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?

The project itself will be a steampunkish lamp with the voltmeter affixed in the base. When the lamp is turned on, the meter should indicate ~50% of it's full range, which would be ~375vdc. If the lamp will include a dimmer(undecided), the meter reading should reflect the dimmer output voltage.

Building a voltage quadrupler is much preferred over modifying the voltmeter. For those with safety concerns, I'm well aware of the risks involved and have made a conscious free-will decision to accept such risks. And this isn't my first rodeo either.

 

Hi CC,
I know it's your call, but removing two assembly nuts and replacing the 2Cents resistor would be my option.
Using a 'C' or 'D' 1.5V battery as the driver.

E

 

The project itself will be a steampunkish lamp with the voltmeter affixed in the base. When the lamp is turned on, the meter should indicate ~50% of it's full range, which would be ~375vdc. If the lamp will include a dimmer(undecided), the meter reading should reflect the dimmer output voltage.

Building a voltage quadrupler is much preferred over modifying the voltmeter. For those with safety concerns, I'm well aware of the risks involved and have made a conscious free-will decision to accept such risks. And this isn't my first rodeo either.

OK, folks: Now we have heard from the TS and we understand that the TS also understands AND is able to construct the voltage multiplier safely. My one suggestion will be to use a smaller value capacitor in that circuit in the position of C4, so that the meter will more closely follow any dimmer adjustments. That is a good circuit, just use adequately rated capacitor voltages. a 600 volt rating will have a suitable voltage margin.

 

Forgive my ignorance, but I don't understand why you need a lamp to be powered by 400V Direct Current. I'm afraid I'm not able to add anything useful here, so - I wish you good luck and success.

 

Forgive my ignorance, but I don't understand why you need a lamp to be powered by 400V Direct Current. I'm afraid I'm not able to add anything useful here, so - I wish you good luck and success.

The lamp is powered by 115vac - the 400vdc is to drive a meter, which is for visual effect only.

 

Well, I'm sure you don't need 400 volts to drive the meter, just change the resistance. At least that's what I would think will suffice.

A meter is just a device that deflects with a given voltage or current. The numbers on the face can be anything from numbers to letters to animals or flowers, or anything else. All you need to do is understand what it takes to deflect that meter.

 

Well, I'm sure you don't need 400 volts to drive the meter, just change the resistance. At least that's what I would think will suffice.

A meter is just a device that deflects with a given voltage or current. The numbers on the face can be anything from numbers to letters to animals or flowers, or anything else. All you need to do is understand what it takes to deflect that meter.

Well, I'd really prefer not to destroy a perfectly lovely vintage voltmeter by mucking about with the internals. And yes, I understand what it takes to deflect the meter to ~ 50% of it's range, and what it takes is ~400vdc, which is how it will be driven.

 

If you potentially want the meter to indicate the light level, controlling a low voltage signal will be simpler than a high voltage signal.

Changing a meter resistor isn't destroying a 'vintage meter' – it's the way it's been done since the beginning.

 

Forgive my ignorance, but I don't understand why you need a lamp to be powered by 400V Direct Current. I'm afraid I'm not able to add anything useful here, so - I wish you good luck and success.

T10, The lamp is a structure, FAR MORE than just the light bulb or LED. "SteamPunk" is a whole style of everything, it is not just a word. I think that it is somehow related to the "Maker" culture, although that may be a stretch. Certainly it includes working towards an interesting appearance and requires creativity on the part of the participants. So while it is "not my thing" I find no reason to dislike it or be critical of it.

 

Here is a good reference on calculating meter shunt and multiplier resistors.

 

I find no reason to dislike it or be critical of it.

Didn't intend to come off as disliking or being critical of anyone else. Just said I don't see good reason for using 400 volts to deflect a meter when it's easier (in my opinion) to modify the meter to measure what's being done.

 

If you potentially want the meter to indicate the light level, controlling a low voltage signal will be simpler than a high voltage signal.

Changing a meter resistor isn't destroying a 'vintage meter' – it's the way it's been done since the beginning.

Since adjusting a 120 volt lightbulb would be done with a triac dimmer, which is not at all isolated from the mains, how would J.C. control the brightness of the LED. The LED circuit is all low voltage and low current, so the method of controlling both at once with a single knob and a single pot is not clear to me.
And for Tony, in many, if not most, instances, the easiest way to do something is not the bet way. I have to remind clients of that on many occasions, that the easiest way for me to do something that I do once in five minutes is very small compared to them having to live with it for many years. Usually they get it, especially since the cost is the same.

 

If you potentially want the meter to indicate the light level, controlling a low voltage signal will be simpler than a high voltage signal.

Changing a meter resistor isn't destroying a 'vintage meter' – it's the way it's been done since the beginning.

There will be no controlling of the dc voltage - the quadrupler will simply convert whatever ac voltage it's been given. And it's my opinion(and it's my opinion that counts here) that unnecessarily modifying the internals of a well-designed and executed vintage instrument is a simple violation of what's good and proper.

 

There will be no controlling of the dc voltage - the quadrupler will simply convert whatever ac voltage it's been given. And it's my opinion(and it's my opinion that counts here) that unnecessarily modifying the internals of a well-designed and executed vintage instrument is a simple violation of what's good and proper.

My mistake. I must have misunderstood post #11, where you said:

"If the lamp will include a dimmer(undecided), the meter reading should reflect the dimmer output voltage."

Of course you are absolutely free to do your project any way you like. Any free to ignore any advice/options given. Sorry I offered any.

 

If the 400 volt supply is fed from the same dimmer as the light, then the voltage should vary some. How much will depend on the dimmer..

 

You don’t have to destroy the meter at all. You can put an additional resistor in parallel with the existing mechanism, keeping it all intact.

Bob

 

You don’t have to destroy the meter at all. You can put an additional resistor in parallel with the existing mechanism, keeping it all intact.

Bob

The existing internal resistor is implemented by coils of resistance wire. I suspect this was done to allow fine tuning of the resistance value and to provide some back emf to dampen transients. I also suspect that paralleling a non-coil resistor would alter the meter's response to transients for the worse.

Bottom line - I have a 0-750vdc voltmeter and want it to read ~400vdc. The best solution by far to my mind is to simply give the meter what it wants.

 

The inductance of the resistor coils will not have much effect on the meter reading and especially not on any transient response that would actually move the pointer. And the meter may also be damped by that magic scheme that is used to damp meter motion. Somehow they add dampening when they build some meters. I think it is done by controlling the resistance of the copper coil form that the deflection coil is wound on. That is the handy thing with that particular kind of meter movement, that it can be magneticly damped very easily.

And also the voltage from that voltage multiplier may not vary as nicely as the intensity of the light, depending on how the dimmer reduces the power.

 

it's my opinion that counts here

Well then have at it.

Happy new year.

 

Well then have at it.

Happy new year.

That's a rough thing to say to those trying to help him. Yikes.