high charge voltage causing LED Headlights to Flicker

[Jetronic]

The voltage going to the headlamps is not regulated, the voltage regulation is being done inside the bulbs themselves (typically PWM voltage regulation in LEDs), this is why I called the aftermarket bulbs crap. How much you pay for the bulbs doesn't automatically make them not crap.
Something that you might want to check is the amount of A/C ripple voltage in the DC when the engine is running. It shouldn’t exceed .05V. High ripple voltage can/will wreak havoc with PWM regulation circuits. Excessive ripple can be filtered-out by putting an electrolytic capacitor on the positive power leads of each LED as close as possible to the LEDs themselves, 4700 mfd 35v capacitors should do the trick.

On cars with BMS it is done, to prevent the headlights to change in intensity. at least, on the ones I had to deal with. The regulator is set up for halogen.

 

[meep]

So… several things.

Yes BMS. My ford will charge anywhere between 14.8 (super cold, startup) to 12.4 (straight cruise, vehicle is warmed), or 13.5 (lights on, or AC is cranked down). So there’s that.

Something else I learned recently is that the power to my headlights and fog lights is not smooth. I tried to run a relay off the high beams to run an aux pair, and the relays buzzed (!) around maybe 440 hz or so … so bad that I couldn’t use the relays and went down another path.

Idk why it’s not sending straight 13V … high beams on command (not DRL) need steady current, maybe they are looking for bulb condition, but either way it wasn’t straight DC.

It’s getting harder to mod cars these days.

 

[berniedd]

I second wag123's idea of trying to rule out ripple with the capacitor trick. But I would add a diode between the 12V B+ hot lead and the capacitor. Said diode would drop the voltage slightly and also keep the rest of the circuitry of the car from sucking up the capacitor's juice. To survive the intial inrush current the capacitor would suck up, choose a diode with at least 5x the normal drain of the LEDs. A Schottky diode rated at 40 amps or more would be a good bet. Its forward voltage is very low and hopefully not need a heat sink.

 

[_LeO_]

The voltage going to the headlamps is not regulated, the voltage regulation is being done inside the bulbs themselves (typically PWM voltage regulation in LEDs), this is why I called the aftermarket bulbs crap. How much you pay for the bulbs doesn't automatically make them not crap.
Something that you might want to check is the amount of A/C ripple voltage in the DC when the engine is running. It shouldn’t exceed .05V. High ripple voltage can/will wreak havoc with PWM regulation circuits. Excessive ripple can be filtered-out by putting an electrolytic capacitor on the positive power leads of each LED as close as possible to the LEDs themselves, 4700 mfd 35v capacitors should do the trick.

what i'm saying is the voltage reading without the bulb in them was at 13.7xx volts when the battery voltage was reading 15 volts on my multimeter.

the Canyons system has never required a PWM module to run. as mentioned i've been running them for 4 years, 200,000km.

my biggest issue is with the charging system, when the systems seems to be running properly i have no issues with the LED headlights, but the smart charge system running at 14.5 volts all the time is not normal. the LEDs are just amplifying the problem

 

[wag123]

the Canyons system has never required a PWM module to run

There is a PWM regulator/driver built into the LED headlamp bulb cartridge itself. This is standard practice with high output LEDs.
Upon further reading, I was wrong when I said that PWM voltage regulation was not being used in the vehicle's headlamp circuit. I have never personally seen this used in any vehicles except for the DRLs in GM trucks where they have been used for many years. BMW and GM are using them in the headlamp circuits of SOME models. How this works is that pulsed DC is sent to the light bulbs (or LEDs) to control their brightness and current draw. If your truck has this I suspect that there might be interference between different PWM regulator frequencies being used in the LED headlamp bulbs you are using and your truck's PWM regulator.
I reiterate that you really need to look into the possibility that you have a high ripple voltage in your truck's 12vdc when it is running. This can/will wreak havoc with the digital PWM regulators/drivers. They mention the use of filter capacitors and diodes to correct this problem in the following forum thread...
https://www.candlepowerforums.com/threads/pwmd-voltages-for-automotive-lighting.263719/

 

[_LeO_]

i'll check for this, is this something that has to be tested at the headlight socket or can i test it at the battery? i'm assuming any ripple would be though the whole electrical system

 

[wag123]

i'll check for this, is this something that has to be tested at the headlight socket or can i test it at the battery? i'm assuming any ripple would be though the whole electrical system

It is the alternator that generates the A/C ripple. The battery will absorb some of the ripple so you shouldn't check it at the battery terminals (you need to check it further away from the battery), and you can't check it at the headlamp terminals because there might be pulsed DC there if it has a PWM regulator in the truck, it would be best to check for it on a positive terminal at the fuse box (engine running of course, and with a good load applied, like the heater on full blast and rear defogger on).

