12 volt wiring diagram - Fiberglass RV


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Old 07-21-2007, 10:46 PM   #1
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I have to admit I am not too electrically inclined.

After a couple of months of reading and searching I think I finally figured out what I have to do to get all the 12 volt systems wired. I don't know too much about Volts, Watts, or Amps, nor do I know what all them fancy electrical symbols mean, but I do under stand the ones for positve, negative and ground. The attached diagram deals with only the 12 volt power system, and not the electric brakes or various trailer signal or marker lights.

For simplicity, I left the two parts of the "trailer plug" connection as one box in the diagram. Likewise I left all the different circuits in the trailer coming off my fuse box (lights, fridge, fans, etc.) as one box labelled "Load"

So does this look right? If not what needs to be fixed? Any other suggestions?


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Old 07-21-2007, 10:59 PM   #2
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You still need a 30 amp. auto re-set circuit breaker on your charging circuit, and the one on the brake circuit should be a 20 amp. auto re-set breaker.
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Old 07-22-2007, 01:24 AM   #3
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Quote:
You still need a 30 amp. auto re-set circuit breaker on your charging circuit
Thank you for the quick reply Con,

Would that "auto re-set circuit breaker" be in addition to the box I've labelled as "circuit breaker" between the isolator or solenoid and the trailer plug? If so where would it go? Or do I have my circuit breaker in the wrong position within the charging system?

And, thank you for providing the info on circuit breaker sizes ... that is something I've been wondering about and was going to ask after getting the basics down.

The brakes are a long way away, that is going to require an axle change first. We've just spent a fortune on getting all of the propane lines replaced and the appliances inspected and serviced. All we need now is a little more sheet metal work and both the furnace and fridge will be considered fully functional and safe to use. I now understand why it has taken many about 5 years to fully restore one of these trailers. If it weren't for Donna D.'s wise words of wisdom before my buying this wreck ... "Consider it a hard tent on wheels" until you are finished ... I'd be by now.
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Old 07-22-2007, 05:38 AM   #4
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Roy,

Excellent diagram.

One change I'd recommend is to relabel what you are calling ground. That's actually the 12VDC return and it's all wiring in both the tow and the trailer. For clarity, I'd recommend calling it the return.

Modern automobiles and other vehicles use a return wire rather than using chassis ground as a return. Electrically, there is no difference, but using chassis ground as a return is less reliable.

In a fiberglass trailer, the only conductive chassis part is the frame. That should NOT be used as part of a circuit.

For safety reasons, the 12VDC return should be connected to the trailer frame at one point. That grounds the trailer frame so that it is at the same potential as the 12VDC return.

The 30 amp breaker Con suggested is on the positive line to the trailer battery. You show an in-line fuse there, the breaker would replace that fuse. I personally would not use an autoreset breaker there; if that fuse blows, you want to fix the problem (probably a short circuit) before replacing the fuse. An autoreset breaker would just keep trying to reapply power to the short circuit periodically.
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Old 07-22-2007, 01:10 PM   #5
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Quote:
Would that "auto re-set circuit breaker" be in addition to the box I've labelled as "circuit breaker" between the isolator or solenoid and the trailer plug?
I'm not sure if Con just missed that one in the diagram, because it is the vehicle-side breaker that I would expect. Mine is an auto-reset breaker; it could be a fuse or manually reset breaker, but I wanted to ensure on long drives that if the power supply was automatically restored if momentarily interrupted by excessive charging current, to ensure the refrigerator could keep cooling.

An even better idea in my opinion would be a breaker which I could reset from the driver's seat, and for which there would be a warning light when it popped. No, this isn't something I've ever seen for sale... so I don't have one.

