reply to post by jtma508
You're right: a standard 12V lead-acid battery will most definitely NOT handle 240 volts! That's not what I was saying, so let me further
As per what I am trying to accomplish, which is 100% self-sufficiency for an average house with enough surge power as to make the fact it is not on
the grid invisible to the occupants, I chose a 240V system for the sole reason that the inverter needed to produce a needed true sine wave AC output
would be simplified to a great degree if the input and output voltages were kept equal. Any inverter which uses a lower voltage than 240V would need
to include a step-up transformer in the output, and the current feeding that transformer would need to be increased from the output current by a
factor dependent on the ratio of the input to output voltage.
As an example, a 240V dual-phase inverter (which is the power supplied to homes in the USA) drawing from a 12V supply such as a marine battery would
need at least 20 times the input current as it supplies in output current (in actuality, a bit more than 20 times, because there will be losses due to
the internal circuitry). So if a power source will produce 200 amps (the typical size most homes are fused for), the draw from a battery would be
Now enough batteries connected in parallel would be capable of delivering that current, but the problem is when one considers the windings of the
step-up transformer. It would literally take a section of copper pipe
to handle that much current! As it is, I will be using 00 gauge copper
for the windings.
The option I chose is to connect 20 batteries in series
rather than in parallel, that is, connecting the positive of the first to the negative
of the second, the positive of the second to the negative of the third, etc. Stacked this way, each battery sees only 12V, the voltage it is designed
for, but the array can still deliver 240V from the negative of the first to the positive of the 20th battery. That can then power the inverter and
allow for smaller wire to be used in the windings, making the entire apparatus more affordable.
There is a trade-off: in order to charge such an array, 20 separate charging circuits will be required, since each battery is operating at a different
voltage range with respect to 'ground'. Of course, since each battery only needs one twentieth of the total wattage produced, each charging system
can be downsized appropriately. In simpler terms, if you were charging this array from a reworked automobile alternator, you would need 20
alternators, each running on an independent circuit, but each only needing to be sized for one twentieth of the total amount of power produced.
That is the reason I am so excited about this new battery design: it can handle the higher voltages directly, further decreasing the costs of
producing the power as well as the complexity of 20 individual production units.
I have also considered using more available units in parallel, such as one inverter for lights, one for hot water, one for the well pump, etc. Such a
configuration could be assembled quicker and would only require the 12V input allowing any number of batteries to be connected in parallel, but this
would also (according to the cost estimates I have run) be a bit more expensive and, I believe, more prone to breakdown. I tend to have more faith in
the continued operation of something I designed and built than something I bought off a shelf somewhere, because I do have a tendency to
I have not been able to build such a system yet, for the simple reason that my resources are going more toward producing the power than converting it
for home use at this time. I have no real water flows that could considered dependable, and wind here is iffy and unpredictable. Solar is simply too
expensive for me to set up a solar generator and continue to work on my present projects. So I need something else (those projects) to power the
That said, all the principles I have outlined in this thread are far from experimental or theoretical. This is all first year electronics.
(Oh, and if anyone else is at all confused by any of my posts and wants to try some of the things I have mentioned, please, please, make sure you
understand what you are doing before you do it! Pumping 240V into a 12v battery will most definitely be a bad thing! Post any questions here, or feel
free to U2U me before you do something like that.)