Cost to run a 30HP motor, for an hour?

[dirk martin]

For the heck of it, I asked ChatGPT the following:

How much does a 30 horse power, 73 amp motor cost to run per hour at 220 volts?

It replied with this:To determine the cost of running a 30 horsepower, 73 amp motor per hour at 220 volts, we need to calculate the power consumption and then multiply it by the electricity rate.

First, let's convert the horsepower to watts.

1 horsepower (HP) is approximately equal to 746 watts.

So, the power consumption of a 30 horsepower motor would be:

Power (in watts) = 30 HP × 746 = 22,380 watts = 22.38 kilowatts (kW)

Now, we can calculate the cost per hour using the power consumption and the electricity rate. Assuming a hypothetical electricity rate of 12 cents per kilowatt-hour:

Cost per hour = Power (in kW) × Electricity Rate (in c/kWh)
Cost per hour = 22.38 kW × 12 c/kWh = 268.56 cents or $2.6856

Therefore, at 220 volts and assuming an electricity rate of 12 cents per kilowatt-hour, the cost of running a 30 horsepower, 73 amp motor per hour would be approximately $2.6856. Please note that actual costs may vary depending on the specific electricity rate in your location.

Now, I'm not an electrician, but $2.68 per hour just seems way too low.
Is that reply accurate?

[David Buchhauser]

This seems correct to me. Simple calculations to make. But just think, if you run that motor 8 hours/day, 5 days/week, then you're looking at around $100 per month added to your electric bill. I will say that I use a 30 hp cnc rotary phase converter in my shop which does see quite a bit of use. So there is actually a 30 hp motor running as part of the phase converter. My electric bills typically run in the neighborhood of $300 to $400 per month, so what you say does not surprise me.

David

[Tom Bender]

David

Just a small adjustment to your math:

$2.68per hour x 40 hours per week x 4 weeks per month = $469

And a closer look at the loading:

A motor or a phase converter will only consume electricity proportional to the loading, which is rarely anywhere near full load on woodworking machinery. Fans are the most consistently loaded (dust collector).

[Jason Roehl]

There are two things that stand out to me.

1. 73A seems low for a 30hp motor. I poked around online, and saw a few rated in that ballpark for a 230V, 3-phase motor, but 73A x 230V = 17kW. Saw some others that were rated around 100A, which seems more realistic. For reference, I have some 208V, 3-phase motors at work, on VFDs, running at 45-50hz, rated 15hp and 20hp, and they may draw around 40A.

2. There’s no accounting for efficiency. A very good motor might get 95% efficiency, so that should be factored in (divide by .95).

All that said, you’d still probably be in the neighborhood of $3/hr to run a 30hp motor at $0.12/kWh—which is low for many residential areas in the U.S., but it could be even lower than that if it’s on a commercial 3-phase service.

[roger wiegand]

Well, to start with, our electric rates are about 34 cents/kWh; not sure who gets power for 12 cents these days after the half dozen "fees" get added on to the base rate. My solar panels keep looking like a better and better investment.

[Alan Lightstone]

Well, to start with, our electric rates are about 34 cents/kWh; not sure who gets power for 12 cents these days after the half dozen "fees" get added on to the base rate. My solar panels keep looking like a better and better investment.

Yup. Those panels just got much more valuable at my house as our local utility raised their rates 20% to $.156/kWh. Much more important to me, they also just raised what they pay me back to $0.06631/kWh from $0.0325/kWh, so since I produce a surplus, I'm doing great this year (the drought and endless sunny days isn't hurting). So, despite their despicable minimum monthly charge of $30.00 plus taxes, my panels just got substantially more valuable to me.

And those calculations seem correct, but you do have to account for efficiency and I agree that 73A seemed low for a 30HP motor, but looking up one Baldor 30A, 230V 3-Phase motor it spec'd at 72 amps. The motor had a power factor of 82, so you really do need to take that into account.

[David Buchhauser]

David

Just a small adjustment to your math:

$2.68per hour x 40 hours per week x 4 weeks per month = $469

And a closer look at the loading:

A motor or a phase converter will only consume electricity proportional to the loading, which is rarely anywhere near full load on woodworking machinery. Fans are the most consistently loaded (dust collector).

Let's see. 2.68 x 40 x 4 = 428.80. Not sure how you calculated your $469. But in any case -

Right you are!! I was thinking per week. My mistake. I think it also goes without saying that it depends on the load. Much like a car - better mileage going down hill than up hill. With the phase converter, it is acting as the "3rd leg" in converting single phase to 3 phase power. So it acts like an "idler". I was not suggesting that it is the equivalent of running a 30 hp motor at full load. In my case, the phase converter is powering several cnc machines with spindle HP ratings of 15hp, 10hp, and 5hp (at full load). Of course the loading on these depends on the work being performed.

But in essence, the OP is correct with his math. The price per kwh is for example only. This also I would think goes without saying.

