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Old 11-29-2011, 11:20 PM   #1
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Selecting the correct alternator?? Any opinions?

After perusing the forum here, i am now beginning to consider installing a 2nd alternator to run the auxillary power system on.
Here way my orignal plan:
Connect isolator to alternator
Connect batter bank on (3) 8D batteries to part B of isolator
Wire alll three together
Run post wire to a 3000 watt Wagan inverter (Do i need any higher)
Run post wire from output of inverter to interior fuse box #4 wire
Run 5 receptacles from fuse box with #12 wire
All to power a few lamps, flatt screen tv, fridge, microwave, small heater, and a coffee maker.

So i suppose my question is, would one alternator on a 6.9 L DT in a GMC be sufficient for this load
0r
should i consider having a secondary alternator? if so here is the one i was considering.
http://www.elreg.com/search?page=shop.product_details&flypage=flypage.t pl&product_id=2280&category_id=558
Thanks!
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Old 11-30-2011, 12:49 AM   #2
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Re: Selecting the correct alternator?? Any opinions?

Sorry, this won't answer your alternator question, but have you looked at your electrical system with regard to the other systems or are you just starting to assemble systems by duplicating what's in your house?
It would take me 3 weeks to get 3-8D batteries down to 50% charge and I don't do anything different than when I lived in an apartment, I just do them a different way.
From your list of electrical stuff mine is only different from yours in three things -

1) Electric coffee maker - I use a Melita coffee maker, just boil water on the stove and pour it through, instead of the electric pot cycling all the time to keep the coffee warm, you just light the stove when you want another cup, heat it up and turn off the stove - unlike an electric pot, it's not 'on' all the time anticipating that you'll want another cup and wasting electricity.

2) Electric heater - I use a propane 'Buddy' heater. I've tried a 1500 watt heater in here before and it doesn't even start to warm the joint up. Propane keeps the inside about 35 degrees above the outside on 'low' and runs me about 12 bucks a week and I use it for cooking as well, I doubt if 3 gallons of gasoline could be turned into enough electricity to do that.

3) Microwave - i usually heat/cook things on the stove. I run my generator about an hour and a half a day to charge the batteries and run it about dinner time if I want to use the microwave. Anything that needs big AC gets done at that time (vacuuming, etc.)

That gets you down to some lights, TV and refrigerator - and of course, now, some propane.
Just some thought in case you want to save a buck or two on that monster inverter and those batteries - wow 6 cubic feet and 500 pounds of batteries!

I have a 700 watt inverter, but haven't turned it on in about 2 years - I normally get by with a 75 watt'er I picked up for 15 bucks in the drugstore. The only thing I run on AC are two lamps - rarely. The LCD TV was powered by a 12 volt wall wart, so I tossed that and just plug it into 12 volts, got a car charger for my laptop, runs off 12 volts.

Sorry I didn't answer your question - there are others here that can answer that one better than me - but I see so many people who 'plan' their systems by just cloning their home systems, when with a little thought and some minor changes in the activities of daily living resources could be deployed a little more, at least in my opinion, effectively.
Seems most of our behavior is shaped by our homes, which are build 'standard', converting your bus gives you the chance to do it the other way around - shape the systems to your behavior.
I don't know anything about how you plan to use your rig - mostly driving, live-aboard or what or anything about your other systems, so this may be helpful or it may be just rambling drivel, so if some helps - good, if not well, never mind

Tom
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Old 11-30-2011, 07:19 AM   #3
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Re: Selecting the correct alternator?? Any opinions?

Certainly not! That was very helpful, i negleted the Hank Hill in me to think about using propane. And i dont mind modifying what i use, because yea, i dont want to have to buy 3 batteries..... or a Frankenstein inverter. However, i do want to do what it takes to have at least 4 receptacles in the bus (part of the fufillment of RV codes and just because its "homy" haha.) But yeah, were taking her out to Colorado in june and wont be using the electrical much when we get to the festival, just mainly on trip out there to keep my friends entertained.
So the buddy heater is fairly efficient versus the small mr. heater (blower style)?
And thank you for your input!
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Old 11-30-2011, 04:21 PM   #4
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Re: Selecting the correct alternator?? Any opinions?

