Help with DC-DC installation

CharlieRN

Greetings all.

Now that I've switched over to LFP batteries for our T@b 320, and changed our TV as well, I'd like to add DC-DC controller. I purchased a 20A Victron Orion Tr Smart charger a while back when you could still get discounts on things, but still need cabling and connectors. I have some questions before doing that however.

The charger will be mounted in the storage box of the T@B, so I will need to run a line to battery in the TV, probably about 15 feet. I will use Anderson connectors at the end of the TV run, with the stub run connected to the charger. Questions:

• Do I need to run both hot and negative lines from the battery to the charger, or is a chassis ground on the TV OK for the negative?
• What gauge for the wire run - can I get away with 8 AWG or must I go to 6? The table I used shows voltage drops of .387 for the 8 ga and .244 for 6 ga for a 15' run at 12v, but it's not clear to me what reduction is acceptable).
• Assume that the hot lead should be protected - is there any reason not to use a switched 20A circuit breaker for that rather than a fuse? 
• Will I need to disconnect the charging wire in the 7-pole harness?
• I'm planning to mount the charger on an aluminum bracket that I will fabricate, pop riveted to the tub wall. Will I need a fan to cool the charger or will the bracket act as enough a heat sink that I needn't bother?
  

Would be grateful for any additional information and/or suggestions on the charger install as well!

Mouseketab

I installed one in my truck.

I used 8 gauge wire to the battery

ground to the chassis

I used a 30 Amp fuse near the truck battery

Yes, I disconnected the charging wire in the 7-pole harness.

Here is a pdf of my install. As I said, I installed it to the truck and just did the wiring harness along the T@B 7-pin cord, but it should be easy enough to just mount it in the camper and run the charge line to the battery.

Dutch061

I installed an18 Amp in our TAB 400 BDL, but I put it under the dinette seat right next to the Power Distribution Center) PDC.

I tied the 2 ground wires together and connected them to the nearby Bus Bar Ground, disconnected the OEM installed charge wire from the PDC and connected it to the input of the DC-DC Controller. I ran a new wire from the DC-DC Controller ouptut back to the PDC. I used 12-gauge wire because combined length is less than 4 ft. According to my chart, 12-gauge is good for up to 10 feet at 20 Amps.

I done it this way because:

1. I don't want any restrictions if I needed to tow anything else.
2. I like the simple method - install took about as much time as typing this reply
3. My TV is brand new (5K miles), and I am not interested in rewiring it
4. Since my TV is set up to turn the charge circuit on or off based on engine running or not, programming was super simple.
5. I have verified that I indeed can get the 18 Amps output via my BMV-712



Brad

RMo

Dutch061 said:

I installed an18 Amp in our TAB 400 BDL, but I put it under the dinette seat right next to the Power Distribution Center) PDC.

5. I have verified that I indeed can get the 18 Amps output via my BMV-71

Brad - I like your approach - simple and it works.  Based on your knowledge, would a 30amp DC to DC charger put out 30 amps if similarly configured?  Our TV has a 150 amp alternator.

CharlieRN

Thanks to all for the replies.

I have a question with respect to Brad's installation:

Dutch061 said:

I installed an18 Amp in our TAB 400 BDL, but I put it under the dinette seat right next to the Power Distribution Center) PDC.

I tied the 2 ground wires together and connected them to the nearby Bus Bar Ground, disconnected the OEM installed charge wire from the PDC and connected it to the input of the DC-DC Controller. I ran a new wire from the DC-DC Controller ouptut back to the PDC. I used 12-gauge wire because combined length is less than 4 ft. According to my chart, 12-gauge is good for up to 10 feet at 20 Amps. 

. . .

5. I have verified that I indeed can get the 18 Amps output via my BMV-712

Brad

This method appears to be using the hot lead that travels to the trailer via the 7-pole harness to power the DC-DC charger. I would not have thought that there was enough current in the small gauge wire of the harness to allow the DC-DC charger to get to its rated output and fully charge the trailer battery bank. Bullet 5 however seems to indicate that the output of the charger (in this case, a Victron 12V/18A unit) does in fact get to 18 amps using the 7-pole harness charging wire, rather than running a large gauge lead directly to the battery.

Is this interpretation correct? Assuming yes, would you think that my charger, the Victron 12/24V - 20 amp unit, would also work using the Brad install method?

Denny16

With a short run wire as in the TaB320, should work.  But on the longer run in a TaB400, a larger gauge wire rated for the current and cable length would be better.
 Cheers 

Dutch061

I chose an 18 Amp DC-DC Victron with Bluetooth due to the fact that the OEM harness on my truck is 10-gauge and fused for 30 Amps. I wasn't comfortable trying to get 30 Amps through the 7-pin and then boosting the voltage which is part of the function (and reason) of the DC-DC controller. In addition, the configuration with the Victron Connect App is super easy. 

I did replace the 7-pin harness and cable to the junction box and the 12 VDC Auxiliary and ground are both 10-gauge wires. I replaced this because the ground terminal was in very poor condition in the original harness, which was poor BEFORE I installed the DC-DC controller. The 12 VDC wire and ground wire from the junction box to the Power Distribution Center are also 10-gauge. In addition, there is a ground lug mounted to the frame adjacent to the junction box. As I mentioned before, I removed the 10-gauge red wire from the PDC and connected it to the input of the DC-DC controller. I used 12-gauge wire for the output back to the PDC and also tying the 2 ground wires together and connected to the Bus Bar Ground. The overall length of the 12-gauge wiring is less than 3 feet, so I am not worried about voltage drop. This is the only wiring that is smaller gauge than the OEM. 

From there, it uses the same 8-gauge wiring that everyone else has that is more than adequate for 18 Amps, but I feel it is marginal for 30 Amps (at least on our 2020 400 BDL). Without digressing into the size of the wire from the PDC to the batteries (which I have made several posts about previously), I will leave any further thoughts or comments out. 

The only "unknown" is the ground circuit on my truck. I don't know if there is a wire front to back (like the 12 VDC) or if it is tied to ground on both ends. However, I am comfortable with the fact that the Engineers at FMC designed it for the 30 Amps that is available. 

Bottom line, I would be very hesitant to go any larger than 18 Amps with the 7-pin and what is likely OEM wiring on most vehicles with a factory equipped towing package. However, there are people who say that I play it way too safe, but I am okay with lower risk.

Brad

RMo

Thanks Brad!