half wave rectifier

You can do that, or... you can string two heaters in series. Doubling the resistance will cut the power in half. It will also cut the current in half. Using a diode will not change the peak current, which may be a problem with a "smart switch".

Power by half of half.

Anyway, this diode should work and I am using it for full bridge rectifier to pull maximum power out of my 220V inverter.

Is the source the AC line, what you folks call "mains" ?

If not, the DC component could be a problem.

I have conjectured that a lot of DC current will slow down an electric meter, disk or electronic.

No, because you have two heaters, which doubles it, cancelling out one of the halves.

As usual, you fail to understand.

P = E^2 / R

If you string two heaters in series, you have the same voltage, but twice the resistance, so half the power.

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OTOH, a 25A, 600V metal base bridge rectifier is isolated from the AC power and can be attached to an earthed box or heatsink with any suitable bolt. Just use the + and - terminals.

..... Phil

If you have two heaters in series, each sees half the voltage.

A good idea, the proper isolation to the heat sink is already present.

Or better, for half the voltage drop, so half the dissipation, use (+) and (both of the ~ connected together).

Note that this rectifier method produces a DC component on the mains. This may play havoc with transformers and motors on that same mains.

I've made phase and PWM controllers for kW heaters on 3 phase systems, and had to be careful to keep things balanced. Also, phase control causes EMI, and PWM control (for whole cycles) causes flickering.

Arie

Yes, that is correct. Not very relevant, but correct.

Do you see something wrong with the equation I presented? If you double the value of R, while holding E constant, P will be halved. No?

There's no need at all, to focus on one heater, unless there is some constraint in the mechanical design that puts the other heater in a different location.

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The DC offset effect you allude to is fairly small and rarely a problem. I have a 1600W hot air gun that uses the same trick to reduce the air temp.

...... Phil

Yes, you're quite right.

Can't do that. The heater element is inside a copper tank.

No, you don't understand this english stuff. Twin heaters are rare in the UK

Yes, it is a houshold mains application..

Yes, AC line, 220/250V 50Hz.Mains :)

Not sure what you are talking about. You want to rig a diode to create half wave AC to drive a heater. That's not exactly "standard" practice anywhere.

If you have mechanical limitations, that's what you have. Electrically, this makes sense.

You could add a resistance in series. It would need to be about 30% of the resistance of the heater. The main element would dissipate half of the original heat. The heat in this added resistance would be about 22% of the heat dissipated in the original heating element. One nice thing about this is that you can tailor the heat in the main element to other than half the original heat level.

TTman wrotr:

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" As part of an experiment with solar, I want to drive my 220V 3kW immersion heater with a suitable diode so that the effective power is ~1.5kW and can be driven by a smart switch so that it doesn't suck too much out of the 9.5kWh battery or solar panels. "

I see the words "experiment " , " solar " & "battery" but no sign of the word "mains".

....... Phil

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....... Phil

It's certainly very antisocial. It may greatly increase the losses in all sorts of wound devices (the distribution transformer, any transformers in his house, induction motors etc.)

Running a resistive water heater from a battery is pretty silly anyway - the energy could much better be stored as heat in a bigger tank of water than in a battery that will wear out due to the unnecessary cycling.