Generator

[JB4310]

Power in Watts is = current times voltage(P = I x E) conversely power divided by either current or voltage will = the other remaining value. Your 10KW generator is capable of providing 1/2,the rated output, or 5KW, on each 120V leg. So 120V X 40A breaker value = 4800W. 240V x 40A breaker = 9600W. So 40A per 120V leg is appropriate for a 10KW generator.

OK I got that so far, so I guess that means I can draw the 9600 watts only if it is equally distributed on both the 120 volt legs, if the load goes over the 4800 watts on one leg, then even if the total draw is far less than the 9600, it will still trip the breaker since the two breakers are attached, am I correct to assume this? and is it correct to say that since the generator is rated at 40 amps @ 240 V then it's also 80 amps @ 120 V ? or am I still missing something here. thanks John,

 

[RonMar]

OK I got that so far, so I guess that means I can draw the 9600 watts only if it is equally distributed on both the 120 volt legs, if the load goes over the 4800 watts on one leg, then even if the total draw is far less than the 9600, it will still trip the breaker since the two breakers are attached, am I correct to assume this?

Yes, since the 240 breaker is a "double" breaker, overloading a single 120V leg will trip the breaker.

and is it correct to say that since the generator is rated at 40 amps @ 240 V then it's also 80 amps @ 120 V ? or am I still missing something here. thanks John,

Yes, that is 40 amps for each 120V leg. For current to flow, you must have a circuit. On a 240V load, the circuit would be from H1(hot1)thru 1 half of the breaker, thru the load and back to the other side of the breaker to H2 to complete the circuit. IF at any time the current exceeds the 40 amp load rateing of the breaker, one or both sides will open, but since they are physically joined, they will both open. On a 120 V circuit, the current flows from H1, thru half the breaker and then thru the load and back to Neutral/Ground to complete the circuit. When this circuit exceeds the 40 amp breaker limit, the breaker opens. Since H2 is independent of H1 for 120V loads, you have 2 separate 120V/40Amps available for a total of 80A.

This is why it is important to keep your 120V loads balanced between H1 and H2. The combination of a 240V load running and one leg of 120 that is loaded heavier than the other can result in more than 40A being pulled thru one of the 120V legs and a breaker trip while still quite a ways below the generators capacity.

 

[Soundguy]

My pto genset actually 'drops' out below a very close range near the 120/240. And doesn't 'kick in' untill you reach enough rpm to get 'right at' your target rpm.

I'd guess this will depend on the gen head.. and more basic versions may simply generate power and votlage based on rpm.. etc.. etc..

Soundguy

Is that only if you're lucky? Unless the generator protects against this I would think you'd still get power out of it, but not necessarily at 120/240V or (more importantly) 60Hz - leading to a big savings in your monthy energy bill until you replace your appliances

 

[Soundguy]

Ron beat me to it.. but he gave you a great answer.

soundguy

OK I got that so far, so I guess that means I can draw the 9600 watts only if it is equally distributed on both the 120 volt legs, if the load goes over the 4800 watts on one leg, then even if the total draw is far less than the 9600, it will still trip the breaker since the two breakers are attached, am I correct to assume this? and is it correct to say that since the generator is rated at 40 amps @ 240 V then it's also 80 amps @ 120 V ? or am I still missing something here. thanks John,

 

[JB4310]

Great, thanks RonMar, now I have a much better/firmer understanding, so the next question is besides going through the entire house and panel and hand calculating the loads, I see on the pre wired transfer switch kits they have the 2 meters, is there an easy way to install the wattage meters myself in line between the gen. and the house?

Soundguy, since yours drops out when out of proper range does that mean your generator has the automatic voltage regulation (AVR)? I could have gotten it on mine for just around $100. more, but actually chose not to get it, not to save money but to keep the electronics as simple as possible. mine just has 2 fairly large (5" long x 1.5" dia.) capacitors, not sure if they regulate the voltage or protect the generator from loads that get out of range like you said, anyway the tech guys at the gen co. told me the capacitors are the only thing that could really go wrong with a non AVR generator/alternator, and on the smaller capacity generators it's easier to stay in range than on the larger 20-50 kw machines, on which AVR is standard and not even an option. (I bought 2 extras caps. @ $20. ea. just plug and play)
They did say they have had very little trouble with the AVR boards , but had a few come back and suspected bouncing around excessively on the trailer mounted units was a bit much for them.

