Author Topic: volt meter and momentary switch  (Read 19749 times)

steve-0

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Re: volt meter and momentary switch
« Reply #30 on: August 21, 2014, 09:02:08 PM »
i purchased some of these before they where mentioned here
some of these are bad.

i think its about 50 50

here are 3 good ones and 3 bad ones.
the good ones only have one blue resistor on the positive side.
the bad ones have the blue resistor on the negative side and other resistors (or something)
the bad ones are also connected pos to neg.
i tried just cutting the connection but that does no good.

i havent tried moving the blue resistor to the pos side.










bud44750

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Re: volt meter and momentary switch
« Reply #31 on: August 21, 2014, 11:42:35 PM »
I think the working ones are wired properly, with current coming in the positive terminal passing through the resistor to get the needed voltage drop to safely move the meter without over driving it and back out the negative terminal.
    The bad ones have some extra components. The diode ( small black cylinder with a white band on one end) is there I think to protect the meter movement from an error in attaching the voltmeter to the circuit (i.e. + connected to - . the white band indicates the cathode , or negative end and since current can only pass through a diode from plus ( the blank end ) to minus ( the band end) you want the band end to be point away from the positive terminal. the resistor has no directionallity and can be on either side of the meter , it just has to be in series with the meter movement. the capacitor will not pass DC current ( so if it is in series, the meter will not work) and probably is there to absorb surges in the current . it should be wired BETWEEN the plus and minus terminals if you use it at all. you might also check the value of the resistor ( un-solder at least one end) . make sure it is not shorted ( would explain the full needle movement described by a previous member) or just open ( would explain the bad ones). hope that helps.
bud

in the last picture it appears to be a diode wired in backward, not allowing current to pass. the band has to be away from the positive terminal

just noticed, the diode in the bottom picture is wired in backwards and is not allowing the current to pass. the band must be away from the positive terminal.
« Last Edit: August 21, 2014, 11:55:24 PM by bud44750 »

spec4don

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Re: volt meter and momentary switch
« Reply #32 on: August 22, 2014, 05:13:04 AM »
Quality stuff there ::)

Don G.
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andy

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Re: volt meter and momentary switch
« Reply #33 on: August 22, 2014, 07:26:27 AM »
good info, ok so im not a rocket scientist, does it matter which way the blue resistor is wired in? one way or either way?
1943 M4A1 (restored to M2A1)

bud44750

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Re: volt meter and momentary switch
« Reply #34 on: August 22, 2014, 11:25:50 AM »
no. resistors are bi directional, only with  the diode do you need to watch polarity. The  band end ( - ) goes toward the minus terminal and in series with the resistor and the meter movement .One way to keep this straight is to think of water flowing through a hose with the source being the positive terminal and the end with the water coming out as the negative end, as you add more hose, ( more components) the old end becomes positive as that is now the source and the new hose end is negative . you keep adding hose ( components ) until you connect back to the negative terminal.The meter is directional too , so watch that you attach the meter wire that originally went to the positive terminal to the same positive side terminal  of the circuit .  if a bit confusing read the short description  on the URL I posted above. that should help. I think all the meters can be easily salvaged . you can google the resistor code and read the value of the resistor in case it is bad. I have a ton of resistors and if anyone needs one send me a SSAE and I'll send you one back.
bud

bud44750

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Re: volt meter and momentary switch
« Reply #35 on: August 22, 2014, 11:36:44 AM »
this might make it easier to visualize.
   the resistance of the meter is 500 ohms. and it takes 1 milliamp to read full scale. R multiplier is any resistor you put into the circuit that will eat up enough juice ( resistors are like toasters) passing through it so the meter gets what is left .....1 millamp. and will read full scale. this is how you can use the same meter movement to measure even huge voltages, just put a bigger resistor in there.
bud
now go design some rockets
« Last Edit: August 22, 2014, 11:43:14 AM by bud44750 »

Monkeypirate

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Re: volt meter and momentary switch
« Reply #36 on: August 22, 2014, 11:59:53 AM »
Its most likely the Diode that is in backwards is there to help with voltage spikes. It has a break down voltage that will allow surges to back feed across it. usually the kind of thing that is attached to a coil to absorb the pulse when the coil is shut off and the field collapses.

bud44750

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Re: volt meter and momentary switch
« Reply #37 on: August 22, 2014, 08:22:37 PM »
Not wanting to turn this into an electronics forum, but how would the current flow through the diode if is in backwards? relying on the breakdown voltage to feed the meter movement seems somewhat esoteric for a cheap meter. Please PM me to teach me about what you were saying.
bud
« Last Edit: August 22, 2014, 11:41:11 PM by bud44750 »

scotty71

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Re: volt meter and momentary switch
« Reply #38 on: August 22, 2014, 10:18:34 PM »
The diode will only let voltage flow in one direction hence it having the white band located to one end which indicates which direction the voltage will flow. It would protect the meter  in case of accidental wiring up backwards.

The capacitor would be to smooth out the voltage to the meter and would allow the meter to show a constant voltage reading despite any voltage fluctuations that might occur in the electrical system. These must be installed correctly because if the are not installed using the correct polarity they will fail with some bad results. Capacitors have an indication on the outside of the covering denoting the negative connection lead. The capacitor needs to be connected in series with the meter. It also acts as a small battery and will power the meter for a few seconds after the power is removed.

Why some meters have some of these parts and not the others and why some are installed incorrectly comes down to poor quality control.

I would recommend that the diode be fitted on the ( - ) terminal and the resistor and the capacitor be fitted to the ( + ) terminal. You don't need to have the capacitor and will work fine without one. I would keep the diode and the resistor in the circuit, and you could always add a separate fuse to protect the meter if you want.

bud44750

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Re: volt meter and momentary switch
« Reply #39 on: August 22, 2014, 11:49:42 PM »
don't you mean install the capacitor across the meter , not in series with it as DC can't really pass through a capacitor ? These are all good ideas and between all of us we should get these pesky meters fixed
bud
« Last Edit: August 22, 2014, 11:52:49 PM by bud44750 »

andy

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Re: volt meter and momentary switch
« Reply #40 on: August 23, 2014, 07:06:43 AM »
just to update, I did contact seller, he acknowledges there were some issues with these, and stated the problem has been corrected. It was stated they used 6v parts in some by mistake,
He is sending me another one, and he says he checked it before shipping
1943 M4A1 (restored to M2A1)

scotty71

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Re: volt meter and momentary switch
« Reply #41 on: July 14, 2016, 11:03:32 AM »
New replacement voltage meters for your halftrack dashboard. Not cheap, but US manufactured by Simpson. Scroll down page to select type of meter you require ie 0-30 volt DC. Come in either 2.5" or 3.5" sizes.
http://www.rammeter.com/simpson-electric-round-style-analog-panel-meter-dcv.php

Ma Deuce

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Re: volt meter and momentary switch
« Reply #42 on: January 14, 2021, 10:08:32 AM »
Found this momentary switch at local Ace Hardware. Looks good and best of all it works!! Only thing is it has spade connectors so if you are a purist this is not for you. I think button is as close to originals as your going to get.
Mike
INMVPA
1948 Willy’s CJ 2A
1953 Willy’s CJ 3A
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BillM3

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Re: volt meter and momentary switch
« Reply #43 on: January 15, 2021, 04:34:21 PM »
Looks pretty good, I hope I will find a Volt meter for my Halftrack someday.