Clearing Up Misconceptions on the CAN Bus, PWM, and Flickering Headlights - Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > JK Jeep Wrangler Forum > JK General Discussion Forum

Join Wrangler Forum Today



Reply
 
Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 01-13-2015, 11:22 AM   #1
Supporting Member

5-Year WF Supporting Member
 
dcgibbons's Avatar
 
Join Date: May 2012
Location: Tabernash, Colorado
Posts: 484
dcgibbons is on a distinguished road
Clearing Up Misconceptions on the CAN Bus, PWM, and Flickering Headlights

I have noticed on the forum there is a persistent misunderstanding about the CAN bus, especially in context of flickering headlights. Hopefully I can clear up a few misconceptions about these different terms so people understand what is happening - there's not a lot of black magic going on here.
  1. Flickering headlights have nothing to do with a CAN bus. Zero. It's because of the PWM (pulse-width-modulation) power signal being sent to the lights.
  2. The CAN bus is a networking technology, used only for the various ECUs in the car to communicate with one another.
  3. PWM and CAN bus are not the same thing, nor are they describing a similar electrical activity.
  4. Likewise, for the 'headlight is broken' signal, that also has nothing to do with the CAN bus. It happens because the wiring to the lights allow the TIPM module to tell if voltage is passing through the light or not.
  5. All Jeep JK's have had CAN bus technology, since the beginning of the design.

I think some of this misunderstanding persists because some vendors are incorrectly labeling their anti-flicker harnesses as defeating the CAN bus - wrong. They're doing that either of out their own misunderstanding, or a marketing desire to make that scary CAN bus look like something that is hard to solve.

A lot of people have gotten this right on the forum, so I won't reiterate everything that has been covered before. But, the gist of it in a bit more detail:

The TIPM (totally integrated power module) is the brain of your Jeep. It not only has a sophisticated group of micro controllers within it, but it also acts as a old-fashioned relay / circuit box for the vehicle. It's the one controlling relays and sending power out of the other circuits in the car.

For the lights in particular, the TIPM uses a pulse-width-modulation signal. If you look at this signal with a oscilloscope, you will see a square wave. The end result is that the lights get approximately 8 volts of power sent to them, in pulses, rather than a constant 12 volts. This increases bulb life and reduces fuel consumption (probably on the order of 1-2%). For incandescent bulbs, this is a great trick as the bulb won't start to dim before the next pulse of power is received. For LEDs or other lights, it doesn't work the same, so that's why you get a flicker.

You'll note that I said nothing about CAN bus in the previous 2 paragraphs because it wasn't in play at all. Where the CAN bus comes into play is when the ECUs talk to each other. For example, your Cab Compartment Node (CCN), aka your dash, talks to the TIPM via a CAN bus connection. So does your radio and the Uconnect module. The engine and transmission ECUs talk to each other and the TIPM through a CAN bus as well. There's a bunch more...

The best way to think about a CAN bus is to treat it 100% like a computer network. If you've ever plugged in an Ethernet cable from one computer to another, or to a hub/switch, you are on the right track. CAN bus is a much simpler technology, and only needs two wires plus a shared ground. You can have a few hundred different ECUs on a single CAN bus, all talking happily amongst themselves.

If you go look at the connection pinouts at Mopar Connection Repair Kit you will see pretty clearly if a CAN bus is involved in your circuit or not. Let's compare two examples, both from a 2008 JK. In the first, the headlamp connector, you see a pretty standing wiring arrangement. It doesn't mention a PWM signal, of course, but that's in the service manual. On the second, you actually do see a CAN bus wiring pair mentioned. So there's never a surprise if a CAN bus is involved or not.

I hope this helps clarify things a bit. If anyone has any more questions or would like more details, I'll do my best to explain.
Attached Thumbnails
Click image for larger version

Name:	Screen Shot 2015-01-13 at 9.18.21 AM.jpg
Views:	682
Size:	137.4 KB
ID:	1805185   Click image for larger version

Name:	Screen Shot 2015-01-13 at 9.19.13 AM.jpg
Views:	728
Size:	138.1 KB
ID:	1805193  

dcgibbons is offline   Quote
Old 01-13-2015, 01:33 PM   #2
Commercial Member
 
Join Date: Apr 2011
Posts: 2,013
xsdbs is on a distinguished road
Thanks for the great write up on the CAN BUS, I'm sure that people will definitely find it helpful.

