What? Watts to Amps?

[DynoDave]

Let me start by saying...I hate home electrical. Give me automotive 12V any day. But, I need to get my shop wired, and am working on a plan/schematic. I've gotten some good advice from some electricians, but thought I'd post this question here...sort of spread the pain around a little.

I have all of the lighting and outlets planned out, including a few special ones.

I'm down to planning circuits for the larger items, including the 220V items. However, the heater manufacturer (Mr. Heater) and the window A/C manufacturer (Samsung) don't provide amps of draw in their owner manuals. The best I can do is the label on the blower motors themselves. While this does not include power for the control panel and sensors (A/C), or the electronic ignition (heater), it's the best I'm going to be able to do, it would seem.

The heater blower motor says 115V, 35W. Using an online calculator (http://www.supercircuits.com/resources/tools/volts-watts-amps-converter), I'm coming up with .304 amps. Is this correct? That seems like next to nothing. I know these blower motors are not huge, but still.....

Also, the A/C blower motor is 230V, 135W. Using the same calculator, I'm coming up with .586A. Again, this doesn't seem like a lot of power. I guess with as much as they will run, you don't want much draw.

Doh...forgot...there has to be an electric motor in the A/C unit to run the compressor! Just ran out to the garage and took another look. It does indeed appear that there is just the one electric motor. The shaft runs through it, driving both the compressor and cooling fans. Again, strikes me as a small amount of current for a window A/C unit, but I bought a 220V piece as they were supposed to be more efficient. I'm sure when the larger electric bills start rolling in, I won't feel so good about it!

Anyway, can someone confirm those watts to amps conversions, so I make sure I'm on the right track? Don't want a design that has too much load on a breaker. Thanks.

 

[Stuart in MN]

Watts = volts x amps, so those numbers are correct.

The amp draw of a Mr. Heater or similar gas unit heater is very small, and yes you need to consider the compressor when figuring the amp draw of an air conditioner. Window units probably require 8 to 10 amps or so, depending on the size.

edit: the 8 to 10 amps above is for a 120vac air conditioner, 240vac units will be different. I looked at the LG window air conditioner website and they give the amp ratings for their various size air conditioners, you could match up with the BTU rating of yours to see what they say. http://www.lg.com/us/window-air-conditioners

 

[rkevins]

To find amps Divide P (watts) by E (voltage) 115v / 35w = 3.3 amps
230v / 135w = 1.7 amps

I have never seen a window ac with only one motor, you should have a compressor and a double shafted motor with a blower wheel on one end and a fan blade on the other

Both manuals should have a supply voltage and suggested breaker and plug amperage listed

 

[2ManyProjects]

Let me start by saying...I hate home electrical. Give me automotive 12V any day. But, I need to get my shop wired, and am working on a plan/schematic. I've gotten some good advice from some electricians, but thought I'd post this question here...sort of spread the pain around a little.

Electricity is electricity. The basic principles remain the same pretty much regardless of the application. Don't let it throw you.

I have all of the lighting and outlets planned out, including a few special ones.

I'm down to planning circuits for the larger items, including the 220V items. However, the heater manufacturer (Mr. Heater) and the window A/C manufacturer (Samsung) don't provide amps of draw in their owner manuals.

I'm about 99-44/100% certain that any electrical or electronic device sold to the public MUST by law be marked/labeled with its supply requirements, or at least have those requirements conspicuously published in the accompanying documentation. There MIGHT be an exemption for extremely low-power (say, under one watt or so) devices; but even if so, that would not apply to your situation. IOW... Look harder for those specs; they are SURELY out there.

The best I can do is the label on the blower motors themselves. While this does not include power for the control panel and sensors (A/C), or the electronic ignition (heater), it's the best I'm going to be able to do, it would seem.

That's not all you're going to miss. The A/C in particular will have a compressor which will use MUCH more juice than the blower motor will. Furthermore, all motor loads are by nature inductive; so "Watts" don't neatly match "Volt-Amps"; and the start-up surges will often be several times the steady-state running draw.

The heater blower motor says 115V, 35W. Using an online calculator (http://www.supercircuits.com/resources/tools/volts-watts-amps-converter), I'm coming up with .304 amps. Is this correct? That seems like next to nothing. I know these blower motors are not huge, but still.....

Your math is correct, as far as it goes. But for the reasons noted above, it doesn't go far enough.

Also, the A/C blower motor is 230V, 135W. Using the same calculator, I'm coming up with .586A. Again, this doesn't seem like a lot of power. I guess with as much as they will run, you don't want much draw.

Same answer.

