# High voltage DC current measurement by inductance?

I'd like to incorporate a few permanent ammeters in a 600V DC circuit. I've found all sorts of nifty panel ammeters, both analog and digital, but most are rated to less than a tenth that voltage.

I have a clamp multimeter, so I know that it's possible to use the Hall effect to get decent current readings without dealing with the high voltage.

But for a permanent fixture: Are there any components that I can wire the high DC in (or through) to measure the current at a much lower voltage? I'm imagining something like this, with some convenient component taking the place of the "Clever Component":

simulate this circuit – Schematic created using CircuitLab

NB: Just because I'm thinking of inductance doesn't mean that has to be the mechanism by which this is achieved. All solutions welcome!

• The voltage an ammeter sees is dependent on its shunt resistance. You should be able to simply use a low shunt resistance. May 12, 2016 at 17:20
• Your ammeter will not see 600V, milivolts at most. Just use any of them.
– user76844
May 12, 2016 at 17:25
• @GregoryKornblum You still need to worry about insulation values for safety. I wouldn't want to run 600 volts into a 12 volt ammeter that my hand would get near. May 12, 2016 at 17:32
• Well, i assume no one touches 600V circuit. I mean, safety must be his priority anyway. With 600V circuit he must know what he does.
– user76844
May 12, 2016 at 17:35
• What range of currents do you need to measure? May 12, 2016 at 17:40

There are noncontact dc analog panel ammeters, I've seen one but I'm not sure where you get them from, they clip onto the cable and need no power, they are entirely passive and mechanical. Failing that, what's wrong with a regular analog ammeter? as long as the metal parts are well insulated from the user, there is no real voltage limit (the actual meter will only have a small voltage across its terminals even though the whole thing sits at a high voltage - just like birds on a power line). There are several manufacturers making active smd current shunts with isolation in the kV range (Avago is on that comes to mind). There are lots of 'clamp' meters that don't open (you get just the fully potted sensor), they have real good insulation (especially the LEM ones), they're pretty permanent (seeing as they get soldered to a pcb and the rings don't open)

A panel mount DC amp-meter with isolated power (120vac) is one easy way. Some of these meters offer a fine-trim control. Look at Simpson and Modutec meters on the web. Digi-Key, Allied and Mouser are possible sources.

For each 600VDC source each meter will need its own isolated supply, but it only needs to provide 10 watts at most. A 1M ohm resistor may need to be inserted from the common input to an isolated AC input power line, for each meter.

Each isolation transformer needs at least a 1500VAC isolation rating, but this is a typical value for well made transformers. Panel meters with a back-light and large display sizes can get expensive.

Because the DC amp-meter (panel meter) is isolated from the main AC line by a small isolation transformer, it does not 'see' the 600 VDC potential on it. Your source voltage is limited to the breakdown voltage of the isolation transformers, about 1500vac.

Just buy a DC amp-meter(s) with a 2 amp full scale rating and a 120vac power input, and a small 120vac isolation transformer for each meter. With 3-1/2 digits of resolution the smallest reading is 1mA. It is a direct reading and can be very accurate. No need to have 4-1/2 digits of resolution as the price gets expensive, unless you need accuracy down to 100uA.

• I can't figure out or find what you're describing, nor can I understand how it would be wired (or, if my guess of your wiring description is correct, then why it would be wired that way). Could you elaborate? May 13, 2016 at 1:59
• @feetwet. I added 2 more paragraphs to clarify the layout better I hope. I can try some drawings, but getting an image from OrCAD is not easy. If you take this path as a solution, I will help you best as I can. I am very familiar with these meters.
– user105652
May 13, 2016 at 4:20
• I think I get it now. Part of the confusion is that it appears you're describing an application to metering an AC circuit, whereas I'm talking about a DC circuit. (Of course, the isolated power to the ammeters could still be AC if convenient.) May 13, 2016 at 17:58
• @feetwet. You got it close. I was referring to DC amp-meters powered by 120VAC through an isolation transformer. The scaling would be as I mentioned in my last paragraph.
– user105652
May 13, 2016 at 18:28