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200ma Won’t Trigger Relay

Printed From: the12volt.com
Forum Name: Relays
Forum Discription: Relay Diagrams, SPDT Relays, SPST Relays, DPDT Relays, Latching Relays, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=103181
Printed Date: May 10, 2024 at 12:11 PM


Topic: 200ma Won’t Trigger Relay

Posted By: juvius
Subject: 200ma Won’t Trigger Relay
Date Posted: March 18, 2008 at 5:52 PM

hello,
i looked at all 41 posts in the relay forum and couldn't find an answer, so here's my last resort before i give up.
i just hooked up a dei automate 553 in my 89 saab 900. everything works except i can't figure out why the relay for the supervised dome lights won't work. when i touch the light tester to the BLACK/ white wire (done supervision negative output) i see that there is a negative output. when i connect it to the relay, it will not trigger. i have the relay set up as follows:
30 - negative dome light input switch
85 - BLACK/ white 200mA negative output from alarm
86 - 12V +
87 - Ground

when i click on the alarm with the tester on pin 30 i get nothing, but there is still a very faint reading on 85 (but not near as dominant as the reading when on the BLACK/ white wire when not connected to the relay). by the way, i have tried three different relays. what is wrong here? Do i need to run a stronger 12v and or ground?

thanks



Replies:

Posted By: sparkie
Date Posted: March 18, 2008 at 6:14 PM
Use a volt meter set to a DC voltage scale of at least 20 volts. Connect the red probe to terminal # 86 of the relay and the black probe to terminal # 85. Leave the relay wired as you have it and watch the meter reading when you activate the unlock feature of the alarm. If you don't get a reading around 12 volts, then place the red probe onto a know good source of 12 volts. like the main power input to the alarm. If you then get a reading after using the unlock feature of the alarm, you need to check the 12 volt supply to the relay for problems. If you still don't get a reading use a jumper wire to temporarily ground terminal # 85. The relay should activate. If it does, either there is a problem with the alarms output or maybe it needs to be programmed to activate.

-------------
sparky




Posted By: juvius
Date Posted: March 18, 2008 at 6:38 PM
now that you mention it, i'm starting to question the 12v source. it's the power wire from the stock alarm that i removed. it's only 16 guage and i'm already running the alarm from it. tomorrow, i'll use a better power supply and better ground on the new alarm and the relay and give the reading a try...

thanks... i appreciate it.




Posted By: juvius
Date Posted: March 21, 2008 at 6:27 PM
well it's not the power supplied to the relay. the relay is hooked up correctly and does trigger when i touch the 85 pin to ground. i went to borrow my dad's meter to test the outputs but he said it's broken. there is definately a negative feed on the BLACK/ white dome light supervision wire from the alarm because it causes my test light to light up when i press the remote unlock button. so now, i'm sure the problem is that the output from the alarm isn't strong enough to trigger the relay. what can i do to make that output stronger?

thanks again




Posted By: i am an idiot
Date Posted: March 21, 2008 at 7:23 PM

Juvius give me a minute  I will draw you a picture.  The transistor is available at Radio Shack  

https://www.radioshack.com/product/index.jsp?productid=2062613&cp=&sr=1&origkw=pnp&kw=pnp&parentPage=search





Posted By: i am an idiot
Date Posted: March 21, 2008 at 7:37 PM
posted_image




Posted By: juvius
Date Posted: March 21, 2008 at 7:39 PM
thank you very much.... i'll get out to radioshack tomorrow and let you know how it turned out...

thanks again....




Posted By: i am an idiot
Date Posted: March 21, 2008 at 7:44 PM

The metal tab of the transistor is connected to the middle leg, which is ground.  If you wanted to eliminate the relay, you could.  If you mount the tab of the transistor to the chassis of the vehicle, it should be good for 4 to 5 amps.  If you do go this route, monitor it for heat.  Leave the lights on via the alarm for a few minutes and see how hot the transistor gets. 





Posted By: mobile1
Date Posted: March 21, 2008 at 11:54 PM
Have you checked your main ground for the alarm? There shouldn't be any reason the dome supervision wire doesn't trigger a relay. Thats what its meant for. It does draw its ground current from the main ground of your system.

Where is this unit grounded? Try grounding it in the driver's kick panel. Make sure to scrape away paint first also. If you have a DMM, you can check the resistance of your ground source to the negative post of your battery. Thats where I would start.




Posted By: juvius
Date Posted: March 22, 2008 at 1:00 AM
i just regrounded it and no change... thanks




Posted By: dualsport
Date Posted: March 22, 2008 at 8:06 PM
If you use a PNP transistor, you have to change the switching of the relay from ground switched to high switched; the emitter should be connected to +12V, and the collector to the relay coil terminal.
The other side of the relay coil should be grounded.
Connect the base from your alarm (-) output through a 1 to 5k resistor.

Before you go through the trouble you should find out why the alarm output isn't able to pull the relay closed. If the output's blown but somehow still able to switch a light load then you can add the transistor stage as a workaround.




Posted By: juvius
Date Posted: March 25, 2008 at 6:53 PM
update: All is well now... i ran positive and negative wires straight from the battery and it didn't fix the problem. so, i added the TIP42G along with a relay and it worked out great. thanks to all who helped....




Posted By: i am an idiot
Date Posted: March 25, 2008 at 7:08 PM
That is why we are here.  Glad to help





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