Testing Electric Brake at Tow 7 Pin Connector - Page 2 - Fiberglass RV
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Old 11-09-2019, 05:47 PM   #21
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Name: John
Trailer: Black Series HQ19
Smith Valley, Nevada
Posts: 2,386
Sometimes, as strange as it seems, the frame is used as the conductor and the trailer is grounded through the ball. This means the braking current must be conducted through the ball and stinger, which is a very poor path. If that is the case here, it is likely a problem. A cheapo fix, just to get you home, is to place a piece of steel wool in the coupler before setting it on the ball, to improve the electrical connection. The brakes should be grounded to a frame grounding lug and bonded to a negative wire from the battery, or ground buss, at the same point. The trailer should have a negative conductor from the seven pin to the battery, or battery ground bus. Grounding through the ball was a problem on earlier Oliver trailers and they would not charge from the tow vehicle. That setup, in some cases, gave a warning on the brake controller. I fixed two of them and talked to Oliver. They simply told me the trailers were wired to "industry standards" and that that method was normal! This situation can be easily diagnosed by disconnecting the trailer from the ball, while leaving the seven pin plugged in. Start the tow vehicle and check the voltage at the battery. If it is charging it will go from about 12.5 up to over 13 and on up to over 14. If not, look for the negative wire in the seven pin. Or, connect a battery jumper cable from the car frame to the trailer frame and see if it then begins to charge. If so, you need a negative wire from the seven pin to the battery or negative buss.

New brakes, or recently replaced brakes will need to get worn in before they will be very strong. On both my Oliver and on my Black Series, the brakes were so weak I was convinced there was a problem. Just last week, when I picked up the new HQ19, I worked to break them in by applying only the trailer brakes while coasting, over and over, and to slow the rig on down grades. I did this hard enough to definitely wear them in, but not so much as to glaze the shoes or overheat them. Then I left the controller on the highest setting until they began to get stronger. When they began to get pretty aggressive, I reduced the setting gradually to keep them from skidding, until they finally, after about 1,200 miles began to work like I would consider "normal".

There is no need to pull the drum off to check the magnet. Just jack up the wheel, and while spinning it, have someone apply the brakes. The magnet will begin to drag and the brakes will either apply, or they won't.

If you do take the drum off, note which way to turn the adjuster to tighten them up. Then, with the drum back on, you can adjust them without trying to look through the adjusting slot. New brakes, or ones in need of adjusting will take about twenty or more strokes with a brake spoon to bring them up to proper adjustment.

Brakes that need adjusting will become weaker and weaker. This can seem like something has failed, or the magnet is weak, but it's just that they are out of adjustment. And after adjustment, there may be another short breakin period.
I only exaggerate enough to compensate for being taken with a grain of salt.
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Old 11-13-2019, 12:33 PM   #22
dfandrews's Avatar
Name: Don
Trailer: 2015 Escape 17A
Posts: 67
FYI: Dexter brake magnets (per the Dexter Manual) have the following specs:
for 7" X1¼ size brakes: 2.5 Amps per magnet; 3.9 magnet Ohms
for 10" and 12" size brakes: 3.0 Amps per magnet; 3.2 magnet Ohms
Don & Teresa
Tow: 2011 Honda Pilot
Trailer:2015 ESCAPE 17A
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Old 11-13-2019, 02:15 PM   #23
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Name: Stebe
Trailer: Casita
Posts: 28
Test the wiring with one of those light bulb style connectivity testers. A voltmeter requires almost no current to measure the correct voltage if the wire has become highly resistive.

The copper wire on my brake line corroded to blue dust. When I measured it with a voltmeter with an internal resistance of megaohms it looked good and measured the correct voltage. The resistance of the wire was such that you could not drive more that a small amount of current therefore my brakes did not work.
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Old 11-13-2019, 03:17 PM   #24
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Name: Wayne & Barbara
Trailer: Parkliner
Posts: 1,168
Voltage in electrical circuits can be compared to Pressure in a home water system. The pressure/voltage will be highest when there is no flow of water/electrons.
Amperage is a measure of FLOW. When there is RESISTANCE (measured as OHMS) in the wires, they get hot. Wires, & connections, must be sized for minimal resistance to avoid heat.
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