Re: Re: [DML] Fan Sequencer (delay box)

[shain@xxxx]

Hey Martin,

Thanks for the input. Unfortunately i'm the only one who had the chance to go over my design until now. In order for the circuit to operate properly i need at least 75 ohms of resistance on the coil, unfortunately the rs model is only 66 ohm, so using the resistor brings it up enough to function. The 3904 (while not as common here as in the Uk) are readly available, and radio shack carries them so why not. The 2n2222 should work fine but i haven't tested them yet. I don't know why your rs part numbers aren't working, i just bought the parts the other day (don't know how rs work in the uk). I'm very eager though to see your fan fail indicator circuit though. As for sparking, i'm not worried about that. I haven't had any sparking yet, and if there is a momentary low of signal, it still takes 2-3 seconds for the capacitor to step back up in order activate the relay. I though the purpose of the fanzilla was to turn one fan on then have a delay on the second. The main fu!
nction of this was to have one fan warm up before the other clicks on, creating a gradual instead of an imediate request of power for the car. If there both delayed i can't see how it would help, if one waits say 4 seconds to activate, the the other waits 12 seconds, one is still turning on before the other, please clairfy on this so i can make the nessary changes.

- Shain

----- In Response To -----

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



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