Baghdad Battery

[Classic]

Most of you are aware of "tesla switch" so called circuit for power transfer between 2 sets of batteries.

Just to make sure you guys and girls understand what I refer to: https://youtu.be/hvnNDTEn51w

What we see here ? Simple explanation using basic knowledge of a secondary school pupil applying Ohm law.

We have 3 batteries fully charged and 3 batteries discharged. Our goal is to charge the empty batteries to a usable level.
In order to do this efficient, instead of connecting them direct "to equalise voltage" we are going to use a voltage regulator in a form of a LED with known voltage drop and current "consumption".

So, we take fully charged batteries and connect them in series to increase the voltage and we obtain 1.4 V times 3 = 4.2 V. Now we connect the discharged batteries in parallel and ready to receive the current they need to increase their voltage and allow for a enough voltage difference from series bank to parallel bank assuming the parallel bank will have 0.9 V as follow: 4.2 V from series minus 0.9 from parallel = 3.3 V ... this is a bit too much to charge such little batteries !

Ok, now we chose as voltage regulator an LED which require about 2.2 V at 20 mA ... now we have 4.2 V (series bank) minus 2.2 V minus (green led) 1.1 V (parallel bank).
Operation: when voltage potential is met the green LED is lit up, by the time parallel bank receive electric charges its voltage start to rise and green led start to fade.

When green led (OUR VOLTAGE REGULATOR) is not lit up anymore it means the voltage is equalised (in theory).

We have we done here ? We have transferred some power from point A to point B using a trafic control.

What is the advantage ? Not much, we have just drained one set of batteries to charge another set of batteries with some potential from which we have dissipated in form of light and some heat using an LED.

Ok, what's the point of doing this ? Well, the point is now we have available some power to reapeat the cycle again and we take the parallel bank and re arrange them in series to rise the potential, we take the series bank and re arrange them in parallel to lower their potential and allow to transfer the power again.

Now repeat this cycle until batteries are drained to maximum level allowed to be discharged, then re-charge only ONE set of batteries, not both.

Ok, what's the point ? Well, the whole point is to recycle the energy and minimise "consumption" by choosing wise our voltage regulator and potential of the source.

It may be obvious now for some of you that we can apply simple Ohm law for a practical application of we need some light ... or anything else, if we can calculate using elementary math what we need and where to keep our "voltage regulator" working for almost free.

So, if anyone currently using a solar/wind/hydro electric generator, may be able to split the battery bank in half and benefit from a much smaller input required to run his home.

Of course, there are many other "tricks" to be added, but this would be just enough to get you started !

Probably some of you already thinking to use a "Joule Thief" circuit as voltage regulator for power transfer between 2 batteries, or 2 capacitors, or 2 inductors ... 

So, there is no magic or mystery ... just simple math and basic physics applied correct to our advantage, for power formula re-arrangement per cycle.

Just don't take my words, and try to lit up an LED or whatever you want direct from a battery bank, make a note how long it last until led is not lit up anymore, then run the test as above and sum up total time run 😉
If you convince yourself and see it with your own eyes, you can ask @citfta to sell or share his setup for automatic battery swap ... or make one yourself.
Eventually add another source of voltage to power providing (series) bank to replenish the loss as and when required.

So, depending on "your voltage regulator" you may have to replenish more or less loss, more often or not so often.

[Classic]

Let's see how it may look such a setup for a 100 w dc motor 24 V.

100/24= 4.17 a

Means our voltage regulator will require 24 V supplied with a 4.17 a per hour.

Now we need to find some batteries able to be discharged at this rate 4.2 ah. Most of batteries are rated for C20, so a simple calculus tell us that we need 6 batteries 12 v 90 ah to run this motor for 1 cycle and this will be:

3 batteries fully charged in series connected in series with the motor in series with 3 parallel batteries.
Swap batteries every hour or monitor voltage for longer run. Eventually use a solar charger to power the motor from batteries to have an automatic cut off when maximum discharge was reach.
Keep swapping batteries until your solar charger won't allow the motor to run. Now is time to charge one set of batteries.
One can choose some deep discharge batteries or C10 or C5 and use them in C20 configuration for much longer run time. Probably some start-stop car batteries will be a better choice if budget allow. Avoid batteries with BMS for this configuration.
This recycling energy doesn't require high power density as Lithium with bms ... one may settle for a much cheaper soultion with even better results.


Apply the same for electric central heating or running your fridge, washing machine, electric vehicle etc.
This system can be further improved using constant voltage and constant current converters.

Rectify AC from grid or your own inverter and allow easy combine of voltage or takeover sources.

Or, charge your batteries at night time rate when needed if you don't have a solar/wind/hydro harvester. It will lower your bills dramatic.

Good luck !