I got one of these Statpowers last fall.  Even though it has
'1000' written in
nice bold letters all over the box,  is only rated for 600
w. continuous.  You
may need to do some power mgmt. with the bread machine on.

Mike Tellup
IV Roman - 34 Mainship II
Havre de Grace, MD

----- Original Message -----
From: Jim Baumgart baumgart@starrstuff.com
To: <trawler-world-list@samurai.com

Hooking the two

additional AC inverter

also run that off

night swinging on the

I wrote:
----- Original Message -----

I was in error.  The Statpower I have is rated for 800w continuous,
1000 w for 5 min. and 2000w surge.

Thanks to Arlid for a private email pointing out I might have misread
the specs.

Mike Tellup
IV Roman - 34 Mainship II
Havre de Grace, MD

At 06:41 PM 03/04/2000 -0800, Mike Tellup wrote:

Arild adds

I would like to clarify  the distinction between  maximum and continuous
rating numbers.
This information  is  essentially  applicable to every brand of inverter.
There are three ratings you need to  be aware of.
Surge
Maximum &
Continuous

The surge rating is the power output which can be sustained  for only a few
seconds before overheating occurs.

The maximum rating is a short term  value  at which the inverter can
operate while cold or at room temperature.
The maximum output is  determined by the design and current handling
capacity of the  semiconductors.

At this power level  some heat is generated which is dissipated by the
cooling  fins. However the heat build up is greater than the  heat
dissipation and eventually the  circuitry cannot sustain  that power level
any longer as the heat sink gets hotter.
A well dsigned unit will scale back the  maximum possible  wattage in
direct proportion to this heat,  until finally  it shuts off entirely.
This is called thermal shut down.

The continuous rating is the maximum  power output which  can be sustained
while  matching the heat dissipation  with the heat generation.  In other
words the  unit only gets so hot and then stays there.  At this power
level the  heat sink can  keep the internal temperatures stable and within
the operating limits of the semiconductor devices.

When assessing which inverter  you need for a particular application  you
need to be aware of the starting surge of the appliance.
This value will be  from  three  to  seven times the running current level.
Check the  manufacturers spec sheet for details.

For short term high power output  such as for a coffe maker, microwave oven
and  intermittent use appliance you  then look at the  maximum rating.
The total load of all devices drawing power from the  inverter cannot
exceed this  amount and it can not be sustained for more than a short
while, say an hour or so.

Continuous rating is  just that.  It is on all the time.
Assuming  that the start surge is not excessive or that the  various loads
are started  one after the other you cannot exceed  the  continuous
rating; or the  inverter will go into  thermal shut down.

This si why  it is so important to locate the  inverter in a cool
compartment away from  the heat of the engines.  You derate the inverter
as the ambient temperature goes up.

A typical  application would be a lighting load or heater running all the
time.
A water tank heater will not run continuously.  It cycles on and off. So
does a refrigerator.  The duty cycle is the ratio of on time versu off time.

A fridge which runs at the 500 watt level and  surges to a 1500 watt level
while starting needs a 1000 watt inverter, not a 500 watt inverter.
Another fridge which runs at  600 - 800 watts and surges to  2500 watts
starting  will not start on a 1000 watt inverter, but it would keep
running  if you  could transfer the load after it was started.

Someone mentioned a TV that  would not start on a 140 watt inverter but
would run if it was first  started on shore power.
The cold start surge  is what  kills the  140 watt inverter.  However once
started and hot then  you can run the  90 watt TV on the 140 watt inverter.

Every brand of inverter has  different performance specs.  It is important
that you do a complete energy budget before you  go and buy an inverter.
Then you can make  an intelligent comparison to determine which  model
best fits your needs and pocket book.

Hope this helps

Arild

Arild Jensen wrote:

Useful load information. However, one nitpick. The duty cycle is the "on" time
divided by total time in use, not "off" time. Thanks for the info otherwise.

           Regards --- Don Dement

on Merrymar -- DeFever 48 Trawler in Annapolis

Arild -

Thank you for a very nice, clear description of the various rating numbers
for inverters. I am in the process of purchasing an inverter for use on our
small cruiser (our trawler is still a couple of years away) and I will use
your information.

Jeff

<<snip>>

<<snip>>

Jeff Kenyon
m/v Paleo Boat
25' Trojan
Algoma, WI
(Retiring in less than four years and looking for a trawler)