battery isolator questions for a trailer

Discussion in 'Trailer Tech' started by wompser, Sep 28, 2009.

  1. wompser

    wompser

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    hello! I’ve been lurking on this forum since I discovered it a few weeks ago, welcome to my first post!

    I’m in the middle of a fairly mild m416 build, and see the collective wisdom of those who've gone down this path before me. I'm building a m416 which will have very modest electrical needs, but I want it to be a couple of things: simple, universal, and expandable. it will have it's own deep cycle 12v battery, and now I’m just trying to figure out the best way to wire it in.

    I've installed a dual battery setup in a camping van before, so I went over to napa and picked up napa part #782-1768, which is a battery isolator suitable for my jeep wranglers 120 amp alternator.

    I had thought it would be as simple as installing this isolator in the trailer and running a heavy gauge 12v wire to the isolator, but after reading the directions, I’m not so sure this is the case. according to the diagram, the installation requires you to install the isolator in between your vehicle's starter. this would mean that the isolator needs to go in your engine compartment, not your trailer. (see diagram)

    [​IMG]


    I want to keep this project simple and universal, my thought was that if I do a standard wiring job with a 7 connector plug to the trailer, any* tow rig should be able to top off the battery as it's being towed. I will run this through pin 4 of the 7 pin connector. (that appears to be what this pin is for anyway!)

    so, what am I missing here, am I over thinking this? do I even need a battery isolator, or should I simply wire the battery directly in, and disconnect the trailer's plug when stopped so I don't run down the main vehicle battery? (the vehicle's battery and the trailer battery will be different types though, so this is a no-no, right?) do I just need a diode so that current flows only TO the trailer, and assume that the accessories on the trailer will be the only discharge for the trailer's battery? after all, I don't really need 2 batteries at once as in a dual battery vehicle setup. 12v solonoid connected to an ignition line? thermal fuses? I’m sure many people have solved this problem, but I couldn't seem to find an answer by searching "isolator" in the forums.


    one other question, what gauge wire do I need to run TO the 7pin connector? I assume charging a dead trailer battery from a vehicle will require a fairly healthy wire, but also suppose that it will only be as thick as the pigtail on the 7pin connector (at least for a couple of inches anyway)


    as a teaser, I'll be posting a full build soon... here's a couple of picts to whet your appetite!

    as purchased (a few years ago)
    [​IMG]
    [​IMG]

    a new jeep, but dosen't it look lonely without a trailer?
    [​IMG]
    [​IMG]
    [​IMG]

    * it will really only be towed behind my jeep (sorry!) but I want to make it as universal as possible, i.e. no custom wiring schematics
     
    Last edited: Sep 29, 2009
  2. Hugh Heifer

    Hugh Heifer In Tenneginia!

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    First I would like to say the trailer looks great.

    Second, I am going to follow the advice given you here because I want to do the same thing. I think there have been some discussions regarding this before. Based on what I learned, it would seem an isolator is the way to go and many also recommend a switch on your dash to turn off the charging of the trailer battery (or any second battery) at your desire.

    I do not think I have notice the connection to the started like that before, but again, I am learning as I go. On the dual battery set up you previously installed, did you make such a connection? I am sure someone here knows what that is for. My guess is that wiring it to the starter either draws current from both for starts or from a selected battery only. I for sure could be wrong.

    And don't feel bad about having a Heep - there are a feww trailer guys here that have them. They have been making up for it by building sweet trailers

    Welcome to Mud :flipoff2:
     
  3. wompser

    wompser

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    the trailer was quite a rust bucket originally, but some sandblasting has done an amazing job of restoring the shine! (more about that in a thread soon!)

    anyway, to answer your question, on the previous isolator installation, i simply followed the directions. I have not opened the hood on my jeep to see if the diagram above is the one I need or not, it seems this may be a litttle more complicated if I have an externally regulated alternator.

    as I sit here thinking about this, it seems to me that a solonoid and a big diode might be the solution: when the vehicle is on (with the accessory line getting power) the solonoid would close, completing the circuit, and charging the aux battery. when the vehicle is off, the solonoid would be open, therefore disconnected from the vehicle, and completely independant. this seems so simple i must be missing something... there must be someone out there more knowledgeable than me on this!
     
  4. wompser

    wompser

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    no one has any comments on this? please help, I'm stuck! I've realized that a simple solonoid won't likely work, because I think you're supposed to use and isolator if you have two different types of batteries. but how do you wire it in?
     
