Power cuts out as soon as load increases

[Chris Maluszynski]

Hey folks,

I installed a KT36/48SVPR-17A with a 48V battery on an old Wisper bike with a BFUN8 250W, and it's been running great until the other day.
Suddenly (after my wife used the bike to pull a heavy trailer) the power cuts out as soon as the load increases slightly.
I noticed this happens both on throttle operation and PAS. If I pedal it cuts out pretty much right away. On throttle I can ease it into running if I increase it very very carefully, but as soon as it's not flat or I pull it just a little too fast it cuts out right away. I then have to release the throttle and start over.

What could be the problem? (I've pulled heavy loads with the bike before, but probably more carefully than the wife may have done - I mention this as I have nothing else to go on that may have caused the problem, but not sure this is related to the heavy trailer)

 

[Benjahmin]

How old is the battery?
Do you know what cells are in it?

 

[Nealh]

Typically one would say the battery has given up the ghost.

 

[Chris Maluszynski]

I was not suspecting the battery. It’s practically new. Hairon with LG cells. 48v 14.5ah. It was stored a few years before being put in use but has been performing well since I started regularly using it

 

[Benjahmin]

So what voltage does it charge up to and can you measure the voltage when it cuts out?
The symptoms you describe are classic for a duff battery. How long was it in storage and in what conditions?.

 

[Chris Maluszynski]

So what voltage does it charge up to and can you measure the voltage when it cuts out?

Charges up to 54.9v
Voltage at cut out 54.4v

was stored in room temperature holding a charge

 

[Benjahmin]

Is the motor running smoothly with no more noise than before? The reason I ask is that you said it failed after pullig a heavy load. Is it possible that the motor connector has gone resitive on one phase causing heat? When this happened on my bike the controller was more prone to overheat cutout.
So I guess I'm asking if the controller is too hot to touch at cutout?

 

[Chris Maluszynski]

The motor does not make any different noise and seems to run like normal. I doubt anything gets super hot as this happens immediately after startup even if the bike has been sitting overnight. Should I inspect any connections?

 

[Benjahmin]

It's worth having a look at the motor connections - nothing to loose.
However it is starting to sound like you may have something wrong with the controller.

 

[Chris Maluszynski]

Checked connections. Nothing looks suspicious. Have not opened the controller though. Should I look inside as well?

 

[Nealh]

Does the display/power stay on ?

 

[Chris Maluszynski]

Does the display/power stay on ?

Yes. Display stays on and shows everything correctly (throttle/pas/brakes/voltage)

 

[Nealh]

If the battery is new and the display remains on then likely there is a controller fault and probably on the voltage regulator circuit, a PMC regulator might be used or and series of resistor and diodes as well. These electronics are way above my head and most users, replacement is usually the cheaper option unless you like headaches.

Opening the controller might show up some component failure but you will need a keen eye and mag glass to look at every small item. The PMC regulator is a three legged mosfet looking component , it might even be a mosfet of some sort ?

 

[Chris Maluszynski]

likely there is a controller fault and probably on the voltage regulator circuit, a PMC regulator might be used or and series of resistor and diodes as well.

Thanks Nealh,

Not sure I understand 100% though: do you mean anything can be done to remedy the controller fault, or do I need to buy a new controller (first one was a lemon, now this!)?

 

[Nealh]

Only if you are an electronics geek.

If the controller worked previously replace with another one the same.

If the wife laboured the drive whilst towing the heavy load the controller may have got very warm if near stalling speed for the chosen gear. Mosfets get very hot under these circumstances and cut out thermally, after cooling the bike works again but damage to them may have occurred. If it is a 6fet controller consider a 9 fet model for towing.
You can check the controller phase wires for possible mosfet issues, but usually they either work or not.

Controllers do fail some times they are reasonably cheap to replace when you look at the bigger picture of an e -bikes overall cost.

 

[Chris Maluszynski]

Only if you are an electronics geek.

I am a wannabe electronics geek. But if I attempt to solder anything, I'll most likely cause considerable damage to the board, the house and myself. So I guess I need to buy a third controller for this project then... I wonder if PSW might replace it, as I only ordered this one in august last year? But I guess not

 

[Chris Maluszynski]

Just checked PSW power. It looks like shipping has increased from 8USD to 80+USD for the controller! Is this to do with Covid? Or some new regulations?

 

[Nealh]

Show us a pic of your controller wiring, you should get it off AliExpress a lot cheaper if it is $80 p &p.

 

[Chris Maluszynski]

Attaching images of the connectors below.
Here's the controller: http://www.pswpower.com/ven.php?cargo.2016-3f-33c0

 

[Chris Maluszynski]

Oh and also - is the number of mosfets variable at the same controller power (20A in this case)?
And I should mention, I won't be able to fit a bigger controller in the space I have available, so if more mosfets means bigger size that could be an issue