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Author Topic: let me see if I got this straight.  (Read 5539 times)
poohbear
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« Reply #15 on: March 05, 2008, 09:27:45 AM »

   Just one question where do you get these smoke Generators ?
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kyle4501
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« Reply #16 on: March 05, 2008, 09:35:04 AM »

   Just one question where do you get these smoke Generators ?

The best smoke generators are expensive electronic gadgets like T.V.s, inverters, computers, etc  Grin
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« Reply #17 on: March 05, 2008, 10:25:56 AM »

Although, preactivated smoke producers can often be acquired on $bay, craig's, classified ads or at flea markets.  Often at reduced prices.  They can readily release their smoke as soon as you plug them in.
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Chris 85 RTS
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« Reply #18 on: March 05, 2008, 10:47:23 AM »

One thing that is critical to understand in these discussions is the concept of power.  I'll start with an example, a simple 120V 120W light bulb.  The power used by a 120W light bulb is 120 watts.  Simple enough.   The voltage is 120V.  The current is 120W/120V = 1A.  So, my 120W light bulb uses 1A of current at 120V.

Okay, so now suppose you want to run that same light bulb off of a 12V battery bank.  For that you would use a 12V to 120V inverter.  Commonly available no problem.  You should by an inverter that supplies at least 120W.  Okay, no problem, we'll buy a 200W inverter.  

Okay, time for the big concept, Power out = Power in.  Actually that is way simplified and never true.  Any time you transform power from one voltage to another you loss a little because nothing is perfect.  So, you will often hear people speak of the inverters efficiency.  For arguments sake, let's suppose our 200W inverter is 90% efficient.  That means you will only get out 90% of what you put in.

So, if I need 120W out for my light bulb, I will need 120/0.9 in or 133W.  Now remember, that power is coming from 12V batteries, so the current required from the batteries is then 133W/12V = 11.1A.  Whoa, wait one second.  Above I said that light bulb only needed 1A, but now I am saying our inverter needs 11A.  That is the price you pay for converting from 12V DC to 120V AC, roughly 10x.

Okay, so why is this 11A important.  Well, if you are using solar, you will need at least 11A solar panel.  Actually solar panels are sold in watts, so you will need 133W solar panel to run that one little light bulb.  If you are using batteries, you will need to consider the capacity of the batteries.  Battery capacity is rated in Amp-Hours.  So, if I want to run that 120W light bulb off batteries for 10 hours, I will need a battery with 11A * 10h = 110 amp-hours.  Okay, that's not to bad, a typical deep cycle battery can provide 250 AH, so I can run my light bulb for 20 hours!  Awesome.

But wait, I don't really want to run a light bulb, I want to run an airconditioner.  Okay, so run the same math above, for an airconditioner.  For example, my 15,000 BTU Carrier uses 13A at 120V.  That's 1560W.   That means my inverter will now need to be at least 2000W (startup loads are much higher than running loads).  Whoa, that one expsensive inverter, but I gotta have AC and not run the genset, so I'll spring for it.  But wait, what about the solar and the batteries?  Okay, how much power does the inverter need.  1560/0.9 = 1733W.  Okay, so I need at least 1733W of solar.  

A 200W solar panel is roughly $1000 and is 4.5' x 3'.  So I am going to need 9 of these panels to run my AC and it will take up about 15' x 8' of roof space.  Whoa $9000 for solar to run 1 AC unit, that can't be right.  Well, it is and it isn't, I'll come back to that in a bit.

Okay, what about batteries?  Okay, so I need roughly 1800W of power, and at 12V that comes to 1800W/12V = 150A.  Cool, my battery is 250 AH, so I can run my AC for 250/150 = 1 hour and 40 minutes.   What, only 1 hour and 40 minutes?  Yep, and then that battery will be completely dead, and need to be recharged.  Well, I really want to run my AC for longer and I want to run 2 of them sometimes, so I'll get 4 really good deep cycle batteries.  Whoa, that costs how much?  Wow, this power stuff is getting exspensive.

Okay, so your batteries are dead and you need to recharge them.  No problem, I'll use my $1000 200W solar panel.  Keeping it simple, that solar panel can supply 16A at 12V to charge my batteries.  (It will be worse than this for alot of reasons.)  Again power out = power in.  So, let's suppose I drained my 4 batteries using 150A for 4 hours (AC cycled on and off all day and night), for a total of 600AH.  My solar cell can supply 16A, so it will take 600/16 = 38 hours to charge my batteries.   Whoa!  Okay, so I wil use a 100A charger off my genset, that will only take 6 hours.  What 6 hours?  Gee I could have just run my genset to run the AC's and only had to run it for 4 hours.  

Okay, so some of that I say is exaggerated, but not by much.  What you need to understand here is power out = power in.  Watts out = Watts in or Amp-Hours out = Amp-Hours in.  All this power stuff costs a huge amount of money.  When figuring out how much power stuff you will need you need to add up all the watts of the stuff you are using, AC/Microwave/TV/Lights/etc and how long you are going to use it on average.  First you can size your inverter or genset with the total Watts needed, then you can size your batteries/solar/chargers depending on how much stuff is used.  If you really plan to boondock with as little genset as possible, you need to get the most efficient of everything, which is going to drive the cost way up.  Getting rid of voltage conversions helps also, so a 12V fridge off batteries is better than a 120V fridge off an inverter off batteries.

Alot of people spend 3-5K on a genset, then another 3-5k on batteries, inverters, solar so they don't have to use the genset.  For me personally, I just use the genset.  It is very quiet, and we don't boondock, so we can get away with that.

Good luck and get your calculator out.
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« Reply #19 on: March 05, 2008, 11:10:22 AM »

Nice job explaining that Chris!
Jim
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« Reply #20 on: March 05, 2008, 11:16:11 AM »

Chris,

Really nice job.  Even I understood that and I only have 30 years in electronics but I am soooooo very dated.

