I fitted some parking sensors this weekend to my 2005 motorhome, a straight forward job, or so I thought.....
I bought a wireless set off e-bay so sensors and control box in the rear of the van, with power to the unit coming straight across the reverse bulb, and in the front of the van the receiver wired up to some aux power point. However, having wired them up in this way they didn't work After many hours of trying to work out why they don't work, I've given up for now to try and find some direction from somebody.
When I connect the control box directly to the battery it works fine, maybe an earth problem I thought but I've checked the earth on the reverse light to an earth at the front of the van an only have 0.7 ohms, so that looks OK. I also connected the earth of the control unit to the earth of the reverse lamp and the 12v to the fuse box and still worked OK. Maybe insufficient current getting to the control unit, so I connected the unit back across the reversing light and measured the current (without the bulb) and that was 32mA, so again looks OK.
Now only thing I did notice was that across the bulb I'm only measuring 10V when the engine isn't running, suggesting the battery voltage is low, but at the engine end I'm getting 12V. When the engine is running I get 12V across the bulb, and the van starts on the button every time, so I don't suspect the battery. Now I know the parking sensor run down to about 8V as I tested them on the bench so it's not that either.
So what am I missing? The parking sensors don't work when connected to 12V across the lamp, but do work when I power them directly from the battery. I know I could connect them to a battery and put a switch in line to turn them off when driving forward, but that means running wires the length of the van which I don't want to do. Can anybody put some new light on where I'm going wrong.
Mike
I bought a wireless set off e-bay so sensors and control box in the rear of the van, with power to the unit coming straight across the reverse bulb, and in the front of the van the receiver wired up to some aux power point. However, having wired them up in this way they didn't work After many hours of trying to work out why they don't work, I've given up for now to try and find some direction from somebody.
When I connect the control box directly to the battery it works fine, maybe an earth problem I thought but I've checked the earth on the reverse light to an earth at the front of the van an only have 0.7 ohms, so that looks OK. I also connected the earth of the control unit to the earth of the reverse lamp and the 12v to the fuse box and still worked OK. Maybe insufficient current getting to the control unit, so I connected the unit back across the reversing light and measured the current (without the bulb) and that was 32mA, so again looks OK.
Now only thing I did notice was that across the bulb I'm only measuring 10V when the engine isn't running, suggesting the battery voltage is low, but at the engine end I'm getting 12V. When the engine is running I get 12V across the bulb, and the van starts on the button every time, so I don't suspect the battery. Now I know the parking sensor run down to about 8V as I tested them on the bench so it's not that either.
So what am I missing? The parking sensors don't work when connected to 12V across the lamp, but do work when I power them directly from the battery. I know I could connect them to a battery and put a switch in line to turn them off when driving forward, but that means running wires the length of the van which I don't want to do. Can anybody put some new light on where I'm going wrong.
Mike