Hi long time reader though first question here. I have a terrarium automated by an arduino mega. Temperature and humidity sensors control relays to activate a heater and fogger plus a fan for the fogger. The 8 relay block i have consisting of songle brand relays AC250V 10A; DC30V 10A. These all work fine for the heater which is 165 w and draws .7 w
The problem i am having is with the 3 compact fluro's i have for the lighting. Each light is 240 v 130 w and draws about .54 of an amp. Using this info I Used 1 relay to run all three. After a day or two i found the relay to be open all the time . The lights wouldn't turn off regardless if relay was open or not. I then tried a seperate relay for each light .Even adding into the sketch to turn them on 15 seconds apart from each other. Alas another 3 relays fused together staying on all the time.
I'm at my wits end as to how to fix or get around this. I have considered getting 30 amp relays but it seems futile as the amperage doesn't exceed 10 amps per light so getting 30 amp relays doesnt seem to be the answer (though it may be)
I am guessing this situation may have something to do with the inbuilt ballasts the cfl's have ? Again not sure.
Any ideas or solutions would be appreciated
thank you in advance
The CFL and Fluorescent type lamps exhibit apon switch ON, a hugh current surge, higher than the normal running current, this is enough to weld the contacts together.
Use one relay per light, that will reduce the current by 3 which might be all you need? Alternatively
use a soft-start circuit - two relays, one has a power resistor in series to limit the current to less
than 10A, the other relay bypasses both. Switch the one with the resistor first, then a fraction of
a second later the "main" relay. Make sure the power resistor is adequately rated should the main
relay fail. The inrush current is then limited to within the ability of the relay.
Hi all thanks for the replies. As im not overly confident with making circuits etc and after reading various links and info that TomGeorge suggested ive decided to go the relay way. I have bought 3 solid state relays SSR-40DA 40A 3-32V DC TO 24-380V AC . One one of the pages i was reading im quite sure it was mentioned that they have a snubber circuit built in. Fingers crossed these may work If not i will have to keep my lights on a mechanical timer as they are now which is ok but why when i have an arduino to do all that for me
Again thanks for the replys. When i try them ill let you all know
I've had several electromechanical relays fuse on me. I was using the relays as part of a temperature control system for a toaster oven. I switched to SSR and I haven't had any problems since.
Ok im back and have added the three ssr's .These work fine "except" they cause the cfl's to flash on for maybe a quarter of a second intermittently though in cycles of no more that 10 seconds. Gives a look of lightning in my terrarium. The led light on the relay does not come on when they flash nor do the pins on my arduino mega go high at that moment . Disconnecting the dc side from arduino has no effect. I know this cant be an Arduino ,or programming issue. Just wondering if anyone has had a similar problem.
I am running a single cfl of 130 watts on each relay. at 240 volts
The CFL would present a capacitive load (leading power factor) and its electronic ballast circuit would exhibit some leakage current. The SSR would also have a minimum load that it can switch.
I bet if you included a small resistive or resistive-inductive load (incandescent lamp, fan, resistor, etc.) this would overcome the effect of CFL flickering as its electronic ballast capacitor fills.
Your mistake was using one relay for all three. You're spot welding the contacts together from the arcing inside. You should use one relay for each and connect SNUBBER circuits (RC) to eliminate the arcing.
I believe you can find off the shelf 240V/20A SNUBBERS
