Cheap LiFePO4 BMS?

[jetzi]

8 minutes ago, peterboat said:

Ivan if you plan to run your panels in series as per your diagram, the solar controller you have listed wont work, its only 150 volts and your panels have an open circuit voltage of over 40 volts, so you would have to put 2 into parallel twice and then series. Its a small point I know but I have fallen foul of it in the past, its because victron panels are rated at at 24 volts rather than much cheaper commercial ones for roof top systems on houses

Thanks Peter, good point. The four panels in series would be 161.92VOC - is that definitely too much for a 150V controller? Victron do make a 250V version of this so I could get that. I also overspecced it current wise in case I wish to add more panels in future.

 

 

Are there pros and cons for running the solar in series vs in parallel? Would the controller "mind" converting 48V of panels to 12V charge for the batteries?

 

[nicknorman]

9 hours ago, Richard10002 said:

I have the 220A Bluetooth Victron Battery Protect as my low voltage protection. I saw it being used with an inverter in one of Will Prowses videos.

 

I'm a bit worried now.... What reason do Victron give for not using it with an inverter?

Firstly it definitely can’t be used with a Combi as it is for unidirectional current only. Secondly I’d guess, as suggested, it is to do with the switch-on inrush current. The first time I disconnected our Combi to move some wiring, I got a right shock (metaphorically, not electrically) when I reconnected it. A massive fat noisy spark almost as if I’d shorted the batteries. I hadn’t, but what I had done is to connect the batteries across now-discharged very large capacitors inside the Combi. These present an effective short circuit for the few milliseconds they take to charge up, so a very large current flows. Even though this is only for a short time, semiconductors junctions even for 220A devices are small with little thermal mass and thus heat up nearly instantly. And it is not just the inrush current with the device’s semiconductors switched on, there is also a (very short) period when the device is in the process of turning on - it doesn’t go from off to on instantly (although it is very quick) and as the FETs are going from open circuit to conduction, they pass through a period of resistance for a microsecond or two which adds to heat dissipated.

 

The 220A device quotes a peak current of 600A but the instantaneous current on reconnection of a big inverter will be much more, albeit for a very short duration. If you can manually control when the device will reconnect, you could “bodge” it by means of a push button and resistor bypassing the isolator. You would press and hold the button for a few seconds prior to switching the isolator on, to recharge the capacitors.

 

I would expect it to be fine when disconnecting the load with high current flowing.

 

I know all this because I have been working with electronic devices since the 3rd century BC.

[redwing]

 Ivan re Are there pros and cons for running the solar in series vs in parallel? Would the controller "mind" converting 48V of panels to 12V charge for the batteries?

 

Have a look at Bimble support 'shading issues' I don't know how definitive it is 

https://www.bimblesolar.com/support

 

I chose Panasonic 245 panels because they are only 800mm wide but had to parallel as the mppt in my Easysolar is 100/50

Re your inverter choice, my inverter, it is a Victron Easysolar 12/1600/70 which is basically a 1600w multi with a 100/50 mppt. It won't run my cheap washing machine. I can run it thru my old 2000w (sunpower?) inverter which shows about 2200w peak during 30C heat cycle

 

Also, I know there are pros and cons re combis but a 3000 Victron multi will also give you a 120a charger for less than seperates

[nicknorman]

9 hours ago, ivan&alice said:

Thanks Peter, good point. The four panels in series would be 161.92VOC - is that definitely too much for a 150V controller? Victron do make a 250V version of this so I could get that. I also overspecced it current wise in case I wish to add more panels in future.

 

 

Are there pros and cons for running the solar in series vs in parallel? Would the controller "mind" converting 48V of panels to 12V charge for the batteries?

 

With MPPT from an electrical point of view it is generally better to have panels in series, thinner cable is needed because the current is less. But definitely not to exceed the maximum controller voltage at all. And you need to bear in mind that the panel  Voc is temperature dependant - it is often quoted at say 25degC but will be significantly more on a cold bright morning.

 

Another upside of series is that you stand a better chance of getting some juice out of it over winter when the panels are doing virtually nothing.

 

A downside is that if one panel of a series chain is shaded, it kills the flow in the entire chain, whereas with a parallel setup only the output from that panel is lost.

 

Life is a compromise! In you case probably series-parallel is best.

[MtB]

5 minutes ago, nicknorman said:

A downside is that if one panel of a series chain is shaded, it kills the flow in the entire chain, whereas with a parallel setup only the output from that panel is lost.

