Ballast resistor improvement
03-30-2009, 06:56 PM
#1
Three Wheelin'
Thread Starter
Ballast resistor improvement
This winter I examined both my AC and oil cooler fan ballast resistors. They were both in need of replacement. Since these commonly fail, are a PITA to reach, and I am frugal by nature, I was seriously tempted by Garth's solution. Somehow, though, I could just not bring myself to implement it. I wanted something cleaner and closer to original. This was my idea:
First, here are the pics of my old resistors. The AC cooler one was actually broken into two parts before I removed it!
I had noticed that pictures of new resistors showed some black material where the potting cement is on the originals. I was hoping it was some kind of moisture resisting material, and it is! It is a very rubbery compound.
The new resistor comes with a baseplate to mount it on. This is a heatsink. Since the black rubbery area on the back of the resistor was countersunk wrt the ceramic base, I decided to fill the bottom with thermal compound.
Next, I added the heatsink and gently pressed out the extra thermal compound and cleaned it up. The compound is geasy so the clamp is used just to hold stuff in place while handling it.
Next, I wanted a way to keep everything from sliding around, ensure the thermal compound didn't get washed away, and the prevent moisture ingress even better. Thus, I put a bead of Permatex ultra black around the edge. The is a high temp gasket forming material.
That is my gloved finger about to apply the UltraBlack. In hindsight, I should have masked part of the resistor to get a cleaner edge.
I let these cure overnight and the result is, hopefully, a pair of new OEM ballast resistors that has better thermal performance and is resistant to moisture ingress.
Time shall tell if this was a good idea or not, or if I should have gone with the bullet-proof and inexpensive mod that Garth devised. Comments from the gallery?
First, here are the pics of my old resistors. The AC cooler one was actually broken into two parts before I removed it!
I had noticed that pictures of new resistors showed some black material where the potting cement is on the originals. I was hoping it was some kind of moisture resisting material, and it is! It is a very rubbery compound.
The new resistor comes with a baseplate to mount it on. This is a heatsink. Since the black rubbery area on the back of the resistor was countersunk wrt the ceramic base, I decided to fill the bottom with thermal compound.
Next, I added the heatsink and gently pressed out the extra thermal compound and cleaned it up. The compound is geasy so the clamp is used just to hold stuff in place while handling it.
Next, I wanted a way to keep everything from sliding around, ensure the thermal compound didn't get washed away, and the prevent moisture ingress even better. Thus, I put a bead of Permatex ultra black around the edge. The is a high temp gasket forming material.
That is my gloved finger about to apply the UltraBlack. In hindsight, I should have masked part of the resistor to get a cleaner edge.
I let these cure overnight and the result is, hopefully, a pair of new OEM ballast resistors that has better thermal performance and is resistant to moisture ingress.
Time shall tell if this was a good idea or not, or if I should have gone with the bullet-proof and inexpensive mod that Garth devised. Comments from the gallery?
03-30-2009, 08:17 PM
#2
Looks good to me.
The only bit of skepticism I have is that I'm not sure the manner in which these parts get brittle and then fall apart is because of moisture, as opposed to age and heat cycling.
I don't have one on my oil cooler anymore, because I installed an override switch. I do have one on the AC, which I'm going to replace at some point. I figure that if the replacement lasts as long as the original one (12 years and still going) I won't have any complaints.
The only bit of skepticism I have is that I'm not sure the manner in which these parts get brittle and then fall apart is because of moisture, as opposed to age and heat cycling.
I don't have one on my oil cooler anymore, because I installed an override switch. I do have one on the AC, which I'm going to replace at some point. I figure that if the replacement lasts as long as the original one (12 years and still going) I won't have any complaints.
03-31-2009, 08:52 AM
#4
Three Wheelin'
Thread Starter
Maybe it was overkill, dunno...Since the black rubbery part did not make contact with the heat sink I wanted to use the thermal compound for better heat transfer. Then I needed the Permatex to seal it in there and hold everything together for installation.
03-31-2009, 03:03 PM
#5
Drifting
There is a latin term for this: ex abuntanti cautela.
And one of the side benefits of being able to do your own work.
And one of the side benefits of being able to do your own work.
Last edited by Rinty; 03-31-2009 at 04:59 PM.
