Reversing Brake Release Solenoid Back EMF Problem

[Hardcrab]

Boblee,
This counter EMF (Electro-Motive Force = Voltage) challenge isn't a problem with the older vehicles and other electrical stuff mostly because mechnanical switches and relay contacts are used to make and break the various circuits. When you "opened" those type circuits by throwing a switch, there was no electrical path for the coils counter EMF to travel anywhere. This fact should not be underestimated.

Now, many power circuits are controlled by "switching transistors" or "drivers". These are turned on or off so as to "imitate" a mechanical switch or contact. But unlike mechanical switches, these transistors are never really "out" of the circuit. There lies the problem. The counter EMF generated by all de-energized coils can become quite high, which can exceed the reverse voltage breakdown point of the controlling transistor. This can cause the transistor to keep conducting even though the rest of it's controlling circuit is telling the transistor to shut off, or even cause the transistor to simply "fry".
They will quit working when you let the smoke out of them.

Hence the shunting diode across the coil.

As far as your thinking about higher rated diodes and surge devices being useful is missing the point I tried to make earlier. A correctly installed parallel shunting diode does not conduct voltage to ground at all (ok,microvolts) during the normal operation of the circuit. The diode is "reversed biased" to the positive feed voltage from the circuit. The diode will only conduct to ground , in this application, when the feed voltage becomes negative, eg. when the coil becomes de-energized and the magnetic field collapses causing the voltage polarity to reverse itself. Then, the negative polarity voltage coming from the coil sees two paths to take. One is the relative high resistance of the control circuit, and the other is the relatively low resistance path through the diode. Electrons will take the path of least resistance. That is how and why the shunt diode works and protects the transistor based control circuit

baldbaby2000,
IMHO, you bring up moot points. A diode wired in series will really do nothing constructive for this circuit. So breakdown voltages or generated heat won't matter at all.

[opie]

I see no reason to use a reverse lockout solenoid. I disconnected mine.
1. If the solenoid wire ever short out, your brakes will grab and that could mean trouble if moving.
2. When you back up (not often in my case, usually only at the ramp) stick the lockout pin in the brake actuator. Keep the pin in since you will need it again at pull-out time at the ramp. Use a red flag on it so that you will reinsert it before going home from the ramp.
3. Backup switches in the lighting circuit sometimes are intermittant and that will cause the embarassing bucking-bronco trailer dance when the brakes are not locked out when backing up. The pin is never intermittant.

Really, what is a good reason for the solenoid? Can anyone convince me to reconnect it? I like to get out and disconnect the lights anyway, just to be safe. They say "waterproof" but why test them? It is good to get out of the vehicle and check the rear of the trailer anyway for ladder-down and motor position, etc. I like also to make sure the fill-valve is closed so that I get the best float-off possible of the boat off of the trailer bunks.

[Hardcrab]

Opie, (cool name)

Jeez, I'm not a professional trailer engineer or anything, but I have learned electronics being gainfully employed in the electrical/electronic field some 35 odd years. With that said, and not to offend or leave anyone confused and lost about this issue, I would like to offer a different opinion on points 1 and 3.

1.
The "solenoid wire" is powered from the tow vehicles back-up lights.
As long as the tow vehicle is not in reverse, (back-up lights extinguished) this entire circuit is dead. Nada. The surge brake itself is free to operate as determined by trailer inertia.
If by some chance the solenoid wire were to short to ground, the response would be a blown fuse in the tow vehicles back-up light circuit when the shift into reverse was first attempted. The surge brake would still be free to operate.
It would be hard to imagine how this can be related in any way with the tow vehicles hydralic brake system. Of course, anything else powered by that fuse would quit also.

3. While in theory you are completly correct, the frequency of such an event is perhaps minimal. Besides, it would be a tow vehicle malfunction not a trailer malfunction.

