Shop OBEX P1 Docs P2 Docs Learn Events
Motors, Darlington's and BS2 stamp capacity — Parallax Forums

Motors, Darlington's and BS2 stamp capacity

NickSrNickSr Posts: 7
edited 2009-02-21 00:50 in BASIC Stamp
Hi,

This is my first post. I have been working on a project with a BS2p24. I'm using:

A) 5 DS2760 One Wire·thermocouple modules.
B) 2 Crydom 3 phase 50A SSR's, 10mA input current·(controlling 2 480VAC sets of heat strips)
C) 1 Crydom 3 phase 25A SSR,·10mA input current· (controlling a 5 hp 480VAC·fan motor turned on by·it's own·starter)
D) 4 Crydom 5V DC 3A SSR's, 18mA max input·current·(Each controlling 1 12V DC 0.5A·process signal light·to be turned on only individually.)


I have tested the code for this with 110VAC using light bulbs as heaters, 10A SSR's and LED's as lights. I have it working OK. But, I need to test it against the heavier stuff above within a few days.

I am most concerned about:
·-Overloading pins on the stamp.
·-Protecting stamp and components from voltage·kickback from controlling the Motor
·-Overlooking·something because of·everything I have yet to learn.

Question 1
I plan to use a·Darlington Array (ULN2803A) for B), C), and D)·on·pins to my SSR's. Primarily to suppress any potential voltage coming back on my motor pin. Are there any max kick back voltages that it might not suppress? What is the effect on input current for all my other pins? eg. What does the spec mean when it says the darlington features a output current to 500mA? could that overrun my 18mA max input current of my SSR's in D)above?? Do I need a resister in the circuit to pull the output on that pin down below 18mA?? What else do I need to know? Particularly in matching the darlington spec to the SSR Spec??

Question 2
Can I / how / do I need to control the input current on my SSR's? Seems to me that if each SSR used its rated input, they would be within the 30mA max per pin and also within the 60mA max per 8 I/O's. (In D) above, only 1 pin will be on at any given time.)

Question 3
What are the two jumpered pins on top of the Crydom DR-ODC5 SSR's for? see attached spec?

Question 4
Comments on things I have missed??

We have a licensed electrician on this project and he assures me that the starter for the motor will absorb any kickback voltage. (I'm not sure what he knows about electronics though). I've read the stamps on steroids NV article.


I look forward to everything I have to learn and I have about a billlion more questions, but hope some of you will take time to comment!

Thanks!

Nick
pdf
pdf
Crydom dr_output_modules.pdf
437K
pdf
pdf
uln2803a.pdf
983K

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2009-02-21 00:12
    Hello,

    When using an SSR the load you’re driving doesn’t affect the input turning it on. Solid-State Relays are designed to be isolated from the input and use an opto-coupler type input, so turning them on is essentially turning on an LED inside. The light from that LED biases a photo-transistor which in turn activates other circuitry. Bottom line is, as long as the current of driving the LEDs in the SSRs doesn’t exceed the BASIC Stamp’s capability for current on I/O pins then you should be fine. As for controlling input current, the SSR should list a valid voltage range. This is because internally they usually have a resistor in series with the LED you’re lighting. The ULN would not work as you described and the only reason for using one would be to drive more than say two or three SSRs. As for the jumpered pins on top it appears your model has an internal fuse that can be replaced.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Chris Savage
    Parallax Engineering
  • $WMc%$WMc% Posts: 1,884
    edited 2009-02-21 00:50
    NickSr

    Welcome to the club.

    __________$WMc%____

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    The Truth is out there············································ BoogerWoods, FL. USA
Sign In or Register to comment.