Bike not working after shunt mod

[John_S]

I had a go at performing a shunt mod on the controller of my Big Bear to give it more torque. I didn't use actual solder but instead used a piece of metal that I formed a bridge with as advised on a Youtube video I watched. Unfortunately, I must have over-amped it and the bike stopped working towards the end of my first ride after doing the mod. I was going up a hill and the power suddenly cut out and has not worked since. The LCD works as usual though when I turn it on. There is just no power from the motor. What might the problem be? Is it likely to be a problem with the motor, the controller, or something else? It looks like I'll have to buy a replacement from Woosh of whatever the component is that is damaged, but first I need to determine what it is that is damaged. I've definitely learned a lesson from this not to attempt to mess around with the electronics of my bike again. Thanks for any help you can give me.

 

[D8ve]

Fuse is first thought. If it was trying to pull too much current.
Worst case is motor or controller burn out was there any smell?

 

[Woosh]

Hello John,
You may have blown some FETs in the controller.
Please email support@wooshbiikes.co.uk on Monday.

 

[John_S]

Thanks for your replies. I'll email Woosh support on Monday.

My bike is not with me tonight so I can't test the fuse right now. I think it may not be the fuse because the LCD still turns on as normal, whereas when the fuse blew once before, the LCD would not turn on.

I didn't notice any smell at the time that the power stopped working, and so I don't think it was a burn out, although I couldn't be sure.

 

[Deleted member 4366]

The LCD works independently from the controller. There's no way you could have damaged it. Also, don't assume that your problem is anything to do with your adjustment to the shunt. It could be something as simple as a wire come loose that got disturbed when you took the controller out., so check every connector, especially any bullet ones on the motor wires if you have them. You can't always see that they are loose, so pull apart, crimp them down a bit and re-connect.

Soldering the shunt is the best way to adjust the power, as the results are fairly predictable. Unless you went nuts and tried to get double the power by shorting out most of the shunt, it's not very likely that you damaged anything unless your wire came astray and shorted something. Can you give us a link to the video and show a photo of what you did?

Start testing rather than worrying about what to replace.:

Connect everything, but don't switch on. Rotate the motor backwards. if it jams, you've blown a mosfet in the controller and will need a replacement. If it doesn't jam, the controller is probably OK.

Switch on and check whether you have 5v between the throttle or PAS red and black wires.

 

[John_S]

Thanks for your reply d8veh.

I checked all the connectors and it looked like they were all connected properly. I also checked whether the battery fuse has blown and it had not.

I rotated the motor backwards with the bike switched off and the motor did jam. Also, when I push the bike backwards, the front wheel moves in a very bumpy way. It looks like there must be a mosfet blown in the controller. I'll email Woosh and see if I can purchase a new controller from them.

 

[Deleted member 4366]

Can you show us what you actually did so that we can advise how to do it properly?

 

[John_S]

What I did was I attached using duct tape a small pole-shaped piece of metal about a mm in diameter and a little over a cm in length between two contact points on different ends of the shunt on the underside of the controller board.

 

[tommie]

think you should have soldered it John

 

[Deleted member 4366]

What I did was I attached using duct tape a small pole-shaped piece of metal about a mm in diameter and a little over a cm in length between two contact points on different ends of the shunt on the underside of the controller board.

So you shorted out the shunt completely. That would double the current, which is way beyond that which the controller could handle. I'm not surprised that it blew the mosfets. 30% is about as far as you can go without problems, but it depends on how much cool air the controller gets and how slow you let the motor go. You need to keep the motor spinning nicely to stop it and the controller from over-heating when you increase the current.

 

[Deleted member 4366]

Can you post alink to the vid?

 

[John_S]

I see. What I did was clearly not a good idea then. I tried searching for the Youtube video just now but couldn't find it. I'll try looking again later and I'll provide you with a link if I can find it. I'm not sure if I should attempt a shunt mod again on my bike but I guess I could if I'm very careful and informed on how it should be done. I'd prefer to do it without having to do any soldering if possible. Is there an effective way to do it without needing to solder?

edit: After doing some browsing online, I've learned that it would need to involve soldering some wire to the shunt in order to be done correctly. I looked at a soldering tutorial and it seems easy enough. What wattage of soldering iron would be recommended?