72 volt systems?

khotton Solar Expert Posts: 38
It seems to me that with the high cost of copper, that there would be a move to higher voltage "off-grid" systems. Currently, the top voltage is 48VDC. I am hoping that systems will move up to 72VDC. Do the experts on this forum have any insight into this? An additional advantange to this higher voltage system is that many "NEV's" neighborhood electric vehicles - could be directly charged with a charge controler for a 72VDC system.



  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: 72 volt systems?

    Above 50V, is the magic realm of "high voltage" and I think something in the NEC makes it non-trival to make a "hi-voltage" battery bank, where a 48 volt bank is just fine. Your mileage may vary
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: 72 volt systems?

    it seems to me that if all you are doing is charging an ev then do it as the nec won't worry about it much and the only batteries involved are in the ev. the mx60 controller could handle this 72vdc output, but the input is a bit trickier. i don't know the current max if it has changed at all, but i believe it was around 125vdc for the cutoff. jim, would you verify this?
  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: 72 volt systems?

    I think the mx60 is 140 vdc but the problem is going above the 48 volt nominal battery bank oppens a huge can of worms within the NEC
  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: 72 volt systems?

    "72 V" systems are problematic. Worst case, using 14.4 V / 15.5 V to charge /equalize a "12 V" battery as a reference, ~93 V would be required to equalize a flooded-cell bank. Allowing for losses due to hot ambient temperatures, cabling loss, and converter loss, a target STC Vmp would be ~93 V / 85% = ~109 Vmp. Since Vmp is ~80% of Voc, STC Voc would be ~136 V.

    The operational limit for the MX60 is 141 Voc, and it's 140 Voc for the T-80. The small difference between 136 V and 140 V leaves no room for the NEC's ambient temperature voltage correction factors, so a "72 V" system is therefore not practical with present products. In fact, even a "60 V" system can be difficult to spec.

    Jim / crewzer