  5. REZARF

    REZARF

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    To give you the short answer, yes you can just run a FAT, read 4ga or bigger wire straight off the alternator to the trialer batteries. You will need a quick disconnect similar to a warn winch setup. If you run anything smaller you will start to tax the whole system. If you run a large gauge wire to the rear it will recharge as fast as your primary batter. I think your isolator is a good idea if you are prone to forget to disconnect your aux batter.

    Otherwise, these are pretty simple setups if you are not power hungry while camping.

    Great looking trailer by the way, I can't wait to see your build up.

    Drew
     
  6. wompser

    wompser

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    hmmmm... well thanks for the advice, but it does not quite fully answer my question. I'd really like to keep all the wires running through the 7pin connector. I definitely understand what you've said above though, a fat wire to the wimpy 7pin connector does not sound like a good idea.

    so there must be a way to lower the amperage before it gets to the wire leading to the trailer? I don't really need it to charge fast, I just need it to charge. there must be millions of small trailers that have a battery in them, and there must be a standard way this is done! ive found some information on battery operated breakaway brake batteries, but these don't seem heavy duty enough for my needs. (the batteries are smaller, like golf cart batteries.
     
  7. CO_Hunter

    CO_Hunter

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    A thread on the Tundra forum discusses charging from a tow vehicle. Here is part of a post that I think gets to your question.

    "The point made about connecting the 12v hot wire to the battery with a fuse, and in such a way to be only energized only when igintion is on, is a good tip. This is exactly what I did. I just got a 30amp relay, connected to my accessory circuit to activate the relay, an auto-reset 20a breaker at the connection to the pos batt lead, so this only makes the connection to the trailer battery hot only when engine is running. If you leave the whole rig hooked up, say overnight, this prevents the trailer batt from dragging your truck batt down." The whole thread is at:

    Trailer Battery Charging - Tundra Solutions Forum

    Another option I read about was using something like this for running a heavy gauge wire connection (LC battery connectors).

    http://meltric.dirxion.com/WebProject.asp?BookCode=mel09flx&SectionIndex=0&PageIndex=171#

    From what I understand how you go depends on how discharged your batteries become and if you are running anything off that trailer battery while your towing, like a fridge.

    HTH
     
  8. REZARF

    REZARF

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    Sure you could use the center pin on a standard 7 pin connector. It takes a 10ga wire, your recharges will take a bit longer but other than unplugging the trialer when you are using the aux battery, nothing else would be needed.
     
  9. marcovgv

    marcovgv

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    what brand tongue box is that .. I really like it
     
  10. wompser

    wompser

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    the box was made by brunner's fabrication of jopin MO. I found their website once, but can't seem to locate it now... I bought this box (heavily) used at a garage sale for FIVE BUCKS, but new, I think they're over $400!

    as for the battery isolator question, I think i'm going to mount the isolator under the hood and run the 12+v to the center pin of the 7pin connector with a fairly heavy gauge wire. going to my local RV place today to talk through this plan though.
     
  11. wompser

    wompser

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    so, i've done a lot of searching around on this topic, and spoke with a LOT of different "experts."

    seems there's a couple of different ways to do this, however the isolator I bought is going back to NAPA, because I've found a much better solution. take a look at this, from hellroaring technologies. Hellroaring Battery Isolator/Combiner notes for Multi-Battery isolation in RV/Camper/Trailer Applications

    after discussing it in a fair amount of detail with the guys at hellroaring, i've opted to go with a vehicle mounted option. it's not cheap (twice the cost of my NAPA isolator!) but it seems to be the most bulletproof solution.

    I'm also going with an optima yellow top battery setup.

    more details once I get it installed.
     
  12. rohitash

    rohitash SILVER Star

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    wompser,

    I researched this quite a bit for my trailer build and I came to the same conclusion as you and went with the Hellroaring BIC-75150B isolator. I've used their 75300B isolator in my Land Cruiser for a dual battery setup and it is bulletproof and works very well. i did however want to put this into the trailer and not the tow rig, so that I had isolation in any rig, so i discussed with the Hellroaring guys and came up with this:

    The main reason they recommend having the isolator mounted closer to the alternator and the main battery is voltage drop across a long wire. The isolator relies in some of its function on the actual voltage it sees to connect or disconnect. In short when it see the higher voltage put out from an alternator it connects the aux/trailer battery so it can charge, but when the alternator switches off and the voltage drops to a certain level then it disconnects the aux/trailer battery. Having it in the trailer with a long wire running to it causes a voltage drop so it it may cause the isolator to 'cycle' as the alternator voltage it sees is lower than what it would be if the isolator was closer to the alternator.

