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Old 07-03-2019, 03:20 AM   #11
autostaretx
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Default Re: Solar Power Needs Question

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Originally Posted by Bigskyvan View Post
Suggestions on my calculations or assumptions are more than welcome.
Just the tiny notational quibble that your loads aren't "4.5 amp/hr, 8 hrs / day = 36 amp-hrs"
There's no "per hour" on the initial number.
It's simply 4.5 amp, which will be multiplied by the 8 hours (per day) ... and that yields the 36 Ah per day.
As many teachers should've told you: keep the units straight.
(since what you wrote was "amp/hr * hr/day" ... the hours would've cancelled out (as written, not physically correct)).

--dick
p.s. MaxxFans draw a lot less power at any speed but "full"
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Old 07-03-2019, 03:34 AM   #12
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Default Re: Solar Power Needs Question

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Originally Posted by Bigskyvan View Post
Now that I have my head tied in a knot. I'm starting to determine my power usage. I know there are many assumptions. Please comment on my assumptions/calculations on power needs before I dive into batteries and charging. Here's what I have:

Lights: 6 LED 3watt 5 hr/day = 7.5 amp-hrs
ARB 50: 2.3 amp/hr, 24 hrs/day = 55.2 amp-hrs (round up to 80 amp-hrs)
MaxxFan: 4.5 amp/hr, 8 hrs / day = 36 amp-hrs
Phone charger: 5 watt, 3 hrs = 1.6 amp-hrs
Laptop charger: inverter, 4 hrs/day = 30 amp-hrs

Total amp-hrs/day = 155 / day

Suggestions on my calculations or assumptions are more than welcome. THANKS
I did some actual measurements. Our fridge is propane, so it did not use much 12V. With an RV full of appliances that were used for meals, Microwave, Toaster, Keurig, LED lights, Fantastic Fan plus operation of a high power Ham Radio, we used between 72 and 100 Ah a day. A set of 500W nominal solar panels in the sun for much of the day fully charged the batteries each day. I don't have an MPPT controller, so with one of those, maybe 400W might be enough. It seems you are in the ballpark but even with the fridge, you may be a little high.

Certainly put as much solar on the roof as you can fit. Bigger panels are cheaper per watt. My van has a lot of stuff already up there, so I was limited and I deploy extra flexible panels up on the awning.

I have 400 Ah of Lithium batteries, so I can last 2-3 days with no sun.

Regards,

Mark
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Old 07-03-2019, 04:28 PM   #13
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Default Re: Solar Power Needs Question

Quote:
Originally Posted by autostaretx View Post
Just the tiny notational quibble that your loads aren't "4.5 amp/hr, 8 hrs / day = 36 amp-hrs"
There's no "per hour" on the initial number.
It's simply 4.5 amp, which will be multiplied by the 8 hours (per day) ... and that yields the 36 Ah per day.
As many teachers should've told you: keep the units straight.
(since what you wrote was "amp/hr * hr/day" ... the hours would've cancelled out (as written, not physically correct)).

--dick
p.s. MaxxFans draw a lot less power at any speed but "full"
Ah yes. Schooling was years ago. Thanks for correcting.
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Old 07-03-2019, 11:34 PM   #14
brownvan
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Default Re: Solar Power Needs Question

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Originally Posted by dorimontana View Post
Hi-
I have a 2017 cargo sprinter van. I am planning to buy an ARB 10800472 Fridge Freezer- 50 Quart, some string lights and would like the ability to charge lap tops and phones when the van is not running. It seems I am likely to need a supplemental power source but I don't know how much. Without supplemental power, I fear I could drain the car batters? Would be grateful for some advice. Thanks!
I've got the same ARB fridge and it pulls about 1 Amp-hour average in hot climates set at 33F.
(i.e. approx 24A per 24-hour period)

Last edited by brownvan; 07-03-2019 at 11:37 PM.
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Old 07-04-2019, 03:59 AM   #15
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Default Re: Solar Power Needs Question

I just installed the equivalent (Classic II - just color/bluetooth change) a week ago and will be anxious to see how well it does in my setup. I kicked it on tonight when it had an temp of 86 degrees F (and it was close to 90 today) - and set it for 41. In an hour it was down to 41 - and below. Drew around 5.5 amps and is now "idle" with a draw around .5 amps. Assuming it tapered off along the way. My SOC went from 100-98% in that time

I have 2, 6V, 220 AH Lifeline batteries setup with 200W of solar and a DC-DC charger.

I have similar "uses" lined up. A few USB's, a fan, the fridge, lights...nothing crazy. Anxious to see if I sized things sufficiently.

Last edited by mtncrawler; 07-04-2019 at 04:25 AM.
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Old 07-04-2019, 02:01 PM   #16
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Default Re: Solar Power Needs Question

Quote:
Originally Posted by mtncrawler View Post
I just installed the equivalent (Classic II - just color/bluetooth change) a week ago and will be anxious to see how well it does in my setup. I kicked it on tonight when it had an temp of 86 degrees F (and it was close to 90 today) - and set it for 41. In an hour it was down to 41 - and below. Drew around 5.5 amps and is now "idle" with a draw around .5 amps. Assuming it tapered off along the way. My SOC went from 100-98% in that time

I have 2, 6V, 220 AH Lifeline batteries setup with 200W of solar and a DC-DC charger.

I have similar "uses" lined up. A few USB's, a fan, the fridge, lights...nothing crazy. Anxious to see if I sized things sufficiently.
Life is easier if you do the calculations in watts and watt-hrs, at least for me.
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