Help with a Voltmeter mod

[FluidZen]

Hello to all!  I've been watching Breaktru's copper mods for a while, as they have been the inspiration for a "Steampunk" design I've been working on.  Basics: VV from 4 AA rechargables (3.6 or 4.8v) since I have lots of those lying around, mechanical switches and safety, and a re-work of a small analog voltmeter movement (scrounged it from a pocket battery meter) that I want to make look like a pressure gauge.

The gauge is where I need some help.  I'm very rusty on my electronics skills and resistance figuring.  How would I wire that up for just 2 voltages, 3.6 and 4.8v?  It doesn't matter where the needle falls, as I'm going to make a new backing for the face anyway.  Sticking to the mechanical theme, you will physically choose either 3 or 4 batteries with a switch.

Thanks for all the great mods and ideas on here, Breaktru!

[FluidZen]

Thought about it, won't be physically selecting 3 or 4 batteries with a switch.  Probably just a pot.

[Breaktru]

Hey FluidZen, Welcome to the forum and glad I could help out with the mods.

I would worry that rechargeable AA batts can not provide the need amperage for PV use.

The voltmeter would need the circuitry inside the meter and not just the dial movement. The proper scale would have to be set as if you where manually setting it to measure your output voltage. In other words, the contact or contacts would be jumped out for a 20 volt DC scale.

Am I understanding your question correctly?

[FluidZen]

I think you've got it.  Just trying to figure out what resistors to solder in for the correct scale.  Would there be a way to decrease the scale to 10 volt dc?  (That would measure 1-10v, if I'm understanding correctly?)  If I'm way off, someone could please point me in the direction of some good review material.  My old bread boards are long gone and I've forgotten so much, but I may have to make a trip to Radio Shack for some new supplies.  As far as the batteries, I was going by the information I found here: 

http://www.e-cigarette-forum.com/forum/ecf-library/129569-rechargeable-batteries.html

But if you've experienced differently, I've got plenty different sizes of copper pipe to play with, and I can always buy new batteries.

Forgive me if I'm a bit scatter brained, my mind tends to bounce around when I'm excited about a project!

[Breaktru]

Are you referring to the Ni-Mh rechargeables? 1.2v per cell. Never used them.

See:
http://www.e-cigarette-forum.com/forum/new-members-forum/155193-4-aa-box-nimh-rechargeables-510-joye-atty-2-3-ohm-5-5-volt-3-second-hits-avoid-burnt-taste.html

Your voltmeter: does it have a 10v scale? If your closes range is 20vdc and you are going to make your own marked scale anyway, I guess you can parallel the existing resistor with the same value resistor so it would full scale on max voltage. Where is the resistor? I have no idea, sorry.
Sounds like a lot of trouble and added power consumption.
But it would be cool if you succeed.

[Breaktru]

How is your mod building coming along? any photos?