PWM idle duty cycle

wes kiser · Post by **wes kiser** » Mon Jan 23, 2006 8:55 am

In the instructions on the ms2 board about the pwm idle, it states that 0% is no current, and 100% is full current. During stim testing mine appears to be reversed (@ 100% duty cycle my fidle led is not lit, and as you lower the duty cycle it gets brighter). Is there a paramter I can change to reverse that? I notice in the port settings, you can choose if making a statement "true" grounds a circuit, or "false" grounds a circuit. Can the same be done with pwm idle? If nothing is wrong with it, I can just go from 0% cold to 100% warm, instead of the other way around.

Bernard Fife · Post by **Bernard Fife** » Mon Jan 23, 2006 9:25 am

wes,

Are you using the standard FIdle transistor? Sometimes these work 'backwards' if the MegaSquirt has seen reverse voltage, even momentarily. this can happen from spikes in the 12V supply, or from accidentally touching the 9V battery the wrong way around to the connector (it won't snap into place, but can supply reverse voltage).

The problem is that while the damaged transistor is sufficient to operate an LED, it is not sufficient to drive a relay or PWM valve.

What I would do is set the idle control to On/Off, and verify that the FIdle LED works as expected. If it is still backwards, the transistor is very likely damaged.

Lance.

wes kiser · Post by **wes kiser** » Mon Jan 23, 2006 9:49 am

I have tried it with 3 different transistors(1 in the proto area, and then when I moved it to the heat sink I didn't like the way my jumper wires looked, so I unsoldered it and the jumpers and went for a 3rd transistor). So if something is damaged i doubt it is the transitor. I am using a tp120 darlington for pwm. I guess maybe I need to hook it up to an actual idle valve and see if it works.

el-hardo · Post by **el-hardo** » Mon Jan 23, 2006 12:58 pm

I have the same problem, but no fix yet!

Now i will try the spare output on FIDLE, perhaps this works well.

Bernard Fife · Post by **Bernard Fife** » Mon Jan 23, 2006 1:40 pm

Wes,

I just tried mine with 2.33 code and PWM selected, with 0 in the bottom bins, up to 100% at 160Â°F (and the standard transistors). This works as expected - the stim FIdle LED is brighter when 'warmer', dimmer when 'cooler'.

What do you have for % values in your bins? are they small at low temps, rising to 100% at high temps?

Lance.

wes kiser · Post by **wes kiser** » Mon Jan 23, 2006 1:50 pm

At 0% my light is on, and at 100% my light is off. Currently I have low numbers when cool, high numbers when warm. My concern is my circuit is behaving "backwards" of how it sounds yours is. I can make the light act like I want it, but if there is something wrong that will make it not capable of driving the IAC valve then I need to figure it out and fix it. I have checked and double checked this part of the install, changed transistors 3 times, and everything else appears to be working fine.

johnsop1 · Post by **johnsop1** » Mon Jan 23, 2006 1:56 pm

I think that the confusion is caused by the way PWM fidle valves work. The high side of the valve is connected to 12 volts, the low side to the collector of the filde transistor. The transistor grounds the valve when it is turned on, opening the valve. In this configuration the settings in the bins are in percent closed. I put 100% in the hottest bin and smaller numbers as the bins get cooler. With these settings the LED on the stim dims as the temperature rises.

Phil J.

Bernard Fife · Post by **Bernard Fife** » Mon Jan 23, 2006 2:01 pm

Wes,

Yes, it does sound backwards to mine. The docs describe the way mine behaves (I have tried this on a number of units, but haven't tried it with the TIP120 yet).

I think you'll have to try an actual valve to see if it works or not. There's no 'issue' with using high numer in low temp bins and vice-versa, some PWM valves require this. However, if there's a hardware problem, the valve won't move at all (which you'll find out very quickly on a real valve).

Lance.

el-hardo · Post by **el-hardo** » Mon Jan 23, 2006 4:29 pm

Hi,
i only tried in the car with 5 real PWM Idle valves.
All of them behaved equal.
When cranking, they are open 100%
After this, they shut down to about 20%

Ok till here.

But when the enginge gets hotter, the valve opens more, and when CLT is at 80Â°C, the PWM valve ist over 60% open -> 2500rpm in IDLE!!

I have changed anything in the settings, tried from 0 to 100%
100 to 0%
0 to 0% 100 to 100%
Didn't get any big change in behaviour.

MS II V3 Firm2.1 with Idle -> TIP 120 upgrade.

wes kiser · Post by **wes kiser** » Mon Jan 23, 2006 5:20 pm

Just tried it with generic port settings, and it behaved "as described". Set PM2 to fidle, coolant as the variable,greater than, threshold to 120 and hysterisis to 5. Trigger value to 1. With these settings when coolant went over 120 the light came on, so the logic isn't reversed. I have not hooked it up to a "real" valve yet though. I guess it is time to break down and drop the 60$ on my 3 bar map and put it in the car.