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Author Topic: mechanical burst generator  (Read 29663 times)

jzeeff

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Re: mechanical burst generator
« Reply #15 on: August 14, 2009, 08:08:34 PM »
I agree that lights flickering could occur without a low PF and that could be fixed with a bigger transformer.  But if they fixed the problem with a bigger capacitor, then it was a PF issue.

> If they put a capacitor on your service it stores a little bit of power, just enough to provide for the short surge of power needed to start the motor.

I cannot agree with this - not in an AC circuit.

compig

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Re: mechanical burst generator
« Reply #16 on: August 14, 2009, 08:13:00 PM »
No , thats correct , the cap does not store , actually cannot store an AC current. It resist's the change in current and therefore corrects the relative phase between voltage and current .
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mobile_bob

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Re: mechanical burst generator
« Reply #17 on: August 14, 2009, 09:38:37 PM »
at the end of the day, there are two kinds of electrical users that should be concerned with power factor
the first and most obvious is commercial/industrial customers which get hit wit a surcharge or tarriff as compig alludes to... and

the other is the offgrid installation, poor power factor eats up generating capacity, you get less work done for each kva you generate
in a system with poor power factor, ideally you want a unity power factor where one kva = one kwatt.

bob g
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(useful forums), utterpower.com for all sorts of diy info

compig

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Re: mechanical burst generator
« Reply #18 on: August 14, 2009, 10:11:41 PM »
No , thats correct , the cap does not store , actually cannot store an AC current. It resist's the change in current and therefore corrects the relative phase between voltage and current .

.... and just to confuse things more for those that want to be absolutely correct and can't recognize a metaphor if they tripped over it (and I am not implying that Compig is such a person !), a capacitor resists a change in VOLTAGE and an inductor resists a change in CURRENT. It is also not possible to 'store a current' no matter if it is AC or DC or any-other-C. It is also impossible to store a voltage (AC or DC) unless you are talking about storing a reading on a meter. A capacitor stores an electric charge and an inductor stores energy in a magnetic field.

Jens

Well I was trying to keep this simple so avoided too much detail , but it seems it needed it all anyway !!  Do you want to explain electron and proton theory or shall I ??!!  Just jokin !
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jzeeff

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Re: mechanical burst generator
« Reply #19 on: August 15, 2009, 01:48:12 PM »
My conclusion on some device to provide surge current is that there isn't anything practical and one has to spend the money on a large inverter.  But some of the non-name brand stackable inverters aren't too expensive and should work.   I assume that a VFD and a 3 phase pump to reduce startup current is another option.








compig

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Re: mechanical burst generator
« Reply #20 on: August 15, 2009, 02:34:36 PM »
Or , a variable speed motor controller with a ramp start could be used. This would start the motor at practically full torque at slow speed and limit the inrush current then automatically ramp up to full speed. All parameters can be user set.
« Last Edit: August 15, 2009, 03:15:04 PM by compig »
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europachris

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Re: mechanical burst generator
« Reply #21 on: August 15, 2009, 03:08:55 PM »
The power-factor correction with capacitors is the same idea as the "easy-start" add-on boxes for motors, right?  Essentially, they just are jumbo sized starting capacitors, but only work on capacitor start motors, correct?

Reason I ask is we have a 3/4hp 2-wire, 240V well pump down about 120feet, and with no other loads on the generator (3.2kVA 2-pole Markon driven by ChangFa R185), it absolutely will not start, even with all the pressure bled out of the tank.  Conversely, I can start my 1-1/2hp table saw, which is 120V, using only ONE HALF of the generator windings because I don't have a 120V full power switch installed yet, so I get 120V from either half right now and 240V using all.  The difference is it is a capacitor start motor.  I can't start the 1/2hp sewage pump (120V split phase) for the basement bathroom either.

So, is there a way to make a 2 wire well pump easier to start?  It's not a huge deal but it would be nice to not worry about water during a power outage, but at least I can keep the food cold and house warm.

Chris

compig

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Re: mechanical burst generator
« Reply #22 on: August 15, 2009, 04:36:58 PM »
Does the genny struggle when the motor is switched in ?
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europachris

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Re: mechanical burst generator
« Reply #23 on: August 15, 2009, 08:49:36 PM »
Does the genny struggle when the motor is switched in ?

Yes, the generator head just packs up and goes home while the ChangFa just grunts a little and keeps on chugging.  The huge current demand just hauls the output voltage down so low the motor can't get going.  The generator is rated for approx. 14 amps at 240V, while the full load run current on the well pump is about 11 amps.  I can only imagine what the starting current must be...

Chris

europachris

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Re: mechanical burst generator
« Reply #24 on: August 16, 2009, 02:20:45 AM »
You say that it is 3/4 hp well pump but it draws 11 amps at 240V ???? Something isn't right. On the other hand, if the well pump is running 11A at 120V (still seems high) then I would suggest you switch the pump over to 240V operation if possible.
Starting amps, as far as I know, are in the order of 2 to 3 times the running amps.

