Hello! I want to use a 8 Channel Relay to switch a small AC 230V 30W blower. The blower looks like this. I have got this blower from the scrapyard and it has no capacitor. What will i need to do to run this savely? What kind of noise suppression capacity and/or snubber can i use and how to wire it? The only thing i did was to give the relay board a seperate power supply until now.
Help would be much appreciated. TIA
PS.: i have one X1 laying around rated 0,47uF K 300v-GMF. could this be helpfull?
I have four 70W Electronic Ballasts and the blower connected to the relay board. First everything was easy fun until suddenly when the 4 ballasts were running and the fan was switching off the relay board was failing switching all channels off. (sorry bad english here?!) Arduino continued working. The power supply for the relay board is rated 5V 500ma and the relay channels peak consuming 80ma each. So i wonder what the problem is.
Ps.: Also it is hardly reproduceable. It works fine for hours switching the blower every 5 minutes or so while all the ballast are under load. then again suddenly it fails.
Are you certain the Arduino continued working? Unlike the Arduino, a relay board will not lock up due to a transient. If the Arduino really did continue working normally, then I suspect you have a bad connection, or your 5V supply to the relay board cut out because of the transient. You could connect a multimeter to the relay board supply and see what happens to the reading when the problem happens.
i have one X1 laying around rated 0,47uF K 300v-GMF. could this be helpfull?
Assuming that 300V is a DC rating, then no. Capacitors used for snubbers must be rated for an AC voltage somewhat higher than your mains supply. so look for a rating of at least 300VAC. However, 0.47uF is in the right ball park for a snubber capacitor. Connect it in series with a resistor of about 220 ohms.
bumsbert:
Oh i forgot the ~ sign, my bad. 300V~ means AC right?
That is normally the case.
bumsbert:
I have 220 Ohm resistors. Is the wattage irrelevant? Because i actually dont know.
The wattage can be quite low, however resistors also have a voltage rating, and you should choose one rated for few hundred volts (although it will only get subjected to that voltage briefly).
TomGeorge:
Hi, can you post up for us a circuit diagram so we can see how your project is connected.
I never did any schematic before and i know this one is ridiculous. What software should i use? I put this together with a grafic tool and fritzing as a basis. Anyway maybe you can understand my wiring. As i said everything works basically its just this issue that occured twice in 5 days of testing.
bumsbert:
I never did any schematic before and i know this one is ridiculous. What software should i use?
When I need to post a schematic to the forum, unless I am making a PCB of the design and so have already prepared a schematic in Eagle, I hand-draw one and then scan it.
Hi, thanks for the diagram, it looks like the ground of the arduino and the ground of the 5V relay supply are not connected together.
They should be so that the arduino outputs have a ground reference on the relay board to bias the driver transistor/fets.
Check if this is a drawing omission or is also missing in the project.
Here it says to not connect gnd to arduino for isolation purposes if you use external power for the relay board. Do you think it is wrong? It was quoted in several threads i read.
If your relay board has opto isolated inputs, then if you run it from a separate power supply, you do not need to connect the grounds (and it is better not to).
Thanks for confirming that. I am now sure the arduino kept working when it happended again yesterday. It seems to be most likely the power supply that cuts off the relay board for some milliseconds and the relay channels switch off. The electronic ballasts then protect the bulbs by not lighting them immediately. Some minutes later the lights go on again. I will get a bigger power supply and i still want to build the snubber. I read i can not use an axial-lead resistor because it can burn in case the capacitor shorts. Is that true? What resistor should i be using? Can i instead of putting the rc-snubber over the relay contacts put it over the load/motor/coil? Whats better? Or should i install a MOV (Metal Oxide Varistor) surge suppressor as stated in the article i quoted above?
bumsbert:
Thanks for confirming that. I am now sure the arduino kept working when it happended again yesterday. It seems to be most likely the power supply that cuts off the relay board for some milliseconds and the relay channels switch off.
If you think that is what is happening, try connecting a capacitor with a value of several thousand microfarads across the power supply input to the relay board. Or use a better power supply.
bumsbert:
I read i can not use an axial-lead resistor because it can burn in case the capacitor shorts. Is that true?
If the capacitor shorts, then the resistor will get very hot and fuse. That's true of any type of resistor. You don't want it to set fire to anything while it is fusing. Some types of resistor burn more than others.
bumsbert:
Can i instead of putting the rc-snubber over the relay contacts put it over the load/motor/coil? Whats better?
Either should work. If the blower is run only occasionally, then I would connect it across the blower, to maximise the life of the capacitor.
bumsbert:
Or should i install a MOV (Metal Oxide Varistor) surge suppressor as stated in the article i quoted above?
TomGeorge:
low output = relay ON,
high output= relay OFF.
Yeah, it can be confusing. Its off if nothing is connected and also if the signal is "high". It only turns on the relay if the signal is "low".
dc42:
Some types of resistor burn more than others.
I will try my tiny lead resistor for now but i think i will have to buy something like this (sorry cant find an english link).
bumsbert:
Either should work. If the blower is run only occasionally, then I would connect it across the blower, to maximise the life of the capacitor.
All right, thanks.
dc42:
bumsbert:
Or should i install a MOV (Metal Oxide Varistor) surge suppressor as stated in the article i quoted above?
PS.: btw i tried the rc-combination. After 20 minutes there was a bang. As i checked two resistors of one of the electronic ballasts had exploded. Anyway i had to replace it and remove the snubber. My tactics for avoiding transients will now be: dont switch the blower off.