xsdbs is offline   Quote
Old 01-13-2015, 02:46 PM   #3
Supporting Member

5-Year WF Supporting Member
 
dcgibbons's Avatar
 
Join Date: May 2012
Location: Tabernash, Colorado
Posts: 484
dcgibbons is on a distinguished road
For a concrete example of what happens, let's go through the flow of what happens when you turn the headlights on. Let's assume this is a manual manipulation of the switch, and not the Auto mode.
  1. You turn the headlamps on using the multi-function switch stalk on the left-side of the steering wheel. This multi-function switch is hard-wired to an electrical module called the Steering Control Module, or SCM.
  2. The SCM senses the switch change, and sends a message to an electrical module called the ElectroMechanical Instrument Cluster, or EMIC. This module is also known as the Cab Compoartment Node, or CCN - either way, this is your instrument cluster. The SCM tells the EMIC about the headlamp switch over something called a LIN data bus, which is a very simple 1-wire serial link bus that runs at a speed of 9.6 Kbps. It is typically used for switches to communicate to an ECU that is monitoring them.
  3. Now that the EMIC knows about the headlamp switch being activated, it sends a headlamp and headlamp beam request message to the Total Integrated Power Module, or TIPM, over the CAN interior bus.
  4. (This text provided directly from the service manual.)The TIPM responds to these messages by providing a pulse-width modulated voltage output to the headlamps through high side drivers on the right and left low and high beam feed circuits to illuminate the selected headlamp filaments.
  5. (This text provided directly from the service manual.)The TIPM also sends the appropriate messages to the EMIC to control the illumination of the high beam indicator.

So as you can see, the digital networking busses in the car (the LIN and CAN busses) are only used to communicate to the ECU about what action to take, and what happened, but the actual voltage control of the headlamps is a simple PWM driver to the headlamps themselves from the TIPM.
dcgibbons is offline   Quote
Old 01-13-2015, 03:07 PM   #4
Jeeper
 
Join Date: Nov 2014
Posts: 175
govdubspeedgo is on a distinguished road
I believe the misconception occurs because new cars use this network "BUS" technology where as before in older cars you flipped a switch that went through the fuse hit a relay and provided voltage direct from the battery, no modules to provide this integrated power, so the word CAN-BUS should be swapped with TIPM to make everything sound legit. PWM could not occur in a car without a BUS type system because nothing would regulate the voltage to pulse. Sometimes computers make our lives worse than better. So maybe I'm to blame for the misconceptions of this forum sort of, but I still understood it was the PWM causing the headlights to be terrible.

A wiring harness gets rid of the PWM because its pulling power direct from the battery and the harnesses that LED lighting people sell just use a capacitor to help store the voltage to correct hold voltage that tricks the PWM.
govdubspeedgo is offline   Quote
Old 01-13-2015, 03:07 PM   #5
Jeeper
 
n3tfury's Avatar
 
Join Date: May 2012
Location: Tucson, AZ
Posts: 2,595
n3tfury is on a distinguished road
This is awesome, thank you. Definitely sticky material.
__________________
.:: 2014 Anvil JKUR | 3.5 Metalcloak | 37" Nitto Trail Grapplers | Teraflex HD Tire carrier | LOD Crawler front bumper | SPod | PowerTank ::.
n3tfury is offline   Quote
Old 01-13-2015, 03:13 PM   #6
Supporting Member

WF Supporting Member
 
Join Date: Jan 2012
Posts: 7,986
m998dna is on a distinguished road
^x2 Mods can you sticky this please?

Excellent overview!

.
m998dna is offline   Quote
Old 01-13-2015, 03:17 PM   #7
Supporting Member

WF Supporting Member
 
Join Date: Jan 2012
Posts: 7,986
m998dna is on a distinguished road
Quote:
Originally Posted by dcgibbons View Post
For the lights in particular, the TIPM uses a pulse-width-modulation signal. If you look at this signal with a oscilloscope, you will see a square wave. The end result is that the lights get approximately 8 volts of power sent to them, in pulses, rather than a constant 12 volts. This increases bulb life and reduces fuel consumption (probably on the order of 1-2%). For incandescent bulbs, this is a great trick as the bulb won't start to dim before the next pulse of power is received. For LEDs or other lights, it doesn't work the same, so that's why you get a flicker.
Question: How does this reduce fuel consumption?

