Charging 24S LiPo with a 12S charger. Is there a simple way?

[Kepler]

I have a 24S 10Ah LiPo setup that I presently charge by removing it from the bike, re configuring it 12S 20AH, and then use a 12S 350W RC charger. This works OK but its a pain to do so I am looking for a way to charge while still in the bike. Looking for the most efficient way of switching the pack to a 12S config and was hoping to use a couple of high capacity diodes to reduce the number of switch points.

Would this work or am just better off biting the bullet and getting a 100V charger?

 

[commanda]

Would this work.....?

In a nutshell..... NO !

You need to use a DPDT (double pole double throw) switch (has 6 terminals) and forget the diodes.
I'll try and explain it, rather than draw it out, scan it, upload image, etc.

Battery 1 is the most negative.
Negative goes to charger neg & controller neg & switch 1 NO.
Positive goes to charger pos & switch 1 NC & switch 2 NO.

Battery 2
negative goes to switch 1 common.
positive goes to switch 2 common.

switch 2 NC goes to controller pos.

switch in the normally closed position, batteries are in series powering the controller.
switch in the normally open position, batteries are in parallel connected to charger.

I'm sure someone has drawn this out & uploaded it here somewhere, years ago.

Amanda

 

[liveforphysics]

I can visualize a way to do it using 3 of Tiberius' clever ideal diodes.

 

[Kepler]

I was reading about those diodes today and was hoping there was a way of doing it without using a multipole switch. Can you sketch something up by any chance? I am sure I am not the only one who has wanted to do this.

 

[texaspyro]

You need to use a DPDT (double pole double throw) switch (has 6 terminals) and forget the diodes.

And make sure the switch has "break before make" contacts. A friend recently built up a similar arrangement. The very nice, very beefy, oh-so-sexy switch that he used did not do this! Flipping the switch basically momentarily shorted everything together... and a not so good time was had by all.

To test the switch connect a beeper between the normally open and normally closed contacts and switch the switch back and forth. Do it slowly, do it rapidly, wiggle it around the toggle point. If you hear so much as a tick from the beeper, beware!

For a double pole switch test each pair of contacts. While you're at it, also test to make sure there are no connections between the poles. A little paranoia now might save you a lot of grief later. There is a lot of crap out there masquerading as good stuff.

 

[liveforphysics]

Just realized my 3 ideal diode method wouldn't allow motor regen unless you added a 4th diode...

I don't have time to sketch it right now, but maybe before bed time in an hour. Or somebody else could sketch it.

 

[commanda]

Texas,

Good point, forgot to mention that. Definitely break before make.

After I posted above, I gave it some more thought. I think you can do it with a single pole double throw switch (3 terminals) & 2 diodes.

Diode 1 goes from charger pos to batt 1 pos.
Diode 2 goes from charger pos to batt 2 pos.

Batt 2 neg goes to switch common.
switch NC goes to batt 1 pos.
switch NO goes to batt 1 neg.
charger neg goes to batt 1 neg & controller neg.

Amanda