Bafang crank drive, heavy rain, no power, now charging problem

[Grlyd47]

Hello,

I Have a Bafang 750watt crank drive & Ping supplied 48V 20AH V2.5 LiFePO4 Battery Pack & standard bms.
mounted to Mongoose full suspension MB

This has been faultless last 4 years but used only say once a week, always kept battery as advised etc so all was good.

Three days ago I went for a short ride (battery fully charged) and was caught in a very sudden torrential rain downpour, the bike motor cut out, visibly no display showing and I pedaled home. Total distance only 500mtrs so battery still full.

So no power and blank Bafang C961 screen.

Back in the garage I immediately checked the battery bag (see image, this is quite watertight) and the battery was still dry, maybe some condensation but no visible water at all.

The most exposed component was a large automotive connector (battery to Bafang MOTOR, see image). This was full of water so would most likely have caused a short.

All other connectors for Bafang controller etc had no sign of water.

I have unplugged everything and let it dry for the past two days.

I reconnected everything and the Bafang controller and motor, throttle and controller display are operating correctly and I went for a 16 klm ride and all is fine, bike still makes 48 klm hr so plenty performance and Bafang controller still showing full capacity on display.

I then plugged in the charger and both LED lights are on and the fan does not start, so no charging? I presume!

I cant see why the charger would be effected but, maybe the BMS is ruined? or controller re charging? if there was the inevitable short at the plug (battery to crank motor)

Any ideas on this would be gratefully appreciated.

Thanks Garry

 

[dogman dan]

Possible the short affected the bms. It does sound like it doesn't want to charge because of the bms, or a connection.

But one thing I REALLY learned over the years. Cause you think and cause it is are often very different. Your problem sounds exactly like you simply have a broken plug, or disconnected wire on the charger or the battery. And just to F with you, it happened on that particular ride.

 

[Grlyd47]

Thanks,

Yes charger is (connecting and disconnecting found plug fault) now charging till all LED on as per normal, controller turns on, throttle works etc whilst charger is connected but shuts down with the charger disconnected and will not start up until charger is reconnected. Checking the sense pins shows cells are pretty even and at acceptable level, discharge side at the connection shown in the image is way down so am now presuming BMS is gone, does that sound right to you?

I have emailed Ping for invoice to purchase one but no reply as yet.
Any thoughts on where else these are available or similar alternative BMS would be appreciated. Replacing with the Ping bms is desirable as sense plugs are same and only a small solder job but if all plugs are the same an alternative will do.

Cheers Garry

 

[Voltron]

I wouldn't try any of the following without a digital voltmeter and steady hands, but first check the charger output..a blown fuse on the charger makes it stay green. Then try to probe the battery before the BMS, and verify its not fully charged, as that will keep a charger from going on. Then see if there is an inline fuse on the way from the BMS to the charger plug, and also see if the voltage out the plug is the same as directly off the battery. If it's not, it's the BMS or a broken wire or something.
Then next one could be easy or dangerous, depending on the location of wires and hand steadiness again, but hooking up two jumper wires from the charger directly to the battery terminals, bypassing the BMS, should make the charger go, if it's not up at the charger high cutoff already. Sometimes you need a scrap plug cut off of something else to make an adaptor as some plugs are hard to hook into, like an XLR type. Others you can get away with just jamming some bare wires in just for a test, as long as they stay separated from each other...

 

[amberwolf]

Yes charger is (connecting and disconnecting found plug fault) now charging till all LED on as per normal, controller turns on, throttle works etc whilst charger is connected but shuts down with the charger disconnected and will not start up until charger is reconnected.

First, check the actual voltage on the output of the battery, with the charger connected, and disconnected.

If the voltage doesn't drop dramatically, but stays close to the same without the charger, then the BMS output is probably not turned off. If it does drop dramatically, then the BMS is turning it's output off, because it thinks something is wrong inside it and is protecting the cells from that.

If the BMS turns on it's output only when charger is connected and powered up, then it's "detecting" a cell that is below LVC.

Depending on BMS design, that could mean a sense wire is disconnected from the BMS, or has a poor connection to a cell. Or it could mean that one of the channels of the BMS has it's LVC-tripped output stuck "on".

The former is something you can fix (and which would probably still be a problem with a new BMS, and may be intermittent). The latter is likely to be a solid failure, and would follow the BMS.

 

[Grlyd47]

Hi,

Battery is charging okay, that was my mistake, connector wire loose.

Voltage at all individual sense pins shows 3.4 - 3.41v each across the 16, (measured 1-2, 2-3, etc

Total both batteries as measured 51.8v

Discharge wires at connector to Bafang motor as shown above after BMS 14.2v

Voltage post bms whilst charging 52v

Any ideas what all that may indicate?

Thanks

Garry

 

[amberwolf]

Voltage at all individual sense pins shows 3.4 - 3.41v each across the 16, (measured 1-2, 2-3, etc

Assuming that is without the charger connected, then that's normal for an older LiFePO4 (taht doesn't hold it's 3.6v balanced top charge anymore). It means that the sense wires are all connected to the BMS, not broken between BMS and cells. Still possible there's a failure between the connector's solder point at the PCB and the balance/sense circuitry, but more likely one of the channels has "stuck" on it's LVC output, disabling the BMS output.

If that is reading with the charger connected, you'd want to check without it too.

Total both batteries as measured 51.8v

"Both"? You only mentioned one battery previously, AFAICT. :?

Discharge wires at connector to Bafang motor as shown above after BMS 14.2v
Voltage post bms whilst charging 52v
Any ideas what all that may indicate?

Depends on what exactly you mean by the above.

Do you mean that with the charger plugged into the wall and the battery's charge port, the voltage on the discharge port reads 52v?

But as soon as you disconnect the charger from the charge port, the discharge port drops to 14.2v?

If you mean both of those, then it means the BMS is shutting off the output port to protect the cells from overdischarge, because it thinks a cel is too low. Or that one of the channels is stuck in LVC mode.

The drive circuitry for the FETs, adn the FETs themselves, must be working, or it could not enable output when charger is connected.


So if those are the condtions and readings, then the BMS is not working correctly and needs repair or replacement.


If the conditions and readings are not those, then we'd need the exact conditions and readings to diagnose further.

 

[Grlyd47]

Discharge wires at connector to Bafang motor as shown above after BMS 14.2v
Voltage post bms whilst charging 52v
Any ideas what all that may indicate?

Depends on what exactly you mean by the above.

Do you mean that with the charger plugged into the wall and the battery's charge port, the voltage on the discharge port reads 52v?
"Yes correct
But as soon as you disconnect the charger from the charge port, the discharge port drops to 14.2v?
"Yes correct"
I have quote from Ping for new type BMS so will order one and get it connected and see if thats a fix and take it from there.

Thank you guys for your assistance

Garry