# Surge watts per pole



## Rene (Feb 5, 2021)

Question on surge AMPs from a portable room AC and whether my 5k genset can deliver.

From a calculation perspective I know that I divide the Genset's rated running watts by 2 to determine the available watts per pole (120v), but do I also divide the rated surge watts by 2 to determine the available surge watts per pole or is the entire surge rating available to either pole as needed.

My genset ratings:

5500 running watts (5500/2 = 2750)
6900 surge watts (6900/2 = 3450)

My AC ratings

1357 running watts
measured inrush with amp meter - 45 AMPs (45 x 120 = 5400 watts, 45 x 110 = 4950 watts)

So will starting my AC exceed the gensets capability because it exceeds a single pole rated capability? I have not attempted to start it yet. On my check list for next cycle of a maintenance run.


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## Browse Deweb (Jan 16, 2021)

You can reduce your inrush current with a soft start kit for your air conditioner. Most larger generators that can supply both 120V and 240V can be configured to supply a higher 120V only plug which puts the generator windings in parallel, doubling your available current on that leg. For example, on the Honda EU7000is, the 120V Only switch position results in the diagram on the bottom of this image:



http://shedheads.net/wp-content/uploads/2017/01/Power-Circuits.jpg


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## drmerdp (Apr 10, 2018)

A 5500 watt generator should be able to power a portable AC unit without issue. The caveat is what other electrical draws are present when the unit cycles on.


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## exmar (Jun 29, 2015)

Surge wattage is only momentary and then rapidly falls back to running watts. Here's a link that does a reasonable job of describing. It also touches on something that folks never notice, e.g. the breakers on a small generator are sized for running watts, surge wattage is much higher which should trip them.









Don't Forget About Starting Watts | Norwall


Starting Watts vs Running Watts—A Generator needs extra capacity for a few seconds while a motor starts and reaches full speed under load




blog.norwall.com


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## FlyFisher (Jun 30, 2018)

Browse Deweb said:


> Most larger generators that can supply both 120V and 240V can be configured to supply a higher 120V only plug which puts the generator windings in parallel, doubling your available current on that leg. For example, on the Honda EU7000is, the 120V Only switch position results in the diagram on the bottom of this image:
> 
> 
> 
> http://shedheads.net/wp-content/uploads/2017/01/Power-Circuits.jpg


Can you explain your post in more detail? What you state contradicts what I have thought. 

The Honda EU7000 is an inverter generator. It is not a rotary alternator. There is a computer controlling the AC output, which I believe is the computer modulating transistors in banks in phase and out of phase (for split phase 120/240). The input to the system is DC, rectified from the alternator off the engine. 

The image you posted, from the full article linked below, describes the coils as being "power circuit A" and "power circuit B". They simply plastered "mystery circuits" with the representation of coils on their schematic. 

Why the details are important is the trick to paralleling the power generation in any generator that is normally split phase 120/240v is that you have to phase the poles correctly. There is zip, nada, no explanation of phasing in the schematic.

For example - a rotary generator with a neutral bonded to ground/frame - the center tap on the alternator (neutral) is pulled down to ground (which technically it should be, in the vast majority of scenarios) and the end taps are your two poles - L1 and L2. What your schematic shows is you simply tie L1 and L2 together and you double the amperage at 120v, while taking out the 240v ability. This is absolutely wrong. L1 and L2 are 180 degrees out of phase. If you short L1 and L2 you blow up your generator. What ever phase L1 is in, you need to shift L2 180 degrees so that it synchronizes back to L1. 

In an inverter that has 2 banks of transistors to generate the two poles 180deg from each other you could rewire them and drive 1 bank "backwards" 180deg to create that synchronization. 

In a rotary generator - what synchronizes the outputs of a center tapped, bonded neutral alternator?

I suppose one way is if the alternator is NOT "neutral bonded to frame", and instead has a broken center that can either allow the windings to connect in series, or be broken and reverse the connection to do that 180deg phase shift to the next coil. In this case, you don't have a real "neutral" because there aren't any opposing waveforms, where "neutral" sits right smack in between. What would have been opposing waveforms are now stacked on top of each other. 