Doh...forgot...there has to be an electric motor in the A/C unit to run the compressor! Just ran out to the garage and took another look. It does indeed appear that there is just the one electric motor. The shaft runs through it, driving both the compressor and cooling fans.

I SERIOUSLY doubt that. Even a relatively modest-capacity unit, such as this 12,000 BTU model:

http://www.samsung.com/latin_en/consumer/home-appliances/air-conditioners/window/AW12PKBCXVN

has a rated running draw of 5.5A at 220V.

Again, strikes me as a small amount of current for a window A/C unit, but I bought a 220V piece as they were supposed to be more efficient.

It's not that simple.

The efficiency of the unit itself is not dependent on its operating voltage. But the larger the unit, the more power it needs. The higher the supply voltage, the less current is needed to make a given amount of power. So larger units tend to use 220/240V, so as to permit sanely sized wiring to be used.

Anyway, can someone confirm those watts to amps conversions, so I make sure I'm on the right track? Don't want a design that has too much load on a breaker. Thanks.

The "bottom line" is, you need to really KNOW what your devices will be drawing, both steady-state AND during their initial start-up cycles. Then, and ONLY then, can you make intelligent decisions about what circuits to provide for them.

 

[ddawg16]

To find amps Divide P (watts) by E (voltage) 115v / 35w = 3.3 amps
230v / 135w = 1.7 amps

I have never seen a window ac with only one motor, you should have a compressor and a double shafted motor with a blower wheel on one end and a fan blade on the other

Both manuals should have a supply voltage and suggested breaker and plug amperage listed

You might want to double check your math.....you transposed voltage and watts.....you have the formula right...but you plugged in the wrong numbers....

So it would be 35w / 120vac

And, yes, I know everyone says 110Vac....or 220Vac....but in reality...if your getting 115Vac....break out the meter...that is a bit low....most houses should be 120/240 Vac....give or take a couple of volts (at the meter)

 

[rkevins]

You might want to double check your math.....you transposed voltage and watts.....you have the formula right...but you plugged in the wrong numbers....

So it would be 35w / 120vac

And, yes, I know everyone says 110Vac....or 220Vac....but in reality...if your getting 115Vac....break out the meter...that is a bit low....most houses should be 120/240 Vac....give or take a couple of volts (at the meter)

Yes I did transpose the numbers My Bad, Need to ware my glasses

 

[rkevins]

Yes I did transpose the numbers My Bad, Need to ware my glasses

So I deleted it

 

[nehog]

First, all electrical items such as heaters, AC units, etc., have specification plates with amperage draw. Also almost all can be researched on the web to find the relevant information.

So what model heater do you have? What model AC unit do you have? Also it is rare that an owner's manual doesn't have amperage draw as well.

Just a hint, don't take the current marked on individual components (such as fans) as that may give a value that is lower than the total draw.

 

[wyliesdiesels]

OP, What type of plug is on the AC unit?

So I deleted it

No need to delete the post. Just hit the edit button and fix it.

 

[Jagmandave]

what wylie says......look at the plug, that will tell you what size circuit you need. For the A/C - my 18K 220V A/C only required a 20A/240V circuit, but I got one that has heating built in, and that pulls more amps than the A/C does, so it required a 30 amp circuit.

Also, the instructions that came with my A/C unit were pretty complete regarding electrical draw and circuit size, did you read the book that came with?

 

[DynoDave]

Thanks guys. This is making more sense as we go here, and confirming what my gut was telling me on the draw for the a/c unit. It's a 220V 18k btu unit, and if I could run it on only a .5A, then I'd be tearing out my central air and installing a few of these! The one motor I can see does indeed have a shaft running straight through it, driving a fan for the condenser, and passing into an interior camber that is walled off, to drive the fan moving air over the evaporator. I'm assuming the compressor and it's drive motor are also inside this interior chamber. As it's a new unit, I wasn't anxious to start disassembling it, but I think your comments above tell me what I need to know about it's internal workings.

I know you'll be shocked , but it is true that I have been known to not read ever page of my owner manuals. So on the possibility that I missed it the first time, I went back and looked at the manuals again.

The a/c unit is a Samsung AW18ECB7. The only technical specs I can find are these....worse than worthless.

I found it in .pdf form on-line...

http://downloadcenter.samsung.com/content/UM/200612/20061227091431109_LOWES.pdf

...and searched it for the word "amp". It only appears two places, and in neither occasion to tell me how many amps this unit needs to function safely (for both my wiring and the motors). But they did give me the same worthless info. in what appears to be Spanish. Does that help?? No, no it does not. There is a drawing of the plug ends on page e22, but unfortunately, the 15A and 30A versions look identical as far as pin layout goes, with only a blade thickness difference between them.

