Generator power

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  #41  
Old 08-30-12, 12:28 AM
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It's really late and I have just been doing some sketching so I could be wrong. It appears that having the 15 ampere circuit breakers in the proper leads from the two generator windings will protect the 240/120 volt output as long as there is an addition two-pole 240 volt circuit breaker just before the 240/120 receptacle. This works because at 240 volts everything is in series and the maximum output is only 15 amperes.

When switched to 120 volt only the two "hot" (in reality there is not hot or neutral when in the 120 volt only position) sides of the two windings, with their individual 15 ampere circuit breakers are then in parallel for one side of the 120 output and the other two sides of the two windings are paralleled for the other side of the 120 volt output. This system is also not "bonded" to earth but has both sides of the 120 volt output floating.

While not desirable and (I think) contrary to NEC rules the two 15 ampere circuit breakers in parallel do allow for a total of 30 amperes output from the paralleled windings.

Note also the schematic calls them "protectors" not circuit breakers. It is entirely possible that this particular generator uses current sensors through a microprocessor controller to coordinate "tripping" depending on the current flow through the various sensors.
 
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  #42  
Old 08-30-12, 09:46 AM
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See that's where my brain is starting to hurt.. I understand paralleling the breakers will sum their ampacity. And it should work, because if one trips the other one will instantly overload and trip too.

What I'm still not clear on - even after looking at it with fresh eyes today - is why the coils are not paralleled upstream of the breakers. If you look closely at the last schematic, each coil is fused upstream of the switch, then when the switch is in 120v mode the opposite coil is tied in downstream of the breaker. Mike's mod to the Coleman is done the same way. I just don't understand how that works to put the breakers in parallel with each other. I see it as a series circuit, which does not sum the breaker ampacity
 
  #43  
Old 08-30-12, 12:22 PM
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Yeah actually I am not sure about the breaker thing. Actually I thought about changing them to 30 amp but here is my thinking.

The gen is a 3250 watt. Is it 80% of 20 amp? That is 16 amp x 120 = 1920 watts. That would put me a little over 50% run capacity. I have more then enough to start my well and fridge. Everything else is irrelevant to some extent.

Now IMO if I ran that gen at full output it would just burn up and melt so why change the breakers.

I thought about testing this theory but I do not have enough load to bring it up past 2000 watts. Only way I could bring it past that would be with my two start loads, well and fridge. That would exceed my surge of 4050 watts. So not sure.

I will do some internet search and see what I can find. Curious to know furds theory.
 
  #44  
Old 08-30-12, 06:09 PM
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Generators are rated at their highest voltage output so if your generator is rated at 3,250 watts continuous, the output is 13.5 amperes at 240 volts. That means that each winding "sees" a maximum of 13.5 amperes so if you reconfigure it to place both windings in parallel for a 120 volt only output the total output will be 27 amperes at 120 volts. In this configuration each winding contributes 13.5 amperes to the total output of 27 amperes.

[I'm going to use some terms now that strictly speaking are incorrect but they will help to understand the connections and protections.]

Call one winding of the generator "phase A" and call the other winding "phase B". In the 240/120 dual voltage configuration the beginning of the phase A winding connects to a "protector" and the other side of the protector connects to the "hot" side of one duplex receptacle and also the X terminal of the 240/120 volt twist lock receptacle. The end of the phase A winding connects to the "neutral" side of the same duplex receptacle mentioned and the neutral terminal of the 240/120 volt twist lock receptacle. The end of the phase A winding also connects to the beginning of the phase B winding.

The end of the phase B winding connects to a protector and the other side of this protector connects to the "hot" side of the second duplex receptacle and also the Y terminal of the 240/120 volt twist lock receptacle. This configuration has the first duplex receptacle fed from the phase A winding and the second duplex receptacle fed from the phase B winding. Each duplex receptacle is limited in output to the setting of the protector and/or the winding's output. In this particular case that is 13.5 amperes. The 240/120 volt receptacle will have all the same characteristics of any 240/120 volt three-wire circuit in that the neutral will carry only "unbalanced currents" from the two 120 volt circuits and if the loads on each of these two circuits are equal there will be no neutral currents and the entire circuit is then considered to be a 240 volt series circuit. Both protectors will be in series with the entire circuit and limit the maximum current in the circuit to 13.5 amperes. There are no protectors in the neutral connections.

In the parallel connection (120 volt only) the paralleling connections are after (or downstream) of the protectors so each protector "sees" only the output of its associated phase winding. I think this is a wildly unorthodox method of connection but it will work. JerseyMatt is correct that if one of the protectors were to trip the entire load would then be on the remaining winding and protector and if the load is greater than the protector setting the second protector will also trip. So, no real need for any but the original two circuit protectors.


