DayTripper Charging and Battery Box flexibility

Peterbug · 08-09-2019, 02:55 PM

Design idea: use two light 100ah LiFePo batteries, each in its own box, charged by DC to DC charger in TV cabin on daytrips. Quick swap of the two battery boxes as needed. Light Battery Boxes make for many portable uses, including as a ‘jump box’ with the right dongle, and also for setting up solar charging in sunny spot many meters from shaded camper. Using rugged Anderson quick connectors, the system can be made portable and flexible for many configurations to optimize for differing camping situations.
I'm not an electrician, and I welcome any suggestions and (importantly!) corrections.
Battery:
I built a 100 ah Lithium Phosphate battery with 8 cells (4S2P configuration using 50ah cells from ebay, as inspired by Will Prowse videos on Youtube).
Battery Box design is inspired by Kickass Battery Box as seen at:

https://www.youtube.com/watch?v=XiGmo6QVEzA

, however, I chose to keep the Dc to Dc charger on a separate portable board, with plug-n-play dongles wired into the charger as seen in the pictures and video at: https://www.australiandirect.com.au/...DCDC25A-AND-WK
Battery box will easily connect to various sources for both charging and supplying power. I chose a standard large battery box from Autozone, with the largeness more for housing internal wiring and busbars than for the LiFePo battery. Being portable, I needed easy connectors with robust resistance to repeated use and safety, so I chose the gray Anderson Plug as shown in the above Kickass video, and found at: https://www.amazon.com/Anderson-Powe...X1THYY31A6ADBR
In order to reduce arcing upon connections, to provide safety, and to allow easy ‘shut off’ of battery input and output, I installed a waterproof switch on the front of the box in the form of a 150 amp waterproof panel mount breaker designed for marine applications. It can be found at: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 I installed this ‘main battery box switch’ between the battery and the busbars, with switch outside the box and wiring inside the box.
I also installed a sub-panel on the outside of the box that provides: A) Voltage meter, B) subpanel switch, C) single 12v cig style supply plug, D) two fast-charging USB outputs. This can be seen at: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Later, I will add a connector panel for smaller Anderson plugs that are commonly used for Ham Radios: https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
Since the Anderson plugs are not female/male specific, I make up two dongles: A) Alligator clip to Anderson plug, and B) post to Anderson plug. These dongles will allow me to use the battery box A) to be a portable ‘jump box’ for jumping dead auto batteries, and B) use any alligator clip device without opening my battery box to expose the fused bus bar posts.
Portable Multi-input Charger and implementation:
I chose the Abso Dc to Dc charger model DMT 1230 as found at https://www.donrowe.com/KISAE-DMT123...-p/dmt1230.htm that is much like the Redarc discussed by others here. I chose it because it offers (A) 30 amp max charging output, (B) MPPT charge control which is designed to boost low and varying voltages from solar panels and (importantly!) will also boost TV supplied voltages that have dropped in the wire path from TV alternator/battery to the back of TV and through the Bargman plug. I boondock some (first year, so lots of learning going on) with my 8 year old son, but we often drive a couple hours from camp going to fishing holes, dino digs, and trailheads.
The charger has many programming options for common battery types, including Lithium. Importantly, there is an ability to custom program the charge profile, which will give you many options for future batteries with different charging parameters. The custom profile can also be set to various TV electrical system constraints, so that you can know (and control) just how and when your charger is drawing from the TV system.
With a charger on a separate portable board (I screw mounted it to a large UHMWPE cutting board and built a small water resistant housing with lots of room for air to cool it), I can switch the charger easily between my first and second battery boxes, and will also be able to move the charger from my TV cabin to my Camper cabin. To reduce vibration damage and enhance ventilation, the board will be mounted vertically, with the bottom edge cushioned by supersoft pipe insulation split lengthwise and fashionable slid onto board edge.
TV Mod : TV Cabin Battery/Alternator Dongle, sometimes called “Daytrip Charging Station”:
In order to charge the Camper battery while on daytrips in TV (Ford Expedition), I installed 2AWG cable (sized to reduce voltage drop, not to allow large amp travel, so 50 amp fuse close to battery) from TV battery positive to inside rear of my Expedition cabin behind third row seats, with a short 2awg ground to TV frame. Those two wires exit a plastic panel in the cabin back of the Expedition with three feet play and a 50 amp gray Anderson Plug. This single wire allows two options: A) Connect this wire to the DC to DC charger to supply power from the TV alternator to the charger. Important note: the programmable functions of the charger allow for protection of BOTH batteries and for optimization of the ‘charge profile’ that is different for various battery types, so you don’t drain your TV battery and you don’t overcharge your camper battery. The charger I chose also has a customizable programming ability to adapt to any charging profile you may desire with future batteries. Option B: If TV battery ever needs help (boost), I can plug my camper battery box directly to that dongle (no charger in between) and the charged camper battery will supply power to the flat (or low) TV battery. I admit that I am unsure how the differing voltages will equalize, and that in such a case I will need to have a much-greater-than 50 amp fuse on hand to replace the 50 amp fuse near the battery. I ask for advice on this, as I have not needed to try this yet, and have no confirmation of how well it will work.
Camper Electrical Mod 1: Anderson connector on External Battery Tray. This just replaces the wiring lugs to a gray 50 amp Anderson plug. Now moving the battery (lightweight! LiFePo4 in my custom Battery Box) from the Daytrip charging station in the back of TV to the Camper battery tray is easy and safe.
Camper Electrical Mod 2: This has not been done yet. I invite suggestions. In order to have the ability for the TV to charge a battery (using DC to DC charger instead of relying upon direct connection) that is in the Camper while towing, I will need to house the DC to DC charger inside the camper to protect from rain, dust, and heat. Additionally, I prefer NOT to have an expensive battery and charger sitting out on the battery tray behind propane tanks. So I will wire up a dongle attachment system under the cushions of the dining benches (forward in my TM 2619). This will free up some cabin space in the TV, which gets loaded more heavily when towing camper. It also allows the single battery that is being charged to run the fridge in DC mode. Note that my particular DC to DC charger has (er, claims to have) a ‘smart’ circuit that can tell the difference between a low battery and a device load, therefore preventing the overcharging that occurs when some chargers cannot tell the difference. Also, recall that my charger has an MPPT feature that regulates the voltage from the TV (or the solar panels) if the voltage has dropped. As stated in the charger directions, this only works if the charger is CLOSE to the batteries, as long wires between the charger and batteries will result in voltage drop, which will mess up both charging AND! accurate measuring of the voltage state of the battery being charged. Because smart circuits respond to the state of the battery, accurate measurement FROM the battery is maybe even more important than the voltage drop of current TO the battery. Now, the little pixies still have a long road (wires and connectors) between the TV alternator and the charger, as they travel from the TV alternator to the Bargman (maybe on small wires with high resistance), through the Bargman (resistance added for every connector), back to the electrical panel at the rear of camper, then forward to my under-bench-mounted charging/battery station. Considering this long trip, I’d like to move the whole electrical panel to the front of the camper, but this is a lot of wiring to re-route. Which is why I’ve not done it yet.
Camper Electrical Mod 3: Not done yet. Add Pure Sine Wave Inverter. Dongles and board as with charger. Remember Ground wire/stake.
Camper Electrical Mod 4: Not done yet. Solar panel brackets on roof, but panels easily removed for setting up in sunny spot meters away from shady camper spot. Utilize portable battery box and portable DC to DC charger that offers MPPT flexibility and no need for long wires.

