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Topic: DPDT relay? (Read 1 time) previous topic - next topic

retrolefty

#5
Feb 27, 2011, 12:23 am Last Edit: Feb 27, 2011, 12:34 am by retrolefty Reason: 1

Good call Lefty.
Maybe 4 of these then, wired up like the transistors in an H-bridge?
(which I am sure I created a drawing of somewhere)
http://www.mpja.com/prodinfo.asp?number=17155+RL



No, just two relays are required, one DPDT to handle the polarity reversal and one SPST to remove DC voltage for the stop condition. I don't have a drawing program presently, but the old X wiring across the NO and NC contacts and the motor wired to the two common contacts and power applied to one NO and one NC contact. The SPST relay contact would just be in series with the batteries positive or negative lead.

Lefty


cr0sh


Using four SP relays is not a safe thing because you can't depend on all of them to have exactly the same switching times. If one relay is "slow" you could end up shorting the power supply.  Much safer to use a DPDT relay to control direction and a SPST relay (or transistor) to control ON/OFF (or speed if using a transistor and PWM).


Actually, it would be best to use two SPDT relays, with the lever of each connected to the motor, and the NO contacts connected to +V and the NC contacts connected to GND. This way, you could switch either one to control direction, and both off (or on) for brake. A couple of Bosch 20A 12VDC automotive relays would fit the bill perfectly, and can probably be found fairly easily at a junkyard for a few dollars each. They are designed for these kinds of loads (ie, windshield wipers, pumps, windows, A/C fans, etc), and so are engineered to take the abuse. Even brand-new they aren't that expensive.
I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

Terry King


...
Actually, it would be best to use two SPDT relays, with the lever of each connected to the motor, and the NO contacts connected to +V and the NC contacts connected to GND. This way, you could switch either one to control direction, and both off (or on) for brake.


Yes, this is what I was going to suggest. 

At up to 10 amps, these are a good $12.50 solution....  http://arduino-direct.com/sunshop/index.php?l=product_detail&p=155  DISCLAIMER: Ones I found for my shop!
Regards, Terry King  ..On the Red Sea at KAUST.edu.sa
terry@yourduino.com  LEARN! DO! (Arduino Boards, Sensors, Parts @ http://yourduino.com

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