If we are running an entire elec. bus, with 2 coleman basement units hooked up to 2 20 amp breakers, extra large fridge, 20 gall. 110 volt ge elec water heater, small insta heat water heater that runs on 240. Kenmore clothes dryer, small, runs on 240 volt, that will run occasionally. Other than that, coffee pot, microwave, tvs, sound system. Occasional one burner electric induction cook top. Can anyone just estimate the size gen we would need? The biggest one Onan makes is a 12.5. ??? I know there are ways to do this to know exactly, just want an estimate by someone who knows this stuff. Thanks
Hi Ruthi ,
I'm sure you won't be using all the systems at the same time.
Come up with a normal "heavy day" useage of which ones will be used at the same time.
For example: the AC running , clothes dryer running , water heater running.
From a list like that a total AMP draw could be found.
I would get that total heavy day and add another 30% to cover coffee and TV.
Thinking how you'll use the systems will help you use the systems better.
Remember the fridge runs about 30% of the time , the Ac will draw full AMPs
for and hour or two when just turned on in a hot day ( but then cycle ).
We have a 10KW gen and watch the AMP meters to see what else we can turn on.
You'll get the hang of load shedding when your meters near the top.
Frank
Ruthi, the Marathon runs a 20kw Kohler with about the same equipment you are talking about guess you could do a little power management and get by with a smaller unit but me I would go with the big unit as I don't like to give up comfort for a little in fuel savings
good luck
Normal day would consist of fridge, 2 airs, hot water heaters, tvs, sound system coffee pot and microwave. dryer, maybe one day a week.
luvrbus, we feel the same way. We have the opportunity to buy a nice gen with a roll out tray, 20 k for 7,500. Only prob. is it is not in Tn, but in Ga. So, maybe the gen we have now will keep running for 2 weeks. Hubby says it needs a seal where the oil is leaking and a filter. It has to be took apart to fix, so, that cant happen now, plus the fact we are not close enough for anyone to work on it. We keep putting oil in it, so, we will see..........
I think you can do just fine with 12.5 with a little power management. It could be automated with a few relays so, for instance, one A/C is disabled when the dryer is running or the water heater is off when the cooktop is on. It's fairly easy to come up with a plan that greatly limits any inconvenience.
I would PM Sean on this or wait for him to respond. 20k will be way to big and you could find yourself in a condition called "wet-stacking". Also it is more efficient and better to run a smaller gen near capacity than a large one at partial. If I wasn't at work I would try to explain better, but I will leave that up to the real experts.
Ruthi; I also have an all electric coach except for gas cooktop and oven and we have no problems running everything we need. Of course you can't run everything at once,but with a little management it's not a problem.
Don
Ruthi, "wet stacking" doesn't happen with the Japan made engines they run at 1800 rpm loaded or not.
Wet stacking is a term used for unburned diesel fuel in a engine doesn't happen in todays engines unless they are running cold.
Bill Harris in Virgina a well respected generator guy in the marine and RV world and he tells me that a generator should be large enough to carry a full load at 80 to 90% capacity for a trouble free unit.
I have followed his advice for years and have never had a problem with a generator but some of these guys may know different.
good luck
Basement airs 2200watts each Based on 20 amp breaker x 110V
large Fridge 1100 watts
110V WH 1500 watts
Instant Hot WH 1500 watts
Small Dryer 4500 watts
Coffee pot 900 watts
Microwave 1500.00 watts
TV plasma 400watts
Sound system 80 watts
Inductive Burner 1500 ?
Lights 300
Misc 800
Total 18480 If you had everything going at the same time!
I think you will be fine with a 15KW, 20 KW if you don't want to load manage
If you had just two large appliances, I think the chances would be pretty good that you would have them both running at the same time. But if you have four large appliances, the chances drop significantly that you would have them all running at once. When you start getting up to James' list with 7 or 8 appliances that draw 1000 watts or more, I really start to doubt that you will EVER see these all running at once. Also, some of these appliances only draw their maximum wattage for a brief period (compressor kicking in) and then drop to a more modest power draw.
