Large and small inverter?

[carlt]

To say "It's 1000 VA which is equivalent to 800 Watts" in relation to an inverter or generator is, to an electronics engineer, about as silly as saying "My car does 40 MPG which is equivalent to 3 people eating peanut butter on toast".

 

Gibbo

Exactly....because, as we know, if we take into acount the "Jimmycarter variance", 3 people eating peanut butter on toast is only actually equivalent to 36.437mpg. They would have to be eating peanut butter sandwiches (on wholemeal) to achieve 40.

 

I'll get my..oh I see someone's got it for me.

[anhar]

I need to clarify something here.

 

The difference between VA and Watts is down the the load. It has NOTHING to do with the inverter.

 

A specification of 1000 VA on an inverter means it is capable of producing 1000VA/230 volts = 4.34 amps. Any more than 4.34 and it will shut down. A specification of 1000 Watts is completely and utterly meaningless.

 

A load of 1000 Watts with a power factor of 1 (say a heater) will work (because that is 1000VA). A load of 1000 Watts with a power factor of 0.5 (say a motor) will not (because that is 2000VA). It will shut the inverter down.

 

An inverter should be rated in VA. To rate it in Watts is completely and utterly non sensical.

 

To say "It's 1000 VA which is equivalent to 800 Watts" in relation to an inverter or generator is, to an electronics engineer, about as silly as saying "My car does 40 MPG which is equivalent to 3 people eating peanut butter on toast".

 

Gibbo

I hope Gibbo that your comments are aimed at Chris, not at me, because I know dick about all this. I responded to the VA point only because Chris had stressed earlier that the wattage rating of my Victron inverter is below the VA figure. I think he was suggesting that this owes more to Victron marketing than useful information and that it is the wattage that really counts. Now you are saying that it should be rated in VA.

 

I'll leave it to you and Chris to slug it out mate. My kit certainly does what I want of it and personally I would have no other brand except Mastervolt.

 

regards

Steve

Edited September 24, 2007 by anhar

[Gibbo]

I hope Gibbo that your comments are aimed at Chris, not at me, because I know dick about all this. I responded to the VA point only because Chris had stressed earlier that the wattage rating of my Victron inverter is below the VA figure. I think he was suggesting that this owes more to Victron marketing than useful information and that it is the wattage that really counts. Now you are saying that it should be rated in VA.

 

I'll leave it to you and Chris to slug it out mate. My kit certainly does what I want of it and personally I would have no other brand except Mastervolt.

 

regards

Steve

 

It wasn't aimed at anyone. There seems to be huge confusion between VA and Watts which I thought I'd clear up.

 

To be clear, an inverter should be rated in VA. To rate one in watts makes ZERO sense.

 

If I wasn't in a position to repair my own inverters I would personally would go for Victron or Mastervolt. That isn't just on a whim. That's a lesson learned from well over 10 years repairing inverters and I know which ones we saw the least of. Barring a few teething problems on early versions of certain models both companies produce inverters that are extremely reliable compaired to anyone else's.

 

Gibbo

[anhar]

...If I wasn't in a position to repair my own inverters I would personally would go for Victron or Mastervolt. That isn't just on a whim. That's a lesson learned from well over 10 years repairing inverters and I know which ones we saw the least of. Barring a few teething problems on early versions of certain models both companies produce inverters that are extremely reliable compaired to anyone else's.

 

Gibbo

Thanks that vindicates my view when someone with wide experience says things like that. I obtained a similar opinion from a couple of boat builders with experience of different brands when I made my decision to go Victron.

 

In these discussions people often respond by saying they've had Brand X for years and it works fine. But that misses the point which is that a buyer should be influenced by the general incidence of problems not one or two personal cases. It is that incidence, and importantly how the company resolves them, which should inform the risks of the buying decision.

 

regards

Steve

Edited September 25, 2007 by anhar

[tomsk]

Thanks that vindicates my view when someone with wide experience says things like that. I obtained a similar opinion from a couple of boat builders with experience of different brands when I made my decision to go Victron.

 

In these discussions people often respond by saying they've had Brand X for years and it works fine. But that misses the point which is that a buyer should be influenced by the general incidence of problems not one or two personal cases. It is that incidence, and importantly how the company resolves them, which should inform the risks of the buying decision.

regards

Steve

 

I would concur

[Gibbo]

In these discussions people often respond by saying they've had Brand X for years and it works fine. But that misses the point which is that a buyer should be influenced by the general incidence of problems not one or two personal cases.

 

Agreed. With any equipment there will always be at least one person who can say "Mine works fine", likewise there will always be at least one person who can say "Mine was rubbish and blew up".

 

It's worthless of course. If lots of people say one or the other then it carries some weight but how will we ever know whether lots of people are going to say one or the other unless the lone peron does stand up and say "Mine works fine" or "Mine blew up/whatever else went wrong".

