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Electrical Discussion of preventative/corrective maintenance and other technical issues regarding your coach's electrical system.

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  #1  
Old 11-10-2010
oldmansax oldmansax is offline
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Angry Need Original 12 Volt wiring info '82 PT40

The original 12 Volt wiring has been extensively modified (butchered!) by somebody. Based on previous posts, I understand the coach system & house system were originally separated and ran in parallel around the coach. My system is no longer like that.

I need to know how the ORIGINAL main feeds were done & EXACTLY (LOCATION) where they were run.

Right now, I have a set of coach batteries that are connected directly to the starter lug. There are 2 smaller wires (maybe #6) from the starter lug to parts unknown. If I disconnect everything except the coach batteries, there is no power anywhere in the coach to anything.

The house batteries are located in the curbside compartment just ahead of the rear wheels. Hot & Ground cables (#00) are run to the curbside engine compartment. Ground is connected to frame ground through the the Heart shunt. Hot (12V main feed) is connected to a smaller (looks like #2 or #0) cable that disappears under the coach & then into the passenger sidewall. When those two wires are connected, everything works; when disconnected, everything is dead.

I know that one feed is not large enough to feed the entire 12V systems. For example, the house battery voltage runs about 13.62 Volts with the coach on shore power. The voltage inside at the main junctions is never above 13V. When I turn on one LP heater, the voltage drops to 12.1V; 2 heaters takes it to 11.6V. Voltage at batteries remain above 13V.

I have already checked every ground I can find. I also made up a 40' ground wire directly to the battery for diagnostics. There has got to be a junction (maybe more than one) where the feed from the engine compartment is reduced and branches to the smaller feeds in the coach.

I don't need to know what is connected to what. I need the LOCATION of any main feeds anyone knows about.

I already have the front overhead open, rear overhead all the way across the back of the bus open, curbside in the salon in the overhead cabinet open, and both outside front doors (where the wipers are) open.

I hate to start ripping out the interior but that would be my next step unless I can find where the main feeds are.

Marcus, if you read this, YOU MADE THE RIGHT DECISION NOT TO BUY THIS COACH!

TOM
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  #2  
Old 11-10-2010
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Ernest Ekberg Ernest Ekberg is offline
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Tom- send an email to Terry Neal. He has your twin and has done extensive work on it.---rovers@mountainrovers.com
I can take photos of my wiring, if that would help- 83PT40
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  #3  
Old 11-10-2010
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Randy Dupree Randy Dupree is offline
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When John got that coach (way back when) there was a gas generator in one of the bays,along with the Perkins in the front.
I would say that nobody would rewire the main feeds inside the bus,too much trouble!

So,i would suspect that any wiring changes done in the 12VDC system would have been done in the battery area/engine area.
Of course,this is all a guess.
I do know that John drove that coach for many years all over the country and it had to be working (somewhat).
Since your coach is an 82PT40,it may be hard to find another coach the same,yours may have been the first coach built.
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  #4  
Old 11-10-2010
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Christian Christian is offline
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Quote:
Originally Posted by oldmansax View Post
The original 12 Volt wiring has been extensively modified (butchered!) by somebody. Based on previous posts, I understand the coach system & house system were originally separated and ran in parallel around the coach. My system is no longer like that.

I hate to start ripping out the interior but that would be my next step unless I can find where the main feeds are.

Marcus, if you read this, YOU MADE THE RIGHT DECISION NOT TO BUY THIS COACH!

TOM
You know if you know where your fuse pannels are you could just disconect your bad ones from the battery and refeed/backfeed the 12v system with the proper size wiring and cap off the too small ones... they should have been fused anyway...
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Old 11-10-2010
oldmansax oldmansax is offline
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Ernie, Thanks! I'll do that.

Randy, That's good info to know. As far as John driving it, I am not sure how much of the 12V stuff he used, and, if you stay somewhere you can have shore power & the generator would work, you could probably use the coach now.......kinda. The low voltage problem is exacerbates the other problems.

Richard, the distribution panel wiring looks to be original & is fused as designed. I'm trying to find where the wiring is between the engine compartment and the various distribution panels. The wire in the engine compartment looks like a # 00. All of the distribution panels look to be #2 or #4 so somewhere between the engine compartment and the panels there has got to be a junction. I am hoping that is the problem(s).

TOM
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Old 11-10-2010
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I have a similar year ~ 83 PT - 36.

It seems like you have some high resistance somewhere. Do you have any way of measuring current in the lines? I have a current meter accessory for my DVM, which is a great troubleshooting tool. It would be nice to measure current from each battery.

When the system is loaded (fans running on furnaces) are you seeing full voltage at the starter lug? Like you are doing, I'd try to isolate where the high resistance is. The measurement at the starter lug will tell you if the resistance is between the batteries and the lug or the branches in the coach. Also, are you getting the same voltage across both sides of the relays on the circuit panels? I had one solenoid that had high internal resistance.

