brakes controller 103 or circuit 101

Diode bridge or bridge rectifier

A breakaway switch and battery is required equipment on any trailer required to have brakes, generally anything over 2,000#.

The 7 wire RV type trailer connector has a defined pin for a charge connection to the trailer. This is used to charge batteries for winches mounted on trailers (hint) or in some cases to charge the breakaway battery. This is normally a 30A charge feed.

A diode will introduce a voltage drop, reducing the maximum voltage that can be applied to the trailer brakes and thus the maximum braking they can provide. I don't recall seeing any trailer brake controllers that stated they wouldn't survive breakaway switch activation if they were connected. If that is the case, make sure that your 7 way connector will pull out before the breakaway cable will will activate the breakaway switch.

Isn't the drop on a diode just a couple mili volts?

I'll want to test the breakaway system by pulling the pin with the trailer connected and pulling ahead with the truck. There is a warning in the controller manual about this causing damage. At least once in the next 20 years somebody will forget and back feed it.

Karl

.600V I believe.

Don't know what to say on this one. If it was a common problem, standard breakaway switches would be SPDT and disconnect the line from the brake controller before applying voltage from the breakaway battery.

I don't recall reading any similar warning for the factory integrated brake controller in my F350. Nope, just read the manual and there is no warning about damage from activating the breakaway switch when connected to the brake controller, indeed it indicates that the brake controller will report "Trailer wiring fault" if it sees this condition.

A lot of trucks don't run the lights in order to power the brakes. If the trailer drops off the truck - power must go with it if power sets the brakes.

Mart> I've got a system to lock up the brakes if the trailer comes off. >

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Yep -- "full-wave bridge rectifier"

Enjoy, DoN.

Nope! More somewhere between 0.600 and 0.700 V depending on various factors. This is assuming silicon diodes, not the much less common germanium ones, which are about 0.150 V, and the even older selenium ones whose forward voltage drop I don't really know.

Enjoy, DoN.

0.6V to 0.7V is about right for signal level and switching silicon diodes. Power rectifiers tend to be a bit higher, e.g. this commodity 15-amp bridge that drops 0.8 volts (per diode) at 1 amp and ~1 volt at 10 amps: Schottky silicon diodes are a different story, not germane here.

On Sun, 14 Mar 2010 01:09:56 -0600, the infamous Don Foreman scrawled the following:

Right, not geranium, my dear Zener.

I'm no EE, but most of the bridge rectifiers I've seen in the past 40 years have been black plastic with a black tarry encapsulation. Those tin guys must be old, or a lot pricier than I'd seen before.

-- I must study politics and war that my sons may have liberty to study mathematics and philosophy. My sons ought to study mathematics and philosophy, geography, natural history, naval architecture, navigation, commerce, and agriculture, in order to give their children a right to study painting, poetry, music, architecture, statuary, tapestry, and porcelain. -- John Adams

If it is tin, they are probably early Japanese parts. A cast aluminum case is common for the 25 A versions to bolt them to a heatsink or chassis.