The fuse at the trailer battery can be really large, so it would not blow due to overloads on individual load circuits (their own fuses in the panel would go first) and thus it doesn't need to be a breaker, let alone an auto-reset breaker. The factory wiring of my Boler has no fuse in this position at all, but I think it would be a good idea.
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Old 07-22-2007, 03:37 PM   #6
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Quote:
The fuse at the trailer battery can be really large, so it would not blow due to overloads on individual load circuits (their own fuses in the panel would go first) and thus it doesn't need to be a breaker, let alone an auto-reset breaker. The factory wiring of my Boler has no fuse in this position at all, but I think it would be a good idea.
I replaced the factory 30A glass fuse on my trailer battery with an auto-reset circuit breaker (I also have one on the truck battery, so now I have the potential for dueling breakers ). Like you said, that fuse can be large because the individual circuits have their own fuses. I like the circuit breaker because I won't know the fuse is blown until the battery is almost dead...

However, that fuse/breaker also protects the wires between the egg battery and the TV connector in the cable; I would purely hate it if my battery charge wire AND/OR my white negative/return/ground wire were damaged by a dead short at the connector end (Say a stray vehicle crushed it on the ground I'd rather replace just the connector than the whole cable! I know I could come up with some more scenarios where the wires could be damaged by the egg battery).
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Old 07-22-2007, 05:57 PM   #7
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I think I would be tempted to go with Morgan's suggestion of not useing an auto reset. I understand the fridge problem but if you had a bad short as mentioned by Peter you would have full potential of the TV feeding it every time the breaker cut back in. Could be a potential problem. I have a regular fuse and will deal with the fridge if it happens. I have travelled long days with my motorhome and never had any problems with the fridge not running as long as I got it on when I stopped and opened it as little as possible during the day. Travelled about 7000 km's last winter and never turned it on on the road and never lost any food.
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Old 07-22-2007, 07:34 PM   #8
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This is a multiple reply:

Morgan;
The diagram is being reworked to cover everyones suggestions. I'll post it in a day or so once I've possibly heard from those still fortunate enough to be still camping and might have more suggestions.

Good suggestion on the return wire for the TV, (I purchased mine before initially posting).
As for the 12V DC being grounded to the trailer frame, that raises a question for me. Having done some recent work on the 120 V side of the wiring I noticed the main breaker box was grounded to the frame as well. I was thinking of making the single 120V circuit GFI protected. So what happens if I have a problem with the 12V side sending some electrons to the frame ... will the GFI trip such that I lose my 120 as well? If so, that might make me want to leave at least one light on the circuit before the GFI. I'd hate to lose all my lights at once.

Brian, Pete and Neil all addressed the Auto-Reset breakers. Yet when I look here on the web, I see that there are 3 types of circuit breakers that can be used in an inline ATC type housing:

ATC Fuse Style Type 1 Auto Reset
These single pole thermal circuit breakers are designed as replacements for ATC or ATO style fuses. Type 1 auto reset will cycle the circuit breaker until the overload condition is removed.

ATC Fuse Style Type 2 Modified Reset
These single pole thermal circuit breakers are designed as replacements for ATC or ATO style fuses. Type 2 modified reset will keep the circuit breaker open until the overload condition is removed.

ATC Fuse Style Type 3 Manual Reset
These single pole thermal circuit breakers are designed as replacements for ATC or ATO style fuses. Type 3 manual reset will keep the circuit breaker open until you manually reset it.

It appears from the BUSSMANN that the Type 1 and 2 are available for the MaxiFuse size blade as well.

From what I see consensus is that the Type 1 auto-reset is best kept for the brakes, and either Type 2 or 3 be used for the 12V "power" coming from the Tow Vehicle.

To me the Type 2 seems like the most logical choice, since if the problem was temporary, you would get your power back. Then again the Type 3 seems to be the safest electrically allowing one's fridge to become a cooler and a trailers battery to be affected.

I'd be interested in hearing what everyone thinks about using either the type 2 or 3 breaker. Is there consensus that 30A is the right protection for the TV power to the trailer? What do you recommend for the trailer battery?

Roy
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Old 07-23-2007, 03:02 PM   #9
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Here's a fixed link for the circuit breaker type description; I know the original link is the one provided by Google, but it does not seem to work consistently.

It is not obvious to me how a "modified reset" breaker works: how does it "know" that the overload condition has been removed? Does it all a small current flow until the observed load impedance is high enough? Anyway, it does sound more suitable to me for the charge circuit and trailer battery than a type 1 autoreset; I guess I should change mine.