I agree with your point about the waterproof light statement. But for me, rather than mechanically locking-out the brakes with the pin, I split the trailer harness to have a "lights" connection and a separate "surge brake" connection. When I launch, I have the solenoid locking feature fully operational while in reverse and yet the trailer lights are not connected. For me, that means never forgetting to leave the pin installed for trips on the road.
It's not "standard", but I'm happy with it.

Smooth sailing to you.

[Oskar 26M]

Hi all. Having started this thread, I thought I'd better return with an update.

After reading all of the helpful information from Hardcrab and Hamin'x I rewired my trailer with the diode ACROSS the solenoid as they described (ringed end connected to the solenoid feed wire, other end to the casing of the solenoid and the common ground on the trailer/tow vehicle). I decided to forego the relay, said a few prayers to Neptune and whatever other gods might play with boat trailer electrics, and plugged it in. It worked, and so far the Toyota (now a Land Cruiser) has controlled it all perfectly.

I now have the same arrangement as Hardcrab described - all lights are removable and the only thing connected from the trailer to the tow vehicle when launching (today) will be the solenoid.

I can confirm that placing the diode in series idea doesn't work. In my ignorance, that is how I installed it originally and fried Toyota relay box number two.

I've found that the lockout pin on my brake actuator works but only partially. It stops the brakes from completely locking up in reverse but has sufficient play to allow the brakes to come on a little, making parking my trailer in the soft sand of the boat storage lot quite difficult. The solenoid release is vastly better.

The advice forum members have provided has been great. My problem appears to have been solved with an AU$ 2.00 diode placed in the correct position. Getting there cost me a AU$230.00 ($130 for a new relay box plus $100 for the Auto-electrician who put in the relay solution and an awful lot of angst.
I sure wish I'd decided to join this forum earlier!!!

Now if only UFP had thought about the diode when they installed the solenoid....

Thanks again to all who contributed

[Boblee]

Was going to disconnect the solenoid like Opie but checked out the workshop manual and there are no electronics except perhaps the flasher in the lighting circuits, there appears no hard connection to the computor except at the fusible links or battery connection.
The other relays are also isolated so there would be no need to change them to a shunt coil.
Perhaps the Kluger is a bit more urban based but having anything with circuits lighting especially that could be affected by feedback would be a recipe for disaster with the average cocky (farmer).
Certainly a point worth looking at as cars are becoming more sophisticated but delicate in their control systems.
Maybe the new Hilux's are different but ours is 2002 vintage.
I do understand shunt circuits for taking spikes out but in my primitive brain it seemed better to isolate the specific problem at the problem by sheilding it rather than allowing it to find it's own path which may or may not be secure in some environments, which I suppose is what Toyota had tried to do unsuccessfully with Oskars fancy box and his auto elec in a more practical way.
I am/was an electrical contractor for thirty plus years but except when logic control was first introduced here have not bothered to follow it up (electronics) and electrical work now leaves me cold or looking for a shrink, auto elecs and practices has me pulling my hair out.
I am sure we all have a far better understanding of the problem but if the car has a problem Opies solution appeals best especially when someone with a laptop is not handy which is my biggest fear with the Etec.

[Boblee]

thought the first post didn't work

[Hardcrab]

Oskar26M,
You are most welcome.

If you ever make it to California,
or I to Australia,
you can buy the first round of cold beers.

[Hamin' X]

Oskar, Glad that it worked out for you and happy to be of service.

Boblee: Possibly Oskar's Hilux had separate turn and brake lamps. If so, this requires either relays, or electronic circuitry to convert to the single system that most trailers use. Mostly done with electronics nowadays, as it is much cheaper than relays. My guess is that there are fewer than $5 US worth of parts in Oskar's $130 Aus box.

Rich---Hamin' X---N7ZH

[Oskar 26M]

Hardcrab and Hamin' X
If either of you do get to Australia, (I doubt I'll make it to Ca - a bit far for an M ) , come to the West and beers are definitely on me