Awl --

In discussing using inverters+car alternator as a backup power supply, and
observing some hefty cobra 5,000 W inverters ($310, google shopping), I was
wondering if these can be made even heftier with stock parts? I wonder if
these large ratings in cobra units aren't like Sears hp....

It seems like the bottleneck in this strategy as a house backup power supply
is the car alternator. 5,000 W would require about a 500 Amp alternator!
But mebbe a regular car alternator + a bank of batteries could handle all
the peak loads/draws, as long as they didn't last forever. Anyone here ever
do this?

Gensets, even nat gas ones, seem to be a real pita, and the noise is
considerable, unless you get real pricey.
--
EA

My guess is that in the end you will spend $2,000 in time plus money,
to replicate a $310 inverter. Additionally, it will not work well.

i

On 2012-10-07, Existential Angst wrote:
Awl --

In discussing using inverters+car alternator as a backup power supply, and
observing some hefty cobra 5,000 W inverters ($310, google shopping), I was
wondering if these can be made even heftier with stock parts? I wonder if
these large ratings in cobra units aren't like Sears hp....

It seems like the bottleneck in this strategy as a house backup power supply
is the car alternator. 5,000 W would require about a 500 Amp alternator!
But mebbe a regular car alternator + a bank of batteries could handle all
the peak loads/draws, as long as they didn't last forever. Anyone here ever
do this?

Gensets, even nat gas ones, seem to be a real pita, and the noise is
considerable, unless you get real pricey.

On Sat, 6 Oct 2012 23:51:42 -0400, "Existential Angst"
wrote:

Awl --

In discussing using inverters+car alternator as a backup power supply, and
observing some hefty cobra 5,000 W inverters ($310, google shopping), I was
wondering if these can be made even heftier with stock parts? I wonder if
these large ratings in cobra units aren't like Sears hp....

It seems like the bottleneck in this strategy as a house backup power supply
is the car alternator. 5,000 W would require about a 500 Amp alternator!
But mebbe a regular car alternator + a bank of batteries could handle all
the peak loads/draws, as long as they didn't last forever. Anyone here ever
do this?

Not particularly uncommon in yachts. Usually to power an AC fridge. It
works. Measure the actual amperage used by the fridge connected to AC
and then amp and volts required by the inverter powering only the
fridge and you get a good idea of the efficiency of the inverter. As
for sizing the inverter most people use a factor of 2, you need 1KW
buy a 2 KW inverter.

Gensets, even nat gas ones, seem to be a real pita, and the noise is
considerable, unless you get real pricey.

Insulated generator enclosure and efficient exhaust system.
--
Cheers,
John B.

On Sat, 6 Oct 2012 23:51:42 -0400, "Existential Angst"
wrote:

Awl --

In discussing using inverters+car alternator as a backup power supply, and
observing some hefty cobra 5,000 W inverters ($310, google shopping), I was
wondering if these can be made even heftier with stock parts? I wonder if
these large ratings in cobra units aren't like Sears hp....

It seems like the bottleneck in this strategy as a house backup power supply
is the car alternator. 5,000 W would require about a 500 Amp alternator!
But mebbe a regular car alternator + a bank of batteries could handle all
the peak loads/draws, as long as they didn't last forever. Anyone here ever
do this?

Gensets, even nat gas ones, seem to be a real pita, and the noise is
considerable, unless you get real pricey.

Of you look around..you should be able to find a nice quiet natural
gas powered genset someplace for very little money.

You will absolutely need a running power source for an inverter. Ive
got a 6000 watt Hart inverter that came out of a brand new but wrecked
greyhound bus sized RV...and I dont have anything big enough to feed
it the 12 volts required to output 6000 watts of 120 volts AC

Ive got a Xantrex 3000 watt inverter in my big van. It has dual
batteries and a second set of paired deep cycle batts mounted inside
the cargo compartment. Works very very well for about an hour or so
when Im running close to 3000 watts of power tools and lights. So I
had to install an oversized alternator to keep the batteries charged
when the inverter is running.

Now if you can stack up forklift batteries in a big enough pile..with
a big enough charger ..you might be able to run the important stuff in
your house for day or so..at most.

http://www.ebay.com/itm/Natural-Gas-...-/400323091362

etc etc

Building a small noise canceling cover for it...like a small shed is
not a big deal

Gunner

--
Adde cruorem stultitiae, atque ignem gladio scruta
To your folly add bloodshed, and stir the fire with the sword (Horace)

On Sun, 07 Oct 2012 01:07:26 -0700, Gunner
wrote:

On Sat, 6 Oct 2012 23:51:42 -0400, "Existential Angst"
wrote:

Awl --

In discussing using inverters+car alternator as a backup power supply, and
observing some hefty cobra 5,000 W inverters ($310, google shopping), I was
wondering if these can be made even heftier with stock parts? I wonder if
these large ratings in cobra units aren't like Sears hp....

