Re: Thanks, for all the responses.

On Sun, 16 Dec 2007 17:07:30 -0700, Dapper Dave <expurgated@xxxxxxxxx> wrote:


1. How about the other side of efficiency, i.e., do some or all
appliances use more energy if being operated from a MSW source?

Nothing waveform-related. Any difference will be because of the voltage difference
between line and the inverter.


2. The one appliance that does not do well with MSW power is the
microwave. It cooks at about half power when run off the inverter.

A conventional microwave oven that uses a transformer/rectifier/voltage doubler (NOT
the Panasonic Inverter oven and similar ones*) is heavily dependent on the peak
voltage of the incoming power. The problem is that no inexpensive inverter that I've
ever seen (just don't know about expensive ones) regulates the output voltage. The
output voltage is roughly proportional to the input minus losses in the inverter. If
say, 80 amps traveling from the battery to the inverter terminals causes a half a
volt drop then that will be reflected as about a 5 volt drop in the output. That has
a major effect on the microwave output.

There are a couple of ways to address this. If the inverter has an internal
adjustment for output voltage then cranking that up a little will help. Running the
engine during microwaving also helps since that keeps the battery voltage up.

The other way is a voltage booster transformer. A 12 volt transformer will add 10%
(12/120). A transformer is selected with a secondary rating approximately that of
the microwave input. If the microwave draws 8 amps then a 10 amp transformer is
perfect. A 5 amp one will probably work since the duty cycle is short. This is a
fairly small transformer. Stripping one out of an inexpensive 5 or 10 amp battery
charger is a good source.

The transformer is connected with its primary connected directly to the inverter
output and the secondary connected in series with the hot leg feeding the microwave.
Polarity matters - one way and the voltages subtract; the other way and they add.

This is the approach I used in my semi truck and am using in my MH. The transformer
can be mounted next to the outlet where the microwave plugs in, assuming that the
inverter is connected to feed the RV's electrical system. Or a short heavy duty
extension cord can be cut and the transformer wired in. The voltage boost won't hurt
the microwave when operated on shore power so it can be left in place permanently.

It
draws do much current that running it from batteries doesn't make much
sense wanyway, though.

Au contraire!! A 1000 watt input (6-700 watt output) microwave will consume about an
amp-hour a minute. Thus, if you take 3 minutes to pop a bag of popcorn, you've only
used about 3 amp-hours from the battery (not including Perkeut, of course). A 10
minute Hungry Man TV dinner uses on 10 amp-hours. That's just a drop in the bucket
against a 3-400 amp-hour house battery.

The key is to have the inverter-to-battery wiring the proper size to drop absolutely
minimal voltage. I use 3 100 amp-hour 12 volt batteries in parallel. All the
cabling is "0". The inverter is no more than a foot away from the batteries. Other
than the inherent voltage drop of a heavily loaded battery, there is essentially no
voltage drop even at 100 amps.

One has to pay attention to connectors too. I found that a heavy eye lug attached to
the steel stud on the battery post dropped a couple hundred millivolts at 100 amps
while a crimped SAE post connector dropped less than 50.

Same thing with a coffee-maker, for that matter. In my semi, I had a Mr Coffee-type
coffee-maker. I set it up at the beginning of a sleep period, loaded with coffee and
water and left it plugged into the inverter. When the Screamin' Meanie pried my eyes
open :-), I swatted at the power switch until I managed to turn it on. When the
Screamin' Meanie's snooze alarm finally woke me up, coffee was hot and waiting. For
me a matter of survival! The whole process used not more than 5 amp-hours.

I REALLY don't like to run my generator for just a few minutes at a time so most of
my nuking and coffee-making and bread toasting is done on battery power when I'm off
shore power. I crank the generator only when the batteries need charging. Or when I
need the AC, of course.


3. I am currently in the slow process of ordering a newer charger for my
Black & Decker drill. I wonder if the old charger failed because we
frequently operate everything from the inverter. Also, our fairly new
KitchenAid blender died last week. Maybe I'll reconsider my opinion that
everything we have is happy with our Xantrex MSW inverter.

I doubt that it caused the failure. My DeWalt charger isn't damaged by the MSW
power, it just doesn't do anything. It uses an ancient but very good reference
design developed by Zilog back when the Z8 processor was hot spit. I know the guy
who wrote the firmware so when I remember to ask, I'll find out why the thing doesn't
like MSW power.

The only other problem I've had, and this time the blue smoke actually leaked out,
was with the Schumacher 40 amp smart charger like Wallyworld sold a few years ago. It
apparently has an input power factor corrector circuit that demands low distortion
input power. Mine instantly smoked when I plugged it in to the inverter. The
replacement smoked when I plugged it in to one of my smaller generators. The
generator waveform isn't EU-quality but it isn't THAT bad. Just a bad design on
Schumacher's part. Too bad. I really liked that charger otherwise.

John

* I have a Panasonic inverter microwave. It kicks ass! It doesn't care about what
kind of power it's fed as long as it's close to 120 volts. The microwave power is
regulated. Variable power is just that, variable and not on/off like conventional
microwaves. It's quite light too, since it doesn't contain that heavy transformer.
--
John De Armond
See my website for my current email address
http://www.neon-john.com
http://www.johndearmond.com <-- best little blog on the net!
Tellico Plains, Occupied TN

*fas-cism* (fash'iz'em) n. A system of government that exercises a
dictatorship of the extreme right, typically through the
merging of state and business leadership, together
with belligerent nationalism. -- The American Heritage Dictionary, 1983

.

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