Found this on Youtube: 

The device is called OptiVolt and it apparently reduces the voltage as supplied by the utility down to a lower voltage, e.g. 220V. It claims that the reduction in voltage results in a saving in power. Ok, so power is A x V, therefore if the voltage is reduced the power will drop but will an appliance use a constant amount of amps regardless of the voltage? If e.g. a television is rated at 500W will it use less power at 220V than if the supply was 240V?

Another question, how would a device like this work? If in fact it can reduce the voltage and control it at the set point it makes sense to me that it should be beneficial for appliances rather than fluctuating voltage received from Eskom.

What do you guys think?

Cobus

 

 

Oh, it's snake oil poured overBS. Look at it this way: You get charged for power, volts times ampere, so this device will only work with an appliance that will actually reduce power if the voltage is lower: purely resistive devices in other words.

Anything with a switch mode power supply will simply compensate for the lower voltage by drawing more current, so televisions, smart phone chargers, laptops, etc will still use the same power.

Your induction motors may use a little less power, but in general they will use as much power as they need to drive the (mechanical) load, so your fridge and freezer will simply compensate by drawing more current. This, by the way, is why low voltage conditions are so dangerous to induction motors. When tasked with doing the same work, they draw more current and that can damage them. 220V is probably safe in that respect, but the basic point remains: It's going to draw the same power.

This leaves us with the purely resistive devices, which are basically kettles, geysers, and incandescent lamps. It takes 1.16Wh to heat one liter of water by one Kelvin. If you reduce the voltage, the power reduces as the square of the voltage, BUT... it still takes the same amount of Watt-hours to heat the water, so it will now take longer to heat it. Since both devices switch off at their designed temperatures, you will end up using exactly the same amount of power AND you'll have to wait longer for that cup of tea.

So that really leaves you with incandescent lamps. They will use less power, but also make less light. You might be okay with the slightly lower illumination levels, and therefore you might consider this a "saving", but the truth of the matter is that you will probably get way more savings by throwing out the incandescent lamps and putting in CFL or LED, instead of buying the "OptiVolt". Pffft.

So how do they work? It's an autotransformer wired in reverse, so to speak, so that it subtracts some of the voltage, and does so very efficiently.

Here big clive reviews one of them:

 

Thanks plonkster. That's what I thought.

What worries me, the company who makes and sells this also produce the geyser controller I want to install... So is that also BS?

Would appreciate some views on them. Here are a couple:
http://www.nuvisionenergy.co.uk/optimisepv-wireless (also the guys who make/sell the OptiVolt)
http://solarimmersion.co.uk/
http://www.marlec.co.uk/product/solar-iboost/?v=68caa8201064
https://www.immersun.co.uk/product/ (this is actually one of the nicer units but seems they went bust on the 15th of July)

Since I'm not getting credit for my grid export I want to dump the excess PV into the geysers.

Cobus

Well, you know, same boat in some respects here. Plumber acquaintance is emigrating and selling off a bunch of old stock. So I have an option to buy a nice 4.8kw heat pump for 3k. But it is made by Tasol. Now if you recall, Tasol was the people who got about 1/8th of the contract on solar geysers installed in a Alex and it was a complete hack job and they ended up on Carte Blanche. Well, the other company, Clean Heat Solar, took why more of a beating as they were also stealing power at their factory and making even shoddier Solar Geysers... so here I am now, not sure at all whether I can trust this device in second-hand form. A bit of googling shows, however, that the heat pumps are simply imported from China, and in that respect it might be as good as any other china-import, of which there must by many, right?

So the situations seems analogous to me. They probably make one device locally and are resellers for the rest... or some such thing, so that the poor reputation of one device might not mean the others are bad too. Just... I wish they'd make it easier to decide by, you know, having some integrity (or something).

I should ask a separate question on that heat pump...