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Old 02-04-2004, 03:39 PM   #1
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Question tow vehicle isolated from A/S batteries??

Hi gang!

Newbie here with a '78 Tradewind International just purchased on eBay. I'm soooo excited!!! Paid too much but, hey, we're in for a penny - in for a pound!!! This was the Arkansas 25 footer that went (to me) for $6900 for those of you who lurk in the largest flea market in the universe.

Had it inspected by local A/S dealer and had brake assemblies, bearings and shocks replaced 'cause I ain't losin' no wheels at 70 MPH!!! Lots of other things wrong but nothing that will kill me. All the rest can be fixed a bit at a time (except for the cracked black tank and 'sprinkler system' split water lines (long story but the moral is -- TEST EVERYTHING BEFORE YOU BUY!!)

However, we're good to go to sunny FLA for some needed R&R at the end of the month. The univolt isn't working so I've got an intellipower package to install. My question is - how is the tow vehicle battery isolated from the A/S batteries (in my case dual A/S batteries and single T/V battery)? Do I need to include an isolator in the A/S circuit when I install the Intell!! I see nothing in the wiring diagram of the A/S to indicate any isolation device.

We often hopscotch down the road, staying one night in each campground and will leave the T/V connected. Will use of the trailer batteries (assume off the grid) pull down the T/V battery? What if I stay a week and don't unplug the umbilical? I'm pulling with an '03 Ford F250 P/U with prewired tow package.

Thoughts - observations - experiences???

Regards,

Bob
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Old 02-04-2004, 03:47 PM   #2
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Welcome to the forum, and our collective spending spree…

To my knowledge the umbilical the isolation switch. You can charge the Tow Vehicle battery with the intelipower if plugged in, but if you have no shore power, and want to be sure you can leave, pull the umbilical…
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Old 02-04-2004, 03:56 PM   #3
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Welcome to the board, and good luck with your new toy.
Oh you are sssoooooo right about testing EVERYTHING before plunking down $$$$$

Why do you want a disconnect?? If you want a disconnect, just pull the umbellical.

The 12v from the tow vehicle will not overcharge your trailer batteries, becaust the tow vehicle 12v comes from a voltage regulated battery.
Dick
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Old 02-04-2004, 04:00 PM   #4
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Bob,

Welcome to the forum!

Your tow vehicle prewire will have a relay that cuts off the current from the T\V when the key is off. This is the standard way it is done, but you can check it with a meter to be sure. This will allow you to drain the trailer batteries without effecting (did I use it right Ken?) the under hood battery. If you are really concerned unplug the cord for the Trailer from the truck.

In some cases the added wiring done by the local shop may not be isolated like the factory stuff is. This is when you can either get into trouble or have a saving grace of being able to charge the T/V battery while plugged in.

Bit of info on batteries. If you have 2 or 3 batteries that you are planning on charging as a bank they should all be of the same type and size or group. Having different sizes and types will normally lead to one battery not getting charged and another being boiled. If you wish to be really retentive then the batteries should also be from the same manufacturer and same age, or lot number. This adds an assurance that they are matched and will work as a pair since there "should" be little or no difference between them.
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Old 02-04-2004, 07:50 PM   #5
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bob

you are correct, there is nothing in your trailer that will isolate your trailer from draining the tow vehicle battery IF you leave it plugged in.

your intellipower will charge the tow vehicle battery if you leave it plugged in when on shore power.

as brett pointed out, fords come with a relay to isolate the battery with the key off. as directed, you can verifiy this with a voltmeter at the plug on your tow vehicle. if you have no voltage on the hot lead at the plug with the key off you have no worries. otherwise you would need to add a heavy duty relay. (inexpensive)

here is how my chevy is wired 3rd batt.

john
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Old 02-05-2004, 08:07 AM   #6
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Thanks, folks! It's amazing how much info is willingly offered on this forum on just about any topic under the Airstream Sun!

The most obvious answer to my concern about draining down the truck battery was just unplug the d*** thing - DUH! Why didn't I think of that! What I was hoping was in Brett's response. I will verify but it makes sense that Ford would put a relay in the circuit to isolate the truck battery. They ARE the greatest truck manufacturer in the universe!

Of course, that prevents the intellipower from charging the truck battery but, I guess I can't have everything, right?.....or can I??? How about this, gang. Why couldn't I yank the relay and replace it with an appropriately sized diode to prevent current flow from truck to A/S but allow current flow from A/S to truck!!! I think dual motorhome batteries are set up this way. Brilliant!!! THEN I could copy John HD's 3rd battery installation. Put a 2nd battery in the Ford, wire it all up so Ford charges all 4 batts on the road (2 in truck, 2 in A/S) and have the Intell charge all 4 batts while camping. WOW! Is that cool or what! What do you think? Is this possible? Probably would toast my alternator AND toast my Intellipower. Can anybody draw a schematic to do it?

Off the subject, I have to tell you that I went through camper shock after I sold my '91 VW Westfalia campermobile after putting 225K miles on it!! Nowhere to go on the weekends! No more trips to the Keys! The master plan was to move up to a monster 5th wheel and drag on down the road to paradise but somewhere along the way, my sweetie whispered "Airstream" in my ear and we diverted from the master plan a little bit. Long story short, I lurked here long enough to get up the courage to buy that '78 Tradewind based on the wealth of info offered here. Now we're getting ready to go AIRSTREAMING!!! ( All I can picture with that word, AIRSTREAMING, is my puppy with his head out the window and his tongue flapping in the breeze - sorry! )

This forum was absolutely critical in providing detailed info on the plusses and pitfalls of purchasing a previously owned vintage Airstream. At least I knew a few of the things to look for when I inspected this trailer. I said the exact same thing when I completed the demographic poll "Was this site instrumental in you buying your Airstream?" But I felt it was worth repeating here.

