83Views13Replies

Author Options:

help with shorting probem on my curcuit Answered

This circuit does not work because of a problem with power shorting to ground at the motor. I think that is the only problem. The servo provides a 4.5v power source and the polarity can switch allowing the original 4.5v servo motor to run forward and reverse. I am making this to run a motor on 12v and the servo on 4.5v. R1 keeps the transistor saturated and the R2 is in there because I read it would help the transistor turn off completely. I made this circuit work (the right voltages went to the right places) in one direction but now it is more complex, I think I’m having a shorting problems. Can anyone help?

Discussions

0
None
kendallickes

9 years ago

the system is ment to reverse the + and - back and forth to make the motor go each direction. stick up one way stick down the other

0
None
lemoniekendallickes

Reply 9 years ago

Ah, I lost sight of what this is supposed to do, that's why you've got two sets of stuff and the diodes... You're after a double-pole double changeover switch in the end. While I go away and think about this, what exactly is the servo thing how is it built and what does it do? L

0
None
kendallickeslemonie

Reply 9 years ago

The servo was originally just an old servo that hooked to an RC air plain to make something move. I tool it apart and removed the small motor. I connected 2 leads onto it where the motor was. Now I have alternating + and - voltage at the servo. Ultimately I'm afraid ill have to use relays for my main app because my big motors draw 3 amps. For now I’m just getting my learn on. Thanks guys

0
None
lemonie

9 years ago

OK how about this, you know how the 4.5V thing works, but roughly this. L

F5ZHF2IFRXUSIJT.SMALL.bmp
0
None
gmoon

9 years ago

Rather than reinventing, why not look to H bridge circuits? It's a solution specifically designed to avoid the difficulties that have you stymied...

There are several types linked from that page (and many, many more if you search.) You'll find a few here on 'Ibles, too.

0
None
Kitemankendallickes

Reply 9 years ago

Is the diagram an accurate representation of what you have made?

If I'm reading it right (and I may not be, I'm tired), the thing you have labelled "4.5V servo" and the motor are both completely shorted out of the circuit. In fact, the green leads don't appear to carry any current at all.

(Is the thing you have labelled as a servo actually one of these things, or is it something else?)

0
None
kendallickesKiteman

Reply 9 years ago

I know it looks messy but most of it works. As long as I don’t connect the leads to the motor it works, I get 12v where the motor would be and 4.5v operates the transistors. It doesn’t short out at the green leads. The diodes prevent that from happening. Also there is a weird voltage overlap at the top line where the 12v and 4.5v flow. It doesn’t really make since to me but it works fine. I haven’t adapted anything specific; I have experimented with a million things and put them together to make that.

If it helps, you can completely ignore R2 it doesn’t do anything. R1 makes sure the transistor is saturated. I got that from this site: http://www.rason.org/Projects/transwit/transwit.htm I did the math and made it all work, the only problem is I cannot figure out how to wire the leads to the motor to keep the 12v from shorting. I know I can use relays but future but in future versions of this circuit I want it to be variable speed so I'm trying to avoid relays.

I asked my wife for help just as an outsider brain. She knows nothing about this stuff. But she came up with an idea that should work. I can hook up another 12v batt and have it connected like I do the 4.5v supply. Then just ground each side to a different batt. I should work I just think it’s very messy. I am going for simplicity and reliability.

Thanks for all of your help guys.

0
None
Kitemankendallickes

Reply 9 years ago

Hang on - you've just changed something - what started as a 4.5V servo is now a 4.5V supply?

And the way that diagram is laid out, you cannot get 12V across the motor.

You really need to post a photograph of what you have put together before we can make any sense here.

0
None
NachoMahma

9 years ago

. There is a dead short around your motor! For all intents and purposes, the motor is not even in the circuit. . I don't think your circuit can even be modified to work as a fwd/rev controller. If you connect the two diodes above the motor to one motor lead, and the other motor lead to "ground," you will have a fwd/fwd ctrlr. Put a resistor inline with one of the transistors and you have a fast/slow ctrlr. I see no way to make it fwd/rev. But I'm no engineer.

0
None
lemonie

9 years ago

Why all the diodes? Never mind that - I don't understand the circuit at all - where did you get it from? Is there some other circuit you're adapting? L

0
None
Kitemanlemonie

Reply 9 years ago

I think we need a photo of what he's made so far.

0
None
lemonieKiteman

Reply 9 years ago

It would help, but I'm interested as to where kendallikes is starting from - you wouldn't put this sort of thing together without any frame of reference?

L