I'm trying to learn about inverters, and how to put a
system together. I want to use it pretty much just
for my refrigerator (about 800W), and my TV/VCR
etc. It seems like it would be cheaper to get two
less powerful inverters, than one powerful one.
So far getting two of the 1200W for $120 each at:

http://store.worldstart.com/customer...=16468&cat=307

seems like the best deal for me. That would leave
me plenty of head room--especially on the TV
circuit--for including other things. Does anyone
know of a better deal?

How do I figure what size batteries to use? Should
I keep the batteries separate for each inverter, or
is it better to connect two or more batteries and go
from there? If so, how to connect the batteries
together, and then how to go from there to the
inverters?

I'm lead to believe that any inverters I can afford
would produce a square wave instead of a sine
wave. How to know what influence that would
have on my TV's performance? The TV works
great using the Generac 4000W generator I'm
using now. Can I expect it to be different using
the inverter?

Thanks for any help!

wrote in :

I'm trying to learn about inverters, and how to put a
system together. I want to use it pretty much just
for my refrigerator (about 800W), and my TV/VCR
etc. It seems like it would be cheaper to get two
less powerful inverters, than one powerful one.
So far getting two of the 1200W for $120 each at:

Ahhh...one of my favorite subjects....

Powerful inverters are now dirt cheap to produce with great profit margins,
especially in marine stores where they command amazing prices.....but,
alas, read on.


http://store.worldstart.com/customer...=16468&cat=307

seems like the best deal for me. That would leave
me plenty of head room--especially on the TV
circuit--for including other things. Does anyone
know of a better deal?

Oh, no problem at all getting the OUTPUT POWER to run just about any 115VAC
product you can buy. POWERFUL INVERTERS are real cheap with the digital
switching technology of today.....but, alas, read on.


How do I figure what size batteries to use? Should
I keep the batteries separate for each inverter, or
is it better to connect two or more batteries and go
from there? If so, how to connect the batteries
together, and then how to go from there to the
inverters?

Oh, oh. The slick salesman in the yacht club shirt, tan yachtie shorts and
expensive deck shoes didn't talk to you about BATTERIES actually powering
it, did they? NOT.

Let's use your load specs and have a look.....

Power isn't produced by inverters...it's converted at a small cost of
efficiency...over 90% in today's technology. Let's look at 800 watts, you
example, at the top. Discount the fridge doesn't run 24/7 while we look.
How long it runs depends on how often you open the door and how hot it is
in the boat.

Volts X Amps = Watts, so Amps = Watts/Volts...whether it's at 115VAC or
12VDC. The important part is the 12V side. 800 watts divided by 12V =
over 66A, about what the boat's starter draws after the engine starts
cranking over. There's the problem.....How long can we crank a starter
before the battery goes dead? Days?...no. Hours?....no. Minutes?...we
getting warmer. Seconds?...ah, there it is. It's about ampere-hours, and
how batteries are rated.....

First, put starting batteries out of your mind. Starting batteries will
produce a LOT of current for a few SECONDS, then they are dead....as any
boater already knows...(c;

Let's look at some common deep cycle batteries made for this kind of
service. A common deep cycle battery, the size of a large car battery, is
rated at 130 AH (ampere-hours), usually at a 20 hour rate (we take 20 hours
to discharge it). In reality, if you drain the battery over 50% of that,
the battery will soon be useless, so you have 65AH of "power" available.
Geez, that battery will only produce 66 amps for ONE HOUR?!! Well, no, it
will only produce 66A for a lot LESS than one hour because we didn't
discharge it over a 20 hour period, giving the chemical reaction time to
eat away at the lead plates in an orderly fashion. No, as you can see,
this isn't going to work, no matter how we're wishing it.

We need 66A of 12V power for a couple of days, not an hour! 66A x 48 hours
= 3,168 ampere-hours! WOW! The biggest 6V golf cart battery, the big tall
one they want $179 for, is only 700AH and we need TWO of them in series to
get 12V! 3,168 AH is gonna take BANKS of these monsters to get 800 watts
for TWO days! That guy in the Sperry Docksiders never said anything about
this problem, eh?

Back in the days of the diesel submarine, the battery banks were made of 2
volt, lead-acid cells that were 6,280 AH capacity, which we could draw
3,168 AH out of without destroying them, easy! Each CELL was about 4'
wide, 7' high and 3' deep. We'll need 6 of them to get 12V. Where we
gonna put 'em? Can we FLOAT 'EM?!! Each cell weighed about a ton or
so....(sigh)

Oh, oh. Now we're gonna have to RECHARGE THEM!.....

