ReCharging a 12 volt Deep Cycle AGM U1 Battery from Vehicle?

[deeve]

Hello, I am trying to figure the easiest way to recharge a 12 volt U1 35AH deep cycle battery from my Wrangler. Ideally, I would like to recharge it while I drive vs a solar panel although solar is an option for some of the time. I have a cigarette to cigarette adapter, but that obviously only puts out a bit over 12 volts. Is there a way to recharge it from the vehicle system without having to use an inverter wired and a battery tender? Im somewhat new to this kind of thing..

Thanks!
DAVE

 

[dwh]

If your vehicle's electrical system is only a bit over 12v then you've got problems.

I'd say put a multi-meter on that cig plug and check it. It should have the same voltage as the rest of the truck's electrical, and the rest of the truck's electrical should be hitting peaks of 14v or more.

Which would mean you could charge off the cig plug just fine as long as you don't end up popping the (probably 10a) fuse.

 

[deeve]

Will do. When I checked the voltage before it was at idle. I guess a little bit of RPM's will boost the voltage? It's a 2016 if that matters

 

[dwh]

Ya, lots of vehicle charging systems put out less at idle.

 

[deeve]

Just checked and Im putting out around 14.4 volts just above idle. Thanks!
DAVE

 

[john61ct]

Charging off the alt nothing to do with inverters or battery "tenders", google learn some basics.

Ciggie plugs fry, often well under 10 A.

Wire up Anderson connectors with greater capacity to match future expansion.

 

[deeve]

Thanks! My plugs are fused at 10a and I believe the deep cycle battery shouldn't pull more than 10a. If it does, something is wrong and I'd want the fuse to pop. Ultimately, I will add a separate fused connection between the vehicle battery and deeo cycle when i set up my power block area. I think that connection to the DC battery will be an SAE type connector, but Im not sure yet. This is a build in progress and some of the stuff is either proof of concept, or an interim fix. Having never worked with deep cycle batteries before, it is a learning experience and I have not been able to find a clear answer for charging basically from a car battery to the deep cycle. The Battery Tender is what I use at home and it, obviously, runs off of 110 volt. For use in the field, I think this current solution should work fine as it is a stop gap if I need more than a few days of power and want to top off the battery some.

If I want to run a long term solution, is there a way to charge and maintain a battery from my vehicle with something like this if my vehicle system is normally pushing 14 ~ volts? https://www.amazon.com/dp/B01MU0WMGT/_encoding=UTF8?coliid=I1MCU0JRJWFOZ7&colid=18V1R3NKNG1O

 

[john61ct]

That's for solar and sux.

You just charge off the alt while car is running, not your battery. Will never get to full, murder the batt early, but if cheap NBD.

Proper way is a DCDC charger like ​Ctek D250S Dual

 

[deeve]

Thank you again! That looks like a great option, just what I was looking for.


DAVE

 

[DiploStrat]

STOP!

Please! Take a moment and do the slightest bit of research before you waste a ton of money!

-- A 100Ah battery, discharged 50%, is going to draw a lot more than 10A. How much? Depends on the resistance of your wiring. (Gauge, length, connectors, etc.) A 35Ah battery, 15Ah usable, is probably too small to do anything useful in a camper. Especially not if you are even thinking of a cooler of any sort.

-- You have an alternator that runs at 14v and you want to pay hundreds of dollars to boost the voltage to, wait for it, 14v?

-- Lead acid batteries die because they are never fully recharged. Everything you are doing is a prescription for turning your battery into a paper weight. A full charge takes voltage, amps, and time. Your alternator already has the voltage, you just need to address the other two.

Read through this forum, all of this has been done to death. Don't blame us if you kill your stuff.

If all else fails, read these, in this order:

https://cookfb.files.wordpress.com/2016/09/plan-electrical-system.pdf

https://cookfb.files.wordpress.com/2016/09/battery-charge-slides.pdf

https://cookfb.files.wordpress.com/2016/09/dual-battery-slides-2016.pdf

Also read the $50 dual battery thread.

Sorry for the rant.

 

[DaveInDenver]

Does a 2016 Wrangler have a smart alternator? Just wondering if the charging system isn't holding the voltage up after dealing with the starter battery or maybe the aux circuits aren't recognized as valid for full voltage.

 

[DiploStrat]

All modern vehicles have reasonably smart alternators. In any case, it doesn't matter much as:

-- You will rarely drive long enough to worry about a long absorb stage, and,
-- The alternator will cut back on amps once the battery reaches the desired voltage. In this case, we know that the alternator has a target voltage of around 14.4v - perfect for an AGM battery at 70F/20C.

If the wiring to the second battery is of reasonable size, the alternator will "see" both. If too small, the second battery will still charge, but more slowly. If you want a simple analogy, compare a soda straw to a fire hose. (Danger Will Robinson: All water to electricity analogies can be misinterpreted, but this one is close enough.)

Grossly, speed of charge depends on the difference in voltage, that is, the charge source has to be higher, and the number of amps available - without boiling or overheating the battery, etc. Completion of charge depends on high enough voltage and long enough time for the chemical reaction within the battery to complete. (It is a chemical reaction, not a bucket to be filled, which is why water analogies are a bit limited.)

 

[deeve]

I should probably clarify what this battery is for. I need it to run a CPAP machine for at the most three days, which it will do on one charge and still be at over 12 volts left. When at home it is on a battery tender jr. What my intended need for recharging from the rig is just to add a bit of juice if needed for more than three days. I went with the U1 size so it is easier to move around and takes up less space. In the future I will probably be building a trailer and want ot add a bigger battery, so all this is great info for that. I certainly do not want to fry or otherwise kill the U1 battery by poor maintence of it. I'm reading more and more, but need someplace to start and to put my situation into perspective. Thanks for the help and reading material!

 

[DaveInDenver]

I know the charging system will see an aux battery if wired straight to the alternator.

The original post asked about using the cigarette lighter. My truck has a dumb alternator so it's always 'on' but I don't know if the newer smart alternators bump up if you ask the aux circuits like a cigarette lighter for 10A or not. They might only look at the SoC on the charging rail and roll back. The logic might only then look at expected large loads, headlights for example, to go back to high while ignoring others so as not to dither when the driver rolls down a window or plugs in a phone charger.

Like dwh says, for a 35 A-hr battery using the cigarette lighter should work fine if it can really source 10 amps and the voltage remains high enough.

 

[deeve]

The Jeep does have a canbus system that in theory could cut power to something if it sees a problem. I *think* the normal way it does it is through pwm, at least that is how it is with the headlights.