I'm thinking that a 15kw unit is all that is needed, and maybe just a 12.5kw with some power management.
I have a 13.5 and I have run the generator for little of nothing and as clifford said no problem with "wet stacking" it also has handled everything I have ever wanted to run --- the only thing I watch is that each leg is balanced but that really is pretty basic. My generator came from wrico.
HTH
Melbo
Update, Ken took the gen out of the bus in the walmart parking lot, after work tonight. Found a filter that was plugged like we thought, dont know about the oil leak yet though. It is running smooth now, and the air in the back room is working now, not sure what this would have to do with the gen, if it does. He will run it tonight and see if it runs all night. If not, we have a plan for Rusty to send us a part. Thanks to all of you for the advice, you guys always come through! Still thinking of getting the larger gen when we get one.
FWIW, a "50-amp shore service" is 12kW. So if you can run everything you need or want on the rig when you are plugged in to a 50-amp pedestal, then 12kW should be sufficient for your needs.
Moreover, most RV accessories such as Automatic Transfer Switches, and, of course, plugs and receptacles, are rated at 50 amps or 12,000 watts. To use a generator large than that requires larger wiring, a larger transfer switch, and some way to "manage down" when on shore power instead of the generator.
For this reason I recommend setting up your system such that a 12kW generator would be sufficient to meet your needs.
As Clifford says, Marathon (and others) uses a 20kW unit. But the mentality there is that if you can afford a Marathon, then you don't ask how much the generator costs or how much fuel it uses. Marathons also come with 8kW of inverter capacity, which few people would need.
Load management is the name of the game when it comes to "right-sizing" a generator. If you have a huge load such as a washer/dryer and you want to be able to run it irrespective of whatever else might already be running, then you will need a bunch of extra generator capacity that you won't (and can't) use any other time. You'll burn extra fuel every time you run the genny just to have this capability available.
If, OTOH, you can plan your laundry for a time when you don't need, say, all three air conditioners, or the microwave, or whatever, then you can get by with a smaller unit, and save money all the way around.
Another factor is whether you have a load-supporting inverter, which can "make up the difference" between generator output and total load to handle those part-time loads. This can make a huge difference in the size generator you need.
Only you can make these decisions, and so it is hard to advise you on "proper" size for your generator. That said, since it appears to be a replacement situation, the sizing of existing wiring, transfer switches, and panels will dictate an upper limit to the size of the generator. So, for example, if what you have now is 12kW, and you have 50-amp switchgear, then the largest you can safely go is 12kW without changing out all the wiring, switchgear, and main breakers.
To give you a calibration, we have three roof airs (and a fourth air for the cockpit, but this is seldom run while parked), electric water heater, induction cooktop, Advantium oven, and the usual "small appliances" like a coffee maker, LCD TV, stereo, laptops, etc.. We can run absolutely everything all at the same time on about 7.5 kW, but because we have a load-supporting inverter, we could easily get by with a 6kW unit. If I were shopping for one today, it would be a 6.5 kW model, because that's a common size. (The one we have is 15kW, because it came with the bus. And, yes, it is wet-stacking, and costing us about 2x the fuel.)
HTH,
-Sean
http://OurOdyssey.BlogSpot.com (http://ourodyssey.blogspot.com)
Maybe time for a little work on your Kubota Sean the only thing that will cause that on a Kubota is a bad injector pump,bad injectors,or low compression.If you are sure it is from carbon buildup run a water through the intake with a spray bottle under a load and it will cleanup.I personally have never seen it and I had 10kw generators for years that never ran anything larger than a 7 1/4 saw same with my light towers.
FWIW reading my manuals last night a 20kw Kubota will burn less fuel at 80% capacity than a 12.5kw under full load .
I can pm you the fuel useage charts on the Kubota engines and generators if you like
Quote from: luvrbus on June 24, 2010, 05:08:44 AM
Maybe time for a little work on your Kubota Sean the only thing that will cause that on a Kubota is a bad injector pump,bad injectors,or low compression.If you are sure it is from carbon buildup run a water through the intake with a spray bottle under a load and it will cleanup.
