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Old 02-20-2013, 07:59 PM   #1
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Running 2 Generators

Hi All,

Newbie here. I'm thinking of getting two Yamaha 2000is gens from US Carburetor with the propane mods. My AS has a propane port under the hitch frame. Any thoughts on the plumbing to hook up both generators to this source?

Any observations on using the propane option? Pros? Cons?

Thanks!
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Old 02-20-2013, 08:09 PM   #2
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The generators, like any other liquid propane appliance, are set to run on a regulated input pressure of 11 to 14 inches of water colum (WC). Most propane bottles that have at least 1/3 of a tank and a properly adjusted regulator will run one or two small generators like this along with your furnace and/or water heater, etc. This is an estimate on my part, but I'm pretty sure that it's accurate.

Where do you intend to mount the generators when they are running? Will they be connected at all times or do you want to have them to remain portable units that are hauled in your tow vehicle? The answers to these questions will lead the way to the method of connecting them to your propane tank(s). You could also have a separate tank for the generator or one for each. However, if I were going to have an independent fuel supply (LP gas in this instance) I wouldn't bother with the expense and complexity of the propane conversions of the generators.

Steve
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Old 02-20-2013, 08:10 PM   #3
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You may need a higher pressure to the regulator on the Generators than is supplied by the trailer system after the regulator on the tanks. The lines to the appliances in the trailer are only operating at 11" WG. I think the pressure needed on the generator regulator is higher, but not sure. Someone else here should know though.
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Old 02-20-2013, 08:19 PM   #4
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Steve and idroba,

Thanks for the responses. This is becoming more complicated by the minute. I intend to get the propane option so that I don't have to carry gas, fumes, etc. I have a diesel TV. I thought I could just run the duel gens from the AS propane tanks. Trying to keep it simple. The gens would be used only when needed and like would ride aft in my trailer, possibly under the rear queen bed? Really like the idea of no gas fumes.

Mad
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Old 02-20-2013, 08:34 PM   #5
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Hi MadMarine

Welcome

The U S Carburetion kits run on propane vapor at 11" w.c. which is what is available from the accessory port on your trailer.

It is possible that you might have problems with the pressure dropping on heavy loads which can lead to "hunting" where the generator has trouble maintaining engine RPM consistently. There's no way to know without trying it. I would guess you'll probably be OK with your setup.

The main problem with propane setups with two generators is all the complexity of running the lines and electrical cords and so on. It's lots of setup.

Like most Airstreamers, I travel without a generator and rely on batteries when I am away from shore power. I have my tow vehicle set up to charge batteries while the engine is running. Of course I can't run the air conditioning in the trailer without shore power but I just plan trips during the hottest months so that I have shore power.

You may find that it isn't necessary or desirable to carry a generator.
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Old 02-20-2013, 08:37 PM   #6
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I imagine that you could tap in to the existing LP hose before the regulator and setup a new port to use for the generators if the existing one doesn't have enough pressure.

I have been considering a similar idea. Mounting one of the regulators that come with the conversion on the propane tanks next to the existing one and using it to power both generators instead of having to use one for each. This would save some space if it works.

-Dwight
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Old 02-20-2013, 08:48 PM   #7
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Maybe you should consider solar panels? Check the adds in Airforums.
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Old 03-09-2013, 09:09 AM   #8
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I was reading through this thread and it prodded me to join the forum, (which I was going to anyway!).

There are electrical implications to running two generators, due to A/C phase considerations, two generators CAN NOT be used to power a common circuit.

I think two generators COULD be used in circuits isolated from each other, but this would mean that the wiring would need to be divided at the fuse panel. Furthermore, the use of two generators, each powering a "leg" of a fuse panel would NOT result in a useable 220V circuit across the two legs.

(There are also probable implications where both generators would backfeed to one another, probably resulting in their failure)

In short, two generators could NOT be used wired in parallel to each other, (nor in series). similar to the way we might add a battery to a DC circuit.This WILL NOT work.
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Old 03-09-2013, 09:18 AM   #9
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Originally Posted by J. Morgan View Post
I was reading through this thread and it prodded me to join the forum, (which I was going to anyway!).

There are electrical implications to running two generators, due to A/C phase considerations, two generators CAN NOT be used to power a common circuit.

I think two generators COULD be used in circuits isolated from each other, but this would mean that the wiring would need to be divided at the fuse panel. Furthermore, the use of two generators, each powering a "leg" of a fuse panel would NOT result in a useable 220V circuit across the two legs.