Here's the actual plug. Those terminals don't look especially large/thick to me, so 15A plug? It says 13.5A on the decal, but I wasn't sure what to make of that.

The hanging furnace is a Mr. Heater (That's MR. HEATER to you, pal!), model MH75. Again, a second pass through the manual produced nothing of value. If anything, it's actually LESS informative than the Samsung manual.

I again found a copy of the manual on-line, searched for the word "amp", and don't find much of value.

http://www.mrheater.com/Upload%5CGeneralManuals%5CGarage%20Heaters%5C60016_MHU_HSU_45_75_rev_b.pdf

Thus far in my plan, I've used 8 of the 20 available breaker slots in the box. I think I'm going to need 4 of those to create 2 220V circuits (one shared for the MIG welder and the four-post lift [I'll never be welding with one hand and raising the lift with another], and one for the air compressor), so that's 12 gone. I want to save one for another project I won't get to before I die, so that's 13 gone. With 7 breakers left, I'm thinking of just dedicating 2 more to create a dedicated 220V circuit for the air conditioner. Does that make sense? That would still leave me 5 breakers not in use.

As for the heater, if it's really .3A draw, I think I can bury that in another circuit that is lightly loaded. I currently (!) have breaker #7 with just two outdoor outlets (which will seldom be sued), and 2 ceiling outlets, which at most might have a drop light on them. Only question with that is, I've been advised no more than 4 20A outlets on a circuit. Would I be pushing it by adding this heater to that circuit?

 

[nehog]

Wow, that is one crappy manual! (Yep, I read it too.)

It says a 15 amp circuit, but again, there should be a plate or sticker on the unit (probably/usually behind the front cover) that will list both voltage and current requirements.

 

[Dick in Wisconsin]

Only question with that is, I've been advised no more than 4 20A outlets on a circuit. Would I be pushing it by adding this heater to that circuit?

You'll need to take a pliers and turn those blades on the plug 90 degrees to plug it in.

When you think about how many "things" to put on a single circuit, think about whether they will be running at the same time. If they will, you might be in trouble.

 

[nehog]

You'll need to take a pliers and turn those blades on the plug 90 degrees to plug it in...

When you post humor you really need a smilie so that people will know you are not serious. There are people who would read what you posted and think you were serious about that.

 

[2ManyProjects]

Thanks guys. This is making more sense as we go here, and confirming what my gut was telling me on the draw for the a/c unit. It's a 220V 18k btu unit, and if I could run it on only a .5A, then I'd be tearing out my central air and installing a few of these!

Exactly. And given the info I found earlier on its little brother, you can be sure this model uses significantly MORE juice.

The a/c unit is a Samsung AW18ECB7. The only technical specs I can find are these....worse than worthless.

You are so right -- that is pitiful. Were I you, I'd be calling up Samsung bright and early tomorrow morning specifically to ***** about this, even if you do manage to find the info you need elsewhere.

There is a drawing of the plug ends on page e22, but unfortunately, the 15A and 30A versions look identical as far as pin layout goes, with only a blade thickness difference between them.

There is also a major difference in their overall physical size. Side-by-side, you would NEVER mistake one for the other.

Here's the actual plug. Those terminals don't look especially large/thick to me, so 15A plug? It says 13.5A on the decal, but I wasn't sure what to make of that.

There isn't much in that image to establish scale, so I cannot be sure. But based on the "13.5A" notation, I'd bet on it being a NEMA 6-15P, meaning it would be rated for up to 15 Amps at 240VAC.

Here is what I would suggest at this point: Take some measurements of the pin sizes & spacing, write them down, then go to your local Home Despot or Low-Uh-Oh's. Take your note and your tape measure with you. Walk down the electrical aisle and find the twin flat-blade variants of both the 6-15R and 6-30R type receptacles. There will be enough of a difference in their physical sizes that you will NOT mistake one for the other. Here is an image of at least most of the possible variants, along with their current ratings:

(Hmmm... The image sn't showing up in "Preview", perhaps because it's an SVG type. If it doesn't show up once this message is really posted, try this: http://upload.wikimedia.org/wikipedia/commons/0/0d/NEMA_simplified_pins.svg)

Once you unambiguously determine the plug type, buy the matching receptacle, and the appropriate wire to support it. The wire MUST be adequate to support the maximum rated draw of the receptacle, even if the device you plan to plug in there won't draw that much.

The hanging furnace is a Mr. Heater (That's MR. HEATER to you, pal!), model MH75. Again, a second pass through the manual produced nothing of value. If anything, it's actually LESS informative than the Samsung manual.

