"auxillary" voltage regulator

couchsachraga
couchsachraga Solar Expert Posts: 87 ✭✭
in Off Grid Solar & Battery Systems #1
I've not had any luck searching, but I'm sure this has come up before....

I'm using a SureSine inverter for the small amount of 110 ac I need (mostly controllers for a hydronic heating loop). The problem is when the temp drops (as it does this time of year) the Midnite Classic charge controller temperature-adjusts the charging voltage (which is great from a battery perspective), But this often means that charging or equalizing is done at over 15.4 volts... which is the voltage the Inverter cuts out at (and needs to be reset to work..difficult if I'm not there, and then the heating isn't working and it just gets colder...).

So... any suggestions for a 50 amp voltage regulator? Just looking for something to keep the "12v" going in to the SureSine below 15v or so.... Yes, the SureSine is rated at 300w continuous, but it is 600w surge. I do have a separate breaker for it (my thought was to put the "voltage regulator" between the breaker and SureSine...).

Another option would be to replace the SureSine with an inverter that wasn't so finicky... But I have to admit that it is nice to have a quiet (no fan) inverter that draws very little most of the time, as it is on 24/7 (or should be!). I'm open to suggestions though.

Thank you all as always!
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  • couchsachraga
    couchsachraga Solar Expert Posts: 87 ✭✭
    #2
    Re: "auxillary" voltage regulator

    Poking around the internet got me thinking - "in theory" I might be able to use another charge controller... it would see the 15.6+ volts (cutout is 15.5...not 15.4 as I stated above) as "power" from the panels and output a max of 14.4 (for simple (and cheaper)) controllers.

    I think I have a C-40 sitting around somewhere....

    Good idea, or terrible idea?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: "auxillary" voltage regulator

    Find a couple of high current diodes and put them in series on the positive line. Each one will drop the Voltage by about 0.5 (depending on the diode) solving the problem. In fact it will also effective raise the Voltage on the low end because when the inverter 'sees' 10.5 Volts and shuts down the battery will actually be higher.
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  • couchsachraga
    couchsachraga Solar Expert Posts: 87 ✭✭
    #4
    Re: "auxillary" voltage regulator

    Won't this always lower the voltage as it "sees" it... which means the LVD (low voltage disconnect) might be tripped when the batter is still 12v or so (depending on how many diodes...)?

    I like the idea though:)

    I also realized that what might be simplest is getting an automotive voltage regulator. Lots of old trucks I've had used them... and the alternators were 80 amp+...


    Thanks as always:)
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: "auxillary" voltage regulator
    couchsachraga wrote: »
    Won't this always lower the voltage as it "sees" it... which means the LVD (low voltage disconnect) might be tripped when the batter is still 12v or so (depending on how many diodes...)?

    I like the idea though:)

    Yes, that's what I was saying. Usually the LVD on 12 Volt inverters is too low anyway; shifting it up 1 Volt would be an improvement.
    I also realized that what might be simplest is getting an automotive voltage regulator. Lots of old trucks I've had used them... and the alternators were 80 amp+...


    Thanks as always:)

    Define "automotive Voltage regulator": you have a choice of the old cut-outs that shift the Voltage to the gen/alt electromagnet between two levels or the transistorized version that adjusts it linearly. None of them are designed to take a variable Voltage on input and have a fixed Voltage on output. Neither are solar charge controllers, which depend on having battery Voltage on their output in order to function.

    To actually regulate the input to the inverter would require some quite complex circuitry, even if only to prevent over-Voltage.
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  • couchsachraga
    couchsachraga Solar Expert Posts: 87 ✭✭
    #6
    Re: "auxillary" voltage regulator

    Ah, NOW I follow you. You are always very helpful, and I tend to learn a lot when I post here, from you and others:)

    A quick search reveals quite a few "high current diodes", with a few different types. Any recommendations from your experience? I may try my local electrical supply store, though they tend to be a bit clueless about 12v stuff.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: "auxillary" voltage regulator

    The Voltage won't matter as much as the current capacity and the Voltage drop the diode causes.

    What you can find ... will probably be a better selection than what I can scrounge in the wilderness here. :p
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  • CDN_VT
    CDN_VT Solar Expert Posts: 492 ✭✭✭
    #8
    Re: "auxillary" voltage regulator

    Why not change the voltages in the classics menu & adjust the temp adjustment also. With Wizzbang & BTS you could just increase times of Absorbing and float with lesser voltage values .
    I limit the Amps in due to Way over panelling , but having 3 weeks of cloud & rain in the winter , Im still good . Summer I have 2 panels that would do the job.

    If you do the Diode Voltage rob , Use large heat sinks. Also if you have the Serial PC MOBUS cable you can change the SS300 settings.