Yup, I'm with ya' on the receptacles - I've got them all over, they're called 'convenience outlets' for a reason .
Of course I'll probably not have electric frying pans plugged into them all at the same time either.

Since our routines are more constant than we'd like to think, it may be of some value to stop from time to time and think on just how much power you're using right now and how much did I use in the last little while to get me here (am I actually using those three light or did I just not turn them off)?
Sorry, I'm not a 'greenie' type - I just don't like to waste stuff - anything I waste is something I could use somewhere else and another buck I don't have to make to pay for it and the longer my 'occasional' retirements last (too much Travis McGee when I was young ...).
Actually I can even make a tortuous argument that I use 'wind power' (chuckle) - Because of the current green energy frenzy I sold a pretty much otherwise worthless parcel of land I owned out in the desert to the wind farm next door for 4 times what I paid for it (their blind offer, not mine) which'll pay for gasoline for my generator and push the current 'retirement' out another coupla years. Thank you fellow taxpayers ...I'm all for green power, just wish I had more land to sell ... Sorry - got off in the weeds there ...

Anyhow, with most systems I start small and get bigger as demand requires - just a personal preference.
Just the thought behind it -
Given the choices - $300 for a 3000 watt inverter, $40 for a 200 watt inverter. (um, just to eliminate confusion, these numbers are just to illuistrate the point, not shopping tips).
Two ways to do this -
1 - buy a big inverter, find out it winds up being way more capacity than you use and either live with it or take tgreat satisfaction in the fact that if you suddenly have a desire, while boondocking, to blow dry your hair while making popcorn in the electric popper, while watch the big screen TV while the stereo blasting out the latest hits, while you fry pork chops in the electric frying pan while the potatoes are baking in the microwave - all lit up light an operating room and a friend in an iron lung drops by - you can power it all! Thank Gawd for that inverter huh?
But anyhow, most of time, if not all the time you have 260 bucks (the amount you spent - the amount you needed to spend) sitting there twiddling it's thumbs that coulda taken you shopping and bought you a nice present..

- OR -

2 - Buy the 200 watt inverter for forty bucks and take the other $260 to Walmart or Costco or wherever you prefer and get a couple deep cycle batteries. If you find out you need more power later, or that friend in the iron lung drops by, go buy the 3000 watter and you're only down forty bucks and a trip to the store and you have a backup inverter to throw in a compartment.

Also, as a side note, inverters have an 'overhead' load, just to power themselves - my 700 watt inverter uses 1.2A just to turn it on - seems like a waste when I power a light that only draws 800 mA. My 75 watt'er drraws only 50 mA for itself.

Sorry, got kinda windy there - enjoy your bus -
Oh, as to the heater, just made a post on the conversion thread
http://www.skoolie.net/forum/viewtopic.php?f=9&t=11157
Hope that works - never posted a link to my own thread before ...

Tom
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Old 11-30-2011, 10:40 PM   #5
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Re: Selecting the correct alternator?? Any opinions?

Thats so helpful...not long winded at all...i like indepth background stories! So land out west ayy? Whereabouts? sounds like a sound investment i'd say. And so youre saying even with a 200 watter i could rig the receptacles?? Im just concerned that #4 wire running from a small inverter to the breaker box sounds wimpy...but then again im an emerging in the electical dept. But after hearing what you've said, realistically, i would be powering a tv, a few phone chargers, lights, stereo, and mabey some other small things. Not at the same time of course. And thanks for the link...ill checker out!
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Old 12-01-2011, 03:34 AM   #6
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Re: Selecting the correct alternator?? Any opinions?

