The proper way to carge a rechargeable battery?

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recharged battery.

to charge a

Which one?

Hint: there is no one method that is correct for every battery configuration / chemistry / capacity.

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Rich Webb     Norfolk, VA

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recharged battery.

way to charge a

A "safe" rule: 10% of capacity as charge current. Which results in a charge time of about 10-12 hours.

Safe for common sealed nickel cadmium batteries, perhaps. Bad for lead-acid. Only a bit bad for nickel metal-hydride batteries. Really bad for lithium-polymer.

Etc.

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Tim Wescott
Wescott Design Services

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recharged battery.

way to charge a

I wouldn't recommend that as the charging profile for a submarine's main storage battery. Granted, submarines probably aren't in the OP's problem domain and *usually* C/10 is okay for individual consumer-grade cells. Probably not optimal for a home-brew lithium ion battery pack.

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Rich Webb     Norfolk, VA

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recharged battery.

way to charge a

Each battery chemistry has its own general charging needs, and different battery construction within a battery chemistry can modify those needs.

I general NiCd batteries can be slow charged with constant current; most popular types can be charged indefinitely with a current equal to their capacity divided by 10 hours (i.e., a 2000mAh battery can be charged at

20mA). This is mostly OK, but will lead to slow drying of the electrolyte.

Some NiCd batteries can be quick charged, particularly if you've got a charger that will watch the battery voltage as it dumps in current, and terminate the charge cycle when the battery voltage peaks then starts dropping.

Lead acid batteries need a charge regime where both the maximum voltage applied to the battery and the maximum current are limited. Even with the voltage limit, you have to cut the charge off at some point or risk drying out the battery. If the battery is designed for it you can 'float charge' a lead acid battery almost indefinitely, but the 'float charge' voltage is less than the 'fast charge' voltage. Moreover, the correct charge voltage limit varies with the temperature of the battery

-- which can be different from ambient, if the battery is being charged or discharged rapidly.

NiMH batteries are similar to NiCd, but more delicate.

LiPo batteries are similar to lead-acid, but more prone to damage, and far more prone to bursting into flame if they get seriously cranky.

Etc. Hopefully you get the idea.

Do research, dig, get a copy of "Rechargeable Batteries Application Handbook"

for background, read it, dig some more.

If you find a book that's more up to date than the one above, please let me know.

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Tim Wescott
Wescott Design Services

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recharged battery.

way to charge a

Just add I'm reading that the floated cells are subject to corrosion too :( Volts too high they corrode, too low they sulphate, seems you need temperature compensated float voltage for max life. The old telco style flooded cells were happy with 13.5V for 6 cells. I think 13.7 is better than the old 13.8V for floating SLAs these days, but watch for temperature extremes.

I'd add too that the newer "valve regulated" lead acid batteries operate under pressure (up to 5 atmos.) and can stand or require a little more voltage, there's info on the quality manufacturers' sites.

OTOH cheapie batteries made from your old recycled car batteries can vary quite a bit. Proper charging can be quite involved if they're used for traction batteries, expect an overnight charge.

Yeah, those new Eneloop style (precharged NiMH about 2100mAH for AA) are good, but those high capacity (AA > 2500mAH) are useless unless you have them in high discharge rate toys or frequently used cameras. I still charge them at C/10

Not met one yet ;)

Proper charging info is hard to find. It's an area I have an interest in, some manufacturers are very specific on requirements, others less so. I'm mostly working with SLA (sealed lead acid) batteries.

Grant.

See this

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rom a recharged battery.

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yte.

Yeah that's 13 years old. Still I'll see if I can find a copy.

Say does anyone know where I can find out how many amp-hours are in my lead acid car battery. They list cold cranking amps, but I find nothing about how many amp hours.

Thanks,

George H.

Lead-acid starting batteries are rated in cranking amps and reserve capacity.

Lead-acid deep cycle batteries are rated in ampere-hours.

There may be some way to do a rough translation between AH and reserve capacity. Perhaps you could find the specs for a deep cycle battery in the same case as your starting battery, and assume that the two types would have similar AH capacity - but I'm not sure how true that would be.

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Peter Bennett, VE7CEI  
peterbb4 (at) interchange.ubc.ca  

Starting batteries usually have AH specified, too. You might have to dig some to find the information.

Perhaps within an order of magnitude. There will be no meaningful translation.

...

They list a reserve or standby time instead, since AH rating deemed too hard for mere mortals to understand ;)

Actual AH depends on rate of discharge, I think standby time gives a figure at some agreed discharge rate, but I can't remember the figure.

The standby rate can be found, from there you can work out AH at that rate, then interpolate to what load you want to run. Or, you could measure it yourself, standard method is constant current load X for Y hours down to say 10.5V for 6cell LA. Recharge the battery and try again with different X. Rinse & repeat.

For example I have here a 12V 52AH battery weighs heaps and replacement cost is AU$600, I think it's still at 95% rating (was given to me) -- obviously this thing has far more lead in it than the same physical size car starter battery.

If you are after deep cycle standby battery, be prepared for sticker shock.

Grant.

It's "agreed" to by the manufacturer. There is no standard and indeed there couldn't be since the rate of discharge is application dependant.

No, there is no way of "working" that out. Manufacturers will give different capacities for various discharge rates, however.

Pretty much. ...add a safety margin and you're done. ;-)

Yep. It's a specialty item. You don't get the mass market pricing of a starting battery.

Thanks for the help, Tim. That was quite an informative post. It covered almost all the doubts I had on this issue. Yet, there is one which still lingers on, which is the dreaded "memory effect". I've stumbled on multiple contradictory claims on this issue, with ones claiming that there was no such thing while others defending that it was very real, going on suggesting recharging procedures to minimize this phenomenon.

So, is there such a thing as a memory effect?

I've added the book to my wish list and I plan to purchase it in the near future, preferably if a cheap used version happens to pop out somewhere. It looks quite interesting.

Once again thanks for the help, Tim. Kudos! Rui Maciel

Oh, I though maybe there was some agreement for car starting batteries?

Long time since I looked as my interest is more in the standby and traction area.

That's because they do vary depending on discharge rate, by quite a bit.

Too true :)

Grant.

AH isn't the primary concern for starting batteries. AFAIK, there are standards for CCA measurements.

...and more importantly the construction of the cells. Like all engineering, there are tradeoffs to be made and not all make the same choices. The two parameters cannot be related.

You also get the "marine" adder. ;-)

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Depends hugely on the battery chemistry and any special construction/design limits.

Consult the manufacturer.

Graham