Solar Power Needs Question

dorimontana

New member
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!
 

OrioN

2008 2500 170" EXT
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!
My 'rule of thumb' has always been... put as much PV on the roof as possible, then double it. :smilewink:
 

autostaretx

Erratic Member
Yes, the fridge could drain your starting battery.
Without looking up that *particular* model, i'd estimate 3.5 amps across an hour (hence 3.5Ah),
multiply by 24 for one day: 84 amp-hours consumption.
Your starter battery is 95 or 100 Ah, so it's now flat.

Without knowing oodles more about your situation (location, style of camping, etc etc), i would arm-wave (based upon my usage) 200 watts of solar panel, and at least a 100 amp-hour "house" battery. (me? i have only 67 Ah of house)((my solar "system"))

But i've only had solar for the last year ... the previous 12 years were achieved by a mix of "plug the fridge into the Sprinter when the engine is running", plus occasional use of a plug-in-the-wall battery charger (for the house battery, altho it once saved my Sprinter bacon, too), plus seeking powered campgrounds (Washington and Oregon State Parks have that... California doesn't :wtf:)

Knowing your "reasonable" budget helps, too.

First Step: determine your *loads* .... convert them all to watt-hours to get the grand total per day.
Divide by 12 to get the equivalent 12v Amp Hours. ... that's what you'll need as "generation" per day, and you'll want a battery bank that can supply (your choice) XXX days between "sun" or "driving to recharge the battery"
(if you have an isolation relay to let the Sprinter charge the house ... you can pull at least 40 amps when the engine is running (in truth, depending upon your alternator size, maybe twice that).

Laptop power adapters can be quite power-hungry. 95 watts isn't uncommon ... so that's 95/12= 8 amp hours per hour of usage (with the laptop running ... simply "charging" is the same rate, but stops when filled).

--dick
 
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Graphite Dave

Dave Orton
I had a 85 liter Dometic refrigerator with a single 135 watt panel on sold Sprinter. Panel output would almost keep the refrigerator running with sunny says. Changed solar panel from 135 watts to single 205 watts and that easily covered the refrigerator power usage on sunny days.

On Transit build I installed a single 300 watt panel which was the same physical size as the Sprinter 205 watt panel. Panel is a 32 volt house panel. Today I would install a 340+ watt single panel. Why not get as much solar as you can from a single panel. The cost of the panel support is the same no matter what size panel you select. With panels costing about $1/watt an extra $100 is not much money for the extra capacity which will help on non sunny days.

With high voltage panel you do want a MPPT controller. No need for a outside rack with a single panel. Put the rack inside under the roof.

A single panel install without a roof rack on a Transit:

https://www.ortontransit.info/solar-system
 

Flagster

Active member
I'm running a similar power demand off a simple 2x100 watt renogy panels on roof, into goal zero 1250 (tethered to second 125ah battery), that is then running a 12v marine fuse panel...this runs our engel mt60, roof fan, and misc electronic charging needs. Easy plug and play in a day or two. I've been very satisfied and we have been using the system for over 2 years with no issues.
 

OffroadHamster

Well-known member
I have 200W of solar. In full sun I can pull 75ahr a day off of them. I usually average 40-50 given trees, weather etc. I have 184ahr of batter of which I am comfortable consuming around 100ahr. My fridge will suck down about 40ahr a day, so my solar keeps up with my refrigerator. In fact, even when the van is sitting, the fridge is often on and the solar will keep the starter and house batteries topped up.

For other considerations:

I heat water with electricity, both for hot water service and in an electric kettle for coffee. It takes 2ahr to heat water for 3-4 cups of coffee.

My laptop charger pulls about 100w, but that is 120v AC. If you figure 80% conversion efficiency it is about 1amp per hour of usage. Much less than the 8 amps stated above. I also have a DC charger for it and its about 0.5a per hour of use (6000mah batter lasts 13 hours)

My Espar airtronic D4 will suck down a maximum of 25ahr when it is running full tilt all night in the middle of winter.

To summarize: I can camp without starting the van for two nights in the winter provided decent sun. That includes powering my accessories, heating my water 2.5gallon hot water heater once a day, making coffee 1-2 times a day, running my refrigerator and heating the van at night and not drop below 30% SOC.

In the summer I can camp close to 4 days without firing the van up.
 

JHeiser

Jheiser
For the past 2 years I have run the following in my 2009 Sprinter ERA. I currently have 525 ah worth of house battery storage, 400 watts of solar on the roof and a 5000 watt inverter. I also have an onboard Onan 2500 generator that I seldom use. My setup provides power to my 120V ac refrigerator, microwave, water heater, coffee maker, blender (occasionally), wife’s blow drier and curling iron, computer, phone and camera chargers and 120v ac TV and I might have missed a few things. Regardless, over the past two years I have not had any issues with not having enough power. Most times we are disconnected and remote and like I said power is not an issue.

