On Wed, 21 Sep 2011 06:30:30 -0400, wrote:

Hi

I could use some feedback regarding a brainstorm of mine. I'm in the
process of building an emergency power system for home use.

The main questios are regarding supply and re-charging.

For the supply, for now I'm using 12V starting batteries. The plan is
to pick up 2 (or possibly 4) 6V 156Ah golf cart batteries.

For the charger I mated a 63A Delco alternator with internal 12V
regulatioin to a gas snowblower engine.

I want to use a 1500W inverter to supply about 180 watts of AC, 8x IR
LED surveillance cameras, and about a dozen 20mA LED lamps for
emergency lighting all operating at their native 12VDC

The questions a

Would I be able to use my alternator/generator to charge the golf cart
batteries without damaging them?

Until I'm able to get the golf cart batteries, would the couple
starting batteries I have work OK?

TIA

Bob



Starting batteries don't last long if discharged below the 80% of
charge level. The golf cart batteries will last much longer, but the
best life will be achieved if the discharge is limited to 50% or less.
The 63A altenator will only provide 63A if running at high speed
(5000-6000 rpm) so you'd need to adjust pulley sizes to get full power
when driving it with a 3000-3600 rpm engine. The rate of charge is
also dependent on the battery's state of charge, so it's unlikely that
your proposed setup will harm the golf cart batteries. The bigger
concern is what the end of charge voltage of the golf cart batteries
should be versus the end of charge voltage the alternator and its
regulator are designed for. The golf cart batteries are deep cycle
and *may* have a different end point voltage - check the manufacturers
specs.

Using an oversized inverter usually wastes battery power. Inverters
have their "sweet spot" where they have optimum efficiency - usually
somewhere in the 50%-90% load range. For longest battery life, you
should replace the inverter with a smaller one - and look carefully at
the no-load current requirement. Inverter idle drain isn't usually
high on the list of features people look for - most people are looking
at the maximum power they can get from it. I have a PowerStar UPG400
that idles at about 1 watt (that's about 0.1 amps). I would guess
that your 1500 watt inverter idles at 6 watts (0.5amps) - probably
more. The UPG400 was a serendipity buy - $24.50 plus shipping (couple
of pounds) - from a closeout at hsc.com n Dec 2009. Until I did
research, I had no idea that a 1990-91 vintage inverter could be so
efficient. Only wish I had known more about it sooner and been able
to purchase several.

I'm not an expert on backup/standby power, but I've had emergency
generators (one 1850 watt and one 5000 watt) for some time. Two
generators? Yes, the little one if rotating power to one item at a
time -freezer, fridge, etc - is adequate, the big one if multiple
appliances are needed simultaneously -i.e., furnace and microwave
oven. The little gen runs a lot longer on a gallon of gas than the
big one at the same load.

I've been doing a lot of research recently before setting up a small
solar system (70AH battery, 45 watt solar array) for testing. I've
even measured the drain the solar charge controller puts on the
battery - while it's typically in the milliamp range, some use two or
three times as much as others. Solar amps are expensive, so I'm
looking to get as many of them as possible to the load, not the
control electronics. Lots of LED's on the controller *look*
impressive, but require a lot of milliamps to be visible in sunlight.
An analog meter or an LCD panel with no backlight (or a switchable
backlight) requires less power to operate.

John