DC-DC converters (Trying to kill three issues with one stone)

Kevin_K

Hello all,
Been reviewing the site for a lot of information to try to fix a main dilemma of mine. We are about to hit the road this summer to the Canadian Rockies and although our TAB 400 is a boondock version, I have noticed one significant downside. The lack of charging the batteries while traveling. Granted, there is some that takes place, but not to the level of recharging and keeping the 3 way fridge running during the day. I'd like to have the fridge running off 12V along AND have the batteries recharged. It's not too bad on bright sunny days, but on cloudy rainy travel days, I cringe. I do have a generator, but only use it for emergencies. Plus, I understand most campsites in Canada only allow you to run it for two hours a day.
I just checked the system today and noticed that only 50-90 watts is being provided by the TV (50 if fridge is off, 90 if on DC). My shunt is stating the fridge is drawing 192 watts (first turned on and starting to cool down). Granted this would cycle lower if the fridge has been prechilled, but I'm trying to work with a worse case scenario. Additional power would also come from the solar panels, but you can't guarantee the sun to be out all the time. The trailer was under a cover on a cloudy day during the test. So although the TV is providing power, it simply isn't enough to keep things running and recharge the batteries. Best case scenario, it will sustain the current battery charge before travelling.
The TAB has the two standard 6V 225 ah batteries. Eventually, maybe next year, I will upgrade to the LiTime 230ah model.
I really want to get more power from the TV when in transit and understand that a DC-DC converter is the best to accomplish this. My TV is a 2019 Jeep Grand Cherokee Trailhawk V8. The alternator should be rated at 160 amps. I'd really like to tap into this power source.
So the three issues are:
1. Charging the batteries fully while travelling to the next campsite.
2. Run the refrigerator in DC while in transit. To me, turning the fridge off in transit seems counterproductive to what the unit is supposed to do. We typically place the fridge to run on propane when at the campsite if boondocking. AC/shore power if available hookups.
3. When we do upgrade to the lithium batteries, since the WFCO only puts out 13.6 volts at 50 amps, run the output from the WFCO through the DC-DC controller to charge the newer lithium batteries. This may require a switch unit for the input of the DC-DC converter  (unless there are DC-DC converters that have two inputs). I really don't feel like replacing the WFCO unit with a PD if I can help it.

Is this a sound plan? Where should the unit be placed? I've seen videos where they place it in the TV, but in the forum, it states to have the unit placed near the batteries (I assume trailer batteries). I also assume I'm going to need to run additional heavy gauge wires from the TV batteries to the converter itself. Some have used an Anderson connection to compliment the 7 pin connector.

Thank you for reading and addressing my concerns. I have tried to piecemeal all the information together from other posts, but sometimes they get distracting with too much technical info or go in a different direction.

Kevin K

rfuss928

I think you are addressing all the right concerns and agree that larger gage wiring, positive and negative, are key to success.  
Following...

MarkAl

I have a 30 Amp (non-isolated) DC-DC Victron charger for similar reasons. But I don't get the charging rates I'd like driving: 6-9 amp after a weekend. I believe it's because the Victron is designed for long life charging and Lead Acids prefer to taper the charge so the last 20% really is pretty slow when you have 220AH batteries. I too expect to move soon to Lithium. When I do I expect much higher charging rates to top off the batteries. 

Also in your situation with the 3-way fridge, the DC-DC will help dramatically as it should supply 200 watts easily to the fridge and charge the batteries at whatever rate the charger allows.

Kevin_K

@MarkAl
That is what I am looking at, but the insulated version. How are you connecting the unit to your TV? If you are using simply the 7 pin plug without running direct lines from your TV battery, that could be your issue. There is only so much current that can be pulled through that wire. I'm planning on running 4 gauge from TV battery to the trailer connection, then Anderson connectors for connect/disconnect, continue with 4 to the battery compartment to a fuse block, then run 6 gauge from fuse block to DC-DC unit, and to batteries. Apparently, the unit can only handle 6 gauge wiring at the connection points.

I think I'm going to forego my third option. Between the solar panels and DC-DC converters, they should be able to top off the batteries per other posts I've seen. Thanks for everyone's input!!! 

MarkAl

So far I'm going thru the 7 pin. Yes there is a current rating limit on the pins but I don't care about a voltage drop as that is why you use the DC-DC converter. When I switch to lithium I'll increase the wire size and as everything will move under the bench with shorter wires, the voltage drops between battery & chargers should be not a factor. The only issue will be verifying the wire & pins are good with 30 amps. Now I've doubled the existing wires to carry the DC-DC output with low voltage drop. I'm pretty sure the drop from charger to battery now is small because the DC-DC is right by the battery box. 

Kevin_K

Just wanted to follow up with this as I just installed the converter today. I used 6 gauge wire from the Jeep's jump terminals all the way back to the controller. I found a nice route through the trailer. I used the hole that enters the trailer where the air conditioner is (driver's side under dining table), then routed it through a PVC pipe that happens to go under the bathroom and comes out to the left of the bathroom (had to remove some cabinets that was pretty easy). After that, just had to run it along a channel under the bed and to back where the inverter is.

Entry point into trailer. Must remove the plastic sheet protecting the undercarriage.The lines were run inside the trailer's channel.

From the entry hole, it goes into the PVC pipe that runs under the bathroom/shower.

Comes out other side under the storage/drawer/three way fridge.

Run along the channel at bottom of photo, along left side to rear, to the inverter location.

Completed project. I also installed a controller for the portable solar panel connection in this area.

Overall results after testing is instead of using 100 watts of power from the battery to run the fridge, it is actually running the fridge and charging the battery at the same time (+100 watts). The fridge eats 200 watts in total DC power when in operation.