The house batteries will also charge from the alternator if we have no sun and when we are heading down the road at night. The secret is knowing what your power consumption is, what’s your biggest power consumer and how often you plan to use the biggest power consumer. For you, it’s your refrigerator. We can actually run our AC for anywhere between 1/2 hour to 45 minutes straight off the inverter.

In order to determine how many watts your set up can handle you need to do some math - watts = amps x volts. For example, my dorm refrigerator I have in my van require 1.9 amps (120v ac) when it runs (3.9 to start the compressor). 1.9 x 120 = 228 watts of power is required while running. Now assume the refrigerator ran a total amount of 12 hours combined which would be 2736 watt hours.

Solar panels are commonly used to charge a battery – not to charge a device directly. There are a couple of reasons for having batteries. Solar panels might not generate enough wattage to directly power an appliance, but they can build up a higher wattage via a battery. Another reason is that a battery can regulate the power going in to the appliance at a constant rate. When solar panels are charging a battery it is usually at a varying rate which could damage the appliance if not regulated.

Your battery capacity is measured in Amp Hours (100Ah). You need to convert this to Watt Hours by multiplying the Ah figure by the battery voltage (12V) 100Ah x 12V = 1200 Watt Hours

For Example:
If a battery is rated at 100 amp hours it should deliver 5 amps of power for 20 hours or 20 amps of power for 5 hours. Taking into account a camper with a small 45W fridge running for 6 hours the minimum consumption would be expected is 270W. Take this wattage and divide it by the voltage, 12V, gives 22.5Ah. With the aim of leaving 50% in the battery brings the requirement to 45 Ah per day.

What size solar panel do you need?

Solar Panels power generation is commonly given in Watts (100 Watts). To calculate the energy it can supply the battery with, divide the Watts by the Voltage of the Solar Panel.

100 Watts / 18v = 5.56 Amps (on a perfect day with the controller that can handle it)

Solar Panels are not usually 12v. Any one who works out the Amps of a solar panels using 12v as the voltage calculation does not understand solar or has been misinformed. All solar panel voltages, amps, watts etc. are normally (should be) are displayed on a sticker attached to the back of the panel.

I know all of this can be very confusing so here is a very simple way to calculate how much solar panel you need to charge a 100Ah battery. I will assume the battery is 12V nominal. I will also assume, you are getting 5 hours of full sunlight.

100Ah/5-hours = 20A which means charging your battery at 12 volts and 20 amps for 5 hours will full charge your 100Ah battery.

20A x 12V = 240 watts

So you need to do the calculation/math on how much (watts or amps) your refrigerator is using per day and then compare that to the time needed for your solar panel(s) to charge (keep charged) your battery(s).

I apologize if I have confused anyone on this but this can be a very confusing topic.
 

autostaretx

Erratic Member
My laptop charger pulls about 100w, but that is 120v AC. If you figure 80% conversion efficiency it is about 1amp per hour of usage. Much less than the 8 amps stated above. I also have a DC charger for it and its about 0.5a per hour of use (6000mah batter lasts 13 hours)
I don't doubt your numbers from your experience, but laptops do vary.

100 watts at 120vac is still 100 watts at 12 vdc. All that changes is the current.
IF your laptop demanded the 100 watts continuously for that hour, at 120 v it's drawing one amp, at 12 v it's drawing 10 amps. So that's 10 amp hours from the battery.

My adapter is only 65 watts. My 4400 mah (19v) laptop battery lasts about 2 hours.
So i have a total of 83.6 watt-hours in there (4.4*19).
Our mileage (and battery/adapter demand) will differ.

Your 100 watt adapter is ample enough to both power your laptop *and* charge the battery at its maximum rate. My 65 watt probably takes longer to recharge my smaller battery (due to percentage going to running laptop) than yours does. The actual draw from the adapter will depend upon the battery's state-of-charge.

But when spec'ing a battery/system, i lean towards "worse case" so that you don't end up "empty" unexpectedly

--dick.
 

mikeme

2015 LTV IB: 2015 3500 V6
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!

Get some kind of independent power source and save that starter battery for starting.


Dedicated battery with wired-in charging is best

If you really want to go cheap, there are devices that will disconnect when the voltage gets too low, and still leave enough to start in good conditions.
 

Bigskyvan

New member
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
 

autostaretx

Erratic Member
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"
 

marklg

Well-known member
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
 

Bigskyvan

New member
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.
 

brownvan

2017 4X4 HR 144"
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)
 
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mtncrawler

Active member
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.
 
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HarryN

Well-known member
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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