    I'm getting around this by having a large gauge wire running to the back of the truck to the trailer connector (I have about 14ft of 1/0 gauge which I had already put in for another purpose). There is very little voltage drop on this till where it connects to the trailer connector. From there I have about 8ft of 8G wire running from the trailer connector to the isolator in the trailer. I believe my 1/0G wire is an overkill for this app, but I already had it in place. I believe you could do this with 4G or bigger wire from the engine bay till the trailer connector and an 8/10G from there in the trailer itself.

    Some advantages of this setup:
    - I can have the trailer loads (fridge) running from the rig power when towing in addition to having the battery charged.
    - The isolator has the option for a remote switch which can manually combine the batteries. This can be used in multiple ways, running the rig loads (eg my ham radio) of the trailer battery if the rig's main battery is down. In an emergency you could combine it and leave it for some time to put some charge into the main battery to start the rig if the main battery was down. for me this is a third level of redundancy as I do have a second isolated battery in the rig itself. Point is that the isolator in this setup is extremely flexible.

    I have a detailed drawing of my trailer electric setup (planned) - shoot me an email if you want me to send it across. I've been meaning to start my own trailer thread and put all this stuff there - need to get around to it!

    One important point, protect both ends of the circuit with fuses or circuit breakers. I use a 60Amp circuit breaker near the rig battery on one end of the fat cable and another 40Amp circuit breaker near the trailer battery (on the trailer end of the isolater)

    Rohitash
     
  13. wompser

    wompser

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    that's very good information, thanks! you summarized my conversation with hellroaring much better than I could: I discussed the same thing with them saturday. I'd love to see your detailed drawing.

    I will also be running heavy wire for the same reason, but still havent' decided 100% if the isolator going to be trailer mounted or jeep mounted. I like the thought of any vehicle being able to tow this thing and charge the trailer, but really "any vehicle" that tows it will need a heavy gauge wire running to the connector. leaning towards having a jeep mounted isolator.

    my other thought is around the 7pin connector, which has suddenly become the bottleneck. I don't want to abandon the 7pin and go with some other non-standard connector. i've thought about it, but I want this trailer to be as universal as possible. I've mostly resoved myself to the idea that I'll need to have the regular 7 wire (bundled) and an additional 8 gauge wire running from the 7pin connector to the trailer. it won't look very clean to have 2 wires coming out of the trailer side of the 7pin connector, but I can't really figure out a better option.

    the least "thick" part of the wiring will now be at the connector itself. I hope that's not a big problem, don't want to melt my connectors if too much amperage goes through there.

    and the hellroaring guys recommended circuit breakers to me as well. I'll definitely get those in there.
     
  14. rohitash

    rohitash SILVER Star

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    On other tow rigs: Having the isolator in the trailer gives some flexibility. If the other rig has too much of a voltage drop and the isolator starts cycling, then you have the option of manually combining the isolator (which is equivalent of not having an isolator at all, or manually disconnecting it - all with the flick of the switch. If the voltage drop is within bounds, then the isolator will function normally (ie automatically). I see no downside in this setup if your primary rig has a fat cable.

    On the 7 way connector: I looked at some of them. Most come with pigtails and I believe the wire on the pigtail is what is really the bottleneck. However you can get 7 pin connectors with no wire and screw terminals to put in your own wires. from my visual inspection of the terminals - they seem capable of taking 50-60 amps. The terminals can accept upto 8G wires. My 1/0 cable definitely will not fit them so what i plan to do is make a short (6-8") 8G pigtail and splice that to the fat cable. On the trailer side I then run 8G wire to the connector to the isolator. 8G should be more than enough to carry 40-50 amps which is more than what I plan on doing. with the right circuit breakers on both ends, its a safe circuit. The intent of the fat cable is to prevent voltage drop and not to carry really large currents. My initial concern was with how the contacts on the flat 7 way connectors mate and whether they will be good enough to transfer the 40-50amp max current I anticipate. However from observation, the flat pins slide onto each other, which is good as it increases the contact area as well as does 'elementary' cleaning action on the contacts. I believe this combined with keeping the contacts clean is good for the kind of currents we're talking about.

    Disclaimer: I'm not an electrical 'expert' though I'm fairly proficient. The above is my opinion based on some research and some visual inspection. I'm comfortable doing the above on my rig, but please assure yourself before using this :).

    Here's my diagram:
    Trailer Electric circuit.jpg
     
  15. rohitash

    rohitash SILVER Star

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    Quick correction - the isolator in my trailer is the Hellroaring BIC 95150B and not the 95300 as depicted in the diagram. I was initially planning to use the 95300, but changed it to the 95150 based on Hellroaring's recommendation.

    Btw - the Hellroaring people are great to do business with. Both times I bought stuff with them they spent a lot of time on the phone and emails to discuss my application and make their recommendations before the purchase without any 'sales' pressure.
     
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