 

That doesn't seem to be always the case Nick. Mine are in series and I notice a current still flows if a panel cell is shaded or partly shaded by say a pigeon box. 

 

I know very little about solar panels but I notice some are said to have diodes across the cells to supposedly fix the problem you describe, but I've not managed to think this through properly and figure how these diodes work exactly, but they seem to. Do you know how? Can you explain please? 

 

Much obliged if you can...

 

 

 

 

[TheBiscuits]

34 minutes ago, nicknorman said:

I know all this because I have been working with electronic devices since the 3rd century BC.

We should still check with Peter - he probably knows a bloke who once used an isolator ...

[jetzi]

17 minutes ago, nicknorman said:

Another upside of series is that you stand a better chance of getting some juice out of it over winter when the panels are doing virtually nothing.

For me this clinches it! Series it is... I'll get the larger 250VOC MPPT. Reason being, that I'm getting much more solar than I need in summer, so that I can stretch out the "sunshine power" for 8 months of the year.

 

It might seem like overkill, but I'm planning on having some fun with it (which is how I'm justifying spending 3kGBP essentially for a washing machine!) and having the larger controller means that I can play and experiment. I can try series for a month and parallel the next. I could even do something crazy like have them switchable between series and parallel, depending on where I'm moored!

 

Just fun project ideas, I don't expect them to be "worth it" other than for schoolin' and for foolin'.

[peterboat]

9 hours ago, ivan&alice said:

Thanks Peter, good point. The four panels in series would be 161.92VOC - is that definitely too much for a 150V controller? Victron do make a 250V version of this so I could get that. I also overspecced it current wise in case I wish to add more panels in future.

 

 

Are there pros and cons for running the solar in series vs in parallel? Would the controller "mind" converting 48V of panels to 12V charge for the batteries?

 

Nick post covers it I would choose a better mppt controller like Midnite one it runs at 200 volts plus has some clever features,  it's also cheaper from prism solar. I run mine in series because in summer I power my immersion heater from it direct (3kw) its the same as the inverter I need 2400 watts because I have the washer and dishwasher on board,  I bought the victron because it was cheap at £400, as somebody made the mistake of thinking it was 3000 watts and it wasn't and wouldn't do what they wanted. So if you stick with the controller 2 panels in parallel twice an then in series back or two in series twice then parallel back would work 

7 minutes ago, TheBiscuits said:

We should still check with Peter - he probably knows a bloke who once used an isolator ...

I did field power for a living with very big gennies we could not have failure as our lives might depend on it

[MoominPapa]

11 minutes ago, Mike the Boilerman said:

 

That doesn't seem to be always the case Nick. Mine are in series and I notice a current still flows if a panel cell is shaded or partly shaded by say a pigeon box. 

 

I know very little about solar panels but I notice some are said to have diodes across the cells to supposedly fix the problem you describe, but I've not managed to think this through properly and figure how these diodes work exactly, but they seem to. Do you know how? Can you explain please? 

 

Much obliged if you can...

 

Diodes work in conjunction with MPPT controllers. Silicon solar cells have an open circuit voltage of 0.5 to 0.6 volts, so a panel suitable for direct charging a 12v battery might have 28 cells in series to get the voltage high enough to charge the battery. If you shade two cells, the voltage drops by a volt, goes below the battery voltage, and charging stops. Add an MPPT controller that can boost the voltage (or drop the voltage less, on a longer, higher voltage string) and the loss of a few cells doesn't matter beyond a proportional loss of power.

 

MP.

 

[redwing]

https://docs.victronenergy.com/veconfigure.html#inverter-settings

 

Would the low voltage disconnect settings on the multi along with a BMV 712 solve the under voltage issues ?

[MtB]

12 minutes ago, MoominPapa said:

Diodes work in conjunction with MPPT controllers. Silicon solar cells have an open circuit voltage of 0.5 to 0.6 volts, so a panel suitable for direct charging a 12v battery might have 28 cells in series to get the voltage high enough to charge the battery. If you shade two cells, the voltage drops by a volt, goes below the battery voltage, and charging stops. Add an MPPT controller that can boost the voltage (or drop the voltage less, on a longer, higher voltage string) and the loss of a few cells doesn't matter beyond a proportional loss of power.

 

MP.

 

 

I'm still not 'getting' the mechanism by which diodes in the panels work, or what they do exactly. Or where they are connected even.

 

I fall at the first hurdle when trying to figure ot out as I don't know what happens to a cell when it gets shaded. Presumably if it was put into total darkness its voltage would fall to zero but what happens to its internal resistance? Does it go infinite? Or stay at near zero?

