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Old 04-25-2011, 05:57 PM   #11
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Re: What amp draw ok on common?

Well, 3 phase power does complicate things a bit.

My first recommendation is to find a good commercial electrician that is comfortable with 3 phase power systems. Preferably one that sells generators to companies. It will be worthwhile to talk with them about your system and get a certified solution.

With all that said, you still have a solvable situation. You still have 19KW to 20KW of normal operational power, with 21KW of surge. BTW, what's the specific model number of your generator? Norpro has some information about their generators online, and the only one I thought sounded like yours didn't list it as being 3 phase. What is the actual voltage between either of the Lines and Neutral?

In any case, total available power hasn't changed. All that has changed is the distribution of the power. In a 3 phase system, you have 3 sources of 120V power. You just need to balance things across 3 legs instead of 2 legs.

This is somewhat more complicated. A commercial electrician with a good reputation for generator installs will have a lot of experience with balancing loads. If you were near the DC/MD/DE area, I could recommend a great electrician to talk with, he is our go-to guy for commercial work where I work. He also installed and balanced our 60KW 3 phase generator.

Generating 3 phase power is generally quite efficient. It's basically how they do it at big power plants. Each leg is 120 out of phase with the next leg (360 in a circle, divided by 3 legs, plus a neutral).

Now, the hard part will be balancing 4 major loads across 3 legs. Since nominal draw for an A/C unit is 10 amps, the lights is 10 amps, and the gaming systems is 35 amps, we just need to find a combination that balances them as closely as possible.

The easiest part is balancing the first 3 A/C units. Obviously, 1 per phase.

Then there's the 4th A/C unit, the lights, and the 35A of gaming gear. If you put the 4th A/C on L1 (10A), the lights on L2, and 10A of the gaming load in L3, then we're sitting at nominal 20A on all 3 legs, for a total of 60A. But this leaves us 25A of gaming gear left to power. If you can then put 8A of gaming load on L1 and L2, and 9A of gaming load on L3, that will get you balanced within approximately 1A, using a total of 85A.

Consider your per-leg limit to be approximately 55A. This puts your total limit at 165, which leaves some overhead for error.

With the above scenario, you should end up with loading like this:
L1 10A A/C, 10A A/C, 8A gaming, total of 28A
L2 10A A/C, 10A Lights, 8A gaming, total of 28A
L3 10A A/C, 19A gaming, total of 29A

This is a total of 85A, which is well below your potential limit of 165A (or actual limit of 175A). Also, the heaviest loaded leg has 26A of wiggle room, and the other two legs have 27A of wiggle room. Compressors kicking shouldn't be an issue.

Now, I mentioned getting a good commercial electrician for a reason. Most residential electricians never have to deal with 3 phase power, and aren't used to working with it. It does require some different skills. Believe it or not, many commercial electricians don't have to deal with it much either, as they're dealing primarily with smaller businesses. Many of the A/C guys (even commercial guys) that have the electrical skills to hook up their A/C gear don't understand 3 phase power either. I've run into many of them in my job.

Whether your generator is producing 240/120, 120 straight, or 3 phase power, you have plenty of energy available to run the loads you have. They just need to be balanced properly, and you need to leave some capacity for A/C startup.

I hope this is helpful,
jim
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Old 04-25-2011, 06:04 PM   #12
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Re: What amp draw ok on common?

Quote:
Originally Posted by GameRV
Still confused. Attached photo of genset clearly states phase 1.
That lines up with the information I found on the website for norpro.
http://www.4norpro.com/pdfs/POWER%20MAX%20I/21PMI.pdf

I'm confused why it says 1 phase 120/240 and also lists 4 wires (which is normal for 3 phase).

Very strange indeed.

I still think you need a good commercial/generator electrician to look over this.

At the main point where the wiring leaves the generator and joins the vehicle, is there a junction box somewhere that you could open and count the number and color of the wires coming from the generator? Also, are there breakers on the generator, and if so how many and what size?

jim
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Old 04-25-2011, 06:08 PM   #13
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Re: What amp draw ok on common?

