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Topic: Hehr isolator failure - question for the engineers out there. (Read 1009 times) previous topic - next topic

Hehr isolator failure - question for the engineers out there.

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.
John Cooper
'91 GV 36'
Oshkosh chassis
Cat 3208T 300HP

Re: Hehr isolator failure - question for the engineers out there.

Reply #1 –
Quote from: John Cooper –
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.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Hehr isolator failure - question for the engineers out there.

Reply #2 –
           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--------
Brad Metzger
2010 Phenix 45'

Re: Hehr isolator failure - question for the engineers out there.

Reply #3 –
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.
John Cooper
'91 GV 36'
Oshkosh chassis
Cat 3208T 300HP

Re: Hehr isolator failure - question for the engineers out there.

Reply #4 –
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?
Dwayne Keith
1992 U240
3116/MD3060

Re: Hehr isolator failure - question for the engineers out there.

Reply #5 –
Quote from: Dwayne –
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!
1994 U225
build #4514

Re: Hehr isolator failure - question for the engineers out there.

Reply #6 –
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.
John Cooper
'91 GV 36'
Oshkosh chassis
Cat 3208T 300HP

Re: Hehr isolator failure - question for the engineers out there.

Reply #7 –
Even considered in Isolation, that's a Hehr-raising story...
Dave and Nancy
1999/2013 U270 36' Xtreme
Motorcade # 16774
2013 Subaru Outback
KD0NIM

Re: Hehr isolator failure - question for the engineers out there.

Reply #8 –
Quote from: Dave Katsuki –
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.
The selected media item is not currently available.Kent Speers
Locust Grove, OK
1993 U300 SSE 40' (Restored at FOT 2009) Build 4323
720 watts Solar
6V92TA DDEC Silver Engine
2014 Subaru Outback

Re: Hehr isolator failure - question for the engineers out there.

Reply #9 –
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
Gordy Muetz
Fulltime 8 years
2000 Foretravel 40Ft U270
2004 Featherlite 24Ft 14,000lb GVWR
2010 HarleyDavidson Road King
1986 Suzuki Samurai TinTop
Co-Driver, Wife, Karen