dc - ac conversion - a simple math problem, I think?

[Howard Betel]

I know this is a simple question, but I'm hoping someone can help.

I have a 14 AH lead acid battery (12V). I'm using it to drive a DC-AC
inverter (input: 10-15 VDC 5A max, output 115VAC .5A 50W). Into that I'm
driving a load that draws .3A. Can someone give me an idea how long the
device might run for on a fully charged battery?

Thanks,
Howard

 

[Glen]

On Thu, 14 Aug 2003 02:53:33 GMT, "Howard Betel"

There's a lot of factors involved. If I remember correctly, a 14Ah
battery can discharge(at best), 14 amps during a 1 hour period. That
depends, of course, on the condition of the battery and the load
behavior. If you pull 5A max to the invertor, you can get about 2.8
hours out of it. I could be wrong though.

 

[Howard Betel]

28 hours! ugh. Could it be safer and faster to somehow charge it off a car
battery through some direct connection?

 

[Spudley]

It depends on the efficiency of the inverter circuit.
One should measure how much current drain there is on the battery under the
..3amp load connected to the inverter and then calculate the time it will
take to discharge the battery to a workable level.
The time it lasts will depend on at what point the inverted circuit stops
working, this may not in fact be at the full discharge of the battery as the
inverter requires some hold up voltage to continue it's inverting function
at a nominal output voltage.

 

[Howard Betel]

Well I've tried it now and it ran for at least 3.5-4 hours and was still
running strong. I'm not sure how long I could have got out of it. I'll
have to recharge it now and try it from a freshly charged state. Also since
I'm trickle charging it, is there a way for me to determine when it is fully
charged using a multimeter?

Thanks Ghost for your input, it looks like you were the closest guess.

The other thing I noticed after I had left for my trip was that it was a
lead-calcium battery. I'm certainly no expert, but I haven't heard of that
type of battery before.

Ciao,
Howard

 

[Glen]

On Thu, 04 Sep 2003 23:46:28 GMT, "Howard Betel"

If I remember correctly, there should be relatively no current flow
to the battery. Put your DMV in series with the positive charging
lead. Afterall, it's just a chemical capacitor... Feel the battery
periodically. If it's warm, it's overcharging.

Glen