Generator help

Brandon

Member
I have a Bighorn with two ac's does anyone know how big of a generator I would need to run both of them. Thanks, Brandon
 

Invizatu

Senior Road Warriors
Depends on whether your A/Cs are 13.5k btu or 15k btu for starters.

My 15k btu draws 14.4 amps, and a honda 2000 watt gen is rated at 13.6amps therefor I need 2 Honda 2000s to run my a/c. So If you have 2 15k A/Cs you would need a generator that would be rated at 28.8 amps or more to run both at the same time. There is a formula for figuring amps / watts / volts but It slips my mind at the moment, I am sure someone will chime in. You could run one on a 3000 easily enough, probably need about a 5000 watt to run both at the same time. Keep in mind you'll need more amps to be running other stuff in addition to your A/Cs.
 

rgwilliams69

Well-known member
Are you looking for an on-board installed (like an ONAN) or portable (like a Honda 3000, etc.)? If you are going on-board the best to get is the 5500 as mentioned in the previous comment. If you are going with portable, then you will need to get a big portable. I have a Honda 3000 that I use for backup (have the on-board ONAN 5500 as well). The Honda will run either my 15k or 13.5k separately, but not both at the same time. I've tried a few times to see if it would run both and by starting the 15k first and letting it settle, then starting the 13.5k slowly (fan on first, then compressor following) you can get them both up and running, just barely. If anything changes at all (say a little larger load on the converter or one of the ACs cycles) you lose it all, Honda 3000 overloads. I'm sure pushing the boundaries like this isn't good medicine for the AC units either.

To simultaneously run/start/cycle both you will need 4500 watts and up (marginally), and over 5000 watts would be better because you will have other things running as well. Honda does sell a portable 6500 - my friend has one of those and it runs both just fine. Portable is an interesting description for it however because it weighs 260lbs - and that's without fuel. My buddy never takes it out of his truck bed. Also at a cost of around $4000-$4500 you are likely better off just getting the ONAN installed.

Just one more note also while you are shopping that I wish someone had told me on my last coach (Keystone Alpine 3640). I had a 5500 ONAN installed and because I didn't have an on-board fuel tank got the propane fueled one. If you do that be aware that running two ACs on the ONAN 5500 generator eats up the propane quickly - a full 30lb tank would be empty in 7 hours or less while the ACs are running. On my new coach (Cyclone 4100) the ONAN is gas fueled and I have a 50 gallon capacity. Much better than lugging 7 30lb propane tanks with you (full tank = approximately 7 gallons).

Good luck!
 

PUG

Pug
I had a Onan 5500 watt with my old Cyclone 3250 and it was sufficient to run about anything you could load on it. Very good quality unit but costly. My new Carriage Cameo 36fws did not have a gen so I purchased a Champion 3500/4000 watt gen. You could run both ac units but not anything much else. I went through and made up a chart of all my appliances loads (wh, tvs, bat charger, etc. etc. and wrote down their amp loads and then from that chart I can see what I can and can't run at the same time. All appliances have a wattage or amp rating. Here are conversion charts to do your wattage and amperage conversions.

Converting Watts to Amps

The conversion of Watts to Amps at fixed voltage is governed by the equation Amps = Watts/Volts

For example 12 watts/12 volts = 1 amp
Converting Amps to Watts

The conversion of Amps to Watts at fixed voltage is governed by the equation Watts = Amps x Volts

For example 1 amp * 110 volts = 110 watts

Converting Watts to Volts

The conversion of Watts to Volts at fixed amperage is governed by the equation Volts = Watts/Amps

For example 100 watts/10 amps = 10 volts

Converting Volts to Watts

The conversion of Volts to Watts at fixed amperage is governed by the equation Watts = Amps x Volts

For example 1.5 amps * 12 volts = 18 watts

Converting Volts to Amps at fixed wattage

The conversion of Volts to Amps if the wattage is known is governed by the equations Amps = Watts/Volts

For example 120 watts/110 volts = 1.09 amps

Converting Amps to Volts at fixed wattage

The conversion of Amps to Volts if the wattage is know is governed by the equation Volts = Watts/Amps

For Example, 48 watts / 12 Amps = 4 Volts

Converting Volts to Amps at a fixed resistance

If you know the volts and the load of the resistance the amps are found by Ohm's law: Amps = Volts / Resistance

Converting Amps to Volts at fixed resistance

If you know the amps and the resistance Ohm's law becomes Volts = Amps * Resistance

[SIZE=+1]Explanation[/SIZE]

Amps are how many electrons flow past a certain point per second. It is equal to one coulomb of charge per second, or 6.24 x 10^18 electrons per second. Volts is a measure of how much force that each electron is under, which we call "potential". Power (watts) is volts times amps. A few electrons under a lot of potential can supply a lot of power, or a lot of electrons at a low potential can supply the same power. Think of water in a hose. A gallon a minute (think amps) just dribbles out if it is under low pressure (think low voltage). But if you restrict the end of the hose, letting the pressure build up, the water can have more power (like watts), even though it is still only one gallon a minute. In fact the power can grow enormous as the pressure builds, to the point that a water knife can cut a sheet of glass. In the same manner as the voltage is increased a small amount of current can turn into a lot of watts.

This is also why increasing the volts does not necessarily increase the available power. Power is amps times volts, so if you double the volts you halve the amps unless something in your circuit actually creates power, such as a battery, solar panel or nuclear power plant.
Convert amps to watts. Convert watts to amps. Convert watts to volts, convert volts to watts, convert amps to volts at fixed wattage. How to convert watt to amps. How do I convert amps to watt? Amps converting watt. Volt to watt conversion.


 

Brandon

Member
Ok. Thanks for the help. I think I will go with the Onan 5500. Anyone know how easy or difficult it is to install one in the front of a 2013 Bighorn.
 

scottyb

Well-known member
Am I correct that our 5500 Onans only produce 1/2 as much power as our 50A services from shore power? What is confusing to me is that it still has two legs coming into the transfer switch. Are they really two 25A services coming from the generaor?
 

danemayer

Well-known member
Am I correct that our 5500 Onans only produce 1/2 as much power as our 50A services from shore power? What is confusing to me is that it still has two legs coming into the transfer switch. Are they really two 25A services coming from the generaor?
I think the Onan 5500 is intended to replace 50Amp shore power. Ours powers everything in our Landmark at the same time. If it were only two 25A services, the microwave, TV, lights, converter and 2 A/C units, etc. would surely trip something and it doesn't.

On edit: the Onan spec sheet shows 2 30A breakers, so 2 25A legs does seem reasonable. We've never had a problem.
 
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TedS

Well-known member
Yes, 25 amp per leg, 50 amps total. 110 x 50 = 5500 watts. That's why each a/c is on its own leg. Onan spec sheet shows 46-amp rating; 120 x 46 = 5520 watts.
 
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