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Switch mode power supplies & inverters


pagan witch

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Let us start with I am C&G 224 qualified as an electronics engineer so anyone wanting to put a real 'techy' answer on here please feel free.

 

We are normally hooked up to a shore line but are capable of self sufficiency via a 2kw inverter and if needs be a 2.8kw diesel gen set.

 

I run a Toshiba laptop via its' mains pack and all is well on mains. However . . . . If I try and run this on our inverter the inverter repeateddly trips in and out (although it still seems to output 230v as the fridge / freezer still runs even whilst this 'tripping' is occouring.

 

I also note that one of our many mobile phones' charger also has the same effect, others however run fine.

 

The only common link I can find between the two products that cause the 'tripping' is that they are both 'chargers' and both are 'switch mode' supplies.

 

My other laptop charges OK from the inverter, as do all of the other mobile phones we have but I do have the suspicion that they are really hammering the battery bank even though the inverter's load guage doesn't show it is working hard.

 

I have practical solutions to the problems via a Maplins laptop power supply (see similar topic on the equipment pages) and using the phones' car charger, both via standard 12v cigarette sockets in the boat so this isn't critical but I'd sure like to understand why this 'tripping occurs.

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I don't know the answer to your question - yet (I'm thinking about it!) - but I suspect ALL of your mobile chargers are switched mode.

 

If they are the normal small light-weight charger, slightly larger than the size of a box of matches, then they must be switched-mode as otherwise they would have to incorporate a 50Hz transformer which would make the size larger and the weight noticeably heavier.

 

If that is so the question then becomes, "why does the inverter trip out on some switched mode chargers and not others".

 

Chris

 

PS: is your inverter a modified sine-wave type rather than a pure sine-wave version?

Edited by chris w
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Yep, I am sure they are all switch mode. If nothing else it would be easy to hear or 'feel' the 50hz hum of a transformer based option, so as you say the question should be 'why do some work and some not ?' along with 'Do the ones that work reeally hammer the batteries or is it just my imagination ?'

 

The inverter I suspect given its' price will not be pure sine wave.

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If it is a really inexpensive inverter, it probably won't be modified sine wave either. It will be just a square wave type like the Maplin ones. If someone near you has a "good" modified sine wave type (eg: Sterling etc) it would be useful to try the offending chargers on their inverter.

 

What is the quoted power handling of the one you have (continuous and peak)

 

Chris

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John

 

Actually switch-mode chargers should be more tolerant of supply because the incoming mains is rectified to DC at peak mains voltage immediately, rather than going into a transformer first. After that the supply shape is irrelevant.

 

Chris

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It is made, or at least badged as 'Ring' and is rated at 1600W continuous,2000w for 1/2 hour and peak 4000w for 0.01 seconds. It is described in the blurb as being 'square wave' - which I do understand.

 

It can run (not all at once I hasten to add - our kettle (750w), hoover (700w), fridge freezer, Goerge Foreman style electric grill (720w) so I'd like to think it can manage a phone charger or laptop power supply. Incidentally despite the inverter making triupping noises it does still continue to supply power but as it doesn't sound happy I don't want to risk blowing it up.

 

When we are at the marina we run all electrics via the shore line. When cruising we use the inverter for the fridge freezer, TV / DVD etc. overnight and it quite happily copes with the fridge / freezer and EITHER the kettle OR Froeman grill whilst we are cruising.

 

Starts talking rubbish from here on . . . . .

 

I am wondering, if my understanding of switch modes is correct if the switch mode and inverter are out of synch with each other, the switch mode making a demand, the inverter trying to supply it just as the switch mode stops demanding it then as the inverter stops supplying the switch mode starts demanding again. Maybe some of my understanding on switch modes is wrong (probably in fact) but perhaps the ones that work have a different duty cycle that is more acceptable to the inverter ?

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John

 

Actually switch-mode chargers should be more tolerant of supply because the incoming mains is rectified to DC at peak mains voltage immediately, rather than going into a transformer first. After that the supply shape is irrelevant.