I will take to the pros. Thanks for help.
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Old 04-25-2011, 11:19 PM   #14
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Re: What amp draw ok on common?

Quote:
Originally Posted by GameRV
BTW I have a 21kw isuzu/norpro genset. Ok. Think I got it. Now for the most important piece. I am wired (I believe single phase 240) and therefore my max amps available is 87.5 amps. This is cutting it way too close for my power needs. I am dangerously close to 87.5 and when air conditioner compressor kicks on and amps spike momentarily, the gen dies because it exceeded 87.5. So, I want to rewire the gen for single phase 120 and make my max amps available 175 so I am nowhere near max amps. Only drawback is no support for 240volt devices of which I have none.

Help me confirm I have this right.
RELAX!
The cut sheet Baadpuppy linked to, and the data plate for your machine, both say you have 120/240-volt single phase, not a three-phase machine. Your machine will put out up to 87.5 amps to 240-volt appliances with no 120-volt loads, or it will put out 175 amps at 120 volts, half on Leg 1 and half on Leg 2. The fourth wire mentioned on the cut sheet has got to be the ground. You already said that you have a black Line 1, a red Line 2, and a white Neutral.

To answer the question of your posts, the Neutral current flow is the difference between the 120-volt loads on Line 1 and Line 2. If they are balanced, it is zero. If one leg is fully loaded and the other has no load, the Neutral will have up to 87.5 amps on it. If you put two 120-volt air conditioners on one line and two on the other for balance, and split up the other loads, you will be fine.

Quote:
Originally Posted by GameRV
So, now how do I rewire the gen head from 240 to120?
This could be easy, or it could be hard, depending on the wiring in the alternator head. For example, Onan "Emerald" 6kW generators are easy to re-wire. They have two 3 kW 120-volt windings coming out to terminals inside the wiring cover. You get 120/240 volts at 3 kW per side if you wire them in series (Line 1 on 1, jumper 2-3 for the Neutral, and Line 2 on 4.) If you wire them in parallel, you get 120 volts at 6kW (Jumper 1-3 for Line 1, jumper 2-4 for Neutral. no Line 2). But the amount of available power does not change! If you had a single 4000-watt appliance, you might need the 120-volt option. Otherwise, either choice works.

If the generator windings do not come out to terminals like this, it may mean un-winding and re-winding the alternator innards to get 120-volt only output. You do not want to do this! If you have 120 volts instead of 120/240 volts coming out of your genset, you must have twice the current flow to get the same amount of power, and the ampacity of the wiring used between the genset and the load center must be at least double. Your losses from cable heating will be greater, and you will have greater fire potential if one of the connections goes bad and starts heating up. Instead of rewiring, just balance your loads as you have been doing, and you will come out ahead.

Also, you have an 1800-RPM generator, not a 3600-RPM generator. This is a good thing. The windings are more complex, as the alternator must put out 2 cycles of AC for each turn of the motor crank instead of one cycle per turn. The motor runs slower and lasts much, much longer. (FYI, 60 cycles per second times 60 seconds per minute equals 3600 revolutions per minute.)

But the generator must turn a constant 1800 RPM to maintain the 60 Hz line frequency. When it hits a sudden load, it may bog down for a second until it can serve up more fuel to generate the extra watts at the fixed RPM.

Think of it like cruise control in your car. If you set the cruise at 60 MPH, you are humming along until you come to a hill. Without cruise control, your eyes see it coming, and without thinking your foot presses harder on the gas. But the cruise control cannot anticipate the hill, it only knows that it was going 60 and is now going 59, 58, 57, so it adds more fuel to get back up to 60. When you get to the top of a hill, you instinctively ease off the pedal, but the cruise control does not ease off the fuel flow until it starts seeing 61, 62, 63. It is the same with a genny trying to hold a certain RPM for 60 Hertz.

