59.4v charger is too high for the BMS (58.8)

[SniperGaulois]

I have a charger which is marked 58.8v and 3.5A, The multimeter says 59.3v. When i connect it to the battery, the green light of the charger stays on. The BMS is ok with a 54v charger, so perhaps the 59v charger is being detected as too high.

Perhaps if i put a 1Ohm 12w resistor on it, it would start charging at 57, then it would stabilized at 58 when it's nearly charged, i would have to check to make sure it doesn't go above 58,8.

It came from a decent eBay seller and I need it for the summer, I didn't see a pot inside the charger. Is it a bad combo? perhaps the charger is too high current for the BMS? 3.5A and the BMS is max 5A so current wise it's fine.

 

[Punx0r]

Perhaps your multimeter is just wrong by 0.5V (~1%)...

Also, have you checked the voltage when actually connected to the BMS/battery or just when open-circuit?

 

[SniperGaulois]

I checked the multi meter against the cycle analyst reading on my other battery, it reads 54.39 volts when the cycle analyst is 54.21, a difference of about .2V, and on the charger i am getting .5V too high. When it's plugged in it says 59.3V. I mistakenly bought "SLA charger" hidden in a list of Li-ion chargers (they put the same photo and 100 word product titles) , because i was looking at the 58.8v figure. perhaps they are less stringent for SLA voltage.

Here is the shunt, perhaps i have to change a resistor on it? it's version 80nf70 0z04b. The resistor is 750KiloOhms, its purple green yellow, perhaps i can put a pot adjuster on it? I want it at 58.4V

 

[Punx0r]

Lead acid (flooded cells especially) is more tolerant of excess voltage, as it just gasses it off...

If your charger is intended for lead acid are you sure it is CCCV and so suitable for li-ion?

Your meter over-reads by 0.2V so, your charger is actually 0.3V too high (0.5V - 0.2V)? If so an extra 0.3V on a 14S li-ion pack means 4.22V per cell instead of 4.20.

Many BMS won't even start balancing till >4.20V and won't cut off unless a cell is over 4.25V.

If the cells are high quality I would have no problem at all with 4.22 Vs 4.20V per cell charging. Especially since some cells are rated for 4.35V!

 

[SniperGaulois]

The best solution is perhaps to use 2 silicone diodes, because they drop the voltage by about .8 volts each: http://www.ebay.co.uk/itm/10pcs-6A10-6-Amp-1000V-6A-1KV-Axial-Rectifier-Diode-NEW-CK-/191947149754?hash=item2cb0f111ba:g:xlEAAOSwMtxXsq1O

some 6a10 diodes should do to adjust a 50-100v charger of <5A down by 1-2 volts.


The BMS requires a CC/CV charger, the cells are panasonic.