 

Obviously the view of someone who has experience with 100 different units has a view that is far more valuable than someone who has experience of 1 unit.

 

Gibbo

[smileypete]

It wasn't aimed at anyone. There seems to be huge If I wasn't in a position to repair my own inverters I would personally would go for Victron or Mastervolt. That isn't just on a whim. That's a lesson learned from well over 10 years repairing inverters and I know which ones we saw the least of. Barring a few teething problems on early versions of certain models both companies produce inverters that are extremely reliable compaired to anyone else's.

 

Gibbo

Hi,

 

Has the design or quality of the cheaper or mid-range (eg Sterling) inverters improved over the years?

 

Also do they fail for a wide variety of reasons or are most failures down to a few reasons.

 

cheers,

Pete.

Edited September 27, 2007 by smileypete

[Gibbo]

Hi,

 

Has the design or quality of the cheaper or mid-range (eg Sterling) inverters improved over the years?

 

Also do they fail for a wide variety of reasons or are most failures down to a few reasons.

 

cheers,

Pete.

 

There's not really any consistency.

 

The 1500 Watt puresine inverter that Rich Electric make and sell (the one Sterling badge) is a brilliant inverter. Likewise the 3000 watt unit.

 

The 1500 watt puresine unit that Kotek make and sell (badged mainly by Sinergex) is also a brilliant inverter. Internally it's almost identical to the Rich Electric one. Only the case and front panel is really different.

 

But there are also some absolute horrors available. I've seen several different puresine inverters in extruded aluminium cases and they have been absolutely attrocious. Badly designed, dreadful circuits, badly put together etc.

 

The modified sinewave units are all rubbish.

 

On the high frequency modified sinewave units nearly all the failures are due bad circuit design.

 

On line frequency MSW it is nearly always user abuse.

 

On pure sinewave it's nearly always user abuse. Backfeeds, reverse polarity, water damage etc.

 

Before anyone starts crying note the use of the words "nearly always".

 

Gibbo

Edited September 27, 2007 by Gibbo

[carlt]

All of my inverters have failed due to water damage.

[cugsey]

All of my inverters have failed due to water damage.

 

carlt when you say water damage

how so

was the inverter badly situated

was it an accident

i needs to know

[Bojangles]

...........................

The 1500 watt puresine unit that Kotek make and sell (badged mainly by Sinergex) is also a brilliant inverter. Internally it's almost identical to the Rich Electric one. Only the case and front panel is really different............

 

Gibbo

 

Anybody know where I can get the Sinergex 1500 watt puresine unit at a reasonable price?

[carlt]

carlt when you say water damage

how so

was the inverter badly situated

was it an accident

i needs to know

Wooden boats sir! wooden boats.

[cugsey]

Wooden boats sir! wooden boats.

aha i see

ta

[chris w]

The modified sinewave units are all rubbish.

Gibbo

 

 

In what way specifically, in your opinion?

 

Chris

[Gibbo]

Anybody know where I can get the Sinergex 1500 watt puresine unit at a reasonable price?

 

Merlin do it at (I think) about £500 including VAT. Not seen them cheaper anywhere else but haven't looked. Don't buy the 1000 Watt unit. It has problems.

 

Gibbo

 

In what way specifically, in your opinion?Chris

 

The low frequency ones (ie that have a transformer running at 50Hz) are ok.

 

The high frequency ones have a fundamental design problem in that if a huge load is put on them (say a short circuit or something close) the current increases way past the output mosfet safe limit before the protection circuitry can act. The output mosfets then go bang. For the same reason high voltage spiky back emf (from power tools, large motors etc) can also fry them. There is *nothing* that can be done about this without reducing the efficiency of the inverter. It's just the laws physics.

 

Pure sinewave inverters have a huge inductor between the outputs mosfets (actually usually IGBTs on PSW) and the output terminals which limits the rate of rise in current to a slow enough level for the protection circuitry to catch it before it becomes dangerous.

 

No they can't just add an inductor to a MSW inverter for technical reasons due to the way they work.

 

Gibbo

Edited September 28, 2007 by Gibbo

[chris w]

the low freq

 

 

I don't think that will mean much to most readers - can you amplify your answer please.

 

Chris

[Gibbo]

I don't think that will mean much to most readers - can you amplify your answer please.

 

Chris

 

The low frequency ones have a massive transformer in them (about 13kg per kw). The high frequency ones have one or more small transformers in them and weigh about a fifth as much.

 

Gibbo

[chris w]

Now you've edited the original post, your point is clear.

 

However, even PSW's are not immune to blowing. I recently tried to repair one for a friend who had accidentally back-fed it on the output with mains from another source. Most of the MOSFETS had blown along with the 12v regulator. However, having changed these, the device was still not functioning correctly - it would fire up for a second and then die. I suspect the PIC is blown, but with no access to the source code it's a dead duck.

 

Chris