Breaker- Battery match up

trumpets3u
trumpets3u Solar Expert Posts: 35 ✭✭✭
I just ordered a Xantrex 250 amp breaker with enclosure, I'm running a 24 volt system, and using (8D- 12volt) 255 AH batteries, how many batteries can I put thought this 250 amp breaker, or better is that a good way to do the math on this?
Thanks

Comments

  • crewzer
    crewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Breaker- Battery match up

    I believe the battery breaker size should be specified based on load specs rather than battery bank capacity. For example, if your 24 V inverter's maximum continuous DC input current rating is 120 A, and the NEC says you need a 125% derating multiplier, the NEC Amps rating would be 120 A x 125% = 150 A. Accordingly, you'd need to use a breaker spec'd for that current or the closest size up (175 A?).

    HTH,
    Jim / crewzer
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Breaker- Battery match up

    There is also the other ratings that you have to worry about... Maximum voltage and maximum interrupting current.

    http://www.xantrex.com/web/id/121/p/438/pt/5/product.asp

    Maximum DC load on circuit breakers:
    250 amps
    Maximum DC system voltage
    125 VDC
    Maximum high fault current interruption at 65 VDC
    25,000 amps
    Maximum high fault current interruption at 125 VDC
    10, 000 amps
    Maximum stranded wire size
    #4/0 AWG - dual #2/0 AWG may be used with appropriate adapters

    So you need also to understand the maximum current the batteries/wiring system can place into a dead short. Too many batteries in parallel with heavy/short wires could weld the breaker contacts shut if there was a dead short fault.

    The more difficult part is finding the maximum current that a storage battery can supply... Battery output current and wiring harness resistance need to be known to find that maximum fault current.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2
    System2 Posts: 6,290 admin
    Re: Breaker- Battery match up

    I have found great deals on Ebay for this same breaker for less than $25.00 each. I have several floating around the garage I picked up very cheap that are brand new. Check Ebay next time and you might be able to save a few bucks. Example a dual 225 amp DC breaker new for less than $25.00, a dual 400 amp DC breaker new for less than $30.00, and several 125 amp DC breakers new for $10.00... Just trying to save you some money, arcandspark