Club 80-90 Forums

I'm going to take the plunge and rewire the dash onto a veroboard as per the Wiki.
I'm also going to use all new LEDs and resistors.
I have the resistor ohm values but I haven't been able to get hold of any info on wattage.
This is only really an issue for the 150 ohm resistor that connects to the alternator (as all the others are only driving an LED).

Does anyone know how much current flows through that resistor to the alternator on start up?
The resistor on the original blue film (that I am replacing) is significantly 'bigger' in size than the others on there (which makes sense as the others only have to drive enough current to light an LED) so this implies that there is a larger current going through this chap.
Anyone got any ideas??

(Note: Ultimately, current only flows through this resistor just before start up so its never 'on' for very long - but thought I may as well ask and see if anyone has an idea??)

I have no idea but the Max current that can flow through 150 ohms at 14 volts is 1.3 watts
That assumes all has no resistance so it will be lower than that.

Fair point - hadn't thought of doing it that way .....
Also voltage shouldn't be quite that high as it would battery voltage only (as the alternator isn't turning yet).
So, something around the 1-1.5W value should do the trick then - Cheers!!!

MidLifeCrisis wrote:
Does anyone know how much current flows through that resistor to the alternator on start up?
The resistor on the original blue film (that I am replacing) is significantly 'bigger' in size than the others on there (which makes sense as the others only have to drive enough current to light an LED) so this implies that there is a larger current going through this chap.
Anyone got any ideas??

2 watt. They are also non flammable resistors note they are also mounted in a cut out in the circuit board due to if the ignition is accidental left on the resistors can get very hot, also the reason two resistors resistors are used in parallel to reduce the amount of heat in each resistor.

Interesting - thanks.
I always assumed the parallel resistors was incase the LED packed in there would still be a path to the alternator for the excitation signal.

MidLifeCrisis wrote:Interesting - thanks.
I always assumed the parallel resistors was incase the LED packed in there would still be a path to the alternator for the excitation signal.

No that is not really a problem the alternator will self excite itself once the engine is revved.

bigherb wrote:the alternator will self excite itself once the engine is revved.

Eee, by eck, that reminds me, I must get round to testing this in the real world, there was a thread a while back where this was mentioned, I agreed with you, but most said they won't self excite.