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Constant Negative when Power Lost


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ewingr 
Copper - Posts: 60
Copper spacespace
Joined: February 21, 2007
Location: United States
Posted: April 16, 2019 at 4:03 PM / IP Logged Link to Post Post Reply Quote ewingr
I need to send a constant negative signal when power lost, no signal when power on.
Also need to just send positive when / during receive positive.
I suspect I need two relays to do this. The relay diagrams I find are for specific solutions, for which I'm not familiar enough wiht relays to pull out my needs.
Help appreciated.
Thanks
Roger
i am an idiot 
Platinum - Posts: 13,667
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 16, 2019 at 5:26 PM / IP Logged Link to Post Post Reply Quote i am an idiot
Ground terminal 85
power to terminal 86
Terminal 30 is output, power when there is 12 volts across 85 and 86. Ground when there is not 12 volts across 85 and 86
Terminal 87A is to be grounded.
Terminal 87 gets power.
ewingr 
Copper - Posts: 60
Copper spacespace
Joined: February 21, 2007
Location: United States
Posted: April 16, 2019 at 5:37 PM / IP Logged Link to Post Post Reply Quote ewingr
REally appreciate your input.
I need to check with the device mfgr... but don't think I can send 12v to the device. So, for the power source that would kick off the negative, when that is on, I do NOT want to send 12V through the output. I only want to send a ground if I lose power, nothing if I have power.
It sounds like the above will send power out the output. Am I misunderstanding?
I don't know, maybe what I want to do can't be done.
Thanks
Roger
i am an idiot 
Platinum - Posts: 13,667
Platinum spaceThis member consistently provides reliable informationspace
Joined: September 21, 2006
Location: Louisiana, United States
Posted: April 16, 2019 at 8:52 PM / IP Logged Link to Post Post Reply Quote i am an idiot
Remove power from 87
I misread your first line.
What do you mean by you need positive during receive signal?
ewingr 
Copper - Posts: 60
Copper spacespace
Joined: February 21, 2007
Location: United States
Posted: April 17, 2019 at 5:30 AM / IP Logged Link to Post Post Reply Quote ewingr
i am an idiot wrote:
Remove power from 87
I misread your first line.
Thanks so much. I wondered if it would be that simple.
i am an idiot wrote:
What do you mean by you need positive during receive signal?
Sorry, that really was poorly worded.
Let me explicitly explain what I'm trying to do:
I have several things that rely on when I press the brake. So, I'm wanting the wire on the brake switch that goes hot when I press the brake to feed a relay, which then sends power to a power distribution block for the various things that need that signal. Does that make sense?
FYI...the other one you already answered is to feed the negative to a brake indicator on the dash if the power feed to the brake switch should blow a fuse. That will alert me to the blown fuse.
Thanks
Roger
ewingr 
Copper - Posts: 60
Copper spacespace
Joined: February 21, 2007
Location: United States
Posted: April 17, 2019 at 8:06 AM / IP Logged Link to Post Post Reply Quote ewingr
i am an idiot wrote:
Ground terminal 85
power to terminal 86
Terminal 30 is output, power when there is 12 volts across 85 and 86. Ground when there is not 12 volts across 85 and 86
Terminal 87A is to be grounded.
Terminal 87 blank.
I just want to confirm the above. Two questions.
1. I presume that the power on 86 should be the power from my brake switch, which if a fuse blows, then I get the negative signal on 30
2. If I did put power on 87, then 30 would get power if 86 is powered. Whereas if I remove power from 87, then when there is power on 86, nothing at all will feed through 30.
I apologize for being a pest.
Thanks so much. I really do appreciate your input.
Thanks
Roger
ewingr 
Copper - Posts: 60
Copper spacespace
Joined: February 21, 2007
Location: United States
Posted: April 29, 2019 at 11:23 AM / IP Logged Link to Post Post Reply Quote ewingr
I want to have a relay that when a particular circuit loses power that it sends a negative to the output wire. I was told to wire it like this:
85 and 87a -> Ground
86 -> Power (NOTE: I am using this terminal as the one that I want to monitor. So if it loses power, the end result is that the relay has no power on any ports)
30 -> Output (I have wired this to the negative side of an indicator. So when I lose power, which is the power on 86, then a gnd gets sent here)
I find it to not be working.
Have I misunderstood the instructions I received?
Any help appreciated very much.
Thanks
Roger
geepherder 
Platinum - Posts: 3,668
Platinum spaceThis member consistently provides reliable informationspace
Joined: October 27, 2003
Posted: April 29, 2019 at 1:56 PM / IP Logged Link to Post Post Reply Quote geepherder
First verify your relay is a SPDT configuration. If it isn't, it may have two terminals labelled 87 rather than one 87 and one 87a.
Also ensure 87 and 87a are not reversed.
The connections listed will work, but the relay will remain energized unless power is lost (blown fuse), which places a constant drain on the battery.
My ex once told me I have a perfect face for radio.
ewingr 
Copper - Posts: 60
Copper spacespace
Joined: February 21, 2007
Location: United States
Posted: April 29, 2019 at 4:02 PM / IP Logged Link to Post Post Reply Quote ewingr
I will check your suggestions.
And your comment about constant drain on battery is another topic I was concerned about. The relay is warm...which I figured it shouldn't be. By being a constant drain on the battery, that would make it warm.
Do you have a better solution I could/should use to avoid that? Two relays?
Thanks
Roger
ewingr 
Copper - Posts: 60
Copper spacespace
Joined: February 21, 2007
Location: United States
Posted: April 29, 2019 at 4:45 PM / IP Logged Link to Post Post Reply Quote ewingr
geepherder wrote:
First verify your relay is a SPDT configuration. If it isn't, it may have two terminals labelled 87 rather than one 87 and one 87a. Verified...have 87 and 87a
Also ensure 87 and 87a are not reversed. Verified
The connections listed will work, but the relay will remain energized unless power is lost (blown fuse), which places a constant drain on the battery.
Also, as you pointed out...it is in fact using juice...the relay is warm. I pulled it out for now.
Thanks
Roger
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