The Importance of a Voltmeter

I learned vacuum tube radio theory when I was 14, I bought a power supply/
Short Wave receiver/ Transmitter kit from a Midwest firm called Walter Ash.
They sold surplus military electron tubes, etc. It came in a box full of
pieces starting with bare circuit boards and empty chassis and tube
sockets. It was a superhet circuit, 7 1/2 watts TX output. CW only. Late at
night, when the ionosphere settled down and there was a good skip, I could
easily contact ham radio nuts in Australia, Japan, Russia. I spent many
sleepless nights in my radio shack. Never followed it much after
transistors were invented. Hated change then almost as much as I do now.
(GRIN)
Jim Hupy
Salem, Oregon

> Keith,
> I travel with a Heathkit tach/dwell meter in the GMC to this day.
> I don't use it very often but it's the same vintage as my coach and makes
> me smile when I see it.
> Shop music is from a vintage iPod through a heathkit power amp my dad made.
> Garage music is a Heathkit AM/FM radio from the same era.
> --
> Douglas & Virginia Smith,
> dsmithy18 at gmail,
> Lincoln Nebraska,
> ’73 “Sequoia” since ‘95: "Wanabizo";
> Quadrabag/6 wheel disks/3:70 final/Paterson QuadraJet/Thorley’s/Alloy
> wheels/Sundry other
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
I bought 10 or 12 or of those (voltmeter only) out of China for under $3.00 each and occasionally handed them out to GMCers. I have 2 in my coach
left on 24x7 for several years that monitor the engine and house batteries. I also keep one in my volt meter bag for quick checks when working on
cars and airplanes. I have never had one read wrong or fail.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
So, related to this topic;

I DO have a volt meter AND an amp gauge, both installed by the PO, right next to each other. I have found that when I am driving with the lights on,
and the heater or air conditioner, and the refrigerator on 12 volts (3 way Norcold), the voltage reads low, while the amperage reads high.

When I turn the lights off, the volt meter goes back up to normal, while the amp meter still reads somewhat high, but not as high as it did before,
obviously because the coach is drawing less power without the lights being on. BTW, this condition throws off the factory electric gauges as well.
The oil pressure reads a little lower and thew temp gauge reads a little higher, when the lights are on.

I understand the amp meter fluctuations, but I'm not clear on why the volt gauge reads low under a high current load. Can anyone with a better
aptitude for electrical stuff than I (most of you) please explain what is going on?

Thanks
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
 
Carl,

Bruce's explanation is (of course) real good but from your description, I wonder if that ammeter isn't installed in the alternator output. The
original intent of vehicle ammeters (back in the DC generator days) was to know if the vehicle battery was being charged. That was always a serious
concern. If the meter never goes positive, that is what you have. And, while that may be interesting, it is really useless data for the larger
part.

Easy Test #1 - Turn the headlight on. Does the reading show negative?
If yes, if might be right
If no, then it is not a real useful meter

Easy Test #2 - If carburetor, don't set the choke.
If Fuel Injected, leave the headlights on a few minutes and shut off.
Now her fire up. Does the reading go positive?
If yes, it might be right.
If no, let it back to low idle and see if there is any reading at all.

I suspect you have an alternator output meter. They are interesting, but not real useful.

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
 
Thanks for the explanation. I think What Bruce said in his third main paragraph is the case. I do have the original alternator, three wire, but no
isolator. The PO had replaced it with a combiner, and I just replaced that with an LI BIM as part of a LiFePo4 battery conversion.

The ammeter is hooked up in such a way as to read the load on the entire system. I can tell whether or not I turned my fridge back on after a stop,
by looking at the ammeter. If it is reading less than 15 amps, I know I have forgotten to turn it on, if it is reading about 25 amps, it is on.

When the voltage is low, the amperage is reading high, in the area of almost 50 amps. When I turn off the lights, the voltage reads 12V+ and the
amperage drops to about 25 - 35, depending on what is running. With the APU running, the amp gauge reads near zero.

Thanks again
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
 
I have 3 dead Flukes sitting here now. They were company issued and we had our own department to fix them. Because so many of them failed it was
cheaper and faster to do it in house. We had several thousand of them out there and they were used daily. So when they failed you needed a
replacement now. We kept about 3 spares in the office and the Centralized Parts Center kept some too. So you could get a replacement on the once or
twice daily parts courier runs. They moved the repair facility called ICAR (Instrument Calibration and Repair) to the Centralized Parts Center for
direct access to the Parts Courier delivery and pick system. You always got your original one back in 3 to 5 days. We did the same thing with
Tecktronics Scopes but they seldom failed. They still got sent in for calibration annually.

Anyway, when I left I kept two Flukes, and Laurie kept one. They all 3 have failed in different ways over the last 22 years. I have no access to ICAR
any more to send them in for repair. They are still used by field techs today. They were a good meter but for daily use their reliability is
questionable.

