Microwave or Grill?
- Thread starter Catdickens
- Start date
That and the "Doesn't Suffer Fools Gladly" award.
The usual thing that catches folks out is the start up surge load, sometimes also called inrush current. The rate on the labels tends to be maximum load in steady state. At home a short surge is nothing as you have the National Grid with massive capacity, in the van there's not that capability. This is why inverters often list a surge load they can cope with for a few seconds.
Usual things that surge badly are motors and resistive heaters. This is because at the start they are essentially a short circuit until the motor starts moving or the element reaches temperature. Motor starter inrush current can be massive but it's very short lived. Resistive heater inrush is lower (as they are natively resistive even when cold) but lasts longer (because they have to heat up rather than spin up)
A lot of resistive heaters, especially those in things like coffee machines, are designed to be self regulating. They reach a steady state where they hit a target temperature and the resistance balances. It's very simple, robust and pretty safe but it does mean that they can be pulling higher current for quite a while and the watts consumption by any specific device can vary quite a bit, so a measured 1460 against a nominal 1300 wouldn't be unexpected.
Generally anything that actively regulates the power won't do this, or will do it very briefly as the switch mode power supply starts.
Thank you @roadtripper , I'm still at a bit of a loss as to why the inverter whinges under the load from the Tassimo when the induction is a greater load? The Inverter with the induction hob at 2kw to boil a kettle has no issue but that blessed Bosch... The family love the Tassimo because of its ability to create wonderful hot chocolates and differing coffee, I obviously have to think of them, the wife tells me! Thank you so much for taking the time to reply, a swift beer or two due to you when we meet!
Power Factor is certainly a thing too, but I think it's a lesser effect in this situation.
An attempt at a short summary:
Mains power is AC, so the voltage and current rise and fall 50 times a second.
Think of voltage like the pressure to move and the current as actual movement.
The classic intuitive resistive loads like heaters the voltage and current rise and fall together.
However inductive loads (like motors) and capacitive loads (like mains LED lights and electronic power supplies) behave differently. Remember a spinning motor as also a generator, so an inductive load also generates some voltage. Capacitors are like small short term batteries so also store and then release charge.
These effects mean that voltage and current don't rise and fall in sync, because the load is also either adding or removing voltage during the cycle.
Why does this matter? Well the whole point is to transfer power, and power is voltage x current, so if they are not in sync you end up having to have higher currents to transfer the same power.
Loads that are in sync are said have a power factor of 1, loads out of sync have a lower power factor. So for instance a power factor of 0.5 means there is twice as much power flowing in the circuit than is actually being used by the load.
That's bad for 2 reasons:
1. Your source of power (IE inverter) still has to supply that power
2. Loses in the cabling are resistive, and power loss in cabling is resistance x square of the current - so higher currents dramatically increase the losses
This is why in any industrial setting you will find that equipment has power factor correction. Because inductive and capacitive loads offset things in opposite directions you can use one to balance the other. This is why you often see a large capacitor (capacitive load) across a motor (inductive load).
An attempt at a short summary:
Mains power is AC, so the voltage and current rise and fall 50 times a second.
Think of voltage like the pressure to move and the current as actual movement.
The classic intuitive resistive loads like heaters the voltage and current rise and fall together.
However inductive loads (like motors) and capacitive loads (like mains LED lights and electronic power supplies) behave differently. Remember a spinning motor as also a generator, so an inductive load also generates some voltage. Capacitors are like small short term batteries so also store and then release charge.
These effects mean that voltage and current don't rise and fall in sync, because the load is also either adding or removing voltage during the cycle.
Why does this matter? Well the whole point is to transfer power, and power is voltage x current, so if they are not in sync you end up having to have higher currents to transfer the same power.
Loads that are in sync are said have a power factor of 1, loads out of sync have a lower power factor. So for instance a power factor of 0.5 means there is twice as much power flowing in the circuit than is actually being used by the load.
That's bad for 2 reasons:
1. Your source of power (IE inverter) still has to supply that power
2. Loses in the cabling are resistive, and power loss in cabling is resistance x square of the current - so higher currents dramatically increase the losses
This is why in any industrial setting you will find that equipment has power factor correction. Because inductive and capacitive loads offset things in opposite directions you can use one to balance the other. This is why you often see a large capacitor (capacitive load) across a motor (inductive load).
Oh and don't get fooled into scams offering to correct your power factor at home and save you money.
For a start true power factor correction is tricky unless it's done in the appliance - so any little plug in gadget won't cut it. Some do actually have a capacitor in but it's often not connected, all's that's connected is an LED (ironically on a capacitive dropper supply with terrible power factor)
Secondly domestic users are not billed for this "wasted" power as traditionally home users were just resistive heating or incandescent lights so there was no point putting fancy meters, nor having to explain the whole complicated Power Factor thing.
Industrial users certainly are billed for this and PF correction in that environment is vital.
With the huge increase in low voltage power supplies and LED at home it is becoming an issue. The extra components to do good power factors cost money, but things still work without them. So guess what gets left out of all the bargain USB power supplies and LED lights... A lot of them have PF near 0.5 which is appalling, at scale it would mean 50% of power stations would be needed for... nothing useful.
