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Thread: Solar UPS feed

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    Junior Member CRCinAU's Avatar
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    Default Solar UPS feed

    Hi all,

    So to change the tempo a bit in this post - I recently got a double-online UPS that has an external battery connector. The bus voltage is 36v, and seems to float about 41v.

    As this UPS goes AC -> DC bus -> AC, I've been thinking of the possibility of adding a different input to the battery connector - as well as some bigger batteries to try and offset some of the usage to stuff connected to the UPS.

    The current draw from the wall socket is currently around 180w - with a really crappy power factor - so about 280VA.

    My questions:
    1) If the batteries float at 41v, what input voltage will I need to provide to offset what comes in via the AC->DC stage of the UPS?
    2) Is this kind of thing even possible?
    3) What type of panels / MPPT combo should I look for?



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    What your trying for is a UPS on a UPS sort of.............
    What information do you have regarding the external battery connections. Make and model here may help others give you the info your seeking.
    Solar panel to UPS, UPS to Load but because Solar is Power is variable (and doesnt work well at night) to 'smooth' out any variables, would you need a set of batteries ??
    I stand unequivicably behind everything I say , I just dont ever remember saying it !!

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    Junior Member CRCinAU's Avatar
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    The UPS is a CyberPower OLS1000E - link:

    The pre-made external battery packs are BPSE36V45A - link:

    I have a feeling the connectors are somewhat like anderson plugs - but I haven't verified this as yet.

    Might not need a second set of batteries - but I was thinking of adding them purely to give the UPS a longer runtime...

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    i have APC units in my place with added much larger external battery setups.

    i also looked at trying to setup a solar charge for them but in the end just gave up
    because it was getting to over complicated with panels - wiring - mmpt controller - inverter etc

    so stock standard plug in the wall one of my setups runs a external twin 220ah SLA 24v battery setup on power outage for 7hrs

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    Last edited by fandtm666; 12-02-18 at 06:29 PM.

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    Quote Originally Posted by CRCinAU View Post

    1) If the batteries float at 41v, what input voltage will I need to provide to offset what comes in via the AC->DC stage of the UPS?
    2) Is this kind of thing even possible?
    3) What type of panels / MPPT combo should I look for?
    1) if the batteries are gel SLA the the float should be 39.2V, if you add external flooded wet type car batteries the float needs to be increased to 40.5V, and if you spending real money on AGM cells then 40.8V. These voltages are valid for 25 deg C, if it's a bit colder the float should increase, if warmer it should go down.

    Don't mix battery types.

    Start here:



    2) Yes, but 36VDC is not a great system voltage. You'd be better at 24 or 48VDC if you want to expand and add solar with a MPP controller.

    3) Before doing this I'd look for a better inverter rather than trying to re-purpose a UPS.
    Last edited by Tab Number 3; 12-02-18 at 06:43 PM.

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    Junior Member CRCinAU's Avatar
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    Yeah - I figured 36v was a bit weird - but the price was right.... I couldn't find a 900w 12/24v pure sine wave inverter only under the price I paid for this whole UPS.

    I was originally going to look at a 24v charger + 2 batteries + 24v->240v inverter - but it was over the price point of this entire UPS by a factor of 2-3...

    On battery mode, this UPS will run forever as long as it gets fed 36v - so its really kind of an economic decision that the panel + MPPT + batteries will probably still be cheaper than getting a full DIY option...

    So I pulled the cover off the external battery connector and found this:





    Measured the voltage between the red and black terminals = 41.3v

    Hmmmm.
    Last edited by CRCinAU; 12-02-18 at 08:44 PM.

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    thats fair enough and at 180W it must not be a vary
    large device connected .

    so firstly need to look at battery size rounding up your assessment of 180w to 200W to be safe


    A battery’s capacity is rated in amp hours (Ah). As such, you’ll need to convert your total Wh to Ah.
    You can do this by dividing the watt hours by the battery voltage. You’ll also want to include your
    ideal depth of discharge (what percentage you want to drain from the battery before charging it).
    The formula is then: Wh / battery voltage / DOD.

    200w / 36V / 0.3 DOD X 24Hrs = 444.44 Ah 19amp per hour

    so to run it for 24hrs a day at a discharge depth of .3 you will need 444 ah worth of batteries
    that means 3 x 150ah batteries.remember the deeper the discharge the quicker they die

    now to charge them this is going to be the issue that will cost more than a 12 - 24 - 48 volt system
    something similar to this one that has the auto voltage recognition and has a 40 amp charge factor covering your
    hourly usage

    .

    The unit above requires for a 36V System Rated solar panel Input Power 1560W thats a shit load of panels

    so the number of panels needed will come down to the size and open circuit voltage they supply the ones i have here are
    250W @ 37.8VOC - others i have seen are anywhere between 12.8 and 26 .
    Last edited by fandtm666; 13-02-18 at 10:24 AM.

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    Junior Member CRCinAU's Avatar
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    I have a feeling I can scale this down somewhat... I'm not really interested in going battery only for it - however it would be nice to use solar to offset the amount of AC used from the mains to keep the kit running...

    At the moment, I think I'd be happy in just reducing the AC power requirement - ie if it draws 200W - and it can get this from the solar source instead of the AC source, then sweet. If not, it drops back to keeping things on AC to keep batteries charged and the load running.

    If the batteries are fully charged, I'm happy to 'waste' excess solar generated if I generate more than the unit requires from the AC outlet... But having 3 x 21Ah or higher SLAs on the external chain would add quite a bit of runtime... Right now, the 3 x 7Ah internal batteries say it will last ~1hr without AC - so anything external would boost this considerably...

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