Electronics Question

[whisky]

Hi

can someone assist with an electronic question please. How do i install a resistor or diode across a headlamp bulb to stop voltage spikes. I have two new bulbs blow in as many weeks.

any values or drawings would be appreciated.

[stef123]

Hi

can someone assist with an electronic question please. How do i install a resistor or diode across a headlamp bulb to stop voltage spikes. I have two new bulbs blow in as many weeks.

any values or drawings would be appreciated.

Are you using good quality bulbs and fitting them without touching the glass? there should be no need to fit anything to prevent spikes

[Preee]

Fitting a diode or resistor across will not stop any spikes , if you are getting spikes causing the bulbs to fail , then you need to look a little deeper with perhaps an auto electrician guy.

I would side with Stef and say the bulbs are a bad batch or maybe make sure you keep fingers away from them.

Also check your earthing points and wires from the bulb holders , as they could be getting damp and arcing across.

[Dan62]

See here for the TSB solution.

As for your question, fitting something like a Zener diode and resistor is not possible because of the current the lamps draw.

Something I have seen used before is a resistor across the switch, providing a continuous current through the lamp filaments, enough to keep them warm.

Best to keep car electrics as is and go for the Ford fix.

[whisky]

Ok Guys Thanks.

Ford do say for the fiesta they have a retro fit device that fits across the headlight that should eliminate these spikes blowing lamps. they are about £13 each and didn't want to buy them if it was just a case of buying some bits from Maplin that would do the same thing,

[Dan62]

The Maplin solution would be a lot cheaper.

An 0.22 ohm resistor in series with the lamp would give you 0.9v drop and an 0.47 ohm resistor 1.8v. (approx assuming 12v)

A 10w wirewound will be adequate, your looking at approx 4w for the .22 ohm and 8w for the .47 ohm.

They will dissipate heat so keep them away from other wiring, putting them in the earth return side of the lamp will protect the high beam filaments as well.