Ever installed an Amp meter ?

[Rick Fisher]

Hello ..

I am considering installing an after market Amp meter on a machine which has an FLA of 20 amps. I am hoping that someone here has done it before.

I have been reading online, and this is what I believe.. hoping someone will correct me if wrong..

This is a good example.. pictures at the bottom .. http://www.ebay.com/itm/Blue-LCD-AC-100A-Digital-Amp-Meter-Mutual-Iinductor-/170515174773#ht_3583wt_901

Does one of the two hot wires simply pass through the " Current Transformer " .. like a clamp meter ? This would make it pretty simple to install ?

I wanted to go analog but wonder.. A 0-30 AC analog meter would be nice, but does it harm them if the Amperage exceeds 30 ? This motor is single phase, so I figure the start up current would be 80-90 amps..

Do Amp meters need power ? or are thy powered by the current in the line somehow ?

And finally, anyone know a good place to get one in the USA or Canada ?

[Rick Lizek]

What machine and why do you think you need an ammeter? Typical start up is 25% higher. Where did you get your numbers? In the commercial shops ammeter are on widebelts and we would put them on straight line rip saws to see when the blade was getting dull as it was a constant load. Putting one on most other machines gives no beneficial info.

When asking a question give more info!!!!!

[Rod Sheridan]

Hi Rick, the one you have illustrated comes with a 100 to 5 ampere current transformer.

The center hole in the current transformer is where you pass through one wire from your motor, the output of the current transformer goes to the meter.

One output lead of the current transformer must be grounded, and the output has to be connected to the meter, or shorted if current is passing through the current transformer.

The digital meter does need power. Surplus electronic places may be able to supply you with one locally................Regards, Rod.

[John Lanciani]

Typical start up is 25% higher.

Actually, locked rotor current on an induction motor started across the line (no soft start) is typically anywhere from 4 to 10 times full load current depending on the motor design. The inrush spike only lasts for a few cycles and it will not normally damage an ammeter that is fed from a current transformer like the one in the link is.

(I've actually measured the spike (with the appropriate equipment) and I've seen locked rotor currents over 125 amps on a singe phase 1.5 hp motor that had a FLA rating of 18 amps at 120v.)

[Myk Rian]

I see no need for a permanent mounting.
Just buy one of these, and use it on anything AC.
http://www.harborfreight.com/clamp-on-digital-multimeter-95683.html
Of course it's cheap, but they work.

[Ole Anderson]

Twenty bucks? I gotta get me one of those! It would be great for monitoring the draw on your dust collector to help judge performance under varying uses and changes. Disconnect the input duct to see full load amperage, then reconnect, close all gates to see motor load under minimal air flow so you have two reference points. Not quite as useful for that as a manometer, but for $20? I have a good digital clamp-on (and an older analog one too), but accessing a single wire for my DC in the closet is not real convenient. With the digital readout shown, I would mount it next to the starter in full view.

[Rick Fisher]

Ole..

That is exactly what I am talking about, and why I want to do it ..

Accessing a single wire is not simple on my DC..

I read on the FOG about a similar DC that drew 13 amps will all the gates closed, and 21 amps with no resistance at all.. The motor was rated for just under 19 amps FLA ..

As you say its no Manometer but its $20 bucks..

I have one on my sander and as the belt loads up the amperage rises .. once I learned to pay attention to it, its pretty cool.

[Van Huskey]

Actually, locked rotor current on an induction motor started across the line (no soft start) is typically anywhere from 4 to 10 times full load current depending on the motor design. The inrush spike only lasts for a few cycles and it will not normally damage an ammeter that is fed from a current transformer like the one in the link is.

(I've actually measured the spike (with the appropriate equipment) and I've seen locked rotor currents over 125 amps on a singe phase 1.5 hp motor that had a FLA rating of 18 amps at 120v.)

+1 the inrush spike is so short though not many meters are designed to read it correctly, show a significantly smaller spike as they can not react fast enough.

[Rick Fisher]

Hoping someone can help ..


I am wondering if there is a bad run cap in this motor ?


The motor is an ATB made in Germany 4hp x 220V PH 1 with a FLA of 19.0 Amps .. It runs a dust collector .. The dust collector has a warning sticker on the front saying not to run it without the ducting attached or it could go over current..

The ducting is 6" .. Blast Gates are all 6" ..

I took the cover off the starter and attached a clamp meter to one of the hot wires, between the starter and the motor ..