 

 

 

 

[jetzi]

10 minutes ago, peterboat said:

better mppt controller like Midnite one it runs at 200 volts plus has some clever features

Peter you seem very keen on Midnite kit. Like I say I have my little heart set on the blue stuff, mainly because it's well known, well supported and very interoperable. When I was comparing brands of MPPT there was almost nothing in it when it came to power output, and I know I'm paying a Victron premium. Could you explain what makes the Midnite kit "better" than Victron?

 

https://www.bimblesolar.com/victron-mppt-250-100

@ 815 GBP from Bimble

 

vs

 

https://prismsolar.co.uk/shop/classic-250-sl-mppt-with-hypervoc-technology.html

@ 825 EUR (725GBP) from Prism

 

17 minutes ago, peterboat said:

I run mine in series because in summer I power my immersion heater from it direct (3kw) its the same as the inverter I need 2400 watts because I have the washer and dishwasher on board,  I bought the victron because it was cheap at £400, as somebody made the mistake of thinking it was 3000 watts and it wasn't and wouldn't do what they wanted

For a later phase I want to be able to dump the excess sun into my calorifier, but that's a later phase. It's heartening to hear that you run a washer and dishwasher off of the 3000VA / 2400W Victron inverter.

 

56 minutes ago, redwing said:

I know there are pros and cons re combis but a 3000 Victron multi will also give you a 120a charger for less than seperates

I've only been on shore power once in two years, and CCing is the only kind of boating that appeals to me. So I'm not going to bother with an installed charger. I have a 240V to 12V mains battery charger for that situation. Only going for separates because it gives me more flexibility to play.

[nicknorman]

5 minutes ago, redwing said:

https://docs.victronenergy.com/veconfigure.html#inverter-settings

 

Would the low voltage disconnect settings on the multi along with a BMV 712 solve the under voltage issues ?

To some extent, but the problem with a big inverter is that it pulls the system voltage down when under heavy load which might cause the thing to shut off. Current draw stops, system voltage rises, inverter goes back on again and so the cycle repeats. The settings recommend a 1v difference between the shut off and turn back on voltages, which will go some way to alleviating this problem and of course lithium batteries suffer much less than LA batteries from voltage drop under load, but there is still drop in the wiring, connections, isolator switch etc. When 250A is flowing, it doesn’t take much to drop a volt or two.

 

You would end up with a system that shut off early when under heavy load, much later when under light load.

 

The other thing to bear in mind is that presuming the Li cells are top balanced, unless their capacities are all identical they will not be bottom balanced and so one cell will become catastrophically flat before the others do, its voltage crashing. I think one doesn’t really want to ever get to that stage and so the monitoring of individual cell voltages is better, and (bearing in mind the very flat voltage curve of Li) some sort of SoC determination (eg Ah counting) to shut things off when SoC of worst cell gets to 10%, 20% or whatever. Lead acid has a much more progressive fall off in voltage and so having a minimum overall voltage setting works, even though it’s not ideal due to the load dependence. I am not convinced it would work well for Li.

[peterboat]

8 minutes ago, ivan&alice said:

Peter you seem very keen on Midnite kit. Like I say I have my little heart set on the blue stuff, mainly because it's well known, well supported and very interoperable. When I was comparing brands of MPPT there was almost nothing in it when it came to power output, and I know I'm paying a Victron premium. Could you explain what makes the Midnite kit "better" than Victron?

 

https://www.bimblesolar.com/victron-mppt-250-100

@ 815 GBP from Bimble

 

vs

 

https://prismsolar.co.uk/shop/classic-250-sl-mppt-with-hypervoc-technology.html

@ 825 EUR (725GBP) from Prism

 

For a later phase I want to be able to dump the excess sun into my calorifier, but that's a later phase. It's heartening to hear that you run a washer and dishwasher off of the 3000VA / 2400W Victron inverter.

 

I've only been on shore power once in two years, and CCing is the only kind of boating that appeals to me. So I'm not going to bother with an installed charger. I have a 240V to 12V mains battery charger for that situation. Only going for separates because it gives me more flexibility to play.

I bought mine from them last year via ebay from them 618 squids it's my second one, its for the drive solar,  the first has been in use for many years and am very pleased with its performance and warranty 5 years have a look on American sites 

[nicknorman]

4 minutes ago, Mike the Boilerman said:

 

I'm still not 'getting' the mechanism by which diodes in the panels work, or what they do exactly. Or where they are connected even.

