Hi Tom,
If you are feeding the splitter with a signal that is referenced to ground, and are using split supplies (+/- 12V) then you don't need a capacitor between the generator and the splitter.
As far as the decoupling capacitors are concerned there are two main schools of thought;
One suggests that a single capacitor should be between the supply pins, 4 and 8, another that two capacitors should be used, one from pin 4 to gnd and the other from pin 8 to gnd. There is even a school of thought that both these should be used
I normally find that a single cap between the supply pins is enough.
If you are feeding the splitter with a signal that is referenced to ground, and are using split supplies (+/- 12V) then you don't need a capacitor between the generator and the splitter.
As far as the decoupling capacitors are concerned there are two main schools of thought;
One suggests that a single capacitor should be between the supply pins, 4 and 8, another that two capacitors should be used, one from pin 4 to gnd and the other from pin 8 to gnd. There is even a school of thought that both these should be used
I normally find that a single cap between the supply pins is enough.
Hans, that really makes the circuit so much simpler, but since I have no understanding of solid state, I have a few questions. Please bear with me, as I'm one of those persons that has to be very clear on something before building.
Questions:
1 Do I run V1 and V3 simultaneously, or is one set for one frequency, lets say 60hz, the other at 81 hz? In other words, switching speeds would be switching channels.
2 If I run both simultaneously, what phase angles do I use for V1, and V3? If I run both simultaneously, I assume I'd have to reset the frequency for both channels for speed changes.
3 If I do run separate frequencies, and switch back and forth between channels (V1, and V3) for speed changes, which frequency should I use for V1 and which for V3?
4 If I do run separate frequencies does it matter what phase angle I use for V1 and V3?
5 Are we still talking about the NE5532 opamp?
Thanks again Hans, you have undoubtedly spent a lot of time helping others with this project, I appreciate it so much. Of course there have been many others that have helped as well. Gives me hope for humanity, something in short supply in this day and age.
twystd
Questions:
1 Do I run V1 and V3 simultaneously, or is one set for one frequency, lets say 60hz, the other at 81 hz? In other words, switching speeds would be switching channels.
2 If I run both simultaneously, what phase angles do I use for V1, and V3? If I run both simultaneously, I assume I'd have to reset the frequency for both channels for speed changes.
3 If I do run separate frequencies, and switch back and forth between channels (V1, and V3) for speed changes, which frequency should I use for V1 and which for V3?
4 If I do run separate frequencies does it matter what phase angle I use for V1 and V3?
5 Are we still talking about the NE5532 opamp?
Thanks again Hans, you have undoubtedly spent a lot of time helping others with this project, I appreciate it so much. Of course there have been many others that have helped as well. Gives me hope for humanity, something in short supply in this day and age.
twystd
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Hi Tom,
Maybe I can Add some to what Ralph already said:
The circuit itself has no reference to whatever voltage, but the input voltage should be within its + and - voltage supply.
So when feeding this circuit with the 24 Volt from the main amps, all you have to do is to give the generator a DC offset if that is possible with your generator.
Since the splitter output voltage with your main amps will be approx 0.7V rms, the offset can be anything between 3 Volt and 21 Volt DC.
However if your generator cannot produce a DC offset, you will have to feed the splitter with +/- 12 Volt.
In both cases you won't need a input cap.
Insert 0.1 uF between pin 4 and 8 if a single supply is used, and two caps from pin 4 and 8 both to ground when +/- 12 Volt is used.
Hans
My understanding is that you have a 3 phase motor and that you are going to use a 2 phase generator, right?
1) In that case both outputs will either produce 60 Hz or 81 Hz, where one output is always shifted 90 degrees.
2) When changing frequency, you can recall an earlier stored value with all stored parameters like amplitude, phase angle and frequency.
3+4) Does Not Apply
5) yes we are.
Hans
Hi Hans
So if I understand this. If I use +15v on pin 8 and - 15v on pin 4 I need to put a .01cap from pin 8 to ground and a .01 cap from pin 4 to ground. Do not bridge 4 to 8 with a cap.
Next option would be to feed 24v from amps power supply to pin 8 and pin 4 to ground. With a .01 cap across/bridged pin 4 and 8. This is with DC offset.
I am not following the DC offset thing number wise. My udb 1005s gen states a +/- 2.5 offset you said between 3-21 so that puts me .5 short??? I could feed pin 8 with the 12v regulated supply already on chassis if that would change the offset to fall in the 2.5 off set range. You can see I am not getting the concept. Where the 3-21 window comes from how to check it and where we are checking it. I know where the pot is to adjust it.
