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  #1  
Old 02-06-2014
HarryHansen's Avatar
HarryHansen HarryHansen is offline
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Join Date: Apr 2009
Location: SoCal
Posts: 32
Default 83 PT40 AC Faulty Ground

Assuming that the monitor panel was the same in all BBs in 1983, there
are two AC voltage meters, one above the other, on that panel and a
notation underneath that "No light indicates faulty ground connection". As
you can see in the photo there is a green LED lit under the lower meter but
the upper green LED is not lit.

I have just replaced the generator with a brushless 15kw unit and the
ground strap from the Perkins to the tray is connected.

There are 4 x T105 6v batteries for the coach and Detroit starting.

There is a large battery isolator in the engine bay, which I assume (!!!!)
isolates those batteries from the generator battery, which is a huge 12
volt in the front of the coach, but allows that battery to be charged by
the alternator or convertor. However when I start the generator the house
lights dim badly.

The generator battery seems to discharge at the same rate as the
house/start batteries whereas I would expect it to hold its charge if it is
isolated.

It seems there are several questions here.

What circuits do the upper and lower AC meters attach to or which is leg 1
and what is on that leg and what is on leg 2 ?

What "faulty ground connection" is being reffered to by the unlit green LED
on the upper AC meter. ?

Is there a seperate battery isolator, or solenoid, for the generator battery
up front.

Is the dimming of the house lights when the generator is started related to
this "faulty ground connection" ?

Where are all the main ground straps on a PT ?

I have a Xantrex invertor ready too install but I want to resolve these
problems first.

Any suggestions or the number of a good electric guy in SoCal would be
appreciated.
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68 Travco, 78 Argosy MH & Trailer

Last edited by HarryHansen; 02-07-2014 at 03:20 PM. Reason: Accuarcy
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  #2  
Old 02-07-2014
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gcyeaw gcyeaw is online now
Gardner
 
Join Date: Dec 2007
Location: Ridgewood
Posts: 8,799
Default

Harry,
I had burned resistors in the meter/LED circuits in the control panel on my 83 fc. Most likely you have issues with the panel rather than the coach. The ground refers to the shore line ground mainly, the generator ground is probably fine. I assume you are using 50 amp shore power or a 30 to 50 amp adapter?

What circuits do the upper and lower AC meters attach to or which is leg 1
and what is on that leg and what is on leg 2 ?

What "faulty ground connection" is being referred to by the unlit green LED
on the upper AC meter. ?

Is there a separate battery isolator, or solenoid, for the generator battery
up front.


There should be an isolator (Originally a big heat sink with a diode). I think it is in the left front outside compartment on a PT, but I an not sure. Most folks replaced it with a more modern electronic unit. There is a momentary switch on the dash of my FC labeled AUX BATTERY. It closes a relay connecting the generator and coach batteries. Mainly it is for starting the gen if the battery is weak.




Is the dimming of the house lights when the generator is started related to
this "faulty ground connection" ?


It sounds like the gen and coach batteries are tied together on your coach.
Bad grounds will cause all kinds of strange behavior, and finding them is not easy. I don't know where all the grounds are on a PT, but there are many (at least one for each DC electric component.). Start with the heavy 12 volt wiring (battery, starter, etc) checking grounds and positive connections as well. Work back to the smaller components, particularly things that seem to have issues.


Where are all the main ground straps on a PT ?

First is the main battery connections, second is the starter which should have a heavy ground strap connected to the frame or other common ground point. There are others but a PT guy might know of more locations to look.

It is important to differentiate between DC grounds and AC grounds, but all connect to the coach chassis in the end.
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  #3  
Old 02-07-2014
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OldGrandad OldGrandad is offline
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Join Date: Nov 2010
Location: Decatur, TX
Posts: 267
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Harry:

I hesitate to reply because I'm by no means an expert...but we both have 83 PT's so I thought maybe I could volunteer a few ideas. At the very least, it will bump your post to the top so the real experts can see it.

The generator battery does not have it's own isolator as far as I know on an 83. The momentary "aux battery" button that Gardner mentioned closes a solenoid which is located near the steps underneath the bus. If this solenoid failed in the triggered position, it could permanently tie your generator battery to your main batteries, causing the lights to dim when you start the generator and to discharge at the same rate.

I'm just wondering if that spring inside the solenoid would prevent it failing in the triggered position...but it's an idea at least.

I'm sure you've done a deep dive through the forum archives. There are several posts related to the "aux solenoid" which might give you some ideas.

Did you have any faulty ground conditions before your generator replacement? That issue may be as simple as a panel problem like Gardner mentioned.

From the relatively little work I've done on my bus, I find that many times when you "fix" one problem, it causes another. I'm sure the experts will come along soon to give their ideas. Wishing you the best.

Mike
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1983 PT40 (sold)
2007 Coachmen Mirada 300QB
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