On Fri, 11 Dec 2009 09:53:50 -0800 (PST), sid
wrote:

On Dec 10, 7:11Â*pm, wrote:
On Thu, 10 Dec 2009 14:24:50 -0700, "charlie"

wrote:

"sid" wrote in message
...
I have a project to decorate the family "Little Red Wagon" with
Christmas lights. So I stated experimenting with LED light strings and
battery combinations. Â*I finally decided to use an Inverter and not
cut up any light strings. Â*The LED light set that I found has 80
lights and the specs state it uses 12 watts. Â*So as a test I connected
two 6v lantern batteries in series and ran the leads to the inverter
(rated at 100watts), connected a lamp with 40 watt bulb.

80 watts at 120 volts is the same as 960 watts at 12v. add in the losses in
the inverter, and you're gonna need a large battery

Â*No, 80 watts at 120 volts is the same as 80 watts at 12 volts, give
ot take the percentage of inefficiency.
80 watts at 120 volts is .67 amps. At 12 volts it is 6.7 amps, give or
take according to efficiency. The lanmtern batteries are generally
good for about 10 watts at 6 volts - or 20 watts at 12, more or less.
Generally Alkaline batteries are good for about 2.5 to 2.9 amps
MAXIMUM draw. The old Manganese Dioxide carbon-zinc batteries put out
a bit more, but for significantly shorter time.

This is the results of my initial test using two Energizer 6v Alkaline
Lantern batteries in series.
Here is what I measured:
voltage not connected = 12.5v
voltage connected = 11.4v
current connected = 1.3 amps
So: R = E/I
(12.5 - 11.4)v / 1.3a = .85 ohms of internal resistance.
I need a source with a much lower resistance or more batteries in
parallel.

I found an old "APC Smart UPS 650", Specs show it should have a 12v
650va battery.
Tomorrow I will post what happened.




The SmartUps 650 I have sitting here takes 2 6 volt batteries of I
believe 12 AH. They are no longer here - scrapped them but have not
replaced them yet. The SmartUps 1000 is a 24 volt unit.