[EMAIL PROTECTED] wrote:
I'm not an engineer like some of you, but I run my computer on a
square wave inverter (as in cheap) and have no problems. I perceive
that as long as the battery is in the computer it absorbs (filters)
whatever comes in and cleans it up enough for the computer to handle
it okay. This may not be great for the long term, but I've had no
problems.
REPLY
There are many aspects to this issue. Unfortunately most people seem to
focus only on the cost aspect.
Arguments have been made against using inverters saying is inefficient.
Arguments have also been made against power bricks andso on.
The fact of the matter is these are all versions of the same
technology and are used multiple times inside the computer itself. BUT
other real world issues are also present.
Ham radio and short wave reception is very prone to interference. and
cheap MSW or worse squarewave converters are known sources of
radiated interference. In the US part 15 of the FCC regulations
used to be taken as a guide that the product was approved and it was
implied it was adequate. Not so! Part 15 simply states that if the
device is found to emit
RF interference it must be shut down. In Europe the subject of
interference was taken a step further.. CE certified products had to
be measured and tested to prove they did not cause interference. It was
a big improvement but may not be sufficient for ham radio. Back when I
worked for Xantrex and the new European CE specifications were
announced, it was decided to withdraw the products from the European
market because the cost of compliance was not warranted given the
sales volume at that time.
At that ime I conducted a test using a ham operator who I think was a
member of this list at that time.
We provided two inverters one a 1kW sine wave and the other a 1kW
MSW inverter. Lab quality spectrum analyzers were used to measure the
extent and nature of the emitted interference and subjective tests
were also made as to how it affected reception in the normal ham bands.
It was obvious that th e pure sine wave inverter was far superior.
It had much less radiated and conducted noise emissions. It was possible
to carry on normal ham radio operations. This suppression of RF
interference was due to the nature of the design required to make a
pure sine wave inverter. This is not an advertisement for Xantrex.
The argument is equally valid for all makes of sine wave inverters as
far as I know. CE certified products are definitely better than non
CE certified products in that respect.
DC-DC converters are in effect also inverters with an added
rectification step included on the output. This is how you get the DC
from AC. So you cannot argue that a DC -DC converter is inherently
more efficient than an inverter..
You can rectify a rough MSW output to give you rippled DC but it
will still emit RF interference.
you have to look at individual brands and models to determine anything.
Cigarette plugs for 12V. These are probably among the least efficient
power sockets available anywherre. Their sole saving grace is
convenience. Automotive DC sockets are made from plated steel.
Marinco offers a stainless steel model. While it is true that SS
metal does not corrode like plated steel does, it is equally true that
SS has much higher resistance than copper or even brass. I refer you to
Nigel Calders book for more details on this aspect.
Automotive sockets are designed to carry 8 amps per SAE spec. Marinco
DC power sockets are rated for 15A. A 100 watt inverter draws 10
amps at 12V and a 200 watt inverter draws 20 amps.
In other words even a modest 200 watt inverter will draw in excess of
what the hardware connectors are rated for. Someone made the excellent
suggestion of hard wiring the small portable inverters using #10 Ga
wire. Absolutely correct!!
Someone else suggested that using the existing large inverter on board
is a waste due to inefficiencies. Also correct! Every inverter has a
minimum idling current needed just to keep th esystem running.
Maximum efficiency of any inverter is reached when it is delivering 80 -
90 % of its full continuous rated output. If you are concerned with
reducing battery drain, then smaller dedicated inverters for various
equipment is a batter choice than on ebig unit to drive everything. Of
course in some cass you have no choice but to run the big inverter. But
not for ham operation unless you are runnign a 1kW linear on the
output and you have a whole shack full of equipment besides. This is
where a modest 500 Wat pure sine wave inverter makes sense. And there
are now half a dozen brands available.
Laptop power bricks. Yes it is true that the newer universal voltage
units can and do burn up when powered from MSW inverters. They do fine
on sine wave power from inverters. It has to do with the method of
detecting which voltage is coming from the power source.
Computer power supplies are themselves a kind of inverter/converter.
Every such power supply has a minimum voltage threshold below which
it cannot function. BUT long before it reaches that low threshold it
pulls much more current from the source to deliver the same output
power. It is this increased current draw that creates internal
heat. This is the real reason why laptops went to higher voltages
early on.
Goin gto a 18V supply reduces internal losses, reduced heat from
current and in most cases allowed a bigger margin before the power
supply gave out. Trying to power the laptop directly from ships DC
power is a big step backwards.
regards
Arild
the inverter guy
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