Measuring Voltage
Measuring Voltage
(OP)
If I have a voltmeter that measures voltages up to 300 Volts, how can I use that same voltmeter to measure a signal between 300 volts and 600 volts? Specifically, this is for measuring the no load secondary voltage of a transformer.
Thanks
Thanks
RE: Measuring Voltage
Then, there are several ways out. It depends on what power your transformer is. If it is a small (few hundred VA) unit, you can use a voltage divider hooked up from a couple of resistors. Use a low resistance to avoid capacitive influence and resistive loading by the voltmeter. Make sure that you understand what you are doing. Especially when it comes to power dissipation in the voltage divider and flash-over voltage of the resistors, which accidently (no pun) happens to be around 250 V.
If you are in doubt regarding the resistor's tolerance, you can easily check that by switching resistors. If you get the same reading - then your resistors are close enough.
If your voltmeter is an analogue one with typically 1000 ohms/volt, then you can simply double the range by adding 300 kohms between hot terminal and transformer terminal. If the consumption is something else, use that number.
If the transformer is a power unit, then just don't do it. The risks are too big. Arc-flash and all that.
Don't even measure the output of such a transformer with anything without a fuse (like in a fused measurement lead) or on the downstream side of a low-amp fuse.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Measuring Voltage
RE: Measuring Voltage
A transformer - that's somewhat out-of-the-box. But surely doable.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Measuring Voltage
Google some keywords such as: high voltage probe DVOM
The advantage is that they're off-the-shelf and (presumably) safety approved.
They seem to about $100-$200 price range.
You wouldn't want one with too high a division ratio as you'd lose resolution. But 10-to-1 would be nice.
I presume it would put a slight load on the source, due to the resistive divider.
RE: Measuring Voltage
If you will need to spend any money, it will be better spent buying a meter intended and certified for 600 Volt use.
Bill
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"Why not the best?"
Jimmy Carter
RE: Measuring Voltage
But I got the feeling that there were no money to spend. If someone uses a DMM that cannot handle more than 300 V, then there are no money to spend at all.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Measuring Voltage
RE: Measuring Voltage
My meter is Cat 3 rated and can handle many functions... doesn't seem to have one for Homework though.
RE: Measuring Voltage
No danger with 300VAC , I have never seen s probe that would not withstand that Voltage - at least as long as it take to get the reading.
Kurt
RE: Measuring Voltage
by adding a voltage divider of 2 resistors
the resistors value shall be about 1/100 of the input resistance of the meter
that will give you an error about 1%
good luck
RE: Measuring Voltage