VFD Voltage/RPM fluctuating

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martyscncgarage
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Re: VFD Voltage/RPM fluctuating

Post by martyscncgarage »

ChrisAttebery wrote: Sat Feb 06, 2021 11:14 am That’s great news. I added a 1mf tantalum cap to my analog output too.
Work for you Chris?
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ChrisAttebery
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Re: VFD Voltage/RPM fluctuating

Post by ChrisAttebery »

It helped. I still see .1-.2 Hz fluctuations on my VFD. It isn’t noticeable like it was before though. The machine plows right through aluminum.
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Re: VFD Voltage/RPM fluctuating

Post by ShawnM »

ChrisAttebery wrote: Sat Feb 06, 2021 11:14 am That’s great news. I added a 1mf tantalum cap to my analog output too.
Did you add a .1mf or a 1mf cap?
ChrisAttebery
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Re: VFD Voltage/RPM fluctuating

Post by ChrisAttebery »

A 1 micro Farad cap.
eng199
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Re: VFD Voltage/RPM fluctuating

Post by eng199 »

ChrisAttebery wrote: Mon Feb 08, 2021 12:32 am A 1 micro Farad cap.
Adding too much capacitance to opamp outputs can also cause stability problems. I would try 0.1uF or less. A low value resistor (10 to 50 ohm) in series between ACORN and the capacitor can also prevent oscillation from too much capacitance.
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Re: VFD Voltage/RPM fluctuating

Post by ChrisAttebery »

I'll have to see if I have anything smaller. Most of the electronics components I have are from projects 20+ years ago.
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Re: VFD Voltage/RPM fluctuating

Post by martyscncgarage »

eng199 wrote: Mon Feb 08, 2021 2:45 pm
ChrisAttebery wrote: Mon Feb 08, 2021 12:32 am A 1 micro Farad cap.
Adding too much capacitance to opamp outputs can also cause stability problems. I would try 0.1uF or less. A low value resistor (10 to 50 ohm) in series between ACORN and the capacitor can also prevent oscillation from too much capacitance.
Matt,
Could you draw a simple sketch of what you are describing and how it connects to Acorn's analog output for clarity's sake please?
In what cases might this help?
Thanks
Marty
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Re: VFD Voltage/RPM fluctuating

Post by ShawnM »

eng199 wrote: Mon Feb 08, 2021 2:45 pm Adding too much capacitance to opamp outputs can also cause stability problems. I would try 0.1uF or less. A low value resistor (10 to 50 ohm) in series between ACORN and the capacitor can also prevent oscillation from too much capacitance.
I'll give it a try, I have a few .1 uF tantalum caps laying around. #104 I think they are. My machine is pretty solid but I may even try one on mine to see if it makes a difference or not.
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Re: VFD Voltage/RPM fluctuating

Post by stutaylo »

ShawnM wrote: Mon Feb 08, 2021 8:11 pm #104 I think they are. My machine is pretty solid but I may even try one on mine to see if it makes a difference or not.
Can confirm I put in a #104 (0.1uF) and have no movement at all on the Frequency
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Re: VFD Voltage/RPM fluctuating

Post by ChrisAttebery »

I checked my VFD tonight. It was rock solid with a 1 micro farad cap.
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