# Providing a 16Arms waveform....50Hz

#### Flyback

##### Well-Known Member
Hi,
We are making a device which switches up to 16A rms in the 240VAC mains into a device. It also needs to measure the 16A. We measure it with a Current transformer in mains live.
When we test the equipment, we currently load it up with a 16A load, so that we can see that it measures it properly. -But this means us dissipating 3.8kW in a dummy load during production test......not good.

Therefore, we wish to simply synthesize a 16Arms sine wave and shovel it through the current transformer, of course doing this while the live conductor around which the current transformer torroid sits is energized....it needs to be in phase with the mains voltage.
....We believe we can do this using a kind_of Class D amplifier stage with a 60V isolated DC input power supply as attached. it feeds into a 30V battery, but of course, there is no overall load in this as it receives AC current.
What do you think of this?
By the way, the control loop hasnt yet been completed in the attached.
(LTspice sim and pdf schem attached)

#### Attachments

• Sine wave current _16Arms.asc
8.2 KB · Views: 8
• sine wave current 16A.pdf
163.7 KB · Views: 8

#### Les Jones

##### Well-Known Member
Why not just use a step down transformer with an output of 6 volts for example at a current rating of more than 16 amps. Then put a load of 0.375 ohms on the output. You would then be dissipating 96 watts instead of 3.8 Kw. In practice you would probably need a resistance of a bit less than the calculated value of 0.375 ohms to allow tor cable resistance.

Les.

#### Nigel Goodwin

##### Super Moderator
Why not just use a step down transformer with an output of 6 volts for example at a current rating of more than 16 amps. Then put a load of 0.375 ohms on the output. You would then be dissipating 96 watts instead of 3.8 Kw. In practice you would probably need a resistance of a bit less than the calculated value of 0.375 ohms to allow tor cable resistance.

Les.

You can't beat a bit of 'old school' and common sense

#### Diver300

##### Well-Known Member
I agree with using a step-down transformer.

To control the current, you can vary the input voltage to the input of the transformer with a variac. The downside is the expense because variacs are not cheap.

Transformers with output currents of 16 A are expensive. It could be a lot cheaper to buy a toroidal transformer and wind a few turns of large cross-section through the hole in the centre. I would guess that fewer than 5 turns will be needed. You will only need about 1 V.

Alternatively, you could use one of these:-
https://uk.rs-online.com/web/p/soldering-irons/2027855 which is basically a transformer with a single turn output. The current in the tip is around 500 A. They are not rated to run continually.

#### alec_t

##### Well-Known Member
we wish to simply synthesize a 16Arms sine wave
1) ? Your sim gives a 7.2A RMS current which is far from being a sinewave.
2) What is "the equipment"? I can see that a step-down transformer or your synthesizer would be useful for testing the current transformer and meter, but if you need to test the current switching capability of the device then you need to pass 16A RMS through the switch itself to a load. Whether that load is an electronic one or just a resistor it will dissipate 3.8kW.

#### Flyback

##### Well-Known Member
Thanks, but i am thinking now of a bridge setup....switch one diagonal pair for 10ms, then the other, and make the current half sinusoid in each direction.....we cant have mains transformers made up.

...ive managed to do this with a boost from 30v to 60v, but its just a train of half sines, not bipolar.....the 60v could be bucked back to the 30v so "no energy" was used.

Last edited:

#### kubeek

##### Well-Known Member
Why not use a second current transformer? Just make a short circuit loop through both cores, and inject appropriate voltage into the secondary winding.

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