Wondering

As I get some noise in the Empeg when I turn on my headlights, I searched around the web, and I found the following:

NOTE: Pulse Width Modulated headlight switches (like some Honds cars use) can cause a whining type of noise when on, verify this type of problem by turning lights on and off while listening for noise. If this is the problem, the headlight switch may need to be replaced with an alternate type.

Anyone who can explain PWM, and why it is used for lights??

TommyE

Let me first say I have not had to deal with this particular system before.
Very basically, Pulse Width Modulation is in effect turning on and off a signal very quickly. The time off compared to the time on is called the duty cycle. By adjusting the duty cycle, you are adjusting the equivalent DC value (RMS value).

How does this apply to your system, you ask. I am assuming by lights you mean the dash illumination. By adjusting the duty cycle and raising or lowering the RMS value, you increase or decrease the illumination intensity. This is a very effecient way of varying the voltage. It is very common to see PWM in DC motor control for this very reason. I'm suprised Honda would make the PWM frequency in the audible range.
If this information is correct, get someone to help you determine the frequency of the PWM so you can choose an appropriate capacitor value to fix the problem.


Alex Lear

Thanks for the answer.
I understood the note that it was for the headlights, and not for the dashlights.

What can they use PWM for in the headlights?? Dim a bulb to different 'modes', headlights on, parklights etc.???

TommyE

I don't think that there's a use for dimming the headlight to parklight. All cars should have a special lamp for parking light.

TeeMcBee
Reg#948 - already ordered a Mk2.

Hmm
could it be like on some of the newer/larger BMW's that if the eg. the leftturnsignal is broken the left breaklight takes over for function??

TommyE

Don't know something about that.

TeeMcBee
Reg#948 - already ordered a Mk2.

I'm pretty sure even though they may have said headlights, they mean headlight switch which turns on the dash lights. I can see a way to control which lights are on with PWM but don't know why they would do it that way. Anyway, its still a matter of isolating the PWM frequency and filtering it to get rid of your noise problem.


Alex Lear

PWM is used on most modern cars to control the dash illumination level. Both our A-Class demo car and Hugo's own Beetle have Mk.2 players installed, with PWM dash illumination fed in (our software copes with this) and we don't get any crosstalk.

I'd say it's a supression issue, but you could try disconnecting the headlight sense input from the empeg to see if that's the problem. It would take an experienced installer to comment on common causes and cures for this problem - Dominic?

Rob