Post by thread:[OT] Reed Relay problem for 16C84 based truck ligh

I am using a 16C84 PIC to create a light bar for the 5 marker lamps (Cabover lights) on top of a Chevrolet Truck. The lights scroll left or right when that respective blinker is on. They also all blink in sync with the Emergency Flashers and are all on solid with when the parking lamps are on (with no blinker or flashers). For the record, I have 3 inputs: left / right blinker, and parking lights. The 5 light outputs from the PIC are input into a 74LS04, Hex Inverter. The 5 outputs of the Hex Inverter drive the coils of 5 Radio Shack 5VDC Reed Relays (part# 275-232). The relay contacts are passing 13 to 13.8V to the lights. The current for each light is about 275ma (.275 Amps). The problem is the CONTACTS of the reed relays are sticking intermittently. Any of the 5 contacts may stick. The coil voltage is not the problem. The contacts may still be stuck after powering down the circuit and powering back up without any power to the coil. I have also shorted the coil while the contacts are stuck to no avail. Heat is NOT the problem for the sticky contacts. The contacts have become stuck immediately after the entire system had sat for hours. However, sometimes it is necessary to cool the system for several seconds to unstick the contacts. I would appreciate any technical input anyone might be able to provide. On a lesser note, I have been unable to locate the manufacturer of the relay. There is an 'OMR' or 'DMR' and a 'DEG' name on the relay. Any ideas on who and where this company is located. Thanks.... ------------------------------------------------- Work all day & night, deliver on time & on budget, Regards, and justice for all... Bill Bryson

See if the contacts stick even when not passing current. I think really you should use conventional relays, or transistors. Reed relays do tend to suffer from this problem when switching a load. Remember the lamp inrush current is much larger than the steady-state current. This is possibly the reason for the problem. You could possibly alleviate it by placing a wirewound resistor in parallel with each relay to pass sufficient current to preheat the lamp filament (it will last longer, too). Enough current to make the lamp glow very dimly in absolute darkness is sufficient. {Quote hidden}> ---------- > From: Bryson, William G (Bill)[SMTP:spam_OUTBRYSOWGTakeThisOuTTEXACO.COM] > Reply To: pic microcontroller discussion list > Sent: Thursday, January 22, 1998 9:43 AM > To: .....PICLISTKILLspam@spam@MITVMA.MIT.EDU > Subject: [OT] Reed Relay problem for 16C84 based truck light bar > scroller > > I am using a 16C84 PIC to create a light bar for the 5 marker lamps > (Cabover > lights) on top of a Chevrolet Truck. The lights scroll left or right > when > that respective blinker is on. They also all blink in sync with the > Emergency Flashers and are all on solid with when the parking lamps > are on > (with no blinker or flashers). For the record, I have 3 inputs: left > / > right blinker, and parking lights. > > The 5 light outputs from the PIC are input into a 74LS04, Hex > Inverter. The > 5 outputs of the Hex Inverter drive the coils of 5 Radio Shack 5VDC > Reed > Relays (part# 275-232). The relay contacts are passing 13 to 13.8V to > the > lights. The current for each light is about 275ma (.275 Amps). > > The problem is the CONTACTS of the reed relays are sticking > intermittently. > Any of the 5 contacts may stick. The coil voltage is not the problem. > The > contacts may still be stuck after powering down the circuit and > powering > back up without any power to the coil. I have also shorted the coil > while > the contacts are stuck to no avail. > > Heat is NOT the problem for the sticky contacts. The contacts have > become > stuck immediately after the entire system had sat for hours. However, > sometimes it is necessary to cool the system for several seconds to > unstick > the contacts. > > I would appreciate any technical input anyone might be able to > provide. > > On a lesser note, I have been unable to locate the manufacturer of the > relay. There is an 'OMR' or 'DMR' and a 'DEG' name on the relay. Any > ideas > on who and where this company is located. > > Thanks.... > > ------------------------------------------------- > Work all day & night, > deliver on time & on budget, Regards, > and justice for all... Bill Bryson >

