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

[Carl Emerson]

Steve...

Thanks for the response.

As I suspected the DC option wins every time if the issue is only efficiency.

Now to the second part of my question...
Some DC motor manufacturers are closing down. Apart from getting a motor that
might be specifically designed for a fork lift or a golf cart where can one get
a supply of DC motors ??
Typically my clients demand energy efficiency and luxury. They are often
wealthy green professionals who have escaped from the US and want heaven in
clean green NZ.
They typically want large pools that require lots of pumping. Commonly these
pumps will draw about 2.5 kW AC
As I normally use a 48 Volt battery bank I would like to run the pool pumps
with 48 Volt DC motors but have found them hard to obtain.

As a second option, is there a controller available that will reduce the power
requirement of an AC motor after start-up ?? I have heard of such a unit being
developed but nothing concrete.

Any thoughts welcome...

Cheers

Carl E

info at backwoodssolar.com wrote:

> 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

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