Your genset is big enough to power 3-5 RVs. It is at least double your loads with everything on. So the question is, does the genset actually stop when an air conditioner comes on, or does it just stumble while it is turning up the fuel flow? If it stops or stumbles badly, I would look for a defective air conditioner, or a problem with the engine, maybe fuel flow. Is is plumbed into the bus's tanks? Is there a way for air to replace the fuel drawn from the tanks, or are you sucking fuel against a vacuum? If you had a propane genny, I would be asking about enough surface area to boil vapor fast enough (horizontal tank, or multiple vertical tanks in parallel on a manifold).

I seriously doubt that the alternator load and bus "entrance" wiring is the problem. I would look at the air conditioners, the fuel filters, lines, and vents, and if necessary have the engine looked at. If all you are hearing is a stumble and recovery, that may be completely normal. Losing 100 RPM out of 1800 will seem much worse than losing 100 RPM out of a 3600 RPM screamer. You may also want to rig the air conditioner controls for staggered starts, so all four do not try to start in unison.

Good Luck!
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Old 04-25-2011, 11:45 PM   #15
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Re: What amp draw ok on common?

Fuel draws from main tank. Previous post says going from 120/240 and 87 amps to 120 and 175 amps yields no additional power. This is one thing I cannot grasp. 175 sounds better than 87 to me. 50% of load sounds better than 100% but like I said, I can't wrap my head around that concept. If I'm wired 240 and maxing out at 87 I am worse off than Gamerbus with 13kw and 3 ac's. I have 21kw and 4 ac's. My brain says I should be ok but gen sure sounds like it is maxing out at 87. Gamerbus days he needs all 110amps from his 13kw if gen.
Maybe I can shed some light. The other day we ran like 4 xbox's and tv's and 3 ac's for couple hours no problem. I could run all 16 systems for an hour with all 4 ac's in max cool. Thought there was being on max cool would eliminate spike in amps when compressor goes off, then comes back on. I killed the gen (it died) when I threw the a breaker for an electrical heater (double breaker connected to each leg). Thought process was that the extra amp pull from the heaters put it over the max. We had the bus since September and have run the ac's with no problem and lights on. My novice opinion is that I am at the limit of the generator. That's what bugged me, at 21 kw I shouldn't be. Only thing I could think of was 240 vs 120.
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Old 04-25-2011, 11:54 PM   #16
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Re: What amp draw ok on common?

Your machine will put out up to 87.5 amps to 240-volt appliances with no 120-volt loads, or it will put out 175 amps at 120 volts, half on Leg 1 and half on Leg 2.

Does this mean NO re-wiring necessary?
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Old 04-26-2011, 01:25 AM   #17
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Re: What amp draw ok on common?

Quote:
Originally Posted by GameRV
FPrevious post says going from 120/240 and 87 amps to 120 and 175 amps yields no additional power. This is one thing I cannot grasp. 175 sounds better than 87 to me. 50% of load sounds better than 100% but like I said, I can't wrap my head around that concept.
Lets look at watts. 240 volts X 87.5 amps = 21,000 watts. 120 volts x 175 amps = 21,000 watts. It's the same thing.

I say half the load because you were adding 120-volt loads up toward the 87.5 amp limit, which when split evenly between the legs should be about 43.75 amps per side, well under the 21,000 watts the machine can produce when running correctly. The loads you were adding should be compared to the 175-amp capacity of the machine, not the 87.5-amp capacity of each side.

Let's say you had two 2400-watt, 120-volt air conditioners, one wired on Black from L1 to Neutral, and the other wired from Neutral to Red on L2, the two units "share" the 240 volts in series, each taking half. Here's how it works:

*geek alert*
L1 and L2 are wired to opposite sides of the alternator, so when L1 = zero L2 also = zero, using Neutral as a reference. When L1 is rising to +120 volts, L2 is falling to -120 volts. When they hit peak/minimum voltages, L2 starts rising from -120 through zero to +120, and L1 is exactly opposite falling through zero to -120. Neither line is ever has more than 120 volts referenced to neutral, but they are always 180 opposite each other. The 240-volts is only found when measured from Line 1 to Line 2 across the middle.

