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Old 10-04-2019, 03:43 AM   #1
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Electrical Considerations

As I poke around more on this forum I've noticed that power consumption comes up a fair bit. My original idea was to mount a pair of 8D batteries under the floor and call that good for our house electrical needs but I'm starting to get the impression that this could be woefully inadequate.

Not that we have one yet, let alone a place to store it, but our bus will be geared more so for a 4-6 person bro-wagon with trips most likely not lasting more than a few days to a week. So our primary electrical loads are most likely going to be a minifridge, a microwave, some fans, maybe 5 laptops, 6 cell phone chargers, and LED overhead lighting possibly with Day/Night modes. I do not expect to find shore power where ever we might end up.

Any thoughts, suggestions, or experiences?
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Old 10-05-2019, 04:44 PM   #2
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You'll need to know the power consumption of each component you plan on using to determine correct battery/solar requirements.
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Old 10-05-2019, 06:03 PM   #3
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Quote:
Originally Posted by Truthseeker4449 View Post
So our primary electrical loads are most likely going to be a minifridge, a microwave, some fans, maybe 5 laptops, 6 cell phone chargers, and LED overhead lighting possibly with Day/Night modes. I do not expect to find shore power where ever we might end up.

Okay, sounds like you have a list of things to power- this is good, that's half the battle. Now:
-How much time is each of these going to be consuming electricity during the day/night
-How do you intend to recharge the batteries: solar, or alternator?
-Try to ascertain how much each device uses. You can either read the rating on the device, or, test them with something like:
https://www.amazon.com/P3-P4400-Elec.../dp/B00009MDBU


I'd be glad to help you figure this out.
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Old 10-08-2019, 08:49 PM   #4
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Originally Posted by kazetsukai View Post
Okay, sounds like you have a list of things to power- this is good, that's half the battle. Now:
-How much time is each of these going to be consuming electricity during the day/night
-How do you intend to recharge the batteries: solar, or alternator?
-Try to ascertain how much each device uses. You can either read the rating on the device, or, test them with something like:
https://www.amazon.com/P3-P4400-Elec.../dp/B00009MDBU


I'd be glad to help you figure this out.
Thank you.

Alternator is my preference atm, don't really want to clutter the roof with a bunch of stuff. Not that's out of the possibility, especially if we elect to go with an actual transit bus. I would like to build the system to have an safe endurance of 24 hrs, but this is just a number I pulled out of my butt without knowing all the factors that go into it.

Reading the information on my laptop charger, which is a decently powerful laptop, it says an input of 100-240V~50-60Hz 2.4A. Let's assume a run time of 10 hours for 6 of these.

Not having a physical minifridge to look at, I gave Amazon a quick look and found a popular minifridge and its rating is 115V~60Hz 120W 1.5A. Also says it consumes 219 kwh a year. This will be a full time load.

I consulted one of the dome lights I have readily available at work and it says it consumes 0.38 amps. Let's assume 10 of these running for 8 hours.

Checked amazon again for a water pump and found one that has a max draw of 2.7 amps. 2 hours is probably max run time for this.

USB outlets appear to be rated 2.1 amps so let's presume 6 of those running full time.

Before I start crunching numbers what formula should I be using? Also I understand invertors have a draw of their own?
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Old 10-08-2019, 11:36 PM   #5
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Quote:
Originally Posted by Truthseeker4449 View Post
Reading the information on my laptop charger, which is a decently powerful laptop, it says an input of 100-240V~50-60Hz 2.4A. Let's assume a run time of 10 hours for 6 of these.

So, some math:



120V multiplied by 2.4A = 288 Watts. This is the maximum supported by your brick, the laptop will likely not draw that much (I have a gaming laptop and it doesn't draw that much even when under considerable load). Keeping that in mind: 288W is the power rating, or the rate of consumption. Multiplied by 10 Hours, you get 2880 Watt-Hours of energy, how much it would consume over that time period.


Again 288W is the max. Use a device like the one linked to get a real-world idea of what your laptop will consume. Most laptop batteries are well under 100Wh capacity- which would give you 100Wh/288W = .3472 Hours, or 20 minutes of runtime, and most laptops exceed that easily. If I have a 100Wh battery, and I get 2 Hours of runtime, that means I'm consuming 50W on average, a more realistic number.



Going back for a moment:



Quote:
Originally Posted by Truthseeker4449 View Post
Alternator is my preference atm, don't really want to clutter the roof with a bunch of stuff. Not that's out of the possibility, especially if we elect to go with an actual transit bus. I would like to build the system to have an safe endurance of 24 hrs, but this is just a number I pulled out of my butt without knowing all the factors that go into it.

This means you'd be investing mostly in batteries. Batteries are the most expensive part of a system, bar-none. For daytime loads, sometimes it is more cost effective to add generation capability, than to add battery capacity. For example, lets say you have a single 100W appliance. If you want to run this constantly for 24H, you need 100W * 24H = 2400Wh of battery.


A 12V, 100Ah (1200Wh) AGM battery costs around $180. A 100W solar panel costs around $110. (Amazon). Now the battery can only be discharged to around 50% safely, so that $189 is really only getting you 600Wh, or 6 hours of runtime, whereas the panel can get you up to 8 hours of runtime during the day for nearly half the price. Keep in mind panel angle matters here (you wont get 100W out of a 100W panel most of the daylight, etc), but I just want to illustrate that a couple panels can greatly offset your consumption and thus battery requirements, at least during the day.



Quote:
Originally Posted by Truthseeker4449 View Post
Not having a physical minifridge to look at, I gave Amazon a quick look and found a popular minifridge and its rating is 115V~60Hz 120W 1.5A. Also says it consumes 219 kwh a year. This will be a full time load.
120W * 1.5A = 180W, and that isn't constant. Its realisticly like a 30% duty cycle during the day, so about 60W on average. 60W * 24H = 1440Wh.



My Alpicool chest fridge uses around 40W at full tilt, for about 500Wh per day usage. You can find very efficient units on Amazon.



Quote:
Originally Posted by Truthseeker4449 View Post
I consulted one of the dome lights I have readily available at work and it says it consumes 0.38 amps. Let's assume 10 of these running for 8 hours.
Voltage? My LEDs use about 6W a piece. If yours use 8W * 10 units * 8 hours = 640Wh per day.



Quote:
Originally Posted by Truthseeker4449 View Post
Checked amazon again for a water pump and found one that has a max draw of 2.7 amps. 2 hours is probably max run time for this.
2.7A at what voltage?



Quote:
Originally Posted by Truthseeker4449 View Post
USB outlets appear to be rated 2.1 amps so let's presume 6 of those running full time.
That's max, and its 2.1A * 5V * 6 ports = 63W. Times your hours of use.... you get the picture.


So now add all those Wh up. The numbers you come up with are likely to be far larger than what you'll actually end up needing in battery capacity, but that depends entirely on your ability to actively generate power. Remember that batteries are the most expensive part of a solar setup to begin with- How much do you want to be running that alternator during the day or night? I hear you on roof space, but modest solar will greatly, greatly offset your battery requirements. You could use panels that plug in and sit on the lawn, alternatively- and its possible that even a few of them would completely cover your application as described.
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Old 10-08-2019, 11:45 PM   #6
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I see, thank you this explains things very nicely. I'll have to poke around a little bit more on solar then. I have begun considering exterior roof insulation perhaps I could blend insulation into the panels and keep a nice looking roof line.
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