Technical Tips > Post 84

Courtesy lights dimmer module - parts info/tech tip here

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Cameron 77C3:
Yeah it's a throw away world.  But I'm from the old school.  My test is "now what would the old man say if I did it that way."  That always keeps me on the straight and narrow.

I relation to your parts to clarify my statement in more detail.  What I posted was not quite true.  I just couldn't be bothered going right into it

The part 047 GE 8708 is not actually listed.  That number is an in house part number.  [companies often do this so that other companies can't copy what they are doing. I do it my self by rubbing the part numbers off IC's] Knowing how that circuit would work by your schematic circuit diagram I took an educated guess as to what it would be.  MJE 3055's, an NPN transistor, are as common as sand on the beach.  It's a safe bet that the 047 GE 8708  is actually an MJE 3055.  These have been around for decades.

I made the assumption that the unit is taped to the wiring loom or stuck up under the dash some where, where there is not a lot of air movement.  This is what I was actually referring to about over engineering.  If this is the case I would have put on a larger heat sink in the original design.

When a circuit is designed one also has to look at where it is going to be mounted.. Heat sinks work on being able to dissipate heat from the transistor.  If you could keep a transistor cool enough you could pull many, many amps through it.  [This is why computer fans are used.  To reduce the size of heat sinks.  A heat sink can be much smaller when used in conjunction with a fan.]

Any time I build a circuit to go in a vehicle I usually over spec the heat sink as the customer does not always mount them where he said he was.

So if you want to ensure your unit is OK, make sure there is plenty of "breathing" space around it.  It should last for a long long time.

Your electronics man did well.  Not many guys these days want to reverse engineer to work a circuit out.  Most just want to throw it out and build a new one.  [now where is the fun in that]

NOTE:-  Putting higher wattage light bulbs in than originally speced can cause the unit to over load the transistor [MJ 3055] again.

[I now have writers cramp] :22

Stingraynut:
Quote "[I now have writers cramp]"

Ha ha - thanks v much, I understand what you'r saying.

In fact the heat sink is the same size as the circuit board, about 50mm square, it clips onto the board and that assemble slides into an open ended plastic case - which prevents airflow, then it's taped by GM to the wiring harness, behind the centre of the dash above the transmission tunnel - could they ensure it'd get any hotter ?

I'm planning to fit a switch to it, so that I can disable the interior lights for any reason, like working on the car with the door open, which happens very often - I pull the fuse but then also loose the memories in the CD/radio.

I checked out your pics this morning - looks like you did a lot of good work to that shark - what are you doing over here, with the 'modern' cars ?

BTW my favourite vette would be a C3 body on a C4, although now the C6's are out I'm beginning to like the C5!

S'nut

Cameron 77C3:
I'm always trolling the different forums.

On the list for the C3 is the composit type suspension front and back.  Gota get the slug to handle.  But thats going to have to wait 6 months or so till my bank account recovers.

It would actually be better if the transistor was directly bolted to the heat sink.

Anyhow I'm sure if it lasted 15 years, it'll last another 15 years.  Catch ya.

Stingraynut:
Quote "Gota get the slug to handle"

don't be fooled into thinking the C4 handles Aussie roads- on a dry smooth surface Oh yeah - with 11" wide tyres what wouldn't ?

But the suspension travel is way to short and I've done a heap of research into the handling problems - not helped at all as our Far North Qld roads are often described as 'Moonscape' etc.

S'nut

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