Question regarding DC to DC Chargers

[Son_of_Norway]

I am installing a Renogy 20-amp DC to DC charger. My question is regarding the negative cable connections. The instructions say to connect the input negative cable to the chassis battery and the output negative cable to the house battery.

My chassis battery is a good 15 feet away from where I'm mounting the charger and it would take some tricky cabling to get it there. Both the chassis battery and the house batteries are grounded to the frame. The charger will be right next to a negative post on the frame. What difference would it make if I just connected both of the negative cables of the charger to the same post? Can this cause a problem?

I will contact Renogy next week with the question, but I am trying to get this install done this weekend, so I would appreciate any advice. Thank you.

[EMD360]

If this is a motor home doesn’t it have the solenoid that switches between chassis chargIng and alternator to starter battery charging? That is how my Renogy is hooked up. Except I used an ANL fuse instead of a breaker.

And it looks like this. The LiFePo4 batteries are below the dc to dc converter.

This means the positive input to the dc to dc piggybacks on the solenoid connection and does not go all the way to the starter battery. And the negative on my install does go to the chassis ground not back to the battery. It works when connected this way. Even though the install diagram does show a direct connection to the battery before grounding.

But I’m sorry I think I misread the problem. Why is the install 15 ft from the chassis batteries? I read it as 15ft from the starter battery. So definitely need a positive wire to the chassis batteries on the output side. And it seems the negative ground would also work for the negative as long as the batteries are properly grounded.

[eric1514]

theoldwizard1 wrote:

eric1514 wrote:
You need to run a positive cable up to the battery. Why can't you run a negative as well?

No, you do NOT need to run a positive wire to the battery !

This is the reason DC-DC chargers were invented ! As long as you meet the specified input voltage AT THE CHARGER you are good to go. Most factory 7 pin trailer connectors can handle 40A-50A.

It's my understanding this is a motorhome, not a trailer. Page 10 of the linked manual clearly shows a connection to the positive post of the starter battery.

[theoldwizard1]

eric1514 wrote:
You need to run a positive cable up to the battery. Why can't you run a negative as well?

No, you do NOT need to run a positive wire to the battery !

This is the reason DC-DC chargers were invented ! As long as you meet the specified input voltage AT THE CHARGER you are good to go. Most factory 7 pin trailer connectors can handle 40A-50A.

[theoldwizard1]

Son of Norway wrote:
My chassis battery is a good 15 feet away from where I'm mounting the charger and it would take some tricky cabling to get it there. Both the chassis battery and the house batteries are grounded to the frame. The charger will be right next to a negative post on the frame. What difference would it make if I just connected both of the negative cables of the charger to the same post? Can this cause a problem?

Ground is not ground, especially if you are going to use chassis at the rear of your vehicle. Don't ask me to explain it, I have CRS !

Does matter ? Not really ! As long the voltage at the "vehicle battery" wire going into the charger and the point you are goinG to use meet the minimum in the specifications. This is the beauty of a DC-DC charger !

[eric1514]

Son of Norway wrote:
I am installing a Renogy 20-amp DC to DC charger. My question is regarding the negative cable connections. The instructions say to connect the input negative cable to the chassis battery and the output negative cable to the house battery.

My chassis battery is a good 15 feet away from where I'm mounting the charger and it would take some tricky cabling to get it there. Both the chassis battery and the house batteries are grounded to the frame. The charger will be right next to a negative post on the frame. What difference would it make if I just connected both of the negative cables of the charger to the same post? Can this cause a problem?

I will contact Renogy next week with the question, but I am trying to get this install done this weekend, so I would appreciate any advice. Thank you.

It should work but I guess I don't understand the problem. You need to run a positive cable up to the battery. Why can't you run a negative as well?

[Tom_Barb]

Son of Norway wrote:
I am installing a Renogy 20-amp DC to DC charger. My question is regarding the negative cable connections. The instructions say to connect the input negative cable to the chassis battery and the output negative cable to the house battery.

My chassis battery is a good 15 feet away from where I'm mounting the charger and it would take some tricky cabling to get it there. Both the chassis battery and the house batteries are grounded to the frame. The charger will be right next to a negative post on the frame. What difference would it make if I just connected both of the negative cables of the charger to the same post? Can this cause a problem?

I will contact Renogy next week with the question, but I am trying to get this install done this weekend, so I would appreciate any advice. Thank you.

https://www.youtube.com/watch?v=EcVjPap9dkY

[BFL13]

Should work. wiring and grounding info here.

https://www.renogy.com/content/RNG-DCC1212-20-BC/DCC1212-204060-Manual.pdf

I have my neg input via the frame but have the output neg to the house batt post.(via monitor shunt) It ought to work by going to the frame first then to the house neg post.

You might have more voltage drop on the output that way, but depends on the house batt connection to frame how much.

[Tom_Barb]

go Victron Energy equipment, they are simply better, and have all the Videos to explain them.

I just installed 4 BattleBorn 100 AMP batteries Mulitplus 3000 inverter/charger, with a 500 AMP smart shunt, with gauge, and a 12-12/30 DC to DC .

brick simple to install, all done by Blue Tooth on my phone.