Balance charge cradle for 4 x AA NiCad

[oldcelt]

TVM - ordered!

[Mike Sanders]

As the TVM has been ordered that will solve the problem. I don't think it would be too difficult to get a standard 4 cell balance lead and solder it up to the nicad holder in the same way that lipo and life batteries are done. Would work for Nimh also.

[waveydavey]

Is there a charger that would do that Mike, I've had a quick google but can't find any that even mention this.

[oldcelt]

As the TVM has been ordered that will solve the problem. I don't think it would be too difficult to get a standard 4 cell balance lead and solder it up to the nicad holder in the same way that lipo and life batteries are done. Would work for Nimh also.

TVM means "thanks very much"

Your suggestion is pretty much the advice I was looking for to start with!

[oldcelt]

Is there a charger that would do that Mike, I've had a quick google but can't find any that even mention this.

Have a look at Soshine H4 Li-ion NiCd NiMh LCD Digital Intelligent on AliExpress.com

[waveydavey]

Yep get that for single cells. What I can't find is a charger that would do the same based on balance taps as in a LiPo

[oldcelt]

But it does up to 4 cells (batteries) of any mix and adjusts the charge to suit. Unless I'm going totally bananas? Isn't that doing the same job as the jury-rig that Mike suggests?

Sorry, misread the thread - I see what you mean now.

[Mike Sanders]

I haven't actually tried it but my i charger always tells me whether or not a balancing lead is connected. I just expected that it would when set to nicad or nimh. I will have a look tomorrow.

[waveydavey]

I haven't actually tried it but my i charger always tells me whether or not a balancing lead is connected. I just expected that it would when set to nicad or nimh. I will have a look tomorrow.

Don't think it will care whether you've got one on or not as it's not expecting to balance them.

The I charger uses dv for sensing when the cell(s) is at peak voltage, don't think it gives a rats about balancing

[Mark_T]

Hmm.. had a couple of goes at this so far, let's hope this one makes sense once I've finished typing

We can easily balance Lipo packs because of the way the chemistry of these packs works. We can prevent overcharging merely by capping the voltage and just letting the cells take the current they need via the balance wires in the final stage of the charge.

NiMH requires us to force the current through the cells and then stop doing it when we decide the pack is full, but the ways that we can determine how full it is are few and imprecise and difficult to perform on an individual cell in a welded pack. Temperature can be used but it is not easy to reliably monitor the temperature of a single cell when it is being warmed by the cells on either side of it.

Generally, it is easier to feed the pack with a low enough current that the full cells can dissipate the unwanted current as heat while the cells that need it continue to charge.

[oldcelt]

OK guys; correct me if I'm wrong but this is how I see it:-
LIPO packs are nothing more than a group of single cells with connections that enable a smart charger to monitor and adjust charge rates to ensure each cell gets a balanced charge. To supply their power the cells are wired in series in order to achieve the higher voltages required.

Why can't any type of cells be connected in a similar manner (with a specialised cradle) so that exactly the same connectors can be attached to the same smart charger and achieve the same balanced charge result as for multi-cell LIPOs? The smart chargers are already programmed to deal with nicad and nimh batteries after all.

[Grumpy]

FWIW, most decent chargers don't balance lipos by feeding current through the balance wires to 'top-up' the cells. It's actually the opposite. To balance current is actually drained through the balance wire to bring down the charge of the higher cells to match the lower ones, all the charging is done via the main power connector. This is why 'ballance drain current' is so important in the specification of a charger. It is the maximum drain current from any cell and is a measure of a chargers balancing capability.

Why other chemistry batteries dont have or dont need balancing connectors I'm afraid i don't know....

[waveydavey]

OK guys; correct me if I'm wrong but this is how I see it:-
LIPO packs are nothing more than a group of single cells with connections that enable a smart charger to monitor and adjust charge rates to ensure each cell gets a balanced charge. To supply their power the cells are wired in series in order to achieve the higher voltages required.

Why can't any type of cells be connected in a similar manner (with a specialised cradle) so that exactly the same connectors can be attached to the same smart charger and achieve the same balanced charge result as for multi-cell LIPOs? The smart chargers are already programmed to deal with nicad and nimh batteries after all.

You might be right but the fact that you can't (I've yet to find) get a charger to do this makes it either unrequired or unimportant otherwise there would be chargers capable of this. NiCd, NiMh have been around for years so you would have thought there would be the equipment to do this if needed.

I can only speak for my chargers a PL6 and Icharger and they don't expect you to be connecting these chemistries in this way in order to balance them

[Mark_T]

I think the short answer is, if you slow charge NiCad/NiMH they are self-balancing.

If you charge them quickly you can't accurately balance them, but most fast chargers drop back to a trickle charge on completion of the fast charge so if you leave it long enough they will get balanced anyway.

[oldcelt]

You might be right but the fact that you can't (I've yet to find) get a charger to do this makes it either unrequired or unimportant otherwise there would be chargers capable of this. NiCd, NiMh have been around for years so you would have thought there would be the equipment to do this if needed.

I can only speak for my chargers a PL6 and Icharger and they don't expect you to be connecting these chemistries in this way in order to balance them

My logic is this: all equipment using (say) 4 x AA batteries will have an instruction in the user manual to refrain from mixing older batteries with new. That suggests to me that it is important to have 4 cells with the same level of charge to make the best use of the equipment (and probably the batteries). If, therefore, rechargeable AA cells are used, the same logic must surely apply and balancing the charge must be equally beneficial.

I'd have thought that wiring a balance charge plug to a 4 x AA battery holder must be reasonably straightforward in order to use one's universal charger. The batteries get wired in series with the power plug connected across the extreme ends and the balance plug gets a wire from the extreme ends and another wire from each cell junction. That's how lipo packs are wired - see attached image for a 3-cell pack.