Crude 12V Split Charge? Will This Work?

[ashleywakeling]

Hi All, This forum is an absolute gold mine of minds for those, like me who have literally no idea how electricity really works! (I have skills elsewhere I promise!)

I have an old Renault Trafic ex builders van which has been converted into a basic camper. There's no split charge system on the van so the only way I can charge the leisure battery is via a mains input. I have since found in the van (only recently purchased) a male to male 12v long extension with inverter on one end (very basic 150W type by the looks of it) and three lights on it, one saying charging.

Would it work if (whilst the vehicle was in motion and running) I plugged this into the 12v outlet from the engine, and also the 12v from the leisure battery. Would this charge the battery as a crude split charge system? I know it's probably not great for the batteries, but we've not got any way of charging it until I manage to install the solar panel.

Many thanks in advance!

 

[John From Detroit]

In theory yes. however why not put in automatic charge system. like B.I.R.D. which now only will charge your house but your starting battery as well from either source. or a straight one-way isolator that charges house from engine? Easy to do and way more efficient.

Converting 12 to 120 you lose about 10% of your pwoer.. Converting back at least 10% of the power so that is a minimum of 19% power loss

 

[Ex-Calif]

I am confused - the charger you found runs on 110V? How will that charge the batteries while in motion?

Are the chassis and house batteries near each other?

The cheapest solution is a pair of booster cables. After starting the van hook up the cables. The alternator will charge both batteries. After shut down disconnect them so the house systems don't drain the start battery.

One step more elegant is to by a 1-2-All battery switch. It' a few bucks but will be a lot more secure than driving around with booster cables hooked up.

As John says the "right" answer might be a ACR (automatic charge relay) which is like the 1-2-All switch but automatic. It senses when the van alternator is making power and hooks the batteries together.

 

[Mark_K5LXP]

When I had a popup camper I'd charge the house battery in it using an inverter powered by the vehicle, just as you're proposing to do here. It works very well, in fact better than just connecting the house battery to the vehicle 12V charging system. Yes, there's an efficiency penalty but I wouldn't consider that a factor because with the engine running there's lots of power to spare.

The important factor to verify is how many watts your 120V charger draws. If it's less than the 150W inverter you're fine. If the charger draws more, then the inverter may trip out or blow a fuse. Another point to look at is how the inverter connects to the vehicle 12V supply. If it's via a "cigarette" plug those really aren't up to supplying more than about 10 amps, or about 120 watts.

Mark B.
Albuquerque, NM

 

[Gary RV_Wizard]

Please explain a bit more about this "inverter" and '12v cord". Is it an inverter (converts 12v to 120v) or a charger (converts 120v to 13+dcv for charging) or maybe a mix of both? You could charge leisure batteries simply by connecting a pair of wires from the Renault chassis 12v system to the leisure battery/12v system. Or you could power an inverter from the Renaults 12v system and use that inverter to power a standard "mains" battery charger. Whether you get more or less charging hat way depends on the capabilities of all the components involved and the amounts of efficiency losses.

You could utilize a smart battery isolator module that connects for charging but prohibits the secondary (leisure) system from discharging the Renault's chassis battery. Here's an example found on Amazon.com, but similar products are readily available elsewhere.

https://www.amazon.com/Dual-Battery-Isolator-KeyLine-Chargers/dp/B00WTAFR5W