Wiring for Renogy DC-DC charger w/MPPT

[rockyeades]

Hi, I have a Renogy 50amp DC-DC charger w/MPPT. I want to run from the battery in my tow truck to Anderson connectors (about 20 feet) and then to the charger in my travel trailer. The spot that I want to put the charger, batteries and inverter is under a dinette bench towards the back of my trailer, about 20 feet from the tongue. I have 50 feet of both black and red #4awg copper cable. Is that sufficient to do that run? If not, would it be okay if I move the setup to the front of the trailer, about 6 feet from the tongue? Of course, I can't do anything about the run in the truck, but I would like to know if my first choice would work in the trailer. Thanks for any help.

 

[sunshine_eggo]

40' of 4awg @ 13.5V and 30A (assuming you're charging with 25A as that's the limit if solar is also charging):

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

0.6V or 4.42% drop.

I would find that acceptable unless there's something special to consider.

At 60A (from the alternator) or 50A of charging to the battery, that gets a little more onerous... 1.19V drop or 8.83%. The charger might object to that voltage drop.

 

[rockyeades]

40' of 4awg @ 13.5V and 30A (assuming you're charging with 25A as that's the limit if solar is also charging):

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

0.6V or 4.42% drop.

I would find that acceptable unless there's something special to consider.

At 60A (from the alternator) or 50A of charging to the battery, that gets a little more onerous... 1.19V drop or 8.83%. The charger might object to that voltage drop.

Thanks for your reply. I won't be running solar and DC-DC at the same time. My solar panels are ground deployed only when the trailer is parked. So I'll be getting full 50amps from the battery. Will the #4awg work with the charger in the second choice forward position, about 30' total run? Or should I go to #2 wire? And if I do, will that work for the longer run?

 

[sunshine_eggo]

Give the calculator a try.

 

[rockyeades]

Give the calculator a try.

Thanks. Something I've never understood about calculators. Is the "One way" distance (40' in my case) sufficient for dc circuits or do I need to double it for round trip? Some calculators advise on that; this one doesn't seem to.

 

[OTRwSolar]

Thanks. Something I've never understood about calculators. Is the "One way" distance (40' in my case) sufficient for dc circuits or do I need to double it for round trip? Some calculators advise on that; this one doesn't seem to.

This is the same VDC we use. Right after "Distance", in parentheses, it says "one way".

 

[rockyeades]

This is the same VDC we use. Right after "Distance", in parentheses, it says "one way".

Thanks for your reply. I saw that, but I've seen the "one way" thingy on other calculators I've used, but in the explanation for how to use it, it said to use round trip distance for dc circuits.

 

[OTRwSolar]

Thanks for your reply. I won't be running solar and DC-DC at the same time. My solar panels are ground deployed only when the trailer is parked. So I'll be getting full 50amps from the battery. Will the #4awg work with the charger in the second choice forward position, about 30' total run? Or should I go to #2 wire? And if I do, will that work for the longer run?

We have a ~25 ft. cable run from our truck's battery/alternator to our 40a Renogy dc2dc charger located in our truck camper. Used 2 gauge cable for all the positive run (and the truck's frame for most of the neg run), plus two 175a Anderson-type connectors in the bed of the truck. With 40a of charge current, we typically have a 43.5a load on the alternator. Could have used 4 gauge as Renogy recommended, but we wanted to keep the voltage drop and load on the alternator to an absolute minimum. Not sure about your charger, but our dc2dc charger can draw as much as 60a from the alternator to produce 40a of charge current if the voltage drop is excessively high.