I tried to build a simple circuit that would send current through a resistor...

Thread Starter

eyik66

Joined Dec 15, 2012
30
I tried to build a simple circuit that would send current through a resistor if it was no longer being drawn by the load.

I thought I could do it with a PNP transistor with the charger on the Base, the resistor on the collector, and the voltage source on the emitter. That didn't work.

Any simple circuits that you guys know about that will do what I need. I've attached a block diagram. This idea is that a stepper motor will create a 5V power source, but if the battery is charged, the 5v power source will bleed off through the resistor. View attachment 100490

 

Veracohr

Joined Jan 3, 2011
694
Why waste power by diverting it to ground? Why not just cut off the connection to the circuit?

I don't know anything about motors, maybe there's a factor I'm not aware of.
 

ian field

Joined Oct 27, 2012
6,539
Why waste power by diverting it to ground? Why not just cut off the connection to the circuit?

I don't know anything about motors, maybe there's a factor I'm not aware of.
That wasted power might make a wind turbine take just a little energy out of a weather system that could turn destructive.

If everyone did that, there might be slightly less - or less destructive tornados.

An unloaded generator could over-rev in strong winds.
 

Thread Starter

eyik66

Joined Dec 15, 2012
30
The motor is being used as a generator and will always be rotating. So if the circuit isn't drawing current, the AC gets too high on the rectifier circuit and ruins it.

I've been messing with PNP transistors all day, I must be on the wrong path. This can't be that hard though, any ideas please???
 

Thread Starter

eyik66

Joined Dec 15, 2012
30
Are you wanting to make a wind turbine or generator from a stepper motor?
Yes, it is a stepper motor generator. The stepper motor will always be driven and I have no control over that. So I need to have a way send the power somewhere before the AC gets too high on the rectifier circuit.

I was under the impression that a PNP transistor would connect the emmiter and collector if no current was being drawn from the base. So I was hoping to connect the battery charger circuit to the base, so that when it stops drawing current, the current is diverted through the collector and a resistor. Unfortunately, it isn't working.
 

AnalogKid

Joined Aug 1, 2013
8,227
While the current direction changes between NPN and PNP transistors, they function identically. With no base current, both are "open" from collector to emitter.

Is it the Inverter/Regulator that is failing in the unloaded condition? If so, what is the normal voltage range under load, and what is the open circuit voltage range that is "ruining" the rectifiers?

And of course, a schematic of the inverter would be very helpful. Without it, everything is just guessing. Maybe high-quality guessing, but still...

ak
 

ronv

Joined Nov 12, 2008
3,770
I'm just using these from amazon:

http://www.uxcell.com/l7805-three-terminals-voltage-stabilizer-regulator-module-5vdc-p-456483.html

Im not sure what component is failing, but it is in that part of the circuit. I assume the AC voltage is getting too high for something on there.

I'm open to suggestions, I just need something to keep the AC voltage from getting too high on the input
Would it be possible for you to measure the ac input voltage to the regulator? Any idea how much current the motor can supply?
 

AnalogKid

Joined Aug 1, 2013
8,227
That is a complete AC-to-DC power supply (minus the AC source),. It is a straight 7805 regulator with a full wave diode bridge input, so the input must not exceed 17 Vac RMS or 24 Vdc. There are other regulator assemblies with a higher input voltage tolerance, but without a measurement of your unloaded generator voltage there is no way of knowing if they will survive.

What you are trying to do is a version of what is called a shunt regulator. A less complex approach is to figure out what your actual input voltage range is, and find a module or combination of modules that can handle it.

ak
 

Thread Starter

eyik66

Joined Dec 15, 2012
30
I can try and figure out how high the DC voltage will get. Won't the voltage just keep increasing at the regulator input if there is nothing drawing from the regulator output?

I'll do some google searches on a shunt regulator. Hopefully there is a simple circuit example somewhere.
 
Last edited:

Dodgydave

Joined Jun 22, 2012
8,589
Yes, it is a stepper motor generator. The stepper motor will always be driven and I have no control over that. So I need to have a way send the power somewhere before the AC gets too high on the rectifier circuit.

I was under the impression that a PNP transistor would connect the emmiter and collector if no current was being drawn from the base. So I was hoping to connect the battery charger circuit to the base, so that when it stops drawing current, the current is diverted through the collector and a resistor. Unfortunately, it isn't working.

Can you measure the ac from your stepper motor going into the bridge rectifier with no load, to see what its giving out, then we can see what the peak dc would be, also which stepper motor are you using, 4wire or 6 wire,? mosfets would be best for shunting the dc.
 

AnalogKid

Joined Aug 1, 2013
8,227
Won't the voltage just keep increasing at the regulator input if there is nothing drawing from the regulator output?
No. There is a maximum value for the unloaded output, based on the strength of the magnets, rotating speed, wire gauge and lengths, magnetic coupling, eddy currents, and on and on. A real motor expert probably could tell us which ones matter in the real world.

ak
 

Thread Starter

eyik66

Joined Dec 15, 2012
30

Dodgydave

Joined Jun 22, 2012
8,589
So does the stepper motor charge the battery and feed the Arduino, and when the battery is full, dump the stepper voltage into a resistor?
 

ian field

Joined Oct 27, 2012
6,539
The motor is being used as a generator and will always be rotating. So if the circuit isn't drawing current, the AC gets too high on the rectifier circuit and ruins it.

I've been messing with PNP transistors all day, I must be on the wrong path. This can't be that hard though, any ideas please???
You can add the PNP transistor to a TL431 programmable-Zener in the manner of a Szicklai pair.

You set the shunt voltage with a pair of resistors, make sure the added emitter follower PNP is enclosed in the nfb loop and the whole thing is as precise and sharp knee as the TL431.
 
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