Capacitor for relay flicker - Jeep Wrangler Forum
Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > JK Jeep Wrangler Forum > JK Tech Forum

Join Wrangler Forum Today


Reply
 
Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 12-01-2015, 01:52 PM
Thread Starter
  #1
Jeeper
 
Join Date: Dec 2014
Posts: 430
Capacitor for relay flicker

I'm using a relay to turn on my off road light. I'm using the high beam power wire to activate the relay. What capacitor do I need to keep the relay from flickering.
Still have a Radioshack near by as well.

Thanks in advance.

adr1601 is offline   Quote
Old 12-01-2015, 02:58 PM
Thread Starter
  #2
Jeeper
 
Join Date: Dec 2014
Posts: 430
To be a little more specific this is for the high beam wire powering the coil of the relay.

adr1601 is offline   Quote
Old 12-01-2015, 03:20 PM   #3
Jeeper
 
Join Date: May 2015
Location: Austin, TX
Posts: 766
Across the relay coil I used a 220uF 35vdc capacitor.

Radio Shack part number: 272-1017
__________________
____________________________________
2015 JKUS purchased new with leaky hard top option. Added faulty electrical harness upgrade in 2017.
Austintatious is offline   Quote
Sponsored Links
Advertisement
 
Old 12-01-2015, 05:36 PM
Thread Starter
  #4
Jeeper
 
Join Date: Dec 2014
Posts: 430
Quote:
Originally Posted by Austintatious View Post
Across the relay coil I used a 220uF 35vdc capacitor.

Radio Shack part number: 272-1017
Thanks!!

No need for a Diode?

On our 2013 I did the same wiring with no need for a capacitor. I'm guessing it's a matter of different relays.
adr1601 is offline   Quote
Old 12-01-2015, 06:56 PM   #5
Jeeper
 
Join Date: May 2015
Location: Austin, TX
Posts: 766
The capacitor is to smooth out the PCM voltage supplied to the headlights. The best way to visualize what the voltage is doing is to use an oscilloscope - you'll quickly see how the voltage to various circuits on the Jeep are pulsed at a high frequency instead of constant. Thus the relay making a buzzing sound.

I only use a diode (or diodes) when I am switching from multiple sources. For instance, if I wanted the fogs to come on with the hi beams OR anytime I flipped a switch, I would put a diode on the hi beam relay trigger wire to keep voltage from going to the headlight harness when I flip the switch.
__________________
____________________________________
2015 JKUS purchased new with leaky hard top option. Added faulty electrical harness upgrade in 2017.
Austintatious is offline   Quote
Old 12-01-2015, 07:41 PM   #6
Jeeper
 
7ekken's Avatar
 
Join Date: Feb 2012
Location: Carolinas
Posts: 248
__________________
2013 JKU Sport Gecko 3.73Auto, Premium Soft Top, Rubi Rails, Ace Rails
7ekken is offline   Quote
Old 12-02-2015, 11:56 AM
Thread Starter
  #7
Jeeper
 
Join Date: Dec 2014
Posts: 430
Worked.

Thanks again!!!
adr1601 is offline   Quote
Old 11-17-2016, 08:51 AM   #8
Jeeper
 
Join Date: Aug 2016
Posts: 225
Quote:
Originally Posted by 7ekken View Post
The indicated diode polarity in the schematic seems backward to me, if the intent is to prevent feedback to the supply side. Maybe I'm missing something. Is it correct or incorrect?

[EDIT]Never mind. I see I was wrong.[EDIT]
__________________
Frank
2017 JK
BadRoad-GoodTimes is offline   Quote
Old 11-18-2016, 10:21 AM   #9
Jeeper
 
Join Date: Nov 2015
Posts: 405
220 pF is orders of magnitude too small. I suspect that it should be 220 uF. If you measure the relay coil resistance then the time constant is easy to calculate.
dstevens is offline   Quote
Old 11-18-2016, 11:55 AM   #10
Jeeper
 
Join Date: Aug 2016
Posts: 225
Quote:
Originally Posted by dstevens View Post
220 pF is orders of magnitude too small. I suspect that it should be 220 uF. If you measure the relay coil resistance then the time constant is easy to calculate.
You are correct about the 220pf - which would be 0.00022ufd and I don't think a capacitor of that value is even made - and if it was, I doubt you could find one. I started to point that out, but the thread is old.

I bought 100uf capacitors to see how they work.... should unload faster than 220ufd and hopefully not create a funky switch-over between high and low beams - it's bad enough on the OE setup.

Cold coil resistance measures 67 ohms on one meter scale, 85 ohms on another, so if I can trust my meter, it's probably about 75 ohms.
__________________
Frank
2017 JK
BadRoad-GoodTimes is offline   Quote
Old 11-18-2016, 07:41 PM   #11
Jeeper
 
Join Date: Nov 2015
Posts: 405
Yep, 100 uF sounds like a good starting point. It also depends on the PWM frequency, because even 220 uF is a fairly low time constant with 67 ohms.
dstevens is offline   Quote
Old 11-18-2016, 08:10 PM   #12
Jeeper
 
Join Date: Aug 2016
Posts: 225
I don't know what influence the OE PWM system might have as relay triggers after a change to B+ supplied to lamps from the battery through the relays, but if 100uf shows a long delay due to relay hold decay, I'll try 47uf, then 10uf, but I doubt I want to go below that.

__________________
Frank
2017 JK
BadRoad-GoodTimes is offline   Quote
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off






All times are GMT -5. The time now is 01:49 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.1
User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.

Jeep®, Wrangler, Liberty, Wagoneer, Cherokee, Gladiator, Mopar and Grand Cherokee are copyrighted and trademarked to FCA US LLC.
Wranglerforum.com is not in any way associated with FCA US LLC.