RE: Frequency for SSRs using PWM

["Flier" <flier-at-sbcglobal.net>]

Off the Allen-Bradley website:

Long Life Expectancy
Solid-state relays use electronic instead of mechanical devices for load
switching while providing a life cycle expectancy of approximately 100,000
energized hours or 11.4 years. This reduces product replacement and
downtime.

I don't think we have to worry about life.  I think the tracks will fail
first...

The PWM frequency is dependent on the PIC's oscillator frequency which can
go up to 20mhz.  Max duty cycle is limited by the max turn-on/turn-off time
of the SSR.  I think a MOSFET based speed control would be a lot more
efficient.

Regards,

Ted


-----Original Message-----
From: tanks-admin-at-rctankcombat.com
[mailto:tanks-admin-at-rctankcombat.com]On Behalf Of adt22-at-drexel.edu
Sent: Wednesday, March 17, 2004 2:58 PM
To: tanks-at-rctankcombat.com
Subject: Re: Frequency for SSRs using PWM


----- Original Message -----
From: Joe Sommer <anvilus9-at-adelphia.net>
Date: Tuesday, March 16, 2004 10:02 pm
Subject: Re: Frequency for SSRs using PWM

>
> Ted,
>
> At 07:54 PM 3/16/2004 -0500, "flier" <FLIER-at-sbcglobal.net> wrote:
> >What PWM frequency (or period) are you guys using
> >with the SSRs for your motor speed control?
>
> I use 1 KHz.  You can actually hear the motors whine at
> 1 KHz when they stall.
>

Joe,
Electromagnetic relays usually have a life span that is in the millions of
switches.  Although I can't find it now, I thought I saw a site stating SSRs
were also rated for a minimum number of operations - is that true?

Also what is the range in frequency you have with the PICs?

Hypothetically if the SSR was good for 1 billion ops
and you used a 1KHz frequency your SSRs would last ~275 hours which is
pretty long.  I'm sure many other things would fail before your 275 hour
tune-up.  But I just wanted to bring it up because others might want to
consider the price and life of the SSRs when you are choosing a frequency.

So that being said, anyone know how many ops an SSR will take before it
dies?

Or how about the rating of high end ESCs do they have a known lifetime?

-Amir