Whatever battery bank you use, it must be RECHARGED, FREQUENTLY if it is to
survive for any length of time. Batteries are NOT instant-charging
capacitors. The chemical reaction takes LONGER to recharge one AH than it
did to discharge them. You're also limited by the size of your
ALTERNATOR's output capacity to produce amps....lots of amps. So, if
you're a power boater running the engine all day, this is no problem. The
engine's running, anyways. Ragbaggers take a dim view of running the
engine to recharge big battery banks. My captain is one of them. He
thinks a battery should recharge in 20 minutes....(c;

To put 3000 AH back INTO the battery banks, we're going to have to put in
MORE than 3000 AH because lead acid batteries are AWFUL inefficient places
to store electrons....slowly.


I'm lead to believe that any inverters I can afford
would produce a square wave instead of a sine
wave. How to know what influence that would
have on my TV's performance? The TV works
great using the Generac 4000W generator I'm
using now. Can I expect it to be different using
the inverter?


No longer true. You can buy a 4KW synthesized sinewave inverter for under
$1000, easy. I paid $109 for a 500W Tripplite. Sinewave inverter power is
CHEAP and EASY to build with our computer technology.

All we need now is a 5000 AH battery the size of a starting battery that
can produce 500 AMPS for 10 hours without being destroyed in the process.

It's why there are NO BATTERY POWERED CARS on your street charging in 2
hours from the plug in the garage. It's just not practical at this time
because of the battery power problem.....

The power stored in a 10 gallon diesel or gas tank to run the Generac would
be the size of your garage stored in lead-acid batteries and weigh 20
tons.....Genset is still the answer....

Larry

NOTHING is funnier than a boater with a new 4KW inverter carrying his
electric heater down the dock with a big smile on his face....(c;

Larry's discussion has some very good information. I have a couple of
questions:
1) Why are you running refrigeration through an inverter?
2) Why, with the choices available today, are you running a TV through
an inverter?

I have a (one) 1,000 watt inverter for my 110 volt stuff, and just about
the only thing I run is the microwave oven.

Marine refrigeration is either dual power (110/12) or cold plate (engine
driven), lcd tvs are 12 volt (4 amp draw)

If you are running 110 volt appliances you are not being very efficient.

Opinions, please.
Jim

wrote:

I'm trying to learn about inverters, and how to put a
system together. I want to use it pretty much just
for my refrigerator (about 800W), and my TV/VCR
etc. It seems like it would be cheaper to get two
less powerful inverters, than one powerful one.
So far getting two of the 1200W for $120 each at:

http://store.worldstart.com/customer...=16468&cat=307

seems like the best deal for me. That would leave
me plenty of head room--especially on the TV
circuit--for including other things. Does anyone
know of a better deal?

How do I figure what size batteries to use? Should
I keep the batteries separate for each inverter, or
is it better to connect two or more batteries and go
from there? If so, how to connect the batteries
together, and then how to go from there to the
inverters?

I'm lead to believe that any inverters I can afford
would produce a square wave instead of a sine
wave. How to know what influence that would
have on my TV's performance? The TV works
great using the Generac 4000W generator I'm
using now. Can I expect it to be different using
the inverter?

Thanks for any help!

because he's a power boater and don't know these things

On Mon, 05 Jul 2004 20:20:43 GMT, Jim wrote:

Larry's discussion has some very good information. I have a couple of
questions:
1) Why are you running refrigeration through an inverter?
2) Why, with the choices available today, are you running a TV through
an inverter?

I have a (one) 1,000 watt inverter for my 110 volt stuff, and just about
the only thing I run is the microwave oven.

Marine refrigeration is either dual power (110/12) or cold plate (engine
driven), lcd tvs are 12 volt (4 amp draw)

If you are running 110 volt appliances you are not being very efficient.

Opinions, please.
Jim

wrote:

I'm trying to learn about inverters, and how to put a
system together. I want to use it pretty much just
for my refrigerator (about 800W), and my TV/VCR
etc. It seems like it would be cheaper to get two
less powerful inverters, than one powerful one.
So far getting two of the 1200W for $120 each at:

http://store.worldstart.com/customer...=16468&cat=307

seems like the best deal for me. That would leave
me plenty of head room--especially on the TV
circuit--for including other things. Does anyone
know of a better deal?

How do I figure what size batteries to use? Should
I keep the batteries separate for each inverter, or
is it better to connect two or more batteries and go
from there? If so, how to connect the batteries
together, and then how to go from there to the
inverters?

