Reversable Motor with WC8, DPDT and STSP relays

R

rfeyer

Active Member
OK, if I learned anything at all from the information you all have fed me, then the following should work?
 
Trying to control a 12V 5A reversible motor using WC8
The DPDT is a OMI-5S-212D, the SPST I have not gotten yet, but assume they can be low load 5v 0.5A since they carry no motor load, yes?
 
 DPDT SPST Hen Door.jpg
 
If this correct, I WILL try to convert this to a real schematic diagram as I know I need to learn it.
 
 
 
rfeyer said:
OK, if I learned anything at all from the information you all have fed me, then the following should work?
 
Trying to control a 12V 5A reversible motor using WC8
The DPDT is a OMI-5S-212D, the SPST I have not gotten yet, but assume they can be low load 5v 0.5A since they carry no motor load, yes?
Click to expand...
 
 
Both the SPST and the DPDT relays need to carry full motor current and need to be rated appropriately.
 
I used the wrong nomenclature, my fault.
 
The SPDT relays will only need to be 5V for activation with low amp (i.e.: utilizing the WC8 signals), but able to handle 12VDC 5A at COM, is that correct?
 
Also, do common SPDT solid state relays usually have inherent diodes or should a diode be placed after each, following the load lead?
 
Can you post a link to the datasheet for the relay you want to use?
 
To answer your question about the diode most EMR (electro magnetic relay) do not include a built in diode. SSR (solid state relays) are typically optically coupled and not having to move an armature have much lower current requirements.
 
The 5V relay is going to consume much more current then the WC is able to deliver. You are going to need to add some sort of buffer to drive the relay from the WC. If you only need a single output then a discrete transistor, like a 2N3904 with an diode (1N4148)  will work fine. If you need a lot of relays may want to use a transistor array to drive them to save space and money. The ULN2003APG transistor array is able to drive 7 channels and has  built in clamp diodes.
http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0CC8QFjAA&url=http%3A%2F%2Ftoshiba.semicon-storage.com%2Finfo%2Fdocget.jsp%3Fpid%3DULN2004APG%26lang%3Den%26type%3Ddatasheet&ei=hFy8VLTaLcGegwTPwIPABg&usg=AFQjCNHbTYMeA_ut58vxijibJjzdax-ZVA&sig2=XgFV_Gplt_Li2aXp3LNjrA&bvm=bv.83829542,d.eXY
 
Relay spec
http://media.digikey.com/pdf/Data%20Sheets/Tyco%20Electronics%20P%20B%20PDFs/OMI%202%20Pole.pdf
 
I know you are new to design but an H-bridge would be a lot easier, cheaper, smaller then using relays.
 
/tom
 
I was looking at H-Bridges but as the motor peaks at 5A I did not find anything cheaper, then again, did not really know what I was looking for either.
Should the above work?
 
Rainer
 
The contacts on the Amazon relay are only rated at 3A for DC, and coil voltage is 5V. the RadioShack one looks OK it is rated at 5A with a 12V coil.
 
If you want to stay with relays I'd just use two of the Radio Shack ones, one to control direction the other power. Use a general purpose NPN transistor, like a 2N3904 to low side switch the relay and place a diode across the coil. Drive the transistor through a 1k resistor to one of the WC outputs.
 
http://www.onsemi.com/pub_link/Collateral/2N3903-D.PDF
https://www.fairchildsemi.com/datasheets/1N/1N914.pdf
 
Not to make your head explode but not all DC motors are reversible. I assume the type of motor you purchased is a garden variety brush motor, in that case you are good to go.
 
In your code be sure to turn power off to the motor a little bit before reversing direction.
 
Start playing with your design and learn by doing.
 
/tom
 
/tom,
 
 
The transistors above are then used to increase the supplied voltage, allowing the 12V relays coils to open, correct?
 
 
Rainer
 
Correct the transistor allows the low current 5V outputs to control the higher current 12V needed to drive the relays.
 
The relay board you linked to is 24V, you can use a relay module but since you are using 12V motors easiest way to go is to use a 12V relay module. That way you can power the relays from the same supply you are using for the motors.
 
/tom
 
There's another option I've used here.
It's not quite so elegant, but it's effective enough, and inexpensive.
 
Get one of the (cheap) 2-channel (or more, if you have use for other relay outputs) driver boards. Most only have SPDT relays, which is fine.
 
With two SPDT relays, you can have a motor off, forwards or backwards.
 
Lets say OP1 and OP2 drive relay 1 and relay 2.
 
Both relays have their NO contacts to your +V supply. Both have their NC contacts to ground.
Either side of the motor goes to the two relay commons.
Turning on OP1 (and leaving OP2 off) will drive one way.
Turning on OP2 (and leaving OP1 off) will drive the other way
Turning OP1 and OP2 both on, or both off, will stop the motor.
The ONLY critical aspect of this is to make sure relays are break-before-make (most are).
 
TY RossW, I may need to wait doing this until the next project (which I already have in mind).
 
I am a little in overload, meaning, turning in cicles. Luckily had today off, so, spend my day learning about DOPING and BIASING of transistors, reading about NPN vs PNP. so far so good - but still have to read about how these are connected.. I did learn that the Base and Collector are additive and hence give a higher voltage output :)
Then I went a little further getting into Ohm's law thinking I could figure out how to know what transistors to use - came up empty but will leavbe that until the next day off.
Once I have Tom's suggested transmitters, diode and resistor, i will start putting things together and hope I know how to connect them :)
 
I am amazed how patient you all are (and thanks for that), I am a bit of a challenge in electronics :(

Rainer
addendum: believe I found instructions on how to connect Transistor :)
 
When driving relays from logic outputs, I usually just use a BC337, because I have thousands of them, they're cheap, their gain is adequate and their collector current is very high for the package.
 
HOWEVER! For your purposes, by the time you buy relays, transistors, resistors, some breadboard, muck about making the board etc.... I'd just throw a few dollars at one of these: http://tinyurl.com/kpo4hwc
 
This particular one is opto-isolated (a good thing for the WC's safety), active-high (a good thing for the motors if you turn off the WC), has 12V relay coils (so you don't have to draw any substantial additional current from the WC power supply), and claims better than your required 5A. It's also cheaper than buying the parts!
 
The other advantage with the two SPDT relay configuration is that they are plentiful, and you only ever need ONE OUTPUT on at a time, not two (as you may need - say, running backwards with an SPST and a DPDT).
 
If you need me to draw a circuit of how you'd connect the relays, just ask. It's quite straightforward.
 
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