Modifying a Power Inverter
N/A
I saw a 12VDC/120VAC 600 watts Power Inverter at one of the
local Walmart stores. I am wondering if it is possible and
sufficient to modify such an inverter to produce a 240VAC by
replacing the transformer with a 12V to 240V turn ratio
transformer. Also, what would I need to modify if I want the
12VDC/120VAC power inverter to double its wattage from a 600
watts to a whopping 1200 watts? If all else fail on the above,
can anyone suggest/provide some schematic diagram of a Power
Inverter of 12VDC/240VAC, 1200 Watts, 50/60Hz?
TIA.
John Beardmore
N/A <n...@vailable.int> writes
>Hi,
>
>I saw a 12VDC/120VAC 600 watts Power Inverter at one of the
>local Walmart stores. I am wondering if it is possible and
>sufficient to modify such an inverter to produce a 240VAC by
>replacing the transformer with a 12V to 240V turn ratio
>transformer.
It might be possible, but you can't use any old transformer and you'd
almost certainly need to modify at least one or two other bits of the
circuit.
> Also, what would I need to modify if I want the
>12VDC/120VAC power inverter to double its wattage from a 600
>watts to a whopping 1200 watts?
All of the power transistors and all of the inductors and maybe a few of
the other bits. In short, most of it !
Cheers, J/.
--
John Beardmore
Keith Buck
holland. They use them for the boat industry. A type called the "Blue Box"
may be of interest
Keith buck
"John Beardmore" <woo...@wookie.demon.co.uk> wrote in message
news:Cc0oPNLM...@wookie.demon.co.uk...
Bored With the Boring Again
You won't get 1200 watts out of this, but if you need 240 volts at 600
watts, why not a stepup transformer?
Oh, and BTW, you cannot either parallel or series these units because
they share a common ground with the 12 volt supplies and there are
minor differences in thier operating fequencies that would preclude
this even if they -were- solated from ground.
If you -really- need 1200 watts at 240 volts, either consider
importing an invertor from Europe (where they are commonplace) of
getting a small gas-engine driven generator.
Erikc (alt.atheist #002) | "An Fhirinne in aghaidh an tSaoil."
BAAWA Knight | "The Truth against the World."
| -- Bardic Motto
Awarded title of "Defacto CLuM" by "kansan" 2001-05-12
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Gary Lecomte
The transformer usually isn't 12 to 120, its usually 10-0-10 to 120.
They are usually wound with the low voltage close to the core, unlike
step down transformers that have the 120 winding close to the core.
Doubling the output voltage would require a very large transformer and
a fefinate upgrade in the output switching transistors, Mosfets or
SCR's.
Besides, your input current really becomes EXCESSIVE!
BUT it is possible if your good at electronics and can wind your own
transformer!
Gary
John Beardmore
Lecomte <ou...@telus.net> writes
>Doubling the output voltage would require a very large transformer and
>a fefinate upgrade in the output switching transistors, Mosfets or
>SCR's.
>
>Besides, your input current really becomes EXCESSIVE!
If the VA of the secondary is the same, why ?
Bob Wilson
n...@vailable.int says...
ABSOLUTELY NOT! This is basically ridiculous.
I worked for some years at one of the largest consumer inverter
manufacturers designing these things. If memory serves, we are the ones
who made the 600 W inverters that Walmart sells, and I was one of the design
team.
Like most inverters, this uses a high frequency DC-DC converter stage (to
increase the 12V input to around 165 V DC), then a DC-AC stage to convert
the DC to 115V "quasi-squarewave" AC.
The following problems exist with your scheme:
- The transformer is an active part of the DC-DC section and any attempt to
rewind it will destroy the operation of the circuit. DC-DC converter
transformers are **NOT** like 60Hz transformers. Besides, you'd never get it
apart, anyway. It is vacuum impregnated with varnish and you'd break the
ferrite core to pieces if you tried.
- All the capacitors on the output side of the DC-DC section, as well as the
*entire* DC-AC section would blow up due to their voltage ratings being
grossly exceeded.
As for getting double the power out of it, it should be patently obvious
that it will now generate twice the heat. The typical efficiency of this
unit is around 88%. This means that the normal 80 Watts of heat it generates
will double to 160 Watts. The thing would overheat in very short order.
However, your scheme could never work, so this is a moot point.
