Measure 100 amps with 10 amp meter ?

[seanc]

Steve:

Yep, a multimeter works great, but sometimes it's not convenient.

In my case, I only have one DMM, and I use it for a lot of other things besides plating, so the dedicated amp meter relieved me of constantly switching the meter around.

But the price of some of these offshore DMMs is so cheap anymore, it might be worth it to get a few of them for dedicated purposes.

Sean

[sdold]

Yeah, no kidding, they are cheap

I thought he was looking for a multimeter, since he said everything he was seeing was 10A, which sounds like the typical DMM. I might have been wrong.

Maybe he could just get a panel-mounted meter, aren't they something like 0-50 microamps? And put some kind of shunt around that. For a hundred amps, maybe a 1-inch piece of copper bar would be about right

[seanc]

Steve:

I didn't read his post carefully enough. I though he already HAD the 10A meter.

I don't know that analog panel meters have any standard rating, but every digital panel meter I've seen has always been based on a 200mV full scale volt meter. You know, the 0-1.999 4-digit type.

Both ammeter and voltmeter are the same except the input wiring. The voltmeter is wired as a 2 resistor voltage divider, while the ammeter is just a shunt resistor. Otherwise, both meters are identical 200mV volt meters.

Copper pipe would work! Or tie into a chunk of the house plumbing and heat your water while you're plating!

Seriously, a large low resistance might possible without too much expense, if you can find the right value parts. I once racked up some 15 ohm , 50w power resistors (the gold aluminum heat sink type) for an amplifier dummy load. 16 of them gave me 800w of dissipation. They were cheap surplus, 50¢ each.

If you could find them in 1 or .1 ohm values, a rack of them would work, and give you a nice hot plate to boot!

Sean

[eprigge]

In the end it doesn't really matter whether you have a DMM in current or voltage mode or a panel meter or what, you still need to buy/make a very low value high power shunt for the meter. You don't want anything much over 0.001 ohms just because of heat dissipation.

Again I'd suggest using a length of 10-12 (or thicker) gauge wire as the shunt. If you can get a known value current source from a power supply, you should be able to make your own shunt to work very accurately with whatever meter you choose.

There usually several power shunts made for this purpose on ebay also.

[HobbyTalk]

1 foot of 10 gage copper wire is .00118 ohms. From this you can easily figure amps by measuring the voltage drop across the wire.

[dadkar2]

If you want a really solid solution, It turns out you can buy a 100 or 300A shunt from Mouser. They are in the $45-55 range. Here is the link which will take you to their online store:

http://www.mouser.com/index.cfm?hand...denumber=52917

You can use these with any standard DMM or analog meter that can measure 50mV. The concern with the previously described solutions is handling the power in the shunt. These shunts are designed for the amperage you're asking to measure. The wire idea is really cool, but calibrating it will be more tricky than you might think at first. Also, it has a tempco of about .4% per degree C. As the wire self-heats, the value will change.

If you prefer an analog meter, they're for sale too, on the same page!

My search on Caswell's page turned up no products for sale or I would have recommended those first. It could be that Ebay might be a source for these...but you might not get what you think you're getting especially if it were abused. My batting average in buying electronic instrumentation on Ebay (and having it work to spec) has been below 50%.

Regards,
Ken

[moto-chrome]

Thanks for all the suggestions. As a cheap solution I followed SDOLD's suggestion. I used a cheap multimeter that can read 200 mV. One lead is connected to the start of my positive bar (1/2 in copper tubing) and the other is connected to the same bar about 5 ft away, at the same point where my anode jumper connects. The only disadvantage is that the jumper going to my anodes must always be connected (welded) at the same point, so I had to make it a little longer to be able to reach all plating tanks. Accuracy is only 95 % at the low and high end but pretty damn good from 5 to 95 A. A reading of 1 mV = 1 A.

I will eventually buy a good shunt.

[sdold]

Right on, that's cool that it works. Dadkar2's shunt idea is a good one, I completely forgot about those.

Steve

[asdco]

stewart warner makes a 100 amp analog (i have one in my shop). If you build a shunt that big you need a special metal, can't remember the name of it (i have a piece of that too lol) its not expensive (i got 3 feet of it for 10 bucks) but you have to build up a bridge with it and it gets super hot when running. The way it works is; the bridge carries the entire current load and the amp gauge just takes a test reading off the bridge. the bridge metal has a known ohm drop per inch. you can adjust the meter by lengthining or shortening the distance between the amp wires. The amp wires hook parallel to the shunt. All in all, its easier to just find a stewart warner gauge, I think I paid around 50 bucks for mine.