 

Chris

 

Can I just point out that the switch mode seems quite happy, it is the inverter that doesn't sound like it is.

 

Steev

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A few questions:-

 

1. Is the inverter line frequency or high frequency switching? ie does it use a big transformer at 50Hz? For that power rating a line frequency one will weight about 18 pounds or more. A high frequency one will weigh about 6 pounds.

 

2. Are the power supplies/chargers that are causing a problem switched dual voltage? Automatic dual voltage or continous voltage range?

 

3. Can you check that it is actually square wave as opposed to modifed squarewave? No one has made one of those since Oliver Cromwell was causing trouble.

 

I'm guessing that it's a line frequency inverter. If not I'll have another ponder after you come back with answers to the above.

 

Gibbo

Edited by Gibbo
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3. Can you check that it is actually square wave as opposed to modifed squarewave? No one has made one of those since Oliver Cromwell was causing trouble.

 

Gibbo

 

Some (maybe all) of the Maplin range are square-wave. They were selling off 600W versions at £19.99 last year so I grabbed one on the basis that, at that price, it's effectively free and may somewhere, someday actually have a use. Checked it on a scope and it's definitely just a simple square wave one.

 

I also made a couple of squarewave versions for friends who wanted a shaver inverter/charger on their boat. Used 2 x power op amps as squarewave oscillators bridge feeding a reversed mains transformer. Crude but effective and fine for 10W or so.

 

Chris

 

Chris

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Some (maybe all) of the Maplin range are square-wave. They were selling off 600W versions at £19.99 last year so I grabbed one on the basis that, at that price, it's effectively free and may somewhere, someday actually have a use. Checked it on a scope and it's definitely just a simple square wave one.

 

I also made a couple of squarewave versions for friends who wanted a shaver inverter/charger on their boat. Used 2 x power op amps as squarewave oscillators bridge feeding a reversed mains transformer. Crude but effective and fine for 10W or so.

 

Chris

 

Chris

 

That's just plain disgusting!

 

If OP's inverter really is squarewave then that could be related. Let's see what he says.

 

Gibbo

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A few questions:-

 

1. Is the inverter line frequency or high frequency switching? ie does it use a big transformer at 50Hz? For that power rating a line frequency one will weight about 18 pounds or more. A high frequency one will weigh about 6 pounds.

 

2. Are the power supplies/chargers that are causing a problem switched dual voltage? Automatic dual voltage or continous voltage range?

 

3. Can you check that it is actually square wave as opposed to modifed squarewave? No one has made one of those since Oliver Cromwell was causing trouble.

 

I'm guessing that it's a line frequency inverter. If not I'll have another ponder after you come back with answers to the above.

 

Gibbo

 

Answers to above :-

 

1) As it weighs more like 6 pounds than 18 I'm inclined to believe it is high frequency but it doesn't say on the blurb and I don't fancy taking it off the wall to weigh

it.

 

2) The 'problem causing' laptop suuply states it will accept 100v - 240v so is continuos voltage. Haven't checked the phone charger but gues it will be the same as I don't recall there being any kind of changeover switch on it anywhere.

 

3) A closer inspection of the inverter's blurb says that the output is "Square wave or modified sine wave. It is a stepped waveform designed to have characteristics similar to the sine wave shape of utility power" On the back page the tech spec stuff says it is "Modified sine wave"

 

Just a thought here ( and a digression too) but I bet there is a case for arguing that description from a legal point. Surely it is a modified square wave - i.e a square wave that has been modified to represent a sine wave rather than a sine wave that has been modified to represent a square wave ?

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Answers to above :-

 

1) As it weighs more like 6 pounds than 18 I'm inclined to believe it is high frequency but it doesn't say on the blurb and I don't fancy taking it off the wall to weigh

it.

 

Then that counts out my first theory.

