"Dave, I can't do that" wrote in message
...
I have a 3d printer with a 12vdc-30A power supply (PS). The PS has a
common +/- rails with three screw connectors for positive and three
for negative. The printer has two sets (+/-) of wires coming from the
PS to a junction block. Then there are two sets of wires (+/-) going
to two screw terminals on the controller card.

I recently bought a clamp meter that does DC-Amps, pretty clever and
seems to be very accurate when compared with an in-line Amp meter.

So here's the issue.
If I clamp around one wire from the PS when both the heated bed and
nozzle are drawing current I get 11A on one wire and 9A on the other.
If I clamp around both wires I get about 14A so I am confused.

Can I clamp around both wires for a total current reading?
If I clamp one, is it showing a true reading?


ASCII Art

0-vdc ----+-+ +-+----- 12vdc [ PS
| | | | [ measure each 11A and 9A
| | | | [ measure both 14A
+---+ +---+
| | | | [ Junction block
+---+ +---+
| | | | [ measure each 11A and 9A
| | | | [ measure both 14A
Hotbed --+ | | +--
Nozzle ----+ +----

Thoughts?

Thanks

===================

If you pass all the power supply wires through the clamp the reading
should be zero, whether the printer is on or off, on AC or DC.

Clamp meters are intended to read the magnetic field around a single
conductor. If more than one wire passes through the clamp they should
show the difference between the currents, which is zero if the same
current passes through in opposite directions.

The Hall Effect sensor in a DC clamp-on is very susceptible to zero
drift, from temperature changes (your hand) and on sensitive ranges
from orientation in the Earth's magnetic field. My UT210E which
resolves to 1mA DC varies by 25-30mA depending on whether the clamp is
perpendicular or parallel to Earth's field lines. I need to hold it in
the measuring position, zero it, then clamp around the wire and read
within a few seconds before it drifts.
-jsw