Instead of a balancing transformer...

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Out There
Out There Solar Expert Posts: 96 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
So I'm sitting here, with a broken-down 8kw Generac Guardian generator, preparing for the arrival of my new "back-up" generator and thinking about utilizing all of the Generac's output (after it's repaired). As has been pointed out in other discussions, I really don't need the 8kw - it's overkill. When it's running, I'm only utilizing one leg of its 240 VAC output. A balancing transformer seemed like a good idea, so I could use the power of both legs equally but when I started asking about them and looking into purchasing, I saw that they were really rather expensive.
So here's my "new" thought: What if I ran one 120 VAC leg to my inverter (as it is currently configured), and with the other leg, I powered a 24 volt battery charger? Since the generator runs only when called for by the inverter, if the other leg was also charging the batteries, it seems to me that more charging current would go to the batteries, charging them quicker and shortening the run time on the gen set. Am I way off in this thinking?
I was looking at golf cart (24 volt) chargers.
-Brian
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Instead of a balancing transformer...

    Yes, more or less.

    If one 120 VAC leg is charging through the inverter and you load the other leg with a stand-alone charger the gen will be more evenly balanced.

    Caveats: the combined charging rate shouldn't exceed the batteries' maximum charge rate, and the more even the rate from each half is the better for the generator. So as an example if the maximum charge rate is 40 Amps you'd dial down the inverter charger to 20 Amps and put a 20 Amp charger on the other leg. Then the gen would be as evenly loaded as possible and the charge rate would be the same.

    You want the stand-alone charger to function in the same 3-stage manner as the inverter-charger. This would include the Voltage set points for Absorb and Float.
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  • Out There
    Out There Solar Expert Posts: 96 ✭✭✭✭
    #3
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    Re: Instead of a balancing transformer...

    Thanks! So are you familiar with 24 volt stand-alone chargers? The ones at which I was looking were for wheelchairs and/or golf carts. How would I check the charging set points? The inverter is adjustable, but the strand-alones didn't seem to be.
    -Brian
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: Instead of a balancing transformer...
    Out There wrote: »
    Thanks! So are you familiar with 24 volt stand-alone chargers? The ones at which I was looking were for wheelchairs and/or golf carts. How would I check the charging set points? The inverter is adjustable, but the strand-alones didn't seem to be.
    -Brian

    You'd have to get the specs from the particular charger. Most of these stand-alones are not adjustable, much less full programmable. Iotas http://www.solar-electric.com/bach1.html apparently can be opened and adjusted for Voltage. I don't know of any that are as good as the built-in chargers.

    The initial Bulk stage is where the gen will be the most loaded and as such the most unbalanced. Once you reach the Absorb level the current should be down to where the difference between two chargers won't make much trouble.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #5
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    Re: Instead of a balancing transformer...
    Cariboocoot wrote: »
    If one 120 VAC leg is charging through the inverter and you load the other leg with a stand-alone charger the gen will be more evenly balanced.

    Unless he has AC loads on the Trace (which, I presume, passes the generator AC through to the loads).
    Out There wrote: »
    Thanks! So are you familiar with 24 volt stand-alone chargers? The ones at which I was looking were for wheelchairs and/or golf carts. How would I check the charging set points? The inverter is adjustable, but the strand-alones didn't seem to be.
    -Brian

    You're right, there's not much out there. The Iota's have issues with huge inrush currents and low power factor (more an issue with generators than grid). I've been researching the relatively new Xantrex Truecharge2 chargers... I've seen a couple of decent reviews, but I'm waiting for someone I know and trust (like on this forum) to chime in.

    btw, if you're using the charger primarily for bulking the batteries, you don't really need 3-stage charging. Some of those wheelchair golf cart chargers are power factor corrected and require 240 volt AC. If you can get one of those, you could do DC coupling... using the Trace as an inverter rather than a charger.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Out There
    Out There Solar Expert Posts: 96 ✭✭✭✭
    #6
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    Re: Instead of a balancing transformer...
    Cariboocoot wrote: »
    The initial Bulk stage is where the gen will be the most loaded and as such the most unbalanced. Once you reach the Absorb level the current should be down to where the difference between two chargers won't make much trouble.
    If I'm loading the generator most during the bulk charging phase, what would happen if they weren't closely matched? Wouldn't the stand-alone's algorithm drop to a float charge at somewhat close to the same point as the Trace inverter? And once the inverter sensed the right voltage, wouldn't it then stop the gen set?
    On the Generac forum I learned that the generator could probably handle being unbalanced up to almost half it's rated output on one leg. I was looking at 8 or 10 amp chargers which would not place nearly the same load on the other output leg. It would be unbalanced, but less so than if I had nothing on that other 120 VAC leg.
    What am I missing?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
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    Re: Instead of a balancing transformer...
    Out There wrote: »
    If I'm loading the generator most during the bulk charging phase, what would happen if they weren't closely matched? Wouldn't the stand-alone's algorithm drop to a float charge at somewhat close to the same point as the Trace inverter? And once the inverter sensed the right voltage, wouldnt it then stop the gen set?
    On the Generac forum I learned that the generator could probably handle being unbalanced up to almost half it's rated output on one leg. I was looking at 8 or 10 amp chargers which would not place nearly the same load on the other output leg. It would be unbalanced, but less so than if I had nothing on that other 120 VAC leg.
    What am I missing?