 

 

2) The 'problem causing' laptop suuply states it will accept 100v - 240v so is continuos voltage. Haven't checked the phone charger but gues it will be the same as I don't recall there being any kind of changeover switch on it anywhere.

 

And that gets rid of my second theory.

 

 

3) A closer inspection of the inverter's blurb says that the output is "Square wave or modified sine wave. It is a stepped waveform designed to have characteristics similar to the sine wave shape of utility power" On the back page the tech spec stuff says it is "Modified sine wave"

 

Well you got me beat then. There are a few things that could have caused what you are seeing but other than an overload (which clearly isn't the case here) they all rely on the inverter being a line frequency type or the power supplies being switched voltage (either manual or automaitc) as oppose to single voltage or continuous voltage. None of this applies here so I haven't got a clue! Sorry.

 

The most common problem is a line frequency inverter and a switched voltage power supply that switches to 230 volts by ignoring one half of the waveform (diode placed in series). It's effectively 115 volt equipment. Some hair dryers switch to half power using a diode. It causes the inverter to go nuts as current is only drawn on half of the waveform so the output transformer goes into saturation and the inverter isn't happy as it see huge current being drawn up the battery leads (as the transformer is saturated) but very low output power. Most of them object in some way, some shut down, some buzz like billyo, others blow up.

 

Just a thought here ( and a digression too) but I bet there is a case for arguing that description from a legal point. Surely it is a modified square wave - i.e a square wave that has been modified to represent a sine wave rather than a sine wave that has been modified to represent a square wave ?

 

Couldn't agree more. Clearly the marketing department got hold of that one.

 

Gibbo

Edited by Gibbo
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Just a thought...

 

If the inverter and the switch-mode power supply have the same internal operating frequency could they 'interfere' with each other?

 

I ask because the problem seems to be with some power supplies and not others - so the internal frequency might be different for different power supplies.

 

Given this, would a suitable capacitor across the inverter output make things better?

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My Sterling pure sine clicks in and out with a Nokia phone charger, or ANY LOAD UNDER 40 WATTS. Charles told me that it only does this in the "standby" mode .

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I've got cheap inverters, two of them, and everything I have ever used them for has worked perfect, except one thing and that was a touch sensitive lamp. Each time you touch it it gets brighter, that didnt like it too much and just stayed on?

 

Including an array of charges for phone(s), Mp3 players, walkie talkies, Nintendo DS, laptop, radio and loads of 12v power supplies for both expensive and cheap stuff, crikey it seems at times all I've ever got plugged in is those bulky black transformers. I have hair dryers, hair straighteners, various video game consoles, fridge, grill, toaster, TV etc etc.

 

Never missed a beat, I'll not bother with expensive pure sine wave.

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I've got cheap inverters, two of them, and everything I have ever used them for has worked perfect, except one thing and that was a touch sensitive lamp. Each time you touch it it gets brighter, that didnt like it too much and just stayed on?

 

Including an array of charges for phone(s), Mp3 players, walkie talkies, Nintendo DS, laptop, radio and loads of 12v power supplies for both expensive and cheap stuff, crikey it seems at times all I've ever got plugged in is those bulky black transformers. I have hair dryers, hair straighteners, various video game consoles, fridge, grill, toaster, TV etc etc.

 

Never missed a beat, I'll not bother with expensive pure sine wave.

I know others who report much the same. Problem is our washer is very fussy and needs pure sine.

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My Sterling pure sine clicks in and out with a Nokia phone charger, or ANY LOAD UNDER 40 WATTS. Charles told me that it only does this in the "standby" mode .

 

I did think that the low demand may be a problem but even when the 720w kettle is on we still get the tripping noise - still get power from it though.

 

Must admit it has me beaten so the solution thus far is to use 12v adaptors to run said troublesome items.

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I did think that the low demand may be a problem but even when the 720w kettle is on we still get the tripping noise - still get power from it though.

 

Must admit it has me beaten so the solution thus far is to use 12v adaptors to run said troublesome items.

