I tested pin number 25 JS0 (On the 37 pin connector) that I have 4.87 volts to turn on a relay for a cooling fan. What is the maximum amprage draw that can be used to operate the coil side of a relay through that 25 pin? Is there a typical relay used with the Mega squirt out puts to operate 12 volt equipment such as a fan motor? Also I assume that all the JS out puts would do the same load function. Is this correct? Thanks for the Help.

 

You need to build a transistor circuit in the proto area to power that coil. Do NOT try to power that coil directly from a pin on the CPU, all you'll do is fry parts of the CPU if you do that.

Basically, all you need are a pn2222a transistor, 1N4001 Diode, and a 1k resistor, wired like this:

http://www.msextra.com/manuals/MS_Ex...elayOutput.JPG

That diagram says to use a 2n2222 transistor, but I've always just used the pn2222a.

Ken

 

Also, to be clear, MS normally switches loads to ground. It is not normally wired to provide 12v output signals directly. In other words, provide 12v (hot when key in run) to one side of the relay coil (see the pic in muy's link), and connect the other side to the MS. Also, be sure to put that 1N4000-series diode across the relay coil, or you run the risk of popping the transistor in short order. Some automotive relays include this diode internally, so you may want to check your relay first. If it's got one inside, you can eliminate that component from the circuit.

 

I printed off the drawing for the system to pull ground for the relay. What wattage should the resistor be? How do I tell which side of the transistor do I hook to ground and the other side to SPR 1 (Pin 3)? Thanks Renns I understand the use of the IN4002 diode you explained it very well.
Best Regards

 

Any general purpose NPN transistor should be fine. Type in the part number of the transistor you are using, and you find a data sheet in short order. It'll show the base, collector, emitter pins for that part. Emitter goes to ground, collector is connected to the relay, and the base is driven via the microprocessor through a resistor to limit current. There's only a few milliamps flowing through the base circuit, so your common 1/4 watt resistor would be fine.

 

I understand your directions clearly. I have to go to my shop and pick up two of my Mega Squirt V3 boards and the parts. I have one in my race car and a back up in my tool box.

Now I have to add in a circuit for each relay that I want to set up a 12 volt ground system and protect it with the diode. I have the resistors and I am going to use the 2N3904 transitors that I have left over from repairing my transitor Q15 on the secondary injector out put circuit. This I assume will work.

So if I use the out put signal on pin #25 of the DB37 connection can I built a relay grounding circuit out side of the Mega Squirt box? If so can pin # 25, 29, and 31 on the DB37 connector all be used in this manner? I have not looked yet but I think I can put three systems on the proto area. If not this idea is my second plan. Would it work with no problems?
Thanks Guys,
Kim

 

To add to my last post could I use IN4007 Diodes to make the system work instead of IN42002 type? I have an extra 20 at the shop to use up.

 

Sure, that's fine. The only difference is peak voltage, with the 1N4007 up at 1000V instead of 100V.

 

I'll use up what I have and test it out next week in the car. I'll use the IN4007 diodes, 2N3904 transistors and 1K 1/4watt resistors. I will be making three separate circuits for fan control, over temperature light and alternator cut out system. Thanks again
Kim
SCCA RX7 RACER

 

I tested all three relay systems on both Mega Squirt systems that I have today and they seam to work out fine.
Thanks for the help!
Kim