Another battery charging problem

johnebike

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Feb 5, 2014
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I have a problem with my 36v Li-ion battery (rack mounted) not charging. The battery voltage measures 39.1v and the charger 41.9v.
From my reading on here it seems that than an inspection/ repair of the battery wiring is required which is beyond my competency.
Can anyone suggest where I can get this problem sorted. I live in Derby.
 

johnebike

Finding my (electric) wheels
Feb 5, 2014
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Thanks for your suggestion.
I have checked the external fuse (30 Amp, blade type) on the end of the battery, and this looks OK . Should there be another one somewhere ?
 

Nealh

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Aug 7, 2014
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Some batteries also have a fuse on the internal charge side will need opening to check.
Also with out teaching any one to suck eggs, if the BMS has an on/off switch it needs to be on when charging as most don't simply allow battery to switch on but activates the BMS.
 

vfr400

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Jun 12, 2011
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Thanks for your suggestion.
I have checked the external fuse (30 Amp, blade type) on the end of the battery, and this looks OK . Should there be another one somewhere ?
Some batteries have more than one fuse, and they're often hidden. Some have them accessible from the outside and some on the inside. Have a look under the handle. The charge fuses are normally 5 amps.
 

Nealh

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As you have it a part disconnect the white multi connector with the 11 thin wires and with a volt meter measure the voltage between the Black and Red, also you can measure the 10 cell group voltages and write each voltage down for us to see if a group has an issue which won't allow the BMS to communicate with the charger.
Place your Black probe on the Black pin of the connector and the Red probe on each of the other ten pins, start first with the White pin next to the Black and then move the Red probe along each pin till you finish with the Red pin.

If one cell group voltage is low and below 3 or 3.1v then the reason for no charging will have been found.
 

vfr400

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I can confirm that there is no fuse there. Also, the wiring looks quite robust, so things don't look so good.

Before going any further, you need to check the voltage on the charge socket. If it's above 30V, the battery is probably OK. If its zero volts, you have a broken solder joint on the connector. If it's between 7v and 24v, that circuit board (BMS) is switched off because it's detected a problem. Find out which of those three you have, then we can proceed to the next step.
 

johnebike

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Feb 5, 2014
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Thanks both for your suggestions.
I haven't yet managed to measure the cell voltages suggested but I have measured the voltage at the charging socket and I found this to be zero whatever the position of the on/off key. However I have been unable to see any broken wires/joints on quick inspection.
I presume that to measure the cell voltages, that I will need to remove the "bundle" from the case and unwrap it ??
 

vfr400

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There's no point in measuring cell voltages if you have zero volts on the charge socket You now need to measure the voltage between the points where the yellow wire is soldered to the PCB and the thick red is soldered to the cell pack, which might be at the other end of the battery. Alternatively, if you can't get at where the red is soldered, you can use the positive output terminal on the outside of the battery because it has a direct connection to the cell-pack. Only if you have zero volts there should you check the cell voltages.
 

Nealh

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For cell voltages no need to unbundle anything, the White BMS multiplug/connector is there in front of us /you in the pic on the rhs towards the bottom. Simply pull the wide white mutiplug (with 11 thin wires) out and take voltage measurements from the plug/connectors wire pins.
If one of those 10 cell groups gives a low voltage reading < 3v then BMS will not switch to allow the charger to operate.
 

Nealh

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vfr and I have differing procedures of checking for battery fault finding.
If battery is open I always start with cell group voltages first and write them down as a list 1 -10 readings for 36v lion to rule out a cell fault first. Then I work backwards from here, if they work out ok and are ok I carry out wire continuation and pack voltage readings from and to the BMS via pack charge/discharge and from discharge and charge ports to BMS not forgetting any switch if fitted as these can malfunction.
Sometimes a bad/dry solder joint can be the issue.
 
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vfr400

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have just measured the voltage between yellow and red points 39.2 volts
That means that the interruption is between there and the charge socket. Check continuity (beep) between each of those two positions and the corresponding pin on the charge socket to find out which wire it is, then you need to follow along the wire to find where the interruption is - normally solder joints.
 

vfr400

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Jun 12, 2011
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vfr and I have differing procedures of checking for battery fault finding.
If battery is open I always start with cell group voltages first and write them down as a list 1 -10 readings for 36v lion to rule out a cell fault first. Then I work backwards from here, if they work out ok and are ok I carry out wire continuation and pack voltage readings from and to the BMS via pack charge/discharge and from discharge and charge ports to BMS not forgetting any switch if fitted as these can malfunction.
Sometimes a bad/dry solder joint can be the issue.
Zero volts on the charge socket means that there's an interruption between it and the cell pack. I already said that if the BMS was switched off, there would still be some voltage on the charge socket, so no point in checking the cells. Logic and testing tells you where and what to check, not just go round randomly checking whatever comes to mind, starting with the most difficult things.

For no charging, simple steps to discover the problem:
1 Measure the charger voltage and the charge socket.
2. If either has zero volts, that's the one to investigate. Goto 5. and 6.
3. If you have any volts on the charge socket with a value below the voltage output terminals, the BMS is switched off so open the battery and check the cells to find out why.
4. If the two voltages are the same, but low (say less than 33V for a 36v battery), one or more cells have dropped below 2.5v, so open the battery and charge those cells.
5 Zero volts on the charger - check the fuse and the connector.
6 Zero volts on the charge socket - check the charge fuse (if it has one), open the battery and check where the interruption is.
 
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johnebike

Finding my (electric) wheels
Feb 5, 2014
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It must be my lucky day!
I was just starting to examine the wiring to the charging point and moving it a bit prior to testing and I decided to check the reading on the charging port just for practice, only to find that it was 39v and not the zero I was expecting. So I plugged in the charger and its going and no wire moving would stop it.
If I was any good at soldering I would probably redo some of the wiring as I imagine the fault will return. Thanks to Nealh and vfr400 for their help.
 

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