Voltage limiting w/ C40 [RE-wrenches]

[Windy Dankoff, Dankoff Solar]

<x-flowed>
Wrenches,

I agree with Daryl on a regulation method. I can clarify other 
factors that contribute to decoupling of a mag-coupled pump.

Decoupling is caused by exceeding the TORQUE capacity of the 
coupling. Once the magnetic poles are pulled out of the range of 
strong attraction, the thing completely decouples. The motor keeps 
spinning, but the impeller just sits still. (No harm is done to the 
pump, and it will re-couple when the motor stops.)

The torque increases with speed (voltage). So, in a given 
installation, there will be a critical voltage at which it will tend 
to decouple.

In all centrifugal pumps (including blowers), the torque (load on the 
motor) DECREASES as the head increases. (That's why a vacuum cleaner 
speeds up when it's blocked.)

This means that an efficient hydronic system (with low friction loss) 
will put greater load on the pump -- BUT the pump will push a 
proportionally greater flow. The pump is doing more work and is more 
energy-efficient. However, this type of system is more likely to 
decouple!

The variance in head in various applications helps account for why 
some March pumps may decouple at 27V and others at 32V.

Factors that will cause unwanted decoupling include ANY factors that 
cause excessive torque at the coupling. In other words, any source of 
mechanical friction at the impeller. A pump that is decoupling 
mysteriously should be taken apart and inspected for debris or 
deposits that make it harder to turn. An impeller that is harder to 
turn at one point in the rotation tends to bounce against the 
magnetic force. The torque peak at the low point of the bounce will 
cause a very premature decoupling.

Decoupling can be predicted. The torque is proportional to the amp 
draw of the pump. The pump should never decouple within its rated 
amps range. If you are at a site when the voltage is (let's say) 26V 
and the pump current draw is close to its rated maximum, you should 
suspect that it will exceed the max. and may be in danger of 
decoupling.

If decoupling occurs at the max. rated current or less, the pump is 
at fault. If there isn't friction in the impeller, then the magnets 
may be weak, or misaligned.

I ask -- is this a common problem, or a rare one?

Windy



Darryl Thayer wrote:
>Brad
>I have had problems with the March magnetic coupling
>also, I never knew what the problem was however. 
>
>At 26 or 27 volts then you are to close to the limit.
>This small delta is not practical.  First you must
>limit the voltage to the pump to less than 24.
>However, at 26 or 27 the battery is not fully charged.
>
>
>IMO you must limit the voltage to the pump, I would
>use a series regulator.  YOu can buy a three terminal
>positive adjustable regulator that can handle 5 amps
>and your pump is only maybe 2 or 3 amps. If the pump
>is more use a cheaper regulator with a power
>transistor. 
>
>Daryl

- - - -
To send a message: RE-wrenches at topica.com

Archive of previous messages: http://www.topica.com/lists/RE-wrenches/

List rules & etiquette: http://www.mrsharkey.com/wrenches/etiquete.htm

Check out participant bios: www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine

Moderator: michael.welch at homepower.com
--^----------------------------------------------------------------
This email was sent to: michael.welch at homepower.com

EASY UNSUBSCRIBE click here: http://topica.com/u/?bz8Qcs.bz9JC9.bWljaGFl
Or send an email to: RE-wrenches-unsubscribe at topica.com

TOPICA - Start your own email discussion group. FREE!
http://www.topica.com/partner/tag02/create/index2.html
--^----------------------------------------------------------------


</x-flowed>