Mixing panels to charge 48 vdc

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halfcrazy
halfcrazy Solar Expert Posts: 720 ✭✭✭
in Advanced Solar Electric Technical Forum #1
Ok after thinking on this for a while i think i need to grow my pv array a little and i am using 12 shell sq 165's my question is could i wire 2 of these and a sq 80 watt panel in series? the specs for rated amps and max amps look realy close so wouldnt this give me the added voltage to charge in hot summer weather? just curius as to what others think probably not a big issueas soon i can do 3 of the sq165's in series no problem but till then this seemd like a viable idea?
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #2
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    Re: Mixing panels to charge 48 vdc

    1/2,

    That should work just fine. 8) In fact, I had that very discussion with one of our buddies over on the OutBack forum. See: http://www.outbackpower.com/forum/viewtopic.php?p=11168&highlight=#11168

    HTH,
    Jim / crewzer
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: Mixing panels to charge 48 vdc

    to use at a controller output of 48v i don't see any problem if you have enough of the sq80s to place in series with every 2 sq165s you have in series. you gain some on the system due to earlier charge during sunrise, longer time of charging towards sunset, and reaping more on some cloudy periods that would've normally dropped out due to low voltage. as jim has mentioned a few times in the past, you will also lose a bit of efficiency on the controller as you go up in voltage. imho the extra 12v being added in series from the sq80s will do better for you than adding another sq165. both series arrangements should work, but with using 3 sq165s in series x6, the power produced will be close to around the controller maximum.
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  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    #4
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    Re: Mixing panels to charge 48 vdc

    i would think 3 of the sq165's would go over the mx's 140 limit? there voc is 44.5 so that would total 133.5 so on our cold maine days i would be worried there? But i had thought i remembered crewzer mentioning this as a solution f04 48 volt systems somewhere.
    Will be interesting i am told the classic will be very efficient at down converting high voltages so that will be a big plus
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #5
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    Re: Mixing panels to charge 48 vdc

    1/2,

    Going by the specs, the STC Voc for three 165's would be 44.5 V x 3 = 133.5 V. It won't take much of a temperature dip to increase the Voc to the MX60's operational limit (141 V), and not much more after that to reach its absolute limit (150 V). Accordingly, I would not recommend a "72 V" array for your neck of the woods. Remember, the MX60 logs its highest Voc.

    You could take a look at the modules' actual specs, look up your location's actual winter weather data, and then do a specific calulation for your proposed system. I think the NEC will allow that approach starting in 2008. For now, however, the NEC requires that you use Table 690-7 for temperature correction factors.

    Note that the 140 V ~ 150 V limit applies to other items as well, such as the Apollo T-80 controller, the new Xantrex MPPT controller, and to the usual DC rated circuit breakers as well. Frankly, I won't be surprised if the same limit(s) apply to the new products we're expecting, at least initially.

    Based on what's available now, I like the "60 V" array soluation for cold or hot climates and 48 V flooded-cell battery banks. I think 1 each SQ-80 plus 2 each SQ-165's in series is a good "60 V" solution.

    HTH,
    Jim / crewzer
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  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    #6
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    Re: Mixing panels to charge 48 vdc

    Crewzer i think i have to agree that this seems to make sense specially if i can find a crafty way to mount them into the sq165's i should have my inverter next week so will see how it goes it has been hitting 95 or so here today and seeing 59.5-60 volts input but that is with the mx in mppt mode into a 24 volt battery
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  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    #7
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    Re: Mixing panels to charge 48 vdc
    ...it has been hitting 95 or so here today and seeing 59.5-60 volts input but that is with the mx in mppt mode...

    1/2.

    Aha! That's what I had in mind when I made the following comment in this previous discussion:

    "The STC Vmp of two 165’s in series is 70 V. Allowing for voltage drop from summer heat, wiring, and the MX60, I estimate summer operating voltage to be around 61 V. Is that what you see this time of year?"

    All is well in theory-land! :cool:

    Regards,
    Jim / crewzer
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  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    #8
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    Re: Mixing panels to charge 48 vdc

    Well on a good note these 95 degree days are rare here we usually hover around the mid 70's but in this ever changing climate who knows?
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