Custom battery box

DadBodMarathonRunner · 04-03-2019, 01:38 PM

Over the winter I devised a battery box to fit our needs. Almost all of our camping would be considered "boon-docking". No power, water or dumps. I always have my generator but once it is dark, sometimes the kids go inside to watch a movie while we sit outside and enjoy the campfire. Listening to a generator hum for 2 hours just to power AV gear seemed stupid and ruins the tranquility.

We all do things differently so to each their own. Here is how I did things. First I purchased an aluminum truck box and bolted it to the tongue of my trailer. It was kind of hard to find one that was acceptable for height, length and width. Initially I had bought size 27 batteries but they didn't fit so I had to fall back to size 24's.

I now have 3 batteries with the option to add a 4th. 2AWG wire is used inside the box and it all starts by flowing through a 200A circuit breaker. It then connects to a 2 way boat switch (Off - 12V trailer - Inverter). I really like this because I can switch off the trailer with the turn of an knob if we are going to be leaving it unconnected for a long period of time.

The inverter is wired to an electrical outlet mounted to the side of the box. This way when I need to use it, I just plug the trailer AC cord into the box, flip the switch to inverter and turn it on.

I have since put a sealed barrier between the batteries and the inverter to keep the nasty byproducts away from the electronics. I also added some additional vents to assist with airflow. Normally I just prop the lid up an inch or so for cooling though.

oldmanAZ · 04-03-2019, 01:52 PM

Very nice inside and out!

DadBodMarathonRunner · 04-03-2019, 01:54 PM

So where my tech talk comes in is here. Is the OEM battery charger up to the task of keeping my batteries topped off? I read through the manual and it states the charger is a 3 stage which is good.... but how good is it? Would I benefit from upgrading to an aftermarket charger?

I have a battery monitor and after charging for several hours, the nominal voltage is ~12.7. After a days worth of minimal use (charging some devices, listening to radio, fan running above stove for 30 min).. it drops down fairly quickly to 12.2 which is the cutoff. I would have thought 3 batteries would be more than up to the task??? FYI, batteries are Interstate deep cycles from Costco.

Just monitoring the voltage it just seems like it is dropping at the same rate as it used to before I added additional batteries.

oldmanAZ · 04-03-2019, 02:41 PM

You may need to dig a little deeper to quantify the battery discharging rate.

Your batteries appear to be a dual-purpose and not true deep discharge type. Sadly, they are marketed as deep discharge and may be better than a standard car battery, but don't have true deep discharge capacity.

With most battery banks, it is best to have ALL the batteries as identical as possible and of the same age. One of your current 3 batteries may be under performing so adding a 4th may not help.

How the battery bank is wired can make a difference, too. Internal battery resistance and the cable and clamp resistance can result in not sharing the discharge load, or the charging, equally among batteries.

You asked about the trailer's converter/charger. My WFCO converter/charger does well as a 'trickle' charger, but does stay in 'bulk mode' so does not charge my 2 batteries very rapidly. It takes roughly 18hrs for my batteries to be fully charged on shore power.

I hope some of this is of some help to get you thinking. We have a few 12v gurus on this site (I am not one of them). I'm sure one of them will be along soon.

DadBodMarathonRunner · 04-03-2019, 03:18 PM

I appreciate the input!! All is welcome - both good and bad :-)

All 3 batteries were purchased within 6 months of each other. None of them were actually in use during that time. They were just taking up space in the battery box left unconnected.

The pictures do not make it obvious but they are all connected in parallel.

JesseS · 04-04-2019, 05:17 PM

Have you considered going with 4 6V GC batteries? Two sets in series connected in parallel. I found that using 6V GC batteries provided more power than 12V batteries. The GC batteries are taller, have heaver bus bars and thicker plates, and are by default designed to handle heavy current for long periods. Just a thought.

DadBodMarathonRunner · 04-05-2019, 10:35 AM

I actually did look into getting some golf cart batteries but I did the math, looked at my available space and decided against them. Both of the batteries worked out to be about $0.60 each for reserved capacity but I understand the golf cart batteries can go farther down without damage to internal cells so it would have swayed in that direction. The reality is that they would not fit on the tongue of my trailer without a lot of modifications. Besides, I figured 560Ah would be enough for a couple days worth of living once I got 4 batteries installed.

DadBodMarathonRunner · 04-08-2019, 10:05 AM

Quick update -

Over the weekend I had a chance to do some troubleshooting. What I found was that the battery monitor I was using read 0.5VDC lower than the actual voltage. This was verified with a voltage meter. I was thinking my batteries were almost all used up when in reality I had a ton more juice to spare.

I also learned that the battery charger that came with my trailer never gets above 13.8. I hooked up a single battery that I had drained down to about 12.4 which should prompt the battery charger to kick in a fast charge scenario. I left it charging and monitored it with a blue tooth monitor that tracks voltage. According to multiple websites, chargers should get above 14.2V at some point or the batteries become "lazy" over time.

Anybody else experience this lazy behavior??

Rustic Eagle · 04-08-2019, 10:37 AM

DadBodMarathonRunner,

Welcome to JOF

Quote:

Originally Posted by DadBodMarathonRunner

snip...... Anybody else experience this lazy behavior??

The following JOF thread link on the subject should get you started..., but I'm sure others will chime in as well.

https://www.jaycoowners.com/forums/f...e-60417-3.html

Bob

oldmanAZ · 04-08-2019, 10:47 AM

What a difference 0.5v makes!

I'm betting you have a WFCO converter/charger, just like I do. They are known for lacking a good 'bulk' charging mode. I'd suggest replacing your 'lazy' converter/charger before condemning your bank of batteries.

I see Rustic Eagle posted a link for you. There's a lot on this site regarding batteries and charging. I'm surprised some of the 12v gurus haven't gotten wind of your situation - maybe the 'battery box' topic didn't catch their attention.

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