1.5 HP well pump [RE-wrenches]

Tue Aug 9 08:56:36 PDT 2005

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Dan,

That wasn't me who suggested the Allan-Bradley device and I'm not 
familiar with it. However, I wouldn't gamble any money trying to use it 
on a system with a mod-sine inverter. Any electronic power-controlling 
device is almost certain to function well below optimally on mod-sine.

and Travis,

I disagree about reducing pressure switch setting or even pumping to a 
storage tank at 0 pressurizing. 2 reasons:

1. The starting condition that the inverter system can't handle is the 
initial kick from 0 RPM, also known as "locked rotor" condition. That's 
the same (during the very first applied AC cycle) whether the motor is 
on the bench or on a pump or actually locked. The mechanical load on 
the motor only effects the duration of the starting surge, not that 
initial peak of current draw. In the worst of cases, once the motor 
starts to move, it's generally "home free" (disregarding energy use 
after that).

2. The load on any centrifugal pump (that includes all of today's AC 
submersibles) is INVERSELY related to the pressure load on the pump. 
When it is against more pressure, it actually draws LESS current. Did 
you ever clog a vacuum cleaner (a centrifugal air pump)? It SPEEDS UP!  
All centrif water pumps act this way. But as the current draw drops a 
bit with pressure increase, the flow rate drops quickly. So the 
efficiency certainly decreases as should be obvious.

2 1/2.  You are good to suggest reducing the pressure switch setting(if 
feasible), but for a different reason. (Again) it won't help the 
starting condition, but it will speed up the flow rate and thus reduce 
the duration of the pumping cycle. I once dropped a customer's setting 
by about 30% (the upstairs shower etc. still worked fine) and it 
reduced the running time (and energy use) by 50%.

Conclusion: I would take a fresh look at the whole picture. Often a 
well has a water level that is much less deep than the hole itself, but 
the driller sells a pump that is sized to lift the full way, from 
near-bottom -- in case the water level ever does drop down low AND then 
he sizes it big enough to supply that mini-mansion and guest house and 
pool that the customer may someday build AND he can make a couple 
hundred extra $ by having such beneficial foresight.

An optimimally selected conventional AC sub is about 35% efficient (in 
terms of watts per pumped gallon). A pump that is oversized for the job 
is often closer to 20%. That's BEFORE adding inverter losses. You know 
what I'm going to say next -- One of today's helical rotor DC 
submersible systems can be found in the 45 - 60% efficiency range. And, 
some of them are big enough now to handle both lift and pressurizing 
sufficient for most home situations.

Over.
Windy

> Date: Mon, 8 Aug 2005 17:20:05 -0700
> From: "Dan Rice" <danrice at scinternet.net>
> Subject: Re: 1.5 HP well pump [RE-wrenches]
>
> Todd,
>
> Windy once suggested an Allan-Bradley "Starting Torque Controller" to
> address starting surge issues on a well pump. Fortunately or 
> unfortunately,
> I never had the chance to try it out. I did have the opportunity to 
> look the
> device up on the Allan Bradley web site -the document I have is titled
> "Selection Guide, Smart Motor Controllers, Bulletin 150, 154,1560" 
> -you may
> be able to find this document on the A-B web site and see for yourself 
> what
> the unit does. The model number I looked into was a 154-A11NA, good 
> for 11A
> at 240 VAC. They make versions that handle up to 22 amps (I'm assuming
> that's full-load current). Two rotary switches allow you to set the 
> initial
> starting torque (10-80%) and voltage ramp time (.1-4.5 sec.). The model
> referenced priced out at $350, and was readily available through the 
> local
> A-B supplier. Windy may have hands-on experience with these units. I 
> have no
> knowledge of their in/compatibility with mod-sq. (A capacitor sounds a 
> lot
> cheaper and easier...).
>
> Dan Rice
> Abundant Sun, LLC.

Travis wrote:
> What's the pressure switch set at?  If it's a 40/60 you might solve the
> problem most of the time by changing out to a 20/40.
>
> What about using the 240v well pump to fill atmospheric storage tank?  
> =
> Then
> using a small pump (12 volt DC?) for pressure?  You could prove if this
> would work by testing to see how reliably the pump would start when the
> pressure is 0 psi.

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