Bob.
Bob Wilson
<066515D5B68FE377.4591D567...@lp.airnews.net>,
fire...@airmail.net says...
>You won't get 1200 watts out of this, but if you need 240 volts at 600
>watts, why not a stepup transformer?
That makes more sense.
>Oh, and BTW, you cannot either parallel or series these units because
>they share a common ground with the 12 volt supplies and there are
>minor differences in thier operating fequencies that would preclude
>this even if they -were- solated from ground.
>
>If you -really- need 1200 watts at 240 volts, either consider
>importing an invertor from Europe (where they are commonplace) of
>getting a small gas-engine driven generator.
Not entirely true. The el-cheapo bottom of the line types that the Big Box
stores sell (like this inverter), do have a common input-output ground.
However there are inverters that are UL/CSA approved (such as those made my
former employer, who likely also made the one in question here), that not
only ARE approved, but produce a proper sinewave output and have
primary-secondary isolation. We sold these types all over the world, but the
ones like the OP has could ONLY be sold in the US, where regulatory approval
of such devices is not mandatory.
The inverter in question here is designed to be as cheap as possible, as a
result of Walmart's "grinding" of suppliers to the lowest possible price. It
was our experience that Walmart (and other similar stores we marketed our
low-end inverter line to) couldn't care at all if it worked well. That
seemed utterly irrelevant to their buyers. All they wanted was a dirt cheap
price.
Bob.
Bob Wilson
says...
>The transformer usually isn't 12 to 120, its usually 10-0-10 to 120.
>They are usually wound with the low voltage close to the core, unlike
>step down transformers that have the 120 winding close to the core.
>Doubling the output voltage would require a very large transformer and
>a fefinate upgrade in the output switching transistors, Mosfets or
>SCR's.
>
>Besides, your input current really becomes EXCESSIVE!
>
>BUT it is possible if your good at electronics and can wind your own
>transformer!
You need to understand DC-DC converters better. The transformer is not a
10-0-10 to 120V transformer. It is a custom designed high frequency ferrite
core type that is part of a high frequency push-pull converter. The DC-DC
converter in total (not just the transformer) is designed for a nominal
13.2V DC input, and a 165V DC output. The 165V is the peak voltage of the
quasi-squarewave AC output of the inverter.
Your comment that if one is good at electronics, one can wind one's own
transformer, is ridiculous! You fail to understand that the transformer is
*not* a stand-alone part. IT is an active component in the entire DC-DC
converter system. Attempting to rewind it will likely destroy the converter
section stability, requiring changes to the feedback compensation network.
There are also no SCRs in a high frequency DC-DC converter such as this
inverter uses.
Bob.
John Beardmore
<rfwi...@intergate.nospam.bc.ca> writes
>You need to understand DC-DC converters better. The transformer is not a
>10-0-10 to 120V transformer. It is a custom designed high frequency ferrite
>core type
Not always. Depends on the age of the system. You're certainly right
for most modern designs though.
>There are also no SCRs in a high frequency DC-DC converter such as this
>inverter uses.
Before the days of power transistors SCR designs switching into a 50Hz
transformer were the way to go, so it's not surprising there's a
generation who see this technology as 'innovation with semiconductors',
even though these units must be 15 times bigger and 30 times heavier
than modern FET based high frequency designs, and hugely less efficient
!
( I have a 600 VA SCR inverter with good clean sine output, but it has
an input quiescent current of 10A at 24V ! )
Mark Daniels
ergate.nospam.bc.ca> writes
>- The transformer is an active part of the DC-DC section and any attempt to
>rewind it will destroy the operation of the circuit. DC-DC converter
>transformers are **NOT** like 60Hz transformers. Besides, you'd never get it
>apart, anyway. It is vacuum impregnated with varnish and you'd break the
>ferrite core to pieces if you tried.
One word:- "Solvent"
>Bob.
>
--
Mark Daniels
John Beardmore
<j...@third-millennium.demon.co.uk> writes
So what solvent removes epoxy without dissolving the insulation on the
transformer winding ?
Indeed - what solvent dissolves epoxy at all ?
Bob Wilson
says...
>
>In message <u56vihc...@corp.supernews.com>, Bob Wilson
><rfwi...@intergate.nospam.bc.ca> writes
>>In article <9d4cbfcf.02012...@posting.google.com>,
ou...@telus.net
>>says...
