A little confused. Pretty sure it's something simple, but still new.

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Offgridandlovingit
Offgridandlovingit Solar Expert Posts: 38 ✭
in Solar Beginners Corner #1
Hi guys. I bought some new panels the other day and a combiner box that had been modified to include an amp meter and voltage meter right in the case. Pretty slick setup. Here is the problem though. When I connect the volt meter, it shows my 21v input like it is supposed to. However when I connect the amp meter as well, it starts showing amperage, but no voltage anymore...Best I can tell, it is killing the voltage all the way through, as once I do that, my multimeter no longer shows voltage on the lines out of the box. It doesn't seeem to matter which set of wires I connect to which meter, they have the same effect. I also checked by flipping the disconnects one at a time and it doesn't seem to be isolated to a single panel either...what am I doing wrong? Thanks in advance.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: A little confused. Pretty sure it's something simple, but still new.

    What are the "lines out of the box" connected to? If nothing it should show no Amperage.

    Basically the Volt meter would be connected across (+) and (-) and will read Voc under almost any amount of illumination on the panel(s). The Ammeter would be connected in series with the positive output from the combiner box and would show nothing unless the panels are illuminated sufficiently to produce current and there is some load on the output of the combiner box.

    If you connected the Ammeter across (+) and (-) you've created a short across the panels which will read current produced. This would pull the Voltage down to zero because you've just shorted the panel(s) and the meter is reading Isc.
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  • Offgridandlovingit
    Offgridandlovingit Solar Expert Posts: 38 ✭
    #3
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    Re: A little confused. Pretty sure it's something simple, but still new.

    Thanks. Yeah, that's pretty much exactly what I did. I had the meter connected (+) and (-) just like the volt meter. The joy of buying a used setup like that. No instructions. As for the lines out of the box, sorry I wasn't more clear on that. The lines that were coming out were the ones that will be going to my charge controller. I don't have them connected yet. Maybe you can clear this up for me, because I definitely don't have it connected correctly. The wires from the panels come in to the combiner box. (+) wires go to the 3 breakers, and (-) wires go to an 8 hole bus bar. Then it has a large lug on the end of the bus bar and a large lug that is connected to the breakers. These would be the main connections feeding out to the charge controller. That is basically the setup inside the box. Then the cover has an analog ammeter and volt meter as 2 separate meters attached to it. In order to get accurate readings from both the ammeter and volt meter, how would I need to wire them into the rest of the box? Sorry to even have to ask this, as I am sure it is very basic, but I don't really have much of a background in electricity, so I am learning as I go. Thanks for your patience.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: A little confused. Pretty sure it's something simple, but still new.

    The Voltmeter is easy: positive to the positive bus bar (the one the breakers attach to with the big lug to feed the charge controller) and negative to the negative bus bar. This will measure whatever Voltage is present on the bus bars that connect to the charge controller. With all breakers off it will read zero.

    The Ammeter can be a bit more difficult. The first thing you have to do as ascertain its type and range. Some are "direct read" like those used in vehicles: the whole output is fed in one side and out the other. Some require a shunt and connect across it. If it is the first type and does not have a range that will encompass the Isc from all panels in parallel don't use it; it will burn up.
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  • Offgridandlovingit
    Offgridandlovingit Solar Expert Posts: 38 ✭
    #5
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    Re: A little confused. Pretty sure it's something simple, but still new.

    I'm pretty sure it is the first type. It has a 30A range, and right now I am only connecting the 2 100w 12v panels that I got the other day to it, so it should be ok I would think. If I am not mistaken I think they are rated at 5.63A Isc each, so well under the 30A that it can show. So I just connect the + to it and then go from it out to the controller instead of it being a separate set of wires?
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  • Offgridandlovingit
    Offgridandlovingit Solar Expert Posts: 38 ✭
    #6
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    Re: A little confused. Pretty sure it's something simple, but still new.

    and to be fair, I don't really need the Ammeter working. It was just a cool bonus feature on the combiner box, since I got the box including both meters and 3 breakers for less than most of the combiner boxes alone that I had looked at. If I do end up going above that 30A range I will just have to unhook it.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
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    Re: A little confused. Pretty sure it's something simple, but still new.
    Offgridandlovingit wrote: »
    I'm pretty sure it is the first type. It has a 30A range, and right now I am only connecting the 2 100w 12v panels that I got the other day to it, so it should be ok I would think. If I am not mistaken I think they are rated at 5.63A Isc each, so well under the 30A that it can show. So I just connect the + to it and then go from it out to the controller instead of it being a separate set of wires?

    Yes: the Ammeter would go in series with the positive (or negative) feed to the charge controller. Note that this is probably a "zero and up" meter rather than a "center zero" meter which means it can be connected on either side. If it is a digital meter it won't matter; it should just show "negative current". If it is analog and you connect it wrong for polarity it will damage the meter as the current tries to drive the needle below zero.
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  • Offgridandlovingit
    Offgridandlovingit Solar Expert Posts: 38 ✭
    #8
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    Re: A little confused. Pretty sure it's something simple, but still new.

    Awesome. Thanks a lot for your help. I will try this and in the morning make sure that everything is working like it should, but based on what you have told me, that sounds like exactly what I need to do.
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  • Offgridandlovingit
    Offgridandlovingit Solar Expert Posts: 38 ✭
    #9
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    Re: A little confused. Pretty sure it's something simple, but still new.

