DC-DC 30 amp charger cable

[rarebear.nm]

I'll be installing a Victron DC-DC 30 chrager in my TT from the tow vehicle. A RAM 3500, crew cab, long bed. Overall the truck is about 22ft long.


I figure that the each way distance from truck's battery to TT buss bar is about 35ft. Round trip distance is 70 ft. I'll be using 350 amp Anderson connector at the truck. Various wire size tables and calculators I've looked at suggest every thing from 1/0 to #6 copper wire. Large variance.



Question is for folks who have done this what size of wire did you use? And how hard is the truck/trailer section to handle? Would you do anything differently?

[d23haynes57]

30 amps is easily handled by a 10 gauge wire. If really worried about voltage drop and want a bit more mechanical strength use 8 gauge. If trying to charge a large battery bank and also run other loads the 30 amp charger is the limiting factor. If a multiple battery bank a good minimum is 10 amps per 100 A/H of battery capacity plus consideration for expected connected loads.

[ttavasc]

Originally Posted by rarebear.nm

I'll be installing a Victron DC-DC 30 chrager in my TT from the tow vehicle. A RAM 3500, crew cab, long bed. Overall the truck is about 22ft long.


I figure that the each way distance from truck's battery to TT buss bar is about 35ft. Round trip distance is 70 ft. I'll be using 350 amp Anderson connector at the truck. Various wire size tables and calculators I've looked at suggest every thing from 1/0 to #6 copper wire. Large variance.



Question is for folks who have done this what size of wire did you use? And how hard is the truck/trailer section to handle? Would you do anything differently?

When I installed mine on my F-250 I used 2 awg for the truck run with an Anderson at the rear and using the truck frame for ground next to the Anderson. The max wire size on the VE Isolated 12/12-30 is 6 awg so that is what I used for the umbilical on the trailer side of things.

Routing the wire from front to back on the truck was a little interesting. The battery where the + side comes from is on the passenger side but all the existing wire bundles that run front/back run down the driver side. I elected to route across the top back of the engine bay to get to the driver's side before heading to the rear following along those existing wire bundles. That also lands you next to the 4-pin/7-pin connector so both umbilicals connect close together instead of opposite sides of the hitch.

[Isaac-1]

Does the Victron DC-DC charger support voltage boosting, my Renogy one does, if so go with a smaller wire say 6-8AWG as 10 AWG will support 30 amp with voltage drop.

[Gravelette]

You mentioned round trip but I don't think you have to go all the way back to the engine compartment to find a ground.

[rarebear.nm]

Originally Posted by Gravelette

You mentioned round trip but I don't think you have to go all the way back to the engine compartment to find a ground.

I do not like to use steel chassis as a ground conductor for anything. Steel has about 15% of the electrical conductivity as copper. Look it up if you like. Thus you are designing in an voltage drop. If I can run one hot wire, I can run a like ground wire. Yes I know how auto manufactures have done it for years but that does not mean it's the best method.


Either way the round trip from and to the battery is still the same distance. But with at least two more connections to rust.

[NoviBill]

A good reference on gauge vs distance vs current
https://www.engineeringtoolbox.com/a...uge-d_730.html

[wolfe10]

Originally Posted by Gravelette

You mentioned round trip but I don't think you have to go all the way back to the engine compartment to find a ground.

Yes and no.


The yes is that there are other paths on the truck (frame) to battery negative.


The no is that the correct gauge wire directly wired to the battery is very likely the least resistance solution. Least resistance= less voltage loss.



BTW, I would go with a very minimum of 2 gauge and if operating in an area where it might be exposed to much rain or worse, salted roads, use marine wire like Ancor (high quality fine stranded, tin coated copper).


Below is a link to a voltage drop chart. I plugged into the 3% volt drop table, 30 amps and 70' run. Answer 1 gauge.


https://www.westmarine.com/west-advi...-Ampacity.html

[rarebear.nm]

Originally Posted by d23haynes57

30 amps is easily handled by a 10 gauge wire. If really worried about voltage drop and want a bit more mechanical strength use 8 gauge. If trying to charge a large battery bank and also run other loads the 30 amp charger is the limiting factor. If a multiple battery bank a good minimum is 10 amps per 100 A/H of battery capacity plus consideration for expected connected loads.

I would agree that #10 is fine for 30amps over a short distance. Done that many times for some of my shop tools with 3 - 5HP motors. In designing you need to consider AHr of the battery bank as well as what the alternator can provide without damage. Sort of like a budget and spending. I see no point in losing voltage you don't need to lose.

[rarebear.nm]

Thanks for the Marine wire sizing table link. I have frequently defer to marine and/or aircraft products and methods over standard automotive/RV products and practices. I like these tables better. Also they spec out degrade requirements for different installation issues.


I'm already chosen marine wire for nearly all aspects of this job. I've used it in RVs for some years now.



I'm looking at #1 or #2 wire for at least the run under the truck which is about 70% of the round trip distance. In serious question is how well would #1 or 2 wire work for the truck - trailer connection with the added stiffness and weight of that cable over say #4 or 6. Considering the bouncing and flexing that occurs in that section of run. At the trailer end I have to fit the cable into a connection made for #6 at most. If needed in the last foot or two I could use a pair of single post "busses" and terminate a heavier cable to a short section of #6 wire. Hum, is a single post buss a unicycle?

Originally Posted by wolfe10

Yes and no.


The yes is that there are other paths on the truck (frame) to battery negative.


The no is that the correct gauge wire directly wired to the battery is very likely the least resistance solution. Least resistance= less voltage loss.



BTW, I would go with a very minimum of 2 gauge and if operating in an area where it might be exposed to much rain or worse, salted roads, use marine wire like Ancor (high quality fine stranded, tin coated copper).


Below is a link to a voltage drop chart. I plugged into the 3% volt drop table, 30 amps and 70' run. Answer 1 gauge.


https://www.westmarine.com/west-advi...-Ampacity.html

[wolfe10]

Marine wire would be just fine-- just secure it as in any marine or aviation installation.


I promise, we have been in sea conditions that make the roughest road seem glass-smooth. Never a wiring issue.

[rarebear.nm]

Originally Posted by wolfe10

Marine wire would be just fine-- just secure it as in any marine or aviation installation.


I promise, we have been in sea conditions that make the roughest road seem glass-smooth. Never a wiring issue.

Im not questioning any of the length that can be secured. But the 5-6ft length between the Anderson connector on the truck to the a-frame on the trailer. Also some concern about securing a heavy weight wire at the Anderson connector so as not wriggle too much at the connector or pull partly lose. Other trailer cables at the truck end have a latching tab to hold it in place, eg. 7-pin connectors.

[ttavasc]

I used 6 awg for the cables between the Anderson and the DC-DC charger on the trailer tongue and have never had any issues or concerns about the connector coming loose. I have the environmental boot on the connectors and the connection is very snug.

[SafariBen]

We've been around and around on this question of a DC to DC converter in a trailer many times. A LOT of the thinking comes from lead batteries where a small voltage drop will dramatically lower the charge current into the battery. Lithium is different from lead, and the DC to DC converter will INCREASE the voltage to compensate for voltage drop. You do not have to size this for lead, or for stationary voltage drop percentages. I would not use bigger than 8.


Interestingly, my Safari has most wiring run with it's own ground, including starter, alternator and all house circuits, which is a little funny with changing lights to LED, and all the white ground wires run back "home" when it has a welded aluminum structure.