Modern smart meters are perfectly capable of doing either billing. There are some theories that billing may change for domestic users if domestic PF gets very bad. I think it's unlikely due to the confusion PF causes (even in me and I have degree in physics) but I also can't think of another way to encourage people to ensure they buy "good" equipment...
For a start true power factor correction is tricky unless it's done in the appliance - so any little plug in gadget won't cut it. Some do actually have a capacitor in but it's often not connected, all's that's connected is an LED (ironically on a capacitive dropper supply with terrible power factor)
Secondly domestic users are not billed for this "wasted" power as traditionally home users were just resistive heating or incandescent lights so there was no point putting fancy meters, nor having to explain the whole complicated Power Factor thing.
Industrial users certainly are billed for this and PF correction in that environment is vital.
With the huge increase in low voltage power supplies and LED at home it is becoming an issue. The extra components to do good power factors cost money, but things still work without them. So guess what gets left out of all the bargain USB power supplies and LED lights... A lot of them have PF near 0.5 which is appalling, at scale it would mean 50% of power stations would be needed for... nothing useful.
Modern smart meters are perfectly capable of doing either billing. There are some theories that billing may change for domestic users if domestic PF gets very bad. I think it's unlikely due to the confusion PF causes (even in me and I have degree in physics) but I also can't think of another way to encourage people to ensure they buy "good" equipment...
Without delving into the interaction between that particular machine and that inverter it's hard to say, you'd have to really look at high speed measurement on the mains side.
If you know anyone with different Tassimo machines might be worth borrowing one to see what it does and if it's kinder to your inverter. I've had a few Nespresso machines and while I've not had them on an inverter the power profile can be quite different.
Above and beyond @roadtripper I have an A level in Physics, but still so much to learn. Next step try the newer house Tassimo machine, just to see.... Massive thanks again..
Before we get to bogged down in power factor correction and whether the CIVIL acronym applies I think this is more a case of me being a numpty and assuming that 700 watts was the microwave oven input power and not the available cooking power plus what must be a shed load of additional losses.
As others have pointed out a microwave in the camper is probably surplus to requirements so it's an induction hob then and some staggered Judds... sod it, just the Judds!
Sounds reasonable!
As a bread and butter sparky I always thought that the capacitor on a larger motor was there to control the motor direction upon start up much as as compensate for the current lagging voltage due to the inductance of the motor field windings?
In my illustrious yoof I have been party to the installation of power factor correction across the incoming mains supply but this was many moons ago when Nacanco at Milton Keynes were making drinks cans for the Coca Cola factory next door and I was a callow apprentice seeing the AC theory hammered into me at Tech being put into practice.
Not sure if power factor correction is a thing these days with switch mode power supplies and thyristor soft starts on previously star/delta motor contactors?
So shaken as we are, so wan with care, find we a time for frighted peace to pant. Bill Sparkespeare, made as much sense....
Without wanting to further divert the subject yes SMPS continues to need PF correction. They're much smaller and overall efficient but as thier trick is to run a small transformer at high frequency they demand power in a very odd way that causes harmonics on the power lines. This has to be corrected in the SMPS itself, rather than en mass like classic PF loads, and is again often left out.
Switched-mode power supply - Wikipedia
And the moral of this story is….unless you’re prepared to invest huge amounts of money in Lithium & high end inverters. AND the associated copper that you’ll need to connect it all, running significant 240V loads from 12V batteries is a nonsense.
I think the current... tee hee... problem is that we're stuck in the mind set of leisure power being derived from a 12 volt battery when maybe we should be stepping up the voltage from the alternator and juggling the solar panels to provide say a 48 volt leisure battery and reduce those huge 12 volt current values?
But then you’re going to have to change the whole van system to 48V, all so you can use your hair straighteners
I did help look after a yacht with a Sea Panther(?) engine that had a wierd approach of running the engine electrics at 24v for more efficient charging but used pairs of starter and leisure 12v battery. Then a complex battery isolator would switch them between serial and parallel when you moved from running to non running.But then you’re going to have to change the whole van system to 48V, all so you can use your hair straighteners
I get the idea but the result was that several generations of owners had simply given up and wired equipment in anywhere they could find 12v between 2 terminals and it was a nightmare.
Of course when we all move to 400/800v EV it's really easy - plug a Vehicle to Load adapter in and use as much mains as you want trading off range...
A whole new subject for family arguments await I suspect
You can get electric BBQs to plug into some EVs now. Now then kids, would you rather have another burger & walk home…..I did help look after a yacht with a Sea Panther(?) engine that had a wierd approach of running the engine electrics at 24v for more efficient charging but used pairs of starter and leisure 12v battery. Then a complex battery isolator would switch them between serial and parallel when you moved from running to non running.
I get the idea but the result was that several generations of owners had simply given up and wired equipment in anywhere they could find 12v between 2 terminals and it was a nightmare.
Of course when we all move to 400/800v EV it's really easy - plug a Vehicle to Load adapter in and use as much mains as you want trading off range...
A whole new subject for family arguments await I suspect