I don't get that! When ours is doing this in/out thing and the fridge happens to kick in, then it settles down and stays on. Obviously a different issue.

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I don't get that! When ours is doing this in/out thing and the fridge happens to kick in, then it settles down and stays on. Obviously a different issue.

Now you come to mention it the fridge was making noises so I assumed the compressor was running . . . however . . . with hindsight I recal that the fridge does make a noise even after the compressor has switched of so I'll try and time the two uses together and see if I can force it.

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I suspect that if you connected an oscillascope to the inverter output you would find some "spikes" These can be at the output frequency, (easy to identify) or at the Inverter switching frequency or harmonics thereof.(Not so simply identified) These spikes could easily interfere with your laptop converter switching oscillator.

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My Sterling pure sine clicks in and out with a Nokia phone charger, or ANY LOAD UNDER 40 WATTS. Charles told me that it only does this in the "standby" mode .

 

The standby-mode only applies to the pure-sine wave model not the modified sine wave version. Pure sine wave inverters have a high quiescent current (around 3 - 8 amps) depending on manufacturer. This is the current that the inverter consumes over and above the current drawn by any load - in fact even when it is not driving anything. By comparison, a modified sine wave inverter (like the Sterling) will have a quiescent current of around 1 amp. (The Sterling pure sine wave model is around 3 amps).

 

To save power the (pure sine wave) inverter goes into a standby-mode when it detects there is no load on the equipment. This is the relay clicking you are hearing. Some manufacturers (not Sterling actually) play specification tricks and quote only the standby current (< 1 amp) which makes it look great. In fact, when driving a load, there is an additional few amps (and hence ampere-hours) wasted. It's one of the disadvantages of pure sine wave inverters.

 

Chris

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Let us start with I am C&G 224 qualified as an electronics engineer so anyone wanting to put a real 'techy' answer on here please feel free.

 

We are normally hooked up to a shore line but are capable of self sufficiency via a 2kw inverter and if needs be a 2.8kw diesel gen set.

 

I run a Toshiba laptop via its' mains pack and all is well on mains. However . . . . If I try and run this on our inverter the inverter repeateddly trips in and out (although it still seems to output 230v as the fridge / freezer still runs even whilst this 'tripping' is occouring.

 

I also note that one of our many mobile phones' charger also has the same effect, others however run fine.

 

The only common link I can find between the two products that cause the 'tripping' is that they are both 'chargers' and both are 'switch mode' supplies.

 

My other laptop charges OK from the inverter, as do all of the other mobile phones we have but I do have the suspicion that they are really hammering the battery bank even though the inverter's load guage doesn't show it is working hard.

 

I have practical solutions to the problems via a Maplins laptop power supply (see similar topic on the equipment pages) and using the phones' car charger, both via standard 12v cigarette sockets in the boat so this isn't critical but I'd sure like to understand why this 'tripping occurs.

 

Hi,

 

How do you know it's tripping, does it beep or make a buzzing noise?

 

IF it's RFI upsetting the inverter it MAY be worth trying a Belkin Surgecube/Mastercube as they have RFI filters built in.

 

P0045277_C0000192_P0000000.jpg

 

http://www.ebuyer.com/customer/products/in...oduct_uid=45277

 

cheers,

Pete.

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I've had exactly the same problem, various inverters and always low voltage chargers, I did try and get to the bottom of it and blew up a few chargers in the process, so don't recommend experimentation. In the end I decided simlpy to match chargers and inverters so they didn't do it, I suggest buying a cheap inverter and forgetting about it.

 

Possible causes:

backfeed on the line tripping 'autoprotect' function, there was some, whether it did or not I don't know.

something mucking about with capacitance, never did measure it.

gremlins

 

It was pointed out to me wasting several days to try and find out what was causing it, could be solved by swaping plugs, then there wasn't a problem, see.

 

To digress to your other point, I suspect someone in the marketing department has been talking to a mathematician, after all a square wave could be described as a 'modified sine wave', they only have to be truthful, not helpful.

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