With a single 6" Blast Gate open, I started the DC .. The Amperage settled at 13.1 Amps..
I opened a second 6" Blast Gate and the Amperage jumped to 13.8 Amps.

Again, FLA is 19 Amps.. So this seemed healthy ..

I shut the DC off .. and opened up 6 gates.. Wanting to know if this was the problem ..

When I fired it up, it settled in at 23.4 Amps and stayed there .. Way over current..

So I shut it down .. Thinking " Holy **** "

I then closed every gate, this is the first time with zero air flow .. Fired it up and it settled at 17.4 Amps..

Now I am confused..

So I opened the original gate.. The one the machine started with and ran at 13.1 Amps..

The Amperage jumped to 20.4 Amps. Again, over current..

Question..

Could it be the Run Capacitor ?

I have no idea what the symptoms of a bad run cap are .. Could it be a bad start cap ? Is it still feeding power ?

There is no centrifugal switch on this motor ..

[Rod Sheridan]

Hi, the run capacitor is in series with the start winding, and allows current to flow through the start winding to improve the power factor and provide some power to the motor.

An intermittent run capacitor, or a loose connection on the run capacitor could cause higher than normal current flow.

Also check the operation of the start contactor to verify that it does open once you release the start push button.

Regards, Rod.

[Ole Anderson]

I ordered one of those $20 ammeters, it was delivered directly from China. I finally got around to installing it yesterday. I took a piece of 12 ga wire from my DC receptacle, led it out of the receptacle box, through the current transformer, and back into the box, wire nutted to the wire I had just removed from the receptacle. I used some 16 ga speaker wire to go from the 2 terminals on the transformer to the 2 terminals on the meter labeled input. I then took an old 12 volt "wall wart" transformer to give the meter the 8-12 volts it needed. I flush mounted the meter right in the OSB wall in my shop, near my 2 saws. Works like a charm. With all the gates open it reads 10.7 amps (vs 10.37 amps as read by my Amprobe Pro, about 3% difference). With all 6 gates closed (but each leaking a bit) it reads 8.8 amps. My 2 hp Oneida Super Dust Gorilla lists FLA at 11.5 amps at 240 volts. At startup, the meter reads about 72 amps. The power strip the 12 volt transformer plugs into has an off switch which I throw as I leave the shop so the ammeter is not powered on all the time as there is no off switch on it. It provides interesting data, but at this point, somewhat limited in usefulness. Here are some pics:

[Jim Neeley]

Ammeters for monitoring the power draw on our tools are generally only needed once in a while (such as when first checking out the system or when something seems haywire) but are handy on new or different tools as you wire them up. This is why the clamp-on's like Myk's are so popular.


Jim

[Rick Fisher]

There are some tools that I think they are kinda pointless on .. Table saws and band saws would be a great example, because you should be looking at your work when using one, not a meter..

Dust collectors are IMO a great place .. especially larger ones.. My DC has a warning sticker on it that says not to run it without ducting connected to the system because it will over draw ..

Another great application is sanding machines like Drum sanders or Wide Belts.. Really easy to go over current on a sander and not even know it .. Good indicator that your taking too much off, or the paper is all bunged up and needs cleaning ..

[John Lanciani]

Another great application is sanding machines like Drum sanders or Wide Belts.. Really easy to go over current on a sander and not even know it .. Good indicator that your taking too much off, or the paper is all bunged up and needs cleaning ..

I agree. The planer and wide sander are the only two machines that I care about current, I want to be able to run both of them as close to 100% as possible. For me, a manometer is much more valuable on the dust collector; it lets me know when it's time to look at the filter. Current readings on the DC are really only valuable at initial setup to verify design parameters.

[Curt Harms]

There are some tools that I think they are kinda pointless on .. Table saws and band saws would be a great example, because you should be looking at your work when using one, not a meter..

Dust collectors are IMO a great place .. especially larger ones.. My DC has a warning sticker on it that says not to run it without ducting connected to the system because it will over draw ..

Another great application is sanding machines like Drum sanders or Wide Belts.. Really easy to go over current on a sander and not even know it .. Good indicator that your taking too much off, or the paper is all bunged up and needs cleaning ..

Yup, I found an ammeter on a Performax 16-32 drum sander very useful. I was tripping the overload often before adding the meter, now I never trip it. I bought a direct read analog and wired a switched bypass for startup. I doubt a 20 amp. analog chinese meter is gonna be overbuilt;).