Quote:
So land out west ayy?
About 50 miles southeast of Bakersfield, 80 miles north of LA, 50 miles west of Barstow - and of course everyone knows where Barstow is! Home of the World's Largest Thermometer!
EDIT: Silly me everybody knows the World's Largest Thermometer isn't in Barstow - it's in Baker, which is of course 60 miles east of the 'NEXT GAS 60 MILES' sign just outside of Barstow! Hope nobody left before I edited this ...

Quote:
#4 wire running from a small inverter to the breaker box
Don't follow this ... that's on the AC side and unless you plan on becoming an itinerant executioner with your own electric chair you won't need anything that big for AC.

Using this pretty basic electrical system -

If you use a hulking inverter it would look different than this.

For the 12 volt stuff the wires are sized by how long they are and how much current they carry.
Here's a calculator for that -
http://www.freesunpower.com/wire_calc.php
It's made for solar panels, but it's the most straight forward one I've found - ignore the labels and for step 2 put in the load on your circuit and step 3 put in the length of the wire.
So before you go deciding on wire sizes you need to come up with a general layout of the components, so you know the wiring lengths, then, using the loads you've calculated for each circuit and the wire lengths of the corcuits calculate the wire size using the calculator.
The picture above is essentially the same as my system, no bells or whistles. You can get things from the marine or RV supply stores that put the 12 volt fuses and stuff in en enclosure with the 120 volt stuff and it gets pretty pricey and fancy. I just used an auto accessory fuse block from Autozone for the 12 volt stuff and a breaker box from the hardware store for the 120 volt stuff.
So anyhow, you need to come up with the equipment layout first, if you haven't already.
Then do the same thing for the branch circuits, like this one -

The soffitt lights are on one circuit (6 of them), along with the bathroom light, each one uses 0.8A.
Use a little common sense when you're calc'ing the load and round liberally - I used 1 amp for each light and even when several people are here, I don't sponsor the local embroidery club, so I don't need every light on over every seat at the same time, I figger'd 3 on at any one time and the bathroom light - so 4 amps for this circuit and that's only for as long as the bathroom light's on. The wire run is 35 feet from the fuse block to the furthest light - wire calculator says #11 wire - rounded down to the next smaller standard size, since we're not worried about wire failure, just voltage drop. And bingo - wired it with #12 wire. If you wanted to wallow in trivia (I don't), you could take all this stuff out to several decimal places and tighten everything up, but in practical terms it wouldn't change much.

You'll hear a lot from people telling you to use huge wire sizes and 'better make that one size bigger - just to be safe!
Well, if you just don't know about whether it is or not - give it a whirl and see for yourself about stuff - If you don't know whether a wire will get hot enough to cause a problem with your planned load, like the circuit above, pull out a 35' length of #12 wire, hook a car headlight (5 amps give or take) to the end, put the wire (but not the headlight) in a paper bag and hook it up to a battery and come back in an hour or so and see what happened - nothing. No flaming mass of debris - nothing. And you bus ain't made of paper. There is also enough information on the internet to calculate that the bag wouldn't catch fire as well, but it's easier to test it. Lots of what you hear comes from the fear of the unknown (notice that once we found out what caused earthquakes we stopped sacrificing virgins to appease the gods?) if you don't know if what you hear is right, test it or research it and use common sense. Simple tests like the above can answer a lot of questions, save you money and time.
Anyhow, if we use the picture from above, saying that's a 200 watt inverter figure it'll need about 20 amps max. - again with the liberal rounding - divide the watts by 10 instead of 12 it makes it easier to do in your head and also leaves a little elbow room, as you're calc'd load will be higher than the actual load. If we say the length of the green wire from the fuse box feeding the inverter is at most 10 feet, putting 12 volts, 20 amps and 10 feet into the calculator gives us a #10 wire for the inverter. So as long as we mount the inverter within 10 feet of the fuse block we're good with #10 wire,

You do the AC the same way, just use a different calculator.

Maybe this answered a question or two, maybe you knew all this already, if so - well if people can upload videos of cats playing the piano, I can waste a little bandwidth too, no?

Tom
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Old 12-01-2011, 07:22 AM   #7
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Re: Selecting the correct alternator?? Any opinions?

