>Exactly, and the easiest way to get the fastest coil field collapse is to just use no catch diode and have a switching transistor rated for the 250v spike that the coil produces. I found this to be true in the lab, Roman. I could get almost the same speed with nothing in parallel with the relay, and also with a 6.2K in parallel with the relay but with signifigantly less pulse, about 100Volts. But, sadly, there is no way to turn off this relay fast enough due to excessive bouncing. I changed the relay topology around signifigantly, so that the relay shorts across the power diode to achieve full wave or half wave power. voila! Very little noise on switching. Didn't have to resort to even more extreme measures like parallel triacs. The key point here is, when a mechanical relay switches, the NO and NC contacts are MOMENTATILY SHORTED TOGETHER. This causes a great amount of noise if they are at different voltages and also both in low impedance power circuits. I am talking like playing-polo-on-the-antenna-of-a-commercial-radio-station kind of noise, that I could not ever filter out of my power supply with any sane measures. When I changed the topology so that the NO and NC contacts weren't at different voltages (one of them isn't connected to anything) suddelny I was able to see but a tiny blip on the scope when the relay switches and no bounce. If you don't believe the momentarily shorted together bit, consult the details of a relay technical catalog. One contact draws an arc which continues to conduct as it approaches the other contact. If a high current can flow at that time, BOOM! it does for one half cycle until the arc is extinguished. OTOH, once the NO contaact finally closes, it, too can draw an arc and remain closed. If both contacts are involved in an arc, look out FCC here we come transmitting noise! This is especially true at higher voltages and when there is a big inductance anywhere nearby. -- Lawrence Lile Roman Black Sent by: pic microcontroller discussion list 11/03/02 05:03 AM Please respond to pic microcontroller discussion list To: PICLIST@MITVMA.MIT.EDU cc: Subject: Re: [EE]: Speeding up a relay - zero crossing detection Dave Tweed wrote: > > Wagner Lipnharski wrote: > > Supposing it could be possible, what would happens if you wrap a secondary > > coil (with the diode) around the actual relay coil? > > All the magnetic collapsing field would be drained by this secondary coil > > in short (by the diode), with few energy generated at the primary coil, is > > this correct or not? > The actual turn-off time of the relay would be essentially > unchanged, and this is what we were trying to improve. Exactly, and the easiest way to get the fastest coil field collapse is to just use no catch diode and have a switching transistor rated for the 250v spike that the coil produces. The only faster way to get the field to collapse is to reverse the *current* at turnoff by applying a voltage, which would in effect "squash" the field as someone mentioned before. But if the field collapsing into an open circuit produces 250v, wouldn't forcing it to collapse quicker by using a reverse current source cause this back-emf voltage to spike even higher?? And doesn't that mean the reverse current source must have a voltage greater than 250v to have an effect? -Roman -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics