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Author Topic: Alternators - Single Phase And Three Phase Resistive And Inductive ?  (Read 12136 times)

Amarbir[India]

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Guys ,
    I would Like To Ask You That Why Will a Person Buy a Three Phase Alternator ,If He Has The Options Of a Single Phase .Also Can a Resistive Load Alternators Run Motors .I Just Got a 6 KVA Resistive Load Alternator But i Am Able To Run Motors .Also When i Run A AC On 6 KVA The Voltage Drops To About 139 Volts From My Set Voltage Of 250 Volts On The Engine .On AC The Engine Is On Load As I Have Decreased The RPM To Around 600 And This Has Decreased the HP Of This Engine  .My Question is That Is i Had a Inductive +  Resistive Load Alternator Would That Have Been Better ? .
 
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Amarbir Singh Dhillon [ www.indianlisteroid.com ]
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ronmar

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #1 on: June 30, 2010, 04:26:34 AM »
Three phase power is usually used for industrial applications.  Larger motors are a bit more efficient run on 3 phase. 

An alternator is an alternatorthey are not specific for an inductive or resistive load.  They are usually rated for a given purely resistive load as this is the easiest to gauge generator performance.  An alternator is less effective powering an inductive load.  The inductive load(motor) also requires a massive inrush of electric current at startup.  Usually many times what is required to run the load. 

You have a 6KVA alt.  What size HP engine is it connected to again?  How big is the A/C you are connecting to it.  230 to 139 is a huge voltage droop.  How much is the RPM dropping off during this voltage drop?   
PS 6/1 - ST-5.

buickanddeere

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #2 on: June 30, 2010, 05:22:01 AM »
Guys ,
    I would Like To Ask You That Why Will a Person Buy a Three Phase Alternator ,If He Has The Options Of a Single Phase .Also Can a Resistive Load Alternators Run Motors .I Just Got a 6 KVA Resistive Load Alternator But i Am Able To Run Motors .Also When i Run A AC On 6 KVA The Voltage Drops To About 139 Volts From My Set Voltage Of 250 Volts On The Engine .On AC The Engine Is On Load As I Have Decreased The RPM To Around 600 And This Has Decreased the HP Of This Engine  .My Question is That Is i Had a Inductive +  Resistive Load Alternator Would That Have Been Better ? .
 

  The alternator requires an engine driving it with enough power. To prevent alternator rpms from dropping 20-30rpm from no load to full load.
  Power Factor correction capacitors will reduce loading and heating of the wiring and alternators windings. PF correction caps also reduce voltage drop between the alternator and load.
  Is there a voltage regulator? What is it adjusted to? 

M61hops

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #3 on: July 01, 2010, 07:44:35 PM »
If the 6KVA 3 phase alternator is driving a large single phase AC compressor, that could be the problem right there.  Is the AC compressor also 3 phase? Leland
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Amarbir[India]

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #4 on: July 01, 2010, 07:55:17 PM »
Three phase power is usually used for industrial applications.  Larger motors are a bit more efficient run on 3 phase. 

An alternator is an alternatorthey are not specific for an inductive or resistive load.  They are usually rated for a given purely resistive load as this is the easiest to gauge generator performance.  An alternator is less effective powering an inductive load.  The inductive load(motor) also requires a massive inrush of electric current at startup.  Usually many times what is required to run the load. 

You have a 6KVA alt.  What size HP engine is it connected to again?  How big is the A/C you are connecting to it.  230 to 139 is a huge voltage droop.  How much is the RPM dropping off during this voltage drop?   

Sir ,
   The engine Is 8 HP 850 RPM running At Around 600 RPM .The AC Is a 1.5 Tonn Typical One Eating 9 Amps To 12 Amps When running .The engine Was Running At Load when i ran just this .Also Now i am not at the farmhouse and hence cannot measure the voltage drop .BTW thanks As Usual For Explaining The alternators .The Dynamic Brand Once i Got Have great built quality ,i bet even better then ST once you use in usa and uk i am quite sure .
Regards

Amarbir Singh Dhillon [ www.indianlisteroid.com ]
Indian Listers - Research ,Repair And Spares

Amarbir[India]

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #5 on: July 01, 2010, 07:57:06 PM »
Guys ,
    I would Like To Ask You That Why Will a Person Buy a Three Phase Alternator ,If He Has The Options Of a Single Phase .Also Can a Resistive Load Alternators Run Motors .I Just Got a 6 KVA Resistive Load Alternator But i Am Able To Run Motors .Also When i Run A AC On 6 KVA The Voltage Drops To About 139 Volts From My Set Voltage Of 250 Volts On The Engine .On AC The Engine Is On Load As I Have Decreased The RPM To Around 600 And This Has Decreased the HP Of This Engine  .My Question is That Is i Had a Inductive +  Resistive Load Alternator Would That Have Been Better ? .
 

  The alternator requires an engine driving it with enough power. To prevent alternator rpms from dropping 20-30rpm from no load to full load.
  Power Factor correction capacitors will reduce loading and heating of the wiring and alternators windings. PF correction caps also reduce voltage drop between the alternator and load.
  Is there a voltage regulator? What is it adjusted to? 