    Oh, I had one more question, if you don't mind. Would shorting the system the way I was doing by connecting the Ammeter in parallel instead of in series cause it to show more amps than the panels are rated to produce? The reason I ask is these are 100w panels, but when I had it connected incorrectly it was showing almost 16 amps of current from the 2 panels, even though they are only rated at 5.63 amps each.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: A little confused. Pretty sure it's something simple, but still new.
    Offgridandlovingit wrote: »
    Oh, I had one more question, if you don't mind. Would shorting the system the way I was doing by connecting the Ammeter in parallel instead of in series cause it to show more amps than the panels are rated to produce? The reason I ask is these are 100w panels, but when I had it connected incorrectly it was showing almost 16 amps of current from the 2 panels, even though they are only rated at 5.63 amps each.

    It well could. For one thing a panel's Isc rating (current short circuit) is higher than its Imp rating (current maximum power). Usually this difference isn't more than half an Amp. Sometimes certain insolation conditions can cause a panel to produce higher than rated current. Finally, the Ammeter itself may not be that accurate.
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  • Offgridandlovingit
    Offgridandlovingit Solar Expert Posts: 38 ✭
    #11
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    Re: A little confused. Pretty sure it's something simple, but still new.

    That's kind of what I figured. These are the panels http://www.mwands.com/index.php?main_page=product_info&cPath=55_75&products_id=608. When I saw that current reading I was kind of blown away, because that would put them at about 8 amps a piece. Considerably higher than the ratings. Guess we will see for sure once I get everything hooked up properly and can monitor it for a few days.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #12
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    Re: A little confused. Pretty sure it's something simple, but still new.
    Offgridandlovingit wrote: »
    That's kind of what I figured. These are the panels http://www.mwands.com/index.php?main_page=product_info&cPath=55_75&products_id=608. When I saw that current reading I was kind of blown away, because that would put them at about 8 amps a piece. Considerably higher than the ratings. Guess we will see for sure once I get everything hooked up properly and can monitor it for a few days.
    Hmmm. 8A is a lot more than 5.63A (Isc for the module), like over 40% more. That's more than I would think could be explained by excess insolation.
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  • Offgridandlovingit
    Offgridandlovingit Solar Expert Posts: 38 ✭
    #13
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    Re: A little confused. Pretty sure it's something simple, but still new.

    Well, if the ammeter is correct, then these panels are producing seriously more power than anticipated. Got it hooked up correctly and they are still showing around 16-17 amps from the pair.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #14
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    Re: A little confused. Pretty sure it's something simple, but still new.

    In general, solar panels are pretty good at "reporting" the exact amount sun falling on the solar cell/panels (a shorted panel should be within 5-10% of the value of the solar radiation * panel conversion efficiency of somewhere around 10-18%). And the output current is not affected by the panel temperature very much (output current rises very slightly with increasing cell temperature).

    So--If your panels (array current) are outputting much more than their Isc rating... Then either you have a lot more sun than expected (reflections from sand/water/snow), or your current meter is not calibrated/configured correctly.

    If this is the output to the battery of an MPPT type charge controller, then it is very easy to see that:

    Vmp*Imp*0.95 controller eff = Vbatt-charging*Imp-battery charging.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Offgridandlovingit
    Offgridandlovingit Solar Expert Posts: 38 ✭
    #15
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    Re: A little confused. Pretty sure it's something simple, but still new.

    Thanks Bill. I don't have an MPPT charge controller, so not quite as easy to verify, but I am assuming the meter is off. I can't imagine a company would be selling 140w panels at 100w prices.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #16
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    Re: A little confused. Pretty sure it's something simple, but still new.

    Nope--If they are crystalline panels, they will usually be somewhere in the +/- 5% range of accuracy (of course, the "sun" and the weather is probably going to be "more variable" than the panels).

    However, if these are thin film panels--It is not unusual for the panels to have much higher output over the first few months. The panels "burn" in to specifications in about a ~3-6 month period (to lower output values that will remain relatively stable over the life of the array).

    Mono Crystalline panels can also have a "burn in" effect--But that is something on the order of 3% reduction in power over the first year.

    It is not unusual for Solar Appliances to have a 5-10% error in their reported readings... And in some cases 30% error. The "errors" do not affect the operation of (for example) and MPPT Charge Controller (which are doing A/B current/voltage measurements over a fraction of a second to a few minute periods--Absolute accuracy is not required). And for cost savings (and efficiency) the values that they report have some error in them.

    From years past, it seemed the errors (if present) typically over estimated the current from solar charge controllers (i.e., +5 to +10% errors). Almost nobody "complains" if their solar array/controller are doing "better" than expected. If the controller erred to the -30%--you can bet there would be a whole bunch of phone calls to tech support.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Offgridandlovingit
    Offgridandlovingit Solar Expert Posts: 38 ✭
    #17
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    Re: A little confused. Pretty sure it's something simple, but still new.

    Agreed. Very rarely will anyone complain about getting errors in their favor. The only thing about it that kind of worries me is, if it is accurate, I may have to have a larger charge controller than expected in order to expand my system further. That wouldn't be a bad thing either though. I am still learning how to check the different performance aspects of my system, so I guess we will see. I was thinking that at 5.63 Imp, I could run 5 of those panels no problem on my 30A charge controller, but if they are in fact peaking closer to 8-9A each, 3 is going to be about the limit for both that gauge and the charge controller. I am planning on upgrading to an MPPT charge controller eventually anyway, so just interesting observations at this point.
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