Smart LVC

[Dee Jay]

If we can't have smart cells, could we at least have Smart LVC? Someone here mentioned the very same thing I had in mind, I believe it was DrunkSkunk, in which any cell that hits LVC gets kicked out of the game and the rest of the team plays on running lower voltage. How hard could it possibly be to make a Smart LVC??

Been skimming the web for products like this is all that I found

http://www.rcgroups.com/forums/showthread.php?t=380731

But these guys are flyers that need instant recovery from cell bypass. As Ebikers it wouldn't be a problem.

EDIT:Woops, still trying think how a multiple bypass could work . .

J

 

[safe]

I like this idea.

Yes, we don't need the whole elaborate API and Intel based computer communication protocol, all we really need is the ability to allow the pack to carry on for a while after the weakest cell(s) drop out of the system.

I've been using the idea of controlling the "On State" and "Off State" with MOSFET's but maybe you could do some sort of shunt regulator bypass system to do the same thing?

Maybe the LVC needs just a slight "tweek" to give it that extra edge to make the more elaborate Smart Battery unneccessary. (it's already mostly unneccessary, but this would make it completely pointless) The nice thing about cutting a cell out of the system but allowing the pack to go on is that this allows you more notice that you are losing power. Rather than a sudden cutoff of the whole system you would experience a orderly shutdown.

"Smart LVC"

That's a good name for it too...

Ideally whatever bypass mechanism you use should be recycled so that it's also useful during charging. That way you get perfect charging and perfect discharging all in one package.

It also might be a good idea to increase the voltage at which a cell is cut out. This will extend the life of the weakest cell longer and allow the stronger cells to be used more. It's the continuous overworking of the weakest cell that will wear it out and (we presume) increase the disparity between the strong and weak.

 

[Dee Jay]

Hi safe, good to know you like my idea!

I only thought of this cell bypass system with cells in series in mind. Not sure how it could work on packs with cells in parallel then series though...

Ideally whatever bypass mechanism you use should be recycled so that it's also useful during charging. That way you get perfect charging and perfect discharging all in one package.

That's a fine idea... a "Charge Mode" would be very cool and to keep really simple, you can use the fastest single cell charger available to charge one cell at a time. Just plug the single cell charger to the power leads, set the SLVC in "Charge Mode" and it will:

-bypass all cells except one, the first cell.

-single cell charger gets to work

-3.6v sensor kicks in signaling the SLVC to

-bypass all cells except the second cell

-single cell charger gets to work again

-3.6v sensor kicks in again

and so on

So it's not just a Smart LVC, in Charge Mode it's a Smart HVC

t also might be a good idea to increase the voltage at which a cell is cut out. This will extend the life of the weakest cell longer and allow the stronger cells to be used more. It's the continuous overworking of the weakest cell that will wear it out and (we presume) increase the disparity between the strong and weak.

And that's another fine idea. Having adjustable LVC on each cell would be great for known weak cells so they can "punch-out" early.

One more thing: Remember Doctorbass' cheap cell voltmeter?




http://endless-sphere.com/forums/viewtopic.php?f=14&t=3833

If a tiny thing like that can hop from cell to cell reading voltages, then a Smart LVC can be made in the same way.

J

 

[safe]

Rotating Pulse Charge

I like that idea too...

You could charge the cell with the lowest voltage for one second, then stop, search through all the cells to see which one is lowest now, charge it for one second, then continue on and on until all the cells are charged to their correct full voltage.

I've read that pulsing can be good for some chemistries because it allows the cells to rest a little between pulses. It would be good to investigate to be sure that it's not bad for the particular chemistry you have in mind.

The nice thing about this is that you only need one charger with it's one chemistry specific algorithm.

Hmmmm.... NiMh might not like this though because you are supposed to watch it "tip" over it's peak current and it's when it "tips" that's when you are supposed to stop charging. However, for NiMh you might want to simply use the temperature method and skip the delta approach entirely. Or just forget NiMh and use LiFePO4 exclusively.