I'm lead to believe that any inverters I can afford
would produce a square wave instead of a sine
wave. How to know what influence that would
have on my TV's performance? The TV works
great using the Generac 4000W generator I'm
using now. Can I expect it to be different using
the inverter?

Thanks for any help!

Jim wrote in message link.net...
Larry's discussion has some very good information. I have a couple of
questions:
1) Why are you running refrigeration through an inverter?
2) Why, with the choices available today, are you running a TV through
an inverter?

I have a (one) 1,000 watt inverter for my 110 volt stuff, and just about
the only thing I run is the microwave oven.

Marine refrigeration is either dual power (110/12) or cold plate (engine
driven), lcd tvs are 12 volt (4 amp draw)

If you are running 110 volt appliances you are not being very efficient.

Opinions, please.
Jim
The answer is very simple. I use the inverter because I am using all
standard, cheap household applienaces, like a household TV, VCR,
Microwave, Toaster, Coffeemaker, Power tools ( drill, saw, soldering
iron). I expected these appliances to last maybe a year, but so far
they have been lasting 3 years with no sign of corrosion. BTW My Boat
is in San Francisco Bay and it is perfectly dry.
I also have a normal apartment size fridge which I run on shore power.
I can put the stuff in the evening before, fill up the freezer
compartment and then it keeps cold for most of the weekend. I don't
use the fridge with the inverter since the drain on the batteries is
too great and I don't use the microwave for anything but heating
something. For cooking I have a propane 2 burner stoven and oven.
Rolf


wrote:

I'm trying to learn about inverters, and how to put a
system together. I want to use it pretty much just
for my refrigerator (about 800W), and my TV/VCR
etc. It seems like it would be cheaper to get two
less powerful inverters, than one powerful one.
So far getting two of the 1200W for $120 each at:

http://store.worldstart.com/customer...=16468&cat=307

seems like the best deal for me. That would leave
me plenty of head room--especially on the TV
circuit--for including other things. Does anyone
know of a better deal?

How do I figure what size batteries to use? Should
I keep the batteries separate for each inverter, or
is it better to connect two or more batteries and go
from there? If so, how to connect the batteries
together, and then how to go from there to the
inverters?

I'm lead to believe that any inverters I can afford
would produce a square wave instead of a sine
wave. How to know what influence that would
have on my TV's performance? The TV works
great using the Generac 4000W generator I'm
using now. Can I expect it to be different using
the inverter?

Thanks for any help!

"Jim" wrote in message
ink.net...


Larry's discussion has some very good information. I have a couple of
questions:
1) Why are you running refrigeration through an inverter?

Well, one reason is that you can buy a small household refrigerator for
about $200 and the same sized 12 volt refrigertor will cost you about $1200.
There are reasons that the 12 volt refrigerator is better, such as automatic
switching to 110 and likely to have greater efficiency, but I know that a
lot of people prefer to go the household route just because of the cost.

2) Why, with the choices available today, are you running a TV through
an inverter?

What choices? There are a lot of 9" TVs that run off of 12 volts, and I have
seen a couple of 13", but if you want a 25" TV it is going to be 110 volts.

Rod

wrote in message
...

want to use it pretty much just
for my refrigerator (about 800W),

That is either a very large refrigerator, a very inefficent one, or the
rating is way above what it actually draws. If this is a "frost free"
refrigerator then you would be best to get rid of it and get one that uses
lots less power. Frost Free refrigerators use more energy creating heat
(directly, not counting the byproducts) then they do "cold".

and my TV/VCR
etc. It seems like it would be cheaper to get two
less powerful inverters, than one powerful one.

It is possible that dedicating a smaller inverter to the refrigerator might
be more efficient. An inverter uses power even when there is nothing
drawing AC power. This "idle" power can be significant, especially on the
larger inverters. There are advantages to a good expensive inverter,
however.


seems like the best deal for me. That would leave
me plenty of head room--especially on the TV
circuit--for including other things. Does anyone
know of a better deal?

I would go with a minimum of 1500 watts, then you can run just about
anything (coffee maker, blow drier, belnder, etc.). You can decide if it is
wise to run such things, but at least you will have the option.



How do I figure what size batteries to use? Should
I keep the batteries separate for each inverter, or
is it better to connect two or more batteries and go
from there? If so, how to connect the batteries
together, and then how to go from there to the
inverters?

One large battery bank is much better than two smaller ones.

The first step will be to establish how much capacity that you need.

The refrigerator is going to be the biggest consumer. 800 watts will force
the inverter to draw about 76 amps out of the battery system, after
adjusting for the inverter efficiency loss. I would guess that the
refrigerator would run about 50% of the time, which means that you would
need 919 amp-hours per day.

