Using a Multimeter

SurfpathSurfpath Solar Expert Posts: 439 ✭✭✭
My new panels and combiner box are all wired up.
I want to "flip the switch" & turn on my PV. But before I do so I'd like to test my total panel voltage (at the FM charge controller's PV + and -).

This may be a silly question, but can I safely use my multimeter to do this? I have a Ancor? meter that has 2, 20 and 200 and 1000 volt selections on the voltage portion of the dial.

Suggestions appreciated.
SP
Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using a Multimeter

    No reason why not. Except that without any load on you will be reading Voc which isn't particularly telling.
    Just be sure to select the range that is likely to cover the anticipated string Voltage.
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Using a Multimeter

    If the "switch" is a disconnect between charge controller and panels then there will be no voltage on the charge controller terminals before you "flip" it. If you want to measure it anyway you can do that at combiner box. You can also measure individual strings. When measuring with multimeter, select a DC (as opposed to AC) range.
  • SurfpathSurfpath Solar Expert Posts: 439 ✭✭✭
    Re: Using a Multimeter
    NorthGuy wrote: »
    If the "switch" is a disconnect between charge controller and panels then there will be no voltage on the charge controller terminals before you "flip" it. If you want to measure it anyway you can do that at combiner box. You can also measure individual strings. When measuring with multimeter, select a DC (as opposed to AC) range.

    Yes, you are right. I would not get a measurement in the CC if the breaker is off. But I believe I could put the + at my GFDI (where the positive PV comes in from the combiner box on the roof) and the - at the combiner box to get an overall voltage reading.

    How would I measure individual strings (I have a fused MNDC)? Sorry if this is all mundane stuff, but I don't want to risk getting zapped. 8)
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using a Multimeter

    You can only measure individual strings by disconnecting them. How many strings do you have? Where are they combined? Usually on the roof.
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Using a Multimeter
    Surfpath wrote: »
    How would I measure individual strings (I have a fused MNDC)?)

    You put - on the negative bus, and + where the wire from the panel connects to the fuse.
    Surfpath wrote: »
    Sorry if this is all mundane stuff, but I don't want to risk getting zapped. 8)

    Make sure your multimeter is set to measure Volts.
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Using a Multimeter
    You can only measure individual strings by disconnecting them.

    Yes, that's right. You would need to take the fuse for the string being mesured off. Make sure they're not connected to the controller, or it may arc. It would be easier if you had breakers.
  • SkippySkippy Solar Expert Posts: 308 ✭✭
    Re: Using a Multimeter
    Surfpath wrote: »
    Yes, you are right. I would not get a measurement in the CC if the breaker is off. But I believe I could put the + at my GFDI (where the positive PV comes in from the combiner box on the roof) and the - at the combiner box to get an overall voltage reading.

    How would I measure individual strings (I have a fused MNDC)? Sorry if this is all mundane stuff, but I don't want to risk getting zapped. 8)

    What I did with my system, was too open up the combiner box, and test each connection 1 by 1, so for my 12 V system, with my tester set at 12 V, I disconnected panels 2 and 3, and tested number 1 - then disconnected number one, connected number 2 and tested - then removed number 2 and connected number 3 and tested again. The big thing I was worried about, was shorting out the panels, but the quick connects that came with my panels are protected from that happening. . ..
    2 - 255W + 4 - 285W PV - Tristar 45 MPPT CC / 3 - 110W PV -wired for 36V- 24V Sunsaver MPPT CC / midnite bat. monitor.
    1 KW PSW inverter 24V / 2.5 KW MSW inverter-24V ~ 105 AHR battery.
    3 ton GSHP.- 100 gallon warm water storage / house heat - radiant floor / rad
    9 -220W PV - net meter - Enphase inverters and internet reporting system.
    420 Gallon rain water system for laundry.***  6" Rocket Mass Heater with 10' bed for workshop heat.
    Current project is drawing up plans for a below grade Hobbit / underground home.
  • SurfpathSurfpath Solar Expert Posts: 439 ✭✭✭
    Re: Using a Multimeter
    Skippy wrote: »
    What I did with my system, was too open up the combiner box, and test each connection 1 by 1, so for my 12 V system, with my tester set at 12 V, I disconnected panels 2 and 3, and tested number 1 - then disconnected number one, connected number 2 and tested - then removed number 2 and connected number 3 and tested again. The big thing I was worried about, was shorting out the panels, but the quick connects that came with my panels are protected from that happening. . ..

