Rear AC 120v / 100 watt plug and a battery charger

[WoodyCreature]

I’m putting together a quick power supply for a Dometic 75 cfx in my 200. My plan is to dual battery later this summer. But for now going to just use a group 35 agm in a battery box in the back. Will run solar during the day and hoping to run a small charger off the rear 3 prong 120 ac plug to help charge the battery while driving.

My question is: will this even work? Limited info found on the draw of the charger itself and the max output of the plug. Combined with my limited electrical knowledge I’m kinda stuck.

Thanks.

 

[TeCKis300]

I believe your plan can work depending on some details.

Specifically to your question about that particular charger. Looks like its output is rated for 12V @ 4amps, or approximately (12*4) 48W output. Conversions are not perfect so expect the input draw to be incrementally higher. I know the rear 120V output is rated at 120W, which should give you enough overhead. The amazon comments are a bit confusing as they talk about 10amp output? Which would indeed be much closer (12*10=120W) or possibly over the rated 120V output.

The other side of the coin is making sure you have enough overall charging going into the battery. A 4 amp charger is rather small. Will greatly depend on how much actual drive time you have. Then the other aspect is solar. A 50W panel will give you something like 2amps, over ~7hrs a day (seasonal and really depends on condition), for something like 14Ah.

How many amp hours do you expect the fridge to draw a day? You can save a bunch by pre-cooling the fridge/contents, and minimizing opening the fridge.

 

[WoodyCreature]

Th

I believe your plan can work depending on some details.

Specifically to your question about that particular charger. Looks like its output is rated for 12V @ 4amps, or approximately (12*4) 48W output. Conversions are not perfect so expect the input draw to be incrementally higher. I know the rear 120V output is rated at 120W, which should give you enough overhead. The amazon comments are a bit confusing as they talk about 10amp output? Which would indeed be much closer (12*10=120W) or possibly over the rated 120V output.

The other side of the coin is making sure you have enough overall charging going into the battery. A 4 amp charger is rather small. Will greatly depend on how much actual drive time you have. Then the other aspect is solar. A 50W panel will give you something like 2amps, over ~7hrs a day (seasonal and really depends on condition), for something like 14Ah.

How many amp hours do you expect the fridge to draw a day? You can save a bunch by pre-cooling the fridge/contents, and minimizing opening the fridge.

Thanks. That is incredibly helpful. The fridge says near the plug that it draws 1.4 (IIRC) Ah.

Maybe will look for an 6-8amp charger??

 

[TeCKis300]

Thanks. That is incredibly helpful. The fridge says near the plug that it draws 1.4 (IIRC) Ah.

Maybe will look for an 6-8amp charger??

I presume that you mean the fridge draws 1.4 amps, or 1.4 amps/hour. This over a day (24hrs) means 24*1.4 = 33.6 Ah total power consumption.

Assuming you drive ~7 hrs per day. The Noco charger will be able to put in 4amps * 7 hrs = 28 Ah per day. Not too far off.

So total solar input based on a 50W panel is (14Ah) + charger input (28Ah) = 42Ah.

42Ah charge is greater than 33.6Ah consumption, with a nice 25% margin.

Math tells me you're set based on those assumptions, which could have you run indefinitely.

On reserve, a Group 35 battery has ~55Ah, which could power the fridge for ~1.5 days without support.

Let's say you didn't bother with solar and relied only on the charger with a bit of shortfall in charging, you could still go 9-10 days.

 

[WoodyCreature]

So it seems that there are very limited 6amp chargers out there. I have found two 7.2amp chargers (CTEK and NOCO).

7.2*12=86 watt draw (+a little more for the conversion) Pretty sure the cover on the LC plug says 100 watts, not 120. Do you think this would be a safe call?

 

[TeCKis300]

Ah, thanks for the correction. 100W it is.

I'd be comfortable that an 86watt charger would work. The 100W rated inverter probably has some slight margin/headroom within its rating too.

Best of luck!

 

[bemerritt]

Just as another option, I’m running a dometic in my rear wired straight to a hybrid starter battery that is 100 ah.

If you drive every day of a trip, you’ll be fine. If you stay parked, I have a fold up 100 watt panel that I connect to the battery.

 

[TeCKis300]

Just as another option, I’m running a dometic in my rear wired straight to a hybrid starter battery that is 100 ah.

If you drive every day of a trip, you’ll be fine. If you stay parked, I have a fold up 100 watt panel that I connect to the battery.

Not a bad way to do it. I think most fridges have low voltage cut-off relays built in to preserve some starting power?

 

[bemerritt]

Yeah, that is correct. Still in the process of testing whether having the fridge run the battery down to where it cuts off power leaves enough juice to start the car or not. Guess i have been driving it too much to really test it.