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Trailer battery charging tech

DRTDEVL

DRTDEVL

Mothfukle
Joined
May 19, 2020
Member Number
78
Messages
766
Loc
Austin... TX? Nope. Minnesota!
A few weeks ago, I "rebuilt" my PJ car hauler, adding a battery box, a powered tongue jack, and a 12k winch. When wiring up my van last month, I used a 12 ga wire and a 30A circuit breaker for the 12v+ pin on the 7-way in order to keep the battery charged (and the breakaway battery at the same time, although I really need to put a diode inline on that one).

Fast-forward to last week. I picked up a parts vehicle about an hour away. I winched it up, brought it home an hour, and winched it off the trailer the next day. I then disconnected the trailer and brought the van to the front of my house where I parked it... but forgot to unplug my heated seat cover from the outlet (the power outlets aren't switched, they are constant).

Thursday morning, I went to fire up the van to go get the second parts vehicle from the same place. My battery was totally dead, so I grabbed a spare van along with my jump pack to jump it, and connected the trailer, driving an hour to get the second one. Upon arrival, I disconnected so the engine (on a pallet) could be loaded into the back of the van, and reconnected to load the parts van. When winching the van up, the battery was too weak to get it more than halfway up, so I connected my jump pack and finished loading. When I got home, the battery was too weak to complete the unloading, and I had to use my jump pack to finish the job. Afterward, I parked the trailer by the shop and hooked it up to my 6 amp battery charger for the rest of the day. Yesterday, while working out in the shop, I had it hooked to the charger for another 4 hours before parking it back where it belongs.

Questions:

Why did the battery run out of power? Was the alternator too busy trying to charge the flat van battery the entire trip that no power was left over for the trailer's charge circuit? Did I not size it large enough to keep a group 35 marine battery charged after pulling a heavy load? After all, it is sized to push 30 amps, but is it tripping the breaker when the battery is low due to the draw, thereby not charging the battery at all? If that is the case, how can I restrict the draw to under 30 amps?
 
Lemme guess..
winching with van engine OFF? Edit nope.
Old shitty batteries? Edit nope.
Bad ground?
 
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Clb said:
Lemme guess..
winching with van engine OFF?
Old shitty batteries?
Bad ground?
Click to expand...

No, the van was running the entire time and was not shut off between the time I left the house and the time I was done unloading (I feared the dead battery in the van from that morning might leave me stranded in the middle of nowhere had I turned the van off), brand new deep cycle battery from Napa, and all brand new wiring harness throughout the trailer and battery system.

I literally just built the entire electrical system on the trailer a few weeks ago.
Click image for larger version Name: IMG_20210309_170932890_HDR.jpg Views: 0 Size: 581.7 KB ID: 367736
 
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I have a warn 9k winch in my enclosed.

There's a marine deep cycle in there too.

I have no idea what the wiring is for charging the battery of the truck. It's a factory installed battery so it's probably shit wiring and barely adequate.

I added a battery tender brand solar charge controller. Ran some 12/2 to the tounge with a random connector I had off some parts car.

When I'm not using the trailer I bungee the solar panel to the tounge with no concern as to where it's facing or how much direct sun it actually gets.

When I am using the trailer I could probaby load/ unload 5 or 6 cars before it even thinks about slowing down.
 
Thatg9659 said:
Using the center pin on the 7 pin connector to charge the winch battery? run 4ga P&G

I have one of these I scavenged from a decommissioned K9 outfitted F150 it seems to work when the sun shines. I've been keeping it on my ranger cause the battery is getting weak.

https://www.specialized.net/pulsete...erm=4581115203271983&utm_content=All Products
Click to expand...

No, I used the standard layout, where the upper right pin is the charge pin and the center is the acc/reverse circuit, as I plan on eventually tying the light bar into the reverse circuit on the trailer.

I might have to get a solar maintainer in the future, but for now I'd like to figure out how that battery died after so little use.
 
DRTDEVL said:
No, I used the standard layout, where the upper right pin is the charge pin and the center is the acc/reverse circuit, as I plan on eventually tying the light bar into the reverse circuit on the trailer.

I might have to get a solar maintainer in the future, but for now I'd like to figure out how that battery died after so little use.
Click to expand...


I don't know the pin layout from memory so I pulled the center pin thing from my ass, Isn't that 20 amps max at the plug? not enough to charge a battery in my opinion.
 
google you "trail charger"
it's a unitized boost converter for this exact situation, looks like those blue anodized aluminum dual battery isolator dealieos you put in the alternator charge wire on a motorhome

you got too much voltage drop in the 30' of wire and the corroded 7pin to get charging voltage at the trailer battery
if the alt put out enough voltage to charge the trailer's battery you'd cook your cranking battery or something like that
 
My car trailer has a 110v 2amp trickle charger that I plug in when parked.
Both my car trailer and boat trailer have electric winches with yellow top batteries. Each trailer has a 30amp fuse then ran through 2 NC relays in series to the battery. The relays are wired to the winch contactor. When the winch is engaged it opens one of the two relays that way the winch can't pull current through the 12v from the truck plug and burn up the wire.
The boat trailer used to have a ATV battery with a 2500lb winch. It didn't have enough ass so I replaced it with the yellow top. Never had a problem with the car trailer.
 
