The proper way to carge a rechargeable battery?

[Rui Maciel]

After searching for information on how to recharge batteries I was left with contradicting
suggestions regarding the proper way to do it and even what to expect from a recharged battery.

So, in order to sort this out, can anyone tell me what's the proper/optimal way to charge a
rechargeable battery?


Thanks in advance,
Rui Maciel

 

[Rich Webb]

After searching for information on how to recharge batteries I was left with contradicting
suggestions regarding the proper way to do it and even what to expect from a recharged battery.

So, in order to sort this out, can anyone tell me what's the proper/optimal way to charge a
rechargeable battery?

Which one?

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

 

[Sjouke Burry]

Which one?

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

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

 

[Rich Webb]

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

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.

 

[Grant]

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.

Just adding to what Tim says:

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.

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.

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.

NiMH batteries are similar to NiCd, but more delicate.

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

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.

Not met one yet

Etc. Hopefully you get the idea.

Do research, dig, get a copy of "Rechargeable Batteries Application
Handbook" (http://www.powells.com/partner/30696/biblio/9780750670067)
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.

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.

 

[Herman]

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" (http://www.powells.com/partner/30696/biblio/9780750670067) 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.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

See this http://batteryuniversity.com/partone.htm

 

[[email protected]]

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

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

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

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.

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

 

[Grant]

....

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.

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.

 

[[email protected]]

...

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.

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.

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.

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

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.

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

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.

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

 

[Rui Maciel]

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" (http://www.powells.com/partner/30696/biblio/9780750670067)
for background, read it, dig some more.

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?

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

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

 

[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.

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.

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

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

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.

Too true

Grant.

 

[[email protected]]

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

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

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.

....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.

Too true

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

 

[Eeyore]

After searching for information on how to recharge batteries I was left with contradicting
suggestions regarding the proper way to do it and even what to expect from a recharged battery.

So, in order to sort this out, can anyone tell me what's the proper/optimal way to charge a
rechargeable battery?

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

Consult the manufacturer.

Graham