Home » Public Forums » GMCnet » [GMCnet] Isolator -- bypass?
| Re: [GMCnet] Isolator -- bypass? [message #326803 is a reply to message #326802] |
Wed, 06 December 2017 13:27   |
James Hupy
Messages: 6806
Registered: May 2010
Karma:
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Senior Member |
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That "dismal 12.0vdc" is with the engine running, or with it not running?
If not running, then you are reading the battery voltage. 12.0 vdc would
indicate to me that the battery shows a low state of charge.
Under ideal laboratory conditions, a wet cell with a specific gravity
of 1.260???? at 70° farenheit, and humidity of 30.00 in hg, should render a
2.2 volt electrical potential. Multiply that by 6 and ideal state of charge
should "potentially" be 13.2 volts. Now deduct resistance, meter
fluctuation, etc., etc., and your real world state of charge should be 12.8
volts or so. Just sayin'.
Now, if your engine is running and alternator output is normal (whatever
that is) you should see AROUND 14.5 VOLTS on the center tap of the
isolator, about .7 volt less on each leg if your isolator is good. If not,
sumpthin' ain't right.
Jim Hupy
Salem, Or
78 GMC ROYALE 403
On Dec 6, 2017 11:05 AM, "Emery Stora" wrote:
> Both batteries should NOT be connected to the same isolator post. Keep
> one that goes to the “vehicle battery positive pole”. Disconnect the other
> one. It should go to the second isolator post.
> Most transmodes have a boost switch on the dash and a second battery (the
> “house” battery).
>
> If you are certain that you don’t have a second battery (look in the back
> by the Onan) then you can connect the wire from the alternator (center
> isolator post) to the vehicle battery positive pole.
> However, if you do have a second battery for the Onan or the house
> circuits that battery would not be charged.
>
> Emery Stora
> 77 Kingsley
> Frederick, CO
>> On Dec 6, 2017, at 11:47 AM, Dave Stragand dave.stragand@forwardlook.net> wrote:
>>
>> Hi All,
>>
>>
>>
>> Just started poking at the no-charging issue on our 1978 Transmode
>> (403).
>>
>>
>>
>> Thanks to whomever created that great flowchart for troubleshooting
>> charging issues. I was able to determine that the alternator voltage
>> (center pole of the isolator) to battery terminal ground was 14.70
>> volts, so the alternator seems within spec..
>>
>>
>>
>> However, both of the output poles on the isolator (top and bottom) are
>> connected directly to the same point - the "vehicle battery positive
>> pole". On a Transmode that may not have had a second or house battery,
>> that kind of makes sense to me, but if that were the case, why would GM
>> bother to install an isolator? In any case, the reading from either
>> pole on the isolator is a dismal-but-steady 12.02V - and that's too low.
>> It matches the 12.0 on the cheapo cigarette lighter voltmeter inside.
>>
>>
>>
>> That leaves me with a few questions, and I was hoping y'all might be
>> able to help.
>>
>>
>>
>> 1) Is the low voltage on the battery sides of the isolator possibly
>> caused by the fact that both the upper and lower outputs are connected
>> together?
>>
>>
>>
>> 2) Considering I don't really have any house circuits at present (it's
>> a Transmode with a partial homemade interior), can I simply bypass the
>> alternator for the time being, connecting the alternator wire directly
>> to the "vehicle battery positive" pole?
>>
>>
>>
>> 3) If my isolator is indeed shot, does anyone have a good used spare
>> they'd like to sell, or should I just buy a new one from one of our
>> awesome vendors?
>>
>>
>>
>> Thanks, All!
>>
>>
>>
>> -Dave
>>
>> 1978 Transmode (403)
>>
>> Pittsburgh, PA
>>
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