Inverter powering a fridge?

[Darren]

Hi, I have sold a guy a 600w modified sine inverter, was tested before it
was sent away, he received it but he couldnt get it to work (he wants it for
his fridge), so he brought it back to me. I tested it and it didnt work so I
gave him a new one, I tested it infront of him with a 500w jigsaw, worked
fine. I got a call from him two hours later, he said he tested it on his
drill it workd fine then he put it on his 300w fridge but it didnt work so
he tried the drill again and that didnt work either. So now he has blown up
two inverters.
The inverter has a overload cut off so I dont see how the fridge could blow
up the inverters, anyone have any idea?

Thanks
Darren

 

[John Crighton]

On Sun, 2 May 2004 17:48:59 +1200, "Darren" <no@email.com> wrote:

Hi, I have sold a guy a 600w modified sine inverter, was tested before it
was sent away, he received it but he couldnt get it to work (he wants it for
his fridge), so he brought it back to me. I tested it and it didnt work so I
gave him a new one, I tested it infront of him with a 500w jigsaw, worked
fine. I got a call from him two hours later, he said he tested it on his
drill it workd fine then he put it on his 300w fridge but it didnt work so
he tried the drill again and that didnt work either. So now he has blown up
two inverters.
The inverter has a overload cut off so I dont see how the fridge could blow
up the inverters, anyone have any idea?

Thanks
Darren


Hello Darren,

high start up current maybe. Just guessing.
Regards,
John Crighton

 

[KLR]

On Sun, 2 May 2004 17:48:59 +1200, "Darren" <no@email.com> wrote:

Hi, I have sold a guy a 600w modified sine inverter, was tested before it
was sent away, he received it but he couldnt get it to work (he wants it for
his fridge), so he brought it back to me. I tested it and it didnt work so I
gave him a new one, I tested it infront of him with a 500w jigsaw, worked
fine. I got a call from him two hours later, he said he tested it on his
drill it workd fine then he put it on his 300w fridge but it didnt work so
he tried the drill again and that didnt work either. So now he has blown up
two inverters.
The inverter has a overload cut off so I dont see how the fridge could blow
up the inverters, anyone have any idea?

Thanks
Darren

the massive startup current of the compressor (especially if its

piston was sitting just before TDC when it last stopped) - the
inverter probably isnt able to handle it and is being destroyed by the
massive overload. being not a sine wave system wouldnt be helping
matters too I would imagine.

This is a major problem as the fridge will start and stop many times
over a day and this problem will reoccur.

same with air conditioning units too
turn one off then on without waiting a couple of minutes and you will
get a blown fuse or safety cutout internally will activate.

for something like this - he probably needs a much larger sine wave
inverter, however a better option would be for him to use a petrol /
diesel driven alternator as a power source - or buy a LP gas powered
fridge

 

[atec]

starting current is 6 to 8 x the required indicator . needs at least 2.4
kw ,

Darren wrote:

Hi, I have sold a guy a 600w modified sine inverter, was tested before it
was sent away, he received it but he couldnt get it to work (he wants it for
his fridge), so he brought it back to me. I tested it and it didnt work so I
gave him a new one, I tested it infront of him with a 500w jigsaw, worked
fine. I got a call from him two hours later, he said he tested it on his
drill it workd fine then he put it on his 300w fridge but it didnt work so
he tried the drill again and that didnt work either. So now he has blown up
two inverters.
The inverter has a overload cut off so I dont see how the fridge could blow
up the inverters, anyone have any idea?

Thanks
Darren

 

[Darren]

Hi,

What about the inverter having a overload cut out, shouldnt that have stoped
the inverter from blowing up?

Darren

"atec" <"atec77(notspam)"@hotmail.com> wrote in message
news:40949817.CDCF366A@hotmail.com...

starting current is 6 to 8 x the required indicator . needs at least 2.4
kw ,

Darren wrote:

Hi, I have sold a guy a 600w modified sine inverter, was tested before
it
was sent away, he received it but he couldnt get it to work (he wants it
for
his fridge), so he brought it back to me. I tested it and it didnt work
so I
gave him a new one, I tested it infront of him with a 500w jigsaw,
worked
fine. I got a call from him two hours later, he said he tested it on his
drill it workd fine then he put it on his 300w fridge but it didnt work
so
he tried the drill again and that didnt work either. So now he has blown
up
two inverters.
The inverter has a overload cut off so I dont see how the fridge could
blow
up the inverters, anyone have any idea?

