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cullengw 07-21-2015 12:41 PM

Electrical For Dummies.
Hi all,

I have been reading through some of the Electrical system threads and I notice a lot of high level jargon being tossed around that even I, an electrical engineer minor, cant understand.

I have not worked with electrical circuits like this for 10+ years so I need to understand the basics first.

I know that:

1. I do not want to use the batteries that start the bus to power any appliance that will continue to suck their juice. (maybe I do and I am being paranoid IDK :redface:)


3. I want to have a primarily AC circuit running off of 12V volt house/deep cycle batteries.

4. I want to be able to charge those batteries with the engine and/or camp-site hook up (which ever makes more sense)

5. Here is a list of what I would be running:
-Mini Fridge
-Laptops charging x4
-Phones charging x4
-A monitor of some sort (for like a back up cam)
-led light strips (hopefully 12V ones)
-Microwave perhaps?
-Reading lights x4
-Throw in another 50W in case i am missing something

6. I want to use a 110V circuit for my AC devices Right?

So really what I want to know is how realistic is this list, how many batteries would I need, what size inverter would I need?

Also if you think I am explaining something wrong, I probably am. I think I will be doing a lot of :banghead: throughout this thread. :)

Thank you again for keeping the replies dumbed down :)

M1031A1 07-21-2015 12:48 PM


Originally Posted by cullengw (Post 117307)
Thank you again for keeping the replies dumbed down :)

Don't forget to wet BOTH hands for good contact!!!

turf 07-21-2015 01:19 PM

convert all that into amp hours per day.
decide how long you want to go between recharging.
multiply the first number by the second number.
then double that because you only discharge your batteries half way.
then double that for safety.

100 AH per day times 3 days = 300AH times 2 (battery capacity)=600 AH times 2 (safety factor)....... i'd be looking for a bank between 600 and 1200 AH

there are lots of online calculators to help you out.... check out some solar stuff,even though you arent heading that way.... they have the calculators you want.

austin1989us 07-21-2015 02:49 PM

Lets say you have an A/C that draws 15A. At 120V, that's 1800W. Lets say your inverter is 90% efficent. That means you'll need to get 2250W out of your 12V battery to give the A/C 1800W. That's 187.5 amps. Say you only wanted to run your A/C for 10 hours before recharging the battery. And, just for fun, lets not have a safety factor. You'll need an 1875 amp-hour battery (like the forklift battery below).

Crown Industrial Battery - 12 Volts, 1875 Amp-hours

roach711 07-21-2015 02:54 PM

Keep in mind that any time you change from DC to AC you lose about 15% of your battery power in the process.

AC to DC uses a Converter.
DC to AC uses an Inverter.

Much will depend on how you'll be using your bus. If you'll mostly be parked with shore power available you'll be able to get by with a much smaller battery bank than if you'll be boondocking for days at a time.

ElizaHasAPlan 07-21-2015 03:20 PM

Are you forgetting hot water? Water pump? I think you need to be very accurate as far as your needs are concerned. Looking up manufacturer's specs is helpful as well.

Anything that produces heat will be a power hog. Like a hair dryer for instance.

Get yourself a piece of paper, and write every single thing down.

cullengw 07-21-2015 08:31 PM


Originally Posted by ElizaHasAPlan (Post 117327)
Are you forgetting hot water? Water pump? I think you need to be very accurate as far as your needs are concerned. Looking up manufacturer's specs is helpful as well.

Anything that produces heat will be a power hog. Like a hair dryer for instance.

Get yourself a piece of paper, and write every single thing down.

Eliza Thank you for thinking of that, At the moment we will not have a water pump/water heater since there will be no shower/toilet/sink.

As far as the hair dryer and other excessive power consumers like space heaters/air conditioners. I am not going to include those in my plans for now but they are definitely in the back of my mind.

I have been doing research on charging laptops and realized I'm a dope.

Laptop is powered by battery (DC), when you charge it you use an adapter for the (AC) plug. So why would I want to go from a DC battery to an AC inverter to a DC battery again. lol I mean unless certain laptops cant get the dc charging cable.

Thank you all for the feedback and help AH are definitely something I will be adding up over the winter :) . Question I still have is what is the best way to charge these "accessory" batteries?

Oh and How much does everyone run off their starter batteries?

roach711 07-21-2015 09:00 PM

Best to leave the starting batteries to their intended purpose. Starting batteries are meant to output a big slug of energy to start the engine and then be recharged quickly by the alternator. Your deep cycle house batteries are meant to output energy much more slowly over an extended time then be recharged slowly.

You can recharge deep cycles with the alternator, most RVs do just that, but be aware that repeatedly asking an undersized alternator to charge both the starting bank and a large, depleted house bank can cause the alternator to burn out.

Regardless, you'll want some way to disconnect the house bank from the starting bank. A simple manual battery disconnect switch is the simplest solution but requires you to be "the brains".

There are a few options that will "automate" the charging of multiple battery banks but I haven't kept up with the latest technology. Maybe others will chime in.

cullengw 07-21-2015 09:06 PM

Alrighty good good ya I am the "electrician of the group" so if the alternator dies its on my dime lol.

Ya I think I will start with ways to charge the batteries and let that determine the number of batteries I get. I know this is me being paranoid again but, if i can help it, After 5-6 hours of continuous use, I wouldn't want my group of batteries to have less than 75-80% used. (This is while driving)

Also another thought, sorry they just keep popping in my head rapid fire and you all are very wise so I want to ask them now :D.

At an RV campsite with a power hook does that work :P :P :P do you like hook it up to your batteries? or do you like have a seperate circuit for that?

bubb, the real one 07-21-2015 09:13 PM

without knowing all the elec requirements I will just talk mostly about the 2 big draws, the fridge and the microwave,
everything but those two items can be handled with 200 to 300 map hours of batteries and a 1000 watt inverter,

amps = watts/volts 1000 watt microwave / 120v = 8.3 amp draw
generally speaking you dont want to draw more than 10% of your battery banks power at any one time so to run a microwave that draws 8 amps you will need a 800ah battery bank, if you go much over the 10% draw the banks voltage will drop and if it drops below about 11v the inverter and the other devices will stop working,

since you will only use the microwave a few minutes per day your 800ah battery bank will be able to handle the rest of your power needs fine, just make sure your fridge does not turn on when the microwave is running,

You really need to test the fridge to see what its actual draw is and how many minutes per 24hrs it runs,

just because of the microwave and the fridge you will want a 2000 watt inverter unless you want a +800 watt bank and dont mind the microwave and fridge running at the same time, depending upon the fridges draw 800ah might not be enough for the fridge/microwaves usage.

you can charge the bank with the bus but it is very inefficient and the alternator is not designed to run for long periods and most important it is not efficient at charging,

you will want a 3 stage charger that does not give more than 10% of the banks capacity in AH, such as a 200ah bank can be charged up to 20amps but not more, check the battery manufacturers web site to confirm this,

make sure your charger is designed for the type of batteries you get such as agm/gel or wet lead acid, dont get a battery that even lists a cca rating since it wont last long,

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