Source for in-line amp meter?

[Tom Jones III]

I'm interested in the idea of monitoring sharpness of power tool blades with an amp meter. The idea is to wire a meter in the power line so that it comes on whenever the power is on and it will display only the amps in the circuit. I'm guessing that after some use, the operator will get a sense of the amount of amps that should be used for standard work and will notice an increase when the blades are getting dull.

Has anyone ever seen this in practice? Will it work? I wonder if the amount of increase in amps will be so small that it will not be noticeable. Does anyone know where I can get a very cheap amp meter to wire in? Could I accomplish the same thing by monitoring the resistance? This would assume that volts are relatively constant. I'm thinking that an amp meter may be hard to obtain for a low price but on ohm-meter should be really cheap.

[Don Baer]

with AC circuit you can use a resistor (sometimes called a shunt resister) you can however use one of these.

http://www.mcmaster.com/catalog/112/gfx/small/8264tp1s.gif (javascript:chgimg(6);)

It a device called a Clamp-On amp meter. You use it by clamping it on one leg of the incoming power. Costs about $80-$90.
If you want a perminate installation you could get a current tranformer and an appropriate meter. If your interested you can google CT and I am sure you would find all kinds of sources. In terms of would it work. I would think so but if your paying attention to the amp meter you wouldn't be paying attention to the part you are cutting so I don't think it would be safe. Of course this is all my opinion.

[Ed Lang]

I expect the problem will be keeping a constant feed rate and constant material density. If you change any of the above as well as the sharpness, you will change the current as well.

Good luck, sounds interesting.

[Tom Jones III]

For clarification, I was specifically thinking of attaching this to a planer. With a jointer you can feel it, with a TS I'd rather be looking at what I'm doing. This solves issues with feed rate and differing depth of cut and safety.

[Don Baer]

Then I would say it would work. The MacMaster Carr catalog has a whole bunch of CT and meter that you can get and It wouldn't cost you that much.

[Carl Eyman]

Tom: Before spending the money for a permanent system, I'd use a clamp-on to try to see if you can get meaningful results. For this you'd need a helper, of course. If you did conclude it is viable zi'd suggest the surplus outfit in Nebraska. I've bought a bunch of neat stuff there. If You can't find it with a search let me know and I'll get out a catalog - they're down at my shop. Since you'll want a meter that is pretty sensitive to read small differences in current, I'd suggest you wire it so it reads on demand only. That is have a push button that activates the ammeter only when pushed and held. This will take starting loads out of the mix and save some "bent needles" from pinning. I'll be interested in what the real gurus on matters electrical will have to say. Alternatively, you might get a smoke detector. When it goes off you have a dull blade.

[Brian Hale]

I've been wanting to do this to my Performax for some time now. I'll be real interested in what you come up with.

Brian :)

[Don Baer]

Along these same lines I am thinking of getting one of these things.

http://www.mcmaster.com/catalog/112/gfx/small/65795kp1s.gif (http://javascript<b></b>:chgimg(7);)

It's a current tranformer with an adjustable relay. Thinking about putting it in the circuit that will feed my TS,Router etc to automatically turn on the DC when I start a tool. That and a little off time delay timer and I should be set....:D

[tod evans]

lotsa sanders use this technology but i can`t recall ever seeing it used on a planer? i can usually tell by the cut how the blades are doing....02 tod

[Rob Will]

I have several motors on a grain handling system that each have a CT and a digital amp meter. We can actually tell when the grain moisture changes coming in from the field. Digital works well for "at a glance" readings on what your motors are doing.

Rob

[Rick Christopherson]

Just go to a surplus store and you will find analog meter faces. That's all you need. Some are placed in-line with the circuit, and some are inductively coupled to the circuit. If it's in-line, just make sure it can handle the full load of the motor.

These are the same meters you will find on tools (such as widebelt sanders) from the factory.

[Carl Eyman]

http://www.surplussales.com/ This is t6he source I referred to above. but the seem to have multiplied their prices by a factor of much since I last did business with them

[Charles McCracken]

Tom,

I have wired an extension cord with an inline ammeter and it works great for testing. The cord is wired for 220V but I also made an adapter to 120V that is simply a 220V male on one end and 120V female on the other wired to one leg. I used a digital meter that I think came from Digikey and a project case from Radio Shack. HTH

Edit: I think I may have used one of the M1-AA series meters from this company:
http://www.temp-inc.com/digital-panel-meters.htm

[Larry James]

I'm interested in the idea of monitoring sharpness of power tool blades with an amp meter. The idea is to wire a meter in the power line so that it comes on whenever the power is on and it will display only the amps in the circuit. I'm guessing that after some use, the operator will get a sense of the amount of amps that should be used for standard work and will notice an increase when the blades are getting dull.

Has anyone ever seen this in practice? Will it work? I wonder if the amount of increase in amps will be so small that it will not be noticeable. Does anyone know where I can get a very cheap amp meter to wire in? Could I accomplish the same thing by monitoring the resistance? This would assume that volts are relatively constant. I'm thinking that an amp meter may be hard to obtain for a low price but on ohm-meter should be really cheap.

Tom, a typical 120 volt, single phase motor usually draws about 3-5 times the name plate running current as the motor starts. This may be a problem If you select an inline meter based on name plate running amps. An analog meter would likely be damaged when the motor starts.

A meter selected based on starting amps may have a scale with a range so large small measurement changes would be difficult to read.

A clamp-on meter would seem to be a better choice. No wiring to do, and the ability to change ranges as needed. It would be easy to start the motor without a load, measure current, and then measure the current again with the tool under load.