Head scratching...


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## FlyFisher (Jun 30, 2018)

Rene said:


> Question on surge AMPs from a portable room AC and whether my 5k genset can deliver.


I stopped at a chain store a few years ago that sells a LOT of generators and the guy I talked to called the store manager. Between the two of them they could not answer the question I had - which really is the exact question you have - can a generator provide x amount of power on 120v? 

You have a good understanding of the numbers from what you describe so you are in the right spot on your thinking. 

The take-away I got from researching it is the limiting factor to an alternator on a generator is the AMPERAGE, not the WATTAGE. That Amperage is 1 value across the whole alternator. That means L1 (120v) has the same amperage limit as L2 (120v) and they all have the same amperage limit as L1+L2 (240v). If your amperage limit is (using your numbers here) - 
5500 running watts - 5500/240 = 22.9 amps
6900 surge watts - 6900/240 = 28.75 amps

Your limit for starting amperage is 28.75 amps on one leg for 120v. 

You state that your AC draws 45 amps on start up surge. You are way over the starting amperage limit of the generator. 

The only way to maximize the wattage of a generator (yea I switched over from amps to watts here) is to balance your loads on a split phase set up. You can't draw all that wattage at 120v from one side of the alternator - your limit (going back to amps) is the current rating of the alternator. 

A caveat to the ratings - sometimes alternators can be rated for more power than what the generator itself is spec'd or advertised as. If there is a larger alternator on the unit with a lower rating then it might be that the engine doesn't have the power to drive it, even though the alternator itself might take it. My old rotary generator I believe is this way - they put a 30 amp breaker on it and an L14-30 connector, but it won't touch 30 amps. If you draw more than about 18-20 it will stall the engine. So the 30 amp breaker is rather useless. 

Going back to your power supply issue - your starting draw is close to 20 amps over the calculated current rating of the unit, yet your running wattage is 1357. That comes out to about 11.3 amps. That is well within the running amperage of the unit. So try it and see what happens. If your AC is like mine here - it will sense the voltage sag and the thermostat will trip to cut off the compressor off. It won't blow itself up, but I suspect if I kept trying to run it in that state with the low voltage tripping it would be a problem over continued use.


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## Browse Deweb (Jan 16, 2021)

For 120V/240V inverter generators, there will usually be a 30A 120V receptacle available for up to 30A at 120V. Other standard 120V outlets can also be used. The power from the stator to the inverter apparently can be summed and phase aligned by the inverter for use with this plug, assuming the switch is set to 120V only. This would also explain how two inverter generators can also be paralleled together and double the output of a single generator (via phase matching).

No idea about non-inverter generators.


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## drmerdp (Apr 10, 2018)

FlyFisher said:


> Can you explain your post in more detail? What you state contradicts what I have thought.
> 
> The Honda EU7000 is an inverter generator. It is not a rotary alternator. There is a computer controlling the AC output, which I believe is the computer modulating transistors in banks in phase and out of phase (for split phase 120/240). The input to the system is DC, rectified from the alternator off the engine.
> 
> ...


The eu7000s Inverter assembly has internal master and slave units. One for L1, and one for L2, the master and slave will either sync or offset 180 degree depending on the 120v-120/240v switch position.




FlyFisher said:


> I stopped at a chain store a few years ago that sells a LOT of generators and the guy I talked to called the store manager. Between the two of them they could not answer the question I had - which really is the exact question you have - can a generator provide x amount of power on 120v?
> 
> You have a good understanding of the numbers from what you describe so you are in the right spot on your thinking.
> 
> ...


Inrush is the highest measured current which occurs for only a fraction of a second. It is not the end all be all measurement. I’m certain that a 5500 watt generator will start that AC, the only issue being how much the generator is already loaded before the AC cycles on. Basic load management required…


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## Rene (Feb 5, 2021)

drmerdp said:


> The eu7000s Inverter assembly has internal master and slave units. One for L1, and one for L2, the master and slave will either sync or offset 180 degree depending on the 120v-120/240v switch position.
> 
> 
> 
> ...


