Center tap microwave transformer.

MisterBill2

Joined Jan 23, 2018
7,007
To read DC voltages reliably you really need a voltmeter. Reading them with an inexpensive scope is not likely to be even close to accurate. Especially on a small screen scope like that one. Reading DC voltages on a $3000 scope is still not as good as with a decent digital meter.
 

Thread Starter

Hutch2793

Joined Jul 7, 2020
133
To read DC voltages reliably you really need a voltmeter. Reading them with an inexpensive scope is not likely to be even close to accurate. Especially on a small screen scope like that one. Reading DC voltages on a $3000 scope is still not as good as with a decent digital meter.
Multiple people have told me you cannot get accurate readings with a digital meter. That second statement is completely inaccurate as well. Why would professionals use a 3000 dollar scope more often then their digital multimeter if this is true? I’m not a professional, so maybe you are referring to a different type of digital meter. Two people in this thread that have been right about everything else so far have told me I need a cheap scope to read the rectified dc voltage to get an accurate understanding of what dc voltage my MOT power supply is outputting. Someone else will elaborate I’m sure. The scope has peak and minimum voltage.
 

MisterBill2

Joined Jan 23, 2018
7,007
Multiple people have told me you cannot get accurate readings with a digital meter. That second statement is completely inaccurate as well. Why would professionals use a 3000 dollar scope more often then their digital multimeter if this is true? I’m not a professional, so maybe you are referring to a different type of digital meter. Two people in this thread that have been right about everything else so far have told me I need a cheap scope to read the rectified dc voltage to get an accurate understanding of what dc voltage my MOT power supply is outputting. Someone else will elaborate I’m sure. The scope has peak and minimum voltage.
An oscilloscope will show you what sort of wave form you have and that is quite useful. A decent digital meter will show you the effective value of the voltage. That is not usually the RMS value or the peak value. Unless your application is intended to use the unfiltered and unregulated output of the rectifier circuit, why does it matter? Normally rectified power is also filtered and then the filtered voltage is used for some purpose.

And another question: do you need 7 volts or does the application require 7.00 volts? How tight is the voltage specification? That matters a whole lot.

Is this power supply for the process of electrolysing some liquid to obtain some type of gas? We have seen severalof those information requests.
 

Thread Starter

Hutch2793

Joined Jul 7, 2020
133
An oscilloscope will show you what sort of wave form you have and that is quite useful. A decent digital meter will show you the effective value of the voltage. That is not usually the RMS value or the peak value. Unless your application is intended to use the unfiltered and unregulated output of the rectifier circuit, why does it matter? Normally rectified power is also filtered and then the filtered voltage is used for some purpose.

And another question: do you need 7 volts or does the application require 7.00 volts? How tight is the voltage specification? That matters a whole lot.

Is this power supply for the process of electrolysing some liquid to obtain some type of gas? We have seen severalof those information requests.
DL324 hasn’t steered me wrong. I have a multimeter, but the application is not a subject I need help with. I am experimenting for fun. I may learn enough to safely rig up a free power supply using broken appliances. If your wondering why the values I’m trying to achieve keep changing it is simply because I am attempting a baptism by fire on myself with circuits, the different components, and how they all play together. My guidelines are based off of electrochemistry, but this isn’t my job.
It cannot be higher than 7 volts and it cannot be lower than 6. I would like to be able to have one at 6 volts and one at 7 to switch between, or build a variable voltage supply. I have given up on the high amperage I have seen elsewhere. This is just for the fun of seeing how it could be done before I am in a real electrical engineering class learning the proper techniques.
 

dl324

Joined Mar 30, 2015
11,508
DL324 hasn’t steered me wrong. I have a multimeter
I don't know what you're being told, but that $20 scope can be useful.

I just made these measurements using my Velleman lab supply (LABPS3003U).

Set to 7.5V on its display, I measure the following:
Fluke 8010A: 7.50V
Cen-Tech P37772 (my daily use HF meter): 7.47V
Tektronix SC503 scope: 7.6V, 10mV ripple
DSO138: Vmax 7.53V, Vmin 7.293V, Vpp 0.24V

So the voltage measured is within 1%, ripple is way off.

When I set the DSO130 to 10mV/div, it gives 2mV of ripple

It doesn't compare with much more expensive equipment, but for work to one decimal place or so, it's fine.

I'll do some measurements on rectified AC later.

You don't use an oscilloscope to measure DC voltages. When the SC503 is calibrated, it only has to be within 3% (IIRC). Scopes are used to view waveforms and voltage measurements within 5% are generally acceptable.
 

dl324

Joined Mar 30, 2015
11,508
Did measurements with a transformer. Secondary was 6.8VAC, used 1N4148 to rectify. Measured about 8V peak on the full wave rectified output (1k load) on Tek SC502 and DSO138. Calculated peak as 6.8V*1.414-1.4V=8.2V.
 

Thread Starter

Hutch2793

Joined Jul 7, 2020
133
I don't know what you're being told, but that $20 scope can be useful.

I just made these measurements using my Velleman lab supply (LABPS3003U).

Set to 7.5V on its display, I measure the following:
Fluke 8010A: 7.50V
Cen-Tech P37772 (my daily use HF meter): 7.47V
Tektronix SC503 scope: 7.6V, 10mV ripple
DSO138: Vmax 7.53V, Vmin 7.293V, Vpp 0.24V

So the voltage measured is within 1%, ripple is way off.

When I set the DSO130 to 10mV/div, it gives 2mV of ripple

It doesn't compare with much more expensive equipment, but for work to one decimal place or so, it's fine.

I'll do some measurements on rectified AC later.

You don't use an oscilloscope to measure DC voltages. When the SC503 is calibrated, it only has to be within 3% (IIRC). Scopes are used to view waveforms and voltage measurements within 5% are generally acceptable.
“You don’t know what I’m being told?” Was I wrong about something I said.
 
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