Thanks
Darren

 

[atec]

it should but its a very big spike , perhaps the switching device fails
with such a sudden surge , Im sure some one will be more conversant than
I , either way be assured the unit he is trying to use wont cut it.

Darren wrote:

Hi,

What about the inverter having a overload cut out, shouldnt that have stoped
the inverter from blowing up?

Darren

"atec" <"atec77(notspam)"@hotmail.com> wrote in message
news:40949817.CDCF366A@hotmail.com...
starting current is 6 to 8 x the required indicator . needs at least 2.4
kw ,

Darren wrote:

Hi, I have sold a guy a 600w modified sine inverter, was tested before
it
was sent away, he received it but he couldnt get it to work (he wants it
for
his fridge), so he brought it back to me. I tested it and it didnt work
so I
gave him a new one, I tested it infront of him with a 500w jigsaw,
worked
fine. I got a call from him two hours later, he said he tested it on his
drill it workd fine then he put it on his 300w fridge but it didnt work
so
he tried the drill again and that didnt work either. So now he has blown
up
two inverters.
The inverter has a overload cut off so I dont see how the fridge could
blow
up the inverters, anyone have any idea?

Thanks
Darren

 

[budgie]

On Sun, 2 May 2004 18:49:05 +1200, "Darren" <no@email.com> wrote:

Hi,

What about the inverter having a overload cut out, shouldnt that have stoped
the inverter from blowing up?

Usually overload cutouts have time constants measured in tens of seconds even at
3xFLC. Your electronics can be nuked in milliseconds. Instead of an overload
cutout, it needs an instantaneous current limit on the INPUT side.

"atec" <"atec77(notspam)"@hotmail.com> wrote in message
news:40949817.CDCF366A@hotmail.com...
starting current is 6 to 8 x the required indicator . needs at least 2.4
kw ,

Darren wrote:

Hi, I have sold a guy a 600w modified sine inverter, was tested before
it
was sent away, he received it but he couldnt get it to work (he wants it
for
his fridge), so he brought it back to me. I tested it and it didnt work
so I
gave him a new one, I tested it infront of him with a 500w jigsaw,
worked
fine. I got a call from him two hours later, he said he tested it on his
drill it workd fine then he put it on his 300w fridge but it didnt work
so
he tried the drill again and that didnt work either. So now he has blown
up
two inverters.
The inverter has a overload cut off so I dont see how the fridge could
blow
up the inverters, anyone have any idea?

Thanks
Darren

 

[Dafydd]

You need an inverter of a minimum 2,0kw and preferably 2.5kw to start a
fridge of 300w. You can bank on seven times run current for start current.
If he is going to use this long term, he would be better off equipping the
fridge with a 12/24v BD35F or BD50F Danfoss compressor.

--


"Darren" <no@email.com> wrote in message
news:sZ%kc.971$8J.34810@news.xtra.co.nz...

Hi, I have sold a guy a 600w modified sine inverter, was tested before it
was sent away, he received it but he couldnt get it to work (he wants it
for
his fridge), so he brought it back to me. I tested it and it didnt work so
I
gave him a new one, I tested it infront of him with a 500w jigsaw, worked
fine. I got a call from him two hours later, he said he tested it on his
drill it workd fine then he put it on his 300w fridge but it didnt work so
he tried the drill again and that didnt work either. So now he has blown
up
two inverters.
The inverter has a overload cut off so I dont see how the fridge could
blow
up the inverters, anyone have any idea?

Thanks
Darren

 

[Ken Taylor]

"atec" <"atec77(notspam)"@hotmail.com> wrote in message
news:40949AD1.4A78BFCC@hotmail.com...

it should but its a very big spike , perhaps the switching device fails
with such a sudden surge , Im sure some one will be more conversant than
I , either way be assured the unit he is trying to use wont cut it.