It seems like the bottleneck in this strategy as a house backup power supply
is the car alternator. 5,000 W would require about a 500 Amp alternator!

Or a couple/three smaller ones.


But mebbe a regular car alternator + a bank of batteries could handle all
the peak loads/draws, as long as they didn't last forever. Anyone here ever
do this?

Gensets, even nat gas ones, seem to be a real pita, and the noise is
considerable, unless you get real pricey.

Of you look around..you should be able to find a nice quiet natural
gas powered genset someplace for very little money.

Then you'll find out why they're going for cheap. I've heard the cost
to run them is simply -outrageous-. From the Generac website:

--snip--
7) How much does it cost a month to run the generator when it runs for
15 minutes a week?

Depending on the price of natural gas, it shouldn’t cost more than
$4 or $5 per month to run the unit in test mode. During a power
outage, under 50% load expect to pay less than $30/day for gas usage.
A lot cheaper than a hotel room or spoiled food!
--snip--

That's up to $900/mo ($10,800/yr) for gas at half power! IF The
pipeline remains pressurized. (yes, worst case scenario)


You will absolutely need a running power source for an inverter. Ive
got a 6000 watt Hart inverter that came out of a brand new but wrecked
greyhound bus sized RV...and I dont have anything big enough to feed
it the 12 volts required to output 6000 watts of 120 volts AC

That's a whole lotta inverter!


Ive got a Xantrex 3000 watt inverter in my big van. It has dual
batteries and a second set of paired deep cycle batts mounted inside
the cargo compartment. Works very very well for about an hour or so
when Im running close to 3000 watts of power tools and lights. So I
had to install an oversized alternator to keep the batteries charged
when the inverter is running.

How often do you use it for more than an hour? And what tools are
hooked up to it? Will it handle a good sized welder?


Now if you can stack up forklift batteries in a big enough pile..with
a big enough charger ..you might be able to run the important stuff in
your house for day or so..at most.

http://www.ebay.com/itm/Natural-Gas-...-/400323091362

etc etc

Building a small noise canceling cover for it...like a small shed is
not a big deal

....but it's a necessary thing. Engine noise really grates on nerves.
Especially non-tool-user nerves. vbg

--
You never hear anyone say, 'Yeah, but it's a dry cold.'
-- Charles A. Budreau

On Sun, 07 Oct 2012 10:39:32 -0700, Larry Jaques
wrote:

On Sun, 07 Oct 2012 01:07:26 -0700, Gunner
wrote:

On Sat, 6 Oct 2012 23:51:42 -0400, "Existential Angst"
wrote:

Awl --

In discussing using inverters+car alternator as a backup power supply, and
observing some hefty cobra 5,000 W inverters ($310, google shopping), I was
wondering if these can be made even heftier with stock parts? I wonder if
these large ratings in cobra units aren't like Sears hp....

It seems like the bottleneck in this strategy as a house backup power supply
is the car alternator. 5,000 W would require about a 500 Amp alternator!

Or a couple/three smaller ones.


But mebbe a regular car alternator + a bank of batteries could handle all
the peak loads/draws, as long as they didn't last forever. Anyone here ever
do this?

Gensets, even nat gas ones, seem to be a real pita, and the noise is
considerable, unless you get real pricey.

Of you look around..you should be able to find a nice quiet natural
gas powered genset someplace for very little money.

Then you'll find out why they're going for cheap. I've heard the cost
to run them is simply -outrageous-. From the Generac website:

--snip--
7) How much does it cost a month to run the generator when it runs for
15 minutes a week?

Depending on the price of natural gas, it shouldn’t cost more than
$4 or $5 per month to run the unit in test mode. During a power
outage, under 50% load expect to pay less than $30/day for gas usage.
A lot cheaper than a hotel room or spoiled food!
--snip--

That's up to $900/mo ($10,800/yr) for gas at half power! IF The
pipeline remains pressurized. (yes, worst case scenario)

Indeed. But as you indicated..worst case secenario. If one is trapped
somewhere for more than a couple months with generated power...its
cheap enough.


You will absolutely need a running power source for an inverter. Ive
got a 6000 watt Hart inverter that came out of a brand new but wrecked
greyhound bus sized RV...and I dont have anything big enough to feed
it the 12 volts required to output 6000 watts of 120 volts AC

That's a whole lotta inverter!

It sure is. Want to buy it? Works great! The bus had a pull out
drawer on electrically operated slides that had batteries so big it
looked like a landing field when we managed to get the drawer open.

