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Old 31-07-2020, 07:27   #61
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Re: Non-Marine Generator Choices?

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Can you clarify? Thatís 5.5KW continuous output?

Hot water heater is on demand propane (located outside) so itís not a factor in electrical loads thankfully.
Figure conservatively that your pair of A/Cs will draw about 20 amps while running. So with the 5.5kw, that leaves you 25 amps of headroom. Another 10 - 15 amps for a decent size battery charger and you've still got some headroom to run another device without turning an A/C off or to handle an A/C starting while the other one and the charger, etc. are running.

Based on that, the 5.5 seems reasonably sized. Going smaller won't save you much, as you don't have as many good generator choices that aren't too small.
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Old 31-07-2020, 07:41   #62
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Re: Non-Marine Generator Choices?

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Are any of the soft start units not compatible with those types of air conditioners?
They are compatible but are quite expensive. I do already own one because my current 5.5kw generator couldnít start a window unit I had for construction purposes.

So maybe putting the soft start on one of those ACs would do the trick actually. Good thinking!
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Old 31-07-2020, 07:48   #63
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Re: Non-Marine Generator Choices?

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Originally Posted by rslifkin View Post
Figure conservatively that your pair of A/Cs will draw about 20 amps while running. So with the 5.5kw, that leaves you 25 amps of headroom. Another 10 - 15 amps for a decent size battery charger and you've still got some headroom to run another device without turning an A/C off or to handle an A/C starting while the other one and the charger, etc. are running.

Based on that, the 5.5 seems reasonably sized. Going smaller won't save you much, as you don't have as many good generator choices that aren't too small.
From the air conditioning specs, itís 15 amps per unit, for a total of 30 amps running both.

The LRA for these is 61 amps each.
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Old 31-07-2020, 07:53   #64
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Re: Non-Marine Generator Choices?

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They are compatible but are quite expensive. I do already own one because my current 5.5kw generator couldn’t start a window unit I had for construction purposes.

So maybe putting the soft start on one of those ACs would do the trick actually. Good thinking!
They do make soft start systems and they are quite popular for folks using the 2000w inverter generators. They also make controllers that delay the start of the 2nd unit. Only delays by 30 sec or so to allow the start up load on the first unit to dissipate before kicking on the second unit.

We run our RV and boat air/con with a 2400w Yamaha. Is your current 5.5kw an inverter type? I never found any documentation but was once told there is a surge system with the Yamaha inverter units, so for a second or two it actually puts out more amps to get motors started. With 5.5kw, it should easily handle a 12-15k btu air/con startup. Really if the 1st unit is drawing 1.2-1.5kw (typical for what we've measured), there should still be plenty of juice to get a second unit started.

We measure between 10-12amp while running for the air/con. There are lower amperage RV units but they do cost a little more.
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Old 31-07-2020, 07:59   #65
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Re: Non-Marine Generator Choices?

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Originally Posted by Chotu View Post
From the air conditioning specs, itís 15 amps per unit, for a total of 30 amps running both.

The LRA for these is 61 amps each.
In that case, those units are a bit less efficient than I was expecting. 15A is about what I figure for a 16k BTU marine unit including the pump. Based on that, I definitely wouldn't go smaller than a 5.5kw for having enough headroom for battery charging and such while both A/Cs are running.
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Old 31-07-2020, 08:20   #66
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Re: Non-Marine Generator Choices?

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Originally Posted by rslifkin View Post
Figure conservatively that your pair of A/Cs will draw about 20 amps while running. So with the 5.5kw, that leaves you 25 amps of headroom. Another 10 - 15 amps for a decent size battery charger and you've still got some headroom to run another device without turning an A/C off or to handle an A/C starting while the other one and the charger, etc. are running.

Based on that, the 5.5 seems reasonably sized. Going smaller won't save you much, as you don't have as many good generator choices that aren't too small.

Note that one way of dealing with startup and other short term loads is with a charger/inverter with Power Boost like a Victron Multiplus. This works extremely well and can make a smaller generator work fine. A 3kVA Multiplus can do about 5kW of Power Boost for short periods, like many full seconds, plenty long enough to start electric motors.



OTOH, with a petrol generator (especially an inverter generator), unlike a diesel one, you probably prefer to run it at a lower load as a % of max, and the lower the better. So other than weight and maybe slightly worse efficiency there's not much downside to a bigger one.
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Old 31-07-2020, 08:28   #67
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Re: Non-Marine Generator Choices?

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In that case, those units are a bit less efficient than I was expecting. 15A is about what I figure for a 16k BTU marine unit including the pump. Based on that, I definitely wouldn't go smaller than a 5.5kw for having enough headroom for battery charging and such while both A/Cs are running.
Ok. Thanks for the help with the specific numbers.

Always nice to have additional input on generator sizing.

I had been thinking like Dockhead.

One size up is just easier on the generator not having to run at high loading. There is definitely a weight penalty though, so it’s a “pick your poison” situation.

Also, the Victron type power management unit is looking very attractive. I had always split up my inverter and charger and manually controlled everything. I figure that was better if something breaks.

However, if it has a power boost and cleans and corrects ugly shore power and stuff, providing a nice pure sine power... it could be the way to go. And to get away with a smaller generator.

What KVa for an unsure American working in Watts and amps?
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Old 31-07-2020, 08:45   #68
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Re: Non-Marine Generator Choices?

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Originally Posted by Chotu View Post
Ok. Thanks for the help with the specific numbers.

Always nice to have additional input on generator sizing.

I had been thinking like Dockhead.

One size up is just easier on the generator not having to run at high loading. There is definitely a weight penalty though, so itís a ďpick your poisonĒ situation.

