2N222 for spare ports

[Bender142]

I'm planning on using two of the spare ports to drive a (relay controlled) electric cooling fan and a (relay controlled) TCC.

Does anyone have any experience with using 2N222 transistors to drive devices on the spare port circuits (V3 board).

Thanks

[roarin_mouse]

I would not use it. It would better to use a darlington transistor or a MOSFET for the following reasons: In order for the transistor to stay cool, it must be switched from off to saturated. Although the small signal gain of the transistor looks fine, when you want to saturate it you should have a base cuurent of about 1/20th to 1/10th of the load current. With that said, assume you have a relay that draws 300mA. That means that the microcontroller must push 15 to 30 mA through the base-emitter junction. That's a lot of currrent! A darlington is basically two transistors so the current gain is much higher. The MOSFET is also a god choice because it uses zero current (steady state). Both types of devices are readily available and in the same TO-92 package.

[66fb]

Bender,

You mean 2N2222 I think.

Short answer: No, but here is a link to a "howto"
http://www.DIYAutoTune.com/tech_article ... _Output_v3

If you are not already using the GM style IAC outputs for something they will drive a 1 amp load, IIRC. I'm using one to pick a fan relay and works great.

[Bender142]

Good input, thanks for both previous responses.

BTW - I'm using the GM IAC so that's not an option. Looks like the MOSFET device is a better way to go.

Thanks

[Bender142]

I just checked out the link that 66fb sent, thanks....

I'm using the FIDLE on the relay board to provide a 5v ref for my 7-pin HEI ignition. My bad for not including my set up.

So now that the horse is loose, I'll close the gate....here's my set up: MS-II V3 w/relay board, 2.88 code, GM TPI hardware and sensors w/IAC.

Cheers

[91gmck5]

Can the 2n2222 transistors for the LEDs simple be switched with darlingtons or do the resistors need changed also? I want to be able to run both the LED and an external relay.

[91gmck5]

Forgot to add that its a MSII v3. Also, I am wanting to replace the 2N3904 with a transistor better than the 2N2222.
Thanks -Matt

[kjones6039]

FWIW..........

The various manuals often suggest using the 2N2222A to drive common automotive relays. I have used them extensively without any failures. (ie. coolant fan, tcc, etc.)

Just my experience tho..............

Ken

[trakkies]

Forgot to add that its a MSII v3. Also, I am wanting to replace the 2N3904 with a transistor better than the 2N2222.
Thanks -Matt

A 2N2222 can handle 800mA. That's way more than enough for a standard 30 amp relay. And an LED. Signal LEDs take no more than 30 mA or so. The relay about 200mA. But do wire a diode across the relay coil to prevent the back EMF when the relay is switched off damaging the transistor. The cathode goes to the positive side of the coil.

[91gmck5]

Thanks for the help. Will probably end up staying with the 2N2222 then.