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Old 06-20-2015, 10:29 AM   #1
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Electrical Systems Sanity Check

Hey guys I Just thought I would post my planned electrical system incase someone saw something that didnít seem right, what do you guys think?

I first calculated my expected power consumption:
Shower Pump: 1A, 0.5 Hours a day = 0.5AH
Fans*6: 6A, 12 Hours a day = 72AH
Stereo: 15A, 3 Hours a day = 45AH
Lights: 8A, 4 Hours a day = 32AH
Laptops: 1A, 5 Hours a day = 5AH

~154.5AH total

and therefore decided on 3 100 AH leisure batteries.

To charge the batteries I am going to use split charging with a manual switch. The switch will be turned on once the engine has been running for a few minutes and off isolating the starter battery once the engine is switched off.

finally, I drew out this schematic for how I plan to wire everything up:


image link: Imgur

I am hoping to install the system in this week, but I wanted to first check and see if it all looked correct to you guys?
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Old 06-20-2015, 10:41 AM   #2
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Are you only charging the batteries from the engine? or are you going solar or generator? You should have a warning light to show when you have your switch on,if you forget to turn it off after you shut down the engine you will kill your start battery, or you can just run it off a ign wire that is hot only when the key is on. I have most of my stuff wired with 3 way switches, separates house and start battery.
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Old 06-20-2015, 10:42 AM   #3
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A laptop is closer to 8-10 amps at 12v. I would also expect the water pump to require more amperage.

Be careful how you connect up the batteries so they charge/discharge equally.

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Old 06-20-2015, 11:12 AM   #4
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Originally Posted by Timelord View Post
A laptop is closer to 8-10 amps at 12v. I would also expect the water pump to require more amperage.

Be careful how you connect up the batteries so they charge/discharge equally.

wow 8-10 amps! good to know, I am assuming that is to do with the reduced efficiency of inverters?

also thanks for the battery connection tip, I have changes my schematic accordingly
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Old 06-20-2015, 11:12 AM   #5
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Originally Posted by gbstewart View Post
Are you only charging the batteries from the engine? or are you going solar or generator? You should have a warning light to show when you have your switch on,if you forget to turn it off after you shut down the engine you will kill your start battery, or you can just run it off a ign wire that is hot only when the key is on. I have most of my stuff wired with 3 way switches, separates house and start battery.
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for simplicity and budget constraints I am planning to charge the batteries using the engines 105Amp Alternator.

A warning light is a brilliant idea! I will definitely wire one in.
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Old 06-20-2015, 11:40 AM   #6
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Originally Posted by yannik View Post
wow 8-10 amps! good to know, I am assuming that is to do with the reduced efficiency of inverters?

also thanks for the battery connection tip, I have changes my schematic accordingly
No, a standard laptop is 80+ watts. The standard wall plug adapter will take ~1amp of 110 volt power. On the 12 volt battery side, this is about ~10 amps of power.

For every ~1 amp of 110v power, your inverter will pull ~10 amps of 12v power.
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Old 06-20-2015, 11:51 AM   #7
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What Timelord said. If you're just reading the labels to calculate your power demands, multiply the amp rating for 110v(120v) items by 10. Really, I'd multiply by 11 or even 12 to cover any inefficiencies of the inverter.
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Old 06-20-2015, 01:09 PM   #8
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you might want to consider a 6 volt or even a 2 volt battery option. multiple batteries in series parallel will provide more power than straight 12 volt batteries. i have lifeline 2 volt batteries in mine two banks of 6, they have over 1000 ah per battery, this is over kill for most i realize but we do a lot of off grid camping i have 1000 watts of solar and 1000 watts of wind power a generator back up as well. i know most people don't do this much off grid parking but its what we like to do. this type of system isn't cheap at all the 2 volt batteries are over $600 each retail.

also you might consider going all LED on your lights, you could also mount a small tank for water up high to use for low flow facets so you don't have to pump it. still need the pump for somethings but for drinking and cooking water it doesn't have to come out with such force (pressure) as your shower or washing machine has to have.
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Old 06-20-2015, 01:28 PM   #9
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Quote:
Originally Posted by yannik View Post
for simplicity and budget constraints I am planning to charge the batteries using the engines 105Amp Alternator.
.
You would be money ahead to buy a small inverter generator.

You will spend as much for fuel and burned out alternators as the generator cost in a short time.

That poor small frame 105 amp alternator is not made to run at full output for more than around 15% of the time.

A large frame 200 amp and up alternator will have a 80% or better duty cycle.

However it's still a waste of fuel and ware and tear running your main skoolie engine to charge battery's.

I have a simple $20, 7 watt solar panel charging a big 8D battery and I can run my lap top min 2 hrs a day. Possibly more, I haven't tried.

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Old 06-21-2015, 01:29 AM   #10
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Remember, the standard for deep-cycle battery rating is C/20. That means a 100 Ah battery is rated for 5 amps for 20 hours, not 100 amps for 60 minutes. This is to reach a discharged voltage of 10.5 volts in a 12-volt system. If you drain them faster than 1/20 of the rating, they will not last as long as you might calculate.

And the more times you run a battery to the end point, the fewer times it will hold the rated charge. Very few people will drain a battery bank by 80% to 20% remaining capacity. Most people figure about 50% drain and then recharge is a good compromise between battery life and usable capacity. Some very particular people will not let their banks go below 75% or 80% charge in order to make their batteries last and last.

So figure that into your usage.

p.s. The meter in your drawing will only measure voltage, which only gives you a rough idea of the state-of-charge. A real battery monitor like the Bogart tri-metric calculates the charging current in and the load current out over time, in order to give a real "fuel gauge" type of reading.
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