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## Rene (Feb 5, 2021)

Thanks to everyone for their input. I understand most of the responses and options (managing load, softstart, 120 v only (mine doesn't have that option and I have an 30 amp 240v interlock solution installed). My instincts along with other readings on inrush values are that it does not represent whether a Genset can start the equipment on not. So I will test sometime this month and report back.


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## iowagold (Jan 22, 2020)

yup add on a soft start for sure!
they help even when on grid power!


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## FlyFisher (Jun 30, 2018)

For what it is worth - I did some testing today with my EU2200i inverter generator and my room AC. The AC is said to draw 7.5 amps. Measured while running it is about 6-6.5 with the compressor running, or in the range of ~730 watts. Interestingly, the highest peak starting amperage that registered on the meter (that registered - it could very well have been higher) was 15.7 amps when the compressor kicked on. I have the AC and generator along for the weekend camping to test out so we'll see how it runs the next couple days when I get set up.


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## iowagold (Jan 22, 2020)

was that with a micro air easy start?
and have you seen the inverter small air con units now out?


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## FlyFisher (Jun 30, 2018)

iowagold said:


> was that with a micro air easy start?
> and have you seen the inverter small air con units now out?


AC does not have easy start. No I have not seen the inverter AC units. The AC unit is the one I use in the house. Its an older Delonghi Pinguino. 

The results from the weekend are that with eco mode off it will perform best, but still isn't great. With eco mode on it would trip the "breaker" on the AC unit (there is a little red reset button that once it trips will cut the compressor off but leave the unit on with the fan otherwise = no cool air when it trips, with eco mode off the "breaker" wouldn't trip nearly as much). When the compressor would start it would bonk the voltage protection as the power from the generator would sag, but the engine would go to high RPM and then catch the compressor on the next cycle. In eco mode you could hear a relay slapping several times. I assume that is what the voltage protection tripping the relay to stop the compressor. I am thinking that cycle is what would pop the "breaker" on the AC. with eco mode off it worked a lot better, but still not what I would call "great".

If the AC was a usual load for portable use then I would say the EU3000 would have the head room to get the AC going a lot easier as it sits. 

Perhaps with a soft-start/easy-start that would alleviate the start up challenge on the AC with the EU2200i. I am not sure that I want to go that route. In all honesty, I've never used this room AC outside of the house, and it is a tank. It lives up stairs and is a pain going up and down the steps. So getting something lighter, at least, if not smaller, would be ideal to cart around. Maybe that will be down the road.


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## iowagold (Jan 22, 2020)

yea they can be modified with an easy start.

watch for the new units on the way....
as soon as production is ramped back up the new units will be 9 months from now...
i hear you on the weight!
lol
the 2200 was heavy today as i am still sore from the big fall 2.5 years back...
doing better...
but it was a long weekend working...


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## Rene (Feb 5, 2021)

Rene said:


> Thanks to everyone for their input. I understand most of the responses and options (managing load, softstart, 120 v only (mine doesn't have that option and I have an 30 amp 240v interlock solution installed). My instincts along with other readings on inrush values are that it does not represent whether a Genset can start the equipment on not. So I will test sometime this month and report back.


Test complete. The AC started without issue. Amp meter read 50.8 inrush at start up of AC, then it dropped down to ~8.0 and slowly climbed to 10.4 which is what the specs call for. The AC was the only load, then I added a toaster oven rated at 1350 watts to the second pole. No problem. Then I added my reciprocal saw rated at 6.5 amps on the same pole as the AC. It started without issue. Cycled the saw on and off several times and held on for about a minute. Final test was starting AC while the toaster oven was on. All tests were successful.

I at least know that I can run the AC and some additional load like the fridge and some lights. In real world I think I will push it harder at least in the early part of the night. Will see what happens.


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