Submitted by Anonymous on Sun, 09/27/1998 - 06:04 Forums: LML Archive From: Ed Armstrong <ed [at] testelectronics.com> Subject: Protecting Switch Contacts Date: Sat, 26 Sep 1998 23:04:12 -0700 To: Lancair [lancair.list [at] olsusa.com] (E-mail) <lancair.list [at] olsusa.com> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> Marv asks: the question is what can we do to protect those relay contacts to prevent arcing when we fire-up/shut-down those motors? Yes good point, electric motors are also inductive loads, and you can use the same flyback circuit on the motors to protect the relay contacts. So, first use the low current diode circuit to protect the switch from the flyback that the relay coil produces. Next, use the high current varistor circuit to protect the relay contacts from the flyback the motor produces. This will help eliminate welded contacts. Make sure to physically place the flyback circuits as close as possible to inductive loads which produce the flyback, this will help reduce noise in your electrical system. The diode I added in series with the MOV is only for noise reduction if you have noise sensitive instruments. You could try it first without this diode and then add it later if you need it. The schematic for both these circuits is at http://www.testelectronics.com/ftp/flyback.gif The term "welded contacts" is a very good description of what makes the switches stick. This just made me think of an arc welder. A simple arc welder is nothing more than a large coil in series with a power supply. This may help more of you understand just how important a flyback circuit is. Regards, Ed. Post a Reply You must have JavaScript enabled to use this form. Your name Subject Comment * Switch to plain text editorMore information about text formats Text format Filtered HTMLPlain text Filtered HTMLWeb page addresses and e-mail addresses turn into links automatically.Each email address will be obfuscated in a human readable fashion or, if JavaScript is enabled, replaced with a spam resistent clickable link. Email addresses will get the default web form unless specified. If replacement text (a persons name) is required a webform is also required. Separate each part with the "|" pipe symbol. Replace spaces in names with "_".Allowed HTML tags: <a> <em> <strong> <cite> <blockquote> <code> <ul> <ol> <li> <dl> <dt> <dd> <h1> <h2> <h3>Lines and paragraphs break automatically.Plain textNo HTML tags allowed.Each email address will be obfuscated in a human readable fashion or, if JavaScript is enabled, replaced with a spam resistent clickable link. Email addresses will get the default web form unless specified. If replacement text (a persons name) is required a webform is also required. Separate each part with the "|" pipe symbol. Replace spaces in names with "_".Web page addresses and e-mail addresses turn into links automatically.Lines and paragraphs break automatically. Attachments Add a new file Files must be less than 512 MB.Allowed file types: jpg jpeg gif png txt doc docx xls xlsx pdf ppt pptx pps ppsx odt ods odp mp3 mov mp4 m4a m4v mpeg avi ogg oga ogv weba webp webm. Leave this field blank
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