I started a similar thread on PTO gens in the ford forum and was going to update it once I got mine, well I got mine but it was slightly damaged in transit and the company wanted to replace it, well with the holidays now it's been 3 weeks and still not resolved. I'll just use this thread to further educate myself and when I finally get the generator coupled to the Ford I'm pretty sure I'll have many more questions. Thanks and Happy New Year!!!

 

[RonMar]

Great, thanks RonMar, now I have a much better/firmer understanding, so the next question is besides going through the entire house and panel and hand calculating the loads, I see on the pre wired transfer switch kits they have the 2 meters, is there an easy way to install the wattage meters myself in line between the gen. and the house?

I do not know of an easy way to add that metering. Those typically use a very low resistance shunt resistor in series with the "Hot" lead, and the meter measures the voltage drop across the resistor which directly equates to the current being drawn thru the resistor.

The Kill-a-watt is handy for this, but it has a 15A current limit thru it. If you don't have one, I would highly reccomend one as you can plug it in anywhere in the house to monitor generator voltage and frequency(that's what I do) and it is pretty handy to calculate your 120V loads with actual use wattage of any 120V device that is plugged into it.

IF you are using two 120V power cords from the generator to the house, you could make up a measureing pigtail and use a clamp-on amp meter to measure the current draw on each 120V leg to check balance that way. One could also be made up for a 240V feed if you are feeding a distribution panel that way. This pigtail consists of a male and female plug connected by a short length of heavy duty extension cord material. You remove a section of the outer insulation, carefully to not damage the inner insulation on each wire and expose a loop of the "Hot" lead to get the clamp-on probe around. You can then switch this pigtail from one side to the other to compare balance.

Soundguy, since yours drops out when out of proper range does that mean your generator has the automatic voltage regulation (AVR)? I could have gotten it on mine for just around $100. more, but actually chose not to get it, not to save money but to keep the electronics as simple as possible. mine just has 2 fairly large (5" long x 1.5" dia.) capacitors, not sure if they regulate the voltage or protect the generator from loads that get out of range like you said, anyway the tech guys at the gen co. told me the capacitors are the only thing that could really go wrong with a non AVR generator/alternator, and on the smaller capacity generators it's easier to stay in range than on the larger 20-50 kw machines, on which AVR is standard and not even an option. (I bought 2 extras caps. @ $20. ea. just plug and play)
They did say they have had very little trouble with the AVR boards , but had a few come back and suspected bouncing around excessively on the trailer mounted units was a bit much for them.

I started a similar thread on PTO gens in the ford forum and was going to update it once I got mine, well I got mine but it was slightly damaged in transit and the company wanted to replace it, well with the holidays now it's been 3 weeks and still not resolved. I'll just use this thread to further educate myself and when I finally get the generator coupled to the Ford I'm pretty sure I'll have many more questions. Thanks and Happy New Year!!!

Yes, his sounds like an AVR type head, and that is one of the great advantages of most of them. IF your engine should shut down unexpectedly(ran out of fuel), most AVR heads will shutoff the voltage output(drop excitation) below a certain point and keep from browning-out your house as the mechanical stored energy spins down the generator slowly. This isn't a real problem on a small box-store generator, as their low mass spins down quickly, but on a tractor with flywheel, spinning gears and the flywheel/pully arrangment used to get 540RPM to the 1800 or 3600 generator RPM, they have quite a bit of spinning mass.

A passively or harmonically excited/regulated generator will not do this. It's voltage output is dependent somewhat on RPM, and calibrated to deliver the rated voltage output at near the 60HZ RPM, but it will start to output voltage shortly after it starts to spin. You also want to make sure you always disconnect the load from this type generator before shutdown as shutting them down with the load still connected can bleed the residual magnetism from the rotor and they may not generate any power the next time they are spun-up. If this happens, you will need to "flash' the field to build some magnetism in the core from which the generator can build an output.