David

[Edwin Santos]

David



A motor or a phase converter will only consume electricity proportional to the loading, which is rarely anywhere near full load on woodworking machinery. Fans are the most consistently loaded (dust collector).

If you wouldn't mind educating a simpleton - let's take a machine like a table saw. Does this comment mean there is a difference in power consumption between the saw simply running versus when it is actually cutting wood i.e. under load?
Is it a significant proportional difference or a relatively tight range of deviation?
Thanks

[Bert McMahan]

If you wouldn't mind educating a simpleton - let's take a machine like a table saw. Does this comment mean there is a difference in power consumption between the saw simply running versus when it is actually cutting wood i.e. under load?
Is it a significant proportional difference or a relatively tight range of deviation?
Thanks

I don't have actual numbers for a table saw, but yes, there will be a large difference. The motor will barely pull any current when running with no load, and will pull more current as you add more load. Cutting a thin piece of plywood will draw much less power than cutting a 2" thick piece of oak.

A more common example would be to compare your gas mileage if you're towing a heavy trailer- you'll use a lot more gas pulling something heavy than you do without. Another common example is a cordless power tool battery. You will drain your batteries a LOT faster drilling 2" holes in oak than drilling 1/8" holes in balsa.

Matthias Wandel did some good power testing comparing jointer heads here: https://www.youtube.com/watch?v=rehZ8SqszAk

His main focus is on the comparison of the heads, but he has "no load" values in there too. He idles at around 500 W, and it jumps up to about 1000 W when planing 1 mm off some wood. He basically found the load doubled in his case, but that's just for that particular piece of wood that was only 5" or 6" wide. A piece of wood half that wide would need half as much additional power (~750 W total, or 1.5x more), and a piece twice as wide would need twice the additional power (1500 W total, or 3x more).

I would suspect that his numbers are skewed since unloaded planer blades are (in my experience) much louder than unloaded table saw blades, meaning the wind load on the teeth alone makes up a lot of the power draw when idling.

(Side note: Matthias seems to have some issues with his Shelix head's bearings which he talked about in a followup video, so don't use this video by itself to compare helical and straight knives.)

[Malcolm McLeod]

...our electric rates are about 34 cents/kWh... not sure who gets power for 12 cents these days ...

Sorry. Average for TX is ~13.4 cents, depending on which source you believe (or don't). ETA - We're still paying a NG fuel surcharge (~2-3 cents, last I looked), but over last few months we're basically selling NG for cost ($2.30-ish/MCF), so surcharge should come off - and get us back to ~11 cents.

.. their despicable minimum monthly charge of $30.00 plus taxes, ...

Sounds pretty reasonable for a back-up 'generator' that someone else provides and maintains. And they even buy your intermittently generated surplus power. Some might call your surplus 'unreliable'. YMMV.

I'd check into a whole-house Generac with NG or LP fuel system as less despicable.

[Cameron Wood]

Then there's start up draw vs run draw. Literally running for an hour would average the start up current draw- a large multiple- into the current use for the hour, which at a rough guess would 1.5 or double the cost.

[Steve Demuth]

Well, to start with, our electric rates are about 34 cents/kWh; not sure who gets power for 12 cents these days after the half dozen "fees" get added on to the base rate. My solar panels keep looking like a better and better investment.

We pay 11.3 cents/kWh for power used. That's after $1.67/day basic service fee, which we pay regardless of how much power we use. We've got the largest solar array the REC will allow us to have on the line, so last year we used only roughly 1000kWh net draw from the grid. All in, we paid just about $750 for the electric service, which figured against our actual net draw, is $.75/kWh.

[Dan Friedrichs]

Then there's start up draw vs run draw. Literally running for an hour would average the start up current draw- a large multiple- into the current use for the hour, which at a rough guess would 1.5 or double the cost.

Say the motor draws 10x normal current for 1 sec while coming up to speed. The average of the first minute is then 1.15x, and the first hour 1.0025x.

Inrush current makes no difference.

[Joe Calhoon]

Your numbers seem about right. My rate is about 13 cents per and about $50 per month service charge. The kicker could be if due to more usage they put you on a demand meter. If that is the case you will be paying a lot more. My DC is 25 hp and a couple other machines are over 50 hp with multiple motors. Working by myself now part time and the bill is usually $180 to $220 per month. When I had a crew and working more it would be 3 to 400$ per month. A few years ago we hit the threshold for demand and the bull jumped to about $1500 per month. Just working one day a month would set the demand. Myself and a couple local ranchers negotiated with the utility to raise the threshold for demand and we would pay more per KW. I don’t mind paying for what I use.
I feel like what I pay now is very fair but fully expect electricity is going to get very expensive in the future.

[Cameron Wood]

Say the motor draws 10x normal current for 1 sec while coming up to speed. The average of the first minute is then 1.15x, and the first hour 1.0025x.

Inrush current makes no difference.

Hm, my rough guess was not good.

No idea what "inrush current" means.