Electric Brake Voltage Drop

Willdoe · Member

Electric Brake Voltage Drop

hako · Guru

I'd reckon that's about the same as mine and I'm guessing the brake figure is with brakes fully on so the controller is feeding full power down the line. Maybe polish/expand the pins on plug for service brakes and earth but you've probably done that already.

Good Luck

patrol03 · Senior Member

Your voltage at the magnets when stationary will always read very low. The reason for this is that your brake unit is stationary. When on the road it senses + or - variations in motion and produces the appropriate voltage when the pedal is operated to cope with the situation. Full brakes..full voltage depending on your personal settings on the unit. Hopes this helps your situation. Ian

Willdoe · Member

Ian, Thanks but I believe I have line losses due to resistance in the system which can come from undersized wiring circuit or bad contacts. I was wondering if my losses were within normal range.

My understanding the power from the brake pedal is not a variable depending on how hard we press on the brake, it is either on or off. When braking power from the brake pedal switch is available and the controller has an output proportional to the deceleration inertia.

Alternatively the override can be used to apply a variable output to apply van brakes without applying the towing vehicles brakes.
I tested while stationary. Pushed the override lever over fully - Controller Output indication 4.8V and at brakes terminals 3.6V,- a 1.2V loss.

swamp · Senior Member

Hi
Ideally brake feed would be 8mmsq / 8B&S cable
brake current draw 6-8 amps typically and 10 amp absolute max for 1 axle of 10 inch drum brake

Around 9mtr of cable
In your case 5mmauto ==2.9mmsq WAY SMALL !!!!!!!!!!!
volt drop 1.1 volt

same spec
with 6mmauto ==4.5 mmsq
volt drop .65 volt

same spec
with 8mmsq // 8B&S
volt drop .38 volt

Brake Magnets are 12v dc nominal

In a perfect world 8mmsq but 6mmauto ok

That's for a single axle braked ,,,, a twin axle 4x braked is different

A LARGE EARTH MUST BE USED THRU OUT TRAILER INCLUDING THE BRAKES

A brake earth must run thru t/plug onto controller earth wire then to battery terminal and CONTINIOUS !!!

Teknoshia recommend 10AWG or 5 mmsq cable min

-- Edited by swamp on Friday 2nd of February 2018 08:51:06 PM

-- Edited by swamp on Friday 2nd of February 2018 08:52:21 PM

Aus-Kiwi · Guru

Depends on how the brake system works ? Our new one has initial voltage then as controller senses retardation it ramps the voltage up applying more brake . It has a voltage LED voltage display . Brake pedal only activates the system .

swamp · Senior Member

Hi Kiwi

That's how the Prodigy works .
Controller starts to regulate once brake pedal depressed
Variable Volts regulated as a result of variable vehicle inertia when braking
Higher than 0 volts when brake first applied is called boost function by teknoshia .

regards

Aus-Kiwi · Guru

^^^ Thatâs it ^^^

dorian · Guru

AISI, the actual voltage drop is 3V.

         40% duty cycle


   .-.  .- 12V           .-.  .- 9V
   | |  |                | |  |
   | |  | 4.8V avg  -->  | |  |  3.6V avg
   | |  |                | |  |
 --' '--'  0V          --' '--'  0V

 at controller         at brakes


Edit:  The OP is not measuring the voltage drop per se. Instead he is measuring the average voltage
drop. For 40% of the time the voltage drop is 3V, while for the other 60% it is 0V.

If you can stomach the legalese in this plurality of embodiments, you'll find that they all employ
pulse width modulation (PWM) to drive the brake solenoids. This means that the solenoids are
being switched on and off rapidly, with a varying duty cycle.

http://www.patentgenius.com/assignee/TekonshaEngineeringCompany.html
http://patentimages.storage.googleapis.com/pdfs/US5050937.pdf (brake controller)
http://patentimages.storage.googleapis.com/pdfs/US3909075.pdf (brake controller)
http://patentimages.storage.googleapis.com/pdfs/US6068352.pdf (Microprocessor-based control)
http://patentimages.storage.googleapis.com/pdfs/US6626504.pdf (Tekonsha BRAKEbuddy)
http://patentimages.storage.googleapis.com/pdfs/US7504920.pdf (Tekonsha magnetic brake assembly)

The patents beginning with "D" are "ornamental designs", ie just the boxes, not the electronics.

http://patentimages.storage.googleapis.com/pdfs/USD468705.pdf

-- Edited by dorian on Saturday 3rd of February 2018 06:26:53 PM

Flame Man · Member

After a recent brake service I found at full power on the vehicle Redarc brake controller, 8.6V at all four electric magnets, virtually no brakes on the caravan, decided to check the wiring and found the negative return wire (3mm auto size) grossly inadequate in both the caravan and vehicle, I have since upgraded all the brake wiring to 6mm and now get 10.2V at the magnets which means I now have much better brakes on the caravan but not ideal ( 12V at the magnets) The reason it is not ideal is because the Redarc controller output at source is only 11V which makes it impossible to achieve 12V at the magnets.

With this in mind I have installed a Dexter stability controller in the caravan which uses the house battery (14V) in the event the caravan starts to sway, emergency braking.

This has been a real eye opener for me when you consider that both the vehicle and caravan (2016) were wired by professionals and their actions put me and my familys safety at risk, I am sure this is not an isolated case.

Whenarewethere · Guru

Brakes, solar, battery, fridge, all wiring is too thin to save money.

Often the total length of + & - is not calculated in the total length of resistance & one's precious volts & amps simply going too waste.