    Update: All good. Before flipping the PV breaker to on for the first time, I measured overall VOC with my multimeter by placing the + on the GFDI (breaker) and the - at the CC. Got ~ 104V in full sun (was expecting that from each string). I figured all was well so turned the PV on (this was about 3 days ago) and got 24+ amps, which I was expecting +/- from all three strings combined (each string = ~7.35Isc). I'll give more of an update on the actual CC charging later.
    Thanks for the help with this pretty basic stuff.
    -SP
    Outback Flexpower 1 (FM80, VFX3048E-230v, Mate, FlexNetDC) 2,730watts of "Grid-type" PV, 370 AmpHrs Trojan RE-B's, Honda 2000 watt genny, 100% off grid.
  • PhotowhitPhotowhit Solar Expert Posts: 5,655 ✭✭✭✭✭
    Re: Using a Multimeter
    NorthGuy wrote: »
    ... It would be easier if you had breakers....

    ...or a clamp meter to measure output under load.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • vtmapsvtmaps Solar Expert Posts: 3,739 ✭✭✭✭
    Re: Using a Multimeter
    Surfpath wrote: »
    Before flipping the PV breaker to on for the first time, I measured overall VOC with my multimeter by placing the + on the GFDI (breaker) and the - at the CC. Got ~ 104V in full sun (was expecting that from each string).

    That's unusual. Usually the PV breaker is between the combiner box and the GFDI. If you are getting Voc at the GFDI before you close the PV breaker, something may be wired wrong.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Using a Multimeter
    NorthGuy wrote: »
    Yes, that's right. You would need to take the fuse for the string being mesured off. Make sure they're not connected to the controller, or it may arc. It would be easier if you had breakers.
    You shouldn't use breakers as DC load break switches, either.
  • NorthGuyNorthGuy Solar Expert Posts: 1,913 ✭✭
    Re: Using a Multimeter
    ggunn wrote: »
    You shouldn't use breakers as DC load break switches, either.

    Probably. However, most DC breakers do have anti-arcing protection. If you use a breaker as a switch 5-10 times during its lifetime, it shouldn't hurt it.

    I have 14 DC breakers in my system. Not counting initial turn-on, I used a breaker as a switch 6 times, mostly because I had problems wih components.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using a Multimeter

    It is safe to use breakers as disconnects. Even DC ones under load.
    It is not a good idea to use them as switches.
    Yes, there's a difference. It's how often it gets flipped ON/OFF.
  • RybrenRybren Solar Expert Posts: 351 ✭✭
    Re: Using a Multimeter

    Okay, I'll bite.

    What is the difference between a disconnect and a switch if any (beside On/Off frequency)?

    And...

    What would you use as switch between the array (~60Vmp, 74Voc) and the CC?
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Using a Multimeter

    From my point of view, circuit breakers are "low duty" cycle switches... Basically, from what I have seen, they wear out pretty quickly if used daily. If you keep a spare, I would say why not use it and see how it works for you.

    I would monitor how the breaker sits in the panel/holder too. A fair number seem to have "too much slop" and I would worry about wear and tear on the bus bar/wire connection, etc. too.

    What would be a good high current switch--I am not really sure I have have seen any reasonably priced ones in large DC systems. The boat 1/2/both battery switches, I would probably put them on the low duty cycle side of the list too.

    Perhaps look at marine equipment. A fair number of boats use larger DC systems, perhaps you can find some salvage switches there. Or look at marine power websites such as BlueSea.com.

    I have always like the concept behind their bi-stable relays, but I have never used one. I just was never in a job/place that needed to use these types of high current DC switches for daily use.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Using a Multimeter
    Rybren wrote: »
    Okay, I'll bite.

    What is the difference between a disconnect and a switch if any (beside On/Off frequency)?

    Not a lot. :p
    And...

    What would you use as switch between the array (~60Vmp, 74Voc) and the CC?

    I wouldn't, as you do not need to turn the array ON/OFF even yearly, much less multiple times per day. I don't even have a disconnect on mine because all I have to do is cover them to drop the current then pull the plug. I've had to do this once since I put the array up five years ago, and that was because I was re-roofing.
  • RybrenRybren Solar Expert Posts: 351 ✭✭
    Re: Using a Multimeter

    Thanks guys - looks like I was overthinking - again. :p
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