| Isolator adventure begins [message #347686] |
Wed, 11 September 2019 15:04  |
Christo
Messages: 109
Registered: April 2019
Location: Weymouth, MA
Karma: 0
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It started as a simple project: Replace the 12V house glass fuse panel with a ATC-based one. The furnace fuse position had melted at some point during the PO's tenure and it had been rewired using an inline glass fuse holder with undersized pigtail wires. Arrrgh. So, first step, kill the house power. I unplugged the shore power connection and disconnected the convenient knife switch at the house batteries. What? The panel's still live? Hmmm, what might the culprit be? I'd better go up front and have a look at the isolator.
Wow, there sure are a lot of wires connected to the isolator -- two on the top terminal, three on the middle, and two on the bottom -- better find the wiring instructions for my Sure Power 952. Aha! The center terminal should only be connected to the Bat terminal of the alternator. Arrrgh. Time for some wire tracing, and I'd better test the isolator with everything disconnected. This might also explain why my voltage when running read lower than I thought it should. To be continued...
Christo Darsch
GMC Nor'easters
1977 Eleganza II - "The Komet"
3.50 Power Drive, Disc Brakes, Alcoas
Weymouth, MA
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| Re: [GMCnet] Isolator adventure begins [message #347705 is a reply to message #347686] |
Wed, 11 September 2019 20:15  |
Richard Denney
Messages: 920
Registered: April 2010
Karma: 9
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Senior Member |
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Christo,
Some background reading, which you may not need...
http://www.gmceast.com/technical/Denney_GMC_Electrical_Sys.pdf
And the pictures that go with it, including the 12-volt panel I installed
(a marine unit from BlueSea):
http://www.gmcmhphotos.com/photos/g3677-electrical-wiring-concepts-for-2773-230.html
Rick “preferring newer fuse types” Denney
On Wed, Sep 11, 2019 at 4:04 PM Christo Darsch via Gmclist <
gmclist@list.gmcnet.org> wrote:
> It started as a simple project: Replace the 12V house glass fuse panel
> with a ATC-based one. The furnace fuse position had melted at some point
> during
> the PO's tenure and it had been rewired using an inline glass fuse holder
> with undersized pigtail wires. Arrrgh. So, first step, kill the house power.
> I unplugged the shore power connection and disconnected the convenient
> knife switch at the house batteries. What? The panel's still live? Hmmm,
> what
> might the culprit be? I'd better go up front and have a look at the
> isolator.
>
> Wow, there sure are a lot of wires connected to the isolator -- two on the
> top terminal, three on the middle, and two on the bottom -- better find the
> wiring instructions for my Sure Power 952. Aha! The center terminal should
> only be connected to the Bat terminal of the alternator. Arrrgh. Time for
> some wire tracing, and I'd better test the isolator with everything
> disconnected. This might also explain why my voltage when running read
> lower than
> I thought it should. To be continued...
> --
> Christo Darsch
> GMC Nor'easters
> 1977 Eleganza II - "Komet"
> 3.50 Power Drive, Disc Brakes, Alcoas
> Weymouth, MA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
'73 X-Glacier 230 "Jaws"
Northern Virginia
Offlist email: rick at rickdenney dot com
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| Re: [GMCnet] Isolator adventure begins [message #347716 is a reply to message #347705] |
Wed, 11 September 2019 21:48 |
Christo
Messages: 109
Registered: April 2019
Location: Weymouth, MA
Karma: 0
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Senior Member |
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Great backgrounder, thank you! Here's where my troubleshooting has led so far:
- Isolator checked out okay.
- Light gauge voltage sense line for a!ternator is non-original and was connected to middle terminal of isolator. Wrong! Moved it to top (chassis) terminal of isolator. This line has an inline 20A fuse in it near the isolator. Is this where the voltage sense line would normally be connected? Top terminal also has heavy gauge line to battery positive lug on firewall.
- Middle terminal of isolator has heavy gauge, non-original line to bat terminal of alternator.
- Bottom terminal of isolator has heavy gauge line to house side of bridging solenoid.
- There were two additional heavy gauge lines that I disconnected. One, which appears to be the original line to the alternator, was connected to the middle terminal of the isolator. The other, a non-original line, was connected to the top terminal of the isolator. These two lines were connected to each other near the alternator, thus tying the top and middle terminals of the isolator together. Wrong!
In this configuration things are working much better. When running, I have about 14.7v at the middle terminal and 14v at the top and bottom terminals of the isolator. When not running, and with the house batteries and shore power disconnected, I no longer have power at the house panel.
The only issue that has cropped up is that the dash blower no longer works at the highest setting. I know it's on a separate circuit operated via a relay on the firewall; the problem probably has something to do with the heavy gauge lines that I've disconnected. I'll dig into that tomorrow.
Good to know that I'm no longer under-charging my chassis battery and that my fridge might work a bit better on 12V while driving. It's a good day.
Christo Darsch
GMC Nor'easters
1977 Eleganza II - "The Komet"
3.50 Power Drive, Disc Brakes, Alcoas
Weymouth, MA
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| Re: Isolator adventure begins [message #347737 is a reply to message #347727] |
Thu, 12 September 2019 09:49 |
Christo
Messages: 109
Registered: April 2019
Location: Weymouth, MA
Karma: 0
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Senior Member |
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Agreed, Bruce. Just went through the wiring diagram and I see that the HI fan taps the line between bat terminal of alt and middle terminal of isolator. There's also a fusible link in that HI fan line.
Christo Darsch
GMC Nor'easters
1977 Eleganza II - "The Komet"
3.50 Power Drive, Disc Brakes, Alcoas
Weymouth, MA
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| Re: Isolator adventure begins [message #347748 is a reply to message #347737] |
Thu, 12 September 2019 13:21 |
Christo
Messages: 109
Registered: April 2019
Location: Weymouth, MA
Karma: 0
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Senior Member |
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Restored operation of HI fan successfully, so I continued with the original job of changing the house fuse panel over to ATC vs. the original AGC. I'm finally at the point where I can measure the current draw of my furnace fan now that it's properly connected to the panel. Whew, exiting PO hell for now! BTW I just picked up a Klein CL380 Digital Clamp Meter that can measure DC voltage and amperage via the clamp. $80 well spent, nice meter.
Christo Darsch
GMC Nor'easters
1977 Eleganza II - "The Komet"
3.50 Power Drive, Disc Brakes, Alcoas
Weymouth, MA
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