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Author Topic: Genset.  (Read 6118 times)
chazwood
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« on: March 09, 2008, 07:04:03 AM »

To help me narrow down the size.... What's the range of KWs I should be looking at? Please don't tell me to start adding up the wattage of every light bulb I will be using; compensate for the coefficient of expansion, and arrive at my own conclusions. I'm just trying to get a general idea. You know ...ballpark. Grin

Thanks.

Chazwood.
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Stan
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« Reply #1 on: March 09, 2008, 07:07:11 AM »

4 to 15 kw. HTH
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chazwood
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« Reply #2 on: March 09, 2008, 07:11:31 AM »

HTH?  So My estimations of around 10kw would handle just about anything. (outside of that hot tub and full laundromat my wife was talking about.)
« Last Edit: March 09, 2008, 07:16:39 AM by chazwood » Logged

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« Reply #3 on: March 09, 2008, 07:31:01 AM »

Chaz,

A significant part of your decision rests with using propane or not.  I you use propane for cooking then I think 6-8 kw is more than adequate  With a little power management, you can have 3 1 ton air conditioners and electric hot water.
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« Reply #4 on: March 09, 2008, 07:36:57 AM »

Mineis all electric and can reach 10 KW load withheat and cooking . Jerry
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Nick Badame Refrig/ACC
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« Reply #5 on: March 09, 2008, 08:08:58 AM »

Hi Chazwood,

I'm also all electric and I have a 12.5 kw.  Most likely, more then I need but, I have powered a fellow busnuts coach

when his genset crapped out last fall. I also powered my house last fall during a power outage.

Ask yourself, What will your needs be?

Anything worth doing, is always worth Overdoing.... Grin

Good Luck
Nick-
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redbus
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« Reply #6 on: March 09, 2008, 08:16:06 AM »

I have a household type water heater and refriderator and use electric heaters on 10k.
I think a 7k or 8k would be fine.
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« Reply #7 on: March 09, 2008, 08:30:56 AM »

Probably the key here is use management.  Be sure to include an ammeter in the system so that you will know where you are in terms of capacity usage (multiply amps time volts to get a "measure" of  usage)

I have a 10 KW and wish I had a 12.5 at times.  I wired my 10KW for 240V because of our dryer (general consensus is that you should not wire anything less than a 12KW for 240V).  That means I have to work at balancing the loads on each leg (using two ammeters). 

When the dryer is on, I have to limit air conditioning etc.(that is when I wish I had 12.5KW).  With the dryer off, I can run most anything (three roof airs, microwave, house fridge, etc.).  I have each AC labeled as to which leg it is on, and can play with the load balancing.  The microwave is a hog, so if I am going to use it for more than just a simple warm-up, I will turn off an AC on that leg.

Most folks do not have their generator wired for 240V and that makes life a bunch easier.

Folks will warn you not to go too big, as a lightly loaded generator is supposedly hard on the generator engine.  I don't think that is as much of a problem with modern diesel engines.  Having said that, when I just want to "exercise" the generator, I will turn on heavy loads (like the useless heat strips in the ACs) to make the generator work hard.  I am on the road quite a bit so I don't have to exercise the generator very often (mostly when I get ready to change the oil).

Jim
« Last Edit: March 09, 2008, 08:45:06 AM by rv_safetyman » Logged

Jim Shepherd
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« Reply #8 on: March 09, 2008, 10:46:09 AM »

7.5 or so will suit most
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TomC
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« Reply #9 on: March 09, 2008, 10:55:53 AM »

Depends on if you have over the road A/C or not.  Since the vast majority of us do take out the over the road A/C, the rule of thumb is if you have two tons (like two roof tops) of cooling 8-10kw. If you have three (like I do) 10-12kw.  If you have four 15-20kw.  If you're all electric, then you should be on the high side. My only propane run appliances is the furnace (35,000btu Atwood) and a 3 burner stove (also Atwood) and with 3 roof tops have plenty of power with the 10kw Powertech.  If you use a 12kw, then you'll have 50amps per leg for a total of 100amps at 120vac.  This means then your 50 amp land line will be the same power capability as the 12kw generator.  Good Luck, TomC
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Sean
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« Reply #10 on: March 09, 2008, 11:14:44 AM »

What's the range of KWs I should be looking at? Please don't tell me to start adding up the wattage of every light bulb I will be using; compensate for the coefficient of expansion, and arrive at my own conclusions.


Umm, you know, you really can not answer this question at all without first doing the very work that you say you don't want to do.

Stan's answer, in that case, was dead on -- 4 to 15 kW.  How can you possibly expect anything more precise than that?

Here are all the things I'd need to know to even begin to tell you which end of that scale to start from:

How many cubic feet of coach?
How much insulation?
Single- or double-pane windows?
Diesel, propane, or electric heat?
Diesel, propane, or electric water heater?
Propane or electric stove?
Propane or electric oven?
120-volt, 12/24-volt, or propane refrigerator?
Size of refrigerator?
How many days in a row will you boondock (away from power hookups)?
Washer and/or dryer on board?  Dishwasher?
Any 240-volt loads?
How big is your battery bank?  How about the coach alternator?
Any solar panels?
Number and type of air conditioners?
Inverter?  How big, and load-supporting or not?
And, yes, even how many light bulbs, and what type (incandescent, fluorescent, or LED)?

When we got our bus, it had a 17kW(!) genny on board, and that was just enough for the way the conversion had been designed (no ventilation at all, four basement airs, 240-volt cooktop, inefficient battery charger, 100% incandescent "indirect" lighting, yada, yada.).  We still have the darn thing -- it was one of the very few items we were able to salvage from the original conversion.

