Charging the Trailer Electric Brake Battery

[69RoadRunner]

Should the trailer brake battery be charged if you have the trailer wiring harness connected to the truck's 7 pin connector, even if you don't have a brake controller hooked up without the truck running?

 

[B.G. Smith]

If the trailer has a breakaway switch, the brakes won't work if you lose the trailer and the battery is not charged. Is that what you are asking? The 7 pin hookup has a circuit to charge/maintain the trailer battery if the trailer is wired for that. I have seen flatbed/lowboy type trailers with dry cell batteries for the breakaway system. bg

 

[69RoadRunner]

OK, so the battery is only for the breakaway, and has nothing to do with regular braking from the brake controller?



I was trying to figure out how the trailer brake battery gets charged. Will the 7 pin connector charge the battery with the truck parked and off, or does the key need to be on?



I got the trailer inspected today (even though I forgot the controller, it passed). The breakaway didn't provide much braking, probably because the battery is very low. The trailer has been sitting a lot, even though it's less than 1 year old. It's an open car trailer.



My other problem was when I tried to install the Tekonsha Prodigy controller with the Dodge harness.



I hooked it up without mounting just to see where I could put it. I went to disconnect it, but the harness was very tight on the controller (I was pushing the release). Anyway, it was part way out, and the Prodigy started smoking!!!



I think the wires shorted when I tried to unplug it. Anyway, now I need another controller.



Today was a bad day. I won't even mention getting caught pulling into an area without a way out. I've never had a trailer before. I had to get a professional semi driver who was there to turn it around. It even took him a while. Grrrrrrrrrrrrrr.

 

[GaryOwen]

You should have power to batteries, but it is best to test with voltmeter or test light. Here's a helpful website that shows wiring connections.



Marksrv.com 7 way wiring diagram page



Connect voltmeter between 12v and ground.

 

[JimBob24]

If you do not have any other electrical accessories on the trailer then the battery is for the emergency breakaway only. The 7 pin plug should be wired to provide 12V charging current no matter if the ign switch is on or off. For that reason you do not want to leave the trailer plugged in for extended periods while the truck is not running or your truck battery may be discharged.

 

[PToombs]

I have seen some breakaway systems with only a battery, and some with a battery and a small charger in the battery box. I assumed the single you had to take out to charge and with a charger was hooked to the harness. I think you are only supposed to charge those batterys with 2 amps or a trickle?

 

[B.G. Smith]

Another note on electric trailer brakes. They have to be adjusted quiet often to work even madestly, they dont have a lot of travel and run out of stroke pretty quick. That pulling into a blind place with no exit sounds like some of my tricks. bg

 

[69RoadRunner]

I don't have any other accessories right now. I might get a winch some time.



Thanks for the link to those diagrams. I'm going to head out and disconnect the connector tonight.



The trailer is less than a year old, and the previous owner didn't have a brake controller, so the brakes have never been used.

 

[jnelson]

Swing arm on the brakes will some times freeze up if not used. Adjust the brakes and use them for a few hours. If they dont work and you dont have a wiring problem youll need to pull apart the breaks and check them out. Its easy and they're not too exsensive. Your brake-away battery box will have to have a trickle charger (like my 18ft car hauler) or buy a solar cell and hook it to your batttery (like on my 36ft). the solar cell works great.



Electric brakes can make you pull your hair out, but if you study the system and learn how they operate, it's not to bad.

 

[JPope]

Might want to check and make sure that a fuse is in place for the trailer charging circuit. I have been told by a RV repair company, that many of the Dodge trucks are missing the fuse, even if sold with the towing package.

 

[Loren]

69RoadRunner,



If you have an RV with a "house" battery, that battery is used to power the breakaway brakes. It will charge anytime it is plugged into your truck via a 7-wire connector. A 7-wire connector has a ground wire and a separate hot wire that always carries 12 volts.



If you have a utility trailer, or something similar that does not use a battery for anything except the breakaway brakes, then the battery MAY OR MAY NOT charge when it is plugged into the truck.