    VT
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  • couchsachraga
    couchsachraga Solar Expert Posts: 87 ✭✭
    #9
    Re: "auxillary" voltage regulator

    I dI can likely track down a cable, but looking at the manual it looked like you couldn't increase the high voltage disconnect further (the others you can tweak).

    But you are right - I should go in to the Midnite settings and see if I can set a max. voltage regardless of temp. easier way of getting to the same place - and having less fire hazards around:)

    If I can't do that I'll be back on the diode tracks....

    Thank you both!!!
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  • CALLD
    CALLD Solar Expert Posts: 230 ✭✭
    #10
    Re: "auxillary" voltage regulator

    I used to have the same problem with my old set of silver calcium batteries that needed a ridiculously high absorption voltage (15.5 to 16.5 volts for a 12v battery).

    1st problem is that charging at such a high voltage is very inefficient so you are using a lot of useful power just trying to get your batteries up to 100%. This problem is obviously a lot worse in winter when the daylight hours are short and you have to cram us much power into them as possible very quickly, the low temperatures just make it worse. You could try getting AGM batteries instead as they charge at a lower voltage (14.4 to 14.8v) and can take a higher charge current. If getting new batteries isn't an option then try keeping them at a higher temperature if possible? Using a diode is very inefficient as you will be effectively converting 5 to 10% of all your hard-earned electricity into heat before it has entered the inverter:( If you don't want to spend any money fixing the problem then the best thing you can do it just switch off the inverter during absorb phase...
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  • couchsachraga
    couchsachraga Solar Expert Posts: 87 ✭✭
    #11
    Re: "auxillary" voltage regulator

    Keeping the batteries warmer is one of the goals of needing the little bit of AC power - solar thermal heats an 80 gallon water tank (hot water in summer, "heat bank" in winter). Once it is over 100 degrees a pump turns on (two coils in the tank -lower one to heat it, upper one to cool it!) and runs hydronic baseboard. The controller is unfortunately AC... From the installation last late winter worked "ok", but this will be the first full winter. I am hoping to get the floor insulated (2nd floor of a barn..) which should help. The walls are R20+, ceiling is R30+... floor is 2" of pine....
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
    Re: "auxillary" voltage regulator
    CDN_VT wrote: »
    Why not change the voltages in the classics menu & adjust the temp adjustment also. With Wizzbang & BTS you could just increase times of Absorbing and float with lesser voltage values .

    NOTE: this does not actually work. If the batteries aren't brought up to their proper charging Voltage they do not properly charge. You can't simply trade time for Volts or Volts for time.
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  • couchsachraga
    couchsachraga Solar Expert Posts: 87 ✭✭
    #13
    Re: "auxillary" voltage regulator

    Ah, but if the temperature compensation was OFF it would be charging at lower voltage anyway....

    We're not talking a huge change here - the highest I think I've seen it is 15.8... so capping it last 15.4 (in my mind) isn't a huge difference, especially as if things warm back up the charging would go back to working properly (I'm assuming I can set a max. voltage that will not impact the others). Searching a bit online I found what appears to be the way to get to that menu.

    I'm surprised no one has recommended a different inverter with wider tolerances:)
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  • couchsachraga
    couchsachraga Solar Expert Posts: 87 ✭✭
    #14
    Re: "auxillary" voltage regulator

    I haven't managed to turn down the max. voltage below 15.5, so on the high current diode hunt I go:)

    I already have a 450w one coming from Mouser... might try that just to see exactly what the voltage drop looks like.

    Floor is almost all insulated now - I'll be bringing everything up to "comfortable" temp just after Thanksgiving, so the week after will be a good test to see how quickly the indoor temp drops now. Here' hoping it is very slowly!

    Thank you Cariboocoot for your great advice as always, even if it takes me a while to listen:)
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  • AuricTech
    AuricTech Solar Expert Posts: 140 ✭✭
    #15
    Re: "auxillary" voltage regulator
    couchsachraga wrote: »
    Another option would be to replace the SureSine with an inverter that wasn't so finicky... But I have to admit that it is nice to have a quiet (no fan) inverter that draws very little most of the time, as it is on 24/7 (or should be!). I'm open to suggestions though.

    While the Exeltech series of 12V inverters have a maximum input Voltage of 16.5VDC (which helps with your first requirement), they don't appear to have a stand-by mode (which conflicts with your second requirement). Against the SureSine's no-cooling-fan operation, this section of the Exeltech 250W inverter's user manual implies that it also operates without a cooling fan:
    The XP-250 will perform best when mounted vertically. This will allow warm air to rise through vent holes on top, drawing cool air through vent holes on the bottom.

    It's always a matter of trade-offs.... :p
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