Mhhh my gosh, i didnt know you were the proud owner of the rolling motel room!!? That is one of my favorites on here...so simple, and very creative ! nice work! And yeah your right about the fear factor, i got the gauge number from my step father whose an engineer at Duke Power. However, this of course seems like the biggest electrical hazard to him, but i'd assume thats because they do not teach "Bus electrical 303" in an engineering major! hahah
But yeah i'll soak this in and do some calculations!
One more question, i have to run the wire from the inverter to a fuse panel then to the fuse box? (I'm a bit slow) And if a converter does no have output terminals for wire do you just plug in a heavy duty drop cord and spilt the other end to wire it accordingly??
Thanks soooooooooooooooo Much ! Big help! and i love your sense of humor!
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Old 12-01-2011, 03:54 PM   #8
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Re: Selecting the correct alternator?? Any opinions?

Quote:
i have to run the wire from the inverter to a fuse panel then to the fuse box?
Guessing you mean breaker box (in the basic diagram above) when you say fuse box - no - it goes
Battery -> fuse panel -> inverter -> breaker box.
Um, if you could stick to the labels in the drawing it'd help me a lot. Ex. when you say 'fuse box' and 'fuse panel' I don't know exactly what you're referring to, since neither of those labels are in the drawing. I don't know if you referring to the 12 VDC fuse block or are using another term for 120 VAC breaker box (also known as a fuse box or fuse panel.

SInce many of these devices have a bunch of different terms used for them - for example the breaker box shown in the diagram above is also sometimes known as a fuse box or as a fuse panel - so's the 12 VDC fuse block, so when they're in the same picture I don't know which one you're talking about. SInce I embraced senility at an early age I'm also easily confused - which doesn't help much but I'm sure it'll add something to the highlight reel in the end. .

Also a mite confusing to me -
Quote:
And if a converter does no have output ...
Um, again with the diagram - what converter?
There actually is such a thing on most RV's, just don't know as that's what you're referring to, since we haven't gotten to that part yet, or if you mean something else. If you plan to use a converter it's aways off yet. #4 below.

It kinda goes like this -
1) Develop DC power circuits and some way to power them
2) Develop AC power cirsuits and some way to power them.
3) Connect 1 & 2 together.
4) Find some way to get external power into the system to 'refill' it.
I've added a converter/charger section to the 'basic diagram' -


It's a lot easier to take it a step at a time or you start getting all kinds of information that really has no value at present and your research will be pretty helter-skelter. I'd stick to one system at a time, get it set-up (not built and not necessarily set in stone, but at least a good handle on what you want to do and how you want to do it) and move on to the next one.
Anyhow, I've just always found it easier to break big things down into smaller things if I can and solve them a piece at a time. It's hard with systems like this, since you're hit with all the information at once and it's hard to get your head around all at once just wading in.

Just to put a 'real' face on the diagram above - here's what I used for the 12 volt fuse block -

As mentioned before, these things can get much more snazzy and pricey, but this works for me. In the picture battery comes in on the right and individual circuits come off the individual crews near the center, obviously fuses go in between. I have no idea what the brass strip on the left side is for.

Breaker box (this ain't pretty - brace yourself) -

Power comes in at the bottom and goes out the left side to the two outlets there.
i 'bout got decapitated by trying to hold the engine room door open taking this picture a little bit ago - winds here currently 25 mph, gusting to 55.

Well, I'd answer your questions if I knew what the hell you were talking about
Pitch 'em again, I'll take another swing ...
Thanks for the kind words on the bus.
Tom
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Old 12-01-2011, 06:11 PM   #9
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Re: Selecting the correct alternator?? Any opinions?

Intellipower "Mighty Mini"


But what do I know?


Oh and this thing has a "smart charger" built into it... whatever that means.
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Old 12-01-2011, 08:31 PM   #10
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Re: Selecting the correct alternator?? Any opinions?

You can also use Square D QO panel and breakers for 12 volts dc. An inverter would need a seperate fuse.
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