Flame Man · Member

The point I was trying to make is brakes are a safety issue unlike solar or fridge wiring and when we need to rely on our brakes in an emergency situation you would expect them to work, mine did not and I had no idea they were ineffective, at least I found out before we had an accident, I just hope other caravan owners are aware of the issue.

PeterD · Guru

What you have to remember is that motor vehicle wiring is not substantial in sizing. The auto systems are designed with a bit of voltage drop in the system. You should be able to get good braking with 8 V at the magnets.

Flame Man · Member

PeterD wrote:
What you have to remember is that motor vehicle wiring is not substantial in sizing. The auto systems are designed with a bit of voltage drop in the system. You should be able to get good braking with 8 V at the magnets.

What I found is with 8.6V at the magnets I could rotate the wheels by hand with the wheels jacked up and new magnets installed.

I would say the minimum is 10V under normal braking and ideally 12V under aggressive (emergency)braking, which is why I installed the Dexter system.

PeterD · Guru

William, One of the caravan service people I used way back used 4 cells of a 12 V battery to check the brakes on vans he had serviced. When someone spun the wheels and the tester was turned on the wheel under test would comet to a very abrupt stop. The battery was often not very well charged when he was testing.

Flame Man · Member

PeterD wrote:
William, One of the caravan service people I used way back used 4 cells of a 12 V battery to check the brakes on vans he had serviced. When someone spun the wheels and the tester was turned on the wheel under test would comet to a very abrupt stop. The battery was often not very well charged when he was testing.

Peter, what you described is a functionality test, ( on or off) the wheels will behave differently under the full weight of the caravan when the brakes are applied. The point I am trying to make here is the magnets need 12V to be fully effective and at 8.6V they are totally ineffective. After oversizing the cables I still only got 10V at the magnets, (mainly due to the voltage drop across the Redarc) which in my view is inadequate in an emergency braking situation. I have since installed a Dexter stability control unit which uses the caravan house battery instead of the the vehicle battery in an emergency braking situation, which should give full 12V to the magnets. ( I have no affiliation with Dexter) I just wonder how many caravan owners are unaware their caravan brakes are only partially effective and under emergency braking totally ineffective.

PeterD · Guru

Flame man, you are wrong. With 8 V or less on the tester the service people do not just look to see if the brakes will grab. They look to see how abruptly the wheel rotation ceases when the brakes are applied. Also remember that when they spin a wheel it is turning slower than when you are travelling on the road. At slow speeds the friction of the magnets provides more stopping than when you are at travelling speed.

I am not familiar with voltages with my current Redarc controller but is have done some serious testing with the Tekonsha Prodigy. Also when I test the brakes I use an analogue meter rather than a digital model. With the Tekonsha set to lock the brakes up the measured voltage when you operated the thumb controller was 7 V at the trailer plug. If your brakes toke a full 12 V to get good operation then I suggest you take them to someone who knows how to fix them.

Flame Man · Member

PeterD wrote:
Flame man, you are wrong. With 8 V or less on the tester the service people do not just look to see if the brakes will grab. They look to see how abruptly the wheel rotation ceases when the brakes are applied. Also remember that when they spin a wheel it is turning slower than when you are travelling on the road. At slow speeds the friction of the magnets provides more stopping than when you are at travelling speed.

I am not familiar with voltages with my current Redarc controller but is have done some serious testing with the Tekonsha Prodigy. Also when I test the brakes I use an analogue meter rather than a digital model. With the Tekonsha set to lock the brakes up the measured voltage when you operated the thumb controller was 7 V at the trailer plug. If your brakes toke a full 12 V to get good operation then I suggest you take them to someone who knows how to fix them.

Peter, we obviously have two completely different experiences, if I am reading your comments correctly at 7V the brakes will lock the wheels up, that is approximately half the amps and half the grabbing strength of the magnets.
Just to be clear I now have 10V (2.8A) at the magnets which has improved the braking considerable, I just believe their is more to be gained by having the full rated 12V (3.1A) at the magnets, especially under aggressive braking when the full weight of the van is acting on the wheels.

PeterD · Guru

Flame man, the only way you will get anything near full battery voltage out of a brake controller is if you have the gain control wound right up to maximum. Normal operation generally has the gain control down around half way. If you are operating with your brake controller on maximum there is something wrong with your brakes.

Flame Man · Member

PeterD wrote:
Flame man, the only way you will get anything near full battery voltage out of a brake controller is if you have the gain control wound right up to maximum. Normal operation generally has the gain control down around half way. If you are operating with your brake controller on maximum there is something wrong with your brakes.

The Redarc Pro is a proportional brake controller, the start position for the van brakes is set by a manual controller set from 1(min) to 10 (max) I have mine set at 5. (Approx 6Volts)The Redarc will automatically increase the braking from the start position to maximum (12Volts) depending on how aggressive the vehicle braking. It also has a manual bypass button which puts maximum power (12Volts) to the brake magnets if pressed.

The issue discussed here in my original post and subsequent replies is the maximum power the Redarc puts to the magnets in reality, my original maximum was 8.6V and is now 10V after upgrading the wiring. The point being it should be 12V as per the spec of the Magnets. In an emergency braking situation where maximum power is applied to the brakes if all the magnets get is 8.6V the rig will take a longer time/distance to stop, obviously 10V is better, in my view I want to be sure that full power is available to the magnets in an emergency to give me the best chance of stopping in time, with the Redarc 10V is the most I can get as explained earlier, which is why I also installed a Dexter unit which works of the van battery.