Mike, do you have any portable electric space heaters? These make great "load banks" for testing portable generators to their limits. They can be augmented with portable halogen work lights (150, 300, 500 and 1,000 watts each) to get up to the maximum rating of the generator. You might need use a "spider' or "octopus" multi-receptacle adapter to have enough places to plug in the various loads. This is what I used when I converted my gennie to gaseous fuel and needed to put a full load on the gennie to adjust the maximum fuel flow.
 
  #45  
Old 08-30-12, 08:57 PM
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I have some to add to this but I have other things going on this week. So stand by.

Furd you know your ohms law....LOL. Just kidding, but so many don't.
( I say because you are right on with my rating plate....)

Mike, do you have any portable electric space heaters?



And what am I supposed to do a test? I am content trust me....


In the parallel connection (120 volt only) the paralleling connections are after (or downstream) of the protectors so each protector "sees" only the output of its associated phase winding. I think this is a wildly unorthodox method of connection but it will work.
Why unorthodox? Its a gen. Different then home electric?


JerseyMatt is correct that if one of the protectors were to trip the entire load would then be on the remaining winding and protector and if the load is greater than the protector setting the second protector will also trip.


Of course........


In the end we are only stipulated to the windings output. Simple math. But the final answer is I should be able to get my 3250 watts out of the gen in theory ?????
 
  #46  
Old 08-31-12, 12:06 AM
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I thought I had read earlier that you wanted to test the generator at full load. You use the heaters and lamps to achieve full load.

Circuit protection (circuit breakers or fuses) are generally NOT allowed to be connected in parallel. You will NEVER see paralleled protection in residential installations.

Absolutely you should be able to get the full 3250 watts output from your generator regardless of whether or not you have it wired for 240/120 volt output or 120 volt only output. However, if your steady-state output rating is 3,000 watts with a 3,250 maximum (surge) output you do NOT want to exceed 3,000 watts for more than a few seconds or you risk overheating the generator windings. (Note to others reading this, inverter generators also have to consider power factor in determining steady-state and peak outputs.)
 
  #47  
Old 09-20-12, 12:10 PM
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Absolutely you should be able to get the full 3250 watts output from your generator regardless of whether or not you have it wired for 240/120 volt output or 120 volt only output.


Yes Furd its a 3250 watt run and 4000 surge watt. 27 amps 120v and 13,5 amps 240.




Now I did the test today. I got the well pump running 8.5 amps and the re-fridge 4.5 amps. Started one then the other. Then I turned on a hairdryer that drew another 11.5 amps

( tested all these with a kilowatt meter)

That is 24.5 amps. No breaker tripped. I figured the 20 amp breakers at the gen would trip. Nope...

So I was not satisfied and turned on another 200 watts of lights ( 1.6 amps) at the ceiling fans. I believe I was in the 26.1 amp range, and the watt meter at the transfer switch read 3000 watts. ( I know they are inaccurate, but it was right on from the watts I got from testing the amps from the three appliances. I do not have a clamp on style meter external meter. Just one with probes)

3132 watts/ 26.1 amps...

With that said I did not want to take it any further.

My goal was to see if I could get the generator breakers to trip, or at what load they would. I could not get them to trip.





Now my breakers on my mod are placed the same as the breakers on a factor gen with 120 only option, drawing off both windings for full amps. I see no difference. But they do have 15 amp breakers. ( Note that c46540 is a 3500/4000 watt gen.)





Now if I did not have this mod I would only be able to pull 13.5 amps from each winding at 120v. I would of carefully had to balance the loads across both windings.

No way would I be able to run the well pump and hair dryer on one
winding trying to draw 20 amps.

Also I did this mod because my well pump draws 12.6 amps start. The gen started it, but I did not have enough load on the other winding, so the gen would get a bad vibration.

Plus I did not want to buy a new and bigger generator I do not have to worry about load balance. ( Remember, I have no 220v loads in my home.)

Also mid test I did go out and adjust the governor a tad. I dropped to around 58 Hz and wanted to keep it as close to 60 Hz as I could.

Also voltage dropped off pretty good, and that's the price you pay for a less expensive gen I believe. I was down to 108 v in the end of the test at 59 Hz. I did not keep it there that long. Less then a minute, took my final reading, and I killed breakers at the transfer switch.

If I ever reach a high load I would tweak the Hz up to 61 to keep the voltage up.

With that said the question is,

1. I would think these breakers would not trip at the gen until 32 amps. Does that sound correct?

2 I believe I may change these to 15 amp breakers, if the above is true, but I would not be able to draw the full power from the gen. Only 24 amps right?


( I don't plan on drawing that since the max I pull is about 17 amps during normal use, and only if I have to run the well pump. So 8.5 amps run is normal during a power outage)

Plus I don't want to melt the poor thing...LOL

OK end of my test, and sorry to bore you all. That's my story and I am sticking too it.


Hope this helps the OP or anyone else looking to buy a gen that has a 120/240 switch.......


 
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