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type of relay or suggestions


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webpager 
Member - Posts: 24
Member spacespace
Joined: February 23, 2014
Location: Connecticut, United States
Posted: February 23, 2014 at 7:49 PM / IP Logged  
I had always heard of what I am about to describe as a drop relay, but I was informed recently otherwise. Now, I need to buy/build one and am not sure of what to call it.
Relay - normally open. Closed via Momentary. When power is interrupted, ie the car is turned off, the relay opens again. I want to add switches for a few items (a USB block to charge stuff, radar detector, inverter, more). I don't want it on as I start the car. So once I start it, I can hit the momentary switches, the relay(s) is(are) activated, and I have powered items. I turn off the car and these items go off and stay off until I restart AND hit the momentary again.
Suggestions? Names? Electromechanical or SSR?
TIA from a newbie to these forums.
Webpager - Upfitter, computer guy, car guy. I can't tell the difference between Columbian or African coffee, but I knew at age 4 the difference between volts, watts and ohms.
KPierson 
Platinum - Posts: 3,527
Platinum spaceThis member consistently provides reliable informationspace
Joined: April 14, 2005
Location: Ohio, United States
Posted: February 23, 2014 at 10:45 PM / IP Logged  
Use a standard 30A Bosch style automotive relay. Connect the momentary switch between the (+) side of the coil and an accessory wire in the vehicle. Accessory wires are powered in the "ON" key position but not the "crank" key position.
You will then need to latch the (+) output of the relay back to the (+) coil to make it stay on after you push and release the button
Pin 85 - ground
Pin 86 - (+) coil, connect to accessory feed through momentary switch, also connect to pin 30
Pin 87 - Fused 12vdc source
Pin 30 - 12vdc output, also connect to pin 86
Kevin Pierson
webpager 
Member - Posts: 24
Member spacespace
Joined: February 23, 2014
Location: Connecticut, United States
Posted: February 24, 2014 at 1:08 PM / IP Logged  
Thank you Kevin. For some reason I had thought it was a different relay. This makes perfect sense. I appeciate you breaking it down to the specific pins.
Webpager - Upfitter, computer guy, car guy. I can't tell the difference between Columbian or African coffee, but I knew at age 4 the difference between volts, watts and ohms.
webpager 
Member - Posts: 24
Member spacespace
Joined: February 23, 2014
Location: Connecticut, United States
Posted: February 24, 2014 at 6:45 PM / IP Logged  
type of relay or suggestions -- posted image.
To be sure, this is what you described Kevin. Is this correct?
Webpager - Upfitter, computer guy, car guy. I can't tell the difference between Columbian or African coffee, but I knew at age 4 the difference between volts, watts and ohms.
the12volt 
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Joined: March 07, 2002
Location: Louisiana, United States
Posted: February 24, 2014 at 7:12 PM / IP Logged  
Yes, that will work, but make sure terminal 87 is going to an accessory 12V+ source and not a constant 12V+ source, otherwise it will not turn off with the key.
type of relay or suggestions -- posted image. the12volt • Support the12volt.com
webpager 
Member - Posts: 24
Member spacespace
Joined: February 23, 2014
Location: Connecticut, United States
Posted: March 15, 2014 at 1:37 AM / IP Logged  
OK - been working on this one. Any expertise is appreciate. What do you think? I figure that instead of the Bosch style auto relays I'll see if I can find electronic ones. But either way, here's what I hope to do with it. I would also run a common ground (not shown on the graphic).
Thoughts? Comments? Suggestions?
type of relay or suggestions -- posted image.
Webpager - Upfitter, computer guy, car guy. I can't tell the difference between Columbian or African coffee, but I knew at age 4 the difference between volts, watts and ohms.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 15, 2014 at 2:06 AM / IP Logged  
I'd forget electronic relays. If space is a premium, used the micro-DIN relays.
howie (aka: harryharris)
Silver - Posts: 355
Silver spacespace
Joined: February 17, 2014
Location: Florida, United States
Posted: March 15, 2014 at 8:11 AM / IP Logged  
The micro DINS are smaller than PCB standard pin relays.
Test before boxing up.
oldspark 
Gold - Posts: 4,913
Gold spacespace
Joined: November 03, 2008
Location: Australia
Posted: March 15, 2014 at 10:26 AM / IP Logged  
Yeah - a micro is about half the volume of the mini - 22.5mm x 15mm x 25mmH + 11mm spade protrusion noting that the coil spades (86 & 85 = 1 & 2) and NO spade (87a = 4) are 4.8mm whereas 30 & 87 = 3 & 5 are normal 6.3mm.
2 micros side by side are a bit wider than a mini.
And mechanical relays are more reliable than solid state.
webpager - one consideration with your wiring is that until the relay actuates and closes 30 to 87, the switch will supply the load current.
If that's an issue, a diode can be inserted between 87 & 86; line end towards 86. Hence when actuated, 87 supplies +12V thru the diode to 86 to keep the relay energised, but the switch +12V to 86 cannot flow thru the diode to 87 and hence the load. Any 1N400x diode will do, but if buying diodes, get 1N4004 else 1N4007 as they can be used for spike prevention - ie, across the coil 86 to 85 with the line end towards the more +ve (namely 86 by convention and as per your diagram). Spike suppression diodes are used when electronics control the relay coil or if spikes are undesirable to minimise system noise (voltage transients).
webpager 
Member - Posts: 24
Member spacespace
Joined: February 23, 2014
Location: Connecticut, United States
Posted: March 15, 2014 at 11:57 PM / IP Logged  
I notice I saved the graphic with an extra connection in each relay - power going back from 30 to 86. Didn't mean for that - I thought I unchecked those layers when creating the graphic.
They were from the original relay with momentary and drop when power removed relay.
Webpager - Upfitter, computer guy, car guy. I can't tell the difference between Columbian or African coffee, but I knew at age 4 the difference between volts, watts and ohms.
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