(There are also probable implications where both generators would backfeed to one another, probably resulting in their failure)

In short, two generators could NOT be used wired in parallel to each other, (nor in series). similar to the way we might add a battery to a DC circuit.This WILL NOT work.
It's true that two generic generators not designed to be paralleled cannot power one system, but there are generators designed to do so either with the addition of an external adapter that syncs the two, or a special cable that connects built-in sync systems. Honda and Yamaha have these systems built into some of their generators, and some others like Champion have an external optional adapter that includes the 30A plug.
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Old 03-09-2013, 11:45 AM   #10
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I have the two converted Yamaha generators that you are thinking of buying. Technically, they are inverters, not generators, which as I understand have more stable power than generators as the main difference. More stable is better for sensitive electronics. The Yamaha EF2000iS are pre-configured for running in pairs called "Twin Tech" using a special adapter cable. The cable connects two inverters for a combined 120 volt, 25.5 amp output. The adapter has a 30 amp twist lock outlet which will require another adapter to hook up to your 30 amp cord to the AS. The amperage will allow you to run your AC but not a whole lot more, so you have to be careful. A toaster or high wattage hair dryer could overload the inverters and shut them down. We used the two paired together to run our AC at a rally during a 96 degree day and they worked fine as described above.
Honda also does something similar using a "companion" inverter as part of the mixed pair and a lot of people on this forum like those as well.
You can also buy a larger converted inverter and have more amperage. We chose the twin inverters because I didn't want to drag a 80-90 inverter in and out of the truck. Second reason is if you dry camp in cooler weather, you only need one inverter since you not likely to use AC. However if you use the heat pump, I'm not sure if has enough amperage and have never tried it since its slow to warm and very, very noisy.
As far as the propane/natural gas use, I haven't had much time to try it. I did once and it started but requires adjustments to fine tune. If you read the instructions on the use of propane or natural gas, it is important to have an understanding of the supply requirements. The people at US carb are very helpful.
I think if you do a search here on the forum, you will find a lot of information and experience.
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Old 03-09-2013, 12:23 PM   #11
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Technically, they are inverters, not generators,
Not exactly, they are called inverter/generators. I believe technically, they are generator-inverters. This means the engine powers a generator which provides electricity to the inverter which produces stabilized 120V@60Hz electricity for use at the plugs.

Yes, the main reason is the power is more stable and better for electronics.

Another reason is with this system the inverter can supply stable power at any RPM (unlike the contractor generators that need to run at a set RPM to produce 120V@60Hz) which allows the inverter/generator to be quieter and use less fuel when not producing much power.

This also allows the inverters to sink with each other which is probably the only reason 2 inverter/generators designed for it can be hooked together since I have never heard of 2 regular generators that were able to be hooked together. So J. Morgan is right that 2 generators can't power 1 circuit, but 2 inverter/generators can if designed for it.
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Old 03-09-2013, 06:46 PM   #12
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Wazbro,
Since there is some interest in how this is done and what is going on, I'm venturing out to try to give a straight-forward, accurate explanation. I'm now retired, but during my working career, I was an aviation electronics engineer for an aircraft manufacturer and worked with this sort of thing among others.

Actually, two or more pure AC generators can be phase-locked (synchronized) and two or more AC or DC generators can be voltage matched to run seamlessly together without the inverter part of things, but only if they have control circuits that are specifically designed to run together. Examples of this sort of thing are the generators in hydro-electric dams, other power grid applications or airplanes or ships with multiple generators, multiple diesel-electric train engines, etc. But, when it comes to portable generators like those used with travel trailers, the only ones that can generate AC in a synchronous manner are inverter generators (industry term, could have also be called generator inverters as you suggest and would perhaps have been more correct).

Here's a basic description of how an inverter generator works:
1. The engine crankshaft turns the rotor of an alternator (internally produces AC power) that has diode rectification and ends up putting out DC power after this rectification. This is exactly how your vehicle alternator works.
2. The engine speed (and therefore horsepower output) is controlled by an electronically controlled throttle that maintains the output voltage at a regulated value (let's say for the purpose of explanation about 165 Volts DC). Actually, let's take this a step further and say that the alternator puts out two outputs + 165 VDC and - 165 VDC for a 115 VAC system.
3. The plus and minus 165 VDC outputs feed the inverter which then converts the output into a stable 115 VAC electrical power. This process starts with a 60 Hertz sine wave oscillator that puts out a tiny amount of 60 Hz AC power (maybe 1 Watt or less). The small 60 Hz signal is then amplified through a series or cascade of amplifiers using the positive DC input for the positive portion of the AC power and the negative DC input for the negative portion of the AC power.
4. As you turn on more appliances in the trailer and the AC electrical load goes up, the inverter demands more DC input power from the alternator. This demand for more DC power from the alternator decreases the DC voltage output and the engine speed increases to supply more power and return to the regulated voltage. A decrease in the load will result in the a decrease in engine speed.

Now to the part about paralleling two inverter generators, for those who are still with me!

The second (slave) inverter generator works just like the first (master) inverter generator as far as steps 1 through 4 are concerned...well almost. In step 3, instead of using a 60 Hz oscillator as the reference for AC generation, the slave inverter generator uses the sine wave output of the master inverter generator. The slave inverter generator also matches it's output AC voltage to the master using the same electronic throttle feedback control loop as described in step 2.

Hopefully, this isn't too much detail. But since it's being discussed, I just wanted to try to put out some information on the process.

Steve
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Old 03-09-2013, 08:06 PM   #13
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The limiting thing will be how long you can run on portable propane tanks under an AC load.
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Old 03-09-2013, 10:12 PM   #14
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Both Yamaha and Honda offer versions of the 2kw gen sets that can be connected to provide enough juice to power the Airstream AC. The technology may be complex, but they do it for about the same price as the inverter models. The Yam connector cable costs about $120 the last time I checked.
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