Think of it like the left and right pedals on a bicycle. 240 volts like is a normal person riding a bicycle with two pedals, one foot going up, one foot going down. 120 volts is like a one-legged person riding a bicycle with only one pedal, working that one leg twice as hard to keep going.

So each air conditioner uses 120 out of the 240 volts, and passes the rest of the current in series to the other unit. If one wants to draw more than the other is using, the difference goes through the middle to/from the Neutral to maintain balanced voltage on each hot leg. In this examples the air conditioners draw 20 amps at 240 volts, each unit using half of the voltage, for 4800 watts combined. .

Now let's rewire for 120 volts. Each unit draws its 20 amps at 120 volts in parallel between Line 1 and Neutral. Both wires now have to supply 20 + 20 amps, or 40 amps. The feed coming to the circuit breaker box now has to handle 40 amps, not 20. The units now draw 40 amps at 120 volts, but still for 4800 watts combined. Each unit is still individually drawing 20 amps at 120 volts to make its own 2400 watts. The power source still has to provide 4800 watts for both. But using the higher voltage and series wiring reduces the need for higher current, reducing heat losses in the wires and devices.

Quote:
Originally Posted by GameRV
Your machine will put out up to 87.5 amps to 240-volt appliances with no 120-volt loads, or it will put out 175 amps at 120 volts, half on Leg 1 and half on Leg 2.

Does this mean NO re-wiring necessary?
That is what I am saying. Split your 120 volts as evenly as possible between Line 1 and Line 2, and if your 120/240 volt wiring was done correctly, it is better not to change it.
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Old 04-26-2011, 08:58 AM   #18
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Re: What amp draw ok on common?

Ok. Leave wiring alone and back to square one as to why gen shuts down. New air filter & fuel filter. I'll look at gas cap for possible vacuum, checking vents as well. Diesel mechanic is of the opinion fuel lines are good.
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Old 04-26-2011, 01:10 PM   #19
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Re: What amp draw ok on common?

Redbear, thanks for jumping in here. Great information!

Quote:
Originally Posted by GameRV
Maybe I can shed some light. The other day we ran like 4 xbox's and tv's and 3 ac's for couple hours no problem. I could run all 16 systems for an hour with all 4 ac's in max cool. Thought there was being on max cool would eliminate spike in amps when compressor goes off, then comes back on. I killed the gen (it died) when I threw the a breaker for an electrical heater (double breaker connected to each leg). Thought process was that the extra amp pull from the heaters put it over the max. We had the bus since September and have run the ac's with no problem and lights on. My novice opinion is that I am at the limit of the generator. That's what bugged me, at 21 kw I shouldn't be. Only thing I could think of was 240 vs 120.
GameRV,

That is a good test. The numbers added up just don't support the genset hitting its limit, unless there is a load that hasn't been accounted for.

I would love to know the results of doing that same test, with a clamp on ammeter on each of the Line legs (L1 and L2), with it set to hold the peak value. Then run all the systems + A/C units on max, and write down the values. Then, flip that breaker to turn on that heater again, and after it dies, write down the new peak values.

As long as both of them are beneath 87.5A, then this would point more to a loading issue with the generator motor rather than an electrical issue with the generator itself, which I think Redbear has alluded to in one of these posts. If either are above 87.5, then this would point more to an electrical load issue, and would also tell you which leg to focus on.

jim
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Old 04-26-2011, 07:51 PM   #20
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Re: What amp draw ok on common?

It seems the load is balanced perfectly. 2 ac's on each leg. Heaters balanced between legs obviously due to double breaker. Now that I think about it, the electrician showed me the main breaker which I think he said equated to 150 amps. That is located at the top of the panel. Without being in front of it, I can't recall how four breakers added up to 150 though. With that being said, if I was reaching max of 75 for one leg or 150 total, that breaker would have tripped.
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