That's a lot! If you want to last a three day weekend you would need 2700
amp-hours. To treat the batteries reasonably well you don't want to
discharge them below 20%, so you really would need ~3300 amp-hours. That's
a bunch of some very serious batteries. A lot of weight, a lot of room, a
lot of cost. Since you started off saying that you were concerned about
cost I would think that this would be a major issue.


I'm lead to believe that any inverters I can afford
would produce a square wave instead of a sine
wave.

There are sine wave inverters, square wave inverters, and modified sine
wave.

A square wave inverter goes from +60 volts to -60 volts in one step.

A modified square wave would go from somthing larger than 60 volts, to zero,
then to somethng larger (magnitude) than - 60 volts. The pause in the middle
would approximate the zero crossing of the sine wave and would make
inductive loads much happier.


How to know what influence that would
have on my TV's performance?

If the TV was made in the last 20 years it probably would be very happy with
the output of any inverter. Most electronics these days use switching power
supplies that would actually have better efficiency off a square wave than
they would off a sine wave. Where you can get into trouble is with
inductive loads (some motors) and transformers.

On a sine wave AC, the peak voltage is ~1.4 times the RMS voltage. Thus, if
you had a device that uses a "wall wart" transformer it would be expecting a
" 6 volt" output to actually peak at 8.4 volts. When rectified, this would
produce a useable amount of 8 volts DC, which could be used recharge a 6
volt battery operated device. If you connected this up to a square wave
inverter than the rectified output would only be 6 volts, which might not be
enough for the circuit to operate. The modified sine wave would certainly
be better and they probably make the "modification" such that the peak is
the same.

Square wave inverters are great for running series wound motors (drill
motors, blenders, saws, etc.). They will run most electronic items that
have swicthing power supplies or that aren't too sensitive on the voltage.
They are a lot cheaper and more efficient than modified square wave or sine
wave.

There are other factors to consider for the total installation.

If you go with something like a Xantrex marine inverter you will get the
following features (which will not be available from the inverters you have
indicated)

1) Automatic AC input cross over. When you have 110 Volts available you
will not want to be running off the batteries. The Xantrex will sense the
incoming AC and pass it through, switching the load over without ever
powering it down. With the cheap inverter you will have to pull the plug
out of the inverter and plug it into the normal AC outlet. (that can be a
real hassle if the refrigerator/TV is recess mounted).

2) The Xantrex inverter includes a battery charger, suitably sized for the
job. If you install that 3300 amp-hour battery bank you will need a way to
charge it. If you don't have a really good charger it could take a week to
get the batteries recharged!

3) I have some amount of faith in Xantrex products. They have been around
for a while and I know many people who have used them. Some fly by night
company off the internet is a gamble.


My recommendations:

1) Get a refrigerator that uses a lot less power. The "old" style, where the
cooling coils are the floor of the freezer, and you have to manually defrost
them occasionally, are the best for this application.

2) Install a battery bank that will provide at least twice what you think
you will need for the length of time you will be away from shore power.

3) install a single inverter that will cover all your needs.

Rod McInnis

various posters - inverters, Threat or Menace?

I'd leave all that crap ashore.

I have a cooler that kept ice for five days. Got a percolator
that sits on the stove, and if I wanted toast I guess I could
fork it over the flame. I'd fix drinks that didn't require a
blender.

And a television? Spare me.

LCD tvs are 12 volt. I have a Sharp 20 inch in my salon that
runs off the cabin light circuit. I haven't checked the larger ones,
but I'll bet they are the same.

15" draws 4 amps, 20" uses 4.5, at 12 volts.


Rod McInnis wrote:

2) Why, with the choices available today, are you running a TV through
an inverter?


What choices? There are a lot of 9" TVs that run off of 12 volts, and I have
seen a couple of 13", but if you want a 25" TV it is going to be 110 volts.

Rod

I'm with you. If you want to sail your living room mount
your mast on the roof of your home and never worry about
heeling over again! And imagine all the power capabilities
you could have, even surround sound on your computer.

Seriously though just the essentials keep it simple and you
will be happier in the long run.

John

"Steve Daniels, Seek of Spam" wrote in
message ...
various posters - inverters, Threat or Menace?

I'd leave all that crap ashore.

I have a cooler that kept ice for five days. Got a
percolator
that sits on the stove, and if I wanted toast I guess I
could
fork it over the flame. I'd fix drinks that didn't
require a
blender.

And a television? Spare me.