Analog Ammeter

How to keep the Cessna 170 flying and airworthy.

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Analog Ammeter

Postby Mschwarzkopf » Thu Feb 08, 2018 11:13 pm

My ammeter has recently been intermittent, and now I think it has failed (at least it appears that way). Do you have any good suggestions on troubleshooting and testing the ammeter in/out of the aircraft?

I can't recall the last time I saw a large charging draw after startup, and only recently have not been getting a huge drain with landing lights on. Now, I don't get any indication at all on the gauge, + or-.

Should I just pull it out and connect it in series with a 12V battery and lamp to test it? Could I also connect a digital multimeter in series to verify the ammeter reading?

I would like to install an EI amp/voltmeter at some point, but if I have an easy fix on this gauge, that's what I'd like to do right now. I could use a good reference to send the gauge to be checked out, too. I was given Paul Malkasians (sp?) number in AZ (Instrument Rebuild); sounds like he was a pretty knowledgeable guy, but he passed away last year. So, if anybody has any other good shops, please let me know.

On a final note, I talked to Whelen last week, and they are now saying that they expect PMA on their Chroma LED nav lights in April.

Thanks, Mike


IMG_2578.JPG
Any idea what manufacturer?
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IMG_2590.JPG
Not sure why there's a tie-wrap in there!
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Re: Analog Ammeter

Postby gahorn » Fri Feb 09, 2018 4:30 pm

That's a common automotive type instrument and is so inexpensive that it's not worth spending money at an instrument shop, IMO.
The Ammeter requires a "shunt" appropriate to the amperage of the meter and charging system. Most of them are internal shunts, but confirm it when ordering. NAPA or any good automotive shop can supply a geniune Stewart-Warner guage.
https://www.amazon.com/Stewart-Warner-8 ... ds=ammeter
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Re: Analog Ammeter

Postby Mschwarzkopf » Fri Feb 09, 2018 6:26 pm

Thanks, George.
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Re: Analog Ammeter

Postby Mschwarzkopf » Tue Feb 13, 2018 2:15 am

While I’m waiting for a cheapo gauge to come from Amazon, I decided to pull my ammeter and check it out. I must have spent an hour cleaning 25 years of gunk, if not more, off of the terminals, case and mounting brackets. Hooked it up to a few 12v halogen bulbs, and whatdya know, matched up perfectly with the multimeter. Back into the airplane she goes.
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Re: Analog Ammeter

Postby gahorn » Tue Feb 13, 2018 6:49 pm

Great news!

I once found my airplane battery would not hold a charge and it was only a year old. :cry:

I bought a new battery and it died within 6 months. The charging system tested fine. I disgustedly bought a new battery. It died within the month.

....long story....(with expletives deleted)....

Bottom line: Bad connections at the Ammeter.

Knowlege gained: ALL current passes through those Ammeter connections. Keep 'em shiney/tightey.

Add the following to your "Post-Start Checklist": After engine start-CONFIRM high charge-rate. (Charging system is working.)
Add the following to your "Pre-T/O Checklist": Battery charge rate almost completely diminished. (Battery is re-charged)

Keep in mind that the REAL REASON for a battery is NOT to start your engine. Starting your engine is only a GOOD TEST of your battery capacity.
After engine start...you battery should have a need for a healthy RE-CHARGE...and that should show up as a high-amperage charge rate. (something on the order of 20A or MORE....for a minute or two.)
The REAL REASON for a battery on an airplane is for EMERGENCY ELECTRICAL POWER in the event of failed generated power. Therefore...MAKE CERTAIN YOUR BATTERY IS essentiallY RE-CHARGED BEFORE FLIGHT. This will be indicated by that ammeter greatly reducing the charge rate having re-charged the battery from it's losses incurred during the start.
These checks are almost as important as checking for oil-pressure after engine-start, so ADD the checks to your check-list.

Keep in mind that landing/taxi lights are not a continuously operating item. The above comments are made without the use of land/taxi lights which will obscure/confuse the ammeter readings. In other words, use the ammeter readings to measure your battery health without the land/taxi lights interference.

Hope this helps.
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Re: Analog Ammeter

Postby gfeher » Tue Feb 13, 2018 10:47 pm

But does anyone know who manufactured the original ammeters like those shown in Mike's first pic? I have one and it doesn't have any markings on it anywhere. A previous owner of my plane swapped the generator for a 50 amp alternator and changed the ammeter to a modern 60 amp one. I'd like to see if the manufacturer of those original 30 amp ones also made a 60 amp version. (I know Stewart-Warner now makes a similar 60 amp one, but the graphics are not quite the same.)
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Re: Analog Ammeter

Postby lowNslow » Tue Feb 13, 2018 11:37 pm

Mine actually says "Cessna" on the bottom, but not who made it.
Last edited by lowNslow on Wed Feb 14, 2018 2:38 pm, edited 1 time in total.
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Re: Analog Ammeter