.
m998dna is offline   Quote
Old 01-13-2015, 03:23 PM   #8
Supporting Member

5-Year WF Supporting Member
 
TerryC6's Avatar
 
Join Date: Jan 2014
Location: Everett, Wa
Posts: 1,812
TerryC6 is on a distinguished road
The theory would be less power draw, the alternator does not need to work as hard. The reality because of the computer systems we now have a standard 160 amp alternator inside of the old 35/60 amp alternator.
TerryC6 is online now   Quote
Old 01-13-2015, 03:37 PM   #9
Supporting Member

5-Year WF Supporting Member
 
dcgibbons's Avatar
 
Join Date: May 2012
Location: Tabernash, Colorado
Posts: 484
dcgibbons is on a distinguished road
Yeah light bulbs running can actually be a bigger draw on fuel than you'd expect. I remember reading some GM data years ago that DRL's were 2-3% economy hit. This is old, old data (pre-2000), so who knows what the numbers are today.
dcgibbons is offline   Quote
Old 01-13-2015, 06:09 PM   #10
Jeeper
 
ASE_MasterTech's Avatar
 
Join Date: Feb 2014
Location: New Jersey
Posts: 713
ASE_MasterTech is on a distinguished road
This is helpful info & I agree it should be a sticky.
Good write up..
__________________
2014 JKURX-Black
ASE_MasterTech is offline   Quote
Old 01-13-2015, 06:53 PM   #11
Jeeper
 
AAJDad's Avatar
 
Join Date: Sep 2013
Posts: 30
AAJDad is on a distinguished road
Thank you for the great write up!!!
AAJDad is offline   Quote
Old 01-13-2015, 07:19 PM   #12
Supporting Member

5-Year WF Supporting Member
 
dcgibbons's Avatar
 
Join Date: May 2012
Location: Tabernash, Colorado
Posts: 484
dcgibbons is on a distinguished road
Quote:
Originally Posted by govdubspeedgo View Post
I believe the misconception occurs because new cars use this network "BUS" technology where as before in older cars you flipped a switch that went through the fuse hit a relay and provided voltage direct from the battery, no modules to provide this integrated power, so the word CAN-BUS should be swapped with TIPM to make everything sound legit. PWM could not occur in a car without a BUS type system because nothing would regulate the voltage to pulse. Sometimes computers make our lives worse than better. So maybe I'm to blame for the misconceptions of this forum sort of, but I still understood it was the PWM causing the headlights to be terrible.

A wiring harness gets rid of the PWM because its pulling power direct from the battery and the harnesses that LED lighting people sell just use a capacitor to help store the voltage to correct hold voltage that tricks the PWM.
Yeah you are mostly right - you're not likely to see PWM without a micro-controller somewhere in the mix, but it's not a mandatory thing. The reality is, that's what's been going on in automotive since the 1980s so this isn't a new thing, really. Memories of how bad cars really were back then when all of this was new...

The engineering decision to go with PWM for the headlights seems weird to me, so I wish we had some real data from the engineers to share and speculate about. I mean, the TJ didn't do that, correct?

The harnesses that use direct battery feed and use the main headlight driver just as a signal switch is totally the right way to go as a work-around. It's clean and simple. The CAN bus controller project I'm working on is another way, but it's more complex/powerful so we'll see if that ever comes to fruition or not.
dcgibbons is offline   Quote
Old 01-13-2015, 07:40 PM   #13
Jeeper
 
Steve G PW's Avatar
 
Join Date: Oct 2014
Location: Central Oregon
Posts: 72
Steve G PW is on a distinguished road
Quote:
Originally Posted by dcgibbons View Post
The harnesses that use direct battery feed and use the main headlight driver just as a signal switch is totally the right way to go as a work-around. It's clean and simple. The CAN bus controller project I'm working on is another way, but it's more complex/powerful so we'll see if that ever comes to fruition or not.
Excellent info. Thank you, Dr. DC!
__________________
2014 JKURX
Steve G PW is offline   Quote
Old 01-13-2015, 07:55 PM   #14
Jeeper
 