 

I fall at the first hurdle when trying to figure ot out as I don't know what happens to a cell when it gets shaded. Presumably if it was put into total darkness its voltage would fall to zero but what happens to its internal resistance? Does it go infinite? Or stay at near zero?

 

As I understand it (and we don’t have any solar) you can put diodes across an entire panel. When the panel is producing juice,  the diode is reverse biased and so does nothing. If that panel gets shaded, the other panels trying to force more current through the string than the shaded panel can take, results in that panel becoming reverse biased and blocking the flow. At that point, the normally reverse biased diode would go into conduction and bypass that entire panel. Obviously the output from that panel is lost but the output from the other panels in the string remain effective.

 

Just thinking about it, this would only work with a series set up - the MPPT can happily adapt to the reduced string voltage. If you had series -parallel into one MPPT then the loss of one panel in one series string would mean that string did nothing, so no point in fitting the diode.

 

For the avoidance of confusion panels normally have diodes in series, so that at night current doesn’t flow backwards from the battery through the panel.

 

I think this is complementary to MP’s point which is that individual sections within a panel can have diodes built in to give a similar effect on a smaller scale.

[MoominPapa]

16 minutes ago, nicknorman said:

As I understand it (and we don’t have any solar) you can put diodes across an entire panel. When the panel is producing juice,  the diode is reverse biased and so does nothing. If that panel gets shaded, the other panels trying to force more current through the string than the shaded panel can take, results in that panel becoming reverse biased and blocking the flow. At that point, the normally reverse biased diode would go into conduction and bypass that entire panel. Obviously the output from that panel is lost but the output from the other panels in the string remain effective.

 

Just thinking about it, this would only work with a series set up - the MPPT can happily adapt to the reduced string voltage. If you had series -parallel into one MPPT then the loss of one panel in one series string would mean that string did nothing, so no point in fitting the diode.

 

For the avoidance of confusion panels normally have diodes in series, so that at night current doesn’t flow backwards from the battery through the panel.

 

I think this is complementary to MP’s point which is that individual sections within a panel can have diodes built in to give a similar effect on a smaller scale.

Interesting. I found this: http://depts.washington.edu/cmditr/modules/opv/physics_of_solar_cells.html

 

The implication is that a solar panel behaves pretty much like a silicon diode, with the exception that when it's reverse biased AND illuminated current flows through the junction in the opposite direction to a normal forward-biased diode. That would explain why diodes in the opposite polarity are required to allow current through a series string when some cells are shaded: a shaded cell is a reverse biased diode and no current flows through it. That would imply that a backwards current from the battery at night shouldn't be a problem, but there's likely some wrinkle which I'm not aware of.

 

MP.

 

[nicknorman]

10 minutes ago, MoominPapa said:

Interesting. I found this: http://depts.washington.edu/cmditr/modules/opv/physics_of_solar_cells.html

 

The implication is that a solar panel behaves pretty much like a silicon diode, with the exception that when it's reverse biased AND illuminated current flows through the junction in the opposite direction to a normal forward-biased diode. That would explain why diodes in the opposite polarity are required to allow current through a series string when some cells are shaded: a shaded cell is a reverse biased diode and no current flows through it. That would imply that a backwards current from the battery at night shouldn't be a problem, but there's likely some wrinkle which I'm not aware of.

 

MP.

 

Whilst a night time panel is like a reverse biased diode, I think it is a pretty leaky one, hence a “normal” diode to fully block the reverse leakage flow.

 

On the general subject, there is a simple explanation of diodes here:

 

https://www.altestore.com/blog/2016/09/bypass-diodes-blocking-diodes-solar-panels/#.XocPmC_TWhA

 

It also mentions that most (but not all cheap PWM) solar controllers have built in diodes to prevent reverse flow at night.

Edited April 3, 2020 by nicknorman

[MoominPapa]

1 minute ago, nicknorman said:

Whilst a night time panel is like a reverse biased diode, I think it is a pretty leaky one, hence a “normal” diode to fully block the reverse leakage flow.

That's believeable.

 

MP.

 

[Tom and Bex]

19 hours ago, Dr Bob said:

it may switch to float early as 90A may need a constant voltage phase in the charge cycle.

