SMD Capacitor on Mobility Scooter Controller.

I found an ants nest in a mobility scooters controller so to open it up and clean it I had to dig out the hot glue gun deposits over the spade connectors. While doing this I dug out 2 SMD capacitors C4 and C5 while I was at it. C6 is still intact but my Fluke 87V doesn't register anything when I try to read the remaining C6 value? Any ideas what I could replace them with? I have some 1uf SMDs and some others I could scrounge from some boards laying around the place. They look like they connect to the B+ and B- rails and ground.
 

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kevinkr

Administrator
Paid Member
A couple of those caps appear to be across battery connections and motor connections. I wouldn't scrounge - and I would try to get the actual schematic if possible.

You haven't mentioned what the package size is, looks big - 1206 in ceramic dielectrics are typically above 1000pF unless very high voltage types.

I would recommend new caps not scrounged and suspect X7R 100V 0.1uF might be in the range.
 
Hot melt glue also melts and drips off when hot. Basically its not really usable for a vehicular environment (melts in the sun, breaks/cracks in the cold). Perhaps it was a silicone encapsulant, not hot-melt?


These capacitors are for RF suppression I think, 100nF 50V X7R will be suitable at a guess, they should not be necessary for functional testing of the scooter - just for passing EMI emissions certification process.


BTW I like the surface-mount massive current-shunt resistors on the PCB, not seen that type before.
 
Most shops have freeze spray. "Circuit chiller".

Hot melt glue gets real brittle when sprayed with freezit. Then you can easily shatter it with a screwdriver or something. No digging required and no collateral damage. Brush the little pieces away.

I've got some freeze spray too. I use it to freeze my pre-skin cancers with though. Its the same stuff doctors use to freeze them with. Come to think of it that stuff wasn't hot glue, it took me hours to get out whatever it was?
 

phase

Member
2004-10-04 11:59 pm
Hot melt glue will absorb moisture and free itself from whatever it had been applied to.

The older designers would use that garbage on large mock-ups until we took over the model building part of the business. The lightweight paper and foam parts would be on the floor after the weekend nearly every time, just from the moisture in the air around here.
 
Hot melt glue also melts and drips off when hot. Basically its not really usable for a vehicular environment (melts in the sun, breaks/cracks in the cold). Perhaps it was a silicone encapsulant, not hot-melt?


These capacitors are for RF suppression I think, 100nF 50V X7R will be suitable at a guess, they should not be necessary for functional testing of the scooter - just for passing EMI emissions certification process.


BTW I like the surface-mount massive current-shunt resistors on the PCB, not seen that type before.

I think you are right about those missing caps on the B+ and B- rails being RF suppression caps! I downloaded the Curtis PMC 1228 motor controller manual, it didn't have an internal schematic but it's big on EMI that's for sure, if it doesn't interfere with my stereo gear I'm Ok with leaving them out. What if I used ''No More Gaps'' to seal the spade connectors when I put it back together? It's waterproof and grips pretty well.