Measurement of DC current

Hello, can I use the SENSE SOLAR CT to measure DC current coming from the PV?

My SYSTEM is not GRID TIED because we don’t have net metering tariff and our prepaid meter wouldn’t accept power export through it.

CT sensors, whether ours or anyone else’s, cannot measure DC current. That’s just an aspect of how they work. They rely on alternating current.

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Are you sure about that?
Fluke meter clamps do.

@samwooly1

Only DC clamps measure DC current and they are 2-3 times more expensive than standard A/C current transformers. My Fluke DC clamp on was $195 a decade ago while an A/C clamp on was about $35-45.

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Not grid tied and not tied to your house panel providing AC?

Meaning: You don’t have an inverter (DC-to-AC)?

If that’s the case you would also have the issue of a DC CT potentially producing the correct mV output (corresponding to the current) but the necessary supply to Sense is 240V and matches an assumed inverter output voltage.

In theory if you can match the mV input range AND wangle the voltage multiplier you can make something workable with a non-Sense clamp. But that’s a stretch that would probably void warranty and support.

But somehow I suspect you have an inverter.

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I’ve got the same one @dwleckie
They haven’t come down much in price either but @RyanAtSense stated nobody’s clamps measured D/C.
That threw me off

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You guys made me go look, since I know that a transformer is useless when measuring DC currents because a transformer only passes dI/dt - that’s why they are used for DC isolation. The jaws/clamp on a DC measurement device do not contain a transformer - they contain a near loop made out of metal with a hall effect sensor embedded in the gap. They look the same from the outside, but the insides are very different.

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@kevin1

:rofl: LOL! You just sent me on a 40 year old memory from Navy electronics tech school !!

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Indeed, I do have a hybrid inverter (off grid) which has two inputs, one for the 240V grid AC supply and the other for the DC PV input vide inbuilt MPPT. The issue is that the output could either be PV or
GRID or a combination of PV and GRID. Other configurations which include battery storage also exist.

Interesting.

Are you the first on the forum with this setup? Hmmm.

Well there is a fudge that will get you the numbers you’ll need for tracking while giving you full detection and (embedded) solar tracking. Or maybe I didn’t have enough coffee yet?

  • Put the Main CTs on the inverter (hybrid) output. This is the load-side that will need detection, but as you say will be grid, G + PV.

  • Put the solar CTs on the grid feed, which isn’t doing any detection.

  • Your grid bill (GB) numbers will give you the monthly solar output: G + PV - GB.

There may be a mod Sense can do to your processing that would give you the real-time PV and G calculation but that’s just me being optimistic.

The problem is the detection is going to be thrown during solar generation without any real-time processing.

Ahhh, coffee kicking in, just realized there’s a partial solve here: You need to run MULTIPLE wires through the Solar CTs:

  • Put Solar CTs on your hybrid inverter output and also run the G wires backwards through the CTs to subtract the grid current. Might be tricky mechanically but that would work.

  • Put the Main CTs on the same hybrid inverter output … which will still be G + PV, but at least the Solar waveform will be correct.

Anybody have a better idea?

Get a different inverter?

What’s your total PV wattage? What’s the MPPT model?

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My 2 cents… Or maybe a nickel…

The best way to measure DC current is with a shunt. You wire it in your DC circuit just like a fuse. You can put in on the positive or negative side. Put it right on the last ‘leg’ of your battery bank. Right on the battery post if possible. You can make long runs of the leads back to meter. It is only reading millivolts and does not carry any of the load.

There are AC and DC ‘meter clamps’. Very pricey. Goto a welder or automotive supply. I used a clamp on meter for years in welding and have used one on a car battery to check the draw on a starter motor or the charging system.

Here is a very cheap shunt for 50 amps if you choose. Later…Gerry

https://www.jameco.com/z/DFR0245-R-DFRobot-LED-Current-Meter-50A-Red-_2190776.html

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Actually thinking about this further, and it could work without any mods to your gear or the need for DC shunts and whatnot as I suggested above by running the grid wires back through the Solar CTs. This is effectively “Config B” here

Hey Ixu,

I believe I might be the only one in Africa with the Sense energy monitor. While Grid tie may be the best scenario, the current electric regulations and metering infrastructure does not allow grid feed in from PV generation.

Your Idea of running back the grid feed through the solar CT appears to be the best so far as it will not require a lot of support from the Sense technical team. Thanks a lot, man! I was literally at my wits end on what to do so as to make solar monitoring via Sense possible.

I will give it a try and give you feedback; however, I will need CT extension cables to realize the setup.

Cheers

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Hope it works out @johnwekesa, keep us up-to-date … sounds like you may be able to tell a story one day and either post it in SenseSaves or the Community.

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Hi Ixu!

The system! worked as per your suggestion/ direction. I’m now able to accurately measure my solar energy production/consumption inclusive of battery storage that is normally discharged in the evenings.

Please the snapshots!
image|375x500

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Excellent!

The only thing left to do now is harvest energy from the night!

https://www.cell.com/action/showPdf?pii=S2542-4351(19)30412-X

Wind and water can provide power at night.
They are not always reliable.

We need battery technology to take a quantum leap to make them more viable and reliable, and less expensive for personal use.

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Or a really efficient grid … it’s always sunny somewhere on Earth!.

That “Generating Light from Darkness” paper in my previous post is quite fascinating. For those who have access, here’s the related NYT article:

The article is very interesting as it presents entirely new possibilities of powering the globe… Thanks for sharing…

But only 4W vs 200W+ for a solar panel. Still transformative in places without a grid !