How to measure voltage with a multimeter?

September 30, 2018 at 05:47:05
Specs: several
I have an appliance that has an electrical connector to
power a subsidiary device that includes a motor. I don't
have that device and don't want it. Instead, I want to use
power from the connector to power a small lamp. I don't
have the specs for either the appliance or the subsidiary
device. I don't know the voltage supplied by the connector.
I don't even know if it is AC or DC. The connector looks
vaguely like a Molex connector, with compartments for 8
contacts, but it looks like only 4 of the compartments have
contacts in them, in an alternating pattern.

How do I use a multimeter to determine the voltage and
whether it is AC or DC? How do I determine if one of the
connectors is to ground?

-- Jeff, in Minneapolis

message edited by Jeff Root


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#1
September 30, 2018 at 06:01:22
Why so vague? You post on here often enough; you should know what's required. Why not mention what the appliance is & the make/model? We have no idea what you're working with. We also know nothing about the lamp. Did you try searching for the specs or electrical diagram for this "appliance"?

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#2
September 30, 2018 at 06:19:59
I take it you know how to use your multimeter to measure voltage. (If not, read the instructions that came with it - it's nt possible to safely give generic instructions as all instruments are different.) So your main problem is to determine whether it is AC or DC. Have a look at this thread: https://www.edaboard.com/showthread...

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#3
September 30, 2018 at 08:21:27
I should have said that my multimeter is analog and fairly basic.

There isn't any need to know what the appliance is to answer the
question. It is a general question calling for a general answer that
will apply to a wide range of situations.

I ask the question because all instructions for measuring voltage
(including the instructions for my multimeter) say to measure
across a load. Across an existing circuit. I don't have a circuit.
I don't have any idea what the load would be from the device that
plugs into the connector. I just want to measure how much juice
comes from the power supply, which is hidden inside the appliance
where I can't examine it directly. All I know is that it is enough to
power a small motor. And that it must be lowish voltage since it
isn't a standard 120 volt AC outlet.

Also there are four conductors, so I wonder what they all are.
The third could be ground, but what is the fourth?

-- Jeff, in Minneapolis


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Related Solutions

#4
September 30, 2018 at 08:32:44
"There isn't any need to know what the appliance is to answer the
question. It is a general question calling for a general answer that
will apply to a wide range of situations."

OK, if that's the way you want to play it...I'm going to assume it's a dishwasher. Maybe this will help: https://www.doityourself.com/forum/...


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#5
September 30, 2018 at 15:20:47
"Turbidity sensor", eh? Interesting. I wonder how that works.

One thing I notice is that only two wires come in: A black wire at
top-left labeled "L1" (If I read the fuzzy JPG correctly) and a white
wire at bottom-left labeled "N". Maybe for "neutral". No ground.

Another thing I notice is that I don't see any voltage-reducing
components. No transformers or resistors. Nor do I see any
indication of voltages anywhere. Since one of the connectors
in the "sensor" connector block is labeled "LED", I know there
must be some reduction from 120 volts AC to low-voltage DC.

It isn't clear that this helps answer my question, though it is
moderately interesting.

If I want to find out what kind of voltage my wall outlets provide,
do I just set my multimeter to 250 V AC and thrust the probes
into the socket? Or does that let the smoke out of my meter?

-- Jeff, in Minneapolis


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#6
October 3, 2018 at 05:44:58
No EEs here?

-- Jeff, in Minneapolis


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