[andyr]

I wonder if:
a) anybody has experienced this, and
b) whether you can explain why this should happen?

I have built a new battery-powered phono stage and am running it for a few days, to see how the current draw pulls down the voltage from the 5x6 SLAs.  (I'm hoping that I will be able to leave it on for a week, so it can "warm up", and then recharge it once a week ... and it only drops a couple of volts, max.)

So I have my Jaycar digital multi-meter set to "Volts" and connected to the '+' DC rail and ground.

I'm reading 31.9v (the SLAs are fully charged) ... but then when I put my hand near the meter, the voltage drops by 0.1v.  When I take my hand away ... it goes back to 31.9v! 

Obviously, putting my hand near the meter is introducing some capacitance ... but why should this near-to-the-meter capacitance decrease the reading?  Is this occurring simply because it's a cheap Jaycar meter? 

Regards,

Andy

[Speedskater]

Yes, it's called "phantom voltage".  Modern DMM's have  very high (almost infinite) input impedance, so your test leads become small receiving antennas picking up stray AC fields.  Electricians often have trouble with this, measuring  voltage on dis-connected wires. The cure is to place a high value resistor (100K to 10M) across the ends of your test leads.  For electricians a 5 Watt nightlight will do the trick.

[andyr]

Yes, it's called "phantom voltage".  Modern DMM's have  very high (almost infinite) input impedance, so your test leads become small receiving antennas picking up stray AC fields.  Electricians often have trouble with this, measuring  voltage on dis-connected wires. The cure is to place a high value resistor (100K to 10M) across the ends of your test leads.  For electricians a 5 Watt nightlight will do the trick.

Thanks, speedskater.  I'll just keep my hands away from the meter. 

Regards,

Andy

[Speedskater]

Now that I re-read your first post, what I thought I read is not what you wrote.  Phantom voltage only happens with very high impedance loads (like wires that are not connected to anything).  So now I'm not sure what's happening.  Try twisting the test leads together.  Maybe the meter is being affected by an AC field even though it's on a DC range.  Try it on your car battery.

[Bob in St. Louis]

Andy, if you really want to drive yourself nuts, put a digital voltmeter on the AC setting and hover the leads around the back of your equipment.
If that doesn't make you scratch your head, try this:
Put one lead on a clean unpainted screw/bolt of a piece of equipment, then hold the other lead on the insulation of the power cable.
Let us know how many volts you get.

Have fun with that. 

Bob

[andyr]

Andy, if you really want to drive yourself nuts, put a digital voltmeter on the AC setting and hover the leads around the back of your equipment.
If that doesn't make you scratch your head, try this:
Put one lead on a clean unpainted screw/bolt of a piece of equipment, then hold the other lead on the insulation of the power cable.
Let us know how many volts you get.

Have fun with that. 

Bob

Thanks, Bob,

I subsequently tried putting my hand near one of my other meters (a more expensive meter) and it doesn't happen with this one.  So I guess it's just "an undocumented feature" of the cheapo meter! 

Regards,

Andy