How to cheaply add 12 V (10 A) DC charging to mobile solar package?

[naigm]

I'm a noob building this simple setup for the purpose of powering a 12 V fridge in my truck. This build will replace a Jackery system. I have two questions:

1) What do I need to add to the build to be able to charge this battery from the 12 V (10 A) outlet in my truck? It seems like a 12 V trickle charger may work(?) or a DC-DC charger (more expensive). I'd like to keep this build as inexpensive as possible.

2) Is it possible to have this battery setup connected to the 12 V (10 A) outlet in my truck and the 12 V fridge such that when I am driving, the 12 V (10 A) outlet is charging the battery while the battery powers the fridge (thus the battery is ideally not losing its charge), but when I turn the truck off and the 12 V (10 A) outlet no longer supplies power, the fridge is powered solely by the battery?

More details:
I'd like this battery to be chargeable via solar, AC, and 12 V DC. The build guide I linked covers the solar and AC charging, and it explains how to incorporate a DC-DC charger to charge the battery from the alternator. However, it doesn't explain the easiest way to charge the battery from a 12 V (10 A) cigarette plug.

 

[MisterSandals]

I hate myself already for recommending a Renogy product but this sounds like one of the few good uses for this product:

Amazon.com

It should accept solar (minimal which is what you were talking about) and alternator current easily and do what you are asking.

Do you know how much power your refrigerator actually uses?

 

[MisterSandals]

Renogy DC DC Charger w/ MPPT

Finally reviewed it! People asked me repeatedly, and I was too busy with the solar shed. For the last few days, I tested it like crazy.. And I love it! I should have tested it months ago. Works extremely well, and it's fool proof. I pushed it to every limit, and if it cut off, it would restart...

diysolarforum.com

 

[naigm]

An owner of the fridge posted on Amazon that the idle draw is 0.13 A; startup is 11 A for first 5 minutes; running current is 4.77A.

So with that Renogy DC-DC charger, rather than setting it up as intended with alternator -> DC-DC charger -> battery -> fridge, I could instead do 12 V (10 A) truck cigarette plug -> DC-DC charger -> battery -> fridge? If I'm not connecting to the alternator, is the DC-DC charger overkill (any cheaper option to just interface with the cigarette plug)?

 

[MisterSandals]

If I'm not connecting to the alternator,

Yea, that sounds daunting.

I installed a DC-DC charger for a friend with a Transit van. It had a fused 70A power line that terminated behind the passenger seat pillar that I tapped into. Maybe there is power with sufficient wiring that you could find on your truck? Things like running lights are pretty much "connected to the alternator (and battery) but they would not carry the 25A that would be required.

If you post info about your truck maybe someone knows (or create a new thread asking?). Or maybe ask your specific cigarette lighter question on the above referenced thread? (sorry i did not read the thread).

 

[naigm]

No worries! Thanks for the help. I'm basically trying to emulate the Jackery 500 solar generator, which can be charged via solar, AC, or 12 V cigarette plug (video link). DIY cigarette plug charging is more confusing than I anticipated.

 

[MisterSandals]

I'm basically trying to emulate the Jackery 500 solar generator,

Just out of curiosity, why are you trying to eliminate this? Maybe solving the problem(s) you are having with this is easier?

 

[naigm]

I'm expecting a DIY approach to be cheaper. For $325, I can build a 100 Ah AGM vs. $500 for the Jackery 24 Ah lithium-ion. If I can solve this cigarette plug charging problem, the DIY build will do everything I need with higher battery capacity and a lower price.

 

[MisterSandals]

Ah, you made it sound like you owned a Jackery that you wanted to eliminate.

Have you looked at the blueprints on the sister site? Maybe find something close and come back here for help to customize it, if necessary, for your specific needs.

Mobile Solar Power: Made Easy! DIY Off-grid Solar Power!

Building a vehicle mounted solar power system? Let me help.

www.mobile-solarpower.com

 

[naigm]

I'm following this build (https://www.mobile-solarpower.com/minimalist-on-a-budget.html), and I think I just realized something... This build includes solar charging and AC charging. Could I just connect an inverter to my truck's cigarette plug and then use the AC charging?

 

[MisterSandals]

Could I just connect an inverter to my truck's cigarette plug and then use the AC charging?

Yes. Keep in mind that you specified 10A cig plugs so...

(sorry, i gotta use watts, the long way)

10A x 12.8V = 128W <--- the limit of the AC inverter it will support without blowing a fuse or melting something.

So your AC charger would need to be a bit less than 10A for this to have a chance.

You're not interested in finding power on your truck to tap into? A cig plug is about the worst you could ask for. I would consider removing the cig plug and seeing what the wiring to it looked like with hopes it would handle more power (and a bigger fuse).

 

[Batvette]

Youre really asking for trouble trying to tie that much current demand into a circuit clearly not designed for it. Most cigarette lighter circuits are 10a, some even share that with other things.
The dc dc charger wants to output 25a, which is going to mean about 30a draw minimum.
I have found when adding accessories to a vehicle the less you tie into the vehicles wiring the better. I would run a fused 8 or 10 awg wire (depending on distance) to the battery or alternator and dismiss the idea of altering the cigarette lighter circuit.
I have a 2awg from the alternator to my dc dc charger in my old van install, the one Im doing now is 1/0, but its a 20 ft run so I wanted overkill.
I know youre trying to do this on a budget but its not going to be cheaper when parts of it have to be done over again when they didnt work.
You need the dc dc charger because the voltage that far from the alternator is insufficient to charge the battery, and you need a dedicated large wire to feed that.

 

[Batvette]

Yes. Keep in mind that you specified 10A cig plugs so...

(sorry, i gotta use watts, the long way)

10A x 12.8V = 128W <--- the limit of the AC inverter it will support without blowing a fuse or melting something.

So your AC charger would need to be a bit less than 10A for this to have a chance.

You're not interested in finding power on your truck to tap into? A cig plug is about the worst you could ask for. I would consider removing the cig plug and seeing what the wiring to it looked like with hopes it would handle more power (and a bigger fuse).

A bit less? When the AC charger has about a 14.6v output? With the losses in efficiency in both the inverter and charger involved, by the time you turned the voltage available at the lighter back to 14.6 I dont think a charger greater than 6a wouldnt blow that fuse. And trying a bigger fuse in the OEM circuit is strictly verboten. Excuse my French!