Need for DC-DC Charger?

[ncitro]

That's a lot of copper to charge with. Personally, I can't see why anyone would go over #10. Thats covers 30a of charging current from the TV. If anyone needs to charge at over 30a, maybe look at what you are expecting your 12v systems to do. Just my opinion. I'm happy enough with the 7a my stock charge setup delivers. I could see in the future stepping up to a 20a dc/dc...maybe... and I'll run #12 for it...but #4? that's good for 80amps.

Is a length and voltage drop issue. 4Awg is recommended in the manual for the 40 amp version at 25 feet I recall. We run a 120v residential fridge, so on cloudy rainy drive days where we aren't getting much or any solar, the 40A version can bring my batteries back to full in just a few hours of driving. I love it.

[Scott'n'Wendy]

Is a length and voltage drop issue. 4Awg is recommended in the manual for the 40 amp version at 25 feet I recall. We run a 120v residential fridge, so on cloudy rainy drive days where we aren't getting much or any solar, the 40A version can bring my batteries back to full in just a few hours of driving. I love it.

But if you look at the electrical code....for wire run lengths......that 4awg is extreme overkill. While oversized wire will never hurt - other than the wallet - your money is being wasted on such short runs. And 25-30 feet are short runs.

[Jlawles2]

Scott'n'Wendy Don't forget the DC runs are round trip. So on a standard truck that's about 50' total vs the 25' in an ac system.

[Scott'n'Wendy]

Scott'n'Wendy Don't forget the DC runs are round trip. So on a standard truck that's about 50' total vs the 25' in an ac system.

Not sure what to make of that statement Joseph. AC, as with DC, require going to and from the source. AC reverses every 16 milliseconds and DC doesn't, but they still have to return to source. So they both have two wires......cct length is the same

But regardless of how you. 'look' at electricity, all I'm saying, imo, #4awg is overkill. I would never do it unless I needed a sustained 80amps flowing..AC...or DC. But I dragged this off topic...apologies.
To the op, I would only add a dc/dc charger if the regular TV charge cct (supplying 7 amps) was not enough while travelling. For the way we use our trailer, 7a is lots to keep the battery charged.

[ncitro]

Keep in mind the 40A rating is on the output of the charger. The input far exceeds that so it can step up the voltage to what's required at 40A. I used to have a breaker at my truck battery of 60A and it would occasionally trip,so I know it draws on excess of that.

[glennco]

I installed a renogy 20A dc/dc charger on my f-250 for 2 reasons.
1: charging lithium can utilize a greater voltage than you could get out of a 12v system on my truck.
2: I’m really using it to charge my battery during travel, not just maintain it.

if I were to do this again I would run wire and get a larger charger so I could fully charge the battery in less time. In my situation I will be dry camping for a couple days, then driving for a few hours and dry camping again. It would be nice to fully charge my 200A lithium battery in 2-4hrs


in regards to this wire size discussion, here is a great article including links to the wire size chart.

https://learnmetrics.com/12v-wire-size-calculator-chart

[Guest]

An ampacity chart is also useful in determining wire size. A DCDC can draw up to 50% additional load from the TV charging system. I measured startup current on my 20amp DCDC to be as high as 27amps with a running current of 25amps from the TV.

Jim