The capacity for the charge circuit breaker in my setup is based on the wire gauge of that circuit. I would have to look at some old notes or under the hood of the van to be sure whether I used 20A or 30A with my 10 ga wiring. The 7-conductor cable attached to the trailer connector is 10 ga, and since it would be surprising to find commercially assembled cable with any heavier charge or return wires, 30A seems to me to be the safe upper limit.
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Old 07-23-2007, 04:10 PM   #10
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Quote:
The capacity for the charge circuit breaker in my setup is based on the wire gauge of that circuit. I would have to look at some old notes or under the hood of the van to be sure whether I used 20A or 30A with my 10 ga wiring. The 7-conductor cable attached to the trailer connector is 10 ga, and since it would be surprising to find commercially assembled cable with any heavier charge or return wires, 30A seems to me to be the safe upper limit.
Even though my modified "commercial trailer connector" (see below) is 10 ga like yours, I am running 8 ga as much as possible as close as possible from each battery. I've estimated approximately 40 feet return from the front of my truck to the trailer plug and back, as well as 10 feet return from my trailers fuse panel to the trailer battery. Between that there is a maximum of 10 feet return in the trailer harness between the fuse panel and my trailer plug.

Correct me if I am wrong, but from what I've read I will have less resistance and less voltage drop using 50 feet of 8 ga along with 10 feet of 10 ga over using a straight 60 feet return of 10 ga. alone. And possibly less heat as well.

I suppose if I was a real fanatic about this, I could replace 9 of the 10 feet of 10 ga in my harness with 8 ga as well.
Oddly my Boler American has a 7 pin round male in the front of the trailer wall while my truck has a 7 pin blade. This may sound weird but the harness between the two that came with the trailer has the two different ends spliced together. When I park my trailer, I pull the cable ends from both the truck and the trailer making it a little more difficult to steal and less likely to get damaged. Plus I can easily make a 4 flat to 7 round connector to swap it with ~ if someone wants to use my trailer without the right plug on their vehicle.


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Old 07-23-2007, 06:27 PM   #11
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Roy, I agree that the increase in wire gauge helps total resistance and thus total voltage loss. The larger-gauge wire sections will run cooler (and waste less power), but the heat generated by resistance per foot of the 10 ga wire will still be just as much - for the same current - as if the whole circuit were that gauge.

The capacity of the circuit to handle current is still limited by the least capable component in the series connection, just as a chain is only as strong as its weakest link. The connector with 7 round pins is likely a typical commercial truck unit - they are not intended for charging current and I think you'll find that those contacts are not intended for 30 amps, while the blades of the 7-way RV/Bargman connector are.
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Old 07-23-2007, 09:44 PM   #12
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The connector with 7 round pins is likely a typical commercial truck unit - they are not intended for charging current and I think you'll find that those contacts are not intended for 30 amps, while the blades of the 7-way RV/Bargman connector are.
Yikes!

Thought I'd look into that and change the female on my trailer and then run 8 ga right through the connecting wire between the TV and trailer. Ace Harware has some specs for the Hoppy 7 Pin RV Kit # 48465 which states "6-12 volt, 8 amp max".

Yet the Hoppy site instructions for Part # 48495 indicates 20 Amp.

Both of which are well below the 30 Amps on the charging circuit everyone is talking about here.

So have we all been misled, or am I missing something?
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Old 07-23-2007, 11:26 PM   #13
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Try www.wiringproducts.com Go to trailer wiring, their 7 pin connectors both male and female are good for 40 amps. the prices run from $13.15us to $15.35us each. These would easily handle 30 amps and I'm sure there are many more out there.
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Old 07-24-2007, 11:19 AM   #14
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Try www.wiringproducts.com Go to trailer wiring, their 7 pin connectors both male and female are good for 40 amps...
Neil, if you mean the Wiring Products Seven Pole Trailer Connectors, these are the flat-blade RV style, which do have suitable current capacity. The round-pin connectors are different (both styles have round bodies) and my understanding is that Roy has a round-pin connector on the trailer.

I'm not sure why Hoppy specifies only 20A, and my guess is that the Ace Hardware site is just wrong.
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