Tseg's Avatar
 
Join Date: Jun 2014
Location: Michigan
Posts: 224
Tseg is on a distinguished road
Quote:
Originally Posted by dcgibbons View Post
Yeah light bulbs running can actually be a bigger draw on fuel than you'd expect. I remember reading some GM data years ago that DRL's were 2-3% economy hit. This is old, old data (pre-2000), so who knows what the numbers are today.
If any truth to the above would LED headlights improve Fuel Economy since their draw is so low?
Tseg is offline   Quote
Old 01-13-2015, 07:58 PM   #15
Supporting Member

5-Year WF Supporting Member
 
dcgibbons's Avatar
 
Join Date: May 2012
Location: Tabernash, Colorado
Posts: 484
dcgibbons is on a distinguished road
Quote:
Originally Posted by Tseg View Post
If any truth to the above would LED headlights improve Fuel Economy since their draw is so low?
You know, I would say yes, but can you perceptibly measure a 1-3% gain either way? You'd go from say 17 mpg to 17.5 mpg in that case... I wouldn't notice it.

I think it matters more across the fleet of vehicles when they're doing the CAFE stuff, but otherwise?
dcgibbons is offline   Quote
Old 01-13-2015, 08:16 PM   #16
Jeeper
 
Join Date: Apr 2014
Posts: 123
NOIWILLNOTFIXURPC is on a distinguished road
Thanks for the information! Just a quick question, is that true of all lights in the vehicle? Suppose I put an led 3rd brake light, same thing?
__________________
I'm not a pessimist!
I'm an optimist with experience

If life gives you lemons, freeze them, and then throw them at the people that are making your life difficult
NOIWILLNOTFIXURPC is offline   Quote
Old 01-13-2015, 08:24 PM   #17
Jeeper
 
HRPinDC's Avatar
 
Join Date: Mar 2013
Location: Washington, DC
Posts: 1,106
HRPinDC is on a distinguished road
Wow! Somebody's making it rain knowledge up in here. Sometimes I miss the good ole days of my '68 Chevelle. Thanks for explaining this to us dummies.
__________________
'13 JKUR, Billet
'88 YJ w/ 4" lift and 33's - Gone but not forgotten
HRPinDC is offline   Quote
Old 01-14-2015, 05:38 AM   #19
Jeeper
 
Lusus_Naturae's Avatar
 
Join Date: Oct 2012
Location: OKC, missing WI
Posts: 3,542
Lusus_Naturae is on a distinguished road
Quote:
Originally Posted by NOIWILLNOTFIXURPC View Post
Thanks for the information! Just a quick question, is that true of all lights in the vehicle? Suppose I put an led 3rd brake light, same thing?
I think this is where it gets confusing for most people. Some light sockets don't have any issue with a flicker from LED bulbs, and some don't have an issue with the LED bulbs itself, but the lack of a higher voltage causes it to believe there is a bulb out and cause other issues.

For example, the dome lights in a 4 door JK from front to back are -
map lights on the mirror
b-pillar lights over the front seats
rear cargo lights over the rear seats

The mirror lights are already LED, the front seats lights are two pods with a 194 sized bulb in each facing sideways, and the rear cargo is a festoon bulb.

You can change out the front bulbs with any 194 LED and it works fine. No flicker, no "CANbus" issues.

If you change out the rear cargo light with a basic (not CANbus rated) LED bulb you'll find everything works but the map lights will stay on after the doors are closed. In doing my LED project, I found the map lights will stay on constant when the Jeep is running, and will time out after about 15 minutes when turned off and parked. Very similar to what happens if the door isn't closed tight and the lights stay on for about 15 minutes before timing out.

To fix this issue with the cargo dome light I ran a tiny 12v standard bulb inline on the hot wire to provide the feedback for the brain to figure out there's a bulb there and it's ok. Now whether that brain is the TIPM or the CANbus, that's where most just call it a CANbus issue and leave it at that. That includes myself, as I understand what's happening but I could really care less as the I know the fix too.

The biggest problem I see is that back when cars began having CANbus systems and bulb issues came up - the label for compatible bulbs was "CANbus compatible" or "CANbus error free", so this pushed the reason for bulb issues to being a CANbus issue.