Bill, Did you add any diodes across the relay coil (anode to gnd, cathode to +12VDC)???? The diode provides path for current to flow once the 12 volts is removed. Remember the coil is just a big inductor. +12DC --------+-------+ | | --- --- /_\ | | Relay coil | --- | | GND --------+-------+ Hope this helps! -Randie ________ Randie Ohtsji / ____/ /__ ____ ____ ___ _________ email: rohtsjiKILLspamglenayre.com / /___/ / _ \/ __ \/ __ `/ / / / __/ _ \ Glenayre R & D / /_\ / / __/ / / / /_/ / /_/ / / / __/ Vancouver, B.C. CANADA \____/_/\___/_/ /_/\__,_/\__ /_/ \___/ Phone: (604) 293-1611 x4555 ________________________/ / Fax: (604) 293-4317 /_________________________/ {Quote hidden}> From .....BRYSOWGKILLspam.....TEXACO.COM Wed Jan 21 12:43:33 1998 > X-Priority: 3 > Mime-Version: 1.0 > Date: Wed, 21 Jan 1998 14:43:02 -0600 > From: "Bryson, William G (Bill)" <EraseMEBRYSOWGspam_OUTTakeThisOuTTEXACO.COM> > Subject: [OT] Reed Relay problem for 16C84 based truck light bar scroller > To: PICLISTspam_OUTMITVMA.MIT.EDU > > I am using a 16C84 PIC to create a light bar for the 5 marker lamps (Cabover > lights) on top of a Chevrolet Truck. The lights scroll left or right when > that respective blinker is on. They also all blink in sync with the > Emergency Flashers and are all on solid with when the parking lamps are on > (with no blinker or flashers). For the record, I have 3 inputs: left / > right blinker, and parking lights. > > The 5 light outputs from the PIC are input into a 74LS04, Hex Inverter. The > 5 outputs of the Hex Inverter drive the coils of 5 Radio Shack 5VDC Reed > Relays (part# 275-232). The relay contacts are passing 13 to 13.8V to the > lights. The current for each light is about 275ma (.275 Amps). > > The problem is the CONTACTS of the reed relays are sticking intermittently. > Any of the 5 contacts may stick. The coil voltage is not the problem. The > contacts may still be stuck after powering down the circuit and powering > back up without any power to the coil. I have also shorted the coil while > the contacts are stuck to no avail. > > Heat is NOT the problem for the sticky contacts. The contacts have become > stuck immediately after the entire system had sat for hours. However, > sometimes it is necessary to cool the system for several seconds to unstick > the contacts. > > I would appreciate any technical input anyone might be able to provide. > > On a lesser note, I have been unable to locate the manufacturer of the > relay. There is an 'OMR' or 'DMR' and a 'DEG' name on the relay. Any ideas > on who and where this company is located. > > Thanks.... > > ------------------------------------------------- > Work all day & night, > deliver on time & on budget, Regards, > and justice for all... Bill Bryson >

On Wed, 21 Jan 1998 14:43:02 -0600, you wrote: >I am using a 16C84 PIC to create a light bar for the 5 marker lamps (Cabover >lights) on top of a Chevrolet Truck. The lights scroll left or right when >that respective blinker is on. They also all blink in sync with the >Emergency Flashers and are all on solid with when the parking lamps are on >(with no blinker or flashers). For the record, I have 3 inputs: left / >right blinker, and parking lights. > >The 5 light outputs from the PIC are input into a 74LS04, Hex Inverter. The >5 outputs of the Hex Inverter drive the coils of 5 Radio Shack 5VDC Reed >Relays (part# 275-232). The relay contacts are passing 13 to 13.8V to the >lights. The current for each light is about 275ma (.275 Amps). > Reed relays are not really designed for load switching. Remember that the inrush current for a 275mA lamp load may be a lot more due to the low resistance of the cold filament. Use Transistors or MOSFETs to switch this kind of load - smaller, more reliable and probably cheaper as well! ____ ____ _/ L_/ Mike Harrison / White Wing Logic / @spam@wwlKILLspamnetcomuk.co.uk _/ L_/ _/ W_/ Hardware & Software design / PCB Design / Consultancy _/ W_/ /_W_/ Industrial / Computer Peripherals / Hazardous Area /_W_/

One source that we use for reed-relays is as follows: Standex Electronics 4538 Camberwell Rd Cincinnati, Ohio 45209 Phone: (513) 871 3777 The application I've used them in is quite different - we use only 1 or 2 (or sometimes even 1/2) turn around the relay to sense very high currents in backplanes. There is some hysterisis associated with the relays, as the primary force that trip them is driven by electric fields. The fields have to be gone for a sufficient amount of time before the switch will open. Reed relays are also subject to close during vibration - this may not be a good thing if it's on top of your truck. Is this going into production? or are you just having fun? You may want to use a mosfet or bjt instead of the relay. A nice p-channel mosfet would do the job. Daniel Najemy - Data General Corporation, Numaliine Power Systems > {Original Message removed}