Regulator resistor

[alanworland]

Lost charging on my Series MM this week, did usual tests and finally removed the regulator which revealed a 63 ohm resistor mounted behind.
This has gone high in value and unable to energise the dynamo field coils and needs replacing.
It's a physically large component but could probably be replaced which something a lot smaller which would still be rated at a similar wattage.
My question is does anyone know the wattage rating of the original?

Alan

[oliver90owner]

What voltage is it fed with? If 12 Volts maximum, it is easy to apply Watts = Volts x Amps, or other variations of the formula for Electrical power. Ohms Law is useful to sort it outif you don’t know the other formulae.

If 12 V, 2 1/2 Watts is not a particularly high value. Temperature rise may be needed to be kept sufficiently low to avoid an increase in resistance as the temperature rises, hence its relatively large physical dimensions.

[alanworland]

Yes, that's the theory I used. I found a 68 ohm 10w wirewound resistor which is still smaller than the original!
Should do the job.

Alan

[oliver90owner]

63 and 68 Ohm resistors could be the same value (if + or - 5%). If smaller tolerance it may not be quite OK.

Adding a 1k resistor in parallel will give close to 63. A much lower powered resistor would be adequate for that.

Inverse law applies to resistors in parallel.

RAB