Solar, ARB Fridge, Sears Platinum PM-1 - Group Size 31M QUESTIONS

[jeffjeeptj]

Since the AGMs are so clean (and i keep it in a box), i place the battery (31M) and box in the driver side footwell behind the front seat, then fold the 2nd row seat to keep it in place. A combination of the front seat, door, driveshaft tunnel, and top of the rear seat makes movement unlikely, even in a crash. A battery fully isolated from the starting system. This is no where close to the features of an ArkPak or other commercially available item, but it works for me.

A fused wire to the rear area feeds the ARB for short trips of 2-1/2 days or less. The trip duration can be extended now, since I added an ARB receptacle in the rear area connected to the starting battery, where the fridge is plugged in when the car is being driven, thus saving the separate battery. If I forget moving the battery source, no harm done for at least 2 days. I can't remember, not remembering. I recharge the battery in the box when I get home using an Odyssey charger.

For extended trips, i have an 8foot adventure (cargo conversion) trailer with a PC2250 Odyssey which lasts a lot longer with the fridge. The trailer battery connects to the car for charging via Anderson SB350 connector at the hitch area.

 

[Scoutn79]

If you are worried about being able to start your truck I would just plug the fridge into the jump pack when you are sitting still or run your engine for 15-20 minutes/day. This may not fully recharge your battery but should bring it up over 90-95%.
I have an Engel 45qt.
I had to get a jump start from a friend after we sat at camp for 2 full days in the 90's. Trucks were closed up and hot inside (well over 100) in full sun all day and my battery was in pretty bad shape before we left on the trip...the friend who jumped my truck has the exact same set-up (truck, battery{grp 34/78} and fridge) and his truck started fine. Both have the same heavy V-8 engines.
I run a grp 24 battery on my pop-up with the same fridge with a 40 watt solar panel flat on the roof ( I don't try to chase the sun) and after 5 days the voltage has dropped less than .2 volt. The pup only has a water pump and lights and we only need the lights about 1/2 hr day.
These days I do what most do. I have two separate electrical systems with a dedicated start battery.
I think I should add when driving I run the fridge at about 32deg and change it to 41deg (these are the temps that correlate to numbers on the temp dial. You don't have to do this but my thinking is the thermal inertia...the colder temp while driving will mean the fridge will be idle longer once I change the temp...I have not done any specific testing but the theory is sound. Of course if you sit for days it won't do you much good.
You could turn the temp way down when you are idling the engine for battery top off and then remember to adjust the temp once you shut off the engine. Just ideas on how to get the most bang for your buck.

Darrell

 

[Scoutn79]

If higher capacity alternator is an option go for it... short trips and idling will not do much for charging the house battery.

I have to disagree with the idling statement. If you are running a modern alternator it will be much more efficient at lower rpm's compared to older ones. At idle my CS144 has been tested at 45 amp output. Your battery won't take that for too long before it will take less amps.

Darrell

 

[comptiger5000]

I have to disagree with the idling statement. If you are running a modern alternator it will be much more efficient at lower rpm's compared to older ones. At idle my CS144 has been tested at 45 amp output. Your battery won't take that for too long before it will take less amps.

Darrell

Keep in mind, the ignition system on your vehicle, ECU (if it's fuel injected) and other things will draw power with it running. That could easily suck up 20 - 30 amps.

 

[Scoutn79]

Keep in mind, the ignition system on your vehicle, ECU (if it's fuel injected) and other things will draw power with it running. That could easily suck up 20 - 30 amps.

True.
I think I should clarify my statement.
My CS144 was tested at being able to put out 45 amps at idle above what the engine (fuel injected) requires to run. Irregardless even 30 amps available at idle is going to go a long way towards charging a battery.

Darrell

 

[PlethoraOfGuns]

Being out in a remote area and having your starting battery die scares the jelly beans out of me. I run two group 31's in my rig, one just for starting and one deep cycle for EVERYTHING else. I have two 100amp alternators, one for each battery. And a 100watt solar panel mounted to the roof, powering the deep cycle when the engine is off. Depending on temperature, latitude, time of year, and length of stay, an individual's setup will vary greatly. Just whatever you plan for, plan a little extra.

 

[sleddogsam]

MPPT Solar Charger is Key to Maximizing Battery Charging

I have an ARB 82, which draws more power than your 50, hooked to a deep cycle group 31 battery. This is being charged by 3 x 40 watt panels thru the supplied "smart" charger. On longer trips , 3-5 days @ 80-90 deg, I found the battery going flat and fridge shutting down. After much research I found that my charge controller was the problem. Non MPPT controllers don't allow the full capacity of the solar panels to be delivered to a battery that has been somewhat drawn down. After getting a MPPT controller problem was solved. Although I currently don't have my aux battery wired to the vehicle, I strongly recommend this especially if you are frequently moving locations. It's far cheaper to charge the battery with the vehicle compared to a good solar setup. If you rarely move once setup, solar is your best option.

Good luck

 

[AndrewP]

At 120 watts, I doubt there is enough difference in PWM vs MPPT controllers to make this kind of difference. With PWM until bulk charge is done, the battery is getting the full output of the panels anyway and it doesn't matter if the battery is "drawn down" or not. It is possible your voltage thresholds are set too low limiting charging but you should be able to figure that out with a volt meter.

120 watts is probably just barely sufficient for your loads, and with that big a fridge, I' likely look at having more solar capacity.

Still, your point is well taken that an MPPT controller is marginally more efficient, though in a small low voltage system, that difference is very small.

 

[LeishaShannon]

With PWM until bulk charge is done, the battery is getting the full output of the panels anyway and it doesn't matter if the battery is "drawn down" or not.

Thats not quite correct. PWM controllers may pass the full amperage of the panels but not the full power output because of the voltage differential of the panel's Vmp vs the Batteries charging voltage. Vmp - Vbatt might be 16v - 13v = 3v or ~20% of the solar panel's output that a PWM controller isn't harvesting. You do also have to consider the DCDC efficiency (or inefficiency) , but quality MPPT controllers like the Victron operate at something around 98-99% efficient.

At higher battery SoC and on hotter days (lower panel Vmp) the gains from MPPT will be lower.

 

[dwh]

Thats not quite correct. PWM controllers may pass the full amperage of the panels but not the full power output because of the voltage differential of the panel's Vmp vs the Batteries charging voltage. Vmp - Vbatt might be 16v - 13v = 3v or ~20% of the solar panel's output that a PWM controller isn't harvesting. You do also have to consider the DCDC efficiency (or inefficiency) , but quality MPPT controllers like the Victron operate at something around 98-99% efficient.

At higher battery SoC and on hotter days (lower panel Vmp) the gains from MPPT will be lower.

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