Appa A1 mini AC DC clampmeter teardown

[bluey]

These mini clampmeters all appear similar. Amazon reviews go back to about 2015.

Amprobe AMP-25 https://www.amprobe.com/product/amp-25/
APPA A1 (?discontinued - no longer on Appatech website) https://www.testequipmentonline.com.au/appa-a1
Extech MA145 http://www.extech.com/products/MA145
RS Pro ICMA1 https://au.rs-online.com/web/p/clamp-meters/1233256/
Voltcraft VC-340 https://www.conrad.com/p/voltcraft-vc-340-clamp-meter-digital-cat-ii-600-v-cat-iii-300-v-display-counts-6000-1405094

All use 2xLR44 button batteries, presumably because the primary design criterion was small size and weight. Suspect the Amprobe came first, as it has a unique button design. Appatech is probably the OEM for the other near identical clones.

Basic accuracy 1.5%+5 digits. Up to 300A.

[bluey]

Battery cover and case have metal thread insert screws. PCB has self-tappers.

[bluey]

More components under the LCD, which would need to be unsoldered to see.

[bluey]

Seems reasonable from a minimum 100mA DC (Cheap chinese 5A lab supply.). Not sensitive to earth magnetic field, but is sensitive to stray fields from electrical wiring.

[bluey]

Fluke 1507 earth bond test current sensing seems a bit variable. (Three separate runs.)

[J-R]

The PCB in my Amprobe AMP-25 is virtually identical.

Mine always reads 120-140mA in AC mode, with no way to zero it out, although LPF mode is better at around 50mA.  But it is still accurate at values just above that.  So if I give it 250mA AC, it is pretty much spot on.

DC accuracy seems similar to what you've observed.

Major gripes are no min/max/average, no peak/inrush in DC mode, no zero/relative in AC mode.

I've attached the calibration procedure for the AMP-25 in case anyone needs it, perhaps it is the same for all of them.

[bluey]

The Appa version quotes slightly different accuracy. 60A range 1.5%+10 digits (vs 1.5%+25d). But says accuracy only covers 5-100% of range. So less accurate <3A.

Mine reads zero in AC mode with no load, seems to not react to AC wiring outside clamp.

“Smart data hold” will flash screen and beep if current increases 50 counts from held value. (Amprobe doesn’t say the beeper beeps for this, just flashes screen.)

[J-R]

Interesting that it reads zero in AC mode.  Can it properly detect low AC currents, or is there a bit of dead zone at the low end?

I think the residual reading on the AMP-25 is very common, I see it a lot in photos.  Amprobe tech support said it was normal.

For my tool bag I typically carry the AM-47 along with the AMP-25.  Gets most jobs done without much size/weight.

[bluey]

Haven’t got a rig to test AC with yet. Probably a dimmer switch with 12V halogen transformer. Otherwise need to rig a line splitter, line separator, test lead adapter or AC breakout box. Curious how expensive those breakout boxes can go - what’s inside??

Amprobe ELS2A and clones have good functionality with banana sockets and loop amplification. But not good hanging out of a wall socket for mechanical safety.
https://www.amprobe.com/product/els2a/

Voltcraft SMA10 test lead adapter - still looking for international version.
https://www.conrad.com/p/voltcraftsma-10test-lead-adapterpg-plug-4-mm-socket-pg-connectorscoop-proofblack-123980

BK Precision TLBB53
https://www.testequipmentdepot.com/bk-precision/accessories/breakout-boxes/breakout-box-tlbb53.htm

DIY
https://www.element14.com/community/groups/test-and-measurement/blog/2018/02/15/building-a-mains-breakout-box

[bluey]

I think the residual reading on the AMP-25 is very common, I see it a lot in photos.  Amprobe tech support said it was normal.

Wondering if that is AC mode or AUTO(default). In AUTO mode it picks up stray fields because it will sense in DC mode. Various video bloggers claim the directional sensitivity of DC clamp meters to be due to earth’s magnetic field and show changing readings with meter orientation. Mine did this inside but not at all outside away from mains wiring and appliances. Clearly this is AC current interference and not earth magnetism.

Mine will easily register 100-250mA (DC) in AUTO mode that changes with proximity and orientation.

Otherwise I presume a non-zero could be adjusted out using the trimpots. Manual says VR53 and VR54 are DC zero offset - ???coarse and fine adjust. If what you are seeing is baseline DC offset, it can be zeroed.

[retiredcaps]

APPA A1 (?discontinued - no longer on Appatech website) https://www.testequipmentonline.com.au/appa-a1

Suspect the Amprobe came first, as it has a unique button design. Appatech is probably the OEM for the other near identical clones.

Appa manual at

http://www.appatech.com/v_comm/inc/download_file.asp?re_id=1855&fid=34932

Amprobe rarely makes it's own meters. They usually get others to make it and just rebadge or customize.

[bluey]

I found another rebadge - Danish Elma 3039.
https://elma-instruments.com/products/electrical-measuring/clampmeters-ac/elma-3039-–-digital-true-rms-ac-dc-mini-clamp-meter.aspx

Benning has a number of meters OEMd by Appa. Curiously, the Benning CM P2 TRMS mini AC/DC clampmeter has different design, but same feature set, smaller but similar LCD, 4000 count (vs 6000), AAA batteries and inferior accuracy. Makes me wonder if the Benning one was the first contract job, and then the design was refined.
https://www.benning.de/products-en/testing-measuring-and-safety-equipment/current-clamp-multimeter/benning-cm-p1-cm-p2.html?sbd=POL?sbd

[bluey]

Did a quick test on a 12V 20W iron transformer halogen desk lamp (live twin arms). Got 660-680mV with repeated measurements (maybe it has a 10W bulb in it?). In AC mode, has no trouble returning to zero. In AUTO mode, can switch from AC during measurement back to DC when clamp is empty anywhere from 20-140mV random or zero AC if it can’t find a DC source.

Tried a 20W halogen running AC switchmode transformer. Only get 20mA AC. Frequency must be too high to register.