tj90

Has anyone tried to home brew a ballast resistor for the oil cooler or AC condensor? It seems like its a simple power resistor and the porsche original seems weak anyway, why not fab one at a fraction of the cost that can dissipate more heat? Has anyone attempted? Maybe its better to buy (but at $55 each x2, its a compelling argument....

epj993

Ah, sounds like you're going at it! Like we discussed at Robin's, I think the primary factor in failure is heat as the resistor generates heat and is mounted in a hot location. I always felt that if it could be mounted in a cooler location - maybe near to intake vents - that it might last longer. I haven't checked this out, however. Mine are still working and I *think* they are the originals. If so, that makes them nearly 10 years old - not bad, really.

Good luck!

tj90

You know I could not resist!!

You can buy ceramic resistors with integrated Al heat sinks built into them - even anodized!! Seems like it would be more robust than the ceramic tab ones......

UPDATE - Ill just replace with original. Its too hard to find the exact power / resistance and its easier to just bolt another one on in its place!!!

TJ

MadMarkie

Pun intended I hope?

Also, remember an anodized surface has higher thermal resistance than bare Al, so the conductive path should be prepared (perhaps some conductive adhesive is in order).

Do report back if you decide to go this route... I am currently running shorted relays for both of my fans, with resistor replacement tentatively on the list when I add an aux oil cooler.

Cheers, Mark.

tj90

Mark:
See my post above. I chickened out. And yes pun intended! Seems like replacing it is a no brainer, but youll be cutting into the old wiring and rigging something. In this case, Ill just unplug the old and plug the new...

JasonAndreas

After the 993 was produced in 2000 Porsche added a heatshield/cooling plate between the ballast resistor and the oil cooler air guide (same thing for AC).

Edward

Of course, the other option is leave the broken one alone and throw in a manual fan switch. I never like to wait until the needle gets that high anyway and end up overriding the resistor's "go" command. When the temp needle approaches 9:00, I flick the switch and the needle drops like the proverbial rock since it bypasses low-speed fan operation and goes straight to high speed. Now the a/c resistor ...there's an important one to fix

Edward

tj90

Thanks for the suggestions. Im going to buy thermal grease and aluminum cooling fins / heat shield to improve heat transfer.... Im hoping I never have to mess with it again as long as I own the car...

c993k

What is the resistance and power ratings of the resistor for the fan and the AC?
I can put together a package quite easily.
I have in stock a large quantity of high power resistors to play with.
Chris

tj90

From carnewal the resistor is printed 0.45 Ohm. I calculated the wattage to be around 25W. However, p-car.com is saying that others have measured the resistance ~0.7 Ohm so my wattage calcculations might be off.

I was having trouble finding a 0.45Ohm (or anything close) resistance so I gave up my search for home brew. I know that I can achieve 0.45 Ohm by playing around with a few, but I did not want to create a crude power resistor pack. I was hoping I could find one component.

Also, there is a guy on ebay right now selling a 0.7Ohm 250W resistor which is more than enough for this application, but its 7 in long!!

I ordered 2 resistors yesterday, I will post the power and resistance rating as soon as I get it.

TJ