Sorry for all the dumb questions. These little op amps require some attention.
Thanks again for all the help Hans!!!
Tom
So if I understand this. If I use +15v on pin 8 and - 15v on pin 4 I need to put a .01cap from pin 8 to ground and a .01 cap from pin 4 to ground. Do not bridge 4 to 8 with a cap.
Next option would be to feed 24v from amps power supply to pin 8 and pin 4 to ground. With a .01 cap across/bridged pin 4 and 8. This is with DC offset.
I am not following the DC offset thing number wise. My udb 1005s gen states a +/- 2.5 offset you said between 3-21 so that puts me .5 short??? I could feed pin 8 with the 12v regulated supply already on chassis if that would change the offset to fall in the 2.5 off set range. You can see I am not getting the concept. Where the 3-21 window comes from how to check it and where we are checking it. I know where the pot is to adjust it.
Sorry for all the dumb questions. These little op amps require some attention.
Thanks again for all the help Hans!!!
Tom
Just in case Hans isn't around at the moment, I'll give you my thinking on his response.
Most op-amps don't like an output that's too close to the supply rails; so biasing the op-amp somewhere the middle is better.
We are only working with an output of about 1V, so its not so critical, but an offset of 3V or more away from the 0V rail is good practice.
I'm 'old school' and like running my op-amps with split supplies, but they do work just as well with a single supply, as long as the signal doesn't get too close to 0V.
If you have a scope try looking at the output from the splitter as you reduce the bias, at some point (depending on the op-amp) you will see obvious distortion.
Your max offset of +2.5V will, in all likelihood, be fine.
Most op-amps don't like an output that's too close to the supply rails; so biasing the op-amp somewhere the middle is better.
We are only working with an output of about 1V, so its not so critical, but an offset of 3V or more away from the 0V rail is good practice.
I'm 'old school' and like running my op-amps with split supplies, but they do work just as well with a single supply, as long as the signal doesn't get too close to 0V.
If you have a scope try looking at the output from the splitter as you reduce the bias, at some point (depending on the op-amp) you will see obvious distortion.
Your max offset of +2.5V will, in all likelihood, be fine.
Correct.
As Ralph already mentioned, with the 5532 you should not come too close to the boundaries of the power supply, 2.5 Volt DC might work in your case with a 24 Volt supply, but it is on the edge.
However there are op amps like the LT1677 that can go from rail to rail.
With +/- 15 Volt you do not have to worry about any DC offset, but this implies the need of using an extra power supply.
The other solution is what Ralph mentioned before, take two 12 Volt supplies, giving you +/- 12 Volt for the splitter and 24 Volt for the Main amps.
Hans
Hi Hans
Will look into the 1677 for next build. I already have a +/- 15 volt supply so I will go that route on the first 2 phase splitter.
Does anyone know if you have to load the generator to test it. And the same goes for the splitter??? If either need a load what value resistor???
Thanks Hans
Tom
Will look into the 1677 for next build. I already have a +/- 15 volt supply so I will go that route on the first 2 phase splitter.
Does anyone know if you have to load the generator to test it. And the same goes for the splitter??? If either need a load what value resistor???
Thanks Hans
Tom
Hi Guys
Ran into some problems!!!
OK finished the Hans post 151 2 phase splitter. I did not put a cap in series with the input. Use 1/2 of 5532 op amp putting -15v on pin 4 and a .1cap on pin 4 to ground. I put + 15v on pin 8 with a .1 cap on pin 8 to ground. Pin 4 and 8 are not connected. The rest is like the schematic.
So here are the issues.
1. The motor will start clockwise one time and counter clockwise other times.
2. The 0 degree phase will start at 130v and the sine wave looks good. The 90 degree phase starts at 130v then after 5-10 seconds drops to 115v and the sine wave distorts. The motor is running rougher also.
The dds generator is putting out 1.597 on 0 degree and 1.321 on 90 degree. Still using Ralph's voltage divider/low pass filter the amp sees .384 on 0 degree channel and .316 on 90 degree channel.
My gut tells me something is going on with the caps/op amp in the splitter.
All help welcome!!!
Thanks Tom
Ran into some problems!!!
OK finished the Hans post 151 2 phase splitter. I did not put a cap in series with the input. Use 1/2 of 5532 op amp putting -15v on pin 4 and a .1cap on pin 4 to ground. I put + 15v on pin 8 with a .1 cap on pin 8 to ground. Pin 4 and 8 are not connected. The rest is like the schematic.
