Switch mode power supplies & inverters

[pagan witch]

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

 

cheers,

Pete.

 

Can clearly hear it doing so. SOunds like a realy conctantly coming in and out at about 1 sec intervals.

 

Have now 'solved' the problem by using one of those Maplin computer jobs - runs direct off of 12V and works a treat. I was just trying to understand why.

[Alastair]

Is the inverter earthed?

[Gary Peacock]

This kind of thing can be a right pain a few years back I used to fit inverters and UPS's to specialist vehicles that used to contains some very advanced boxes of magic that fortunately weren't my problem.

 

We used to get lot's of strange effects where the parts of kit would power up one day from the inverter but the next not, other bits would not run at all but would run from another identical inverter so we would just send the first one back for exchange. It would turn into a continuous battle of continually fitting and returning what were reported to be faulty units that ran other items perfectly!

 

It made me a living swapping the things and I am glad I didn't have to get anymore involved then that, when the things didn't work the manufactures probably got one hell of kicking because of the implications it could cause.

 

Clever stuff all this electrickery until it doesn't do what you want it too!

[RobinJ]

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.

 

Can someone explain to me why somethings trip the inverter one day and not the next, I suspect its to do with battery state!

The problem is there are different types of inverter and different types of switched mode power supply. A good switched mode power supply will work on a bad inverter (i.e. square wave), this is because they 'integrate' the pulse to produce a lower voltage. Cheap switched mode power supplies work simply by chopping the sine wave at the right voltage, so if they don't get one they tend to produce spikes, which the inverter doesn't like and not give out much voltage as they switch off very quickly! Flashing rope light contollers tend to have cheap switched mode power supplies in them, so either blow up or don't light. The same will be true of cheap universal phone charges etc.

[Gibbo]

Can someone explain to me why somethings trip the inverter one day and not the next, I suspect its to do with battery state!

 

Quite possible.

 

The problem is there are different types of inverter and different types of switched mode power supply. A good switched mode power supply will work on a bad inverter (i.e. square wave),

 

Correct.

 

this is because they 'integrate' the pulse to produce a lower voltage.

 

Totally incorrect.

 

Cheap switched mode power supplies work simply by chopping the sine wave at the right voltage,

 

No they don't. That's phase control. Nothing to do with switch mode.

 

so if they don't get one they tend to produce spikes, which the inverter doesn't like and not give out much voltage as they switch off very quickly! Flashing rope light contollers tend to have cheap switched mode power supplies in them, so either blow up or don't light. The same will be true of cheap universal phone charges etc.

 

You're confusing switchmode with phase control.

 

Gibbo

[RobinJ]

You're confusing switchmode with phase control.

 

Gibbo

I have come across a wide variety of 'swicthed mode' type power supplies (although I am including DC-DC converters too)including discrete sine wave, digital psuedo and new 'electronic' transformers. Many of the modern low current ones use an IC with at least a capacitor for 'integration'! I am assuming these chargers are DC output and not AC!

[chris w]

I have come across a wide variety of 'swicthed mode' type power supplies (although I am including DC-DC converters too)including discrete sine wave, digital psuedo and new 'electronic' transformers. Many of the modern low current ones use an IC with at least a capacitor for 'integration'! I am assuming these chargers are DC output and not AC!

 

 

Re phase control vs switched-mode power supplies, I second Gibbo - he's right, you're wrong I'm afraid. Don't confuse switched-mode power supplies either with DC-DC converters.

 

Chris

Edited July 13, 2007 by chris w

[Gibbo]

I have come across a wide variety of 'swicthed mode' type power supplies (although I am including DC-DC converters too)including discrete sine wave, digital psuedo and new 'electronic' transformers. Many of the modern low current ones use an IC with at least a capacitor for 'integration'! I am assuming these chargers are DC output and not AC!

 

Sorry but that's pretty irrelevant. You're still confusing switch mode with phase control.

 

Phase control directly acts on, and manipulates, the incoming AC. Switch mode does not.

 

Gibbo

[larkshall]

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.

 

switch mode power supplies are notorious for this. U must have a pure sine wave inverter, anything just will not do. Most inverters are quasi sine wave (often looks like a squar wave on an oscilliscope). This confuses the switching element and it trips out.

Most kit will work ok ie freezers/fridges etc. Some Triac/thyristor controlled motors as in up market washing machines may also jibe.

[chris w]

switch mode power supplies are notorious for this. U must have a pure sine wave inverter, anything just will not do. Most inverters are quasi sine wave (often looks like a squar wave on an oscilliscope). This confuses the switching element and it trips out.

Most kit will work ok ie freezers/fridges etc. Some Triac/thyristor controlled motors as in up market washing machines may also jibe.

 

I can't agree with your first statement re switched-mode power supplies (SMPS).

 

SMPS rectify the incoming AC to DC at full mains voltage before it ever reaches a transformer and after that the input waveform is irrelevant. This makes SMPS much more tolerant to non-standard AC waveforms than other power supplies.

 

Also, "quasi sine wave" inverters look like a stepped wave rather than a conventional squarewave on an oscilloscope (although some cheap squarewave inverters do exist).

 

Chris

[Gibbo]

switch mode power supplies are notorious for this. U must have a pure sine wave inverter, anything just will not do. Most inverters are quasi sine wave (often looks like a squar wave on an oscilliscope). This confuses the switching element and it trips out.

 

When is this MYTH going to die?????

 

Switch mode power supplies are one of the most tolerant pieces of equipment around. They will run from more or less any old electrical crap you throw at them. They don't give a monkey's about the waveshape, they care little about the frequency and they have about the widest voltage tolerance of anything you will find anywhere.

 

The phrase "sensitive electronic equipment such as computers" is one I see all the time. It's complete horsesh*t. Written by marketing men who know nothing about electronics.

 

</rant>

 

 

Gibbo

[chris w]

The fact that Gibbo and I posted messages with identical ideas at exactly the same moment finally disabuses the urban myth that we are the same person.

 

[Gibbo]

The fact that Gibbo and I posted messages with identical ideas at exactly the same moment finally disabuses the urban myth that we are the same person.

 

 

I personally think you're Charles Sterling

 

Gibbo

[chris w]

I personally think you're Charles Sterling

 

Gibbo

 

 

No, I'm far better looking

[bottle]

Not only posting at the same time also agreeing with each other.

[chris w]

Gibbo and I NEVER disagree with each other (offline)

 

[pagan witch]

My sincere thanks for the ongoing tech discussion that I freely admit to enjoying however . . . .

 

May I just point out howver that the original question was to do with the inverter not liking the power supply and not the other way around. The power supply functions perfectly well on the inverter.

 

As some have said switch modes will run on just about anything that 'wobbles' at somewhere near an appropriate voltage. That is the whole point of them. Gone are the days of manufacturers having to supply and install numerous voltage and frequency options - with the switch mode one size fits all.

 

It seems that the inverter however is a little more fussy about what it runs.

 

When I accidentlly forgot top switch back to mains a few weeks ago we did start running the washing machine on the inverter and it seemed fine. That said I didn't let it get as far as running the heater but the water fill and drum rotate were working fine.

 

In answer to whoever asked if the inverter is earthed the answer is 'Yes'.