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Question regarding DC to DC Chargers

Son_of_Norway
Explorer
Explorer
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.
Miles and Darcey
1989 Holiday Rambler Crown Imperial
Denver, CO
8 REPLIES 8

EMD360
Explorer
Explorer
If this is a motor home doesnโ€™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 Iโ€™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.
2018 Minnie Winnie 25b New to us 3/2021
Former Rental Owners Club #137
2003 Itasca Spirit 22e 2009-2021

eric1514
Explorer
Explorer
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.
2006 Dynamax Isata IE 250
420 Ah batteries
400w Solar

theoldwizard1
Explorer
Explorer
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
Explorer
Explorer
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
Explorer
Explorer
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?
2006 Dynamax Isata IE 250
420 Ah batteries
400w Solar

Tom_Barb
Explorer
Explorer
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
2000 Newmar mountain aire 4081 DP, ISC/350 Allison 6 speed, Wrangler JL toad.

BFL13
Explorer II
Explorer II
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.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

Tom_Barb
Explorer
Explorer
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.
2000 Newmar mountain aire 4081 DP, ISC/350 Allison 6 speed, Wrangler JL toad.