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

graham at solarexpert.com graham at solarexpert.com
Wed Sep 12 14:21:35 PDT 2001


I have witnessed numerous pumps fail to operate after a prolonged "dry run".
Perhaps the submersible pump was self lubricating with water and the
impeller shaft bearings overheated after the lady drained the storage tank.
The result is either a shaft bound pump or a melted plastic impeller that
cannot push water.  Do most submersible pumps have thermal protection
circuitry?

Graham

-----Original Message-----
From: Travis Creswell, Ozark Solar [mailto:ozsolar at ipa.net]
Sent: Wednesday, September 12, 2001 10:37 AM
To: RE-wrenches at topica.com
Subject: Re: blown starting capacitor... X2 [RE-wrenches]


The same is true of the blower motors in "Ozark" furnaces.  It all starts
when they find some used unit for $50 or free (probably because of a cracked
heat exchanger) to set up in their previously unheated shop.  An "Ozark"
furnace has no ductwork and is set up in the middle of a un-insulated metal
building then ran with a 100' 18-2 extension cord and a barbecue propane
tank sitting beside the unit.  Due to the lack of any resistance to air flow
the motor over spins and burns up.

Travis
----------
>From: "Windy Dankoff, Dankoff Solar" <windy at dankoffsolar.com>
>To: RE-wrenches at topica.com
>Subject: Re: blown starting capacitor... X2 [RE-wrenches]
>Date: Mon, Sep 10, 2001, 6:41 PM
>

>>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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