mechanical burst generator

[europachris]

Is your setup using just the pressure switch to operate the pump?

Yep, just a Square-D pressure switch.  That's why they install 2-wire pumps - they are cheaper and do not require any sort of control box like a 3-wire pump.  Franklin also uses a BIAC rather than a mechanical switch to disconnect the split-phase start winding, so it is a pretty robust setup.  Since we have 200A 240V service, nobody cares about starting current demands.  Just bore the hole and drop in whatever is cheapest. 

On a side note - hopefully our water table will hang in there because there are a LOT of people on wells around here and we are in a pretty upscale area so there are quite a few homes with underground sprinkler systems keeping an acre or more watered.  I do like green grass, but I am not going to waste water or electricity to have it.  And of course, it will be MY well that goes dry due to my neighbor watering his yard in the middle of a 90F day with 20mph winds blowing...... 

[panaceabeachbum]

we have had our water table rise over the past few years as they installed a city water and sewer system about two years ago and came around and poured concrete plugs in most peoples wells . Being at sea level the water is usualy within 3 feet or so of ground level.  We are also a few miles from Wakulla Springs , a point where the aquifer comes to the surface

[jzeeff]

3 to 7 times running amps is what I have read for starting watts (or kVA, wasn't clear - but starting PF can be fixed)).

I am interested in the idea that a motor already running helps another motor start.  Could it be that a few small motors (started one at a time) is all that is needed to create a mechanical burst generator?  Maybe flywheels on these small motors would help too?

[12 gauge]

I worked with an uncle drilling wells back in the 80's and i was under the impression all ac submersible pumps required a magnetic starter. All the submersibles we installed included a starter which had a contactor (big relay) to handle the pump and a couple of soda can size capacitors .

panaceabeachbum,
I replaced my well pump a couple years ago with a grundfos pump that didn't require a magnetic starter.  IIRC it has an electronic circuit inside that brings the pump up to speed gradually. Still only about a second or so. 
RH

[panaceabeachbum]

good to hear, my last experience with sub pumps was over 20 years ago and I havent kept up with the latest corner cutting steps to make well pumps cheaper.  The one sub pump I still have in place is a 2hp in a 6" well and it has a magnetic starter.

are the contacts in the pressure switch holding up well at 40 amp starting load?

[Doug]

Too some extent other motors running on a buss can suply a small amount of surge current for a start up but the effect usualy only last for 5 to 10 cylces not enough to start a heavy load

[compig]

EDIT: I found my answers - for a 2 wire pump, I need a 3.75kVA alternator (mine's internally regulated/self excited) according to Franklin's documentation: http://www.franklin-electric.com/pdfs/aws/AIM_05.pdf and looking at the FLA (locked rotor amps) here: http://www.franklin-electric.com/pdfs/aws/AIM_13-14.pdf I see that my 3/4hp 2-wire motor pulls a bit over 40 amps starting current (or ALMOST 6x running current!!!).  No wonder my poor generator rolls over and dies!    The 3-wire motor still pulls about 34 amps starting current, which is 5x running current, and I'm not sure I could even handle that because that's 3x my max continuous output of the generator head, although Franklin states a 2.5kVA head will run a 3-wire 3/4hp pump and I have 3.2kVA available.   I'm thinking I should just upgrade to the 4.8kVA Markon head as it's the same size and would bolt right in.  I don't have quite enough hp to get full load from it, but definitely have enough flywheel to jerk the pump up to speed.

Your going to need at least a 6 KVA genny to do the trick.

[SteveU.]

Hello
Before you go an expensive electronic try solution  .  .  .  since you are also considering up sizing the gen head . . . consider tring one of these Pemanet Magnet generator heads.
They are listed at 3.6, 6.5, and 11 kw with a 1 1/2 to 2x surge capability.
http://stores.ebay.com/Georgia-Generator_Permanet-Magnet_W0QQ_fsubZ823419012QQ_sidZ546

Regards
SteveU
Damn. It won't link directly. Scroll to page #3. three units there.

[jzeeff]

> it's the 3/4 hp split phase motor on the well pump and the 1/2 split phase motor on the sewage pump that I can't start.

Can these be converted to capacitor start by adding a capacitor in series with the start winding?

[Doug]

Yes that can be done.

Try a 250 micro F cap that shopuld be enough to get it rolling.

[jzeeff]

Perhaps the best potential solution to having good motor starting surge capability without greatly oversizing the generator (this is inefficient) would be to have an inverter + battery that could sync with the generator and add current when needed.   It is unclear to me if a grid-tie inverter (or perhaps a stackable inverter + a simple circuit) can sync with the less that perfectly steady output of most small generators.   Has anyone tried this?

Another option (without synchronization issues) is to start a motor on the inverter/battery and then switch it over to the generator.  Ideal would be a device/circuit to do this automatically.

[Doug]

If its a low inertia load what not try a starting resitor and timer. Thats a hell of a lot cheaper and easier to do

[Tom]

Jzeeff,

I have an older Trace inverter that will do that. It is called generator support.

[jzeeff]

I agree, the "generator support" is similar to "grid-tie" and is a good indication that inverters can sync with a generator (vs the more perfect utility power). 

A resistor to minimize starting current sounds great - I would guess that a well pump needs minimal starting torque.  Maybe 20 ohms/2000 watt for a 1HP, 240V motor?  Where does one get resistors that big?

[jzeeff]

It looks like various companies make electronic soft starters, even for single phase motors.  They slowly ramp up the voltage.  So this is the easy way to go to get motors started without large current draws.

   
Telemecanique Altistart 01  is an example.