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Old 04-06-2003, 10:00 PM   #1
 
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Question How to wire truck to charge TT battery?

We will pull our 32' Excella with an International 4700 series. Currently the system is not wired to charge the trailer's batteries. Can anyone describe how I would construct the necessary circuit? The trailer itself is wired, it's the wiring from the truck's charging system back to the umbilical (about 25 feet) I'm concerned about.
The truck has a bank of three batteries onboard, the trailer has two of its own. Should I be concerned about the size of the alternator?

Additionally, for extended use, it might make sense to isolate one or two of the trucks batteries for use by the trailer. How tricky would it be to make that happen?

Thanks in advance for any help offered.
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Old 04-06-2003, 10:28 PM   #2
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i'll look

chantal and mike

i'll look at the fuse block on my 4700 at work.

unless you post a pic before tuesday.

the charging system on that truck is pretty robust. should handle the additional batteries.

you may not want to use your starting batteries for trailer feed while off shore power. some of our internationals have one or two batteries and need all of that to start the 466.

you might get away with setting up a disconnect for one of the three.

i do know those trucks don't jump start well. and they really are hard to pull start if they are stone cold dead.

off the top of my noggin i'd say you will need 10 or 8 gauge wire for the feed to your trailer plug.

possibly even larger if you want to keep voltage drop to a minimum.

you will find it nice to arrive with a fully charged battery when you get to your destination.

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Old 04-06-2003, 10:31 PM   #3
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Based on the fact that you have multiple batteries I would suggect a battery Isolator.

The output of the Alternator is fed into the isolator, the Isolator has 2 outputs, 1 to the truck batteries and 1 to the trailer. This is how it is done in the Motorhomes. The Isolator needs to be sized for the Amperage output of the Alternator, and it will support the diffrent size/tpye of battery banks that you have. It will adjust to charge them as necessary.

It also will not allow the trailer to drain the truck batteries if you leave the pigtail connected.
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Old 04-07-2003, 12:48 AM   #4
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Tow vehicle to trailer wiring

Decisions, decisions. As is required, a plan is needed. Getting voltage from truck to trailer is not a tough task. Some cautions are required. An easy way to get power from the truck is to use a few cube relays. I wire the relays to be energized with the truck key. The relays normally used are the boshe cube type that are used in the over the road trucks and are rated continous duty. I use 2 relays rated at 40 amps each and wire in parallel. Each relay has mostly 5
1/4inch , push on posts. One post will not be used. Two posts are for the coil and will be connected to a quality ground and also to any ignition feed from switch.
Two other posts will be connected to a fused battery power source. The fuse can be a 30 or 50 amp fuse or circuit breaker. An auto reset circuit breaker should NOT be used for this task. Two relays are wire the same so to share the load, with great longivity. I'm not a big fan of isolaters for a couple reasons. This method keeping trailer batteries fully charged will not make any draw on truck batteries. However if some power is to be used from truck battteries, a switch can be used to operate the relays. Of course there are cautions. A multimeter should be a very required tools for checking battery conditions. A rfully charger battery will indicate 12.6 volts on a digital meter. A battery that is 75% discharged will indicate 12.0 volts. Most batteries can only with stand about 8-12 deep voltage drawdowns. The special rv batterys deal with draw down better..
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Old 04-07-2003, 07:34 AM   #5
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Excellent Post, Frank

The reason battery isolators are not the preferred method, is because they use diodes for isolation. You will have a .6-.8 voltage drop through the isolator.
The reason for not using the auto-reset circuit breaker, is if you have a problem, (short) the breaker will keep resetting and eventually run the battery down. Could also allow wiring or components to heat up, possibly causing a fire.
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Old 04-07-2003, 10:12 AM   #6
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Agree with the relay method vs the diodes. In fact, that's what Ford gave me from the factory. When the key is in the "Run" position (not Off, Start, or Acc) a relay is energized and sends current back to the trailer plug. It gets its current from a fuse.

They only use a 20A fuse, 20A relay, and 12 gauge wiring going back to the trailer, which limits charging. I haven't checked the wire gauge going to the Airstream pigtail, but it wouldn't surprise me if it's no larger than 12 gauge, so there would be no point in upgrading the truck. I'm also not sure what the pins on the truck and trailer connector are rated at.

I have measured the voltage on the charge pin of the truck connector, and it's 14.2 volts with the engine running. That's a little below the 14.4V "boost" mode of the Inteli-Power. Using a diode setup would cut that voltage to the trailer, as well as the voltage to the truck batteries, down to at least 13.6V.
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Old 04-07-2003, 02:11 PM   #7
 
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John HD,
Quote:
you will find it nice to arrive with a fully charged battery when you get to your destination.
We managed to get away without it for over 10 years!!! Always tomorrow. The problem is the 1990 trailer is going to be a real power hog compare to our 1970's. Even after we cut down lights as much as possible.

Of course you are right about using the 3rd battery only. We kind of misspoke here. (one brain, 4 hands).
Our original idea when we had the 3rd battery added, was not to use the 2 starting batteries when using the lift gate (that we of course have to use a lot with engine shut off).
We goofed big time when we had the dealer install that battery. We were not thinking very straight (in a rush like usual), but they should have suggested the separate use of the batteries. We learned about that later from another dealer. One reason we are not in a rush to ask their opinion, plus the fact that they charged us $500 to install 2 batteries wrong, take them out, try to find out what they did wrong, redo everything.

It was raining heavily earlier but we managed to get some pix.

Thanks a lot.


thenewkid64 , Pick, Maurice and FrankR

I posted this same question on the RV forum too, and somebody suggested we read a thread about Isolators. I will have Mike look into that, and the various rebutals here.