I find when charging at 70-90A via alternator, then with our setup, the batteries are around 80-85% charged when the voltage hits 14.0v, and if we want to charge them higher, we continue in constant voltage mode. Not sure the same could be relied on with solar due to the variability of it 

 

16 hours ago, ivan&alice said:

he says the cells are a little older and not suitable for current draw > 200A such as for traction applications. I couldn't manage 200A if I tried anyway

I suspect you'll find that he's talking about the current draw per individual cell, so with 3 cells in series then you're looking at limit of 600A! Even with big inverter I doubt you'd be able to get near that! Remember for ev use then those figures are easily achievable, and much higher figures are seen regularly under acceleration, really shows what these batteries are capable of when new. 

 

16 hours ago, ivan&alice said:

Here's a real newbie question: would it be sensible to get to 100% every few months (straight after balancing) to check on capacity and erase any "memory effect"? Of course, discharging the batteries promptly thereafter and not storing them at 100% even overnight.

No memory effect to worry about. Only real reason to get to 100% is to re-sync battery monitor. What monitoring are you planning for soc? Does the bms give this info? If so need to read instructions to see if they recommend charging to 100% every so often to re-sync it. If using the batteries then they'll not be stored at 100% overnight anyway. No reason to deliberately discharge them, just use as normal.

 

15 hours ago, ivan&alice said:

a 7kg washing machine with a true "cold wash" button that completely disables the heating element. This is probably around 500W and definitely not more than 1000W.

2) a 1200W hairdryer.

 

I am surprised that you guys use an electric kettle, I use a stovetop gas one.

 

16 hours ago, peterboat said:

a 2000 VA inverter wont run a washing machine

I was under the impression that the water heating was the bit that consumes a lot of power, which is why I bought a washing machine that didn't do that. How can I calculate how large an inverter in VA I need to power this washing machine, then? I can't get a straight answer on peak W load, but it says it uses 1.05kW per "cycle", around an hour. So I guessed that the peak usage is around 1500W-2000W with the heating on.

We use our washing machine quite happily off our 1500w inverter and it doesn't get near the limit. Ours has control to set wash temperature that overrides program setting - we leave this permanently set to cold, and have it connected via mixer valve so it fills with hot water for the wash, and we switch mixer valve back to cold for rinses (if we remember!)

 

Similarly, sometimes run 1200w iron and hair drier from our 1500w inverter (not both at same time!). As to kettle, we don't have electric kettle, but do sometimes run electric soup maker (1500w) from inverter. These batteries have transformed our electric usage, and we happily run stuff we wouldn't have dreamed of running from the batteries before. 

 

 

Edited April 3, 2020 by Tom and Bex
Remove duplicate post!

[peterboat]

6 minutes ago, Tom and Bex said:

I find when charging at 70-90A via alternator, then with our setup, the batteries are around 80-85% charged when the voltage hits 14.0v, and if we want to charge them higher, we continue in constant voltage mode. Not sure the same could be relied on with solar due to the variability of it 

 

I suspect you'll find that he's talking about the current draw per individual cell, so with 3 cells in series then you're looking at limit of 600A! Even with big inverter I doubt you'd be able to get near that! Remember for ev use then those figures are easily achievable, and much higher figures are seen regularly under acceleration, really shows what these batteries are capable of when new. 

 

No memory effect to worry about. Only real reason to get to 100% is to re-sync battery monitor. What monitoring are you planning for soc? Does the bms give this info? If so need to read instructions to see if they recommend charging to 100% every so often to re-sync it. If using the batteries then they'll not be stored at 100% overnight anyway. No reason to deliberately discharge them, just use as normal.

 

We use our washing machine quite happily off our 1500w inverter and it doesn't get near the limit. Ours has control to set wash temperature that overrides program setting - we leave this permanently set to cold, and have it connected via mixer valve so it fills with hot water for the wash, and we switch mixer valve back to cold for rinses (if we remember!)

 

Similarly, sometimes run 1200w iron and hair drier from our 1500w inverter (not both at same time!). As to kettle, we don't have electric kettle, but do sometimes run electric soup maker (1500w) from inverter. These batteries have transformed our electric usage, and we happily run stuff we wouldn't have dreamed of running from the batteries before. 

 

 

I just use the washer as normal so do need the heater same with the dishwasher I would have liked a hot water fill type washer but they are expensive 

[Tom and Bex]

13 hours ago, ivan&alice said:

Was thinking exactly that about spares! Is there such a thing as a 200A 12V circuit breaker? Could save me a couple quid on fuses in the long run!

 

2/ Victron Battery Protect is a programmable low voltage cutoff. The largest one is 220A and I was originally thinking of using this rather than the relay, but Victron recommends against using this device with an inverter.

