Originally Posted by Max

Andre, does this work with charging too?

I have one of these gadgets:


Most of my packs are 2200, not all are the same brand. I am assuming I can charge either brand of the same capacity. Can I mix capacities as well? Ie 1800 in one and 2200 in the other?

Originally Posted by stegl

If you are convinced that you are right ; all the power to you but my twin will be using matched Lipos (cells , capacity and c- rating). I prefer to keep 'em fly'in .

Originally Posted by Spitball

The principle of storing energy is totally different in a capacitor to an accumulator, be it Pb, Cd or whatever, I'm afraid.

Originally Posted by Dangaras

Batteries are large capacitors. Capacitors hold charge as do batteries but for far shorter periods because of the internal design.

Take two different cells and parallel them. When discharging them monitor the voltage of each cell with a battery monitor and you will see the individual cells will maintain their voltages.

Capacitors have a characteristic called ESR which is the effective series resistance that acts in the same manner as the C rating of a battery. Basic electrical theory 101, when you place two capacitors 10uF & 90uF in parallel the values add to give you a total of 100uf.

Capacitors also have a voltage rating, V that determines the maximum voltage that they can be subjected to. So capacitors must have the same V rating when placed in parallel to withstand the voltage of the circuit, like batteries the V is the exact same & different ESR values will cause different discharge rates like using different C rated batteries.

When two capacitors are placed in parallel, and a voltage applied, they both charge to the Voltage level they are rated to (for simplicity sake, usually a little more), but they hold different amounts of energy. The same way that batteries are charged EXACTLY as a capacitor is except batteries convert a chemical to store energy, when you apply the voltage, the capacitor will absorb as much charge as it is is defined by the following E= 1/2(C(V^2))
Learn more at http://community.myelectrical.com/wi...apacitors.aspx

And when you apply a load to use the stored charge, the load does not see 2 sources it sees one. Both capacitors will discharge according to the charge they have stored regardless of the mismatch. In the background the capacitor with the lower charge capacity will be fed by the higher capacity cap, but the load will continue to receive the full current as demanded.

A high resistance or open cell is less critical in a parallel circuit than the serial configuration but the parallel pack will have reduced load capability and a shorter runtime. It's like an engine running only on three cylinders. An electrical short would be more devastating because the faulty cell would drain the energy from the other cells, causing a fire hazard.

WARNING:

Charging and discharging lithium-ion batteries

Lithium-ion batteries are safe when used as directed. The same safety cannot be assured if individual cells of unknown nature are connected in series and parallel to build a battery pack. Not all lithium-ion cells are suited for muli-cell packs. Only cells that meet tight voltage and capacity tolerances can be used for serial and parallel connection. Mismatched packs are subject to overcharge, resulting in venting with flame and fire. Check with the cell manufacturer if the cells are suitable for multi-cell packs.

Originally Posted by stegl

Sorry but running two diferent capacity batteries in parallel or in series is definitely a NO-NO ! One question ? How does the 2000 mah know to only supply 1/3 and the 4000 mah pac know to only supply 2/3 of the power ??? They don't . The same amount power will be withdrawn from each battery so when a total of 4000 mah is taken out ; the 2000 mah pac will be empty and the 4000 mah pac will still have 2000 mah in it. As you continue to draw power , what was the 2000 mah pac will become toast . That's my story and I am sticking to it .

Originally Posted by Max

It is a top flite kit.
The wings are all sheeted except the nacells. Fuel tanks are already installed.
The fuselage is done, but you have to appreciate the cavernous fuselage for batteries

I know going to electrics for me is an afterthought. I am still on the fence given your suggestions. Just scroll down a few posts and see about a fella asking about a motor combo for making his TF DC3 electric. After looking up the specs for him, I had to pause and go Hmmmmmm.....

On mine the flaps and retracts are installed, and all wing control functions are direct servo links

Originally Posted by Dangaras

There will always be some sort of imbalance from cell to cell, however, you can put a 2000mAh battery in parallel with a 4000mAh battery to get 6000 total as long as they are rated the same voltage and discharge.. If you lose 1 cell of say 6 from 2 packs that are 3 cells each in parallel, you are still able to fly, if you lost 1 cell of a 3S pack in an isolated pack situation, you would lose an engine..

For simplicity they will discharge in the following way, the 2000 mAh battery will supply 1/3 of the required current and the 4000mAh will supply 2/3 of the current as long as they maintain the exact same voltage, then if one drops below the other (which it never will because they are in parallel), the higher one will make up the difference until it's charge is equalized.

It is way safer and better than running two separate packs. I am converting a twin now that was initially setup the isolated way, the pack that runs the receiver and hence servos always hits the low voltage warning before the other pack & that has caused me to learn to fly on one engine a couple of times..

All of my twins are wired this way where I cant get a single larger pack to fit somewhere convenient.