Re: Re: Re: RPM-relay relay

[Jan van de Wouw <jvdwouw@xxxx>]

On 20-07-2002, Walt wrote:

>> The only thing the coil is connected with is pin 15 giving it 12V
>> after ignition and the collector of a BC338. The BC338 pulls
>> the coil to ground (well allmost; you lose about 1,4V because
>> of the transistor and a diode agains reversed polarity).
> 
> I'm not up on transistor engineering like I should be, but my main
> concern would be that you don't put too high a load through the
> transistor with the new relay. Over a period of several hour's
> worth of driving, it could get too hot.

I have the setup working as we speak; the BC338 actually has to put
up with LESS load than the original, since the new relay has higher
resistance, so at the same voltage it allows less current to pass.
The tranny is capable of switching up to 800mA with cooling,
originally it had to cope with 200mA, now only 150mA, so the internal
heat dissipation has gone from 140mW to 105mW, while it COULD stand
upto 800mW, but would need a cooling body then...

Just to be sure I won't get stranded because of some miscalculation
I did I made a jumper wire that I can plug in when my relay decides
to go on strike anyway, but I don't think I will need it...
And if it does its WAY easier to put in a jumper behind the seat
than it is under the trunk (where the previous owner installed a "Hot
After Ign.II wire", making the pump run whenever I had the ignition on.

Thansk anyway, I will post pictures of my relay this weekend,

JAN van de Wouw
Thinking Different... Using a Mac...
Living the Dream... Driving a DeLorean...

#05141 "Dagger" since Sept. 2000

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