On idle...with a deep cycle marine battery about 800 cca...it took 3
hours to go into low battery alarm simply sitting there idling. When I
plugged a tig welder (110vt Weldpak 100) it sucked the battery down
in about 20 minutes of just 20/80 welding time. Probably 5 minutes of
actual welding.

Its very capable! It just needs a crap load of batteries to provide
much power.

http://www.busconversions.com/bbs/in...p?topic=9475.0



Ive got a Xantrex 3000 watt inverter in my big van. It has dual
batteries and a second set of paired deep cycle batts mounted inside
the cargo compartment. Works very very well for about an hour or so
when Im running close to 3000 watts of power tools and lights. So I
had to install an oversized alternator to keep the batteries charged
when the inverter is running.

How often do you use it for more than an hour? And what tools are
hooked up to it? Will it handle a good sized welder?

Ive used it extensively with a Weldpac 100 and a Thunderbolt AC/DC
stick welder (with a big! step up transformer) and its enough to get
the job done if Im quick about it. I dont like to push any inverter
that costs as much as those do.



Now if you can stack up forklift batteries in a big enough pile..with
a big enough charger ..you might be able to run the important stuff in
your house for day or so..at most.

http://www.ebay.com/itm/Natural-Gas-...-/400323091362

etc etc

Building a small noise canceling cover for it...like a small shed is
not a big deal

...but it's a necessary thing. Engine noise really grates on nerves.
Especially non-tool-user nerves. vbg

True indeed. However..if done properly...one simply overlooks that
very very muted "rrrrrrrrrrrrr" in the background...even from the
neighbors.

Gunner

--
Adde cruorem stultitiae, atque ignem gladio scruta
To your folly add bloodshed, and stir the fire with the sword (Horace)

On Sat, 6 Oct 2012 23:51:42 -0400, "Existential Angst"
wrote:

Awl --

In discussing using inverters+car alternator as a backup power supply, and
observing some hefty cobra 5,000 W inverters ($310, google shopping), I was
wondering if these can be made even heftier with stock parts? I wonder if
these large ratings in cobra units aren't like Sears hp....

Well, they kinda are rated in "Sears HP" because nobody ever allows
for start surges on motorized items - like your Refrigerator and
Freezer. The inverter might have enough power to /run/ both at once
along with a few lights and things, BUT it'll take pretty much the
entire inverter output to get either one *started* - the start surge
on an induction motor is usually around 10X the running current, if
not more.

Look up the Locked Rotor Amps if it's listed on the nameplate, that's
the Start Current for the first quarter-second when the motor is at a
dead stop, then the current ramps down as the motor spins up.

It seems like the bottleneck in this strategy as a house backup power supply
is the car alternator. 5,000 W would require about a 500 Amp alternator!
But mebbe a regular car alternator + a bank of batteries could handle all
the peak loads/draws, as long as they didn't last forever. Anyone here ever
do this?

For one, running a 5KW inverter to backup the house will require a
large battery bank to feed it with a low enough impedance to toss a
500A surge toward the inverter. You can use an ultra-low-impedance
battery like a Gates Cyclon or Optima Spiracell, but while the design
can supply huge surges it doesn't have the Amp-Hours of capacity to
back it up for long.

Good old Tank Cells would be better for that - put up a rack in the
garage and load it up with about a half-ton string of cells, and
you're good to go. Get the Lead-Calcium ones, and they'll go 15 or 20
years between replacements with proper care.

You don't really need a 500A alternator to charge the battery and/or
pass-through to the inverter, but it has to be large enough to both
satisfy the constant loads and have enough excess to get the battery
mostly recharged before the next big start surge.

Gensets, even nat gas ones, seem to be a real pita, and the noise is
considerable, unless you get real pricey.

But a genset is the only practical long-term alternate supply -
whether it's putting out 120/240V to run the load, or large quantities
of 12V or 24V or 48V DC to recharge the battery string. Even with
that inverter and battery bank, you still need to recharge the
batteries or your backup won't take you very far.

And it is possible to totally silence a genset if you start out with
one that's intrinsically quiet to begin with - water cooled engine at
a slower operating speed - 1800 RPM is a lot easier to damp than 3600
RPM, but you need to over-rate a gasoline engine running at the lower
speed.

Then it's a matter of building an enclosure that keeps the noise in,
and developing a labyrinth with acoustic damping to let cooling air in
and out of said enclosure without letting the noise out.

The "Movie Generators" they bring out that are almost totally silent
wouldn't cost that much more than a standard 60KW to 200KW unit if
they were mass-produced - half the cost is they're all built custom.

-- Bruce --

On 2012-10-07, Existential Angst wrote:
Awl --

In discussing using inverters+car alternator as a backup power supply, and
observing some hefty cobra 5,000 W inverters ($310, google shopping), I was
wondering if these can be made even heftier with stock parts? I wonder if
these large ratings in cobra units aren't like Sears hp....

