Brake controller/wiring on the fritz

db_cooper

Prodigy P2
Factory tow package
1 successful trip 3 months ago
2015 t@b 

15 minutes into our 2nd trip today controller switched to NC, intermittently comes back for short periods at first but stopped doing that.

Stopped at my car mechanic, they checked 7 pin with volt meter, fuses under hood, checked relay box under t@b. Nothing obvious. All lights working so continuing 4 day trip.  Xterra stops good without trailer brakes so wasn't worried.

Now the weird part.  Electric brakes are definitely engaging both with brake pedal and manual lever.  Can change boost but not number setting.  

1 year old trailer, cleaned the 7 pins good tonight but no change. Next guess is brake magnets?   Probably taking it to a trailer shop next week. Friday the 13th came early for me I guess.

Anybody have this gremlin?

Nomad

Hmmmm - Betting not brake magnets unless you really shorted everything out - at least that's what I got from a trailer guy. And since the brakes are weirdly engaging, the magets are working. Betting it's either the controller or a loose wire.
By the way, the brake wire in the seven pin will show a current. Gotta test resistance. Don't know enough about voltmeters to know if you can test your controller with one. I used a circuit tester with an incadesent bulb to test if it was my controller. Bulb glows brighter as you apply the brakes. And glows not at all otherwise.

ScottG

I recently asked a similar question about using a voltmeter to assess the signal from the controller. I was told it wouldn't tell you anything other than whether you had voltage or not. Apparently the controller applies a constant voltage, but varies the signal by altering the rate that the voltage is switched on and off. Makes sense given my limited understanding of the subject. In short, the incandescent test light is the way to go.

"Weirdly engaging..." Hmmm, I've been described that way.  :-)

Nomad

ScottG - I had more friendly helpers/advisors pull out their voltmeters and declare my controller ok. Started searching YouTube and found the proper incadesent thingy method. Turned out it was in fact ok :-)

irvingj

"varies the signal by altering the rate that the voltage is switched on and off"..Ah.. that would be PCM, I believe-- pulse code modulation. Pretty sophisticated, these controllers. That's what RC aircraft transmitters use-- or used to use, anyway, to get fully proportional control.

I've never had electrically-operated trailer brakes, but that sure is different from the understanding I had of how they worked 50 years ago; cool!

Nomad

I was told it's based on resistance. Is that the same as PCM?

Photomom

PXLated said:

I was told it's based on resistance. Is that the same as PCM?

No.

db_cooper

Oops. I said voltmeter, but he also went over everything with the incandescent tester.  Hate these intermittent things.  Today it showed connected for the first 100 miles and not the last 50, but worked the whole time. If I bumped the boost it would lock iup.  Think I'll wait until it stops being intermittent before I fix it..

  

irvingj

PXLated, I stand corrected… PCM is the general form of changing analog signals (constant, "smooth" variation) into digital signals, but I suppose it would more correctly be termed PDM (pulse density modulation) or PWM (pulse width modulation), where the rate/speed, or else the duration ("width" on an oscilloscope), of pulses changes.

A strong signal (really hitting the brakes) might send a very rapid series of pulses, spaced closely together, where light pressure on brakes would send more widely spaced signals to the actuator-- at least that's my take on it.

If I'm remembering correctly, I think older electric brake systems did use resistance- essentially a very large potentiometer attached to the brake pedal that would vary voltage, most likely, to the actuator. Really old school!

See article: https://en.wikipedia.org/wiki/Pulse-density_modulation

Nomad

Well, these new ones must rely on resistance also, there's no pulsing of the bulb. According to the vids from the controller mfg for checking the controller, it's all based on resistance - At least in every vid I watched.
No brake, no glow - Slight brake, slight glow - Hard brake, bright glow.

Michigan_Mike

From ETrailer:  https://www.etrailer.com/question-22435.html

DurangoTaB

I was under our T@B before taking our first trip of the season and noticed the electric brake wiring takes a sharp turn over/through some frame sheet metal before it gets to the brake(s).  All it had to protect it from abrasion was a little electric tape...I'm wondering if that might be your short spot.  I'm going to find something more protective for the wiring.

ScottG

irvingj said:

PXLated, I stand corrected… PCM is the general form of changing analog signals (constant, "smooth" variation) into digital signals, but I suppose it would more correctly be termed PDM (pulse density modulation) or PWM (pulse width modulation), where the rate/speed, or else the duration ("width" on an oscilloscope), of pulses changes.
...

Yep, whatever it's called, that's what was described to me in a previous post. If you want to assess the system based on voltage, you need to use an oscilloscope to measure changes in pulse width. Might be fun if you have an oscilloscope lying around, but the bulb test probably works fine for most circumstances.

PXL, I suspect the reason you don't see pulsing in the bulb itself is because even "slow" pulses occur quickly enough that the incandescent filament doesn't have time to cool in between. If I understand it correctly, faster switching delivers voltage more frequently, and causes the bulb filament to glow a little brighter overall.

Now that I think about it, my lower-end Tekonsha Voyager controller has an indicator light that glows with varying intensity depending on how hard the brakes are applied. In thinking it might work the same way as that test light.

irvingj

Thanks, Scott, that's sort of what I was assuming. (Yeah, I know, "assume"….)

I did some web research on electric trailer brakes, and, as usual, found umpteen explanations of the "benefits," but no detailed explanation of exactly how they work, i.e., what sort of analog-to-digital system they use (if they use that at all-- but I'm betting they do!). It was my guess that current systems use PWM technology, but I have yet to learn what's actually used.

And yes, an incandescent bulb would show brighter/dimmer in a PWM/PDM situation, whereas a typical TVOM (voltmeter) would only show a presence --or not-- of 12VDC.

Amazing how technological innovations find themselves in vastly different applications!