12VDC vs 12VAC for GU5.3 LED Spots
- Thread starter Seb101
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John is correct. Coils are inductive devices, which can create a high reverse voltage when the current is interrupted. (This is how spark ignition coils work in petrol engined cars.)
The diagram you have shown should be fine. Use a bog standard 1N4004 or 1N4007 silicon rectifier, not a Zener diode. These are available form Maplin for about 50 pence each. Some relay coils come with diodes already connected to avoid damage to driver circuits.
Well the good news is the controller drives and switches the GU5.3 LED lamps just fine, however putting the relay in the circuit causes the controller to behave very strangely.
So I think I'm just going to have to put the extractor fan on a separate circuit with a PIR sensor or something like that, unless anyone has any bright ideas?
So I think I'm just going to have to put the extractor fan on a separate circuit with a PIR sensor or something like that, unless anyone has any bright ideas?
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I love the emergency back up lighting (candles) and PPE (cycle helmet), but I would try diode in the supply as well as across the supply to relay that may stop the relay upsetting the controller.
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Hmmm. I assume you are using the DC output controller?
LED lighting controllers adjust brightness by switching the DC supply on and off at high frequency. This may well cause a problem with an inductive load such as a relay coil.
This could easily be resolved by connecting a diode between the relay and 12 Volt supply, and connecting a small reservoir capacitor (470 μF, 25 Volt or higher) across the relay coil terminals.
This will provide a clean DC supply to the relay coil, and will prevent the relay from interfering with the LED switching regulator.
LED lighting controllers adjust brightness by switching the DC supply on and off at high frequency. This may well cause a problem with an inductive load such as a relay coil.
This could easily be resolved by connecting a diode between the relay and 12 Volt supply, and connecting a small reservoir capacitor (470 μF, 25 Volt or higher) across the relay coil terminals.
This will provide a clean DC supply to the relay coil, and will prevent the relay from interfering with the LED switching regulator.
You're going to have to describe the symptoms more precisely than that to get any useful advice....
Well it's hard to describe, just erratic, basically when the relay is in the circuit it seems to make the capacitive touch panel of the controller hyper-sensitive so that it registers a 'press' when your finger is several centimetres away and also it can't register where you are pressing.
Thanks Nigel.
I put another diode inline with the relay supply as ericmark suggested earlier and it's improved it, however the touchscreen is still a bit 'off' when the relay is active.
I will do as you suggest with a capacitor when I can get down to Maplin tomorrow and see if it solves it completely.
Cheers!
I haven't put mains through the load side of the relay yet, so as described above.
Does the touchscreen work correctly if the relay is connected to the 12V input to the controller? (Obviously this doesn't do anything useful, but it might help understand...)
Normally touch screens behave as you describe when they have some sort of unexpected capacitive connection between them and an external voltage. For example, touch-screen phones that work OK on battery might start misbehaving when connected to a mains charger - and "bad" charger designs with insufficient isolation will be worse.
In the pictures your relay is close to the mains wiring and power supply. What happens if you just move things around?
Normally touch screens behave as you describe when they have some sort of unexpected capacitive connection between them and an external voltage. For example, touch-screen phones that work OK on battery might start misbehaving when connected to a mains charger - and "bad" charger designs with insufficient isolation will be worse.
In the pictures your relay is close to the mains wiring and power supply. What happens if you just move things around?
Is the relay energised when the panel malfunctions ? Does it malfunction with the relay coil connected but not energised.
If the malfunction is only when the relay is energised then maybe the supply to the white LEDs is not able to supply the current to the relay without affecting the supply to the rest of the controller.
Typically a 12 volt octal based relay coil has a resistance of about 100 to 150 ohms. Hence the current it will take could be 120 mA ( equivalent to aprox 1.5 watts of LED )
If the malfunction is only when the relay is energised then maybe the supply to the white LEDs is not able to supply the current to the relay without affecting the supply to the rest of the controller.
Typically a 12 volt octal based relay coil has a resistance of about 100 to 150 ohms. Hence the current it will take could be 120 mA ( equivalent to aprox 1.5 watts of LED )
As I explained above, LED controllers control brightness by switching the 12 Volt line on and off at high frequency. (Reducing the voltage to an LED lamp has little effect on brightness, as (unlike an incandescent bulb) the colour temperature of an LED is constant.)
The output from the controller is effectively a square wave, which creates nasty harmonics at much higher frequencies. Adding a relay coil will result in 'ringing' every time the 12 Volt output is switched off. This happens thousands of times a second, and could be seen very easily on an oscilloscope.
HF radiation from this set up will almost certainly interfere with the touch sensitive switch, and possibly with nearby radio recovers, although the switch probably wouldn't be as sensitive once installed.
Adding a reservoir capacitor across the relay coil will almost certainly resolve the problem. (Observe polarity of the capacitor). However, don't add a capacitor directly across the controller output as this will prevent the lamps form dimming, and may damage the controller.
HTH.
The output from the controller is effectively a square wave, which creates nasty harmonics at much higher frequencies. Adding a relay coil will result in 'ringing' every time the 12 Volt output is switched off. This happens thousands of times a second, and could be seen very easily on an oscilloscope.
HF radiation from this set up will almost certainly interfere with the touch sensitive switch, and possibly with nearby radio recovers, although the switch probably wouldn't be as sensitive once installed.
Adding a reservoir capacitor across the relay coil will almost certainly resolve the problem. (Observe polarity of the capacitor). However, don't add a capacitor directly across the controller output as this will prevent the lamps form dimming, and may damage the controller.
HTH.
My impression is that this "white" output is just on/off, while the RGB outputs are variable.
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