I have found a Chinese meter I like better with more features like higher sample rate etc. Johnny Bridges put me on to them. I have 3 of them (home,
Airport, and Pick up Truck) and have never had a failure. I have checked them for voltage calibration against my Scope and they have always been
right on. At the time I got them for about $20.00 each. Now they are $30.00. I see them on Aliexpress for $25.00 to 35.00. Probably Bang Good has
them too. At that price they are a throw away item if they were ever to fail. I ordered a total of 6 of them and gave away 3. One is a computer
Networking Tech who uses his almost daily. One to a GNMCer and one to my daughter. There may be newer models as this was a few years ago. Both Home
Depot and Lowes had them for around $90.00

Peak Meter PM18C

Someone here on GMC net said they got one that was defective at time. I do not remember the rest of of the story. I assume they got a replacement.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
I've personally never had problems with a Fluke meter.

I have an old Fluke bench meter, an 8060A, it was loaned to me about 30 years ago by an engineer when my Phillips meter blew up in the middle of a
job, the next day he want back to Akron and I never saw him again. His replacement said it was a spare shop meter and not to worry about it.

Soon after I got a Fluke 76 which is a better field tool, it's very similar to the 77 but is true RMS.

More recently we all had to upgrade to CAT IV meters for safety reasons, so I got a Fluke 177. I like this one a lot, true RMS and it has a large
backlit display with bar-graph and a setting to catch either highest or lowest readings which is good for troubleshooting.
I also have a Fluke hall-effect DC clamp-on and a cheap AC clamp-on plus many test probes and clamps/clips.

Cheaper meters are fine in some applications, but I'd rather have a Fluke in my hand when measuring 600volts and up.
--
Burl Vibert
Kingston, Ontario
1976 GMC 26 foot, Sheridan reno, don't know original model but we call her Roxie
 
> I have 3 dead Flukes sitting here now. They were company issued and we had our own department to fix them. Because so many of them failed it was
> cheaper and faster to do it in house.
>
> Anyway, when I left I kept two Flukes, and Laurie kept one. They all 3 have failed in different ways over the last 22 years. I have no access to
> ICAR any more to send them in for repair. They are still used by field techs today. They were a good meter but for daily use their reliability is
> questionable.

Ken,

I am curious what you did to them to require such attention. Mine have not. (Well, things do happen.)

My oldest 77 is about 40yo and I had to repair the range switch a long time ago. I also blew a trace off the current measuring parts (my fault and I
patched that and added a fuse). It is now a bench only meter just out of respect. The newer 77 is only a little over 30 and looks like new. I carry
that in the coach. The 87 I got for a special client's needs and it and its kit is about 25yo, but I needed the true RMS and the Bell probe. That 87
had the display go bad and I bought an Ebay kit for about 20$ to fix that and on of the sections of the lead points went bad and that was another Ebay
part.

Recently, I came across an jewel I just couldn't pass up. 40$us from Amazon. A Thsinde ACM1 says it does DC current as a clap-on! I have not had a
chance to check that out. I do not like the display (no fast bar graph and the decimal gets lost) and it never seems to sit down so I can see it, but
if I should loose it overboard, I won't cry either.

I used to give away the Hazard Fright cheapies to clients that didn't have a meter onboard. He would look at it and tell me he didn't what to do with
it, and I would say when you call me (they all have my work number on the side), I can tell you what you need to do and know. For that reason, I
carried one in my own kit so when we had to do the diagnostic over the VHF or telephone, I knew what he had. It worked very well more than a few
times.

We are cold here now, so I'm going to have to get the coach into the barn soon.

Matt
--
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
 
I've got a Fluke clamp - on with leads and several scales for voltages well, but the most used is the $8 Hashimoto Mouse one I got off eBay. They
were sold under several names. And were famous for being intermittent. A bit of investigation showed that the safety covers on the probe plugs were
a bot too long. I've now resurrected several of these with an X-Acto by trimming the plastic back about an eighth of an inch. They have a
display which dies in sunshine so if you have one keep it out of direct sunlight.

That being said, I was at Ken Henderson's place helping with a coach which wouldn't keep the battery up. No help from a voltmeter, charging voltage
was 14 and a bit, but the coach would sag on the road for lack of spark. Ammeter to the rescue, we determined the battery was drawing way too much
current. Took it out an hour after running it, and the battery was still very hot to the tough. Since there's a warehouse for that brand in the area
we took the battery down there. The guy remarked on it being warm even then. One of the interior cells was failing. It was a week or two out of
full warranty but they honored it anyway ad gave us a new one. An ammeter would have shown this at first crank up and saved a bit of troubleshooting
time. Yes, I'm old fashioned.

DOS Tip: Put your ammeter in the gr4ound lead of the battery, it's safer

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
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