A safer series circuit?

[shortyjacobs]

So I'm really intrigued by all the higher wattage VV circuits I'm seeing. What scares me is the 18650s in series, pushing 10-20 amps. Back in the olden days, when I made OKR-T6 and that TI chip mods, it was two 14500s in series, and I was fine with that, but it was only pushing a couple amps. This is big league.

As I understand it, the issue is the "lead" battery sees more of the load than the "trailing" battery. Thus, they discharge unevenly, and the lead battery has to work more to keep up. The suggestion is to switch batteries halfway, or at least at charging.

What if we could do it automatically?

I have two ideas, but no idea how to implement them, that's where you electronics whizzes come in.

First idea is a circuit that switches which battery is lead battery every time you fire the mod.....I could probably make this work with a bunch of relays, including a latching relay or three, but it seems like there would be a better way with semiconductor solid-state stuff...but in any case, it'd be nifty if you had batteries A and B, and you went FIRE and it fired A-B, then you let go, then hit FIRE again and it fired B-A, and so on.

Second idea is a circuit that switches the batteries to parallel mode when you release the fire button....I diagramed this one out because it's simpler. Basically, you dump the batts back into parallel whenever they aren't firing. The batt with the higher charge will then charge up the lower charged batt....they will even out while they sit in parallel. When you fire the mod, the batts switch into series mode and the sense wire is activated on the buck converter, energizing your atty. How would I do this without a big bulky DPDT relay? Are there "dpdt MOSFETs"?

 

[Bunnykiller]

it called an H-Bridge great schematics are available in the field of DRSSTC ( direct resonate solid state Tesla Coils)

 

[shortyjacobs]

Welp, looked up H-Bridge circuits. Though it's not exactly what I want, what I want is VERY close, so I figured this out:

(Only difference between a "h bridge" and this is I have the buck converter on one of the legs of the h bridge, instead of outside of it.....which means I can't use an off the shelf module, and I have to cobble this together from individual mosfets...damn.)

I also learned that I'll want P-MOSFETS and not N-MOSFETS because the P ones can be run off the same voltage they are controlling, (With a resistor), whilst the N ones need a higher gate voltage than the....uh....Drain voltage + threshold voltage....or something. I also learned I'll want depletion MOSFETS to act like NC relays and enhancement MOSFETS to act like NO relays....

I don't even know if I have the FETs oriented right in the picture above....I got as far as labeling the various traces with what voltage they will be at when the circuit is energized, (S = series and P = parallel)....now I have to figure out if I can even make this circuit work or if I need....uh....voltage boosters or whatever they are called? First I have to figure out what all these different Vs are, (VSG, VGS, VDSS.....digikey hurts my head!)

 

[ADozer]

the other option, would be to use a 2s1p lipo pack (2series1Parallel, standard notation for packs), with a balance plug and balance charter that would balance out the packs as you charged them.

 

[shortyjacobs]

the other option, would be to use a 2s1p lipo pack (2series1Parallel, standard notation for packs), with a balance plug and balance charter that would balance out the packs as you charged them.

Definitely an option, but pure lipos scare me. Seen too many cases of fire with em. I prefer high drain IMR/hybrid batts. Plus, I like the ability to swap out batts.