 

I think in reality you're unlikely to get through many 200A fuses. Don't forget fuses won't blow the moment you exceed 200A, depending on the fuse you will probably have to exceed 200A by quite a bit or for some time before it blows. We have 150A fuse, and not blown it yet, even starting engine from our lithium batteries several times when the starter battery failed. 

 

I don't think you need an additional low voltage cut off. The bms should provide that based on cell voltage, not sure much benefit to be gained by having an additional cut off based on system voltage. 

 

I do like the look of that bms so will be interested to hear how you get on with it. 

 

 

1 hour ago, nicknorman said:

As I understand it (and we don’t have any solar) you can put diodes across an entire panel. When the panel is producing juice,  the diode is reverse biased and so does nothing. If that panel gets shaded, the other panels trying to force more current through the string than the shaded panel can take, results in that panel becoming reverse biased and blocking the flow. At that point, the normally reverse biased diode would go into conduction and bypass that entire panel. Obviously the output from that panel is lost but the output from the other panels in the string remain effective.

 

Just thinking about it, this would only work with a series set up - the MPPT can happily adapt to the reduced string voltage. If you had series -parallel into one MPPT then the loss of one panel in one series string would mean that string did nothing, so no point in fitting the diode.

 

For the avoidance of confusion panels normally have diodes in series, so that at night current doesn’t flow backwards from the battery through the panel.

 

I think this is complementary to MP’s point which is that individual sections within a panel can have diodes built in to give a similar effect on a smaller scale.

I seem to recall reading that nearly all panels have built in bypass diodes. All the ones we've had seem to. Yes you lose the output from the one panel that's shaded, but still get most of the output from the others. Agree it might not work so well with a combination series parallel configuration, not something if thought about before. Another reason to stick with series connection if the controller can cope with maximum open circuit voltage.

[WotEver]

2 hours ago, Mike the Boilerman said:

I'm still not 'getting' the mechanism by which diodes in the panels work, or what they do exactly. Or where they are connected even.

Read this then

https://www.electronics-tutorials.ws/diode/bypass-diodes.html

 

I’m not going to get into the earlier arguments about 1.6kVA generators being marketed as 2kVA because kW should be stated as 0.8 of the VA rating, because it’s nonsense as Nick has already explained. The 80% figure is simply taken as a ‘typical’ power factor, and to state that an inverter is 2kVA when it can’t power an 1800W (which is 1800VA, because it is a non-inductive load and has a PF of 1) is pure marketing BS. Suffice to say that Nick is correct and Peter isn’t. 
 

 

Edited April 3, 2020 by WotEver
Remove an errant k

[nicknorman]

4 minutes ago, WotEver said:

Read this then

https://www.electronics-tutorials.ws/diode/bypass-diodes.html

 

I’m not going to get into the earlier arguments about 1.6kVA generators being marketed as 2kVA because kW should be stated as 0.8 of the VA rating because it’s nonsense as Nick has already explained. The 80% figure is simply taken as a ‘typical’ power factor, and to state that an inverter is 2kVA when it can’t power an 1800W (which is 1800kVA, because it is a non-inductive load and has a PF of 1) is pure marketing BS. Suffice to say that Nick is correct and Peter isn’t. 

It occurs to me that certainly for boating use, all heavy mains consumers are virtually pure resistive loads (washing machine heaters, tumble driers, kettles, hair dryers, cooking elements etc). One doesn’t normally power heavy duty electric motors etc from an inverter. And aren’t domestic appliances that have eg motors all supposed to have power factor correction? All of which makes advertising a 1.6kw inverter with the headline of 2kva a right con!

[WotEver]

Just now, nicknorman said:

All of which makes advertising a 1.6kw inverter with the headline of 2kva a right con!

Yup!

[MtB]

43 minutes ago, WotEver said:

Read this then

https://www.electronics-tutorials.ws/diode/bypass-diodes.html

 

I’m not going to get into the earlier arguments about 1.6kVA generators being marketed as 2kVA because kW should be stated as 0.8 of the VA rating, because it’s nonsense as Nick has already explained. The 80% figure is simply taken as a ‘typical’ power factor, and to state that an inverter is 2kVA when it can’t power an 1800W (which is 1800VA, because it is a non-inductive load and has a PF of 1) is pure marketing BS. Suffice to say that Nick is correct and Peter isn’t. 
 

 

 

Thanks for the link.

 

And yes even I understand power factor and the phase angle between current and voltage. When the phase angle reaches 90 degrees then the power falls to zero IIRC even though the VA remains up at whatever it was to start with. Not that this ever happens in real life but if it did, where does the energy go?