My apologies, these computers are being glitchy. I am currently working on a project that involves a 12v motor attached to a push button. I am messing with the programming, but while I am at school I am just planning. I know in the future I will need it to go CW and CCW, and believe the best way to do this is a relay. However, I am unsure of the math behind the V's and A's that I would need for it.
and believe the best way to do this is a relay.
No the best way is with an H-bridge, with one of these you can change the direction and the speed.
However, I am unsure of the math behind the V's and A's that I would need for it.
There is little in the way of maths. A DC motor will have a voltage rating, when you connect that voltage it will draw some current, that current will depend on the mechanical load on the motor. There will also be a much higher current requirement when the load is so heavy the motor stops rotating, this is often called the stall current. This is sometimes quoted but other times can be worked out from the motor's winding resistance and the rated voltage by using ohms law.
Grumpy_Mike:
No the best way is with an H-bridge, with one of these you can change the direction and the speed.
There is little in the way of maths. A DC motor will have a voltage rating, when you connect that voltage it will draw some current, that current will depend on the mechanical load on the motor. There will also be a much higher current requirement when the load is so heavy the motor stops rotating, this is often called the stall current. This is sometimes quoted but other times can be worked out from the motor's winding resistance and the rated voltage by using ohms law.
Darnit Grumpy Mike, I saw that you responded and braced myself for a grumpy reply. This isn't what the forum has come to expect from you. Calm rationale? :P. Ok but seriously. I think I only shy'd away from the H bridge because I was looking at L298N that was recommended for the arduino and our local radio shack didn't sale them. But I guess I will suffer the mail time. My DC motor is rated 3-12v so I just use a 9V at the moment, but its good to know that I can just get a 12v h bridge with no math for when I get a 12v power supply. Thankfully when I bought my motor they also gave me the stall current requirement, so that's good as well. Once I get an H bridge im sure ill be back to figure out how to add it to the existing set up. thanks mike
I was looking at L298N that was recommended for the arduino and our local radio shack didn't sale them.
I would not recommend that one it is old and does loose too much voltage across it when switching.
I have use a SN754410 dual H-Bridge and found it to be good. However there are many others, get one based on FETs rather than transistors and don't try and make your own.
You might also want to have a read of my four web pages on motors, the other three have links off this one:-
http://www.thebox.myzen.co.uk/Workshop/Motors_1.html
This isn't what the forum has come to expect from you.
Stick around you might be surprised. 
Grumpy_Mike:
I would not recommend that one it is old and does loose too much voltage across it when switching.I have use a SN754410 dual H-Bridge and found it to be good. However there are many others, get one based on FETs rather than transistors and don't try and make your own.
You might also want to have a read of my four web pages on motors, the other three have links off this one:-
http://www.thebox.myzen.co.uk/Workshop/Motors_1.html
Stick around you might be surprised.
Sweet, that was just the first dual H bridge I saw so I will keep looking. I saw some people who made their own and I agree that that does not seem like an ideal route. Especially with such great looking IC's made. I will have to check out FET's im currently hooked up to a TIP120 transistor, so I will check how they work together or if I gotta get rid of the TIP120 all together. I feel like I could learn a lot from your pages, but my school doesn't deem them safe apparently -_-
but my school doesn't deem them safe apparently
Knowledge is a dangerous thing, school is all about keeping you safe:-
From Michael Rosen
Guide to Education.
You get education in schools.
To find out how much education you get,
the government gives you tests.
Before you do the tests
the government likes it if you are put on
different tables that show how well or badly
you are going to do in the tests.The tests test whether they
have put you on the right table.
The tests test whether you know what you’re
supposed to know.But
don’t try to get to know any old stuff like
‘What is earwax?’ or ‘how to make soup’.
The way to know things you’re supposed to know
is to do pretend tests.
When you do the pretend tests
you learn how to think in the way that tests
want you to think.
The more practice you do,
the more likely it is that you won’t make the mistake
of thinking in any other way other than in
the special test way of thinking.Here’s an example:
The apples are growing on the tree.
What is growing on the tree?
If you say, ‘leaves’, you are wrong.
It’s no use you thinking that when apples are on a tree
there are usually leaves on the tree too.
There is only one answer. And that is ‘apples’.
All other answers are wrong.If you are the kind of person that thinks ‘leaves’ is a
good answer, doing lots and lots and lots of practice tests
will get you to stop thinking that ‘leaves’ is a good answer.
Doing many, many practice tests will also make it
very likely that there won’t be time for you to go out
and have a look at an apple tree to see what else
grows on apple trees. Like ants. Or mistletoe.
Education is getting much better these days
because there is much more testing.Remember, it’s ‘apples’ not ‘leaves’.
Grumpy_Mike:
Knowledge is a dangerous thing, school is all about keeping you safe:-
Lol nice, but I just meant ur site was blocked XD once I get home I'll do some studying
Have a look at this list of motor control modules from Pololu; big variety for various V and A. I have a 2130, works great and it's tiny.