[MRCA] Panel Meter Circuit?

[W2HX]

Just a little clarification based on the replies so far. First, I have the milliamps wrong. The vertical axis is not milliamps, but hundredths of amps. So 30 on that scale is really 0.3A. Second, I connected a power supply in series with a few hundred k ohms and measured the current in the circuit to come up with those figures

Sorry for the error

 
73 Eugene W2HX
 

-----Original Message-----
From: J. Forster [mailto:jfor at quikus.com] 
Sent: Monday, October 22, 2012 6:12 PM
To: W2HX
Cc: mrca at mailman.qth.net; boatanchors at mailman.qth.net
Subject: Re: [MRCA] Panel Meter Circuit?

Gene,

It may not need any external curcuitry.

Try just hooking the meter to a variable voltage supply, and increase it from zero slowly.

It looks to me like you have a 0 to 6 VDC meter in series with an internal
24 volt Zener diode. (It looks like your 25 V data point is a bit off.)

Best,

-John

================




> Hi all,
>
> I am doing a battery project, installing 28V battery system in a 12V 
> vehicle with DC-DC converters and charging circuits, etc.  I want to 
> use some traditional round analog meters to monitor voltage and 
> current.  So I picked up a nice expanded scale (24V to 30V) panel 
> meter which can be seen
> here:
>
> http://www.w2hx.com/x/1967LRS2/V-Meter.JPG
>
> I guess in my naiveté I assumed that this would read volts directly. 
> Well, no such luck!  Here's what I know about the meter. First, its 
> resistance reads about 230 ohms. Second, full scale (30V reading) 
> appears to be about
> 360 mA (more precisely, 0.36 A - my ammeter does not have any more 
> resolution than hundredths of an amp). It is very hard to measure the 
> low end of the scale, perhaps 0 mA.  To the best I could, I measured 
> the current that corresponded to each voltage marking on the meter.  
> Here is the result:  http://www.w2hx.com/x/1967LRS2/MeterRange.JPG  It 
> looks pretty linear.
>
> First Question is. How do I build a circuit that when attached to my 
> battery will show the right voltage?
> Second Question is. Are there expanded scale meters that will read 
> direct volts? Or do they all behave in this way?
>
> Thanks!
>
> 73 Eugene W2HX
>
>
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