>
>>You need to understand DC-DC converters better. The transformer is not a
>>10-0-10 to 120V transformer. It is a custom designed high frequency
ferrite
>>core type
>
>Not always. Depends on the age of the system. You're certainly right
>for most modern designs though.
I was referring to the *specific* 600W inverter that the OP talked about. If
he bought it at Walmart, as he says he did, then I know the unit well, and I
was on the design team that created it. The transformers it uses (and there
are 2 of them) are ferrite core types operating at moderately high
frequency.
>>There are also no SCRs in a high frequency DC-DC converter such as this
>>inverter uses.
>
>Before the days of power transistors SCR designs switching into a 50Hz
>transformer were the way to go, so it's not surprising there's a
>generation who see this technology as 'innovation with semiconductors',
>even though these units must be 15 times bigger and 30 times heavier
>than modern FET based high frequency designs, and hugely less efficient
Yes, having been in the business for some years of designing high volume
consumer inverters, I more than aware of the various design topologies. Low
frequency DC-DC conversion stages in inverters whose output power is less
than around 1500 W, have not been used for years. The whole point of a
small inverter (such as the 600Watt unit in question) is that they should be
more portable than a boat anchor.
The only place where low frequency conversion is still used to some degree
is in high power levels where they are built into an electrical system. In
this case, no one really cares that they are extremely large and extremely
heavy, since the batteries needed to supply them are far larger still.
Bob.
Bob Wilson
j...@third-millennium.demon.co.uk says...
You obviously have never tried dissolving this type of varnish. It is baked
at about 100C by the manufacturer (who, in this case, I can name if you
want!), which completes the polymerization process. No solvent will dissolve
it. But that shouldn't come as a surprise since no solvent will dissolve ANY
enamel-type varnish or paint, since it crosslinks during the "drying"
process and thus becomes insoluable. Some really agressive solvents like
methylene chloride may cause the varnish to swell, but they will not
dissolve it.
I should say that I speak from a lot of experience. As I mentioned on other
posts, I worked for the largest North American consumer inverter company for
some years. One of the things we did was to reverse engineer our
competitor's products just to see if they came up with anything interesting.
Part of that was to reverse engineer the transformers to look at things like
turns ratios and so on. As it turned out, I was the only guy there that
could (usually) take (most) transformers apart without breaking the cores.
It too a long time to get the knack of it. The secret is to heat them up
with a heat gun, which softens (somewhat) the varnish. Then you slowly and
carefully try to pull the cores apart, being careful not to apply so much
force as to break the cores. It takes great care, and a LOT of heat, and it
tends to go very slowly at first since the varnish is inside, where it fills
all the cracks between core and bobbin (and where NO solvent would ever get
into!).
Bob.
Da Man
the enamel coating.
"John Beardmore" <woo...@wookie.demon.co.uk> wrote in message
news:PqqLiOUw...@wookie.demon.co.uk...
John Beardmore
<rfwi...@intergate.nospam.bc.ca> writes
>Yes, having been in the business for some years of designing high volume
>consumer inverters, I more than aware of the various design topologies. Low
>frequency DC-DC conversion stages in inverters whose output power is less
>than around 1500 W, have not been used for years. The whole point of a
>small inverter (such as the 600Watt unit in question) is that they should be
>more portable than a boat anchor.
:) Our 600 VA boat anchor at least has a relatively low noise output.
Mixing desks and other stage audio kit don't seem to like non sine power
supplies.
>The only place where low frequency conversion is still used to some degree
>is in high power levels where they are built into an electrical system. In
>this case, no one really cares that they are extremely large and extremely
>heavy, since the batteries needed to supply them are far larger still.
Yes - I've got a 7 kVA inverter with a 50 Hz transformer but it's a
total brute. One person can just about lift an end. It's on wheels,
but there's no way it can be described as portable ! Needs a fork lift
once you are off flat floors.
Da Man
torch. I rarely break them.
What is fun is dismantling potted circuit boards. Can you say small hammer
and fine tipped screwdriver used as a chisle.
"Bob Wilson" <rfwi...@intergate.nospam.bc.ca> wrote in message
news:u591jv7...@corp.supernews.com...
