Power converter question

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System
System Posts: 2,511 admin
in Off Grid Solar & Battery Systems #1
I am off griding in a 1996 travel trailer that has a "Magnatek Converter Charger". Series 900 Model 940-2 and says it puts out 40 amps.

Its a one way converter that takes 120 volts from my generator or grid and charges my 12 volt battery bank. It is not an inverter. It only goes one way.

I do not think this converter has a built in charge controller.

I have put an clamp meter and have seen it charging 12 amps instead of 40 amps to the battery bank before. Is this because it is fighting against the internal battery resistance?

I would really like to run this converter through my Tristar PWM TS-60 so that it could "control" the charge properly. Does this sound like it will work or will it damage something???

Can I wire it up in my combiner box with my solar panels or do I need to add a diode?

Or is this just a bad idea? :confused:
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
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    Re: Power converter question

    To prevent overcharging and destruction of the battery, the charger would automatically limit the charging voltage to a preset voltage, perhaps 14.5 volts. It does this by reducing the charge current as required, to maintain that voltage. The 40 amps mentioned would be the absolute max that it could output. Feeding that approx 14.5 volts through a PWM controller would reduce the available voltage at the battery terminals due to losses through the controller, which would result in undercharging your battery. And it would definitely be a bad idea to wire it to your solar panels. Smoke, despair and regret would in all likelihood quickly be the result. It sounds like your system has been operating properly as is.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
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    Re: Power converter question
    Eric R. wrote: »
    ....
    I have put an clamp meter and have seen it charging 12 amps instead of 40 amps to the battery bank before. Is this because it is fighting against the internal battery resistance?
    ....

    As any lead acid battery bank charges up, its rate (amps) begins to taper off. An hour later, I'd expect to see 6 amps.

    The charge controller would want to be fed at least 17v, which the converter likely can't produce. :cry:
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • dwh
    dwh Solar Expert Posts: 1,341 ✭✭✭
    #4
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    Re: Power converter question

    According to this page:

    http://www.toprudder.com/rv/pd9145.html

    That converter puts out a constant 13.6v but the voltage drops under load due to not great voltage regulation.

    A solar charge controller, will want to take a battery up to 14.4v for the "bulk" stage of a 3-stage charge. In order to do that, it needs more than 14.4v on the input side.

    Wiring up a 13.6v supply to the input of the charge controller would not help anything, since the charge controller would only have 13.6v available to work with in the first place.

    I'd replace it with a more modern converter/charger.


    The "amps" rating of the converter simply indicates the max that the unit can supply. How much actually flows to the battery depends on the battery's state of charge. So if a converter is connected to a battery that is full there won't be any power flow - even if the converter could supply 40a.
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  • vcallaway
    vcallaway Solar Expert Posts: 157 ✭✭✭✭✭
    #5
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    Re: Power converter question

    Those converters are pretty much junk. If you leave them plugged in you will cook your batteries. They are basically a 40a power supply and not very well regulated. They also tend to buzz.

    You can always spot an RV with one because when on generator power the 12v lights will flicker. A sure sign of bad power regulation.

    You can plug it into your charge controller but it will never go into equalize. You would be much better off springing for something like the IOTA charger and IQ4 module. Just a better all around unit. Also takes up less room.

    I changed out the one in my motorhome and am MUCH happier.
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  • Powerguy2011
    Powerguy2011 Registered Users Posts: 6 ✭
    #6
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    Re: Power converter question

    The Powermax converters pm3 series is a 3 stage smart charger. I have been running on my rv batteries for about a year and no problems. They have the 3 modes and there is a pot inside you can adjust(I don't recommend unless you talk to them). I think na wind and sun carries them now
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
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    Re: Power converter question
    Powerguy2011 wrote: »
    The Powermax converters pm3 series is a 3 stage smart charger. I have been running on my rv batteries for about a year and no problems. They have the 3 modes and there is a pot inside you can adjust(I don't recommend unless you talk to them). I think na wind and sun carries them now

    Yes, NAWS handles the Powermax units: http://www.solar-electric.com/pomaxrech.html
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  • Shasta1
    Shasta1 Registered Users Posts: 15 ✭
    #8
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    Re: Power converter question

    I was just told by Northern AZ Wind & Sun that the Tri-Star can be wired to the battery bank and not cause any problems with the Magnatek . The solar panels are regulated by the Tri-Star which also controls the charge going to the batteries.

    Robert Snipes wrote:
    You can have multiple charging systems charging the same batteries without any issues. Which ever is charging the batteries the most will "trick" the other controllers into thinking the batteries are charge and go into float mode. This is very common in RV systems.

    If you plug in to shore power, or fire up the generator, the Magnatek will still automatically sense the condition of the batteries and stay at a “float charge”, same with the Tri-Star controller....and do it's auto switching between shore and generator supplied power in addition to supplying pwr to your coach 12v system.

    That’s my understanding.

    You do not want to wire the Magnatek to the Tri-Star Controller!

    I would add a battery monitor such as the Trimetric TM-2025 to monitor the state of charge and condition of your battery bank(s). Actually, I would do this first :D
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