Pete is correct. Some units have the good breakaway setup with a small charger and some don't. Open the box that contains your breakaway brake battery and see if there is a small unit inside that looks like a transformer. If there is, then your battery should charge when it's plugged in. (I'd still check it with a voltmeter to be sure it's wired correctly. )



If there is nothing inside the box but a battery and some wires, then your battery will NOT charge when it's connected. You will need to charge this battery periodically with a regular 12 volt automotive battery charger. Use the lowest charge rate your charger has. In no case charge faster than about 10 amps. Even 10 amps may be too much for these small batteries. If the battery gets hot while it's charging, the charge rate is too high.



I found out the easy way that my flatbed trailer does not have a charger. My son-in-law told me that the system didn't work when he tested it. I had to buy a new battery because the old one had been dead for so long.



Good luck.



Loren

 

[jnelson]

very helpful site - Dexter Axle - Trailer Axles and Running Gear Components - HOME

 

[Cattletrkr]

My last trailer was over 4 years old when I sold it and it still had the original breakaway battery and it still worked. My current trailer needed a new battery in less than a year. Neither has a charging system.

Most utility type trailers do not have a charger for the breakaway. One line that dad sells uses the clearance light circuit to charge the battery 'cause it doesn't need to be charging all the time.

If the trailer has been sitting for over a year, it's about a 99% chance your brakes are froze. Whoever did your DOT inspection could lose his license if he DOT'd the trailer w/o knowing whether or not your brakes actually worked. Trailer can't pass if the truck doen't actuate the brakes.

 

[jelag]

We've taken all the dry cells and have thrown them away... they usually don't last more than a couple of years with heavy use... and the replacement cost was something like 45 or 50 bucks as I remember... .

Instead we put a medium size motorcycle battery in a protected box on each trailer..... something that we can check the level of... . we're getting almost 4 years on a battery that cost 19. 95 or something like that at Wal-Mart and if you on the road and need one you can get it any where... .

All our work trailers can get inspected at the scales... one of their tests is to pull the trailer connector, pull the brake away cable and have you try and pull ahead to see if the brakes come on... if the truck doesn't try and drag the trailer they RED TAG you and make you fix it on the spot... . so this is something we check every month or so..... Our 2 largest trailers have electric over hyd brakes and need a power supply..... and the small battery isn't enough so on those trailers we've wired in a group 24 battery... ... . so we know the brake away will work and the trailer is good for at least 1000 miles of braking without power to that battery... .

 

[MAshley]

You should also check to see if the + 12 V is even hooked up. Most of the Dry cell batteies don't like to be constantly charged by the truck at the high amperage so some and or most trailer manufactures may not actually have the battery charging. If its just a box with a battery, and no trickle charger then I would Bet the 12V is not connected. And your battery is more of a 1 time use. Mine died in about a year, and DOT wants that small battery to hold for 15 min. I gutted mine, hooked up the 12V + Line, and installed a deep cycle battery. That should hold them brakes for at least 15 min.



Personal experiance with my trailer, YMMV.

 

[69RoadRunner]

Well, I just got back from Carlisle. We tested the breakaway before I left by jacking up the trailer, spinning the wheel and pulling the breakaway cable. It stopped the wheel.



After I fried my first Prodigy, I got another, and it seemed to work well. My only other trailer experience was with a Uhaul that had surge brakes.



I think I'll look into those solar chargers, or keep the battery in my garage and trickle charge it before my next trip.



Thanks for all the advice!

 

[Cattletrkr]

We've taken all the dry cells and have thrown them away... they usually don't last more than a couple of years with heavy use... and the replacement cost was something like 45 or 50 bucks as I remember... .

For that I guess I would switch batteries too. Luckily I get the dry cells for $10-15.

 

[MAshley]

The issue is not how much that battery costs, its what happens when the DOT pulls you over and puts you out of service, on friday night on a long weekend, in the middle of no where, oh and then they hand you a fine to top it off. AND or your bad luck is worse and you loose the trailer and it never stops like it should and kills someone. I know in most situations it would never happen but you never know.