fan speed resistor burns out

[MattK]

Hi,
Hope to get some advice on my fan speed resistor. Mine blew a while back - started with one of the fan speed settings not working and eventually failed completely.

I followed the advice in the fact sheet and resoldered each of the burnt out tracks on the resistor. This worked really well, but only for about 4 hours. I took out the resistor again and found that the middle track (which I think provides power) had blown.

I then decided to remove the fan and loosen up the bearing with a little wd40 (although it felt pretty free when I rotated it by hand). Put it all back together, resoldered the middle track of the resistor, and again it blew after approx 1/2 a day.

I'm pretty sure it would blow again if I just resoldered the track and I don't really want to shell out for a new resistor just to have it blow again.

Anyone have any ideas on what's causing this and how I can get it sorted?
Do you think a new resistor will fix the problem once and for all?

By the way - the drain tube is clear and has always been clear - don't think this problem is caused by water ingress.

[welsh winger]

Hi what wattage was the resistor you fitted? keep the resistance the same but go for a higher wattage.

Nick
Welsh Winger

[MattK]

Hi Nick,
Thanks for replying.

I haven't actually changed the resistor - just repaired the original resistor.

[brorabongo]

Hi what wattage was the resistor you fitted? keep the resistance the same but go for a higher wattage.

Nick
Welsh Winger

I don't think there are any alternatives? Its a standard part, AFAIK.

If the resistor keeps burning out there must a high draw of current from somewhere, which has to be the fan motor? One other cause that springs to mind, is the state of the connections, are they corroded in anyway, either on the resistor or plug?

Good luck.

[mikeonb4c]

Hi what wattage was the resistor you fitted? keep the resistance the same but go for a higher wattage.

Nick
Welsh Winger

I don't think there are any alternatives? Its a standard part, AFAIK.

If the resistor keeps burning out there must a high draw of current from somewhere, which has to be the fan motor? One other cause that springs to mind, is the state of the connections, are they corroded in anyway, either on the resistor or plug?

Good luck.

I rather thought that too Brora. Is there a reason why the fan motor might draw a lot of current even though turning freely. Burned out shellac insulation on the copper windings from having previously been stalled might well cause that (in old money, 'fan motor burned out'). In which case it sounds like either rewinding the copper thingies (I don't think so!) or get a new motor

[MattK]

Ah...........ah.ha.......

You may have something there Mike - A while back I followed your instructions for spraying air freshener into the air intake.

I was driving along later and heard a horrible grinding and then a crunch. Pulled over and found one of the plastic rivets from the air intake cowling had got caught in the fan, so this may have caused the fan to stall. Funny thing is it has worked fine for about 8 months after this and has only recently started to show problems.
Reckon I need a new fan?

Who thinks Mike should buy me a new fan and resistor pack? After all I was following his advice and he didn't say anything about not dropping large chunks of plastic into a rapidly spinning fan. How was I to Know?

[mikeonb4c]

Ah...........ah.ha.......

You may have something there Mike - A while back I followed your instructions for spraying air freshener into the air intake.

I was driving along later and heard a horrible grinding and then a crunch. Pulled over and found one of the plastic rivets from the air intake cowling had got caught in the fan, so this may have caused the fan to stall. Funny thing is it has worked fine for about 8 months after this and has only recently started to show problems.
Reckon I need a new fan?

Who thinks Mike should buy me a new fan and resistor pack? After all I was following his advice and he didn't say anything about not dropping large chunks of plastic into a rapidly spinning fan. How was I to Know?

Ah, now this could get interesting. We'd have to call it the 'Daisy Chain Advice Affair'. Because this was actually not my tip, but (must give credit where its due, phew ) someone else's and I've long forgotten who. I'll have to do a search and see if I can track it down (key word would be Dettol I think, as that was the stuff they used). They should have thought to include the warning about not dropping bits into the fan, but didn't. So I think all legal claims must end up on their doorstep. Furthermore, I think BF needs to review its policy and ban all users from giving advice as they could be liable for promulgating it.

But seriously, sorry to hear it and it sounds like that incident may have stalled the motor and partially burned out the windings. Now I'm no leccie so we really need someone like RoosterUK (Carl) to come in here. I'm guessing, but I would imagine a partially burned out motor would show a lower resistance across it's +ve and -ve connection points than a healthy one. But whether that can be assessing easily given the armature type nature of their design, I don't know. Also, we'd need to know what the resistance of a healthy one is. And also, we need confirmation we are on the right track. But it does sound like a new motor may be needed. At least you can thoroughly clean up the assemble and de-smell it at the same time

I'll fetch me coat....

[waycar8]

strip down your motor!

i fixed my resistor, only worked on 1 setting, it worked again for about 5 days or so, then burnt out completly. stripped the motor down cleaned the rust from the bearing at the back and the contacts, got a new resistor got it to work fine, all worked fine apart from smell of burning, so got a second hand motor and all was well untill i stripped the bongo for spares after the crash

[MattK]

Thanks a lot for the help,

I'm away for a week, but will have a crack at stripping it down once I get back.
I'll let you know once its all gone horribly wrong.

[mikeonb4c]

Aha!! Found a moment and tracked the Dettol tip to source:

http://www.igmaynard.co.uk/bongo/forum/ ... lit=Dettol

Looks like cezeta is going to have to declare bankruptcy after all the law suits that are about to him his way

[Rhod]

Matt
Have you tried connecting 12V directly across the motor terminal (connections direct from a battery)? This should give you a good idea of whether the fan motor is ok, or if you have a problem in the motor, even although the bearing is ok.#
Rhod