Postby n2582d » Wed Feb 14, 2018 12:05 am

Karl, That's interesting. I've yet to see one with a Cessna logo. Does it have a part number (0411020) on the circumference like the oil temperature gauge pictured here? The '48 IPC calls for "Cessna Print 0411020". The later models call for p/n 0411020 or 0411020-1. Like Gene, I too was hoping I could find a 60 amp ammeter that matched the original. The closest I found was Stewart Warner p/n 82202 as shown here:
unnamed.jpg
unnamed.jpg (15.49 KiB) Viewed 3099 times
It does not use an external shunt.
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Re: Analog Ammeter

Postby gahorn » Wed Feb 14, 2018 12:30 am

"Cessna" logos don't mean a thing... except that some instrument shop silk-screened it onto the face. If it's important to you...send it to any competent instrument shop who can duplicate the original.
Most "original" (automotive type) cessna instruments were made by Rochester and Stewart-Warner...some BY Rochester FOR SW who had a supply-contract with Cessna. A very few aircraft-quality instruments were made by Tennstedt (a division of Cadillac/GM) but usually for higher priced models than the 120/140/170s and gov't contracts.
Other major suppliers for the aircraft quality instruments were Pioneer and Kollsman and Garwin.
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Re: Analog Ammeter

Postby gfeher » Wed Feb 14, 2018 1:59 am

Well, the bug caught me on this one and after spending time researching on the Internet and lurking on hotrod forums (apparently where the real experts on vintage engine gauges hang out) I think I found the answer. According my research and the experts on those hotrod forums, the original 30 amp ammeter is a Stewart-Warner "standard" 30 amp ammeter from the 1930's to the 1950's when the graphics of the "standard" series was changed to approximately what it is today. One of the collectors on one of the forums estimates that the graphics were changed in about 1955. Here are some pics comparing the two:

DSCN1866[1].jpg
30s-50s SW "Standard" 30A Ammeter
DSCN1866[1].jpg (25.15 KiB) Viewed 3081 times

s-l225IAUJ3B5U.jpg
Current SW "Standard" 30A Ammeter
s-l225IAUJ3B5U.jpg (9.21 KiB) Viewed 3081 times


This hotrod forum thread has about the best info on it (although there are others with similar info):
https://www.jalopyjournal.com/forum/thr ... in.119647/

And yes, Gary, SW did make a 60 amp ammeter in that early time frame like the 30 amp one. Here's a pic of one I found on the Internet. (It's missing the bezel and glass though):

s-l225MC036AHE.jpg
30s-50s SW "Standard" 60A Ammeter
s-l225MC036AHE.jpg (6.49 KiB) Viewed 3081 times
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Re: Analog Ammeter

Postby n2582d » Wed Feb 14, 2018 5:26 am

Nice sleuthing Gene! Did you happen to get a part number for that 60 amp. gauge?
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Re: Analog Ammeter

Postby gfeher » Wed Feb 14, 2018 10:16 am

No. I haven't been able to find SW part numbers for either the 30A or 60A gauge. I'm hoping to run across a SW catalog from the 40's at some point. But it may take some time for one to surface. It doesn't appear that the gauges themselves are marked with a part number.
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Re: Analog Ammeter

Postby gfeher » Wed Feb 14, 2018 11:56 am

On a hunch, I was able to find a page from a 1949 Stewart-Warner catalog showing both the 30-0-30 amp ammeter originally used in C-170 models and a 60-0-60 amp version of the same gauge. The 30-0-30 amp one used in C-170 models is Stewart-Warner p/n 95245. The 60-0-60 amp version is Stewart-Warner p/n 95367. I've uploaded a pdf copy of the catalog page to the MX Library. Gary, you owe me a beer for this one. I'll collect it at the Cody convention if you are there. :D
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Re: Analog Ammeter

Postby n2582d » Wed Feb 14, 2018 12:23 pm

Amazing! I owe you more than one beer! I was looking for over an hour last night and only found a couple of rusty examples for around $50. I did find that they are referred to as “tulip” needles. Of course, if even the hot rod crowd doesn’t know the p/n it’s going to be tough finding one of these ammeters online.
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Re: Analog Ammeter

Postby gahorn » Wed Feb 14, 2018 1:16 pm

CCF02142018.pdf
(1.49 MiB) Downloaded 75 times
These gauges are listed in the NAPA/Echlin catalog also.
They make the distinction as being "Deluxe" gauges and "Standard" gauges, with the Standard having the "grid" type display and the Deluxe having the plainer type. Click on the pic twice to ENLARGE. Notice the Deluxe version even goes up to 100 Amps. The needles are not the "spade" types found in some early examples tho.
SWAmmeters.jpg

CCF02142018.pdf
(1.49 MiB) Downloaded 75 times
'53 B-model N146YS SN:25713
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