D.C. pumps and motors... [RE-wrenches]

[info at backwoodssolar.com]

There is still quite an efficiency difference, partly due to DC and partly
due to positive displacement versus centrifugal.  Easy to calculate:  A
Grundfos 120 volt AC well pump lifts 5 gpm 200 feet using about 750 watts
from battery to inverter I have measured.  Lets convert that to equivalent
of 150 watts for each 1 gallon per minute lifted 200 feet.

A Shurflo 9300 DC pump delivers about 3/4 gallon per minute if operated on
12 volt DC at 200 foot lift.  It uses about 25 watts.  That is about 33
watts per gallon per minute delivered.  Even if these numbers are a good
deal off, the difference is clear.

But the other argument is that the Grundfos AC pump will go nearly forever
without service, and gives water recovery more quickly.  I think this
explains why people with 2500 to 4000 watt inverters are choosing the AC
pumps, not that they are getting more efficient. Notice where people's
hearts really are.
Steve Willey
Backwoods Solar Electric Systems www.backwoodssolar.com
----- Original Message -----
From: Carl Emerson <freepower at freepower.co.nz>
To: <RE-wrenches at topica.com>
Sent: Monday, May 21, 2001 3:19 PM
Subject: Re: D.C. pumps and motors... [RE-wrenches]


> Hullo there...
>
> I have noticed that it is getting harder to obtain DC pumps and DC motors
in
> general.
>
> There used to be quite an efficiency advantage over AC but recent
> developments in inverter efficiency and motor design would seem to have
> resulted in a swing back to AC and in fact some prominent DC motor
> manufactures are closing shop.
>
> I would appreciate some discussion about this. Clearly the DC option
allows
> the inverter to remain asleep while pumping. Have DC motors had their day
??
>
> Appreciate your comment...
>
> Carl Emerson


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