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Old 08-22-2013, 09:03 PM   #1
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Breakaway Brake Battery

Just bought a new to me enclosed trailer to haul around some motorcycles. In the process of doing a general inspection of things I found the break away battery to be dead. I tried charging it, but it was a goner. So a new one was in order. That got me thinking "How is this battery charged when I'm using the trailer"? I checked the wiring in the junction box under the front of the trailer to see if I could figure it out. It appears that there is no way for that battery to be charged. Am I missing something?
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Old 08-22-2013, 09:18 PM   #2
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With electric brakes you have a 12 v line from the tow vehicle that should keep battery charged.
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Old 08-22-2013, 09:34 PM   #3
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My 20' enclosed has a mini charger in the battery box and gets it's voltage from the charge line going to the trailer connector. The battery is ~3.5x3x4 and is a TAP® 12-5 (12V5AH/20HR). Walmart used to carry one ~ that size. Mine won't take a charge either. Will pick one up at the start of my camping season.
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Old 08-22-2013, 09:38 PM   #4
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Quote:
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With electric brakes you have a 12 v line from the tow vehicle that should keep battery charged.
That's what I thought should happen. Looks like the trailer is not wired correct. The aux 12 v line just goes to the interior trailer lights and not to the battery + terminal.
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Old 08-22-2013, 09:54 PM   #5
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That 12 v line should also go to one of these: Tekonsha Two Stage 12 V DC Battery Charger Tekonsha Accessories and Parts 2024-07
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Old 08-22-2013, 10:49 PM   #6
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There is no way the tow vehicle will keep the trailer battery charged. Not nearly enough amps to do that and if it did supply the correct amps the small wires and long length would reduce the total amps reaching the battery. It may barely maintain it if it is fully charged already. Plugging it into shore power (for days) or using a quality battery (hours) is the only way to ensure the battery is maintained correctly.
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Old 08-22-2013, 10:59 PM   #7
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There is no way the tow vehicle will keep the trailer battery charged. Not nearly enough amps to do that and if it did supply the correct amps the small wires and long length would reduce the total amps reaching the battery. It may barely maintain it if it is fully charged already. Plugging it into shore power (for days) or using a quality battery (hours) is the only way to ensure the battery is maintained correctly.
This is a small 7ah brake breakaway battery on a cargo trailer. Not a house battery on a TT.
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Old 08-23-2013, 08:21 AM   #8
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This is a small 7ah brake breakaway battery on a cargo trailer. Not a house battery on a TT.
But same rules apply.

For those that don't know what we're talking about, the breakaway battery and switch is used to lock the electric trailer brakes in case the trailer gets disconnected from the tow vehicle. So it needs to be in good working order any time you tow that trailer.

Your cargo trailer should have a 7-pin plug. One of those pins (wires) is a constant 12-volt feed normally used to maintain the charge in the breakaway battery. The other wires in your harness are for lights and brakes, not battery charging.

My cargo trailer has that small battery, plus a black box with the breakaway switch and with the electronics to use that 12-volt feed to maintain the charge in the battery. If your trailer is wired correctly, then it should work the same way.

The 12-volt feed in your trailer wiring harness is not intended to charge a discharged battery. If your breakaway battery is discharged, use a battery tender or similar battery charger with not more than 2 amps power to charge the battery for several hours.

But like any lead/acid battery, the breakaway battery can "go bad" over time. If it gets discharged and remains discharged for any length of time, the battery will die and not be recoverable.

So if your breakaway battery is dead, replace the battery with a new one, then slow-charge the new battery with a good trickle charger that includes a "float" cycle", such as a Battery Tender. Let it "float charge" for several hours, or at least overnight.
Amazon.com: Battery Tender 021-0123 Battery Tender Junior 12V Battery Charger: Automotive

Before each trip, use a multi-meter or similar volt tester and check to be sure that battery puts out over 12.5 volts. If it's less than 12.5 volts, then use the battery tender to charge it up before you hit the road.
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Old 08-23-2013, 11:57 AM   #9
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Smokeywren,

I am confused. You said that the wiring on the tow vehicle would not charge the battery. Then, you said to use a charger with a 2 amp maximum. The lowest amp rating I could find for 12 guage wire was 23 amps. That was with the wire in a bundle and an ambient teperature of 212. Could you help my thought process?
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Old 08-23-2013, 12:09 PM   #10
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My guess is he is referring to charging a 'dead' battery instead of maintaining a charged battery.
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Old 08-23-2013, 12:22 PM   #11
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Smokeywren,

I am confused. You said that the wiring on the tow vehicle would not charge the battery. Then, you said to use a charger with a 2 amp maximum. The lowest amp rating I could find for 12 guage wire was 23 amps. That was with the wire in a bundle and an ambient teperature of 212. Could you help my thought process?
That battery is only used in case of a break-a-way. It will be maintained by the 12 v power supplied through the connection to the tow vehicle. Unless left unplugged for a long period of time, the battery charging/maintaining circuitry should do its job. The problem arrises when someone leaves the trailer unplugged so the battery is allowed to go 'flat.' It then can become incapable of being charged or safe to use. The battery should be put on a trickle charger when trailer is not used to keep it fresh. The same is true for batteries in emergency exit signs, power supplies, etc. The batteries are only good if maintained properly.
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Old 08-23-2013, 01:38 PM   #12
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Smokeywren,

I am confused. You said that the wiring on the tow vehicle would not charge the battery. Then, you said to use a charger with a 2 amp maximum. The lowest amp rating I could find for 12 guage wire was 23 amps. That was with the wire in a bundle and an ambient teperature of 212. Could you help my thought process?
It's not the amount of electricity that can flow through that wire that is the problem. The tow vehicle's electrical system limits the amount of juice that flows through the trailer plug and into the trailer. The 12-volt hot wire coming from the trailer plug on the back of the vehicle doesn't flow enough juice to charge a dead or discharged battery. You need a separate battery charger for that.

Overcharging a battery is one of the main causes of dead batteries. So you never want to "fast charge" a small battery such as that breakaway battery with 10 or 15 or more amps. Up to about 2 amps is plenty, and some battery tenders put out less than 1 amp. However, with low amperage charging the battery, it can take several house to fully charge even a very small battery.

The "float charge" cycle on the better battery tenders and battery chargers is designed to prevent overcharging of the battery. That's why you want to be sure your battery charger is the more-expensive 4-stage charger that includes the float stage.

Cheap battery chargers that don't include the automatic float stage will just keep on charging a fully-charged battery, thus overcharging and ruining a good battery.

BatteryStuff Articles | Guide to Understanding Flooded, AGM, and Gel Batteries
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Old 08-23-2013, 01:45 PM   #13
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The Tekonsha charger shown below is rated at 800 ma (.8 amp) output. About the same output as a trickle charger. It is usually in a box, along with a small battery, under the front frame of a cargo or utility trailer and the input is wired to the plug the TV plugs into and will only draw a max of 2a from the TV battery. On a 5th wheel or TT, they use the house batteries for the break-away power.

Tekonsha Two Stage 12 V DC Battery Charger

I wonder how many people with a cargo or other trailer, with a break-away box, even know they have one.
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Old 08-23-2013, 02:49 PM   #14
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Still confused.
You are saying that the tow vehicle limits the flow. Then, that should be a good thing if all you want is 2 amps.

The only reason I am asking all this is I am in the process of re-decking and re-wiring a 30 ft lowboy for the place I am volunteering at. They bought a new breakaway system and it has a built-in charger with a small lead acid sealed battery. I just want to be sure I am not blamed if the battery won't charge or if it blows up from over-charge.
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