Re: [DML] Fan Sequencer (delay box)

[Martin Gutkowski <webmaster@xxxx>]

Hi Shain

First off, before the teccy comments, for all other non-electronically inclined readers,
I should point out that I'm currently working on my own design for the fan delay system.
Mine will emulate the function of the FanZilla, with a few minor changes, and will
restore the function of the fan-fail light (worked out how to do this easily/properly now
- hooray :-)

If you hadn't already worked it out BTW, I am an electronic engineer (who went into IT
and after 3 years am enjoying the chance to get back to some electronic projects!). The
last of the parts arrived today. I will document it in the Tech section of the DOC UK
website. Now for the teccy stuff on Shain's design:

I am having trouble resolving any of your RS part numbers - the only one that works is
the relay which is an 80mm M12 bolt.....

I have had a quick look at your system and several things spring to mind... first off,
you are only delaying one fan. One of the main reasons for the fan delay is to remove the
"kick" when the AC cycles - and therefore you need to delay both fans by different times
so they come on sequentially after the compressor.

You should not need a series resistor with the relay coil. The 3904 tranny (do you mean
RS pn 287-459?) is only a signal tranny capable of 200mA. The 2n2222A (RS pn 295-028) is
cheap, robust and capable of 800mA. It's what I'm using. I don't know from a quick look
how your earth switch works on the relay, but it seems overly complex. You should not
need more than one NPN tranny per relay as a low side switch, and I'm even going to use
it as a poor-man's high-side switch on the fan fail light.

I can't say for certain with the small look I've had, but I don't think you're giving the
relay a solid 12v - 0v switch, but are letting the tranny pull the earth down slowly -
this makes the switching point in the relay very vague and can cause the relay to spark
like crazy (like when you switch a light switch half way).

There's a small typo in your document about connecting up the fan fail light BTW.

All the best

Martin
#1458

shainbrannan wrote:

> Hello,
>
> Fo everyone that inquired about my fan delay box I just got done
> posting the schematics, notes and parts list for the fan delay box in
> the files section. Everything should be their to get you going .
> Please let me know if you find and faults or have questions.
>
> - Shain
> #10140