    In Bulk stage both will be supplying whatever current they can and the Voltage is pretty much set by the batteries' state of charge.

    When the system reaches Absorb, if the inverter-charger's setting is higher it will try to push the Voltage up to that point. This takes the stand-alone's Voltage higher than its set point and therefor will reduce its current contribution.

    The generator will continue to run until something or someone tells it to stop. Usually auto-start gen controls keep the gen running through Absorb, but depending on the exact settings may shut it down if it is meant to do so at a particular Voltage.
    vtmaps wrote:
    Unless he has AC loads on the Trace (which, I presume, passes the generator AC through to the loads).

    Which is why I said "more evenly balanced" not "perfectly balanced".
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  • Out There
    Out There Solar Expert Posts: 96 ✭✭✭✭
    #8
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    Re: Instead of a balancing transformer...

    Curiouser and curiouser….. If you were in my position - both equipment-wise and financially - what would you do?
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  • PhilS
    PhilS Solar Expert Posts: 370 ✭✭✭
    #9
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    Re: Instead of a balancing transformer...
    Out There wrote: »
    Curiouser and curiouser….. If you were in my position - both equipment-wise and financially - what would you do?

    My generator, when running, is charging my batteries through two inverter/chargers, one on each leg. I don't see any difference in what you propose. That keeps the genset legs balanced.

    On another of your points: I do have the option of having an inverter auto-start the gen but, except for a few month trial, I keep that disabled. We have two gen start panels, one in the kitchen and one in the utility room. I prefer to have it run when I want and only when I want. Even DW is used to monitoring the battery voltage (digital meter also in the kitchen) and before running the generator factors in: battery state and whether it is temporary from a load that will stop soon (like microwave or water pump); how long the genset would run (no point in starting it if we are leaving or bedding down 20 minutes after starting it); how much sun (or not) is expected to be hitting our panels in the next day; and probably some other things that I can't think of at the moment.

    I guesstimate the generator costs $5/hr for propane when it's running and try to avoid operating it unless REALLY necessary.

    Phil
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  • northerner
    northerner Solar Expert Posts: 492 ✭✭✭✭✭✭
    #10
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    Re: Instead of a balancing transformer...
    Out There wrote: »
    Curiouser and curiouser….. If you were in my position - both equipment-wise and financially - what would you do?

    I would eventually look at getting a separate charger when finances allow. This will give you charging backup in case your inverter is ever out of commission. If one leg of the generator is sufficient to give good charging current to your system, then a separate charger is not really necessary, unless using one leg is not recommended?

    I recently purchased an Iota 40 amp (24 volt) charger for backup, just in case the inverter goes down.
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  • Out There
    Out There Solar Expert Posts: 96 ✭✭✭✭
    #11
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    Re: Instead of a balancing transformer...

    Do I need some type of isolation circuit/device to use two different charging sources?
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  • Out There
    Out There Solar Expert Posts: 96 ✭✭✭✭
    #12
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    Re: Instead of a balancing transformer...
    vtmaps wrote: »
    I've been researching the relatively new Xantrex Truecharge2 chargers... I've seen a couple of decent reviews, but I'm waiting for someone I know and trust (like on this forum) to chime in.

    Whoa! I took a look at the Truecharge2 24 volt chargers! Lots of $$$! I know you get what you pay for, but ….wow! That one's off the list - at least for now.
    I looked on NAWS for the Iota. That's a little more in the realm of "do-able"… still curious, though, about these 8 or 10 amp golf cart chargers. I wonder if they'd be more hassle than they're worth?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #13
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    Re: Instead of a balancing transformer...
    Out There wrote: »
    Do I need some type of isolation circuit/device to use two different charging sources?

    You shouldn't. The output from either charge source is via semi-conductor so one can't 'back feed' the other.

    I don't know about the golf cart chargers, but it seems to me they are a bit light at only 10 Amps; you want to be able to make 50% of your charge current from each source.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #14
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    Re: Instead of a balancing transformer...

    Out There, what is the exact model of your Generac?
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • Saggys
    Saggys Solar Expert Posts: 189 ✭✭✭
    #15
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    Re: Instead of a balancing transformer...

    I would find a Trace T240 transformer, it is rated for 4.5kva I believe. Ebay would be a good place to start, you can probably find one for $400 or less.
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  • Out There
    Out There Solar Expert Posts: 96 ✭✭✭✭
    #16
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    Re: Instead of a balancing transformer...

    Techntrek,
    It's a Model 6237; 8kw Guardian.
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