Why can't we just see a photo of the meter or a model #?

 

Thanks - this is just what I was looking for. Could you recommend a capacitor type? If electrolytic, how are they arranged with respect to polarity?

 

Here's the meter in question. The resistance across the terminals measures 752k ohms.

 

Thanks - this is just what I was looking for. Could you recommend a capacitor type? If electrolytic, how are they arranged with respect to polarity?

Hi CC,
If you have to ask this question, you are not competent enough to build a non mains isolated supply of 400Vdc
E

 

Could you recommend a capacitor type? If electrolytic, how are they arranged with respect to polarity?

Capacitors:
0.47uF, $0.79 each:
https://www.jameco.com/z/MPP474K-40...tallized-Polypropylene-Capacitor_2236623.html
1uF, $1.95:
https://www.jameco.com/z/MMR105K2G-Mylar-Capacitor-1-uF-630-Volt-10-_2316047.html
ADDED:
For 752kΩ meter you should use this circuit:

Resistor R1 100Ω added (@MisterBill2 recommendation).
Capacitor 0.22uF, $0.69:
https://www.jameco.com/z/MPP224K-40...tallized-Polypropylene-Capacitor_2236607.html

 

hi CC.
I would say that meter requires an external resistor scaling.

Same Model number.
E
https://www.ebay.com/itm/293522515494

 

Here's the meter in question. The resistance across the terminals measures 752k ohms.

Okay.

So change it to a 7.5K resistor then use 4V instead if 400V to drive the meter to the same place. Or any other resistor in the range of 1K to 10K.

Bob

 

I agree with Bob. It looks as though the meter could be disassembled by removing the two terminal nuts and 3(?) small screws (which may be behind plastic caps).

 

Yes, the circuit is non-isolated and the voltage is high, THEREFORE it will need to be enclosed in an insulated enclosure, AND the wires to the meter, along with the connections, will also need to be enclosed or very well insulated. Just because careless working with the circuit can be dangerous does not mean that it can not be used safely. Depending on the form of the meter, and how much is visible, it might even work to put the whole circuit on the back of the meter housing.

And, to open the meter case leave the terminals alone, and instead remove the three or 4 flat-head screws that go thru the side of the cylinder just a bit below the back piece. Undoing the terminals will allow the insides to flop around in the case, abd be damaged.

 

Why is anyone here encouraging this person to build a dangerous non-isolated 400V supply to accomplish something that can be done with a 1.5V battery and a resistor?

This is malpractice.

Bob

 

I agree with Bob. It looks as though the meter could be disassembled by removing the two terminal nuts and 3(?) small screws (which may be behind plastic caps).

Sadly, there are no resistors identifiable as such within the meter enclosure.

 

Sadly, there are no resistors identifiable as such within the meter enclosure.

Picture?

Bob

 

Picture?

Bob

If no reistors are seen, then definitely the battery-resistor check is in order, because if the meter is not working then it become a very simple matter of using the zero-set springs to make the pointer show whatever is wanted, no electrical connections required.

 

There us a resistor inside. He measured it at 750K which is correct for a 750V full scale meter.

Bob

 

Picture?

Bob

 

Sadly, there are no resistors identifiable as such within the meter enclosure.

These 3 spools, connected in series, are resistor:

 

There us a resistor inside. He measured it at 750K which is correct for a 750V full scale meter.

Bob

OK, but the resistor is not easily spotted, if it is a precision resistor then it does not look like a common resistor. Indeed, those 3 spools of resistance wire ARE the resistor, and they do not look at all like common resistor, do they?

It should be possible to connect a common resistor across that precision resistor to set the full scale to 3 volts, and then the 1 1/2 volt battery will show about half scale.

AND there is nothing so very dangerous about a 400 volt supply if the one involved understand what parts are risky and knows what to avoid contacting.

 

....AND there is nothing so very dangerous about a 400 volt supply if the one involved understand what parts are risky and knows what to avoid contacting.....

Rather easier to connect one resistor of the appropriate value and connect a 5 volt phone charger than to construct a 450v supply I should think. To say nothing of being far safer!

 

Why is anyone here encouraging this person to build a dangerous non-isolated 400V supply to accomplish something that can be done with a 1.5V battery and a resistor?

This is malpractice.

Bob

Furthermore I can't see any competent teacher requesting such high voltage for a basic test. I'll never understand the allure of "playing with fire". Anything over 10V gives me the willies just thinking about it.

 

I'm looking for a simple 110vac to ~400vdc conversion circuit. This is for an art project and will only be used to drive a 1000ohm/volt voltmeter. Any help would be most appreciated.

Looks like we've gotten lost on testing the meter and have forgotten the original question (post #1). I'll ask my question again; what is the art project? Why the need for 400VDC?