I again found a copy of the manual on-line, searched for the word "amp", and don't find much of value.

http://www.mrheater.com/Upload%5CGeneralManuals%5CGarage%20Heaters%5C60016_MHU_HSU_45_75_rev_b.pdf

That too is a pretty useless manual; but it does confirm one useful thing: Based on the diagram at the top of Page 10, it is clear that this unit uses only a standard 120V branch circuit. That still doesn't tell you how much current it draws; but given that the electric is used only to run the blower fan and the control system, and in the absence of any info to the contrary, I'd easily believe that a standard 15-Amp lighting circuit is more than adequate. Still, they really ought to spell it out in the manual; and I'm still betting that it's stamped SOMEWHERE on the unit itself.

Thus far in my plan, I've used 8 of the 20 available breaker slots in the box. I think I'm going to need 4 of those to create 2 220V circuits (one shared for the MIG welder and the four-post lift [I'll never be welding with one hand and raising the lift with another], and one for the air compressor),

I'm more than happy to accept the premise that you won't be doing any simultaneous ambidextrous lift-jockeying and arc-welding, BUT... Is there ANY possibility that a "Helper" will ever be in play?

so that's 12 gone. I want to save one for another project I won't get to before I die, so that's 13 gone. With 7 breakers left, I'm thinking of just dedicating 2 more to create a dedicated 220V circuit for the air conditioner. Does that make sense? That would still leave me 5 breakers not in use.

Makes sense to me.

As for the heater, if it's really .3A draw, I think I can bury that in another circuit that is lightly loaded.

That is near-certainly correct. OTOH, given that this unit is gas-fired, if there ever came a reason to disable the heater, would you want to ALSO have to disable whatever else is on that circuit? I wouldn't

I currently (!) have breaker #7 with just two outdoor outlets (which will seldom be sued),

I know we live in a ridiculously litigious society... But when was the last time an electrical outlet was hauled into court as a defendant?

and 2 ceiling outlets, which at most might have a drop light on them. Only question with that is, I've been advised no more than 4 20A outlets on a circuit. Would I be pushing it by adding this heater to that circuit?

From a current-draw standpoint, near-certainly no. But there remains the "isolated disconnect" issue.

Per your slot count above, even if you dedicate a breaker to the heater, then worse case you'll still have six open slots when all is said and done (four, after deducting the two you want to save for your top-secret military skunkworks project). Assuming you've already installed (or at least accounted for) everything your heart could desire (now or later) in the way of electrical gizmos in that shop, that would be enough "fudge factor" for me; but if it's not enough for you to feel comfortable, then NOW is the time to buy a bigger panel.

 

[G_P]

Every window AC I have seen had a sticker on the side listing the specs and amp draw. The sticker is typically placed so that it is visible from inside the house once the unit is installed.

Here is the sticker on my bedroom unit. Yours should have something similar.

Sent via carrier pigeon.

 

[DynoDave]

Sued = Used. Darned S made an *** out of me again. That's one of the many problems with typing with 2 fingers.

Thanks again for all of the answers guys. Looks like I'm on the right track here, which is nice to know.

I'll be driving right by there (Lowes) tomorrow night, so I'll stop in and compare measurements on those plugs. The drawing in that chart shows that the drawing in the manual is yet another FAIL.

No secrets on the mystery outlet, really. I'm out of open breakers in the house. I may, someday, build a deck with screen-room on the back of the house. If so, to get power to it, I thought I'd "borrow" it from the new garage. It's sort of a roundabout way of getting there, but it will work. Again, if I live that long!

Good point on servicing the heater. My home furnace blower has a separate switch mounted in-line in the conduit feeding it. Maybe I'll add one of those up high by the unit, so it can be powered down for service/cleaning when needed.

As for the helper, and the possibility of running the lift and welder simultaneously. Anything is POSSIBLE. But I'm not expecting it. My son might help (assuming I get the shop done before he moves out), but only at my specific direction. My wife and daughter will probably never step foot in the place. It'll just be me for the most part.

I "think" I've accounted for all of my electrical needs. God knows I've been planning long enough. And while I have as much of a garage toy addiction as anyone, I've already got more things to stick in the garage than I ever thought I'd have. Still, if I need more power in the future, the capacity is there.

 

[BFBOB]

Try searching for "Ampere". It should be capitalized since it's someone's name. Some French guy back in the early days of electricity. Lots of electrical terms are named after the early experimenters, like Volts (Volta), Ohms, Gauss, Hertz and Farads (Faraday). Edison came along too late to get one of the big properties named after him, but he did get the nod for a particular size of light bulb screw base. (AKA "medium base")