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Old 04-13-2019, 09:36 PM   #1
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Toad Braking System Power Draw

It may be that various toad braking systems have a significant difference in current draw. The need for a charge line might be dictated by which braking system you are using.
I have an Invisibrake and it is definitely a power hog. You are supposed to keep your pull vehicle lights on as the onboard unit gets power from the taillight wires to supplement what it draws from the battery. My Wrangler was always dead after about 350 miles while running with lights on and with the main 60 amp fuse pulled.....so I began making incremental changes which never seemed to be enough.
I added a knife blade battery disconnect, but still suffered a dead battery after long days.
Then I added a separate charge system consisting of two wires from the bus chassis batteries to the Wrangler with SAE connections at both vehicles, and a fuse close to the batteries on both vehicles as well. I ran 14 gauge, influenced by the 'fact' that the taillight circuit is supposed to be enough to do the job. This worked a lot better until I pinched the wires and flattened my battery yet again. With wires repaired we went on another long run and the battery was very weak after 500 miles or so. It actually wouldn't charge well from the Wrangler alternator as it was fatally wounded from getting flattened so many times over 2 years.
So, with a new and never abused battery, and my battery disconnect, and my properly repaired charge lines, and running with lights on... I am hoping I've finally gotten this sorted out. Our short trip in May won't prove much but I will record resting battery voltage before and after the tow. The real test will come in late June and through July with several very long days on the road.
If I learn anything of interest I'll post about it. Meanwhile, I wonder if other electric brake systems have lower power requirements. This is one area where a surge brake system is superior.
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Old 04-22-2019, 06:01 AM   #2
CCW
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I appreciate the information. Seems Ive got to continue to try alternatives. Was thinking about a portable charger from Harbor Freight. Plug brake system into that and not draw on dinghy.
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Old 04-22-2019, 12:45 PM   #3
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I found my old battery charger and am going to carry it with us, in case the various minor improvements I've made don't get things resolved. I did find one other item. My charge lines were pinched off which explained one flattened battery. I didn't have my soldering gun so simply twisted the wires together and squeezed them hard with pliers and taped them up. Yesterday I took it apart and properly soldered the connections. Resistance of my ~8 feet of charge wire was 2.8 ohms. After soldering, I'm getting 1.6 ohms, so that should help. I really hope the charge line plus battery disconnect plus pulling the 60 amp fuse plus running with lights on so the invisibrake gets juice from the taillights is enough for long travel days.
If that's not enough, I guess I'll have to run the jeep at every stop and throw the charger on it at night. I could maybe replace my charge lines with a larger gauge wire as well.
We have a fairly short trip in May and I'm going to record the Wrangler's resting battery voltage, plus what it's showing when hooked up with the bus running. It really needs to be a net higher voltage or there's something else wrong that I'm overlooking. Then I'll check the resting voltage after we get set up at camp, hoping to see the same voltage as before travel.
Our next long trip is in late June and throughout July. I'll get all the readings for several long travel days and hopefully see resolution.
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Old 04-22-2019, 02:03 PM   #4
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i simply use the 12 volt feed off the 7 pin connector from the rv, and this feeds a dedicated 10 amp line to keep the battery charged while its plugged into the power cord

no need to disconnect battery
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Old 04-22-2019, 05:05 PM   #5
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I wonder what brand/type of braking system you have? I suspect it's not the same as mine, and maybe uses a whole lot less energy? I have the same as you, a charge line. I could have run it through pin 7 but decided I also wanted a dedicated ground line 'to be sure'. It hasn't done me much good so far.
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Old 04-25-2019, 06:15 AM   #6
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I use and RVI Brake unit. I have traveled for 8 hours solid and the Jeeps battery was fine when we got to our destination. I also have an RVI Battery charger, that I have not hooked up yet. It's installed and the wires are run from the Chassis battery to the 7 way plug, but I haven't felt the need to hook it up yet.

Did I read that right? Your brake system gets power from the rear tail light? The RVI gets it's power from a 12v outlet. How does your break away work?

I like keeping things simple. I ran #10 wire from the coaches chassis battery to an unused pin on the 7 way plug. On the Jeeps 6 way round plug, I used an unused pin to supply power to the battery charger. No extra wires running that could get smashed, pinched or shorted. 20 amp self resetting breakers on both ends. Also, you may want to consider using a switched power source, so that when you turn the key off in the coach, you kill the 12 volts to the plug. I will have to unplug the Brake unit, when we stop overnight.
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Old 04-25-2019, 07:00 AM   #7
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Your assumptions about the Invisibrake are actually not quite correct. The unit gets its main power from the TOAD battery. It gets its braking signals from the left and right TOAD brake lights, which are powered by the tow vehicle through the 7 way connection.

If you keep the running lights on, the Invisibrake will use that 12 volt power to "trickle" charge the TOAD battery from the tow vehicle running light circuit.

Actually the Invisibrake itself is not that big a draw as it only runs it compressor and vacuum pump when braking is occurring. This is not that big a load. The logic circuits use negligible power when running and most installations do not even bother to turn the unit off when not connected to the tow vehicle.

The power draw that most of us experience is directly related to what other circuits are left powered in the TOAD. On my Buick Enclave, you are supposed to remove multiple fuses when towing. Turns out this is because of all the stuff that is left running with the transmission in neutral and the key in the ACC position. Rather than removing the fuses I ran the 12 volt charge line from the tow vehicle through the 6 pin and through a 20 amp breaker and direct to the TOAD battery.

Never...ever...had a problem. Have to remember to turn off the auto headlight switch on the TOAD. Not for power draw but it is kind of embarrassing when driving down the road after dark to have the TOAD headlights come on and illuminate the rear of the coach!

Love the invisibrake...nothing to do...just hook up and go!
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Old 04-25-2019, 10:28 AM   #8
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Thank You Messrs. Poland and Brownstein,

As usual, I struggle to communicate with clarity. Indeed, per the Invisibrake instructions, you are to tow with your MH lights on. Properly installed, the taillight wiring provides a trickle charge to the Wrangler battery, and the battery in turn is the source of power for the Invisibrake unit.
I am grateful for your posts. I'm coming to believe I have issues with the Wrangler wiring. Not necessarily a fault or flaw, but my Wrangler is one of the rare ones which require the key being 'on' to prevent the steering from locking.
I started out pulling the main 60 amp fuse, and then migrated to pulling the main 60 amp fuse and a certain other 10 amp fuse that energizes part of the dash. Even doing this my battery wasn't keeping up, so I added the battery disconnect. This helped one thing. Finally the Wrangler quit clocking miles while being towed (even with fuses pulled).
I'm going to review the Invisibrake wiring installation for errors, and then I'm going to look at disabling the steering wheel lock. Even with the battery disconnected, there is still some juice getting to parts of the dash when I turn the key on. The only wires on the 'hot' side of the disconnect are the power wires to the Invisibrake and my extra charge wires coming from the bus. The Invisibrake wiring must be providing a power source to things that don't need it.
It might be less trouble to disable the lock than to chase down the wiring. Oh, for clarity, I have two dedicated taillight bulbs added to the taillight fixtures, powered only by a signal from the Invisibrake, so the factory lights are completely out of it, no diodes.
Taking the key out of the equation is looking to be worth the hassle.

Thanks again!
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