Is there any way a battery can charge other battery through isolated Charging circuit powered by a battery?

Question

Hi all, I am just thinking about developing a circuit to charged a 12 Volt battery and the charging circuit will be porwered by a second battery

kkazem · Answer

Hi Uche,

I'm a master power electronics engineer and I specialize in DC-DC converters, solar charge converters, DC-AC Inverters, Power Supplies, and battery chargers. Yes, you can charge a battery from another battery, if that's what you're asking. I don't know why you need it isolated. However, I've got to agree with D2113F with reference to your other replies to this post. To me, it sounds like a perpetual motion machine wheras you have two batteries that are each connected to relays that can switch the individual batteries to either a load or to a a charging circuit fed by the other battery. Here is the problem. Battery-1 is connected to a load and is discharged to the point that you want to rechage it from the other battery that's been idle. Battery-2 recharges Battery-1 thru a dc-dc converter with a control to ensure that it's not overcharged. Now, Battery-2 is discharged and Battery-1 is charged, therefore, the relay or relays setup the circuit such that Battery-1 recharges Battery-2 and now Battery-1 is again discharged. Hopefully, you see where I'm going with this. It's an (almost) endless loop of the batteries charging and discharging each other. And if you powered a load first, discharging Battery-1, then recharged it with Battery-2, Battery-2 is now discharged and you can power the load only one more time with Battery-1. But now, you can no longer recharge Battery-1 with Battery-2 since Battery-2 is discharged, The only way around this is if you have some additional power from another Battery, or a Solar Cell, or from an AC-DC Power Supply to put the lost energy back into the system.

One of the first things you should have learned in physics is that there is no such thing as a perpetual motion machine. Since you used the energy in Battery-1 to power the load and the energy in Battery-2 to recharge Battery-1, and since you used-up the energy in Battery-1 again powering the load after the recharge, you are out of energy as both Battery-1 and Battery-2 are discharged. Does this make any sense to you? I hope so, but if not, please feel free to reply here or send me a message using the Element-14 internal messaging system.

Best regards,

Kamran Kazem

YT2095 · Answer

a battery charger doesn`t care Where it gets its power from, be it mains, solar or another battery, as long as it`s capable of supplying enough power, a regulator can be made to charge a battery from such supply.

kkazem · Answer

Austine, Yes, of course a battery’s energy can be used to charge another battery thru an isolated or non-isolated charging circuit. But some of what I’m reading below is bordering on being a perpetual motion machine and that violates scientific principles. It simply will not work. Your system described below with the ac motor, car alternator, & car battery will work initially assuming the battery is initially charged. But the losses in the inverter, from the IR drops in the motor and alternator, & from friction will cause the battery to eventually discharge and go dead. You would then have to re-charge the battery from another energy source (like the 120 VAC utility power line or another battery). Once re-charged, you could then re-start the system again until the battery went dead from the losses. So what’s the point? There is no free energy here. If you have the parts, you can build this relatively inexpensively and see for yourself. Many others have had the same basic idea, but always with the same results. There is no such thing as perpetual motion. A better way to get almost limitless, renewable energy is to use the sun, wind, waves, geothermal, and other similar energy sources that are all around us and can easily be converted into useful electricity. Regards, Kamran Kazem, V.P. Magnetic Design Labs, Inc.

Former Member · Answer

Your exact words describe a perpetual energy circuit, which cannot occur without getting energy from somewhere not mentioned. Your exact words seem to say that you ruled out solar as the primary energy source for recharging what gets used by loads. Was that really what you meant? It is possible to shuffle energy from one battery to another with a little bit of loss. A tiny circuit which can move energy from a 1 to 2 volt supply such as one small battery to charge another 1 to 1.3 Volt battery is found in solar garden lights, to move power at 1 to 40mA from a 1 to 2 Volt solar cell to a small battery during daytime. Those also contain another power circuit to provide up to 10mA at 3V to a white LED while it is nighttime. The circuits inside were globbed under epoxy, so I can't tell what was inside but I'll bet that they contain inductor(s), capacitors and a few transisters, possible similar to the Charge Theif circuit which got a writup online. Those are much too small for serious power appliances but worth looking at if you are studying power management circuits.

Former Member · Answer

Yes it is similar function as the UPS, but the main technology invole is to electronically swap the battery lead to a charger circuit with the means of Microntroller to sence the limit in chargered current and simultaneously swap the charger circuit to the empty battery, I also presumed that the both batteries will continually tied to the load in parallel connection, or will be a good ideal to interchange the Ouputs to a load?. Best Regards.

YT2095 · Answer

If I were to do that, i think I would leave the GNDs (the - terminals) common, and just switch in/out the Positive leads, probably with power relays as a Flip-Flop arrangement. your MCU would then only have to switch the base of a transistor to sink the current required for the relays at the right time (battery charged). edited to add: Thinking about it, you probably don`t even need an MCU at all! if the relays have a set dropout voltage, you can simply set it such that when a battery needs charging it cannot supply sufficient power to a relay, the field collapses and automatically switches in the new battery 5086.contentimage_1.png

Is there any way a battery can charge other battery through isolated Charging circuit powered by a battery?

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