I recently replaced my Hehr isolator after I found that it was shorted out between the alternator post and the house battery post. I had noticed a raised area in between two of the posts and I was curious as to what this was so a disassembled the isolator. In doing so I came across something I have never seen. The bottom half of the potting compound was filled with small gravel, yes, that is right, I found rocks in my isolator. A search on the internet showed no mention of rocks as a filler material. i have attached a picture. Has anyone ever seen gravel used as a potting compound filler?
I found the following issued when I disassembled the isolator: corrosion on the aluminum diode common rail, potting compound separating the common rail from the heat sink, and no heat sink compound between the potting compound and the extruded aluminum heat sink. Oh, and then the weirdness - rocks! I don't think I'll buy a Hehr isolator if my current one ever fails.
There are any number of fillers that can be used with Epoxy Potting compound. Sometimes it is just a cheap filler to take up space to save the use expensive polymers. Other times mineral or metalic fillers are used for performance reasons such as using aluminum chunks to reduce weight, copper fillers for heat dissipation and ceramic or mineral fillers for abrasion resistance or dimensional stability. Of course metalic fillers must be fully encapsulated to keep it isolated from and electrical source.
With all of that said, I have no idea why they used gravel in the Hehr isolator.
John ; if it came with your coach when new , I think gravel is A pretty good thing to have in there . Your coach is A 1991 , and that thing still works , That is as good as it gets in my book . Be happy , life is short . -----Brad Metzger--------
Well, Brad, no it no longer works and I have no idea how long it has been broken. I've owned the coach for 6 years and I think the isolator has been bad the whole time. I just finally decided to look into the problem of the lights coming on even though the master switch was off.
I'm sure glad my 92 didn't have lights coming on and off especially with the master switch off. My wife would think it was haunted and never set foot in it again. Then again...what did you do with the Hehr?
Then best to just not broach the subject :o!
After disassembly the heat sink went in the Al scrap, the potting compound with the rocks went in the trash and the diode assembly is a trophy like my blown connecting rod (from the MR2 race car, NOT the Cat 3208!). Other trophies include a very large early laser assembly from a 3D seismic plotter and a 4k X 68 bit word core memory module from a seismic computer.
Even considered in Isolation, that's a Hehr-raising story...
Oh Dave! That's right up my humor alley. I sure wish I had thought of it. Norm, he got us both with that one.
During my racing days, all of our ignition and fuel control components came to me unpotted.
This would allow me access to modify the factory "stock" ;) programing.
The potting mixture came in tubes similar to RTV or silicone and was poured
into the component. If this was done without adding stones (could be aquarium stones)
to carry oxygen into the mixture it would skim over and never set up.
To reiterate, the stones sole purpose was to carry oxygen down into the mixture to get it to kick off.
You will find stones/rocks in most potted electrical components.
Gordy