After I have charged my spare lithum-ion camera battery I like to leave it in the charger with the mains disconnected.
(It's a handy place to keep the battery.)
In that sort of setup, would the disconnected charger still provide a circuit which slowly discharges the battery?
Most any manufacture will state in the instruction manual to NOT leave batteries in a charger. Leaving them in will do as you suspect, slowly drain them.
Yes.
Maybe, but probably yes
Contact the manufacturer of the charger. MOst of the times the instructions not to leave them in the charger assume that it is still plugged into the AC power line
Modern battery chargers do NOT EVER overcharge. They have monitoring circuitry. It is YOU that is doing the assuming.
So, one should not leave them in a NON-energized charger as that WILL deplete them. Leaving them in an energized charger will do no harm, as the charger tapers to nil once the charge condition is met, and resumes higher charging voltages when the criteria for charging is met. Whenever a charged battery goes in, nothing happens (charge wise). When a non-charged battery goes in, the charge cycle begins. There are typically two monitors in a modern charger, and two pairs of cells or two single 9 volt batteries can be charged at the same time, while each pair is separately monitored. Once the charge voltage is reached, that charge circuit goes into an idle watchdog mode.
So the battery in an energized charger will remain "topped off". The non-energized charger will deplete a battery.
Well, to be *pedantic*, your (following) description also makes assumptions. :-/
This depends a lot on the design of the charger. If the load (battery) sits behind a diode (a P-N junction is some form) then there is always reverse leakage. But, this can be very small and, depending on the battery chemistry (speaking generally), can approach the self discharge rate of the "battery" itself.
A charger could also isolate the load from the charger with an "ideal" switch. For example, a relay (I use this in some of my designs as it is a much safer design approach -- though not geared to the "consumer" market)
A charger can also capacitively couple the load to the charger (think: "pulsed charging").
I.e., if and to what extent the charge "WILL deplete them" can't be stated (without ASSUMPTIONS) unless you know specifics of the particular charger.
This also assumes some knowledge of the *particular* charger. Most *modern* chargers do this. But, you can't state that for a fact...
...nor can you ASSUME this, either. Some chargers will neither "float" the battery nor resume charging when/if the battery's state falls back to "in need of charge". This seems to be especially true of newer chargers -- once they determine the battery is "charged", you have to remove the battery and reinsert it to "reset" the charger (charging cycle). [N.B. doing this also seems to force many chargers to *further* charge a battery that they had -- moments earlier -- decided was already "fully charged"]
See above. :<
See above.
Its not plugged in so the circuit isnt complete, you would have to run your own tests to see what happens.
On Tue, 06 Oct 2009 21:40:32 +0100, Paul wrote in :
It all depends on the battery and the charger. Some are safe that way and some are not. Check the documentation.
It is not plugged in, so THAT AC input circuit is not complete.
The circuit that battery is attached to may well be "complete enough" to trickle drain the battery.
You need to continue your education. Hopefully, in a field other than electronics.
Could the charger have some sort of isolating device such as a capacitor in the charging circuit and thereby prevent discharge of the li-ion battery when the charger was not energized?
Batteries are DC, capacitors block DC, so that won't work. Really cheap chargers for less fragile NiCD, NiMH, and lead acid batteries use a diode to provide both rectification and isolation. In either case, a transformer provides isolation between the AC line and the battery.
Generally Li-ion chargers use a mosfet to control current to the cell, and in multiple cell packs there are multiple mosfets to allow individual control of each cell. Li-ion batteries are notoriously fussy and require careful monitoring in both charge and discharge to keep the voltage, current, and temperature within a relatively narrow window. At any rate, when the charger is unplugged, the mosfets will be off, and present essentially an open circuit. Some Li-ion cells even have their own charge/protection circuitry built into each cell. These can be charged using a simple current limited power source and by nature are connected to their charger all the time.
For those curious about the chargers, check out the datasheets for some of the common charge controller IC's out there. Texas Instruments, Intersil, and Dallas/Maxim among others have a number of products in that category.
Probably an effect which is no more than the effective self-discharge of the lithum-ion battery pack, and so nothing to worry about providing you don't leave there for months with no use.
If you leave the charger plugged in and it's a good quality charger, it may periodically do a top-up charge to counteract this. OTOH, it might not be a micropower standby product, and there's always a minisule extra fire risk (probably significantly less than from the lithum-ion battery itself though).
*Pulsed* chargers can work this way. However, even caps have leakage currents so a discharge path still exists through the capacitor. If you really want to eliminate the discharge path, use a hard switch.
A capacitively coupled DC charger? Sounds a bit more than a little unlikely.
Nonsense. It would have to be greater than no connection at all.
Shelf life discharge is pretty slow. Slower even than a few microamps of discharge would be.
Lithium batteries have negligible self discharge. Unfortunately they do wear out just sitting there whether used or not, more quickly than NiCD and NiMH cells do.
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