[Boatanchors] [MRCA] Panel Meter Circuit?

[J. Forster]

That confuses things. I still think it's a 6V meter in series with a zener.

Do this measurement:


 -------------- A.M.-------------------O-----|
  +                                    |     |
Adj DC                                 |     |
Supply                                V.M.   Meter
                                       |     |
  -                                    |     |
 --------------------------------------O-----|

Plot the A.M. v. the V.M. If the thing is a voltmeter and zener, as I
suspect, the current should be about 0 until the supply exceeds 24 VDC.

If the current increases linearly from 0, the meter is a voltmeter with
the zero mechanically suppressed by preloading the hair spring.

-John

===========






> 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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>
>
>
>
>