Previous owner's odd wiring

[Roy Gillett]

I recently posted on this site about my water temp. gauge and fuel gauge varying together from time to time. I was advised to change the voltage stabiliser and was even able to purchase a solid state one - thanks John Clegg.

When I got round to fitting it I found some very odd wiring to the old unit. It had five spade connectors on it. Two had dark green wires attached (as per wiring diagram) One had light green wires to it and one had an earth wire The fifth (the 'pair' to the light green wires had a 1micro-farad capacitor attached to it which was bridging to the eath wire! Thus this seemed to connect the light green wires directly to earth via the capacitor.

When I just substituted the wires onto the (four spade) solid state device earthing the case with the 5th wire, things got very hot very quickly (on reflection not surprisingly)

Doing away with the capacitor bridge link to earth made things work as they should. What I am left puzzling over is why did the old arrangement work at all? What was the PO trying to achieve with the capacitor?

It just seems so odd when you think about it

Any thoughts?

Roy

[ncm]

Roy, I think you will find that the capacitor will have been added as a form of radio supression.

Brian.

[Roy Gillett]

But between a live feed and earth? ANd on a circuit that won't have any switching spikes that I can foresee?

Certainly with the solid state device it just caused it to draw a big current and get very hot very quickly.

Still puzzled.

Roy

[rgh0]

The old voltage regulator worked with a bimetallic strip and heating circuit. The capacitor across the supply to earth would have been intended to suppress sparking when the contacts opened reducing any radio noise and increasing contact life - but given the circuit low switching frequency and voltage and current and inductance it should have not really been need I would have thought.

I presume you new electronic circuit is switching at a relatively high frequency to control the coltage supplied and that the capacitor was flowing a signficant current at this high frequency so it heat rapidly

cheers
Rohan

[rgh0]

The old voltage regulator worked with a bimetallic strip and heating circuit. The capacitor across the supply to earth would have been intended to suppress sparking when the contacts opened reducing any radio noise and increasing contact life - but given the circuit low switching frequency and voltage and current and inductance it should have not really been need I would have thought.

I presume you new electronic circuit is switching at a relatively high frequency to control the coltage supplied and that the capacitor was flowing a signficant current at this high frequency so it heat rapidly

cheers
Rohan

[andyhodg]

I recently replaced my voltage regulator with a solid state device. The old unit had the capacitor in as you describe. I simply left it out and wired the solidstate unit with three wires. Earth, live feed and feed to the instruments. All has been well since.

Good luck Andy

[andyhodg]

I recently replaced my voltage regulator with a solid state device. The old unit had the capacitor in as you describe. I simply left it out and wired the solidstate unit with three wires. Earth, live feed and feed to the instruments. All has been well since.

Good luck Andy

[Alex]

A modern solid state regulator doesn't operate at frequency, so a capacitor across input/output to ground will help smooth out any noise. Its a standard feature on a modern linear power supply.

Problems could arise if the capacitor is an old dried out electrolytic which could short out internally. Just as they can do in a distributor.

Hope this help,

Alex

[alan71]

I think radio interference was a common problem, this is what I found fitted to mine. I binned it all when I fitted an electronic regulator.

Alan

[alan71]

I think radio interference was a common problem, this is what I found fitted to mine. I binned it all when I fitted an electronic regulator.

Alan

for some reason I can't add a picture to this post

[alan71]

there should be a picture with that, not sure what happened.

Alan.