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

[shain@xxxx]

***** Moderator's Note *****
If anyone else is interested in helping Shain and Marting thrash this out, please
do so off list. 

Mike G Moderator of the week
*****


Moderator Note: This is my last email on this subject for the current moment. I too have had a full mailbox of questions, but for the moment me and Martin are going to chatt of the list and discuss things. 

Martin,

My circuit was orgionaly drawn by me several years back when i was into electronics. My notes say that i had to use a 75 ohm relay coil, i had no clue why and it has to be looked over to make sure. The shcematic is drawn correctly, i use t1&t2 to work as a 8-9 volts zener diode, this is used for a high(er) turn on voltage for the darlington transistor (tip120). I am aware about the npn, pnp switch. I drew it this way to make it easy for the people watching to build, one of the reasons why i attached a diagram of the transistor below. I recently added fuseable links to my design, elimanting the circuit breaker (as suggested). Turns out it could be a much better idea incase a motor blows at it won't take down the other. We'll talk off the list for now on to slow down the congestion.

- Shain
shain@xxxx
#10140
PA Lis # TIMELES

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

[Note to moderator: our discussions are getting pretty involved, but I have been receiving private e-mails on a daily basis asking questions and making helpful suggestions - it has surprised me how much interest Shain and I have kicked up!]

Hi Shain

First off, I have realised the source of the part number problems - You say RS to mean Radio Shack - I know RS to be the international reseller of engineering components and materials. rswww.com is always my first port of call for prices, data sheets, and the part numbers are internationally recognised. Ironically I usually end up using Farnell though as they tend to be cheaper.

I have sent your plans to one of my friends who actually works in the electronics industry (unlike me) - he basically suggested you check your diagram because there are some glaring errors and as such the circuit will never work. Particularly one of your NPN transistors is drawn as a PNP and T2 seems to be controlled via a reverse biased base-emitter junction. The circuit as drawn, just plain won't work - sorry mate.

I have looked up the TIP 120 and it's a 5A NPN power transistor. Pretty much all trannys of this type are fully switchable with anything over 5V, and if you download the data sheet (from rswww.com) you'll see that it has an integral driver transistor already. You shouldn't need a 5A tranny in this application, but if it makes you happy :-) Still don't know why you'd need a series resistor - you'd need to find a relay with a DC resistance of some 2ohms before your TIP120 will pop.

>> The kick of the ac compressor (draw on the motor) was totaly overlooked by me (usualy i've drivin v8 were the kick isn't as noticed).

Hehe - I know what you mean. I drive a modern direct-injection Diesel which has very impressive torque figures. It too has twin electric cooling fans which both engage a the precise instant of the compressor. I've never felt it - I only know it does it because for a short time last year the compressor clutch gave a little squeak when it engaged!

>> Added an additional timer is a simple thing to do never the less.

Oh sure - it just means building the circuit twice and twiddling a couple of component values - this is precisely how I'm doing it.

>> All in all with some modifications and some good testing both of our designs will be helpful to all the do it themselfers on the dml. I don't believe that i did so bad for a person who isn't an electronics buff.

Oh sure - you got further than anyone else and a lot quicker than I got around to it too! I've been pestering my former university friends with questions since I started this little "revision"!

>> I think for the moment i'm going to use the stock relay sockets and wire them with test spade connectors so i can test new designs and ideas very easly while maintaining a stock look.

Me too.

>> Were moving int he right direction currently. Now to just make a replacement light dimming circuit ;)

Personally I'm moving towards a door-launcher interface for the Ultrastarters 2250M remote start system which still hasn't arrived (dammit!) and re-working the door lock module so it can all fit in the stock lock
module box.

Keep up the good work

Martin
#1458





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