Amp reading

Chris11Chris11 Registered Users Posts: 71 ✭✭
Can someone 'splain something to me?

Using my new clamp on meter I read 54 amps on each 1/0 wire between batteries.  (4 Costco GC bats.)  But on the final positive 1/0 wire going to the inverter it reads 64 amps. Why?


  • mike95490mike95490 Solar Expert Posts: 8,068 ✭✭✭✭✭
    Were you reading any inverter loads on the wire?   Did you re-zero the meter between readings - stray magnetic fields affect clamp-on meters and each reading should be zeroed.
    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

    gen: ,

  • BB.BB. Super Moderators, Administrators Posts: 28,315 admin
    Also, remember that there is positive and negative current flow (if you "flip" the meter clamp, the -/+ sign will flip for DC current measurements).

    You could have:

    -54 amps from the battery bank (discharging)
    -64 (or +) going to the AC inverter DC input
    +10 amps from the charge controller (as an example)
    64 amps inverter = 54 amps from battery bank + 10 amps from charge controller

    Or it could be:
    +54 amps battery charging
    +118 amps from solar charge controller
    -64 amps to AC inverter
    64 amps inverter = 118 amps charge controller output - 54 amps charging battery bank

    Both are possible answers--We are just missing the battery charger (if turned on running) value (unless you have a very large array, 118 Amps is probably way more than your system can produce).

    Note, you did not say if this was a 12 volt or 24 volt battery bank (2s x 2p 6 volt Costco batteries for 12 volt bank, or 4s x 1p for 24 volt bank).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Chris11Chris11 Registered Users Posts: 71 ✭✭
    edited June 2018 #4
    Thanks guys.

    Mike....I didn't even know it could be  I'll look next time I'm at the property.  And yes, there was a load, I was charging my Plug in Prius that draws 12 amps @ 110 to 120 volts.

    BB....I'll bet it was number one.  I  never even thought about what the array was putting in.  And it was cloudy so 10 amps makes sense.  I didn't know flipping it would change the polarity reading....I'll try that.  
    The most I've ever seen on the CC is 42 amps....and that was today.  I assume the array was cold from the clouds (and rain) , the batteries had been draining, then suddenly the clouds parted for a few minutes and I read 42 .  That's the most I've ever seen.  The previous high was 38 amps.  Oh, and it's a 24 volt system.

    Thanks again for the education.
  • BB.BB. Super Moderators, Administrators Posts: 28,315 admin
    Measuring current polarity is kind of a pain with DC current meters. If the meter is "facing" the battery bank (say the LCD display)--Is a + current reading charging or discharging the battery bank (I can never remember)?

    Generally, I just measure the current from the charging source, discharging source, and the battery and they should all "add up". Or just measure two, and the third is the difference (i.e., alternator/solar charger/etc. never discharges battery bank, and standard inverter never "charges" the battery bank).

    When you get the real fancy stuff like an inverter-charger--Then paying attention to which way the meter clamp is facing matters.

    That is a lot of current for a 24 volt @ ~200 AH flooded cell lead acid battery bank... C/8 would be a nice continuous max load, C/5--Max load for not too long, and C/2.5 maximum surge load:
    • 200 AH / 8 = 25 Amps max continuous (8 hour discharge rate)
    • 200 AH / 5 = 40 Amps maximum current (5 hour discharge rate--Batteries may support for 1-2 hours???)
    • 200 AH / 2.5 = 80 Amps maximum surge current (seconds to minutes)
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 28,315 admin
    Also, s quick check of battery voltage gives a sanity check. Over 13.x volts is charging. Less than 12.7 volts is discharging.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Chris11Chris11 Registered Users Posts: 71 ✭✭
    Once I start charging the car the voltage starts dropping....according to the CC.   The inverter, a cheap Chinese that I'm very happy with since it gives me no problems, shuts off.....(don't yell too loud at me) at 21.5 volts.  So I shut off the inverter, allow the bats to recharge from 1/2 to 1 hour, then finish charging the car.  It usually takes just twice on  a sunny day.  If it's cloudy like today the car doesn't get a full charge since I don't have the time to go through the on/off/on/off procedure more.  Every day I get to the property the bats are back to float...if it's been cloudy sometimes it's still in absorb.  I force bulk and start all over. 

    The bats seem to be holding up...they've always been around 1300 per cell.  Today I had to upgrade some wiring in preparation for adding 2 more panels and I checked the cells again before I turned on the inverter and they were still at 1300 inspite of me abusing them.  When the inverter signalled 21.5 volts an hour later I checked the cells again.  1235 to 1240.  I fully expect to have to replace them earlier than if I treated them "nicely" but I'm 72 and I'm simply making certain that they're not going to outlast
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