Jens

You're correct, Jens - I was mistaken - running amps is 6.8 at 230V per the nameplate, service factor 1.5, max S.F amps 8 and KVA code N (which I recall has something to do with starting current).  I don't know where I got 11A from......  :-[ 

Since I have almost 14A at 240V available, I figured maybe 2x that in surge current (28A), so that would cover 4x running amps for starting current on the pump.  Evidently that's not nearly enough.

Chris

panaceabeachbum

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Re: mechanical burst generator
« Reply #25 on: August 16, 2009, 04:14:51 AM »
I know its old tech and not as effecient as your submersible, but if your not into the dc sub pump at $600 I would consider a deep well jet pump . Unlike the submersible pumps, jet pumps dont start with huge head pressure present like your submersible. Your submersible is having to start while pushing a column of water 1" or so in diam x the distance from the water table to the hieght of the upper water level in your tank 

The jet pump just has the resistence of forcing water thru the jet in the injector at start up which is down below water level at start up and is under much less load.

After loosing a couple of sub pumps to lightning I went to a 1/2 hp jst pump and havent had a minutes problem in over 10 years. I have another well on the property thats had the same pump sitting on it since 1973 and all I have done is change the pressure switch and tank about 5 years ago

apogee_man

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Re: mechanical burst generator
« Reply #26 on: August 16, 2009, 06:44:07 AM »
I agree with Panacea regarding the jet pump...

Also, you might take a look at your wire size that is run down to the pump.

You might just find that they ran too small of a gauge and the reason that you can't kick the motor over has everything to do with excessive resistance.

Just a thought...

Steve

europachris

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Re: mechanical burst generator
« Reply #27 on: August 16, 2009, 01:33:20 PM »
Well (get it, bad pun alert),  I am fresh out of ideas why a capacitor start motor would be a problem. I would certainly think that both the 1/2 hp and the 3/4 hp should start without a problem.

An odd suggestion ..... try starting one of those cap start motors while your 1.5 hp motor is running.

Jens

The cap start motor ISN'T the problem (on my table saw) - 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.

I wonder if I can re-wire the table saw for 230V?  Then I could run it at the same voltage as the well pump and try that trick with having it running while starting the well pump.  I've heard that before (on this board I believe).  I'll have to look at the motor nameplate today on the saw.

Chris

europachris

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Re: mechanical burst generator
« Reply #28 on: August 16, 2009, 01:45:28 PM »
I know its old tech and not as effecient as your submersible, but if your not into the dc sub pump at $600 I would consider a deep well jet pump . Unlike the submersible pumps, jet pumps dont start with huge head pressure present like your submersible. Your submersible is having to start while pushing a column of water 1" or so in diam x the distance from the water table to the hieght of the upper water level in your tank 

The jet pump just has the resistence of forcing water thru the jet in the injector at start up which is down below water level at start up and is under much less load.

After loosing a couple of sub pumps to lightning I went to a 1/2 hp jst pump and havent had a minutes problem in over 10 years. I have another well on the property thats had the same pump sitting on it since 1973 and all I have done is change the pressure switch and tank about 5 years ago

Upon my second look yesterday at the sub pump motor data plate stuck to the pressure tank, I saw that the well is 180' with the pump at 140'.  The well is not too far from the basement location where the power and water lines enter, but swapping to a jet pump would still involve a good deal of digging new lines and the well lines cross under the main electrical and natural gas lines coming into the property, so it would be a lot of hand digging around them all.  It would likely be a lot easier to install a 3-wire capacitor start motor as long as a new power cable could be pulled through the existing conduit out to the well.  Then I could add one of those "easy-start" boxes if I still had trouble starting the pump.  I've looked at the Grundfoss pumps and they are really nice.  I have a Franklin Electric motor.

Conversely, I'm definitely toying with the idea of adding some solar panels the roof of my detached garage/shop building.  It has a roof with a due South exposure and a perfect pitch to capture sun with no obstructions and a good 200 sq.ft. of area to cover.  It would only be a matter of how to handle the power transfer between it and the house since I've already got it wired for 30A/240V with a sub panel out there fed from a 30A breaker in the main house panel.  But that's another topic to start.... 

Chris

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.
« Last Edit: August 16, 2009, 04:58:08 PM by europachris »

panaceabeachbum

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Re: mechanical burst generator
« Reply #29 on: August 16, 2009, 05:14:33 PM »
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 . I know we had to pump the wells out for 12 hours or so to clear all the cuttings before inspection and if no power was present we would leave an 8hp generator with 5 gallon tank to run all night powering the pump . 

Your right at that depth and distance from the pump shed a jet pump would be a lot of work

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