1 hour ago, frivan said:

You won't notice the efficiency gains of a PTC over a conventional element. The benefit will be in using solar power.

You have to compare apples with apples, ie. instead of a 3kW conventional element, you could use either a 2kW PTC element, or otherwise just another conventional 2kW element. You'd pay approx R1800 for the 2kW PTC element vs around R200-R300 for 2kW conventional one.

I can buy into some benefits of the PTC heater, such as that you cannot overheat it, or that you could get away without a thermostat. That could be worth the price right there, if you can avoid a theoretical plumbing failure point and repair cost, or why not even argue for a lowered insurance premium? To be verified if it works this way.

But I think the energy savings are going to be tougher to prove.

Edited May 7, 20251 yr by GreenFields

1 hour ago, GreenFields said:

You have to compare apples with apples, ie. instead of a 3kW conventional element, you could use either a 2kW PTC element, or otherwise just another conventional 2kW conventional element. You'd pay approx R1800 for the 2kW PTC element vs around R200-R300 for 2kW conventional one.

I can buy into some benefits of the PTC heater, such as that you cannot overheat it, or that you could get away without a thermostat. That could be worth the price right there, if you can avoid a theoretical plumbing failure point and repair cost, or why not even argue for a lowered insurance premium? To be verified if it works this way.

But I think the energy savings are going to be tougher to prove.

I agree 100%. My own temperature vs power used between a normal element and the PTC heating a 25L closed container did only show a 5% gain for the PTC when using the AC portion of a PTC. This in itself does not warrant the added cost. The fact that the PTC should never burn out is a plus but one can buy 6 or more normal elements.

The 5% difference can just as well be the uncontrolled environment in which my test was conducted.

11 hours ago, GreenFields said:

You have to compare apples with apples, ie. instead of a 3kW conventional element, you could use either a 2kW PTC element, or otherwise just another conventional 2kW element. You'd pay approx R1800 for the 2kW PTC element vs around R200-R300 for 2kW conventional one.

I can buy into some benefits of the PTC heater, such as that you cannot overheat it, or that you could get away without a thermostat. That could be worth the price right there, if you can avoid a theoretical plumbing failure point and repair cost, or why not even argue for a lowered insurance premium? To be verified if it works this way.

But I think the energy savings are going to be tougher to prove.

Some comments

1: No thermostat means that I cannot control the temperature with a Home Assistant nanny watching it for lower temp action to heat.
2: Not sure what plumbing failure you are referring to here? The element wont cause that. The geyser wall is at highest risk of failure due to the thin material they use to cut costs. I have an old school copper inner.
3: Insurance wil NEVER decrease in light of this element being used over a conventional one.
4: The more I read the more members debunk their outlandish claims of energy savings.

10 hours ago, Scorp007 said:

I agree 100%. My own temperature vs power used between a normal element and the PTC heating a 25L closed container did only show a 5% gain for the PTC when using the AC portion of a PTC. This in itself does not warrant the added cost. The fact that the PTC should never burn out is a plus but one can buy 6 or more normal elements.

The 5% difference can just as well be the uncontrolled environment in which my test was conducted.

this is the only real benefit, you dont need a thermostat, that is it, to heat the same amount of water to the same temperature, will require the same energy, both elements are 100% submerged so the energy transfer efficiency will be about equal... with all thing equal, your results will also be equal. the 5% difference you observed might just as well be due to the small difference in surface area between the PTC and a normal element, its just a theory I have, no proof or calculations.

Is there likely to be an immediate but short term increase in performance because the old element may have deposits from the minerals in the water?

4 hours ago, Bobster. said:

Is there likely to be an immediate but short term increase in performance because the old element may have deposits from the minerals in the water?

My will guess is the deposits will be at the same temp as the element and the water does not care if it is in contact with lime or steel. The same heat transfer should take place.

@stefan44 One of the variables is the time of day. It did take about 2-3 hours to heat the water with one element after the 1st one. Drain it and ensure the steel container is at the same temp as the 1st test before filling up with water to start the same test.

Although the PTC is self regulating I would still prefer to use a thermostat. Just as I don't like a BMS to be what I rely on to switch off a battery at high or low voltage. The BMS to me is the last line of defence if the normal system(inverter) should fail.

Edited May 8, 20251 yr by Scorp007

9 hours ago, Bobster. said:

Is there likely to be an immediate but short term increase in performance because the old element may have deposits from the minerals in the water?

I assume that lower currents lead to less losses in wiring. I also have it that the PTC temperature is lower than the resistive element. That could mean less conduction with wires and the element base... Perhaps everyone should just use 1kW elements.