 

[_LeO_]

Just got a warning message that my Battery Saver is active, still running off the alternator 14.5 volts.

I'll check for an AC ripple but it's a new alternator so i doubt that's the issue.

 

[ctrcbob]

Hi all, new here.

i've been having an issue with my aftermarket LED headlights flickering and dimming for the past few months while braking on my 2019 GMC Canyon Denali. originally i thought it was just a bad bulb since it was only a single bulb on the driver side, so i contacted the place i bought them from and they sent me a new set of Morimoto 2stroke 4.0 under warranty to replace the 3.0s i had for 2.5 years. voltages from the battery and alternator seemed good through the charging system and the resting battery voltage while a little low was still sitting above 12 volts

while waiting for the new lamps to be shipped to me my alternator died, had that replaced but still the headlight issue persisted. once i got the new lamps things got a little worse, at least worse from what i noticed. flickering persisted but for the first few minutes of start up these lamps would dim and flicker randomly from both headlights while driving and not just braking like i was noticing before. upon further investigation of my voltage, i noticed my starting voltage was running at 15 volts for a few minutes before settling down and staying at a steady 14.4-14.5 volts at times it would spike to 15.5 volts for a few minutes. would rarely get to below 14.4 volts.

thinking it was a load issue, i replaced the battery, given that its 5-6 years old i figured it was time to replace it, but still no difference, my mechanic replaced the alternator again thinking that the new one could be a faulty, same issue. did some diagnosis, disconnected the communication connector for the alternator and the voltage dropped to its default output for the alternator. thinking it was a grounding issue, we jumped the alternator to the negative battery and it seemed to do something, so we ran a #4 ground from the alternator to the negative battery terminal. the voltage dropped a little bit for a few days and at a normal voltage of 13.9-14.2 the headlights ran normally, and now the voltage has been back to the same figures and the headlight issues still persists. i guess the lower running voltage was just there until the BCM/ECM re-calibrated to the new ground

at this point we are thinking the problem could be a failed current sensor not relaying the right load back to the BCM which is calling for a higher voltage, but would this cause the headlights to flicker? the current sensor only comes with the negative battery harness and to completely replace the harness is not an easy job on these trucks, looks like the fuse box in the engine bay has to come out and the negative that mounts to the block sits above the front differential and is a pain to get to.

anyone here have any thoughts or opinions/ recommendations to check? has anyone seen such a thing?

i should also not, that when braking the dome lights would also dim for a half second but given that they aren't LED they are not as reactant as the driver/ballast on the LED bulbs.

i'm also an electrician by trade, the only issue is i'm not fully familiar with the system controls in a vehicle, so troubleshooting without fully knowing the order of operation is a little more difficult and i need to do a bit more research on the systems structure so any help would really be appreciated

Like reading a book.

 

[_LeO_]

Just got a warning message that my Battery Saver is active, still running off the alternator 14.5 volts.

I'll check for an AC ripple but it's a new alternator so i doubt that's the issue.

Only reading .001 as far as ripple voltage

Like reading a book.

As long as the story is told that's all that matters

 

[wag123]

Just got a warning message that my Battery Saver is active, still running off the alternator 14.5 volts.

I'll check for an AC ripple but it's a new alternator so i doubt that's the issue.

Battery saver active warning while getting 14.5v? You have some other kind of electrical system problem. Perhaps the main ECU.
Your ripple voltage is really good.

 

[_LeO_]

That's what i was trying to say, the BCM or something. The headlight was just what notified it to me.

Ugh

Question, does a BCM have to be reprogrammed when an alternator is replaced?