Darren wrote:

Hi,

What about the inverter having a overload cut out, shouldnt that have
stoped
the inverter from blowing up?

Darren

The switcher is almost guaranteed to protect the breaker.

Ken

 

[Patrick Dunford]

Dafydd

You need an inverter of a minimum 2,0kw and preferably 2.5kw to start a
fridge of 300w. You can bank on seven times run current for start current.
If he is going to use this long term, he would be better off equipping the
fridge with a 12/24v BD35F or BD50F Danfoss compressor.

Add to that the modified sine wave is not really suitable for many
purposes. It is a stepped square wave. Because a significant part of the
waveform is straight DC they will give poor efficiency and voltage
regulation on any device that will not work on DC. Power transformers are
an obvious example, I think there are some AC motors that will not run on
DC either.

 

[Phil Allison]

"Patrick Dunford" <patrickdunford@nz.invalid>

Add to that the modified sine wave is not really suitable for many
purposes. It is a stepped square wave. Because a significant part of the
waveform is straight DC they will give poor efficiency and voltage
regulation on any device that will not work on DC. Power transformers are
an obvious example, I think there are some AC motors that will not run on
DC either.

** The modified sine wave or stepped square wave contains some odd
numbered harmonics of the 50 Hz fundamental frequency, but considerably less
than a simple square wave does.

In no way is there any DC component that would harm a motor or transformer.




........ Phil

 

[Dafydd]

Patrick fridge compressors are still relatively crude electric motors and
will run quite well from modified sine wave.
The newer energy efficient electric motors fitted to Samsung fridges will
not run at all from sine wave. Interestingly the fridges do absolutely
nothing (not even internal light) on a modified sine wave inverter. Put
them on a sine wave inverter and they run perfectly. Only universal motors
will run on AC/DC and they are far from the epitome of efficiency.

--


"Patrick Dunford" <patrickdunford@nz.invalid> wrote in message
news:MPG.1affa166b06535ed989ba1@news.paradise.net.nz...

Add to that the modified sine wave is not really suitable for many
purposes. It is a stepped square wave. Because a significant part of the
waveform is straight DC they will give poor efficiency and voltage
regulation on any device that will not work on DC. Power transformers are
an obvious example, I think there are some AC motors that will not run on
DC either.

 

[Patrick Dunford]

Phil Allison

"Patrick Dunford" <patrickdunford@nz.invalid

Add to that the modified sine wave is not really suitable for many
purposes. It is a stepped square wave. Because a significant part of the
waveform is straight DC they will give poor efficiency and voltage
regulation on any device that will not work on DC. Power transformers are
an obvious example, I think there are some AC motors that will not run on
DC either.



** The modified sine wave or stepped square wave contains some odd
numbered harmonics of the 50 Hz fundamental frequency, but considerably less
than a simple square wave does.

In no way is there any DC component that would harm a motor or transformer.

DC won't pass through a transformer, so for that part of the waveform, in
fact a considerable part (depends on the exact waveform of course) there
is no power in the transformer, which adds up to poor quality power out
the other end.

We had a keyboard amp, ran fine on the mains but run off one of these
inverters, the result was noticeable hum - only to be expected as the
filter caps in the power supply would not be big enough to work with the
much rougher input waveform.

 

[Phil Allison]

"Patrick Dunford" <patrickdunford@nz.invalid> wrote in message

** The modified sine wave or stepped square wave contains some odd
numbered harmonics of the 50 Hz fundamental frequency, but considerably
less
than a simple square wave does.

In no way is there any DC component that would harm a motor or
transformer.

DC won't pass through a transformer,

** There is no DC component - none - zilch.

so for that part of the waveform, in
fact a considerable part (depends on the exact waveform of course) there
is no power in the transformer, which adds up to poor quality power out
the other end.

** You are totally mistaken. Transformers just LOVE square waves - it
is the MOST efficient way possible to drive them.

We had a keyboard amp, ran fine on the mains but run off one of these
inverters, the result was noticeable hum - only to be expected as the
filter caps in the power supply would not be big enough to work with the
much rougher input waveform.