**rickst29** · 08-11-2019, 12:08 PM

Your long post contains several different scenarios. You seem to using only one battery at a time, for the purpose of "remote charging" the other. (In the Truck on day-trips, or in camp with "remote" Solar). In Camp, the TM runs with only 1/2 of the battery capacity which you built, and complicated swapping schemes become necessary.

Remote Solar certainly has advantages when you are camping under trees... but I wouldn't leave an $800 battery, or a $250 MPPT-with-Boost controller, out in the open unattended. In many campgrounds. You would be inviting them to disappear.
- - - -
I hope that you haven't already bought the battery boxes and high-current Anderson connectors, because I think that both batteries belong in the Trailer, where they can be used together. The Batteries AND a Converter can be stored under the street side dining bench, forward of the propane heater, using just one bigger "12VDC +" Battery Cable back to the Inverter and DC Distribution panel. You may continue to use the frame as the "12V Ground" connection, although it will (probably) need a much larger wire from the A-frame frame lug, up and into the storage compartment. Wire size depends on your NON-INVERTER 12V loads, and the maximum charging capability of your Power Converter. (BTW, you know that you'll need a new Power Converter, right?)

You probably do not need battery boxes - I don't use one with single my "bigger" battery. Since my Inverter blows hot air out a new vent (in the "inside" wall of the compartment, warming up feet under the table), the batteries might benefit when warming up at the end of a charge cycle.

It sounds like more than half of your "swapping" will be into the truck, to re-charge a low battery during day-trips. If you are doing frequent day trips, this saves some gas (in comparision to my in-camp idling). Both systems (your time-consuming swap scheme, and my 'Stockton Booster' scheme) max out at about 440 watts net into the batteries. But mine involves only 3 steps: (1) Connect Bargman Cable; (2) Turn on the SUV; (3) Flick the SUV 'zombie switch' to turn on the Bargman Voltage Boost.

In my SUV, the Boost Converter (under the hood) Converts from SUV Voltage (12-14.4V, usually around 13.5) up to 36V. To provide 475 Watts into my MMPT (~ 93% efficient), @ 36V, barely 13A is needed on the Bargman "Trailer Battery Charge" wire. No overheating, minimal Voltage drop -- it's super easy for the Bargman cable to handle that. This works great for me, and another TM Owner. I think that you should switch to our scheme, and double up the size of your TM battery bank.