Tips for trailer charging?

CRYA

New member
Hey all. I’m looking for any guidance on finding a way to charge a trailer’s house battery from the vehicle side while running. My situation is attempting to charge a trailer battery operating a 50L fridge in the trailer, but which trailer doesn’t really have a way to mount Solar to. Additionally, arriving in camp at dusk and departing in the morning on a Multi-day adventure doesn’t allow for sufficient stationary solar charging. So, any 12V experts out there?
Run a Dc-Dc charger all the way back to trailer? Run Solar from the LR4 to the Trailer battery? Any other ideas?

cheers
 

Dogpilot

Member
The hot wire would most likely require the 7 conductor circular plug. The big issue is how large your trailer battery is. If you flatten your battery down, then the inflow current will be high, real high. So if you did that you would need to put some kind of charge controller between the battery and the trailer connector to regulate the initial inrush current. Otherwise it may ultimately damage the connector contacts. Reasonable battery charging would be between 5-10 amps, for smaller batteries, tapering down. 10 amps is a lot for most trailer wires. So a regulator would keep it something like 5-7 amps. Slower charging, but then it would not tend to fry your wiring.
 

CRYA

New member
Not sure. Trailer has the 7-pin round plug, for lights and brakes etc, just not anything connected to the onboard 100ah FLA.
 

garrycol

Member
In my RRS I have just run a fused heavy duty cable direct from the vehicle battery to the rear of the vehicle with an andersen plug on it. The trailer plugs into this plug - when driving the alternator is charging both the vehicle battery and the trailer battery which the alternator just sees as one big battery. Is simple and no real issues - just remember to unplug the trailer from the car if you are stopped for any length of time so the starter battery does not low.

Garry
 

4000lbsOfGoat

Well-known member
Weird, I just answered this question in another thread not 5 minutes ago...

I use a BCDC1212T from Redarc to charge my trailer batteries (a pair of 100Ah LifePO) while on the move. It is designed to work with the factory 7-pin plug and has worked very well for me.

It isn't a super-fast charge but 12amps is more than enough to keep up with my fridge (Dometic CFX3) while it's running, plus a bit extra. A good days drive will generally get me topped all the way back up after a night of use.

Cheers!
 

Utah KJ

Free State of Florida
I have a Redarc DC to DC in the trailer battery box, and run an anderson plug. I have a dual batt system in my vehicle so it was a short run, otherwise, got to go to the under hood battery. Will charge at as much as 50 amps whilst underway. I'm kind of a big deal tho.
 

CRYA

New member
Weird, I just answered this question in another thread not 5 minutes ago...

I use a BCDC1212T from Redarc to charge my trailer batteries (a pair of 100Ah LifePO) while on the move. It is designed to work with the factory 7-pin plug and has worked very well for me.

It isn't a super-fast charge but 12amps is more than enough to keep up with my fridge (Dometic CFX3) while it's running, plus a bit extra. A good days drive will generally get me topped all the way back up after a night of use.

Cheers!
Cool thanks. 12V is not my strong suit but it sounds like if I can locate the aux power wire in the 7-pin, I can tap it or? Also did you need to connect the blue wire? Something about standard vs. low voltage trigger settings. Looks like the Redarc and Renogy DC-DC do the same things. Thanks.
 

4000lbsOfGoat

Well-known member
12V is not my strong suit but it sounds like if I can locate the aux power wire in the 7-pin, I can tap it or?
Your trailer will have a 7-pin cord that terminates somewhere in the trailer, likely near the tongue. If it is anything like mine it will terminate at some sort of distribution block. Locate the "always on" 12v wherever the cord terminates and tap in there.

I'm not sure about a blue wire...I didn't install it myself...
 

emtmark

Austere Medical Provider
The wire size alone limits it to almost useless levels of charging. Run a dedicated 8 awg line back and not only will your fridge be happy but you will pull into camp topped off and ready to rock


Sent from my iPhone using Tapatalk Pro
 

garrycol

Member
Yes exactly - that is why I ran a separate cable from the battery to the rear of the car with a dedicated socket to charge the camper battery and run camper accessories while driving.

Dc to DC chargers have their place in some circumstances but their main restriction is they are limited to what amps they are able to provide (depends on charger size) where if connected to the alternator via the starter battery, the full excess power of the alternator is available for camper charging - normally far more than is available from a DC charger.
 

4000lbsOfGoat

Well-known member
The wire size alone limits it to almost useless levels of charging. Run a dedicated 8 awg line back and not only will your fridge be happy but you will pull into camp topped off and ready to rock
Interesting observation from someone who has obviously never used the device. I use the device on a regular basis and can tell you that it provides perfectly adequate levels of charging while running a fridge and topping off 200Ah of batteries.....I pull into camp ready to rock every time.

the full excess power of the alternator is available for camper charging - normally far more than is available from a DC charger.
Not really true with a modern alternator...Either way, the alternator doesn't "know" that there are 2 batteries connected so neither will really be charged optimally. An dedicated DC charger on the trailer bank will charge the bank optimally, without regard for the needs of the starter battery.
 

garrycol

Member
Not really true with a modern alternator...Either way, the alternator doesn't "know" that there are 2 batteries connected so neither will really be charged optimally. An dedicated DC charger on the trailer bank will charge the bank optimally, without regard for the needs of the starter battery.
You are correct that the alternator does not see 2 batteries and sees them as one - but disagree about not charging optimally - where the combined voltage of the batteries is lower than what is optimal for them - each will take what it needs from the alternator until combined voltage is optimal - so both fully charged and with 50 to 100 amps available from the alternator the batteries are charged quite quickly - certainly quicker than a Dc dc charger.
 

emtmark

Austere Medical Provider


7 pin constant hot is usually 12 awg, also at the end of a long run meaning high resistance, current and voltage inefficiencies turn into heat.

10awg is called for by the manufacturer in their own instructions because to charge at 12 amps you have to draw more than 12 amps. They know it’s not a great idea to ride the ragged edge and indefensible to advise anyone that they should install their product in a potentially unsafe manner.



Your right old goat I don’t have one nor do I use one but I can read the documentation.

My renogy is a 20 amp unit and pulls damn near 30 when at full chooch. Since you have one and use it all the time what’s the amp draw into the red arc while bulk charging? Would be nice to see the efficiency of the device in question.

100 ah at 10 amps is 10 hours of charge time rough math right?


Sent from my iPhone using Tapatalk Pro
 

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