Any trailer this old will have plenty of things wrong but I feel that this site has a how-to for every problem - from musty interiors to dented exteriors.

Yea, because of you guys I bought an Airstream.

Should be an interesting journey!!!
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Old 02-05-2004, 08:17 AM   #7
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I am almost certain that the factory wiring was hot all the time to T/V connector. verified with volt meter.

I know when I purchased Aftermarket tow vehicle connector for another vehicle, wiring diagram shows connector wired direct to battery with in line fuse. The load is considerable for 12 volt feed to trailer. Therefore, I assume the recommended wiring method would preclude anything other than direct to T/V battery.

Of course I am no Ford man, so I cannot comment on that.

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Old 02-05-2004, 09:39 AM   #8
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Bob,

While I can understand the desire to charge the T/V batteries with the intellicharger, I would heed my third paragraph above. The intellicharger is not going to know that the batteries are different types and I do not think changing the T/V battery to a Deep cycle is a good idea. I would say if you want a backup plan, make sure your trailer batteries have the same post configuration available as the truck. If the truck kills a battery you can always swipe one out of the trailer to get you to a new battery.
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Old 02-05-2004, 10:58 AM   #9
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Bob,

Congratulations and good luck on your great adventure. I can tell how excited you are!

A few cautions:

1. What you plan to do is very feasible, but there are not very many shortcuts or simple schematics. First, I would recommend you think through all the things you want to do in you A/S. Different use patterns require different set-ups.

2. We all want to be able to do everything and cover all contingencies when we set up an electrical system. That can get very expensive very quickly. Example: as Brett pointed out, if you run down the T/V battery, it would be simpler to borrow a trailer battery. You should never need to charge the truck battery from the intellicharger, unless you forget to unplug the umbilical.

3. There are lots of cases where someone bought off-the-shelf components and just plugged them together. While it works, their batteries only last one or two seasons because the charger/converter/isolator/wiring/switches/inverters weren't sized properly to work together as a system.

4. I think a lot of RV shops don't have any idea how to put together a well designed system.

You sound like someone not afraid to tackle a project like this. If you haven't seen this yet, here is a good site I found that explains some of the basics of 12V RV'ing. I have no connection to this guy, just found it full of useful information. I'm going through the same process you are.

12V part 1

Good luck with your project!
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Old 02-05-2004, 12:18 PM   #10
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Store bought kind

There are products on the market called Battery Isolators that are designed to isolate your tow vehicle battery from the trailer battery. I bought mine so long ago I can't remember how much I paid. The unit installs under the hood of the tow vehicle and attaches to the alternator and your 7-way plug. It is automatic, you do nothing but enjoy your trips. Just about every RV dealer I have visited has one for sale.

Rick
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Old 02-05-2004, 12:57 PM   #11
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Stor bought kind

Rick,

Exactly ther kind of off-the-shelf parts that will wreck your batteries. Those diodes will reduce your charging voltage and cause your batteries to sulfphate. OK if you want to buy new batteries every season, or get by with reduced capacity.

They have their place, and some of them have down-line voltage sensing, but most of the off the shelf isolators only serve to increase the sales of batteries.
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Old 02-05-2004, 01:16 PM   #12
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Talking dual battery wiring

Great advice from everyone. Once again, the engineering part of the brain overrides the practical part of the brain. Never occurred to me that I can just steal one of the trailer batteries!!!
I'll be thrilled if I can get the Intellipower installed without blowing up the whole rig!!! The rest of it can come some other day when I run out of things to fix (like in 10-12 years).

Thanks for the help and advice! Do dumb posts count toward my first rivet???
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Old 02-05-2004, 01:35 PM   #13
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Dumb post?

Hardy dumb post, this is one of the best threads yet! Certainly caused me to rethink some of my assumptions and design ideas.

With the sort of hop-scotching you intend to do, a cheap, single deep cycle battery and off-the-shelf isolator would work just fine. It all depends on what you intend to do. If you were a 'boon-docker' with two banks of house batteries, the solution would be a lot different (and more expensive).

I want a battery that will:
1. run my water pump when I pull over for lunch,
2. power my brakes in the event of a breakaway,
3. power my outside lights while I hook up to 120Vac at my campsite.

With those requirements, who would need more than a single battery and an isolator. I might even forgo the Intellipower!
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Old 02-05-2004, 01:50 PM   #14
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Store bought

markdoane

My experience with the isolator is satisfactory and I know why.

I am the type of guy that removes the trailer battery many times during the travel season (and certainly at the end of the season) and connect it to a trickle charger. If I get lazy and leave it in the storage lot, I will pick it up at least the day before going on a trip and charge it overnight because I want to start my adventure with a fully charged batttery.

Because I do this, the tow vehicle charging system is not over-taxed when I hook up the trailer for a trip. If I were to let the trailer battery discharge almost completely and then hook up for a trip, the tow vehicle charging system would be over-taxed (I use a stock GM alternator) and that sort of activity can ruin batteries and alternators in a jiffy.

I am going to brag now; my 31' used the same Interstate battery for 8 years. I guess I am doing the right thing.

Rick

p.s. I don't dry camp much, so that is to my battery's advantage.
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