Thanks and come again,

John
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« Reply #21 on: March 05, 2008, 12:16:22 PM »

Very good reader friendly post.
Thanks for helping and saving someone's mistake from choosing the unwanted choices.

Might add…those batteries have temporary life too, so figure to replaces them when load drains + time test result show too weak to hold charges to meet your desire.

And if in very cold climate region…batteries are temperature sensitive to colds. May needs even bigger or more banks of batteries.

And solar panel is prone to hail damages and any physical object or missile as will moisture getting into panel’s wiring to repair or replace.

Like is already mentioned in above posts…be sure which plans you choose. It only depends what you can spend and enjoy at the same time.

Ideally an extremely quiet power generator that uses very little fuel….if that is possible & practical, that would eliminates all extra division of power sources and less to go wrong. Carry two generators so if one breaks down.

Wish you well.

FWIW

Sojourn for Christ, Jerry
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Bob Gil
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« Reply #22 on: March 05, 2008, 12:37:11 PM »

Ok I think I understand most of that.

I have a house type refergator (120volt ac) in my bus could you guess as to what size inverter I would need to run it.

I guess you would also need to know how many batteries I was using too.

Well I was going to ask if any body knew the way to figure this so I could try to be the correct amount of batteries and right inverter to run the at least two days on the batteries.  

This would help in getting me to understand what I need to have along with the 15KW that I have already.  I just don't want to run it all the time if i am parked and away from the bus for the whole day.  I don't like the idea of runing the genset when I am to going to be there with the price of fuel the way it is.

Thanks for you help with another of my stupid questions.

Bob  bobgil@flash.net  
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Fort Worth, Texas where GOD is so close you don't even need a phone!

1968 GM Bus of unknown model 6V53 engine (aftermarket) converted with house hold items.

Had small engine fire and had no 12 volt system at time of purchase. 
Coach is all 110 w 14KW diesel genrator
Sojourner
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« Reply #23 on: March 05, 2008, 03:25:39 PM »

RV Calculators
Appliance Current Load Calculator to Daily Watt Usage at bottom of page:  http://www.advancedpowerproducts.com/panelcalculator.php
AC/DC Load:
http://www.bdbatteries.com/acdcrv.php

DC/DC Load:
http://www.bdbatteries.com/dcdcrv.php

bdbatteries.com even has NEC code listed.

FWIW

Sojourn for Christ, Jerry
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« Reply #24 on: March 05, 2008, 04:40:23 PM »

I have a house type refergator (120volt ac) in my bus could you guess as to what size inverter I would need to run it.

You'd have to look on the fridge to see how much power it uses cuz they vary.  That doesn't answer your question I know but its the only 100% certain answer. 

In the real world the answer to your question is that you aren't likely to be able to carry enough batteries to run 2 days on battery power with a household fridge.  For a reference point we have 3 8D gel cells, an RV fridge that we run on gas when boondocking and a propane range.  We still run the generator at least a couple of hours every 24.  If you are serious about going off the grid and not running the generator then there are solar panels in your future. 

I've been researching this for a long time (and I still don't know very much) but we are going to put 3 or 4 x 100 watt panels on the roof this summer.  My guess (and that's all it is) is that we will then be able to avoid using the generator at all unless we want to cook a roast or do something else that has big power consumption.

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Bob Gil
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« Reply #25 on: March 05, 2008, 04:56:24 PM »

I go to antque truck shows and I am normaly away from the vehicle for most of the day.  I was hoping that the frig would be ok during that amount of time.

i guess if I have 4 battries and an inverter it may run them down but then it would have power part of the day any way and thins might not go bad.  I figure I will be hooked up in the evenings or at least run the genset for a while.

Bob Gil
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Fort Worth, Texas where GOD is so close you don't even need a phone!

1968 GM Bus of unknown model 6V53 engine (aftermarket) converted with house hold items.

Had small engine fire and had no 12 volt system at time of purchase. 
Coach is all 110 w 14KW diesel genrator
Dallas
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« Reply #26 on: March 05, 2008, 05:10:14 PM »

Bob, remember, your fridge doesn't run 24/7... it only runs when it is called on for more cooling.
We use a 2500W inverter and 2 Marine Deep Cycle lead acid batteries.
Our fridge is about 25 years old and draws 3.9A when running. When we go down the road it keeps icecream frozen all day with no power to it. We plug it in at night when we hook up to a power pole.
If we are boon docking, we plug it in to the inverter as we go down the road, and it keeps all night when parked.
The inverter a marine batteries allow us to run 2 tower computers, the fridge and all the lights for about 30 hours, off an on.

Good luck,

Dallas
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« Reply #27 on: March 05, 2008, 05:33:24 PM »

So....what I hear is ..... for someone who boon docks in hot weather and wants 74 degrees at all times, the only reasonable approach ( cost wise) is a generator. And if it's 85 degrees, that generator will be running all night.
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« Reply #28 on: March 05, 2008, 05:41:25 PM »


  Chazwood,

   I believe this is where somebody is supposed to say

   A well insulated bus can save a lot of energy Smiley


 Skip
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« Reply #29 on: March 05, 2008, 05:41:39 PM »

The design and planning of an electrical system cannot be done on a discussion board. There are just too many variables. Many here will help as much as they can and there are some highly qualified people on this board and others.
 The first place to go is a bus get together of some type. Look at what other people have done, talk ask questions, everybody loves to help. You will be exposed to some of the best there is.
 Buy a book, this one is great,
                                             www.amazon.com/Living-Twelve-Volts-Ample-Power/dp/0945415052 - 167k

                            Only my Opinion Jim
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