** The filter caps in a PSU have far LESS work to do when driven with a
square wave or stepped square wave.

Remember that a rectified square wave is pure DC - requiring NO
filtering.

Any hum in that keyboard amp would be due to the higher harmonics present
(ie buzz) or just possibly the lower peak voltage of the waveform affecting
the operation of voltage regulators inside the amp.





........... Phil

 

[Brian Goldsmith]

"Dafydd" wrote :-
The newer energy efficient electric motors fitted to Samsung fridges
will
not run at all from sine wave.


****** What is this nonsense?????????

Brian Goldsmith

 

[Andy]

"Darren" <no@email.com> wrote in message news:<sZ%kc.971$8J.34810@news.xtra.co.nz>...

Hi, I have sold a guy a 600w modified sine inverter, was tested before it
was sent away, he received it but he couldnt get it to work (he wants it for
his fridge), so he brought it back to me. I tested it and it didnt work so I
gave him a new one, I tested it infront of him with a 500w jigsaw, worked
fine. I got a call from him two hours later, he said he tested it on his
drill it workd fine then he put it on his 300w fridge but it didnt work so
he tried the drill again and that didnt work either. So now he has blown up
two inverters.
The inverter has a overload cut off so I dont see how the fridge could blow
up the inverters, anyone have any idea?

Thanks
Darren

Hello Darren,

There are a few *very* big "gotchas" when using inverters. My comments
assume we are talking about the low end products made in China, Taiwan
etc. I'll try and list as many as I can in no particular order:

1. The inverter *must* be switched on before the load is switched on -
this is very, very important. The power supply for the output control
circuitry (and hence the overload circuitry) is derived after the hf
switching transformers - i.e. the primary side must be up and running
before any voltages can appear on the secondary power supplies and
then there is a finite "settling" time on these supplies - a definite
amount of time is needed after switch on for everything to settle and
the o/load circuitry to become active. If a load is present during
this "settling" time there is no guarantee that any secondary
protection circuits can do their job.
2. The inverter power supply (usually a battery bank) must have enough
capacity and enough charge to meet the load requirements - the same
can be said for the cabling and connectors. I did some testing for a
company that was having similar problems to yours and the results were
very interesting. Let's consider the following extreme (but
common)example: A 1500watt inverter is connected to a standard size
(say 50Ah) car battery. A quick calculation (negating losses) will see
the inverter drawing more than 125amps when fully loaded. The poor
little car battery is not going to take this for too long!!. What
happens next???. The battery voltage is spiralling down until finally
the inverters undervoltage cutout activates and switches the inverter
off (usually around approx 10.5v) - great!! the u/voltage cutout has
done it's job - but now what happens???. Because the load has now been
removed from the battery, its voltage will "recover" back to probably
around 12 volts and the inverter WILL SWITCH ITSELF BACK ON STRAIGHT
INTO THE LOAD (as per No.1 above). This will then drag the battery
back below the u/voltage cutout and the cycle will repeat itself
resulting in one destroyed inverter relatively quickly!! Also consider
this - this battery has copped quite a flogging by now and is
discharged. The inverter output fets fail short circuit because of the
repeated switching on into a heavy load due to the low battery voltage
and recovery cycle. There is 8x30amp fuses in an inverter this size so
we need to draw in excess of 240amps - this aint going to happen
because our undersized battery is on its last legs so what happens
now???. The primary side fets are still switching and doing there job
straight into a short circuit but the fuses can't blow because the
battery can't supply enough current - these primary fets get red hot
and pop one by one in rapid succession causing a real bad smell and
usually cooking the pcb substrate in the process.
3. Inverters should always be rated in VA and not watts in my opinion.
The power factor of an appliance (unless purely resistive)is always
different on a modified sinewave because this type of waveform has
heaps of harmonics. The long and short of it is this - a 600w
appliance may be draw much more current than a 600w resistive load
when connected to a modified sinewave inverter (fluoro lights are a
good example of this because of the power factor correction cap.)

Here it is in point form:
- Always switch on the inverter before switching on the load
- Make sure the battery supply and associated cabling etc is up to the
task
- Don't assume "watts is watts" - think VA and power factor

Change "agw" to "andy" if you wish to send me email


Andy

 

[Rheilly Phoull]

"Brian Goldsmith" <brian.goldsmith@nospamecho1.com.au> wrote in message
news:GK5lc.8350$TT.5359@news-server.bigpond.net.au...