Well ... there is the confusion between Watts and VA
(Volt-Amps). Watts are the real power it can deliver, while VA is the
product of the voltage and the current -- which is the *same* as Watts
for resistive loads (like space heaters and incandescent lamps), but
inductive or capacitive loads (like motors and computer power supplies)
have the current lagging or leading the voltage, so you get less power
than you would expect -- and while the cooling requirements of the
inverters are probably more power based, there is also a limitation on
the maximum current which the transistors can pump out, so you need to
know both the VA and the Watts ratings for most things.

And, I'll bet that the 5000 W rating is *instantaneous* (peak)
wattage, and that it could not run that kind of output steady state.

Are these things not actually made for powering the insanely
loud auto sound systems? You might get that kind of peak load every
time the big pulse of bass comes out, but there are quieter periods
between those.

O.K. Going to their page, I find that the 5000 Watts is the
*peak* power, and the steady state power limit is 2500 Watts.

https://www.cobra.com/detail/cpi-2575-2-500-watt-power-inverter.cfm

I've downloaded the manual, and discovered that the output is
not a sine wave, but rather a "modified sine wave" (synthesized from
square waves), which could make some loads quite unhappy.

Also (on page 12) I find:


================================================== ====================
The inverter can delivery 2500 Watts for about 60 minutes. The
inverter must cool for 15 minutes before it can resume operation
at 2500 Watts. Note: The Wattage rating applies to resistive
loads.
================================================== ====================

So -- you can't even get that 2500 Watts full time -- let alone the 5000
Watts.

O.K. the 5000 Watts is the "Surge rating (0.1 second)". Hardly
useful. :-)

It seems like the bottleneck in this strategy as a house backup power supply
is the car alternator. 5,000 W would require about a 500 Amp alternator!

Well ... I used to have a generator which was good for at least
that much current at 28 VDC. (It was used in an army Tank to power the
really high power searchlights.)

But mebbe a regular car alternator + a bank of batteries could handle all
the peak loads/draws, as long as they didn't last forever. Anyone here ever
do this?

Not I, at least.

Perhaps you could have the auto motor running a bank of
alternators instead? And yes, you would need multiple batteries in
parallel to handle the load current. To do this, you would have each
alternator maintaining the charge on one battery, and you would have all
the batteries connected to the inverter through diodes, so one low
battery would not hog current from the others.

You also want serious sized wire. They are suggesting #4 AWG
wire for runs up to four feet, and heavier for longer. They are
suggesting #2 AWG which may suggest that is the largest which will fit
the connectors on the back of the inverter.

Gensets, even nat gas ones, seem to be a real pita, and the noise is
considerable, unless you get real pricey.

Given the various limitations of this, I think that it would not
be satisfactory for powering the house -- unless perhaps you had
multiple ones, each run off its own set of alternators and batteries, so
you could minimize the load on each inverter. And check out what you
might have which would not like the output waveform.

Good Luck,
DoN.

--
Remove oil spill source from e-mail
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

DoN. Nichols wrote:



You also want serious sized wire. They are suggesting #4 AWG
wire for runs up to four feet, and heavier for longer. They are
suggesting #2 AWG which may suggest that is the largest which will fit
the connectors on the back of the inverter.

Gensets, even nat gas ones, seem to be a real pita, and the noise is
considerable, unless you get real pricey.

Given the various limitations of this, I think that it would not
be satisfactory for powering the house -- unless perhaps you had
multiple ones, each run off its own set of alternators and batteries, so
you could minimize the load on each inverter. And check out what you
might have which would not like the output waveform.
Yes, for anything over a couple hundred Watts, you really want to use a
higher voltage, and put 12 V batteries in series. 48 V inverters are
fairly common, also 24 V for use in aircraft. 12 V inverters are really
inefficient due to the huge currents and massive wires required.

The off-grid people often use 120 V DC battery banks.

Jon

On Saturday, October 6, 2012 11:51:51 PM UTC-4, Existential Angst wrote:
Awl --



In discussing using inverters+car alternator as a backup power supply, and

observing some hefty cobra 5,000 W inverters ($310, google shopping), I was

wondering if these can be made even heftier with stock parts? I wonder if

these large ratings in cobra units aren't like Sears hp....



It seems like the bottleneck in this strategy as a house backup power supply

is the car alternator. 5,000 W would require about a 500 Amp alternator!

But mebbe a regular car alternator + a bank of batteries could handle all

the peak loads/draws, as long as they didn't last forever. Anyone here ever

do this?



Gensets, even nat gas ones, seem to be a real pita, and the noise is

considerable, unless you get real pricey.

--

EA

See http://www.priups.com He uses a prius and a big inverter to run his house. The prius batteries are, I think, 220VDC. Clever idea.