wiring illiteracy

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hsquared
hsquared Registered Users Posts: 5 ✭
in Solar Beginners Corner #1
What is the best way to connect the charge controller and the charger to the battery? I would like to connect both of these to the same deep-cycle battery, keeping the car battery separate.
Also, when should an isolator be used?

Are there any good diagrams out there of a very detailed rv solar system (wiring, fuses, best locations for each component, etc.)? I like pictures :)
Thanks in advance!
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #2
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    Re: wiring illiteracy

    There are two types of so-called "battery isolators". One is the "diode-type" and the other is the "split-charge relay".


    A diode-type isolator looks like a heat sink. It takes the charging input from the alternator and sends it out to two (or more) batteries. Some are smart and will make sure the engine start battery gets a higher priority. The diode-type will not allow current to flow from the aux battery to the main battery.


    The split-charge relay looks much like a Ford starter relay (they are similar, but not exactly the same). What these do is to connect both the start battery and the aux battery together so that they are both charged at the same time. This effectively makes both batteries into a single battery bank.

    These split-charge relays are wired so that they are only activated when there is power coming from the alternator, so that when the engine is not running, and there is no charge current coming from the alternator, the batteries are separate and running down the aux battery won't drain the start battery.


    The primary drawback to the split-charge relay is that (if the aux battery is quite drained or heavily loaded), when you start the engine and the alternator charge current activates the relay, there can be a large rush of current from the start battery to the aux battery.

    A secondary drawback to a split-charge relay, when used on an RV with a solar system, is that when the engine is running, the start and aux batteries are connected into a single battery bank. If there is sun on the PV panels, it is possible that the solar charge controller could put out a high enough voltage to overcharge and/or damage the engine start battery.

    This won't happen with the diode type isolator because the isolator won't let voltage flow from the aux battery to the start battery, and the solar charge controller will be connected to the aux battery.


    I have a small camper van that I bought used. It has a split-charge relay. I will be replacing that with a proper isolator before I replace the existing rv/marine battery with proper AGM batteries.

    You need an isolator rated to take the full output of the alternator. So if you have a 60a alternator, you need *at least* a 60a rated isolator.


    Here's a link to a .pdf file showing how to install and wire a diode-type isolator:

    http://www.countryhomescampers.com/pdf/Multibattery_Isolator_Instructions.pdf


    Here's a link to a page showing what a split-charge relay is and also a wiring diagram:

    http://www.powerstream.com/battery-isolator.htm


    For myself, I will be installing an isolator to send charging current from the alternator to engine battery and to my aux battery bank when the engine is running.

    I will be installing an Iota charger to charge the aux bank when either the gen is running or there is shore power.

    I will also be installing a small "battery minder" or "battery tender" type of charger which will be connected to the engine battery. Again, this will be powered either by the gen or shore power.

    The AGM aux battery bank will need a different charging regimen than the engine battery.


    Later, I'll probably install some solar.
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  • hsquared
    hsquared Registered Users Posts: 5 ✭
    #3
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    Re: wiring illiteracy

    So, I have a RV that uses PV modules to charge a two-battery bank. I also want to use a converter to utilize 120v AC hookups to charge my batteries. I will not be using the alternator to charge my house batteries.
    Currently, my system has PV modules that are wired to a multi-stage charge controller (also referred to as a regulator). From the charge controller I have a wire that goes to the positive house battery terminal, and another that goes to the negative house battery terminal.
    If I were to install my converter, can I just wire it straight to the house battery terminals? Do I need anything to protect the charge controller from the converter and vice versa?
    If there isn't any protection necessary, could I use the same wire that feeds to the house battery terminals from the charge controller for the converter? My converter will be installed next to the charge controller but some distance from the battery bank and I'd love not to have to run more wire.
    Thanks for all the help!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: wiring illiteracy

    If you're talking about adding a DC to AC inverter to your existing 12VDC RV system, wire it directly to the batteries through appropriately sized wires and fuse. Even a small one (say 300 Watts) will draw considerable amperage at peak output (approximately 30 Amps).

    Be sure you have enough battery capacity to handle the additional loads through the inverter (amp/hr capacity) and sufficient PV power to replace it. Otherwise without a back-up charging system (such as a small generator or connection to the vehicle's alternator) you will soon have irretrievably dead batteries.

    What are you planning on running off your proposed 120 VAC?
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  • hsquared
    hsquared Registered Users Posts: 5 ✭
    #5
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    Re: wiring illiteracy

    Sorry for the confusion! I want a converter to turn 120v AC (shore power) to DC current to charge my batteries. I have an inverter to run 120v AC appliances off of my house batteries, but that is not related to where my problems lie.
    Thanks for the response!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
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    Re: wiring illiteracy

    You want a battery charger like one of these:

    http://store.solar-electric.com/bach1.html ?
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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #7
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    Re: wiring illiteracy
    hsquared wrote: »
    So, I have a RV that uses PV modules to charge a two-battery bank. I also want to use a converter to utilize 120v AC hookups to charge my batteries. I will not be using the alternator to charge my house batteries.
    Currently, my system has PV modules that are wired to a multi-stage charge controller (also referred to as a regulator). From the charge controller I have a wire that goes to the positive house battery terminal, and another that goes to the negative house battery terminal.
    If I were to install my converter, can I just wire it straight to the house battery terminals? Do I need anything to protect the charge controller from the converter and vice versa?
    If there isn't any protection necessary, could I use the same wire that feeds to the house battery terminals from the charge controller for the converter? My converter will be installed next to the charge controller but some distance from the battery bank and I'd love not to have to run more wire.
    Thanks for all the help!


    Yes, you can connect both the solar charge controller and the converter/charger directly to the battery bank.

    Both units will be internally protected against voltage coming from the battery bank they are connected to - and the battery bank has a much higher amperage than the other charger. They won't attack each other.


    Yes, you can connect them both to common wiring which goes to the battery bank - IF THE WIRE IS LARGE ENOUGH TO HANDLE THE TOTAL AMPERAGE FROM BOTH UNITS AT THE SAME TIME.

    I.e., If the solar charge controller puts out 15a max and the converter/charger puts out 30a max, then you need wire that is rated to handle 45a minimum - and the same for the fuse which protects that wire.
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  • hsquared
    hsquared Registered Users Posts: 5 ✭
    #8
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    Re: wiring illiteracy

    Thanks, dwh! That's exactly what I needed to know...
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