outside tabs on the fuse holder.

The RED wire splits and goes to the charging port and switch.
The switch causes the parallel wired "volt meter" on the battery to light when on the charger and pressed, not in other position or off charger.

from the switch, the RED wire goes to the power out port.

The thick BLACK wire goes to the BMS board where it is soldered , and another BLACK wire the goes from the BMS board to the Powerout port.

I MEASURED the thick RED and BLACK wires and got 1.24 volts at their first exposure, red at the fuse in tab and Black where it was soldered to the BMS.
ZERO volts at the power out port in all switch positions off power and on , and at the charging port.

I have a picture, but the wires are hard to follow in the un disassembled cap
I get 43.7 v on the charger plug with a green light , unloaded and when plugged into the charger port, in all switch positions

My beginners mind thinks my next move is to gently unplug the 10 pin plug and see if this points to one of cells
I am not sure what the two thin red wires and the
10 pins is a bit confusing (11 would make better sense but I am assuming voltage differences between the wires should point to their origin.

i'll pause and wait for an opportunity to get smarter.

Thanks again
Rich
THanks again

thanks again

 

[dnmun]

you can cut back the plastic around the BMS i you wanna. they use the large black wire with beijing on it as the B- lead to the bottom of the battery and that is the bottom of #1 and that first black wire in the plug is the top of #1 and the next wire is top of #2 and so on. when you get it out you can measure the voltages between each cell on those pins and do it while charging the battery with your new charger.

 

[onemorejoltwarden]

Thanks dnmun
I put my voltmeter from the thick black Bejing wire to the pins on the plug the BMS uses to connect to the ten pin plug, rather than the unplugged connector. Checked my VOM with a new AA cell to make sure I was calabratoid

B- to
#1 black 28mV
#2 white 61 mV
#3 gray 98 mV
#4 purple 113mV
#5 blue 330 mV
#6 green 575 mV
#7 yellow 685 mV
#8 orange 915 mV
#9 red 1063 mV
#10 Brow 1262 mV

pretty linear
i have put the battery in an observed fireproof spot to soak up some volts, but it hasn't shown much enthusiasm in charging.

Rich

 

[onemorejoltwarden]

did a quick spread of cell to cell difference, not so linear as my original glimpse
these are millivolts too
to B-
#1 black 28mV 28 xxx
#2 white 61 mV 61 33
#3 gray 98 mV 98 37
#4 purple 113mV 113 15
#5 blue 330 mV 330 217
#6 green 575 mV 575 245
#7 yellow 685 mV 685 110
#8 orange 915 mV 915 230
#9 red 1063 mV 1063 148
#10 Brown 1262 mV 1262 199

? what are the thin red wire pairs

Rich

 

[dnmun]

if they measured 60mV then what did the alkaline cell measure? that battery is deader than dead.

the BMS has turned off the output mosfets so it will not charge because of that.

do you have a power resistor laying around you can put inline with the charger?

the way to get it started charging is to bypass the BMS and charge it directly but it will help to put the resistor inline to reduce the current when it initially starts charging up.

when it gets up to about 20V then you can remove the resistor and charge at full charge rate from your charger. you should go to harbor freight and buy some jumper wires with the alligator clips on each end to use to make the connections.

does your charger plug match the plug on the battery? once it gets above about 25V then you will be able to charge through the BMS after that.

 

[onemorejoltwarden]

That confirms my beginners sense of things
alkaline cell was 1596mV
checked a couple of other new ones with same reading, a bit high but doesn't seem like a huge error
the bulk charger has an XLR plug, and it sounds like I may need a charger like the battery balancing things that that I have seen.
The plugs are not like the lipo packs they seem to be made for , so I guess I would have to make an adapter ,
as most of the lipo pack chargers appear to only charge 4S to 6S packs with smaller monitoring / balancing plugs

Good news is the bike seems to run OK when I cobbled up a power cord from an old computer
and two motorcycle batteries and the battery off my Silver Streak trailer.
Batts weigh more than bike tho


Rich