 

[JB4310]

"Yes, his sounds like an AVR type head, and that is one of the great advantages of most of them. IF your engine should shut down unexpectedly(ran out of fuel), most AVR heads will shutoff the voltage output(drop excitation) below a certain point and keep from browning-out your house as the mechanical stored energy spins down the generator slowly."

Sounds like maybe I should have gotten the AVR just for that reason, to protect the electrical appliances. I didn't know that, I thought it was just to help regulate the output keeping it closer to what it should be and when they told me the lower KW units where easy to regulate, I figured I didn't need the AVR, if I knew about the auto cut out feature, I probably would have gotten the AVR, since the possibility of the output getting grossly out of range for what ever reason seems very likely.
I was going to buy an extra AVR board if I got the AVR unit, just to have a replacement, they are only a little over a hundred dollars and are easy to swap out according to the manufacturer, for what ever reason the AVR model is not brush less, it has the old style brushes.
I may still be able to change my mind since the order is still in limbo, they said they were shipping another unit over a week ago, but I still have not heard a word from them as they were shut down for the last 10 days, I'm hoping they will be back tomorrow, maybe they never shipped yet.

 

[Soundguy]

Ron is correct about the shunt voltmenters ( ammeter ).

Also.. his idea of using a clamp on amp probe is a good one. Sum your readings for each line.

It is also possible to have the lower cost capacitor / passive regulation head, with the addition of a comparitor circuit. All the comparitor circuit has to do is look for 240v of output.. ( or a range ).. then close a relay or EM latching switch which then supplies output to the head.. this sort of circuit can be built with about 5 $ of radioshack components... While I'm not sure if that sort of circuit is employed on mine.. all I can tell you is that voltage does not come up on the meter till the pto is right at the correct speed.. at which time power comes up and the meter needle on the genny then jumps to a 'green zone'. not that there is a red zone above the green zone, and you can get the needle there by increasing rpm... so whatever regulation method I have is not super sophisticated... My guess is it is just a low voltage cutout circuit like I was aluding to earlier.... there are plenty of ways to build them.. both mechanically and electrically... most of those simple circuits don't cutout at over voltage either.. though I believe you could build them to easilly.. or more correctly.. just beef up field controll to watcht he output and adjust accordingly. vs having a clumbsy under AND overvoltage protection circuit.. ( the undervoltage idea is good by itself... power doesn't kick in till of proper level.. etc.. )

soundguy

 

[JB4310]

I found this meter, seems like just what I would need, mounted next to the new 50 amp outlet I will install next to my main panel, according to manufacturers instructions, just pass each hot leg thru the transformers on their way to the outlet. I guess the transformers act like the fluke on the testers.
Spoke with the gen. manufacturer today and they claim I should be good with the the capacitor model and unless I had very delicate equipment then I shouldn't need the AVR? they also said that if the volts dropped hard with a load on it then the amps would spike and trip the Breaker?

Reliance Controls 50-Amp Indoor Wattage Meter MB125 @ Electric Generators Direct.com - Your Online Portable Power and Home Standby Generator Superstore

 

[RonMar]

I found this meter, seems like just what I would need, mounted next to the new 50 amp outlet I will install next to my main panel, according to manufacturers instructions, just pass each hot leg thru the transformers on their way to the outlet. I guess the transformers act like the fluke on the testers.
Spoke with the gen. manufacturer today and they claim I should be good with the the capacitor model and unless I had very delicate equipment then I shouldn't need the AVR? they also said that if the volts dropped hard with a load on it then the amps would spike and trip the Breaker?

Reliance Controls 50-Amp Indoor Wattage Meter MB125 @ Electric Generators Direct.com - Your Online Portable Power and Home Standby Generator Superstore

That looks like the ticket, basically a hardwired version of the amp-clamp pigtail I described above.

Soundguy, To make an accurate, adjustable over/under voltage monitor/interrupter circuit, is a little bit involved to do it correctly. I know,I looked into it when I was planning my homegrown generator control package. What I ultimately settled on was an off the shelf voltage band relay for about $60. This coupled with a high current contactor is what will make up my monitoring circuit. This voltage band relay, once engaged and monitoring the power output will also activate an automatic shutdown of the engine. This combined with a over-temp switch bonded to the side of the cylinder head and I have a basic yet effective safety circuit to protect my electrics as well as the engine/generator.