Trickle charger in rambox - aux battery setup

[Chunkle]

Folks,

Looking at installing a dedicated secondary AGM battery setup in one of my Ram Boxes to run camping accessories, fridge etc. when engine is off. I don't use the secondary system very often and is at least a couple of weeks between uses. Currently I mount and dismount the battery and just hook it up to trickle charger/battery manager to recharge in my house between uses. This is obviously a hassle and after almost dropping battery on paintwork last weekend I'm looking for a system that doesn't require me to take battery in and out every time for charging. |Truck doesn't go in garage so no real option to charge fro mains power leaving it in the rambox I'm not looking to tie into the primary starter battery with dedicated charging and switiching/isolation system as truck is new and don't want to risk any potential issues with warranty etc. Plus I can't really be bothered with hassle and cost of setting that up.

I am considering just leaving a trickle charger/maintainer hooked up to aux battery and connected to the 110V AC socket in the rambox to charge the battery slowly over time during daily driving between camping trips. That socket is ignition linked, so would only be in use and drawing power when truck is being driven and there would be plenty of daily driving time to boost the aux battery between camping trips even with only a 2A charging system, as the Aux battery never gets fully drained between uses. Problem is that my trickle charger/maintainer doesn't actually specify what the max current it pulls on the AC side however, so not sure if 400W will be sufficient to run it effectively. The maintainer has an LED screen that is driven by the battery when connected so I'd unplug it if not using the car for anything more than 24hrs to avoid slow drawdown, but can't see any other downside of that setup?

Anyone tried running a trickle charger from the AC system before?

 

[jimothy]

Would you consider a DC-to-DC charger with MPPT solar charger? Renogy, Redarc and others make these. Renogy’s will even trickle charge your starter battery after the auxiliary battery is charged.

It’ll also charge your aux battery more efficiently than a DC-AC-DC round trip with the inverter and maintainer hookup to the the 110V outlet, though I don’t know how significant that difference really is.

 

[Chunkle]

Potentially in the long run, but was just looking to work with what i have now rather than spend $$$ for the sake of it. It's an old AGM battery I had laying around and the only thing it runs with continuous draw is a mobicool fridge when camping and my preference is two completely isolated battery systems just in case of issues and not being able to start the truck the next morning when out in the desert with the kids.

 

[jimothy]

Potentially in the long run, but was just looking to work with what i have now rather than spend $$$ for the sake of it. It's an old AGM battery I had laying around and the only thing it runs with continuous draw is a mobicool fridge when camping and my preference is two completely isolated battery systems just in case of issues and not being able to start the truck the next morning when out in the desert with the kids.

That makes sense; my idea (that I’m toying with doing myself) is probably overkill. Do note, though, that a DC-to-DC charger will isolate your batteries, too.

 

[jimothy]

Thinking about this some more…

If the trickle charger charges your battery at 2A, that’s under 30W (assuming it charges around 14V for a 12.8V battery), so you will be well under 400W. So my guess, having not tried this, is that you’d be perfectly safe with this approach. Besides, if you drew more than 400W, the truck would momentarily shut off the 110V outlet, so you’re protected.

But how effective is it? If you’ve got a 50AH battery that’s 20% depleted, it’d still take 10 hours of driving to charge it up.

 

[Richard320]

I think you're overthinking this. You can buy a dual battery isolator for RVs and wire it in. Some just use a big solenoid/relay so it only connects when the key is on. Others have a voltage switch so they disconnect when you're below alternator voltage, like this one. Go browse at etrailer.

 

[Chunkle]

Thinking about this some more…

If the trickle charger charges your battery at 2A, that’s under 30W (assuming it charges around 14V for a 12.8V battery), so you will be well under 400W. So my guess, having not tried this, is that you’d be perfectly safe with this approach. Besides, if you drew more than 400W, the truck would momentarily shut off the 110V outlet, so you’re protected.

But how effective is it? If you’ve got a 50AH battery that’s 20% depleted, it’d still take 10 hours of driving to charge it up.

2A at 14V is 28W, but that is on the DC output - not sure how much AC power the charger draws to deliver that output at 110V- the charger does get quite warm, so there must be additional power draw and energy wastage to consider, but hopefully still well below the 400W system limit.. I think simplest answer is just give it a go and see if it works - i do 20+hrs driving per week, so plenty of time to charge the aux battery during normal use..

I think you're overthinking this. You can buy a dual battery isolator for RVs and wire it in. Some just use a big solenoid/relay so it only connects when the key is on. Others have a voltage switch so they disconnect when you're below alternator voltage, like this one. Go browse at etrailer.

If only i was in the US... not so easy to get parts etc. here in UAE (and make sure they are safe and not chinese knock offs!) plus its a faff and hassle to wire it in when the trickle charger is plug and play and I have all the bits I need...

 

[Eduardowitt]

Hi. I started a new project. I installed a small battery in rambox, and a small battery charger conected to the rambox outlet. So i can turn on the charger indo the car (2500 2020). The wires go througt a hose under the car. The pictures might help.