Hi all,

We have two geysers. One is warmed by a heat pump and we include that in the backed up circuits. This runs well with no problems.

The guest geyser is on the sub DB, thus on the non-backed up sides. Some time ago I had the element in this changed from 3KW to 1KW. It took longer to warm up, sure, but I could use spare PV in the afternoon to heat it, and this was close but I got away with it. 

This geyser is controlled by a timer switch. When the timer was installed, the 3kw element would draw more than the current for which the timer is rated, so the setup is that the timer controls a solenoid which can handle the 3kw. Though I now have a 1kw element.

Today I saw my batteries were charged very early in the day, so just for the heck of it I turned on the guest geyser. Now we need to refer to the graph I am attaching.

You can see that at 10:00, load suddenly shoots up. This is the pool pump (on a time switch) kicking in and co-incidentally the kettle was used. Thereafter the draw stabilises at about 1.2kw - 750w pump, plus all the "backround noise" of the house running.

Then at 10:45 the guest geyser is switching on. Load shoots up to just under 3kw. So this catches my attention: I have a 1kw element in there, but the difference made to total load is 1.8kw. And the 800 w makes a crucial difference, especially in the afternoon when the geyser would be turned on by the timer.

What can explain this discrepancy?

I would like to keep that geyser warmed up actually. Just in case somebody comes to say, and because it's handy to have hot water in that part of the house. And previously I have run it in the afternoon and the draw was not this high and I could manage it (and get it to 55 degrees). Something has changed or degraded.

Any ideas?

Edited September 10, 20223 yr by Bobster.
Grammar

Voltage? HWC element is essentially purely resistive and thus P=V*(V/R)... if the element is rated for 1kW at 220V and your end is actually sitting at 260V, then you are looking at a power increase of more than 15%... I'd say, disconnect the element and take a measurement, if this is a bog standard resistive element, then you can infer by its resistance what the actual power rating should be for the element and see whether that lines up with your power readings...

Thanks. I hadn't thought of that. The incoming voltage is up today, around 240V, which is not enough to make this kind of difference.

But I just checked my historic data on SEMS portal, and I found that when I tested it (just short of a year ago), and in fact it was increasing the load by about 1.7 to 1.8 kw then.

So nothing has changed, and I probably can still get away with it.

3 minutes ago, Bobster. said:

Thanks. I hadn't thought of that. The incoming voltage is up today, around 240V, which is not enough to make this kind of difference.

But I just checked my historic data on SEMS portal, and I found that when I tested it (just short of a year ago), and in fact it was increasing the load by about 1.7 to 1.8 kw then.

So nothing has changed, and I probably can still get away with it.

So it seems that element might be a 2kw and tolerence makes it only 1.8kw. This one can verify on the element but then again it could be fitted with a 1kw label/stamped and still a 2kw element.

Glad you found the element still the same Watts as before. No need to worry about it. 😃😃

Thanks to @Kalahari Meerkat and @Scorp007 for replies.

The geyser is up in the roof, and I am averse to climbing up ladders and onto or into the roof (low blood pressure = dizzy spells) so can't check out markings on the element nor measure it. I suppose I could disconnect it at the DB and measure across the wires.

The question of tolerances had occured to me - it can't be EXACTLY 1 KW. 

21 minutes ago, Bobster. said:

Thanks to @Kalahari Meerkat and @Scorp007 for replies.

The geyser is up in the roof, and I am averse to climbing up ladders and onto or into the roof (low blood pressure = dizzy spells) so can't check out markings on the element nor measure it. I suppose I could disconnect it at the DB and measure across the wires.

The question of tolerances had occured to me - it can't be EXACTLY 1 KW. 

So we nearly in the same boat. I still get in the roof but knees feel it with the push to support the weight when getting in and out. Cannot afford a fall from ladder but still get on with what has to be done.

Tolerance either 2kw minus 10% or 1kw plus 80%.

Do you have access to a multi meter or preferably a clamp meter? If your geyser is cold you can measure the ohm value while the element is switched off, it should measure about 55 ohm for a 1kw element and about 27 ohm for the 2kw element. Otherwise a clamp meter can show you the current drawn when the element is on. It is not really necessary to climb up the roof to measure. 

i have a timer set from.3pm to 9pm.and then from 3am to 9am .i notice that as soon as the time is.on it draws about 10kw in two. hours. i have a 150l geyser.any ideas why it is drawing so.much power. what can i do

11 hours ago, Mags said:

i have a timer set from.3pm to 9pm.and then from 3am to 9am .i notice that as soon as the time is.on it draws about 10kw in two. hours. i have a 150l geyser.any ideas why it is drawing so.much power. what can i do

Check the rating of the element, or have an electrician check it. Check the rating of the timer as well. 10kw is a lot - 43 amps. If the timer isn't rated for that then it will fail. And check the wiring, maybe there's a bad connection. 

It takes a certain amount of energy to heat a fixed volume of water. If you downgrade the element it will consume less power, but will do so for longer.

What you can do is switch to a heat pump. That will cost you, but you will start using less power as it's a far more efficient way of heating water. 

17 hours ago, Mags said:

i have a timer set from.3pm to 9pm.and then from 3am to 9am .i notice that as soon as the time is.on it draws about 10kw in two. hours. i have a 150l geyser.any ideas why it is drawing so.much power. what can i do

Let us just put your question into perspective. You say you are using 10kw in 2 hours so 5kwh(21.7A) load. That means if your figures are correct you have a 5000w element. Your standard 150l geyser uses a 2~3kw element. Maybe you have other loads connected to your geyser breaker.

19 hours ago, Mags said:

i have a timer set from.3pm to 9pm.and then from 3am to 9am .i notice that as soon as the time is.on it draws about 10kw in two. hours. i have a 150l geyser.any ideas why it is drawing so.much power. what can i do

Although you indicate 10kWh used in only 2 hrs of the 6 that the timer is on. 

I would take a wild guess that it could be possible that the element was on for just over 3hrs. As they don't make a 5kW element for our common geysers that the element only uses 3kW. 

You can check it by switching off all loads but the geyser when the geyser comes on but changing the timer switch on time when you can check. 

Also check the element for scaling (especially if using borehole water). If the element is scaled up, the geyser will switch on more frequently and use more power. 

15 minutes ago, abd7 said:

Also check the element for scaling (especially if using borehole water). If the element is scaled up, the geyser will switch on more frequently and use more power. 

Very good tip. On the other side of the coin this will still not cause the element to draw a much higher than 3kW in power. Due to the higher temp of the wire inside the element it will draw less power due to higher temp. Resistance increases with increased temp. 

2 hours ago, Scorp007 said:

Very good tip. On the other side of the coin this will still not cause the element to draw a much higher than 3kW in power. Due to the higher temp of the wire inside the element it will draw less power due to higher temp. Resistance increases with increased temp. 

A 150lt size geyser will take close on to 3 hours to heat from completely cold water (15 degrees C) to 65 degrees C, which equates to the usage of 8.72kW of electricity with a 3kW element.

@MagsThe only real way to reduce electric consumption on a geyser, which will be of financial benefit, is to reduce the amount of water that is heated and drawn off i.e. reduce your hot water consumption, and reduce the temperature setting of the water on the thermostat. Ideal setting is 50 to 55 degrees in summer and 60 to 65 degrees in winter. If you run your geyser off a pv system ensure your timer is set at peak solar production hours 10h30~14h30.

Edited September 1, 20241 yr by TaliaB