# Two questions..

What's the formula for converting electrical motor hp to watts/amps?
Also, a while back someone posted a link for a site that rebuilds battery packs for cordless tools. Could someone repost?
Bob S.
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Bob S. wrote:

One horsepower is 746 watts. But that assumes a power factor of 1.0, i.e., no inductive or capacitive component. Most motors are inductive when running and some have a large capacitive load when starting.
A PF of 1.0 means you can multiply the voltage (120 vac) and current to get watts. Light bulbs behave well this way.
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Stubby wrote:

And, if you don't believe that, use http://www.onlineconversion.com /
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First, go to google.com, and type in "converting electrical motor hp to watts/amps" in the box in the middle of the page. This does a web search. Click on the first result returned.
Then, go to http://groups.google.com/group/alt.home.repair , type in "rebuilds battery packs for cordless tools" in the search box to the right. This does a search of alt.home.repair, where you posted this question. Click on the first result returned.
Sheesh.
-K
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kevin wrote:

OK, wise ass, you type it in and see how many hits you get. None. Ditto for "converting electrical hp to watts" , and a few other variations, which I did before my post. If you can't help, keep your comments to yourself!
Bob S.
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It doesn't really work anyway. There are so many different types of motors and lies they tell about the power that the only valid way to determine the ampacity of the supply conductors is to use the nameplate rating on the motor. If you look at the typical amps to HP in the electric code table you will see they are nowhere near that "watts/hp" theoretical range.
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Bob S. wrote:

Bob - You must be doing something wrong. Do what he said, leave off quotes and remove the '/' in watts/amps and you will get all the info you are looking for!
A little bit of teaching a man to fish vs giving him his fish here. Not that the regulars don't like fishing for other people. Don't get me wrong, we like fish. Mmmm, fish.
Inviato da X-Privat.Org - Registrazione gratuita http://www.x-privat.org/join.php
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Bob S. wrote:

Give a man a fish, and you feed him for one day. Try to teach him how to fish and turn him into an ingrate.
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Well, hold on. Go try those two searches. I didn't even type it in... I just copy and pasted right from your question. The first hit in both cases had a pretty good answer, including the company that hallerb suggested.
-Kevin
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Bob, *even* if seaching didn't work, you're as bad as you think Kevin is. If you wanted to not get the kind of reply Kevin gave, you could have started your first post with "I searched google, but..."
You could have replied that way even now, without resorting to vulgar insults. Do you think it is cool to use them?
And it's your mistake you didn't write down the name of the rebuilder when it was first posted.

No. It's you who should be quiet. Everything is free here. If you didn't like his answer, ignore it or say that you did look in google. Then you'll seem like a grown-up instead of someone on steroids.

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There is no one formula to convert the HP to watts/amps. YOu did not mention if it was a 3 phase or single phase motor. Also some motors are more efficiant than others. I work for a large industrial plant. We get in some 3 phase motors that take 2 amps and some that take almost 4 amps to produce the same ammount of work. When the motors are replaced we have to look at the nameplate and see how much current they take so we can resize the overloads or change the setup for the inverters that drive them.
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Typically small motors on home tools are about 10a(120v)/hp, +/- 20%.

When I looked into rebuilding was more than new batteries. A search will probably turn up vendors.

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From the NEC Full Load Current, single phase AC motors table 430.148 HP 115 Volts 200 Volts 208 Volts 230 Volts
_______________________________________________________________________ 1/6 4.4 2.5 2.4 2.2 1/4 5.8 3.3 3.2 2.9 1/3 7.2 4.1 4.0 3.6 1/2 9.8 5.6 5.4 4.9 3/4 13.8 7.9 7.6 6.9
_______________________________________________________________________ 1 16 9.2 8.8 8 1 1/2 20 11.5 11 10 2 24 13.8 13.2 12 3 34 19.6 18.7 17
_______________________________________________________________________ 5 56 32.2 30.8 28 7 1/2 80 46 44 40 10 100 57.5 55 50
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Toller wrote:

What I was looking for was amperage on a 3/4 hp, 1 ph, 240v submersible well pump. The data plate is 220' underground so it is kinda hard to read from up here.

12v rebuilts are about \$33 vs \$52 for a new pack. But I guess when you add in s&h it'll be about the same. Bob S.
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A clamp-on ammeter will tell you pretty accurately and quickly. Keep in mind that the current will increase some as the pressure builds toward cutoff and there is a short time very high current draw at startup. Clamp-on ammeters have gotten cheap enough that anyone doing electrical work should have one.
Don Young
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Bob S. wrote:

Watts is amperes times volts. Energy conversion says that one HP is about 750 watts. However you will never find a 1 hp motor that uses 750 watts or 6.25 A at 120 V. For example my 1hp saw motor is rated at 12 A, and a rough A measurement is about 10.5 A when the motor is running free. I also have a 1/3 hp motor that is rated at 6 A.
Your best bet is to look at some motor plates of motors similar to what you need. Age, type of motor, and size mean that a simple formula is unlikely to be helpful.
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http://www.primecell.com /
battery pack rebuilder
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snipped-for-privacy@aol.com wrote:

That was it. Thanks.
Bob S.
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