Hybrid Car – More Fun with Less Gas

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Posted by Phil Cook on October 27, 2003, 9:31 pm
 

Is the math below correct? I thought to run longer you had to increase
amp hours?


Most batteries express their capacity in terms of amp-hours at a
particular voltage. 2, 6, or 12V cells may be wired in series to give
higher system voltages.

Although the voltages double or quadruple, the amp-hour capacity of
the battery bank remains the same.

Why?
Volts x amps = watts.

Therefore, A single 6V 220 amp-hour cell produces 1320 watt-hours (1 x
6V x 220 amp-hours.) and 24V string of four 6V 220 amp-hour batteries
produces 5280 watt-hours (4 x 6V x 220 amp-hours).

However, using our equation volts x amps = watts, we can determine
that:

Watts volts = amps (watts divided by volts equals amps).

Using our figures from the 6V 220 amp-hour cell above:

1320 6 = 220

Using our figures from the 4x6V 220 amp-hour cell above:

5280 24 = 220

On the 6V 220 amp-hour cell, a 100 watt load could run for 13.2 hours.

On the 4x6V 220 amp-hour cell, the same 100 watt load would run for
52.8 hours, or four times as long.

Even though the capacity of the battery bank increased by 4 times, the
amp-hour capacity remains at 220 amp-hours.

Posted by dbs__usenet on October 27, 2003, 10:26 pm
 


To run longer with the same load, you need to EITHER increase amp hours
OR voltage.    Remember, you are drawing 100 watts (6v at 16 amps or 24
volts at 4 amps) so the math still works.  This assumes that you are using
a 100watt 24v bulb in one case and a 100 watts 6v bulb in the other case.
If you attach the same equipment (the 6v 100watt lamp) to each battery
bank, the 24v battery will supply 64 amps to the .37 ohm resistance and
probably blow a filiment :-)

I hope I didn't ness up the math.  All values are approximate.



Posted by allmailNOSPAM on October 28, 2003, 12:56 am
 
Take a look at the web site. If you increase system voltage at the
bottom of the page the run times go up. Is that right?

http://www.solarsense.com/Spec_Your_System/Run_Times.html


On Mon, 27 Oct 2003 22:26:01 GMT, dbs__usenet@tanj.com wrote:



Posted by Tom Quackenbush on October 28, 2003, 1:30 am
 allmailNOSPAM wrote:


<SNIP>

  As dbs_usenet said, yes. (in general; I didn't double check the
calculations on the web site). If power remains the same and voltage
increases, amperage must decrease. If amperage decreases and AH
capacity remains the same, run time is increased.

  Once you decide the voltage you want for your system, that's it.
IOW, deciding to bump the voltage from 12V to 48V after you've bought
all 12V appliances is NOT a good idea. Adding batteries in parallel
then becomes you're only option to increase capacity.

R,
Tom Q.



Posted by dbs__usenet on October 28, 2003, 6:56 am
 
Yes, they are correct because they ask you to tell them the AH at the top.

When you draw power you are drawing watts, not Amp-Hours.

If you draw 100 watts from a 200 ah 6v system you get X hours.
If you draw 100 watts from a 200 ah 24v system you get X times 4 hours.

If you had 4 6 volt batteries in parallel to get the 200 AH 6v pack,
it would be able to provide the same number of watts as 4 batteries
wired in series to get a 50 AH 24v pack.

Daniel

allmailNOSPAM@consolidated.net wrote:


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