measuring amps

ws9876ws9876 Solar Expert Posts: 372 ✭✭✭
I have a Fluke 115 meter. You can measure amps on it using 2 plugs ,one for milliamps and the other is labeled 10A fused.
Does that mean you will blow the fuse if you are over 10 amps at all DC?
Also ,I want to measure the amps on a damaged solar panel. It has 9 amps at best and I expect to lose about 25% power due to the cracked
face on it and that I plan to put trim around it to hide the worst damage.That will block several rows of the 20 rows it has. BUt its still useful for 12v applications and in fact would probably still run a DC pump which will operate on 14-30v DC.
But they say you always measure amps times 1.4.
I can measure it just using the pos and neg with the panel in full sun,yes? WOuld you think it would be ok?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    As long as Isc is less than 10 amps, you should be fine (not Imp).

    There is a factor between DC current and AC current / 1.4 (sqrt of 2) conversion to DC value (RMS root mean square conversion).

    As long as you are messing DC amps, you will be fine.

    The problems with the panel, that can be a bigger issue. Watch for hot spots on the panel at full current.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ws9876ws9876 Solar Expert Posts: 372 ✭✭✭
    with some aesthetic trim pieces on the ends and some spider cracking I expect to lose about 25-30% of power.
    are hot spots still an issue then?
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    You have "9 amp cells" in series with "7 amp cells"... The "smaller cells/circuit path" could be heated--Especially if you try to draw more than 7 amps.

    And there is always the possibility of the cracks "growing" as the panels thermal cycle.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mvasmvas Registered Users Posts: 345 ✭✭✭
  • ws9876ws9876 Solar Expert Posts: 372 ✭✭✭
    I measured the voltage on the panel at 37v. But I couldnt get a reading on amps? I checked the fuse on the fluke and it doesnt seem to be discolored or anything... its a fat one..AM I doing it wrong??
  • mike_smike_s Registered Users Posts: 83 ✭✭
    Set to DC Amps? Probes in ground and 10A sockets? If you read a voltage, you should read some current. The manual shows how to test the fuse. If it's bad, they're around $10.

    I have a clamp meter which measures DC Amps. Unless I need really good accuracy, I always us that instead of my Fluke. You can get one for about $35, but watch closely - some only do AC amps with the clamp. The clamp ones are useful for solar, because as long as there's room to get it around a wire somewhere in the circuit, you don't need to disconnect anything to measure amps.
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    If you measure the resistance and voltage of your internal meter parts (i.e., 10 amp fuse, battery voltage), generally the item(s) need to be removed from the meter. If you use the same meter to "self measure" items while installed in the meter, you can get some very strange reads (if not damage).

    Using a small (alkaline/NiMH/etc.) battery + load (like a small test lamp) to see if your meter is measuring current (and you are using the meter correctly) is helpful too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ws9876ws9876 Solar Expert Posts: 372 ✭✭✭
    I didnt know the meter would work without the fuse....the fuse was bad..no continuity. Dont know how it blew.
    Is there a kind of micro circuit breaker 10-12 amps that I could put in there instead of a new fuse. They are WAY overpriced.
    Is it possible I blew it just touching the pos lead when I checked the amps in full sun...??I assume if the volts are good the amps will be too. But I will check it.
    This slightly damaged panel would be used alone and not even in a full sun mount so I am not especially worried about overheating.
    I found that MinWax Polycrylic coating does a decent job sealing the cracks and fractures.
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Yea--You are not the first person to "blow" the 10 amp current measurement fuse... Typically this happens when somebody has 10 Amp mode selected (one led plugged into 10 amp jack) and you try to measure voltage (battery bus, 120/240 VAC outlet, etc.)--The 10 amp fuse will pop right smartly. (I have few 10 amp fuses in my 40 year old DMM box--Have used one or two over the years).

    Another reason I like the Current Clamp Meters (DMM, AC/DC current clamp for our needs). You never can blow anything on the meter, and you can get an "arc flash" when touching a lead to terminals with "voltage source" vs you expecting to measure current (or the current is >> 10 amps). Current is only measured with the clamp (the leads are always "high resistance"--Ohm readings can be an issue). And you never have to "break" the circuit to measure current (much safer).

    You can find DC Current Clamp DMMs (really AC/DC clamp) meters for less than $50... If you are willing to spend a $100, this class is pretty nice (True RMS, lots of other measurements for debugging):

    https://www.amazon.com/gp/product/B019CY4FB4

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ws9876ws9876 Solar Expert Posts: 372 ✭✭✭
    There is  one for 30 bucks on ebay that doesnt look bad.
    I looked for a micro auto style  fuse holder that I could put a 10 a fuse in. I would solder leads onto a blown fuse and bring the leads outside the meter and epoxy the holder on the back of meter. Cant find a 50 volt.32v is too small.That should work.
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    These fuses look to be rated for 1,000 VAC. I guess this is the 11 amp version for most Fluke meters(?):

    https://www.amazon.com/Littelfuse-0FLU011-T-FUSE-FAST-ACTING/dp/9792307095 (1 psc)
    https://www.amazon.com/pieces-DMM-11-DMM-11A-Fluke-Digital/dp/B00MUTUPKO (5 psc)

    Using  a lower voltage fuse would seriously reduce the safety/protection of your meter...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ws9876ws9876 Solar Expert Posts: 372 ✭✭✭
    a 10 amp car fuse is a 10 amp fuse,no? As long as its DC and rated 50-100v.The panel is 38v so....
    I did order the ceramic replacement though for 2$. From China.
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Fuses have many different parameters that they are designed for/support.

