blown starting capacitor... X2 [RE-wrenches]

[Windy Dankoff, Dankoff Solar]

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>I have a submersible pump question for the group. I have a customer with
>a buried water storage tank fed with water from a DC well pump. In this
>tank is a 120 VAC 1/2 HP (fed via Trace SW2512) submersible pump for
>pressurizing the domestic water delivery system's plumbing. All has been
>fine with this system until the customer got a bean in her bonnet last
>week about cleaning out the storage tank. She drained the tank ....


>Questions...
>What would make this happen? The only thing I can see that was different
>with the pump is that it no doubt had air in it when starting after the
>cleaning. The pump is only about 4 years old, and has seen low use
>levels, so I would suspect it is fine, especially since after the
>capacitor was replaced everything operated fine again.
>
>Do people familiar with these capacitor start motors think a bit of air
>in the pump could cause this to happen?

Due to being on the road, possibly somebody has given reply, but here's mine.

When any centrifugal (impeller) pump is under light pressure load, it 
responds by shooting out a lot more volume of water, and this 
INCREASES the load on the motor (contrary to typical assumption).

So, the motor starting against NO HEAD in the depleted pressure tank 
has to come up to speed against more load than usual. The duration of 
startup is therefore longer. The capacitor is active during startup, 
and can blow if startup is prolonged. THAT is probably the cause.

That can happen any time the pressure is depleted for any reason, so 
you should find a solution now.

>
>Maybe running on a "sine wave" inverter is causing this and the
>capacitor's size needs to be changed to accommodate Trace's less than
>perfect replication of a sine wave?

Never heard of that problem. I'd more suspect low voltage/power 
output during startup, especially if you observe dimming lights 
during startup or if it also happens when inverter is heavily loaded 
by other appliances. It could also be excessive voltage drop in the 
wiring to the control box and/or pump. It could also be excessive 
drop in the DC input to the inverter -- any of the above!

Advice I've received from good pump supplier in cases where 
generators (their familiar realm) are slow to start a pump and caps 
blow, is to use approx. 10% higher-MFD capacitor (not more than 
that). It tends to solve the problem, at least that's all I know. If 
it works, make more tests and TRY to blow the cap before smiling. 
Leave at least one spare at the site.

Windy

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