With apologies for hijacking the thread: I haven't actually noticed any accumulation, but neither have I disassembled the exhaust. But I do smell unburned fuel in the exhaust, which is more or less the definition of wet stacking.
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FWIW reading my manuals last night a 20kw Kubota will burn less fuel at 80% capacity than a 12.5kw under full load .
I would guess that would have to do with the fact that the larger engine is turbocharged, and the smaller one is naturally aspirated. So there is something of a stair-step between those two sizes. Generally, the more loaded a generator set is, the less fuel is consumed per watt produced.
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I can pm you the fuel useage charts on the Kubota engines and generators if you like
I'd love to see that, actually, because I've only been able to figure mine empirically. You can send to my email address in my profile.
BTW, as much as I'd like to have a smaller generator, I don't want to give up the Kubota -- these things are bulletproof, and easy to maintain. And in my case, I also have a transformer-regulated head and a set-screw adjusted throttle; there's not a transistor in it anywhere. When I was looking to downsize I was also hoping to find a similar head on a smaller Kubota.
-Sean
http://OurOdyssey.BlogSpot.com (http://ourodyssey.blogspot.com)
Plugged filter was probably causing the generator not to produce 100% thus causing the air conditioner to "hard start",
Ruthi,
We have 20KW EPS generator (with a quiet box, but it isn't as quiet as an Onan) with a Kubota. They gave us a great deal on it. http://www.enginepowersource.com/ (http://www.enginepowersource.com/) A brand new one wasn't that much more then the 20KW you are looking at (and they ship it to you ;)).
Clifford, I agree with you. Our research showed us the same thing. A bigger genset, running at a smaller load, burns less fuel. We were going to get a smaller one, but we thought it is better to be safe then sorry. And we have 8k of inverting power, and five 15k btu roof airs.
On a side note, we know of some folks that have a genset identical to the one that we have on our bus (EPS Kubota, 20KW, but without a quiet box). They are building an orphanage down in Honduras. They use the 20KW to power lights and equipment as they are building the facility. Right now there are running it 12 to 14 hours a day. It is using only 4 gallons (yes you read that right 4 gallons) of diesel a day. Obviously it isn't loaded very much, but I don't care what kind of generator your are running. That is great!
God bless,
John
Yep, Rusty, Ken thinks that may have been the case. John, that is the one we are looking at. It isnt one with the quiet box tho. We are wondering if it may be better to not have the box, and just insulate the compartment instead. Easier access to it on the road. The power tech we have now, has a filter inside of it at the bottom. You have to take the gen out, and disassemble it to change it. We are hopeing to make it as easy to get to as possible. As far as plugging it in at a campground, we never do that anyway. And, it will be going in our new bus. I like to hear all the pros and cons, but, I think we are going to get the 20kw. I know some of you dont understand we are on the road all the time, and power management is one hassle we dont need. There are enough other hassles to deal with as it is. Thanks to all
Hey Ruthi,
I understand youse is always on the road!
Also I we know a man who can tell which light poles in many Wally parking lots have a place to plug into! (since you there working on their stuff anyway! ;))
;D BK ;D
Yea but they are not 50 amps BK lol
good luck
Quote from: luvrbus on June 24, 2010, 08:40:54 PM
Yea but they are not 50 amps BK lol
good luck
No but sometimes every little bit helps! ;)
By the way how the HECK are ya Clifford?
;D BK ;D
Ruthi,
If you have the room, I think you can do just great with one without the quietbox. We just had MAJOR space restraints, and we needed all of the regular maintenance items on one side. Just be careful getting that baby in there. She is heavy!
I do know that they are loud, though. So you will probably have to come up with some pretty good insulation. The open one is FAR easier to work on, I can tell you that. If we would have known that you needed one, we just sold one (20KW, EPS, Kubota, no quiet box) that had less then a thousand hours on it, for $5K.
God bless,
John