Identify and test Indian amp meter pic 2

[rick anderson]

Where do the wires attach and how should I test it.
Check my previous thread for front view of meter.
Thanks, Rick.

[exeric]

I had a 1924 Big Chief with the ammeter/switch housing mounted to the top frame bar. The ammeter works by forming two coils of wire (from the battery) around the base of the ammeter (that's what the clip is for). On my ammeter it actually said something like "wrap twice" or two coils", I can't remember now, but it was on the face of the ammeter, and it was a genuine Indian ammeter. We'll have to get an electrical guy to tell us why wrapping two coils of wire around the base of that ammeter makes it work. I suspect it has something to do with electro-magnetic fields. As for how it works, and I'm really going out on a limb here, I would guess that it responds to the direction of the flow of electrons in the wire. Have I made a complete fool of myself ?

[Perry Ruiter]

I think the faces say "Use two turns". I thought I had a photo of one but apparently not. I think Eric's explanation is bang on (at least that's my understanding how it works too) ... Perry

[exeric]

Thanks Perry, and you're right, I remember now that it did say "use two turns". When I first saw that I thought that was the most cyrptic message I had ever seen on any mechanical or electrical device.

[petri]

I find the induced emf theory from two turns of wire around the meter hard to believe. Any old ammeter I ever saw operated on the shunt principle. The ammeter is in series with the power. Inside the ammeter there ought t be a calibrated shunt that drops a small ammount of voltage, it's just a resistor but of low resistance so it may not look like a resistor, maybe just a wire or flat plate. The voltage drop across the shunt drives the meter.

There are other ways to do this today. But I just can't believe enough field can be generated but two turns of wire around the outside of the ammeter to do anything.

Unless.......that two turns of wire is acting as the shunt and is on the outside rather than the inside of the case. Very strange and a very cheap way to do it. Plus the gauge of the wire would be very important with regards to getting the calibration correct. I have never seen an Indian ammeter or any of the old bike ammeters so I am only relating what I learned a long time ago. Certainly there's somebody on this forum that's had one of these apart.

Howard

[Perry Ruiter]

Howard - I'll freely admit I'm largely self taught in this area. The only formal training I've had in magnetism was Grade 6 science where we wrapped a wire around a nail and hooked it up to a battery to make an electromagnet. Likewise I have no idea how a modern ammeter works. They may very well involve the use of a shunt. However, back in the twenties the 10, 15 and 20 amp units seem to have passed the full load through the meter.

Now first to the meter at hand. I'll preface by saying that I've never actually owned or worked on one of these Westinghouse Indian meters. As I understand it, when they say "use two turns" they're not talking about wrapping the wire around the perimeter of the gauge. There is a "stud" out the underside. I believe it has a hole in it. You wrap the wire around this stud (perhaps looping through the hole). This stud is then turned into an electromagnet and thus affecting the needle deflection. It's important that two turns are used to generate an adequate magnetic field. At least that's how I assume it works.

Ammeters that I am more familiar with and have repaired in the past are the Weston model 354 as used on many makes during the twenties and standard on Harley from 29-33 and the US Gauge ammeter used on 29-31 Henderson and Excelsior. Prior to working on the Weston I ordered a copy of the patent from the US patent office (you need to understand how something works in order to fix it after all). Throughout the patent they talk about how a permanent magnet and an electromagnet affect the needle to indicate "current strength and direction". For example, here's a quote from the claim section of the patent "... an electrical measuring instrument, a permanent magnet, electromagnet, a magnetically polarized needle provided with an index, the poles of the permanent magnet and the the electromagnet being so constructed and arranged as to virtually surround the needle ..." (and so on). Likewise the US Gauge unit appears to be constructed on similar principles. I'll attach a photo showing a stripped down Weston 354 and US Gauge meter. You can see the coils used to create an electromagnetic field. The gauge of the wire used is adequate to pass the full load of the meter ... Perry

[petri]

Well Perry, one learns something everyday....hopefully.

I'm amazed to see it done this way but what you have described and shown in the pictures does seem to be an ammeter that functions by an induced magnetic field. Wrap wire around a ferrous material and you get a magnet. I wonder why they did it this way as the traditional method of a shunt is also simple and cheap? But then, there's always another approach possible and this method also appears to be cheap, probably cheaper.

Your to be commended for digging down to the original patents for this information. Very interesting.

Howard

[petri]

1935 Dykes Info on Ammeters

I'm taking Perry's lead and doing some research about this ammeter. I have a copy of the 1935 Dyke's Automobile and Gasoline Engine Encyclopedia. This is an absolutely marvelous source of information on vintage cars, engines and even has a short section on motorcycles. It's over 1200 pages long. The old timers will know of this book.

There is a nice section on ammeters. There were two types in general use in vehicles. The d'Arsonval movement which was accurate but delicate and used a moving coil. The other type seems to be the one we are referring to which Perry has identified and looks a lot like the US Gauge he pictured. It's known as a fixed coil type ammeter. I have attached a scan from my Dykes of the description of the operation of this type meter. Well, hopefully it's attached.

To answer Rick's question on how to test the ammeter. I would simply get a battery and a headlight and connect the ammeter in series with the headlight and connect the battery from the ammeter to the other side of the headlight. The needle should deflect one way or the other. If it doesn't there's something wrong with the meter. It appears to me all the current passes through the ammeter coil. If the coil is open you won't even light the headlight. Now if you want to calibrate it then you will have to check it against a modern meter in your light circuit. You probably have a standard Multimeter for checking out wiring. I would guess the headlight would draw a few amps but exactly how much I don't know.

I hope this helps.
Howard

[exeric]

You are probably right in regards to this particular ammeter because I see an impressed "+" symbol favoring the left side post. However, the ammeter I had used 2 wraps of wire and the posts on the back were strictly for mounting purposes. The ammeter I had also worked. It wasn't accurate but you could plainly tell charging from discharging.