clamp on amp meter

[Jim O'Dell]

Where can I buy a cheap but usable clip on amp meter to use with my cyclone to verify what the motor is doing? I've never used one before, does it just clip over the 220 cord and measures both lines at once? Wish there was a unit that clipped on, but then ran over to a separate display, say 2" tall numbers, I could mount on the wall to be able to glance at and see what's going on. :cool: Any ideas would be helpful. Don't know if Harbor Freight has anything like that or not, maybe Northern Tool? TIA! Jim.

[Bob Dodge]

I use a GreenLee which I bought at Grainger, but it's probably a little too pricey for what you want. It clamps around one of the "hot" wires.

http://www.grainger.com/Grainger/wwg/itemDetailsRender.shtml?ItemId=1613545656

[Jay Albrandt]

Jim,

I got mine at an electrical supply house, but I have seen them at the box stores, Sears, Radio Shack, speciality tool stores, etc.

Only one (1) hot lead should go through the meter so you will have to expose the jacketed wiring somewhere in the path to the cyclone. I have a junction box near the center of my shop that I use to turn the unit on and off, and that was a perfect location to test mine.

Good Luck.

Jay

[Jim O'Dell]

Thanks for the link, Bob. yeah, that's a little more than I want to go. I did a search on the bay, but didn't see that model. There are a couple of Greenlee 650's. I'm going to watch a couple of the auctions. I'll guess that Fluke is a decent brand, but what about Mastech? Fluke is actually the only brand there I recognize. Is that a....nevermind.:D
Jay, thanks for the info. I was afraid that it needed to be one wire at a time. That will pose a problem I'll have to deal with. I could run a junction box and put the wire through, just not brake the wire, but split the sheathing enough to separate the wires, and be able to access that in the ceiling from above the future work bench. (it's in line between the breaker panel and the cyclone's contactor)
Thanks for the quick help! Jim

[Kent Fitzgerald]

Harbor freight does have one: http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=42396

I'm using a Sperry clamp-amp meter purchased from Home Depot for about $60. I don't know if HD still carries them, but they are on ebay. It's worked well for me.


does it just clip over the 220 cord and measures both lines at once?
As others have mentioned, you'll need to split out one hot wire. Just to forestall any confusion about "measuring both lines at once": In a single phase circuit, the current through one hot wire is the total current through the motor. Do not add together the current measurements from the two hot wires.

[Steve Roxberg]

I've used the Harbour Freight unit and had good luck. It provided me with numbers which I believed.

[Doug Shepard]

OK my interest is piqued. Is this something I should have in my DC wiring path? Or just a neat feature? If it's drawing too much current the breaker will trip and shut it down right? Is there a reason I'd want to keep track of the readings as the unit was running?

[will sanders]

Why? I am in the electronics field and I fail to see why you want this. There are some meters made to monitor current draw on operating machines but those are usually wired in. A clamp on ameter is not designed for 100% duty cycle.

[Jim O'Dell]

Will, I'm saying it would be nice to have one that is hooked up all the time to a read out on the wall, not that I would leave a hand held one hooked up that way. Sorry if I wasn't clear. The hand held would be for testing purposes only.
Doug, the purpose of doing this is to check the load of the motor. With the system on, it should be below the motor's amp rating with all blast gates closed, as that's when it is doing the least amount of work. The more blast gates you open, the harder the motor has to work, to the point that if you open too many gates, the motor will pull more amps than it is designed to, and you can burn it up. Your circuit breakers in the breaker box are there to keep the shop/house from burning down if you do ruin a motor, but they won't save the motor. I want to be able to test the system and make sure what I can and can't do safely. If your motor has an overload button, then that should save the motor if it is working properly. Jim.

[Matt Meiser]

I have a Harbor Freight one and it works well for occasional use. I tried it on some different loads that I could calculate what the amps should be (a 100W and 500W light for example) and the amps were pretty much right on.

[lou sansone]

Will, I'm saying it would be nice to have one that is hooked up all the time to a read out on the wall, not that I would leave a hand held one hooked up that way. Sorry if I wasn't clear. The hand held would be for testing purposes only.
Doug, the purpose of doing this is to check the load of the motor. With the system on, it should be below the motor's amp rating with all blast gates closed, as that's when it is doing the least amount of work. The more blast gates you open, the harder the motor has to work, to the point that if you open too many gates, the motor will pull more amps than it is designed to, and you can burn it up. Your circuit breakers in the breaker box are there to keep the shop/house from burning down if you do ruin a motor, but they won't save the motor. I want to be able to test the system and make sure what I can and can't do safely. If your motor has an overload button, then that should save the motor if it is working properly. Jim.

not sure I understand you properly, but overload heaters in a motor starter are designed to do exactly what you want to do. I guess your motivation is to understand ahead of time how many gates you can have open before you overload the motor. If the heaters are set at the name place amperage value, then the tripping of the motor will tell you the same thing, albeit not with the precision of a amp meter.

