Watts a horse power [RE-wrenches]

Brian Teitelbaum brian at aeesolar.com
Thu Aug 11 14:18:57 PDT 2005


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Windy,

OK...I'll buy the wine...(I didn't realize that there was some fine print at
the bottom of the bet rules!)

Sure, it's probably pretty hard on the SQ to run it on mod-square, but the
SQ is not very expensive, and anyone who still uses mod-square inverters
these days (like me) is in low budget mode. The pump probably won't last 20
years (or even 15), but I'll bet the dinner back that all of these folks
have switched to sinewave before the pump dies. You may have to wait for a
few years...

Cheers (clink!),

Brian
AEE Solar





-----Original Message-----
From: Windy Dankoff [mailto:windydankoff at mac.com]
Sent: Thursday, August 11, 2005 11:50 AM
To: RE-wrenches at topica.com
Subject: Re: Watts a horse power [RE-wrenches]


Kurt, Todd,

In a theoretical world of 100% efficiency, and by definition, 1 HP =
746 watts.

Divide by the motor efficiency (expressed as a decimal) to get the
actual watts. For example:

A high-efficiency motor (or motor/electronic system), like a solar pump
motor, may be in the range of 90% efficiency. So you divide 746 / .90 =
830 watts. (The difference goes off as heat.)

An ordinary submersible pump motor is roughly 70% efficient. That's
because it's long and slender, which lengthens the windings beyond the
optimal configuration, and it's cheap, and there is no concern for the
heat since it's water-cooled. 746 / .70 = 1065 watts.

So our beloved 1.5 HP pump would require about 1600 watts.

Now figure about 20% more for the mod-square wave = 1920 watts.

Now divide by the inverter efficiency, uh, maybe 85? so 1920 / .85 =
2260 watts.

You measure over 2500 watts, but that's probably a little higher than
reality because the current draw of the inverter is pulsating and my
guess is that your meter probably reads it a bit high.

So there you are. It works like a charm!   :-|

As for the 1 HP SQ pump drawing 2400 watts, that sounds excessive. It's
a different motor technology but my impression is that the efficiency
is about the same as conventional pumps (after startup). And, you are
using sine wave, so I can't explain why that's so high unless the meter
responds to peaks of the pulsating DC draw, rather than to an average
(should not!). Might try another meter, like a clamp-on. Don? Have you
measured?

And Todd, yes, some drillers make a habit of putting an oversized pump
in the well. Besides some greed, they may actually feel that they are
doing a favor to the customer IN CASE of extraordinary circumstances.
Some customers love power !! They will take ASK for more if it doesn't
cost much or the driller just happens to have a bigger one on the shelf
that he's itchy to move.

How often does energy efficiency rear it's dainty little head in this
V8 world of ours?

Brian,

I'll buy you dinner when I visit some time, but only if the SQ is still
working, and you buy the wine. The reliability of any electronic device
is reduced on mod-square. It will certainly run hotter, and components
are stressed by spikes and vibration. I'm sure you have heard the
difference in numerous loads -- buzzing noise from transformers, fluor
lights, etc. The risk may be minor, but only collective experience will
tell.

Cheers (hopefully),
Windy

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