Need Transistor to relay help ASAP

[Slobin3d]

A good way to do the wiring is to print a copy of the schematic and do one wire at a time, crossing it off as you make the connection. When everything is crossed off you are done. Then you should use a continuity tester to check each connection on the circuit and mark it again in the schematic.


Bob

That's what I'm doing now, I was working off my phone last night, and this morning both. I only have internet at work What modifications to your diagram need to be made because the signal voltage is halved?

 

[CocaCola]

Another way to do is to print out the circuit after you have done what Bob says and then look at each connection point, not the actual connections...

For example take pin 3 of the IC it connects to +24, one side of the 6.6K resistor, one side of the 3,3K resistor, to the diode and to the relay... Verify all those connections then X off pin 3... When doing this treat every component as polarized... For example pin 4 also attaches to the 6.6K resistor but on the opposite end... It might benefit you to label each end of the resistor say 6.6a for the top and 6.6b for the bottom when doing the point to point verification... When you are done you would have double or better checked every connection, example you already checked that pin 3 connects to 24+ but when you check 24+ you will again verify it connects to pin 3...

I do this when I take a printed schematic and have do a PC board layout...

 

[BobK]

Please re-explain what you are seeing as the signal. Your last explanation seemed to say the neutral position was 2.5V and the forward position was 1.25V which reverses the direction of the voltage change.

In any case you are going to have to redo the divider chain, and you may need to swap the + and - inputs if indeed the forward votage is less than the neutral voltage.

Bob

 

[Slobin3d]

once i rechecked it with my working Multimeter 0V was full reverse, 1.25v was neutral and 2.5v Full forward, Half of everything we were reading in the beginning

 

[CocaCola]

once i rechecked it with my working Multimeter 0V was full reverse, 1.25v was neutral and 2.5v Full forward, Half of everything we were reading in the beginning

Make sure you disconnect anything you have wired up and added when you take these new measurements...

 

[Slobin3d]

Make sure you disconnect anything you have wired up and added when you take these new measurements...

Did, those are taken after everything was removed. On the diagram the transistor, which is C and E, I seem to have trouble getting them correct.

 

[CocaCola]

The 2N4401 is an NPN

Look at this page, first section and mind the direction of the arrow...

http://www.kpsec.freeuk.com/trancirc.htm

 

[Slobin3d]

got it for sure this time! I have it wired as it was drawn on the last diagram. I'm assuming I'm going to need to change resistors because of the changed throttle voltage though. I've looked at a few of the online calculators but I can't seem to understand how you configure your resistors for the voltage drop. Like if I use the 6.6k thats already there then R2 should be 380ohm that sound right?

 

[BobK]

Let's say you are shooting for 2V as the turn on point. Then you want to divide the 24V by 12. Which means you need and 11:1 ratio. You could put your 2.2K on the botton then put a 22K + 2.2K on top. Or you could use a potentiometer like I originally proposed and then you could adjust it for the most natural operating point when turning the throttle.

Bob

 

[Slobin3d]

how about amp draw, How do I ensure that the circuit will be able to supply enough amperage to get the relay to activate?

 

[BobK]

The 3.3K base resistor was chosen to make sure the 2N4401 is saturated at the maximum current spec of 600ma. By the way, hopefully you determined that the relay coil draws less than that. I don't think you ever gave us the specs on the relay.

Bob

 

[Slobin3d]

The 3.3K base resistor was chosen to make sure the 2N4401 is saturated at the maximum current spec of 600ma. By the way, hopefully you determined that the relay coil draws less than that. I don't think you ever gave us the specs on the relay.

Bob

the relay doesn't have a spec sheet with it......

http://www.oreillyauto.com/site/c/detail/HLA0/003437057.oap?keyword=50a+relay

 

[BobK]

Well, it should be less than 600ma at 24V I hope.

It also just occurred to me that, since you were not familiar with which lead is which on the transistor symbol, you also need to pay attention to the diode.

------------------|<------------------
cathode -------------- anode

And on the device the cathode is the side with the band around it. Notice the band can be thought of as the vertical bar in my drawing above.

Bob

 

[Slobin3d]

Well, it should be less than 600ma at 24V I hope.

It also just occurred to me that, since you were not familiar with which lead is which on the transistor symbol, you also need to pay attention to the diode.

------------------|<------------------
cathode -------------- anode

And on the device the cathode is the side with the band around it. Notice the band can be thought of as the vertical bar in my drawing above.

Bob

that much I did get right. I am a Hobby Shop manager by profession, and was a Automatic door repair man before this, Relay, Diodes, Switching powersupplies, Rectifiers I'm familiar with, I have never had to get this deep into a board before though.

 

[BobK]

that much I did get right. I am a Hobby Shop manager by profession, and was a Automatic door repair man before this, Relay, Diodes, Switching powersupplies, Rectifiers I'm familiar with, I have never had to get this deep into a board before though.

Okay, just wanted to make sure you got it the right way, because it would be would go up in flames if the wrong way.

Bob

 

[Slobin3d]

no worries. I did the 22k-2.2k so hopefully tomorrow morning everything works as designed! Where's the crossed fingers smiley?

 

[Slobin3d]

Well, I tested it this morning, and while testing I accidentally shorted the relay wires, got a shard of transistor to the face. Replaced the transistor, and checked my voltage to the comparator. All was well, but not quite at the threshold. So I used a spare 1k Pot, and wired it in line to fine tune the threshold. Plugged in the relay and it clicked when it was supposed to!!!!! plugged it all back together and rode the scooter around, FYI, dont stand on a scooter when it's running, they stop really fast, and well, I don't! lol

 

[BobK]

Hurrah!

Bob

 

[Slobin3d]

Thanks to both you guys! I learned a lot from this whole project.

 

[CocaCola]

Glad to hear it finally works, and yes those failsafe seats can account for some unexpected braking...