    One of the biggest (besides blowing at the right Amperage) is how to stop current flow when the fuse opens. Basically, when the fuse (or breaker) opens, the gap starts to arc. Basically, any voltage over >~12 volts can create and sustain an arc. And DC voltages sustain arcs (much better than AC).

    A fuse for a car, may be designed to interrupt a 100 Amp maximum current at 32 volts. This is not good for the rated operating range for the Fluke meter...

    As an example, here are some of the specifications for the "correct fuse" (I think--Again, I have not found the Fluke meter specified replacement on Fluke.com):

    https://www.cesco.com/resources/pdf_86B/ID-SPE-v1-DMM-B-11A.pdf
    Specifications:
    ● Type: Fast acting
    ● Application: Multimeters only 

    Amperage Rating: 11A
    ● Voltage Rating: 1000 Vac, 1000 Vdc Interrupt Rating: 20 kAIC at 1000 Vac, 20 kAIC at 1000 Vdc ●
    ● Fuse Indicator: Non Indicating
    ● Packaging Type: Standard
    ● Diameter: 10 MM
    ● Connection: Ferrule end X ferrule end
    So--This fuse will not "fail" (explode, sustain arc, let more than ~11++ amp through for more than seconds/minutes) at 1,000 VAC/VDC and 20,000 Amps current (the typical pole mounted AC transformer for your home is rated at 10,000 Amps maximum).

    Vs a 12 volt automotive fuse:

    https://www.littelfuse.com/~/media/automotive/datasheets/fuses/passenger-car-and-commercial-vehicle/blade-fuses/littelfuse_micro2_datasheet.pdf
    Specifications MICRO2 MICRO2 Sn (Silver Plated) (Tin Plated)
    Voltage Rating: 32 VDC 32 VDC
    Interrupting Ratings: 1000A @ 32 VDC 1000A @ 32 VDC
    *Component Level Temperature Range: -40˚C to +125˚C -40˚C to +105˚C
    **System Level Temperature Range: -40˚C to +105˚C -40˚C to +85˚C 105°C and 85°C are typical system level temperature requirements.
    https://www.youtube.com/watch?v=Zez2r1RPpWY (knife switch AC vs DC arcing)
    https://www.youtube.com/watch?v=Cup5fMGaE2g (connecting DC breaker "backwards")

    Sorry to be so detailed about fuses and your Fluke meter... I just don't want to see you injured (or killed) if you are using your meter on a 240 VAC line and are measuring current (or have the meter probes plugged into the 10 Amp Socket).

    Meter Mfg. go through huge amounts of effort to design and build "safe meters".

    And I want to keep all of our members and readers safe too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mcgivormcgivor Solar Expert Posts: 3,074 ✭✭✭✭✭
    The rating of the fuse in a Fluke meter is to conform with the rating of the meter itself, using a fuse of lesser value will invalidate the meter category rating. Attached pdf from Fluke explains this in more detail.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • mike_smike_s Registered Users Posts: 83 ✭✭
    edited September 1 #16
    ws9876 said:
    I didnt know the meter would work without the fuse....the fuse was bad..no continuity. Dont know how it blew.
    Is there a kind of micro circuit breaker 10-12 amps that I could put in there instead of a new fuse. They are WAY overpriced.

    No. You want the same fuse. It's a safety issue, and the proper fuse is needed to maintain the safety ratings. If you don't care about that, you don't need a Fluke - send me your's and I'll send you a cheap meter which takes cheap fuses in return. I can even find one marked "CAT III 600V" (lots of them lie). Triplett, which used to be a respected name, will sell you a meter they claim is CAT III 600V, but which has NO protection in the 10A range! And one of those cheap 3AG sized fuses for the lower range. They say it needs "200 mA, 500 V", but good luck finding one which has that rating for DC, they don't exist. And how they can even try to claim a 600 V rating when spec'ing a 500 V fuse is a mystery.

    Want to guess what happens if you try to measure high voltage DC circuit with that one configured to measure amps? It will cost you more than a $10 fuse.

    The fuses Fluke uses are not overpriced, you can get one for ~$10 on Amazon, shipped (assuming US). You can get a pack of 5 for <$20. Meters which use the small, cheap fuses can be unsafe, especially with higher DC voltages.

    The cost does teach you to make sure the leads and settings are correct before every measurement. They're most often blown when someone tries to measure voltage when configured for amperage. Poof! The meter will try to warn to check, it beeps and displays info any time you change to/from current measurement.
  • jonrjonr Solar Expert Posts: 1,298 ✭✭✭✭
    edited September 1 #17
    > it needs "200 mA, 500 V", but good luck finding one which has that rating for DC, they don't exist.

    0ADAC0200-BE   Bel Fuse Inc.

    IMO, no replaceable fuse means nothing about voltage safety.  But replacing a meter due to excessive current would be really irritating.

    I am available for custom hardware/firmware development

  • mike_smike_s Registered Users Posts: 83 ✭✭
    jonr said:
    > it needs "200 mA, 500 V", but good luck finding one which has that rating for DC, they don't exist.

    0ADAC0200-BE   Bel Fuse Inc.
    Good find. Mouser says it's "New from this manufacturer." Looks like they just came out last year. Didn't exist last time I looked into it. 
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