For reference, I have continuous duty relays and circuit panels above the rear bed in the top cabinet, above the driver's side front couch and upfront behind the driver's side front access below the window. I've also got another in the driver's mid-cabin above the dinette.
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Old 11-10-2010
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Quote:
Originally Posted by DW SD View Post
For reference, I have continuous duty relays and circuit panels above the rear bed in the top cabinet, above the driver's side front couch and upfront behind the driver's side front access below the window. I've also got another in the driver's mid-cabin above the dinette.
I know this might seem elementary to the rest of you.... I thought the 00 circuit is capable of 280 amps...safely then is distributed to say #4 good for say 100 amps say... safley if the 100 amp wire shorted out it would glow with 500 amps or more.... are you guys saying that the big wires are unprotected and the small ones are protected? No big fuses...? 200 amp?
Are you guys pulling my leg?
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Old 11-10-2010
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Quote:
Originally Posted by Christian View Post
I know this might seem elementary to the rest of you.... I thought the 00 circuit is capable of 280 amps...safely then is distributed to say #4 good for say 100 amps say... safley if the 100 amp wire shorted out it would glow with 500 amps or more.... are you guys saying that the big wires are unprotected and the small ones are protected? No big fuses...? 200 amp?
Are you guys pulling my leg?
Just curious, besides the inverter, what in your coach draws 280 amps or more than 100A from a given load center? I've turned on all the 12V lights, fans, water pump, etc. and not been able to draw 100A throughout the entire coach, at least without the inverter. I think I got up to about 70A.

I can't speak to how Tom's is wired.

Doug
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Old 11-10-2010
oldmansax oldmansax is offline
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I can see I am not explaining the situation so that it can be understood.

All of the distribution panels and all the various loads work properly. I can run a temporary feed from the house through the window to the distribution panel in the curbside front overhead cabinet & everything works with no appreciative voltage drop.

THE PROBLEM IS THE MAIN FEED BETWEEN THE HOUSE BATTERIES AND THE DISTRIBUTION PANELS.

There is only ONE #00 wire leaving the house batteries. It goes back to the engine compartment. It is connected to another #00 wire that I goes into the inside of the curbside frame rail. I have traced that wire as far as the drive axle. I can not see where it goes from there. It has to go to a junction somewhere because NONE OF THE WIRES ON ANY OF THE DISTRIBUTION PANELS ARE #00. They are all smaller.

I am assuming the wires to the distribution panels all went to a single junction originally and then the #00 wire went from that junction to the house batteries. I NEED TO KNOW WHERE THAT JUNCTION IS.

TOM
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Old 11-10-2010
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Quote:
Originally Posted by DW SD View Post
Just curious, besides the inverter, what in your coach draws 280 amps .......
I can't speak to how Tom's is wired.
Doug
Not concerned that I will draw 280 amps in normal use of my coach.... I am worried about direct shorts and chaffed wires shorted to ground... causing lots of sparks and burned wires or fire. We should be planning for a failure. Not waiting to see what will happen...when...we have one?

Unless your starting circuit is involved... things should be fused to protect all the wire from any current likely to be imposed.

For instance the events that Tom experienced with the severe voltage drop has another effect.... the more voltage drop the more HOT a wire gets... I did not calculate the heat value in watts but if something is overloaded like the #4 awg to the point of a heated wire would we not rather blow a fuse than melt a wire... I think that the wire in question is allot smaller than we think .... I bet we find a wire that has been overloaded... You should be able to run 4+ LP furnaces on a #4 wire... without significant voltage drop. Voltage drop is more significant in smaller wires...

http://www.nooutage.com/vdrop.htm


select voltage... 12V DC select cable size... ) 4 awg
These are uncoated copper copper conductor select conductor temperature... (95F) (194F) NEC tables assume C operating temperature. If conductor is oversized a lower temperature can be used but this temperature should always be higher than ambient. This value only used for adjusting conductor resistance.
select conduit type... no conduit
select parallel runs... single set of conductors
Length of cable in feet (one-way distance) 15 feet

Load current in amperes 30 amps



Estimated voltage drop

2% of 12 volts is only .24 volts unless Toms heaters are HUGE something is amiss.... Lets change the wire size to #10 and see if that puts Toms numbers closer to the facts....




select cable size... 10 awg (30/25A) These are uncoated copper or aluminum conductor sizes with CU/AL 60C Ampacity listed at 30C ambient for reference.

select conductor type... copper conductor

Length of cable in feet (one-way distance)


Load current in amperes 30amp


Estimated voltage drop

This is still only 1 volt of drop lots try a smaller wire.....


select cable size... 14 awg (15/--A)


Length of cable in feet (one-way distance)15




Load current in amperes 30

Estimated voltage drop



2.4 volts



based on the calculations it looks like your squeezing 30+ amps through a #12 wire or you have 150 feet of #4 one way....


better find that sucker it is hot...or less amps through a smaller wire... or more amps through a little bigger wire
something is dissipating 60 watts of heat..... imagine how hot a 60 watt bulb gets and multiply by 10 the filament is much hotter than the glass envelope...
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Last edited by Christian; 11-10-2010 at 05:39 PM.
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