# Reducing Ripple Control

S

#### Schumaker

My SMPS just died. So, I've got a 3kva transformer controlled on the primary by phase angle firing. It's ... working just OK. However, I still struggle to get an accurate voltage reading from the secondary output. I think this is due to the high ripple.

How can I reduce this?

S

#### Schumaker

I guess I'm wondering what the rule of thumb for capacitors should be.

I've got a figure of 10,000uf per amp on a standard rectified output.

Sorry, I'm just stumped.

#### ron simpson

How many volts (or mV) of ripple is OK?
What is the output current? and Voltage?
I still struggle to get an accurate voltage reading from the secondary output.
Where are you measuring the voltage? DC or AC?

A

#### Arthur James

Are you trying to filter the output to get rid of the ripple or just measure the output?

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#### Schumaker

Just trying to measure the output.

S

#### Schumaker

I've got a panel volt meter and ammeter that don't show the same as my fluke multimeter.

Voltageis 32v ( calculated rms after recification) on max setting. When I reduce it becomes wonky. I am pulling approximately 50 amps.

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#### Arthur James

The panel meter and fluke are just going to have a different response time. They're not going to read the same because the input isn't a SIN wave.

If you are regulating the output level by switching the input you're not going to see anything resembling a SIN wave.

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#### Buster

New here, but ...

I assume the transformer input is AC. And, I'm willing to bet a triac is varying the duty cycle. As the duty cycle reduces the waveform becomes less sin like so the meter and fluke response both will get odd and will be less like each other.

B

#### Buster

If you don’t notice the meter needle vibrating, it probably has a significant filter. Since the fluke is a digital meter, it samples the voltage.

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#### Arthur James

I don't know if it would make a sample in the display rate or has a more integrated measuring technique.

Power Management 3