Very hot charger never changing to green (Kunshan ST Electronics SHC-8100LC)

[karlpedal]

Charging a Promovec 50776-BL-C-36V (36V 17.4Ah) battery with a Kunshan ST Electronics SHC-8100LC charger. The charger becomes dangerously hot and will never switch from red (charging) to green (charged) LED. The battery does get hot. It performs fully ok for a couple of years average use.

The battery (not connected) shows 38.8 VDC fully charged. The charger (not connected) shows 42 VDC. Someone mentioned in another forum post that my battery voltage is way too low. I haven't verified this (yet).

ChatGPT suggests a few components inside the charger that could cause this symptom, i.e. faulty shunt resistor, TL431 op-amp, opto-coupler, etc. It could also indicate a problem with battery cells or NTC-thermistor inside the battery.

I guess I'll have to examine the components inside the charger.

 

[yooper2001]

Have you tried the charger with a different battery? Could the battery have a faulty BMS that doesn't stop taking power when cells are full?

 

[karlpedal]

Have you tried the charger with a different battery? Could the battery have a faulty BMS that doesn't stop taking power when cells are full?

ChatGPT gave me a likelihood of 80/20 charger/battery error. I don't take those figures for granted but in similar troubleshooting it's presented me similar numbers that very spot on. I have access to another charger and will try it out.

I've already started to examine the circuitry of the charger but so far I've only managed to identify the opto-coupler. Still have to figure out where the other crucial components are.

 

[magnie]

Based on your other topic regarding the "error code 2", I kind of wonder if fill is right that the battery is not good. You say your charger (that I assume you've been using for a while) charges to 42v. Li-ion battery cells have a range of 2.5/3.0 to 4.2 with a nominal voltage of 3.6/3.7. A 36v battery has 10 cells in series. If you are only charging up to 38.8v, that is 81%. While limiting charging to 80% in EVs and phones isn't unusual, limiting it to 80% in a PEV like an ebike or standup scooter doesn't seem right because they want you to have as much range as possible.

I was also trying to do the math on determining if it is an LFP battery, but.. the math doesn't add up for the voltages. Plus if your battery isn't charging above 38.8v, then your charger is going to keep trying to charge the battery which is why it gets hot.

Based on those observations.. I personally also think your battery is the culprit. I kind of wonder if it was also the problem on your other thread where you replaced the controller. Maybe the new controller doesn't have the proper error detection/reporting the old one had. If you end up getting a new battery and still have the old controller, you could test if it still works and doesn't show an error code.

 

[karlpedal]

Good thinking magnie. I really lack the experience in deeper troubleshooting of PEV components. fortunately, I have access to a very similar model cargobike (that really helped me troubleshooting the controller issue). Now, in a different light, I might just try the scrapped controller on that other bike to see if the error code is still present. Also, charging my battery with the other (hopefully known good) charger will probably rule out any battery issues. A problem with my charger is that I don't know when the battery is fully charged, so that figure of 38.8 V might just indicate that the charge cycle was interrupted before the battery was fully charged.

 

[karlpedal]

My bad for slow updates. Lately I've been using the cargobike more frequently. A couple of weeks ago the display started reporting error code 4 continuously, which is "low battery voltage". However, the bike keeps on performing without any remarks. The charger still gets very hot, but I've managed to get a full charge and a green charging indicator after a very long charge cycle.

I didn't (yet) do any a/b testing on my scrapped controller and the other cargobike. But I stumbled over a 46.8 V scooter battery and got the idea of eventually replacing my degraded battery with that one. Does anyone know anything about voltage tolerance of a 36 V e-bike-system (motor/controller/display) - would it be possible to use a 46.8 V battery without a buck converter? What specifications (current limit) for a buck converter should I be looking for?

 

[magnie]

Does anyone know anything about voltage tolerance of a 36 V e-bike-system (motor/controller/display) - would it be possible to use a 46.8 V battery without a buck converter? What specifications (current limit) for a buck converter should I be looking for?

Motor will be fine (you will probably get a higher top speed in fact). Everything else may need an upgrade to support a higher voltage. 46.8 is likely a 13s, 54.6v max, battery. Things you would likely need to upgrade:

• DC-DC converter - Check the input voltage range on it. If it supports up to 54.6v, then you should be fine. If not, you'll need to find a 48v version that supplies the same or more current (amps). This is likely the easiest plug-n-play replacement you can do.
• Controller - Same idea, check the supported voltage of the specific controller. Needs to handle up to 54.6v. That being said.. I've heard that if you open up the controller and look at the capacitors, whatever the highest voltage capacitor is on the board is likely the actual max voltage the controller can handle. You would also, probably, have to disable regen if you have it.
• Display - This one is more complicated. If the display runs on purely 12v, then you don't need to upgrade it. If it has any voltage lines that are 36v, then you need to find out the max voltage of the display.. if it doesn't support the max voltage of 54.6, then you need to upgrade it.
• You would need a new charger if the battery doesn't come with one.

With buck converters, while in theory you could totally run everything off of one (assuming it can provide the necessary current), you lose the actual voltage information of the battery. This makes it difficult for the controller to protect against low/high voltage issues, you would have to disable regen, and the display wouldn't be able to show the proper battery level.