Thule electric slide out Omnistep

[Yewhedge]

Hi,

Recently did some modifications to my fridge power supply and have new frustrating issue with my electric step. Hope someone can help?

 

My Thule slide out electric step automatically retracts when the ignition turns on (It has the 5 pin relay with the 2200uf capacitor. There is also a 4-pin relay before this one which has the ignition signal as a switch).

My problem:

When I switch on the ignition the step will retract fully as normal BUT instead of the power supply being cut, it seems to continue to be powered as I hear the motor making noises and a kind of clicking/switching from the step itself.

What have i done so far?:

- I had rewired my fridge so that I could take a 12v feed from the van battery instead of leisure battery. And took an ignition signal from the ignition relay for my electric step (this is the one before the 5 pin THULE step relay) running this to a new relay for the fridge. Whilst doing this work I disconnected from the van battery the earth wires used to power the electric step. Could this have blown something? the capacitor on the electric step relay?

- I have removed the step and checked the limit switch, I tested it with a light bulb and battery and it works fine.

- I tried to test the capacitor on the 5-pin electric step relay, in situ, using my multimeter. I got a constant reading of 81 ohms, not sure if this tells me anything?

 

Any help or ideas gratefully appreciated. thank you all.

 

[Alanb]

A standard Omnistep has 4 wires. The orange and purple connect to the motor, with grey and brown wires, which are interchangeable, being connected to the limit switch. The motor rotates in opposite directions, according to the polarity of its supply, as applied to the orange and purple wires.

 

The manual operating switch, which is in actual function two separate single pole changeover switches, is connected so that both of the motor wires are connected to earth with the switches in the normal unoperated state.

 

If the step "out" button is pressed, the purple motor wire is connected to +12V, and the step is driven outwards. Conversly when "in" button is pressed the the orange wire is connected to +12V, and the step retracts.

 

When the auto retract facility is added, the changeover contact of a relay is inserted into the orange motor wire, with the common contact (30) connected to the motor. The normally closed contact (87a) of the relay is connected to the switch terminal that would have been connected to the orange wire.

 

The normally open contact (87) of the relay is connected to a +12V supply. When the relay coil is energised i.e. the relay is operated, the step motor orange wire is disconnected from the manual switch, and connected to +12V. The step is is moved inwards.

 

The connctions to the relay coil should be coil +ve (86) to controlling source, such as ignition +ve, or D+. A connection to the +12v supply to a 3 way fridge element is often used for this supply. The negative terminal of the relay coil (85) needs to be connected to earth via the step limit switch. (Brown & grey wires). When the limit switch is operated, it opens the circuit for the relay coil and when the relay releases, both connections to the motor are connected together, which brings the motor to a halt.

(I am not aware of it being done, but with steps having an internal switch (2 wires), it should be possible to connect the limit switch in the relay coil positive connection.)

 

In order to ensure that the step fully retracts after the limit switch is operated, a 2200 mFd capacitor is connected across the relay coil. This capacitor slightly delays the release of the relay, and allows the step to drive fully home. As the capacitor is electrolytic, it must be connected with the correct polarity.

 

Given the symptoms described by the OP, I suggest checking that the step limit switch is correctly connected in the relay coil circuit, and also that the capacitor is connected across the relay coil in the correct polarity.

 

It is not really practicable to fully test a capacitor on a multimeter resistance range. You would need to apply the test leads with the correct polarity, and at best you may see an apparently increasing resistance reading, as the capacitor charges, and the current flowing into it decreases.

 

Yewhedge,

 

For the benefit of others, please post your eventual result.

 

Alan

[Yewhedge]

This problem is now resolved. My van is built by Moto Trek and this is the 4th electrical issue identified with it. The company are un-responsive to requests about the electrics. The standard response is that the electrics must have been modified after manufacture, haha!! They are not willing to send a wiring diagram for my build either and the technical team do not reply once detailed questions are posed.

This step wiring, like the other problems, had been there since new. Basically the 2 relays were incorrectly wired since they were installed by the technicians at Moto Trek who clearly were not very skilled. The problem is that these issues take a long time to identify.

Attached is a diagram of what they did:

They had connected an earth lead between the pin 86 of the Thule/Omnistep 5-pin step retract relay (the pin that has the limit switch for cut off) and the pin 85 earth pin of the ignition retract relay (for auto retract). This resulted in the limit switch being ineffective as it could never cut the power when fully retracted.

Thanks to Alan for his expert knowledge.