Canbus Error Free LED bulbs Frequently asked questions
__________________
2013 JKU Sport, billet, auto, 3.73, LSD, 315/75/16 Duratracs on MB 72, 10A springs, Bushwacker flatties

Sold - 2005 TJ, red, auto, 3.73, 33" Duratracs, 4" lift
Ice storm casualty in 2007 - 2003 TJ, green, auto, 3.73, 33" Duratracs, 4" lift
Lusus_Naturae is offline   Quote
Old 01-14-2015, 05:40 AM   #20
Jeeper
 
Lusus_Naturae's Avatar
 
Join Date: Oct 2012
Location: OKC, missing WI
Posts: 3,542
Lusus_Naturae is on a distinguished road
To the OP - You should also link your work back to this thread, you already have a lot of followers.

Hacking the CAN-Interior Bus
__________________
2013 JKU Sport, billet, auto, 3.73, LSD, 315/75/16 Duratracs on MB 72, 10A springs, Bushwacker flatties

Sold - 2005 TJ, red, auto, 3.73, 33" Duratracs, 4" lift
Ice storm casualty in 2007 - 2003 TJ, green, auto, 3.73, 33" Duratracs, 4" lift
Lusus_Naturae is offline   Quote
Old 01-14-2015, 08:11 AM   #21
Jeeper
 
Join Date: Apr 2014
Posts: 123
NOIWILLNOTFIXURPC is on a distinguished road
Thanks!
__________________
I'm not a pessimist!
I'm an optimist with experience

If life gives you lemons, freeze them, and then throw them at the people that are making your life difficult
NOIWILLNOTFIXURPC is offline   Quote
Old 01-14-2015, 09:53 AM   #22
Supporting Member

5-Year WF Supporting Member
 
dcgibbons's Avatar
 
Join Date: May 2012
Location: Tabernash, Colorado
Posts: 484
dcgibbons is on a distinguished road
Quote:
Originally Posted by Lusus_Naturae View Post
The biggest problem I see is that back when cars began having CANbus systems and bulb issues came up - the label for compatible bulbs was "CANbus compatible" or "CANbus error free", so this pushed the reason for bulb issues to being a CANbus issue.
That's basically like saying you need to drain the change your brake fluid in your windshield wiper reservoir every 3 weeks. It's incorrect nonsense. (The label I mean.)
dcgibbons is offline   Quote
Old 01-21-2015, 11:38 PM   #23
Jeeper
 
FingerTight's Avatar
 
Join Date: Sep 2012
Location: ATX
Posts: 872
FingerTight is on a distinguished road
Id think using a PWM on the vehicle's bulbs would have other benefits aside from less parasitic loss and longer bulb life. Some ideas that come to mind, not sure if they're true:

- Better regulation of headlight performance. Regardless of load on the electrical system the PWM logic can maintain the same brightness by adjusting the pulse timing / amplitude

- Programable behavior, factory can set things like DRLs to any light desired and any brightness desired

- Potentially simpler wiring, why not have a tail light be two wire? Simply reduce the voltage for running lights and increase for brake / turn lights

Just imagining the other potential advantages to a system like this, not sure if any of these things are actually being used.
__________________
Mopar Vehicle Protection Plan SCAM
FingerTight is offline   Quote
Old 01-22-2015, 05:48 AM   #24
Jeeper
 
Lusus_Naturae's Avatar
 
Join Date: Oct 2012
Location: OKC, missing WI
Posts: 3,542
Lusus_Naturae is on a distinguished road
My thought of the night - and I'm tired, so maybe it's way off but..

If PWM is good for bulbs, and can extend the life of the bulb, why does turning a old fashioned incandescent bulb off and on repeatedly, shorten its life? It's been said it's better to leave a bulb on because the heating and cooling of the filaments weakens them over time, causing the bulb life to shorten. This would not really apply to the LED bulbs, but the blinkers, dome, tail light/brakes, and headlights are incandescent bulbs as stock. The main difference is, does the research found in household bulbs, apply to vehicle bulbs - or is this a moot point.

Like I said, I'm tired, and this was a random thought tonight.
__________________
2013 JKU Sport, billet, auto, 3.73, LSD, 315/75/16 Duratracs on MB 72, 10A springs, Bushwacker flatties

Sold - 2005 TJ, red, auto, 3.73, 33" Duratracs, 4" lift
Ice storm casualty in 2007 - 2003 TJ, green, auto, 3.73, 33" Duratracs, 4" lift
Lusus_Naturae is offline   Quote
Old 01-22-2015, 07:35 AM   #25
Jeeper
 
Link81's Avatar
 
Join Date: Nov 2014
Location: Upstate NY
Posts: 235
Link81 is on a distinguished road
I believe it has more to do with heat up/cool down cycles, then actual on/off operation.

