Hyper VOC on Midnite Classic 200

[J762]

Question- How do I have 211V with a string of six LG 225W panels with a Max voltage output of 29V?

The Midnite Classic 200 tells me I have 211V, my voltmeter tells me I have 211V, but standard math tells me I should only have 174V. Panel temperature was 60 degrees F today in Central Texas. Even adding a 30 degree correction factor I should only have 191V.

Any thoughts?

Thanks in advance.

J762

[inetdog]

Question- How do I have 211V with a string of six LG 225W panels with a Max voltage output of 29V?

The Midnite Classic 200 tells me I have 211V, my voltmeter tells me I have 211V, but standard math tells me I should only have 174V. Panel temperature was 60 degrees F today in Central Texas. Even adding a 30 degree correction factor I should only have 191V.

Any thoughts?

Thanks in advance.

J762

First of all, the panel specifications do not list a maximum output voltage of 29V. They list a voltage for maximum power output (V_MPP) of 29V and an open circuit voltage of 36.3V.
If the Classic 200 is doing a perfect job of Maximum Power Point Tracking AND the batteries are in Bulk state allowing the Classic to send maximum power to them AND the potential array power is less than the maximum amount the Classic can handle, you should expect to see the V_MPP for the current temperature conditions. (V_MPP does not change much with light level, but if sensitive to temperature, and 60F is lower than the nominal test conditions.)
If any of these conditions is not met, then the Classic will try to operate the array at a power less then its maximum possible output under those light conditions. And it will do that by decreasing the amount of current it draws, letting the output voltage from the array rise.

What you see is not unusual or unexpected.

BTW, welcome to Solar Panel Talk, if you have not been officially greeted yet.

[mapmaker]

Question- How do I have 211V with a string of six LG 225W panels with a Max voltage output of 29V?

As inetdog points out, the voltage of your panels is 36 volts, not 29. You are pushing your luck with such a high voltage. What voltage is your battery bank? Hypervoc on your classic is 200 + Vbatt. If your battery is 24 volts you will exceed hyperVoc at 224 volts, 248 volts if you have a 48 volt battery.

Even if you have a 48 volt battery you are living too near the edge, IMO.

Why do you have all 6 panels in series? Your classic will run cooler and more efficiently if you make two parallel strings, with three panels (in series) in each string. If you have a 24 volt battery you can make three parallel strings with two panels (in series) in each string.

--mapmaker

[inetdog]

Why do you have all 6 panels in series? Your classic will run cooler and more efficiently if you make two parallel strings, with three panels (in series) in each string. If you have a 24 volt battery you can make three parallel strings with two panels (in series) in each string.

--mapmaker

If you go with two strings, you will not need individual string fuses on the input side of the combiner. If you go with three or more parallel strings you will need to use one fuse per string.

[mapmaker]

If you go with two strings, you will not need individual string fuses on the input side of the combiner. If you go with three or more parallel strings you will need to use one fuse per string.

Fuses? yuck! I like circuit breakers. I like combiner boxes. A combiner is a good place to put a lightning arrester outside your home. Circuit breakers on each string very useful for troubleshooting or servicing a system. I recommend circuit breakers on even two strings.

--mapmaker

[inetdog]

Fuses? yuck! I like circuit breakers. I like combiner boxes. A combiner is a good place to put a lightning arrester outside your home. Circuit breakers on each string very useful for troubleshooting or servicing a system. I recommend circuit breakers on even two strings.

--mapmaker

Circuit breakers are indeed fine, but make sure you get ones that are rated for DC. And some of the currently available DC breakers are polarity sensitive. So you get to choose whether to install them so that they will protect against a fault or so that you can use them as a switch. You can't have both with polarized breakers.

[mapmaker]

some of the currently available DC breakers are polarity sensitive. So you get to choose whether to install them so that they will protect against a fault or so that you can use them as a switch. You can't have both with polarized breakers.

Yes indeed... and I find it peculiar that Midnite installs their combiner breakers as switches rather than overcurrent devices, yet the purpose (NEC) of having breakers on each string is to protect against overcurrent.

--mapmaker

[inetdog]

Yes indeed... and I find it peculiar that Midnite installs their combiner breakers as switches rather than overcurrent devices, yet the purpose (NEC) of having breakers on each string is to protect against overcurrent.

--mapmaker

There is some rational basis for it: The fault current going back into a string which has a fault of some sort that allows reverse current will be current limited and hopefully rare. The result of the combination is that the breaker will probably be successful in breaking the arc, but with some possibility of contact damage. The switch function is more likely to be used often and therefore contact degradation would be unacceptable.
On the other hand, a circuit breaker that can only interrupt a fault once is in many ways similar to a fuse.