Voltmeter died

[Hasdrubal]

Happened first time about 7 years ago, changed out the relay, still nothing. A local CUCV guy sent me a used resistor that sits on the back of voltmeter. Worked until the other day. Does anyone have a working resistor kicking about that they could spare?

 

[Tinstar]

Install a 24v voltmeter and never worry about it again.
ISSPRO and VDO both make excellent ones.

 

[MarcusOReallyus]

Happened first time about 7 years ago, changed out the relay, still nothing. A local CUCV guy sent me a used resistor that sits on the back of voltmeter. Worked until the other day. Does anyone have a working resistor kicking about that they could spare?

No, today is December 7th, Pearl Harbor Day. It's NOT April 1st.


You're kidding, right? You want a used resistor?

https://www.amazon.com/s/ref=nb_sb_...tor+2+watt&rh=i:aps,k:300+ohm+resistor+2+watt

 

[Hasdrubal]

Hey.. practically everything on my truck is used..man.

So, did some reading here, seems that I could use a 5 w 300 ohm resistor. If one were to use 2 x 150 ohm resistors, are they still 5 w each and are they installed parallel or in series?

 

[doghead]

Good thing I reread this with my glasses on, the first time I read it I thought a "volunteer died"...

It pays to reread!

 

[Hal O'Peridol]

Wire in series to get 300 ohms. I'd get a new 24 volt one.

Sent from my SM-J120W using Tapatalk

 

[Ordak]

Wire in series to get 300 ohms. I'd get a new 24 volt one.

Sent from my SM-J120W using Tapatalk

I think he wants to keep the original gauge

 

[Hasdrubal]

So I read someone used 2 150 ohm 1/2 w resistors. So, its not 5 w its .5 w? Or it doesn't matter - bigger is better?

 

[Tinstar]

I sold a few NOS factory CUCV 12v voltmeters a few months ago.
None of them had the resistor on back and worked perfect when plugged into factory CUCV plug that is 24v.
Guess they made later internal changes that allowed this.
Part numbers were same, just early to mid 90s manufacture dates. Don't remember exactly.

Doesn't answer your question. Just some trivia

 

[TGP (IL)]

Just put a 24Volt meter from a "M" series vehicle in and be done.
Tom

 

[Tinstar]

Clearly he wants to keep the stock one.
Its fixable.

 

[MarcusOReallyus]

So I read someone used 2 150 ohm 1/2 w resistors. So, its not 5 w its .5 w? Or it doesn't matter - bigger is better?

It must be 300 ohms.

As far as wattage, bigger is better. You would be fine with a 2 watt, but do NOT go lower. 5 watts would be the cat's meow. Two 150s should go in series to make 300 ohms. If you put them in parallel, they would make 75 ohms.

 

[Hasdrubal]

Going by the 1/2 w rating on other threads. I picked up some 300 Ohm 1 watt resistors. I see that you said do not go lower than 2. Why is that?

 

[MarcusOReallyus]

Ohm's Law. 24 volts through 300 ohms gets you 0.08 amps and 1.92 watts. I'm not sure of the circuit diagram, though. I haven't had a reason to mess with it. IF that 300 ohms is in series with 300 ohms presented by the voltmeter (which is easy to believe), then you are okay at a half watt. You'll be dissipating .48 watts in that case.

Still, that's running pretty close to the edge, and a larger wattage would be more robust. Toss a 5 watt in there and it will probably never burn out again. As long as it's 300 ohms, you could run a 100 watt resistor in there, and it would work just fine. Probably wouldn't fit, though!

 

[Hasdrubal]

Finally installed the new resistor. Works..but it reads too high. When its running its right of the tick mark, under the E of GEN. Is the 300 ohm value correct for this application? I checked the resistor code, its 300 but the tolerance band is gold, which is 5%. Could this be the issue?

 

[Tinstar]

The tick mark isn't absolute.
Sounds like you have healthy alternators.
As long as your not in the red your ok.

Did you see with a DMM what it's reading? (Alts)


Mine has always been past the tick mark.
But I use a 24v ISSPRO numbered and colored gauge.

 

[Hasdrubal]

I can tell its off by where the needle sits at key on and where its at when Glowing.

 

[Rvitko]

Are you sure the resistors have no contact to the gauge housing? Best way is to leave the old broken resistor under as an insulator.

 

[MarcusOReallyus]

If you want to dial it in to be accurate, you can substitute a variable resistor and tweak it until you get your gauge to match a DMM reading.

Probably not worth the trouble, though.

 

[Hasdrubal]

Yes, left the old resistor there, so no contact against the case. Wish I had managed to source an original OEM resistor. Yes that's right.. a used resistor.