Having problems running high current solenoid from SX28

eagletalontim

As stated in one of my other topics, I am trying to control a solenoid with the PWM command that is pre-grounded on my car. I have been able to do plenty of bench testing with a small DC motor and a meter and everything worked fine until I actually hook it up to the solenoid on the car. When it is hooked up to the car, the solenoid barely moves like it is not getting enough amperage. I have attached my circuit to show how i have it hooked up. I have tried changing the values of the resistors but when I do that, it heats up the 7805 regulator. I have popped 4 SX's so far so I am really needing some help with this before this project turns into a HUGE money pit.

RobotWorkshop

What are the specs of the solenoid you are trying to control? Have you done any measurements on the current draw? Just temporarily connecting it to a 12v source and measuring the current with a meter would be a good place to start.

What kind of solenoid is this that you are using PWM to control? Is it meant to be switched at high speed? Most of the ones I was familiar with are either on or off and didn't require any PWM.

Since you've had more than a couple of the SX chips get fried you should definitely consider using an opto isolator between the SX processor and the circuitry you are using to control the solenoid. It will help prevent toasting the processor if things go wrong. Also you may also want to try using a FET instead of the TIP42.

Robert

Bean

The schematic looks okay to me. Except you may need a lower value resistor from the base of the TIP42. With a 1K you are limiting the base current to 12mA. The gain of the TIP42 is probably about 30 or so, that gives you only 12mA * 30 = 360mA. That is probably not enough for the solenoid.

How much current (amps) does the solenoid use when connected directly ?

You need to choose a power transistor that can easily handle that amount of current.

Bean.

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Post Edited (Bean (Hitt Consulting)) : 1/6/2009 3:20:07 PM GMT

eagletalontim

sorry for the delay on the reply. The solenoid uses 4 amps at 12 volts. The lower the voltage, the less it protrudes to it maximum capabilities. That is what I am needing to do.....based on a few other factors, the solenoid may need to be at 90% or 65% and so on. It will only be activated for about 1 second two to three times a minute so there should be no problem with excessive heat from current draw. I have read that a MOSFET may be better but I have no idea what kind of MOSFET I would need to get to control the positive side of the power or how to hook it up in a circuit.

EDIT*

One other thing.... "Except you may need a lower value resistor from the base of the TIP42." I tried putting a 100 ohm in place of the 1k and the 100 ohm got HOT quick!

Post Edited (eagletalontim) : 1/6/2009 10:09:45 PM GMT

JonnyMac

You may have to experiment with the PWM frequency to the solenoid; it the frequency is too fast a lower levels you may not be able to overcome the spring/magnetics, etc. I wish I could tell you more, but it's a bit of a mystery to me, too. I've attached a quick demo that does PWM in an interrupt. The original code is by Guenther Daubach with a couple small mods by me (there was not trouble with G's code, I just wanted slightly different behavior).

I've also attached a schematic for you to consider; this circuit is similar to something I used in a high-voltage DC project.

eagletalontim

you would not happen to have a schematic to be able to control the positive side of the solenoid would you? the solenoid is already mounted on the car and is grounded with the case. i cannot change that [noparse]:([/noparse]

JonnyMac

I don't, so let me suggest you do a web search on h-bridge circuits that use MOSFETs as an h-bridge requires high- and low-side drivers.

eagletalontim

ok, I looked over the existing circuitry that was on the car and I drew it out the best I am able to. I attached the file and labeled what I could. I have no idea what the transistors are or if they are NPN or PNP, but I labeled which ones are the TO 220 cases. Maybe that can help get me a little farther on what I trying to do. I am redoing this circuitry so I can control it when I want to....it is just being a pain I know alot of members on here know way more than I do on electronic design so hopefully someone can decipher through my wonderful schematic.

I am also looking into the H-Bridge MOSFET circuits and am finding that it will be more trouble than it is worth since I need to control the positive side of the solenoid which causes more heat since the P channels are slower reacting.

RobotWorkshop

Are there any numbers on the TO220 devices? They may be MOSFET devices. Try to google the part number and see what comes up. If you can't find them post all the numbers and codes from the case and perhaps one of us can help. As long as it isn't a house #'d part it shouldn't be too hard to track down.

eagletalontim

I think it is a factory marked part... the part number on one of them is B595. At the bottom of the transistor, it is labeled Y 2H. On the other one, it is labeled B1335A and at the bottom it has E 213.

RobotWorkshop

Actually those seem to be valid part #'s and they look like they are standard transistors (not MOSFETS). I didn't find much on those part #'s directly but you can look them up on the NTE site and cross reference them to get the generic replacements. With that in hand you can pull down the datasheet and get an idea of what the specs are. As a general rule I always try to get the exact replacement but if needed you can use the NTE parts. You can use the cross reference tool at:

www.nteinc.com

Best Regards,

Robert

Post Edited (RobotWorkshop) : 1/8/2009 2:59:14 AM GMT

eagletalontim

wow... thank you very much! I will look into that as soon as I am done playing with my new toy!!! Finally got me a serial LCD and am trying to make my own functions for it [noparse]:)[/noparse]