The problem I see is you would need a “repeatable load” to make a comparison. The species of wood, size, amount of material removed, etc., would all be load factors.

Now that I think about it, experience with the tool, and tool maintenance, would be a better guide - and don’t forget that smoke detector.

PS - A typical ohmmeter uses a DC battery to measure resistance. Never connect an ohmmeter to a live AC circuit - dangerous to you and your meter!!!! AC motor circuits have what could simply be called AC resistance that cannot be measured with a DC ohmmeter.

Larry

[Dev Emch]

Along these same lines I am thinking of getting one of these things.

http://www.mcmaster.com/catalog/112/gfx/small/65795kp1s.gif (http://javascript%3Cb%3E%3C/b%3E:chgimg%287%29;)

It's a current tranformer with an adjustable relay. Thinking about putting it in the circuit that will feed my TS,Router etc to automatically turn on the DC when I start a tool. That and a little off time delay timer and I should be set....:D

Hey! I know this gizzmo! This is the device that makes the Kay phase converter fly. The wild leg goes theough the ferrite donut and the relay trips a square D three phase contactor relay which cuts the run caps into and out of circuit. Any idea where we can get these at a good price? Dealers being dealers often rip the dickens out of customers who buy one or two at a time! Shame on them!

[Don Baer]

Dev,
$72.20 from MacMaster Carr. Do a search on there web site for Current transformers.

[Dev Emch]

Actually there is no such thing as an inline amp meter esp. when you get into higher voltages. Instead, a shunt current is monitored through a very high reistance precision resistor. In the case of an analog meter, the actual meter is a D'Arnsval movment in which the face has been calibrated to read amps based on the value of the shut resistor. In essence, anything in which you can read a voltage can be calibrated. The fuel gage in your car is based on the same principle but instead of reading volts, its calibrated to read level of gasoline based on the variable voltage measurement comming off your fuel level transducer. You can do the same thing with the planer. You can actually make up a paper face for your meter to read SHARPEN - GETTING THERE - SCARY SHARP. Install a set of dog knives and take a reading of voltage. Then adjust your sensing resistor in terms of OHMs so that the needle is at full deflection or minimal deflection (which ever your looking for) for the dull knife set. Repeat with super sharp knives. Now you have some calibration points to work from. Clearly some are wondering why I mentioned volts in place of amps. Well, if I know the voltage drop across a precision resistor of known ohms, then by OHMS LAW, I now have the amps. Volts = Resistance * Current (I). Simple and oh so cool!

[Brian Dormer]

If you decide to use the clamp on meter (known in the trade as an Amp-Clamp) - you need to be aware of something....

If you just put the clamp around the regular power cord - you will get a reading of ZERO.

You will have to construct a short extension cord that has the hot wire (usually black, the other wires should be white (neutral) and green (ground)) seperated from the other two. You put the clamp around the hot wire to measure the current load. Note that this is for 110v.

IMHO - the amp clamp is BY FAR the easiest and safest method to measure current draw on large machines. It doesn't require any cutting of wires or inserting shunts into the circuit.

Amp Clamps are widely available - I got mine on sale for less than 20 bucks at Radio Shack. Came in a nice plastic case and all...

bd

[Matt Meiser]

Harbor Freight sells a usable clamp on meter for under $20. I did some testing on mine and found it to be plenty accurrate for checking basic loads and such. It might be worthwhile to pick one up to test out the concept.

[John Weber]

Tom,

ebay is a great source. Here is a link to my post about adding a meter to my Performax drum sander.

http://www.sawmillcreek.org/showthread.php?t=8243&highlight=performax

John

[Bruce Wrenn]

Along these same lines I am thinking of getting one of these things.

http://www.mcmaster.com/catalog/112/gfx/small/65795kp1s.gif (http://javascript<b></b>:chgimg(7);)

It's a current tranformer with an adjustable relay. Thinking about putting it in the circuit that will feed my TS,Router etc to automatically turn on the DC when I start a tool. That and a little off time delay timer and I should be set....:D It is a current sensor, probably from SSAC. Look up article on dust collector switch in FWW Aug,2000. I use this with a cube timer from Grainger to operate DC. Cube timers are available in both delay on and delay off. I use delay off as this lets DC run for about 10 seconds after shut down. This allows any dust in pipes to be cleared. By using article on efficent shop wiring in Popular Woodworking and adding a selector switch for 110 recpt. you could have either DC or no DC. Check Grainger as this sensor isn't in their cat., but they can probably get it. SSAC doesn't do direct sales, so you will have to go through one of their distributors.

[Dev Emch]

It is a current sensor, probably from SSAC. Look up article on dust collector switch in FWW Aug,2000. I use this with a cube timer from Grainger to operate DC. Cube timers are available in both delay on and delay off. I use delay off as this lets DC run for about 10 seconds after shut down. This allows any dust in pipes to be cleared. By using article on efficent shop wiring in Popular Woodworking and adding a selector switch for 110 recpt. you could have either DC or no DC. Check Grainger as this sensor isn't in their cat., but they can probably get it. SSAC doesn't do direct sales, so you will have to go through one of their distributors.

Your absolutely correct. It is SSAC which is owned by ABB. You may wish to try the various ABB distributors but McMaster Carr may be your best and most convienent source.

[lou sansone]

well ... back to the original reason for this monitor ...
I agree with tod and carl .. I just don't see the need for a planer.. wide belt yes and maybe some gigantic 50 or 75 hp planer in a large mill, but I really don't think it will show much meaningful info.
Lou