Also, the Victron type power management unit is looking very attractive. I had always split up my inverter and charger and manually controlled everything. I figure that was better if something breaks.

However, if it has a power boost and cleans and corrects ugly shore power and stuff, providing a nice pure sine power... it could be the way to go. And to get away with a smaller generator.

What KVa for an unsure American working in Watts and amps?

KVA -- kilo volt amps -- equal to kW at a Power Factor of 1.0 (see https://en.wikipedia.org/wiki/Power_factor). But not at different power factors. Victron for whatever reason rate their kit in KVA and not kW, so you have to translate. The 3KVA Multiplus is actually 2500 watts in ideal conditions, still less when hot. When I bought mine I thought I was buying a 3000 watt inverter


I highly recommend a charger/inverter (not necessarily Victron; there are other good choices), rather than separate units, EVEN if you have an oversized generator. There are many other cases where Power Boost is really useful -- like on weak shore power, or just if you're running a bunch of loads at once for short periods and don't want to juggle them. ALSO, Power Boost allows you to postively limit the amount of power you take from shore power connection or generator, preventing them from being overloaded. Lastly, a charger inverter, unlike a separate charger, will automatically dial down the charger when you approach the current limit you set. Totally different level of functionality; I would now never want to be without. Downside is non-redundancy, but I have a separate spare battery charger and a small separate inverter available in case of failure in a remote place.
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Old 31-07-2020, 08:55   #69
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Re: Non-Marine Generator Choices?

You are building a bare bones boat but it has a/c? Ditch the gen and the a/c.
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Old 31-07-2020, 08:55   #70
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Re: Non-Marine Generator Choices?

As far as starting loads, if the modern Onans are anything like the old ones (and the engine HP rating vs generator KW rating says they might be), they'll take a pretty big motor starting surge without issue. A half-second overload won't build any noticeable extra heat in the generator head, so as long as the engine has the guts to handle the brief load spike without losing too much RPM, all is good.

I'd worry far more about motor starting ability with the inverter generators where they've got less surplus engine power and likely an electrical limit to their surge output.
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Old 31-07-2020, 09:00   #71
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Re: Non-Marine Generator Choices?

Non marine:
I bought a Chinese made electric start 5k generator a few years back. The first thing I will say is USE NON ETHANOL GAS in your generator. Farm supply and other places sell it.
Since I went to real gas in my small tools, weed whacker, chain saw etc many issues went away. This is important especially in a generator that gets used maybe once or twice a year.
The carb got screwed up after one use from ethanol gas sitting in it . I had to clean it all out and the aluminum carb bowl was heavily pitted just from the gas sitting in it. Since then I've used real gas and it starts after one year immediately.

This $400 generator has run well many times, last time for about 14 hours straight. It's a common name brand but Chinese made.
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Old 31-07-2020, 09:25   #72
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Re: Non-Marine Generator Choices?

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You are building a bare bones boat but it has a/c? Ditch the gen and the a/c.
Ditch your heaters first. Lol
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Old 31-07-2020, 09:41   #73
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Re: Non-Marine Generator Choices?

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Originally Posted by Cheechako View Post
Non marine:
I bought a Chinese made electric start 5k generator a few years back. The first thing I will say is USE NON ETHANOL GAS in your generator. Farm supply and other places sell it.
Since I went to real gas in my small tools, weed whacker, chain saw etc many issues went away. This is important especially in a generator that gets used maybe once or twice a year.
The carb got screwed up after one use from ethanol gas sitting in it . I had to clean it all out and the aluminum carb bowl was heavily pitted just from the gas sitting in it. Since then I've used real gas and it starts after one year immediately.

This $400 generator has run well many times, last time for about 14 hours straight. It's a common name brand but Chinese made.
I’m only going to buy a fuel injected generator. Now that they are available, I’ll never have another carburetor again. Thank GOD.

Fuel injected main engines, fuel injected dinghy engine, fuel injected generator.

So this Ryobi might be a fuel injected Chinese made gender I’m guessing.
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Old 31-07-2020, 09:43   #74
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Re: Non-Marine Generator Choices?

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Originally Posted by rslifkin View Post
As far as starting loads, if the modern Onans are anything like the old ones (and the engine HP rating vs generator KW rating says they might be), they'll take a pretty big motor starting surge without issue. A half-second overload won't build any noticeable extra heat in the generator head, so as long as the engine has the guts to handle the brief load spike without losing too much RPM, all is good.

I'd worry far more about motor starting ability with the inverter generators where they've got less surplus engine power and likely an electrical limit to their surge output.
This is true. They are a step above portable generators. They do fail a lot on rvs and require lots of maintenance. They are really finicky. But they have some advantages .

OOOH!!!! I just noticed these run at 2400RPM!!

Big advantage
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Old 31-07-2020, 10:12   #75
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Re: Non-Marine Generator Choices?

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From the air conditioning specs, it’s 15 amps per unit, for a total of 30 amps running both.

The LRA for these is 61 amps each.
Go down to a campground and see if someone will let you hook up an amp-meter to their rig when the air/con is running.

It varies but when we've done it we get continuous draws of 10-13amps. It varies with voltage but with a properly functioning generator, you should stay up at pretty close to 120v. Campgrounds are notorious for low voltage on hot holiday weekends. We've seen 93v before. We do monitor the voltage and are disconnected and switched over to the generator long before it gets down that low.

Also is the LRA rating you found before or after the capacitor? Even basic RV units include a capacitor. Just helped a friend out selecting a 3100w starting watt (2800w continuous) champion inverter generator...works like a dream on his air/con. 3100w is only about 26amp.

Another thought...is your boat propane free? You can get dual/fuel generators now at minimal cost upgrade. That bypasses the whole gunked up carb issue.
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