| Isolator Performance [message #146587] |
Sat, 15 October 2011 09:08  |
George Zhookoff
Messages: 398
Registered: December 2004
Location: Snellville, GA
Karma: 6
|
Senior Member |
|
|
With all this discussion about isolators mine of course is acting up... During a 1200 mile round trip a couple of weeks ago my dash DC meter was variable showing 11.9 - 16.0 volts. Took out alternator and had it tested at my local rebuilder. Checked out okay. Go figure.
Meter from center post to ground with engine @ idle is 14.8 v. Meter either outside post to ground with engine @ idle is 12.8 v.
Is the isolator on the way out?
Thanks
George Zhookoff
78 EL II
Atlanta
With awesome Reaction Arm Brakes, still!
|
|
|
|
|
|
|
|
| Re: Isolator Performance [message #146620 is a reply to message #146587] |
Sat, 15 October 2011 16:54  |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
|
Senior Member |
|
|
Matt...to tie this back to the other parallel universe charging discussion....
If the isolator is open on both diodes (sides) and the sense back to the alt is on the engine (vehicle) side, with no sense wouldn't the alt output go sky high? Or did it and it is just not noticed as both sides of the isolator have no reference to centre (alt O/P) . HMMM> would need to measure center to ground with engine running.
John Lebetski
Woodstock, IL
77 Eleganza II
|
|
|
|
| Re: Isolator Performance [message #146621 is a reply to message #146587] |
Sat, 15 October 2011 16:58 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
|
Senior Member |
|
|
He says center is 14.8 something (a touch high but maybe OK with no load). I wonder if sense is connected to center and not vehicle side.... this would cause low /incomplete charging by about .5-.7 volts or really quite a bit.
John Lebetski
Woodstock, IL
77 Eleganza II
|
|
|
|
| Re: [GMCnet] Isolator Performance [message #146624 is a reply to message #146621] |
Sat, 15 October 2011 18:36 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
|
Senior Member |
|
|
I agree with you, John, if the isolator is open on the chassis battery side,
with everything working normally, the alternator voltage should go to about
15VDC, trying to pull the engine battery up. The sense line connected to
the alternator terminal could explain the readings, except for one
possibility: If the 12.8 VDC on the batteries is correct, they've been
receiving charge very recently from some source.
Before condemning the isolator, I'd check the voltages of each battery, and
the alternator, at the isolator with some load on each battery. Even if the
isolator tests good when cold, it may still open up when hot.
JWID,
Ken H.
On Sat, Oct 15, 2011 at 5:58 PM, John R. Lebetski <gransport@aol.com> wrote:
>
>
> He says center is 14.8 something (a touch high but maybe OK with no load).
> I wonder if sense is connected to center and not vehicle side.... this would
> cause low /incomplete charging by about .5-.7 volts or really quite a bit.
> --
> John Lebetski
> Chicago, IL
> 77 Eleganza II
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
Unsubscribe or Change List Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
|
|
|
|
| Re: Isolator Performance [message #146626 is a reply to message #146620] |
Sat, 15 October 2011 18:54 |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
|
Senior Member |
|
|
| JohnL455 wrote on Sat, 15 October 2011 17:54 |
Matt...to tie this back to the other parallel universe charging discussion....
If the isolator is open on both diodes (sides) and the sense back to the alt is on the engine (vehicle) side, with no sense wouldn't the alt output go sky high? Or did it and it is just not noticed as both sides of the isolator have no reference to centre (alt O/P) . HMMM> would need to measure center to ground with engine running.
|
| JohnL455 wrote on Sat, 15 October 2011 17:58 |
He says center is 14.8 something (a touch high but maybe OK with no load). I wonder if sense is connected to center and not vehicle side.... this would cause low /incomplete charging by about .5-.7 volts or really quite a bit.
|
John,
You are both astute and observant, but you missed the one remark where George said, "with the engine at idle". He also said earlier that his digipanel was showing 11~16, about right for running down the road.
The isolator is gone, that is a given... When he gave values that indicate a ~2V drop where it should be closer to an half, you know that things are wrong. If he got near the current the system could run, the heat sink would have to handle 100~150 Watts instead of the 40 it is designed for. The epoxy would smoke. If I were there with my DC current probe (I'm not going to suggest anybody buy one), I could get a lot more specific about the nature of the failure. But, there is also no need. When he gets the isolator problem corrected, he will look at things again, and if they are not right then, he will be back.
Another thing I did not bother to write about is that he may have is an alternator that was rebuilt with the regulator designed for the next in the Delco series. These do have an internal system to limit the alternator output voltage to about 18V. This part will go into the case of ours sort of OK, but it has one extra connection and one terminal has to be bent a little to line up. That just doesn't bother a lot of aftermarket people. I have not seen it, but I am told a supplier had a regulator designed to accommodate both series with a single part. You kind of have to know how aftermarket minds work.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
|
|
|
|
| Re: Isolator Performance [message #146657 is a reply to message #146587] |
Sat, 15 October 2011 22:40 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
|
Senior Member |
|
|
Without doing anything else or removing anything.....real quick test. Just jump the terminals on the isolator. You can jump center to chassis and then see if you have 14 at the main engine batt. Then add a jump center to the house side. This will show if the alternator is producing power under load. If all checks out this goes right along with Matt's "isolator is gone" theory. The VOM diode test on the isolator is a good start but yes it can be heat sensitive, test good with a meter but not support current, or even worse.... an intermitent intermittent.
John Lebetski
Woodstock, IL
77 Eleganza II
|
|
|
|
GMCforum
Search
Help
Register
Login
Home