We redesigned the bus to be super-efficient, so we could boondock for two weeks at a stretch.  If I were to replace my generator today, I would replace it with a 6kW.  Just about a third the size of what's on there now.

It is my personal (and widely disputed) opinion that if you need more than 8kW, you've made a design error someplace else (unless, with deference to my good friend Jim, you have a washer-dryer aboard that you want to run off-grid, in which case, you'll need much more -- the dryer alone can use 6-7kW).  But that's just me -- you're own cost/benefit point might lie elsewhere, and putting in a larger generator and, for example, a smaller battery bank or perhaps no inverter might make more sense for a coach that is used only a few weekends a year, or is consistently operated in hot or humid areas where 24/7 air conditioning is a requirement.

FWIW.

-Sean
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rv_safetyman
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« Reply #11 on: March 09, 2008, 02:04:02 PM »

To build on Sean's comments, it does not make much sense to run something like a dryer off grid.  However, we are sometimes forced to do that when we are not hooked to a 50A pole (30A, obviously, does not provide the 240V).  We try to save our washing for the somewhat infrequent 50A pole, but sometimes I start to stink Cheesy

One other consideration is the fuel consumed.  I am not sure that there is "official" consumption numbers, but I have heard that a fairly loaded 10KW uses about a half gallon per hour.  My consumption would suggest that is about right.  That can really add up. Indeed, we have had to fill the aux tank twice on this trip (about 50% on the pole) and each time was well over $100.  At the FMCA show in Pomona they charged $160 for 20A power.  That sounds like a heck of a lot, but we used over $100 in fuel, so their charge is not as outrageous as it sounds.

On this lengthy trip (approaching 2 1/2 months), we have been off grid quite a bit.  In Quartzsite we were off grid for about 10 days and used about 30 gallons (have separate tank for Aqua-Hot and generator).  We did not run the air conditioners, but did have to run the heater in the evenings and early mornings, plus hot water.  The generator was used to recharge the batteries (we run the generator when we know we will have big loads, so we try to kill two birds with one stone).  We have 3 large solar panels (not too efficient this time of year), but that only provide about 1/2 of our needs.  We have 8 golf cart batteries and quite a bit of power usage.  The house type fridge uses more than I would like.  We also have quite a bit of electronic things going as well.  I am very careful not to let the batteries drop below 50% as measured by a Bogart Tri-metric sate of charge meter.

The reason I bring all of this up, is that it DOES make a huge difference what you are running.  Secondly, it does cost more to run a bigger generator than you need.  I can't give you good numbers on fuel vs KW delivered vs KW capacity, but it just stands to reason that running a big generator at less than 50% capacity, wastes fuel.  Having said that, newer diesel engines are probably less affected by partial vs full load conditions.

Sorry about the rambling, but I think there is a point or two worth considering in this post Huh Shocked

Jim

« Last Edit: March 09, 2008, 02:05:45 PM by rv_safetyman » Logged

Jim Shepherd
Evergreen, CO
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Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
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« Reply #12 on: March 09, 2008, 02:06:31 PM »

I'm getting by nicely with a 5500w Onan on LP fuel. To top it off, I'm usually above 5000' msl, and currently at 6880' msl., where I suffer about a 20% loss of output capacity, but can still run my two roof airs or both electric toekicks.

It still leaves me plenty for the microwave, HDTV's, and battery charging.

It works well for me, but may not for you.

Jay
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« Reply #13 on: March 09, 2008, 03:35:30 PM »

I have had RV's in the past with 4KW generators.  For the most part, that was enough.  There were times however when more power would have been nice.  I now have a 7.5 kw which is quite adequate for my needs.  I do use propane for heat, stove and frig though.
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chazwood
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« Reply #14 on: March 09, 2008, 06:25:00 PM »

All good stuff, I'm listening, I'm listening, but could you get out your slide rules and burn through this? (You guys are better than wiki  Wink ) I got a DMc-9 with the  over the road heat and air intact. Every nook and cranny foamed with the closed cell foam.(20r at 2inches) Kept the og windows (I'm a sucker for those double hung, dark tinted green) planning on a lp cook top and on demand water heater. Momma wants a washer and dryer but I might just try to put down my foot....(probably draw back a bloody stump). I love heat pumps because we stay down south and need air more than heat so I'm hoping a heat pump in the bay. Besides that (without the dryer) all I need is a few lights and some microwavage,and of course all the fans. (my kids can't sleep without a fan 3 inches from their nose.) What do you all think? We stay down in the hot humid southeast. This is why a bank of batteries and an inverter isn't making too much sense to me, because.....well, because ......(y'all tell me if I'm missing something)  maybe it's necessary in milder climes where no conditioning of the air is necessary for long periods, but not here.... we run the air in December sometimes.

That being said....get this. Here I am, foaming all the holes in the dad-gum frame, for heavens sake, and I notice for the first time that the whole front of the bus is open to the wind like a blown-out boxer. What is up with that? The whole front bumper gapes open to the wind and weather like a toothless hag and I'm foaming pin holes in the frame? I'm speechless. You can't really insulate the area because of all the stuff down there close to the floor ceiling....you can't insulate under the steps which are solid stainless steel; can we say cold? (maybe that's what the layer of dirt was for.) It seem to my little pea brain that I got a great insulation job, but what good is that, if I always leave the front door open? Oh well, never mind, I digress....I'm more interested in the genset for now. Grin
« Last Edit: March 09, 2008, 06:27:44 PM by chazwood » Logged

1992 MCI 102c3
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