8 Gauge Wire

[BradW]

Got 25' of red and black 8 gauge copper wire, a 40 amp breaker and some lugs. I plan on wiring this truck correctly for the 12v frig. I hate to admit I never wired the three previous trucks correctly and the frig never worked right.

[pianotuna]

One possible solution is a dc to DC charger.

But likely an inverter is a better choice. It can be MSW and about 400 watts.

[theoldwizard1]

I second the use of a DC-DC charger ! You can use the "stock" wiring (including fuse) from the 7 pin trailer connector.

[Siletzspey]

Depending on the calculator or table you use, distance is measured as one-way (as a crow flies) or two-way (round trip). If your battery and alternator are 25' apart, that would be 25' one-way or 50' two-way (25' POS + 25' NEG). The ever popular BlueSea voltage drop table is TWO-WAY based.

As for voltage drop, the 3% and 10% rules apply to most device types, but not necessarily to DC-to-DC converters which are designed boost voltage, aka counter voltage drop.

Sterling has a video where they compare straight alternator-to-battery wiring where the wire has to be "huge" to counter voltage drop, but then with a DC-to-DC converter, the wire can be much smaller and cheaper and still get the job done. For the alternator to DC-to-DC wire, see the manufacturers length to AWG recommendations rather than needlessly oversizing/overspending on AWG based on a 3% or 10% voltage drop rule. At least for Sterling, they support down to 11.0VDC, or roughly a 23% voltage drop off at 14.4VDC alternator. To counter voltage drop on the output side, the DC-to-DC will have to pull a few more amps, and Sterling specs the 60A output could require up to 80A of input from the alternator. I don't recommend pushing the 20%+ limit however.

[LaneW]

Good info, all. The specs call for 4 to 6 awg depending on distance. My distance falls in the middle of the range listed for the run. I would like to run 4 awg from truck batt to truck bed, then step down to 6 for the last 6 or 7 feet of the run. Any concerns with that?

[deltabravo]

I am running a Victron DC to DC Charger in my AF 992.

From the engine bay to the truck bed, I have 4AWG wire with an Anderson connector where it plugs in to the camper.

From the DC to DC Charger to the truck bed pigtail, I used large wire too, but I honestly don't remember what size it is.

Here's a few videos of that project, which might give you some ideas:

Truck to RV High Amperage Battery Charging

Installing a Victron Orion TR Smart 12-12-30 DC to DC Charger

[StirCrazy]

ticki2 wrote:

LaneW wrote:

ticki2 wrote:
If you are 25’ from battery to charger isn’t the run actually 50’ there and back ?

I don't know. Is that true??? Its not AC.

That has been my understanding . Perhaps one of the electrical guru’s will clarify

no, you use one wire to get there (positive) and a different wire to get back (ground). the rating of the wire is the amout of amps for so many feet of lenght so it would be a 25' length of wire.

[ticki2]

LaneW wrote:

ticki2 wrote:
If you are 25’ from battery to charger isn’t the run actually 50’ there and back ?

I don't know. Is that true??? Its not AC.

That has been my understanding . Perhaps one of the electrical guru’s will clarify

[otrfun]

LaneW wrote:
. . . What I am looking at installing is DCC30S 12V 30A Dual Input DC-DC On-Board Battery Charger with MPPT. I am looking at the specs but not finding the input current. I am still looking for that. But, and I’m sure I dont understand as well as you, I will be at a bit under 25 ft from truck batt to charger, which based on the specs I see online would be on the long end fog 6 awg, or safe with 4 awg. Right?

According to the Renogy website, max rated input power for the DCC30S is 400w. Input voltage range is 13.2 - 16v (alternator voltage minus any voltage drop). Supposedly this unit is capable of up to 97% efficiency--impressive. Unfortunately, they don't state what conditions are necessary to obtain 97%, so efficiency could drop off significantly for other conditions. Based on these specs I'd guess-estimate input current would max out around 31a (current varies dependent on input/output voltage).

25 ft of 4 gauge would probably net you approx. 3% of voltage drop at 30-31a. This is based on the one-way distance (using the voltage calculator link I provided earlier). 3% should be fine. I wouldn't want it any higher.

[LaneW]

ticki2 wrote:
If you are 25’ from battery to charger isn’t the run actually 50’ there and back ?

I don't know. Is that true??? Its not AC.

[S_Davis]

Input current will vary depending on wire size and length feeding the charger, that is probably why they don’t list it. I run a 50 amp Redarc and it outputs 50amps with an input of about 53-54 amps, but I have a 1/0 DLO charge line.

[ticki2]

If you are 25’ from battery to charger isn’t the run actually 50’ there and back ?

[LaneW]

otrfun wrote:

LaneW wrote:
. . . I think I need to run a 4awg . . .

What is the max *input* current rating for your dc to dc charger? This input current rating and the length of the cable run would determine which gauge cable is most appropriate for the input. You may find this voltage drop calculator helpful. IMO, a voltage drop of <2% is ideal, but up to 3% is acceptable.

We ran approx. 25 ft of 2 gauge cable from the engine compartment to the input of our dc to dc charger inside our truck camper. Our dc to dc charger is rated for 40a of *output* charge current. The *input* current (i.e., alternator load) will always be higher.

The 25 ft of 2 gauge cable nets us a ~3% voltage drop at 44-45a (nominal alternator load when producing 40a of output charge current). Yes, we could have used 25 ft of 4 gauge, but that would have increased voltage drop, reduced system efficiency, resulting in a higher load on the alternator. If we had used 4 gauge, the alternator load would have increased to approx. 50-55a (or almost 60a using 6 gauge) while still producing the same 40a of output charge current. If you're interested, Ohm's Law describes all these relationships in more detail.

If you're not concerned about the load (i.e., wear and tear) on the alternator, then using a smaller cable is fine. If you are concerned about reducing the load on the alternator, then using a larger cable is the way to go. Your choice.

Well, of course I am concerned about wear and tear on my alternator……..

What I am looking at installing is DCC30S 12V 30A Dual Input DC-DC On-Board Battery Charger with MPPT. I am looking at the specs but not finding the input current. I am still looking for that. But, and I’m sure I dont understand as well as you, I will be at a bit under 25 ft from truck batt to charger, which based on the specs I see online would be on the long end fog 6 awg, or safe with 4 awg. Right?

[otrfun]

LaneW wrote:
. . . I think I need to run a 4awg . . .

What is the max *input* current rating for your dc to dc charger? This input current rating and the length of the cable run would determine which gauge cable is most appropriate for the input. You may find this voltage drop calculator helpful. IMO, a voltage drop of <2% is ideal, but up to 3% is acceptable.

We ran approx. 25 ft of 2 gauge cable from the engine compartment to the input of our dc to dc charger inside our truck camper. Our dc to dc charger is rated for 40a of *output* charge current. The *input* current (i.e., alternator load) will always be higher.

The 25 ft of 2 gauge cable nets us a ~3% voltage drop at 44-45a (nominal alternator load when producing 40a of output charge current). Yes, we could have used 25 ft of 4 gauge, but that would have increased voltage drop, reduced system efficiency, resulting in a higher load on the alternator. If we had used 4 gauge, the alternator load would have increased to approx. 50-55a (or almost 60a using 6 gauge) while still producing the same 40a of output charge current. If you're interested, Ohm's Law describes all these relationships in more detail.

If you're not concerned about the load (i.e., wear and tear) on the alternator, then using a smaller cable is fine. If you are concerned about reducing the load on the alternator, then using a larger cable is the way to go. Your choice.

[srschang]

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