DC power meter suitable for a data logger?

[Maury Markowitz]

I'm installing a multi-part solar PV system to do a head-to-head test
of three different panels. I'll gang the panels into an AC inverter
that I already have, and drive a test load of four 100 watt light
bulbs. My installer wants to grid-tie and pay for the data collection
at least, but I haven't made my way through the maze of local regs
yet.

Since the power is being ganged parallel into the inverter I'm going
to need to log upstream on the DC side. I'll likely end up with the
4-
channel HOBO (U12) as the basic collection system, but they don't
sell
a DC power meter.

Can anyone suggest a DC power metering solution with a suitable
output? The U12 supports "any third-party sensor with 4-20mA or 0 to
2.5 volt DC output".

Thanks!

Maury

 

[Wim Lewis]

I'm installing a multi-part solar PV system to do a head-to-head test
of three different panels. [....]
Since the power is being ganged parallel into the inverter I'm going
to need to log upstream on the DC side. I'll likely end up with the
4-channel HOBO (U12) as the basic collection system, but they don't
sell a DC power meter.

Can anyone suggest a DC power metering solution with a suitable
output? The U12 supports "any third-party sensor with 4-20mA or 0 to
2.5 volt DC output".

How much current are you expecting to measure? (Hmm, 400W at (wild guess)
48VDC = 8A total, 2-3A per panel?) Are you looking for an off-the-
shelf solution or a circuit?

 

[Maury Markowitz]

How much current are you expecting to measure? (Hmm, 400W at (wild guess)
48VDC = 8A total, 2-3A per panel?) Are you looking for an off-the-
shelf solution or a circuit?

About 150 to 250 W for the first install, adding another 75 or so when
the third panel goes up. VDC should be 12 to 25, I can wire parallel
or series into the inverter (although parallel strikes me as simpler
at first glance), so let's say 15 VDC at 10 amps.

Definitely need something off-the-shelf, the logger is going to be
positioned semi-protected so it will have to be well sealed.

Maury

 

[Jasen Betts]

Can anyone suggest a DC power metering solution with a suitable
output? The U12 supports "any third-party sensor with 4-20mA or 0 to
2.5 volt DC output".

could you measure voltage and current separately and then combine the
results to get power? or is that going to fill up the data logger too
fast?

Bye.
Jasen

 

[Maury Markowitz]

could you measure voltage and current separately and then combine the
results to get power? or is that going to fill up the data logger too
fast?

Absolutely, in fact that would be preferable. Although it's not
important to me, the voltage curves are very important for off-grid
battery-charging applications. Existing polysi panels are well
characterized in this regard, other technologies, not so much.

Maury

 

[Maury Markowitz]

Use an analog multiplier such as the AD835 or AD633 to provide the E*I product,
scale the output as appropriate and feed it to the logger.

Well this just moves the problem. I still need to actually measure the
E and I.

Maury