Thanks



As mentioned, we posted this question all over the place, and I am happy to say that the Airstream Forum has for now been the most lively and helpful.

We could use your opinion on an answer we received and are not competent enough to judge:

"Buy a contactor which looks like the old starter solenoid at an auto parts. It's basically a relay. Get one rated at about a hundred amps and for continious duty. The coil voltage comes from the ignition 12 volt so it energizes when the key is on. Connect the contactor in series to the trailer bats. The problem you can have if you don't limit current is overheating the wire back to the trailer.... Test it with low trailer bats and if the wire gets more than slightly warm you may have to lengthen the wire some to get some limiting."

Any idea about that ?

Thanks again.
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Old 04-07-2003, 02:42 PM   #8
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New wiring for trailer batteries

Alas alas, I thot my wiring info was complete.
A device called a contactor is a switch that is used with ac voltages.
There is a wide variety of relays. Many relays are NOT for 100% duty cycle, as the relay becomes hot and self destructs. A starter solenoid/relay is a very short time use relay.
There is a difference between opinions and quality technical information.
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Old 04-07-2003, 03:05 PM   #9
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the other box?

mike and chantal

can you get a photo of the box that resides next to the drivers air seat with all the terminals and led's on it?

also, does your truck have the over head console with the switches for accessories?

i kinda got an idea on how you could configure the wiring depending on the above.

john
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Old 04-07-2003, 03:29 PM   #10
 
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Quote:
over head console with the switches for accessories?
NO.

NOW: the other box????? We do not see another box.

If it is as big as the first one, we shouldn't be able to miss it. (Mike has lost his glasses again !!)
Left side of the base of the air seat is a small label (says something like "do not swallow" or "wear goggle", I forgot)

We have the book somewhere, I will look for that box.

Thanks
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Old 04-07-2003, 03:46 PM   #11
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"Test it with low trailer bats and if the wire gets more than slightly warm you may have to lengthen the wire some to get some limiting."

This is known as "the smoke test." I am not a proponent of it.

Fuse the wire (for example 20A) BELOW the ampacity of the wire gauge (i.e. 25A for 12AWG) and blow fuses rather than overheat the wire when testing.
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Old 04-07-2003, 04:30 PM   #12
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While I agree with both Frank and Maurice on the issue of loss across an isolator, there are some benifits.

No moving parts, no remebering to flip the switch to charge, no relays to find/replace in the dark in route. There is also the benifit of charging the diffrent types of battery banks at the rate they will absorb. If you have all of the batteries on a common charge line (electrically) the Alternator will run at the amperage that is necessatied by the load of lights, fans, and charging the batteries. If this is at night the AMP output of the Alternator may be higher that the batteries can absorb, possibly boiling the batteries, if the trailer batteries are fully charged.

I would rather charge to a float level while driving and have my Magnetk/univolt/charge wizard finish the job if necessary. Will this shorten the life of the deep cycles? I don't know. My experience is abuse, neglect and lack of use is really what kills them the fastest.

The above advice is worth less that what you paid for it!
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Old 04-07-2003, 04:47 PM   #13
 
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The above advice is worth less that what you paid for it!
I take this advice anytime over the NO advice for $$$$ that we got from our dealer.

Thanks, and in the meantime, please feel free to argue all of this between yourselves.

We are listening, and waiting for the punch line.
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Old 04-08-2003, 04:11 PM   #14
 
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Hi Frank,

>> Decisions, decisions...

Tell me about it.

I'll check out the Bosche Cube Relays. Our cars use them, by the way, but I don't think any of them are as highly rated.

>> I use 2 relays rated at 40 amps each and wires in parallel.

Is that one per battery? Or one each positive and negative?

I understood the other wiring detail well enough, thanks.

>> An auto reset circuit breaker should NOT be used for this task.

I understand that an Auto Reset breaker can cause problems by repetedly reseting a shorted circuit.

>> A multimeter should be a very required tools ...

I'm looking into an upgrade of mine. We're getting serious, here.

>> A battery that is 75% discharged will indicate 12.0 volts.

Yep. I have a couple of charts with battery charge details. A also have a decent Hydrometer.

>> The special RV batterys deal with draw down better..

I'll be patching one of my three truck batteries into the trailers Deep Cycle battery system. I hope that doesn't add to my list of problems.

Thanks
Mike


Hi Maurice,

Thanks for your comments re: relay method vs the diodes.

I don't know how completely standardized 7-way RV connector cords are, but here's what I have:

Terminal Function color guage
1 Ground white 10
2 Brakes blue 12
3 Running Lights green 14
4 Battery black 10
5 Lft Stop/turn red 14
6 Rt Stop/turn brown 14
7 Auxiliary yellow 14

I couldn't find Amperage ratings for the pins of the 7-way connector, though they list them for 4 and 5-way connectors.

>> it wouldn't surprise me if it's no larger than 12 gauge,
>> so there would be no point in upgrading the truck.

The only point would be to minimize voltage losses over the length of the run. It's all about subraction - the less you subtract the more you have in the end. You could probably scale the wire in consideration of the bottle-neck effect at the connector and pigtail.

>> Using a diode setup would cut that voltage to the trailer,
>> as well as the voltage to the truck batteries, down to at least 13.6V.

That's discouraging.

Thanks
Mike


John,

>> can you get a photo of the box that resides next to the
>> drivers air seat with all the terminals and led's on it?

I suppose that you mean "LEDs"? We couldn't find any thing that fits that description. Essentially there's nothing near or around the driver's seat. Maybe it's somewhere else, like under the hood ?

What's the function of this box?

>> does your truck have the over head console with the switches for accessories?

Nope. We have a molded plastic gizzmo that serves as an overhead junk bin and CB radio surround. We also have a 3-way overhead cab light module. Nothing very complicated.
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