Power consumption in the shop

[Steve Paxman]

So, I got myself a "kill-a-watt" thingy just out of curiosity yesterday. Basically, I wanted to know how much power each item in my shop actually uses. As winter approaches, my garage gets cold, and I'll be pointing a heater directly at myself while turning on the lathe (I hope it helps!). But I know the heater runs at 1200 watts (10amps at 120volts), and I have a single 20amp circuit out there.

I didn't write down exact numbers for anything, but the results were interesting. The lathe (1.5hp Jet 1642) only uses about 2 amps, give or take an amp. Disc sander, about the same. Drill press, also about the same, as well as the bench grinder. I was surprised to find that all those tools actually draw about the same amount of electricity, and that it was less than I thought.

Bandsaw - I have a small 1/3 hp 12" bandsaw (I need a new one, suggestions???), and naturally it draws much more. Closer to 7 or 8 amps. I didn't test my compound miter saw, but I highly suspect it's up there around 10 amps as well.

Anyway, bottom line is, I should mostly have no trouble running a heater on that circuit while I turn on the lathe, etc. That's a relief.

(Not coincidentally, I now also know how much power almost everything in my house with a plug uses, right down to the 8 amp toaster...)

[Shawn Pachlhofer]

you must be an engineer.

[John Keeton]

Steve, I agree on the engineer thing!! I keep my shop heated to 50* all winter (baseboard heat), and the bill is just whatever it is. In addition, I do have a radiant heater directed down on my neck and back when I am turning. That helps a lot more than a floor heater would IMO.

[Reed Gray]

I put an independent meter on my shop, and compare numbers to the one on the house. Over the course of a year, I use about the same amount of juice. I do heat the shop with a little radiator. The house has electric ceiling heat, but I do 98% of the house heating with the wood stove.

If your little 1/3 hp bandsaw is using that much juice, it is probably because it has to work harder from being a bit undersized. Now, an excuse to buy a new bigger bandsaw for research purposes....

robo hippy

[Kyle Iwamoto]

Yep, us engineers always try to over think everything. Personally, I find the 2 amp draw on your 1642 a little perplexing. I would think it draws much more than that. Perhaps it was not under a load? At any rate, I'd put the lathe on a dedicated circuit, and more so NOT on the same circuit as the heater. The heater is pure resistance, and will always draw lots of current. If it's on the same circuit as your lathe and you take a heavy cut and load down the motor, that could cause the breaker to trip. Something I would not like to happen in the middle of a cut. The voltage droop running the heater and lathe on the same circuit could also be bad. Don't know much about VFDs. I do know they like full voltage. Since you only have 1 circuit, your may want to drop in another while it's still warm.

Just my $0.02.

[Thom Sturgill]

I agee completely with Kyle's comment.

Pull another circuit, preferably not on the same lead as the lathe. If possible use a breaker space next to the one feeding the shop. That way they could be strapped together to provide 220 in the future (although you would need to pull additional circuits then). The idea is to put them on different phase leads so that there is no interaction between the circuits. This way, if the heater cuts in while doing a heavy cut neither affects the other. Too heavy a draw can pull down every circuit that uses the same phase.

[Scott Lux]

Wait until you check your shop vac

[Faust M. Ruggiero]

In the end, other than an electric heater, you will find your florescent lights consume a lot of your total consumption. They are on constantly.
faust

[Steve Peterson]

Yep, us engineers always try to over think everything. Personally, I find the 2 amp draw on your 1642 a little perplexing. I would think it draws much more than that. Perhaps it was not under a load?

I suspect that the Jet measurement was made with the lathe running at idle. It will be much higher when you are roughing a large blank. A VFD only uses as much power as it needs to maintain the requested speed. No load (just spinning) takes very little power.

The Jet manual appears to need 12-16A of current at 120V, although it is well hidden. It would be worth running a dedicated circuit for the lathe.

Steve

[Dave Cullen]

You really need to check power draw under load. A freewheeling induction motor doesn't use much power until you put a load on it. Somewhere 10 - 25% I think is "rule of thumb". Better still, if the tool has a Full Load Amps (FLA) rating on the nameplate, use that instead of your measurements.

Also be aware that starting current can be 150% of FLA. It's only for a second or so, but long enough to pop a breaker if you're on the threshold.

1200 watts won't get you much in a cold garage unless you're sitting on it. My shop heater is a 220V 4000 watt unit that I plug into a 30 amp dryer outlet. If you only have a 20 amp 120V line, I'd consider propane instead.

EE Dave

[Doug Ladendorf]

Not that I need to pile on but I'll echo what Dave said above. Try testing again but put a load on the machines and I bet you will see a big difference. With a single 20 amp circuit you will want to look at a propane heater, ideally vented.

Doug

[Jon McElwain]

Did you run your current measurement while the motors were under a load? Your lathe will draw more than 2 amps when you've got a 15" blank and you make deep cuts with a 5/8 bowl gouge. My guess is that the +/-2 amps you measured was with the motors just spinning (doesn't take much amperage to just spin a motor), but not performing the work they are capable of performing.

[Reed Gray]

I had Brent English help me reset the parameters on my VFD so I could sand bowls at 20 or so rpm. He was concerned that the motor could over heat. I was told by the PM people, that they changed the off speed to 50 rpm because the motors would over heat and fry the motor and electronics when running at those speeds even though I told them I had sanded out thousands of bowls at those speeds. Well, I continue to check when sanding, and the motor runs a lot cooler when sanding than it does when I turn. When I turn, I make my lathe WORK. They do use more when under load than they do when in idle speeds.

robo hippy

[Steve Paxman]

Good points, all. Yes, all my measurements were made with no load.

The heater is no good for the rest of the garage, but it's a parabolic (radiant) heater, so as long as it is pointed right at me while I'm standing there at the lathe, it takes the edge off the cold. It did last winter, anyway, when I only had a tiny bench-top lathe. I will try some more measurements while turning something, or drilling something, etc, and see how it changes.

There is an outlet on the other side of the garage that is on a separate circuit. I may draw from that one for the heater with an extension cord, instead of putting it on the same as the lathe. I guess I'll probably try out a few things and see what works.

To be honest, I'm in the Portland, Oregon area, where the winters just frankly are not as cold as they are in many other places. The few days where it truly gets cold (like in the teens), I just plain won't turn on those days. My little heater will heat my personal space up reasonably when the garage is sitting at 40* or so.

And for the record, I'm not an engineer. My college degree is Mathematics, and I'm an Actuary.

[Shawn Pachlhofer]

And for the record, I'm not an engineer. My college degree is Mathematics, and I'm an Actuary.

just as bad.

I'm an engineer...and if I had that doodad - I would have done the same thing you did.