Lou

[will sanders]

I think there is some false logic here. Your DC will move the same CFM of air no matter how many blast gates are open. IE one gate open at 100cf will move 100cfm at that point 2 might move 50 cfm at each gate etc. This is not like a saw that will overload and die. The DC will just be less efficent at each point, it can't work it self to death. Surely there is somebody here with HVAC expeience (SP) who can help. I think you are worreying too much.

[Frank Hagan]

For full time display, use a panel meter that you wire into the circuit permanently ... they are from $80 to $90, and designed for continuous use. McMaster Carr has them on page 688 of their catalog at http://www.mcmaster.com/

[Frank Hagan]

I think there is some false logic here. Your DC will move the same CFM of air no matter how many blast gates are open. IE one gate open at 100cf will move 100cfm at that point 2 might move 50 cfm at each gate etc. This is not like a saw that will overload and die. The DC will just be less efficent at each point, it can't work it self to death. Surely there is somebody here with HVAC expeience (SP) who can help. I think you are worreying too much.

My understanding from Bill Pentz's site, and the instructions they give you with a DC, that you have to have some resistance attached to it or it will indeed burn up the motor (or trip the thermal overload - if the motor has one). An amp test will tell you if the ducting with all gates open is enough resistance to allow the DC motor to run without overheating.

But I would think you only have to check that once, and then you know if the ducting itself is enough resistance or not. My wild guess is that it would be; seems to me I've seen tests where they attach about 10' of ducting to the DC system to test efficiency, but I don't know if they had a plate on the end of that 10' of duct that provided more resistance to air flow.

[Al Willits]

Having a bit of trouble with the motor overloading too, not sure, but the max work the motor can do is with no ducting hooked up to it, ie. maxium airflow, everything after that is gonna be less air moved ????

Possibly dumping huge amounts of sawdust into the blower might put a load on the impellor though??

Al...who's thinking HVAC though

[Jim O'Dell]

Yes, Lou, that's exactly what I want to know. How many can I open before I start creating a problem.
Will, Frank and I are going on the same information. I've also heard that you don't want to run a system without ducting for long. It's really backwards to me. My thinking has it pulling more amps with all the gates closed, but that's just not how it works according to those in the know.
Frank, thanks for the page at MC. If the numbers were taller, I'd be drooling over the thought....but at 1/2" tall, it's made for a panel that you are close to, and that wouldn't be the case here.
Al, I don't know if it is different from HVAC or not. I do know that HVAC sizes things, (air handler, compressor, duct sizes, etc) by the size of the house and the length of the runs. Don't know if it is for the load on the motor or not, though. Of course, the impeller on a DC and the fan on an HVAC are two totally different animals, except that they both move air. Lots of words to say I don't have the answers. I'm going on what I've read others more in the know that I have said to do, and I want to make sure that I don't ruin my investment in time and money. Jim.

[Bruce Wrenn]

Air has WEIGHT. Think of air as a fluid. With all the gates open, you are moving more air and hence more work is being done. Kinda like pumping water.

[Frank Hagan]

Yes, Lou, that's exactly what I want to know. How many can I open before I start creating a problem.
Will, Frank and I are going on the same information. I've also heard that you don't want to run a system without ducting for long. It's really backwards to me. My thinking has it pulling more amps with all the gates closed, but that's just not how it works according to those in the know.
Frank, thanks for the page at MC. If the numbers were taller, I'd be drooling over the thought....but at 1/2" tall, it's made for a panel that you are close to, and that wouldn't be the case here.
Al, I don't know if it is different from HVAC or not. I do know that HVAC sizes things, (air handler, compressor, duct sizes, etc) by the size of the house and the length of the runs. Don't know if it is for the load on the motor or not, though. Of course, the impeller on a DC and the fan on an HVAC are two totally different animals, except that they both move air. Lots of words to say I don't have the answers. I'm going on what I've read others more in the know that I have said to do, and I want to make sure that I don't ruin my investment in time and money. Jim.

You might look around for a larger ammeter at an electrical surplus store ... used to have one out in Riverside that I frequented, and they often had larger guages for quite a bit less than I could find in catalogs.

HVAC fans typically push against the resistance (ducting) with very little resistance on the negative side of the fan. With a cyclone you are pulling the air into the impeller and discharging against the filter assembly, so I think the relationship is reversed.

I know with water pumps, you can freewheel if you don't have enough backpressure for them to pump against. You get very little flow, the amp reading goes up and you overtax the motor. With some backpressure, you think the motor is working harder (pushing more water), but the amperage actually drops. You would think it would be the other way around. I'm sure there's an explanation, but until I hear it, I'm just going to consider it magic.

[Perry Holbrook]

Jim, looks like item number 250053346626 on ebay will do the job for you.

Perry

[Pat Turner]

Another option if you allready have a multimeter is to purchase a current transformer(CT). This is a doughnut shaped device with say a thousand turns of wire, You slip it over on of the conductors, and you can measure a current from the CT that is proportional to the current going to the motor. 90% of installed current AC current meters use CTs, as do most larger power meters. Cost is a few bucks each, and you can hookup to a multimeter with an AC Milliamps position, or buy a panel mount meter. if the current output is two low, you can loop the wire several times to increase the output.