Household bulbs are operating on ac power at 60 hz so in effect they are turning on and off 60 times per second. But they don't cool off between "pulses" enough to change the apparent light or cause flickering. Cars are dc power, so it's a constant 12v.
Link81 is offline   Quote
Old 01-22-2015, 07:48 PM   #26
Jeeper
 
Join Date: Dec 2014
Location: Houston, Tx
Posts: 31
Bskarpa is on a distinguished road
Quote:
Originally Posted by Lusus_Naturae View Post
I think this is where it gets confusing for most people. Some light sockets don't have any issue with a flicker from LED bulbs, and some don't have an issue with the LED bulbs itself, but the lack of a higher voltage causes it to believe there is a bulb out and cause other issues.

For example, the dome lights in a 4 door JK from front to back are -
map lights on the mirror
b-pillar lights over the front seats
rear cargo lights over the rear seats

The mirror lights are already LED, the front seats lights are two pods with a 194 sized bulb in each facing sideways, and the rear cargo is a festoon bulb.

You can change out the front bulbs with any 194 LED and it works fine. No flicker, no "CANbus" issues.

If you change out the rear cargo light with a basic (not CANbus rated) LED bulb you'll find everything works but the map lights will stay on after the doors are closed. In doing my LED project, I found the map lights will stay on constant when the Jeep is running, and will time out after about 15 minutes when turned off and parked. Very similar to what happens if the door isn't closed tight and the lights stay on for about 15 minutes before timing out.

To fix this issue with the cargo dome light I ran a tiny 12v standard bulb inline on the hot wire to provide the feedback for the brain to figure out there's a bulb there and it's ok. Now whether that brain is the TIPM or the CANbus, that's where most just call it a CANbus issue and leave it at that. That includes myself, as I understand what's happening but I could really care less as the I know the fix too.

The biggest problem I see is that back when cars began having CANbus systems and bulb issues came up - the label for compatible bulbs was "CANbus compatible" or "CANbus error free", so this pushed the reason for bulb issues to being a CANbus issue.

Canbus Error Free LED bulbs Frequently asked questions
Just wanted to throw something in here real quick. My Map lights are soldered into the circuit board. There is no led bulb, I have taken it apart and looked.

Question, can you solder in a resistor for the cargo light to help with the map lights staying on?

I have changed out all my LED's ex. B pillar, cargo, reverse, license plate, and fog lights. I just disconnected my map lights for now (never use them anyways). I like the lighting that the LED's put out and tried buying the "Can-bus" LED for the cargo but wasn't the same light output and got really hot.
Bskarpa is online now   Quote
Old 01-23-2015, 02:08 AM   #27
Jeeper
 
Lusus_Naturae's Avatar
 
Join Date: Oct 2012
Location: OKC, missing WI
Posts: 3,542
Lusus_Naturae is on a distinguished road
I wired in a tiny, rice sized bulb, inline with the cargo wiring and it works perfect. Here are a few photos I took during the project. The overall way I modded this one was a bit ghetto, but it looks good and function properly and unless you took it apart, you'd never know.

Jeep Cargo LED Mod Photos by Lusus_Naturae | Photobucket

Yes, the map lights are COB (chip on board) construction. I changed it to red using glass beads and gluing them into the cone tunnel for the light output. Works perfect, again, a bit ghetto in how I did it. I have heard of a few trying stained glass circles and siliconing them into the cone or tint. Here's my info on this mod.

As a side note, test the light before completely reassembling it again. The photo showing a few beads in the bottom of the cone was the first test. I did find a bit of white light coming through and went back and added one more bead afterwards.

http://s1318.photobucket.com/user/Lu...?sort=4&page=1
__________________
2013 JKU Sport, billet, auto, 3.73, LSD, 315/75/16 Duratracs on MB 72, 10A springs, Bushwacker flatties

Sold - 2005 TJ, red, auto, 3.73, 33" Duratracs, 4" lift
Ice storm casualty in 2007 - 2003 TJ, green, auto, 3.73, 33" Duratracs, 4" lift
Lusus_Naturae is offline   Quote
Old 01-23-2015, 02:16 AM   #28
Jeeper
 
Lusus_Naturae's Avatar
 
Join Date: Oct 2012
Location: OKC, missing WI
Posts: 3,542
Lusus_Naturae is on a distinguished road
Quote:
Originally Posted by Link81 View Post
I believe it has more to do with heat up/cool down cycles, then actual on/off operation.