"Dafydd" wrote :-
The newer energy efficient electric motors fitted to Samsung fridges
will
not run at all from sine wave.


****** What is this nonsense?????????

Brian Goldsmith


I think we got us a 'snakeoil' salesman here ??

--
Regards ........... Rheilly Phoull

 

[Bob M]

The start-up current is most likely what did your inverters in. The
induction motor of a fridge requires a large current surge to start
the unit. Additionally, when the unit shuts off, a 2 to 5 minute
period is required for the pressure difference between the high side
(output) and the low side (input) of the compressor to dissipate.
Until this pressure dissipates, the motor does not have enough torque
to start against the load of the compressor. That is why there is an
internal thermal protection circuit in fridges.

I have a 700 watt unit that I use for various things up at the
cottage. The input is protected by 3 fuses in parallel, soldered
directly on the PCB in the unit. You might take a quick look for
something similar in your units.

It has been my experience with these units that they can only handle a
momentary current surge of 20% to 40% of their rated output. An
induction motor would typically draw 3 to 7 times (i.e. 300% to 700%)
its running current on start-up, depending on the application and
mechanical start-up load. That is why you can see lights momentarily
dim when these motors start in your house.

Generally speaking, it is not a good idea to attempt to drive any
induction motor greater than 1/10 of a horse power with these
inverters. They simply aren't built to handle the starting
requirements.

Cheers from Canada!

Bob Morgoch

atec <"atec77(notspam)"@hotmail.com> wrote in message news:<40949AD1.4A78BFCC@hotmail.com>...

it should but its a very big spike , perhaps the switching device fails
with such a sudden surge , Im sure some one will be more conversant than
I , either way be assured the unit he is trying to use wont cut it.

Darren wrote:

Hi,

What about the inverter having a overload cut out, shouldnt that have stoped
the inverter from blowing up?

Darren

"atec" <"atec77(notspam)"@hotmail.com> wrote in message
news:40949817.CDCF366A@hotmail.com...
starting current is 6 to 8 x the required indicator . needs at least 2.4
kw ,

Darren wrote:

Hi, I have sold a guy a 600w modified sine inverter, was tested before
it
was sent away, he received it but he couldnt get it to work (he wants it
for
his fridge), so he brought it back to me. I tested it and it didnt work
so I
gave him a new one, I tested it infront of him with a 500w jigsaw,
worked
fine. I got a call from him two hours later, he said he tested it on his
drill it workd fine then he put it on his 300w fridge but it didnt work
so
he tried the drill again and that didnt work either. So now he has blown
up
two inverters.
The inverter has a overload cut off so I dont see how the fridge could
blow
up the inverters, anyone have any idea?

Thanks
Darren

 

[The Real Andy]

On Sun, 2 May 2004 23:34:36 +1200, Patrick Dunford
<patrickdunford@nz.invalid> wrote:

<snip>

DC won't pass through a transformer, so for that part of the waveform, in
fact a considerable part (depends on the exact waveform of course) there
is no power in the transformer, which adds up to poor quality power out
the other end.

We had a keyboard amp, ran fine on the mains but run off one of these
inverters, the result was noticeable hum - only to be expected as the
filter caps in the power supply would not be big enough to work with the
much rougher input waveform.

Do you have any idea about what you are saying?

 

[Patrick Dunford]

Phil Allison

"Patrick Dunford" <patrickdunford@nz.invalid> wrote in message


** The modified sine wave or stepped square wave contains some odd
numbered harmonics of the 50 Hz fundamental frequency, but considerably
less
than a simple square wave does.

In no way is there any DC component that would harm a motor or
transformer.

DC won't pass through a transformer,


** There is no DC component - none - zilch.

A square wave is horizontal for a good percentage (in fact most) of its
cycle. A modified sine wave is actually multiple square waves, looks like
a stairway if you get my meaning - instead of going up all in one go it
goes a little bit up, a little bit across, and so on until it starts
going down the other side.