Sir ,
 Engine is 8 HP/1 Cylinder running at 600 RPM .I took a 6 KVA cos i think having better is always good as i am not giving it such load .This restored engine does a wonderful job and bouncing back to the voltage and rpm set by me ,But i think its under powered running my 6 kva with AC ? .I do not have a idea of the capacitors where are they added and picture sir .
« Last Edit: July 01, 2010, 07:58:57 PM by Amarbir[India] »
Regards

Amarbir Singh Dhillon [ www.indianlisteroid.com ]
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Amarbir[India]

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #6 on: July 01, 2010, 08:00:18 PM »
If the 6KVA 3 phase alternator is driving a large single phase AC compressor, that could be the problem right there.  Is the AC compressor also 3 phase? Leland

Well ,
 Its a Single Phase AC ,No IDea Of anything in the AC yet My alternator is also single phase
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Amarbir Singh Dhillon [ www.indianlisteroid.com ]
Indian Listers - Research ,Repair And Spares

M61hops

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #7 on: July 02, 2010, 09:42:13 PM »
Hopefully this AC is a capillary tube metering system type.  If so, you might add a hard start capaciter and solve the problem.  Small generators have a real hard time starting motors for several reasons.  If your generator RPMs drop off a lot when it tries to start the AC and the AC isn't built so that it bleeds off the head pressure when the compressor is stopped you might need to start over with different hardware  :'( ?                Leland
I pray everyday giving thanks that I have one of the "fun" mental disorders!

ronmar

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #8 on: July 03, 2010, 04:59:52 AM »
Well that engine running at 600 RPM is making less than 6HP.  That means you can only support around 3KW of electrical load. If I read correctly you are running 250V single phase out of your alternator?  If that A/C pulls 9-12 amps when running, that is 2.25-3KW of load, or all that engine is capable of powering.  Unfortunatly, the compressor needs several times that curremt at startup.  That is probably what is causing you problems.  As the voltage falls off under load, the A/C actually trys to draw more current to make up for the lost potemtial that the voltage drop causes...
PS 6/1 - ST-5.

Amarbir[India]

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #9 on: July 05, 2010, 08:17:54 PM »
Hopefully this AC is a capillary tube metering system type.  If so, you might add a hard start capaciter and solve the problem.  Small generators have a real hard time starting motors for several reasons.  If your generator RPMs drop off a lot when it tries to start the AC and the AC isn't built so that it bleeds off the head pressure when the compressor is stopped you might need to start over with different hardware  :'( ?                Leland

sir ,
 all AC's in india have starting capacitor
Regards

Amarbir Singh Dhillon [ www.indianlisteroid.com ]
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Amarbir[India]

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #10 on: July 05, 2010, 08:20:34 PM »
Well that engine running at 600 RPM is making less than 6HP.  That means you can only support around 3KW of electrical load. If I read correctly you are running 250V single phase out of your alternator?  If that A/C pulls 9-12 amps when running, that is 2.25-3KW of load, or all that engine is capable of powering.  Unfortunatly, the compressor needs several times that curremt at startup.  That is probably what is causing you problems.  As the voltage falls off under load, the A/C actually trys to draw more current to make up for the lost potemtial that the voltage drop causes...

Sir ,
 I Wanted To know this

Assuming We have a 8/1 @ 850 RPM ,Does that mean One HP is = 850/8 .Is it so ,I mean in this example it means 850/8 = 106 RPM /HP .So For 600 RPM i Am at 6 HP is That Not correct  ???
Regards

Amarbir Singh Dhillon [ www.indianlisteroid.com ]
Indian Listers - Research ,Repair And Spares

M61hops

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #11 on: July 05, 2010, 09:04:08 PM »
At this point about all you can do is change the engine pully so the engine runs at 850 RPM or even faster if that can be done safely to try and get as much horsepower out of the engine as possible.  Also add more capacitence to the start circut.  Check to see if the govenor can respond fast enough to keep the RPMs up during AC start period.  If this doesn't work you will need a genset that can carry about 3 times the running watts of the AC unit so that it can handle the starting watts.  The maker of the AC should be able to tell you the starting watts or the genset size needed.  I'd try and use what I have but sometimes you just have to start over  :'( !  If AC is the main thing you need to run you might consider using the engine to run an automotive AC compressor and do the AC in a more direct manner?                       Leland
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ronmar

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #12 on: July 06, 2010, 05:45:07 AM »

Sir ,
 I Wanted To know this

Assuming We have a 8/1 @ 850 RPM ,Does that mean One HP is = 850/8 .Is it so ,I mean in this example it means 850/8 = 106 RPM /HP .So For 600 RPM i Am at 6 HP is That Not correct  ???

A 6/1 runs at 650 RPM...
PS 6/1 - ST-5.

M61hops

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Re: Alternators - Single Phase And Three Phase Resistive And Inductive ?
« Reply #13 on: July 07, 2010, 11:17:11 PM »
Engine horsepower is not necessarily linear so 600 RPM might or might not be 6 horsepower!  It's probably close but you would have to make a prony brake and test it if you really need to know.  Or you could look at the engine manufacturers spec sheet, they almost for sure have run a power curve on a dyno.  You could also load the genset with resistive load and calculate the output at the point where the exhaust just begins to smoke; that would tell you the max output.  Then you could figure on running a few hundred watts less than the point at which it smokes as to max sustained output.  Leland
I pray everyday giving thanks that I have one of the "fun" mental disorders!