Household bulbs are operating on ac power at 60 hz so in effect they are turning on and off 60 times per second. But they don't cool off between "pulses" enough to change the apparent light or cause flickering. Cars are dc power, so it's a constant 12v.
This was kind of my point. The AC old style lightbulb would run on a 60 Hz setting, the pulse would be quick enough to not normally dim the bulb but how does this translate to vehicle PWM heating/cooling? It's been said you can sometimes see the stock headlights flicker, so it that causing enough heating/cooling of the bulb filament to weaken it? The "constant" in this would be against a vehicle with no CANbus/PWM.

If we go back to the OP's first post, this was stated -

"For the lights in particular, the TIPM uses a pulse-width-modulation signal. If you look at this signal with a oscilloscope, you will see a square wave. The end result is that the lights get approximately 8 volts of power sent to them, in pulses, rather than a constant 12 volts. This increases bulb life and reduces fuel consumption (probably on the order of 1-2%). For incandescent bulbs, this is a great trick as the bulb won't start to dim before the next pulse of power is received. For LEDs or other lights, it doesn't work the same, so that's why you get a flicker."

Based on this, the lights are pulsing in square wave of 8 v, so is this square wave something that would lessen a stock bulb's lifespan and is using PWM worth it because of ?? I can't see this saving gas, or extending the life of a bulb, rather shortening the life of a bulb by causing premature wear of the filament due to the pulsing voltage heating/cooling the filament. Maybe I'm just looking at it differently, but that's my first thought.

Now if someone can explain that the wire would actually be staying cooler and holding a fairly consistent temperature due to the PWM lessening the voltage and therefore lessening the heat pull into the filament, then that makes sense too. Lower heat on the filament could cause less fluctuation in the filament and prolong its life.

The question then becomes, what exactly is occurring? (or which theory of mine is closer to being right)
__________________
2013 JKU Sport, billet, auto, 3.73, LSD, 315/75/16 Duratracs on MB 72, 10A springs, Bushwacker flatties

Sold - 2005 TJ, red, auto, 3.73, 33" Duratracs, 4" lift
Ice storm casualty in 2007 - 2003 TJ, green, auto, 3.73, 33" Duratracs, 4" lift
Lusus_Naturae is offline   Quote
Old 01-23-2015, 07:25 AM   #29
Jeeper
 
Link81's Avatar
 
Join Date: Nov 2014
Location: Upstate NY
Posts: 235
Link81 is on a distinguished road
I suppose it depends on the voltage and frequency of the wave. If the bulbs are flickering(incandescent) then it sounds like either the voltage isn't high enough, or the "on time" isn't long enough. In reality, it should be a fairly easy code change for Chrysler.
Led's on the other hand will need a cap inline to smooth out the voltage supply into more of a flat line vs a wave.
Link81 is offline   Quote
Old 01-23-2015, 09:06 AM   #30
Supporting Member

5-Year WF Supporting Member
 
dcgibbons's Avatar
 
Join Date: May 2012
Location: Tabernash, Colorado
Posts: 484
dcgibbons is on a distinguished road
When I get back to the Jeep this weekend I'll post some scope measurements of the headlights, some other lights, and a CAN bus connection so you can see the general difference (those are on the forum elsewhere but hard to dig up).

As far as bulb life, the pulse is happening fast enough it's helping the bulb not hurting it.

dcgibbons is offline   Quote
Reply

Tags
can bus , ecu , pwm , tipm

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




Download our Mobile App

» Featured Product

All times are GMT -5. The time now is 01:20 AM.


User Alert System provided by Advanced User Tagging v3.1.0 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Jeep®, Wrangler, Liberty, Wagoneer, Cherokee, and Grand Cherokee are copyrighted and trademarked to Chrysler Motors LLC.
Wranglerforum.com is not in any way associated with the Chrysler Motors LLC
« Back

Enter your email address:

Delivered by FeedBurner