So here are the issues.
1. The motor will start clockwise one time and counter clockwise other times.
2. The 0 degree phase will start at 130v and the sine wave looks good. The 90 degree phase starts at 130v then after 5-10 seconds drops to 115v and the sine wave distorts. The motor is running rougher also.
The dds generator is putting out 1.597 on 0 degree and 1.321 on 90 degree. Still using Ralph's voltage divider/low pass filter the amp sees .384 on 0 degree channel and .316 on 90 degree channel.
My gut tells me something is going on with the caps/op amp in the splitter.
All help welcome!!!
Thanks Tom
Hi Tom,
It almost sounds as if only one phase is steering the motor.
Quite a number of questions before I understand what you did:
- Did you remove the Phase shift Cap from the motor
- Are you sure you have connected the motor correctly
- What trafo's did you use, from voltage to voltage and how many Watts
- What value of resistors inline from main amp to trafo
- What is the supply voltage feeding the main amps.
- What are the voltages on the output of the main amps
- how did you connect the phases to the main amps, is one side of the inputs connected to ground?
- What is the frequency from the generator, 50, 60, 81 Hz or what
- What is the value of the RC combination at the + input of the op amp
- The DDS generator is "putting out 1.597 on 0 degree and 1.321 on 90 degree." What does this mean. Do you have a two phase or a one phase Generator??
- The .384 Volt and .316 Volt is measured where ?
Hans
Hi Hans
Well guess what I found when I was double checking the RC leg. The resistor was reading in the mega ohm range. I am thinking I know I did a combo to get right ohms. Then I pulled the board off and guess what I missed a solder joint. *"':;?!;:'"* How did I miss that after checking the rails and the cuts with a fine tooth comb. Well now both phases are the same voltage and the sine waves look good.
Here are the numbers I got so if you think I would be better off I can adjust at gen and play with voltage divider to get a lot of combinations.
With 1.6v out of gen to voltage divider .39v out to amp in to 7.7v out to transformer to 130v at motor.
With 1.2v out of gen to voltage divider .29v out to amp in to 5.9v out to transformer to 100v at motor.
Is there any way to check the phase degrees without a dual phase scope?
The frequency adjustment work like they said .01 each step showed up on the fluke. We can fine adjust now.
Thanks for staying with us Hans
Tom
Well guess what I found when I was double checking the RC leg. The resistor was reading in the mega ohm range. I am thinking I know I did a combo to get right ohms. Then I pulled the board off and guess what I missed a solder joint. *"':;?!;:'"* How did I miss that after checking the rails and the cuts with a fine tooth comb. Well now both phases are the same voltage and the sine waves look good.
Here are the numbers I got so if you think I would be better off I can adjust at gen and play with voltage divider to get a lot of combinations.
With 1.6v out of gen to voltage divider .39v out to amp in to 7.7v out to transformer to 130v at motor.
With 1.2v out of gen to voltage divider .29v out to amp in to 5.9v out to transformer to 100v at motor.
Is there any way to check the phase degrees without a dual phase scope?
The frequency adjustment work like they said .01 each step showed up on the fluke. We can fine adjust now.
Thanks for staying with us Hans
Tom
Twystd they are really close the voltage at the motor was only off a few 1/10's of a volt between phases. Hans nailed it. Not sure if there is a set of voltages that work best with generator and amp, maybe Hans or Ralph will have some thoughts. I just use the voltage divider and low pass filter Ralph used on the 3 phase splitter. Not sure if the different generators like different outputs or if those 100 watt amps like a certain input???
Tom
Tom
Hi Tom,
Glad to hear everything works.
I did a quick search and in a second I found this low cost scope.
USB oscilloscoop en Logic Analyzer - Free Shipping - DealExtreme
I'm sure when you put some more effort in searching, you will find comparable offers,
Having two channels makes checking phases a whimp.
Hans
3 phase motor
I have been following this thread for some time, thanks to all so far.
I have not seen much discussion of motors, I would like to use the three phase solution.
Does anyone have info on motor manufacturers or sources?
I have an old VPI scout with the original hurst motor, making mounting or machining new pulleys is not a concern.
I have been following this thread for some time, thanks to all so far.
I have not seen much discussion of motors, I would like to use the three phase solution.
Does anyone have info on motor manufacturers or sources?
I have an old VPI scout with the original hurst motor, making mounting or machining new pulleys is not a concern.