12VDC (Or 5VDC direct from HV PV?

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XRinger
XRinger Solar Expert Posts: 529 ✭✭✭
in Advanced Solar Electric Technical Forum #1
I'm looking at these little switching power supplies,
811ecmIPQfig1.jpg

And have seen 12Vdc (and some +5 units) on Ebay that use AC input voltages of 100-240V AC 50/60 Hz.
http://www.ebay.com/itm/370435334398

It seems to me, these little Ebay Switchers might also run on DC from 100 to up to 240 volts DC..

Meaning one could use a high voltage output PV source to power small low voltage DC devices..

Anyone here ever try it?

And since 1.414 * 240 = 339, could these things run off of a 339vdc PV array?

Thanks,
Rich
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #2
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    Re: 12VDC (Or 5VDC direct from HV PV?

    Yes, you can put ~370 volts or so into the high voltage section of a "simple" switching power supply (120/240 vac switchable).

    Or, if you find power factor corrected supplies, you might be able to feed 100 VAC - 264 VAC or even 100-264 VDC directly into those types of switching power supplies.

    Either you will have to purchase some "cheap" supplies and do a smoke test, or contact the designers and see if they will give you the information (everyone is afraid of lawsuits).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: 12VDC (Or 5VDC direct from HV PV?

    now isn't this a coincidence as i was just pming nsaspook about my little switchers. you are showing the same ones i have. they work good, but in a high rf environment they blow out.
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  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    #4
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    Re: 12VDC (Or 5VDC direct from HV PV?

    The vendor was selling that same 12V PS for $3, so I ordered one to try on my 145vdc array, unloaded or 115.6v at MPP.

    If this works (I think it might), I'll use it to simplify a little MPPT project I'm planing to build.
    Instead of using a resistor and Zener diode to make a logic supply, I'll just use a plug-n-play Power supply. 8)

    For now, I can test the transistor & heat-sink setup I plan to use, with a function generator.
    While I wait a 2 or 3 weeks for delivery.. :(
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #5
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    Re: 12VDC (Or 5VDC direct from HV PV?

    PV panels are current sources, not a voltage source.

    If you have much more PV power being generated then the wall wart needs and there is a mppt charge controller already loading the panels it will likely work.

    I would not consider it a reliable setup and if the wall wart oscillates coming in or out of some heavy shade occurance it could screw up your MPPT controller's operating point causing it to lose a lot of power harvest.
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  • XRinger
    XRinger Solar Expert Posts: 529 ✭✭✭
    #6
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    Re: 12VDC (Or 5VDC direct from HV PV?
    RCinFLA wrote: »
    PV panels are current sources, not a voltage source.

    If you have much more PV power being generated then the wall wart needs and there is a mppt charge controller already loading the panels it will likely work.

    I would not consider it a reliable setup and if the wall wart oscillates coming in or out of some heavy shade occurance it could screw up your MPPT controller's operating point causing it to lose a lot of power harvest.


    I'm not worried about the PS failing to supply reliable +12v, since the load
    to my DIY MPPT circuit will likely only be 5 to 10 ma, and the PV array will put out
    80 to 100 volts no-load during overcast conditions.

    The source is four CS6P-200 (200w Canadian Solar Vmp 28.9 & Voc 36.2), in series.
    The project circuit looks a bit like the one below, but with the FET, C1 & C3 rated at 200 to 250v.

    I would use the power supply, in place of R1 C4 & Z3.

    pump2-1.jpg

    Theory of operation:
    When the voltage on pin 2 the of LM311 exceeds 5V, Q1 will fire, discharging C1.
    Then the process will repeat, rapidly when it's sunny.
    R3 will be adjusted so pin 2 only sees 5V when the array is => 115.6 volts. (MPP).
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