[486 said:
;n368211]google you "trail charger"
it's a unitized boost converter for this exact situation, looks like those blue anodized aluminum dual battery isolator dealieos you put in the alternator charge wire on a motorhome

you got too much voltage drop in the 30' of wire and the corroded 7pin to get charging voltage at the trailer battery
if the alt put out enough voltage to charge the trailer's battery you'd cook your cranking battery or something like that
Click to expand...

What corroded 7-pin?

I installed the 7-way on the van (new wiring and all) in February. I completely redid the electrical on the trailer(new pigtail and junction box, too) in March.

And its 30 amps max.
 
Voltage drop is the bigger concern. Once your 7-pin connector/socket corrodes in a few years the problem will get worse.

Measure trailer battery voltage when trailer isn't hooked up. Same with truck battery, truck off. Hook up truck and trailer, then cut the engine on. Measure both battery voltages again. If you don't see the same voltage at the trailer battery as the truck battery (you won't because of voltage drop), you'll at least see if you have enough voltage to charge the trailer battery.
 
I figured it out.

When I checked everything today with a multimeter, I found it wasn't charging anymore. I backtracked through the system, and found the upfitter power block I was using only had power when I was connected to the trailer... it was being back-fed from the trailer battery itself. The trailer brakes also operated off this circuit :eek: thereby were running off of the trailers low battery on the way home. Somewhere along the way, the upfitter block's fuse had been replaced in the past with a 20 amp, when it is a 30 amp circuit. That fuse popped the moment I put a load on the winch, thereby causing no charge.

Voltage at trailer freshly disconnected is now 12.6 (it was at 12.1 when I started checking everything and I let it charge for about an hour before disconnecting). Connected is now 13.28 and at the van battery its at 14.14. I get 14.1 at the connector when disconnected.

I think my issues will be solved for now if I actually disconnect the trailer plug before winching. I may just go on out and pick up a thermal breaker for that circuit as well in order to prevent future issues (and make life one step easier).
 
DRTDEVL said:
I figured it out.

When I checked everything today with a multimeter, I found it wasn't charging anymore. I backtracked through the system, and found the upfitter power block I was using only had power when I was connected to the trailer... it was being back-fed from the trailer battery itself. The trailer brakes also operated off this circuit :eek: thereby were running off of the trailers low battery on the way home. Somewhere along the way, the upfitter block's fuse had been replaced in the past with a 20 amp, when it is a 30 amp circuit. That fuse popped the moment I put a load on the winch, thereby causing no charge.

Voltage at trailer freshly disconnected is now 12.6 (it was at 12.1 when I started checking everything and I let it charge for about an hour before disconnecting). Connected is now 13.28 and at the van battery its at 14.14. I get 14.1 at the connector when disconnected.

I think my issues will be solved for now if I actually disconnect the trailer plug before winching. I may just go on out and pick up a thermal breaker for that circuit as well in order to prevent future issues (and make life one step easier).
Click to expand...

Hence why I run two relays in series. It prevents current draw from the truck and blowing any fuses on the vehicle.
 
Resurrecting this thread as I'm wanting to ensure that my trailer battery will stay charged as long as I have it on the truck (which is 80+% of the time). I'm considering installing a battery isolator in between the charging system on the pickup and the trailer auxiliary wire (dedicated 10ga.) Is this overkill? Should I just depend on my 30a inline circuit breaker that I currently have wired to control the load going through the line and not set it on fire in the case where I'm winching and drawing load, and after winching when it needs recharged? Is this overkill? I think that a proper isolator will control the flow of electricity more effectively than a 30a circuit breaker cycling on and off.
 
If you don’t every put it on a battery charger of some type, the battery won’t get a “full charge” and therefore will have a shorter life. Read up on DC-DC chargers, it’s basically a voltage drop issue, more commonly a problem on newer vehicles with variable output alternators.

If you have the ability to plug it in to a charger once in awhile and rely on the truck charging to keep it from getting drawn down too low, you’ll be ok. You do need a heavy gauge wire (fused at the battery), and then I would use a continuous duty solenoid for easy on/off.
 
saw that you got it figured out but figured id throw this out there. I have 2 dump trailers and a trailer with hydraulic landing legs and i use one of these

purkeys.net

BOSS™️ Dump Trailer Charging System - Purkeys

purkeys.net purkeys.net

It steps up the voltage, allows us to do multiple dumps on 20 k dump trailers a day and so far havent had a issue in 3 years.
 
Could you use a disconnect inline to the trailer battery, so it gets some charge while driving? Hit the disconnect to break the charge circuit to the trailer battery before using it.
 
If you're going to do that, put a relay in line and have it switched by the running lights, then it won't charge unless you're running lights are on. Turn off your running lights when you want to dump.

Aaron Z
 
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