Mark Daniels
<woo...@wookie.demon.co.uk> writes
>In message <7xbxrKAW...@third-millennium.demon.co.uk>, Mark Daniels
><j...@third-millennium.demon.co.uk> writes
>>In article <u56udjd...@corp.supernews.com>, Bob Wilson <rfwilson@int
>>ergate.nospam.bc.ca> writes
>>>- The transformer is an active part of the DC-DC section and any attempt to
>>>rewind it will destroy the operation of the circuit. DC-DC converter
>>>transformers are **NOT** like 60Hz transformers. Besides, you'd never get it
>>>apart, anyway. It is vacuum impregnated with varnish and you'd break the
>>>ferrite core to pieces if you tried.
>>
>>One word:- "Solvent"
>
>So what solvent removes epoxy without dissolving the insulation on the
>transformer winding ?
Who cares? When I am stripping a transformer, I don't care about the
insulation on the wire because all of the wire is coming off and getting
binned anyway. The only reason I normally have to strip a transformer is
to copy it, or occasionally to rewind it. The ferrite cores will survive
the solvent as they are sintered metals and metal oxides anyway.
>
>Indeed - what solvent dissolves epoxy at all ?
Who's talking about epoxy? Besides, epoxy will dissolve in the right
solvent at the right temperature. I haven't had to try it, but I would
boil it in a strong solvent for several hours.
>
>
>Cheers, J/.
--
Mark Daniels
Mark Daniels
ergate.nospam.bc.ca> writes
>In article <7xbxrKAW...@third-millennium.demon.co.uk>,
>j...@third-millennium.demon.co.uk says...
>>
>>In article <u56udjd...@corp.supernews.com>, Bob Wilson <rfwilson@int
>>ergate.nospam.bc.ca> writes
>>>- The transformer is an active part of the DC-DC section and any attempt
>to
>>>rewind it will destroy the operation of the circuit. DC-DC converter
>>>transformers are **NOT** like 60Hz transformers. Besides, you'd never get
>it
>>>apart, anyway. It is vacuum impregnated with varnish and you'd break the
>>>ferrite core to pieces if you tried.
>>
>>One word:- "Solvent"
>
>You obviously have never tried dissolving this type of varnish.
Is that right?
>It is baked
>at about 100C by the manufacturer (who, in this case, I can name if you
>want!), which completes the polymerization process. No solvent will dissolve
>it.
We remove this type of "varnish" by boiling the complete transformer in
neat acetone. It takes about two hours for the thing to fall apart.
>But that shouldn't come as a surprise since no solvent will dissolve ANY
>enamel-type varnish or paint, since it crosslinks during the "drying"
>process and thus becomes insoluable. Some really agressive solvents like
>methylene chloride may cause the varnish to swell, but they will not
>dissolve it.
Maybe it does not dissolve, but it certainly softens and falls off the
component quite readily, thus rendering the transformer strippable.
>
>I should say that I speak from a lot of experience.
I'm very pleased for you. Maybe you need a bit more experience in
stripping the things, though.
> As I mentioned on other
>posts, I worked for the largest North American consumer inverter company for
>some years.
Once again, I am very pleased for you.
>One of the things we did was to reverse engineer our
>competitor's products just to see if they came up with anything interesting.
>Part of that was to reverse engineer the transformers to look at things like
>turns ratios and so on. As it turned out, I was the only guy there that
>could (usually) take (most) transformers apart without breaking the cores.
Aren't you the smart one? Most engineers (and trainees) in the magnetics
industry can manage this.
>It too a long time to get the knack of it.
Well, you must be a bit slow, then.
>The secret is to heat them up
>with a heat gun, which softens (somewhat) the varnish. Then you slowly and
>carefully try to pull the cores apart, being careful not to apply so much
>force as to break the cores.
You would do better cooking the thing in your curing oven.
> It takes great care, and a LOT of heat, and it
>tends to go very slowly at first since the varnish is inside, where it fills
>all the cracks between core and bobbin (and where NO solvent would ever get
>into!).
Well, our solvents must be better than the American equivalents then.
>
>Bob.
>
--
Mark Daniels
Spehro Pefhany
> However there are inverters that are UL/CSA approved (such as those made my
> former employer
S... in Burnaby?
Best regards,
--
Spehro Pefhany --"it's the network..." "The Journey is the reward"
sp...@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com