Unplugged charger drawing power, how to solve

[Wnef]

Hello all,

English is not my first language hope I'll be clear.

My question is about chargers left connected to a item they are supposed to charge, but disconnected from mains power.

Let me just explain the context.
I work for a theater compagny, we have a lot of devices wich need to be charged prior to a contract.
Walkies Talkies, smoke machines, ligths etc...
It is often forgoten to charge theses devices leading to problems while working with thoses devices.
A solution was to leave those devices always charging, but I don't think it is good for the batteries, the environement and the electrical bill !
So I tougth about putting the hole charging area on a digital programmable socket with countdown timer for a weekly charge.

I was happy of my system until I noticed that some chargers have a green led still on while mains power (220V) is off.

So here is my question. Is there a simple way to fix it ?
My first idea is to put a diode at the DC output of the charger, but they are charging lithium batteries and I'm worried it could affect the safety of those devices...

Is there a specific term to look for charger that don't behave like this ?

best regards, and happy new year !

[themadhippy]

I was happy of my system until I noticed that some chargers have a green led still on while mains power (220V) is off.

does the light go out if the chargers unplugged from the mains ?as  it sounds like the programmable socket is using a semiconductor instead of a relay and the leakage is enough to power the leds

[Analog Kid]

I have a charger that behaves that same way (LED stays lit when a charged battery is in the charger and the charger is unplugged).

So how long do you leave batteries in an unplugged charger?
If it's a short time then maybe you shouldn't worry. A LED only draws about 10mA or so (maybe less), so it's not going to drain the battery very much at all.

[soldar]

You could easily fit a relay to disconnect the load when no input voltage is present.

[5U4GB]

I was happy of my system until I noticed that some chargers have a green led still on while mains power (220V) is off.

How long had the power been off for when you checked? Some chargers will power an LED (via stored charge in capacitors) for a surprising amount of time after they've been unplugged.

[Halcyon]

Why not just leave the mains power on? They'll stop charging once they are full. Even things like mobile phone won't destroy the battery if left on charge for a long period of time (days, weeks, even months).

[Psi]

Why not just leave the mains power on? They'll stop charging once they are full. Even things like mobile phone won't destroy the battery if left on charge for a long period of time (days, weeks, even months).

For the vast majority of things yeah, the charger won't destroy the battery, it will turn off once the battery is 4.2V and wont turn on again until the voltage has dropped a bit and it needs to be topped up again.
But sitting at 4.2V constantly isn't all that good for the battery long term, but in this case it's probably the best option with the least effort.
Just leave the charger powered on and deal with that tiny amount of battery degradation.

I have come across cheap items where the charging circuit is trash and it absolutely does destroyed the lithium battery in around a month of being left on charge.  I once bought a cheap $20 prepay cellphone as an emergency phone and the battery was trash after around a month on charge.

In this case the equipment Wnef is using is decent quality theater electronics, so it will all have proper charging circuits.
If he does leave the chargers running all the time maybe he should do a one-off check to confirm nothing is getting hot once everything has reached 100% battery. It's a bad sign if there is heat and nothing is charging. Not only because it might be overcharging but because the battery is hot continuously which is very bad.
(I think that's what killed my $20 phone battery, the charging circuit kept the battery hot 24/7)

So I think he should leave it charging unless he want to build some sort of multi usb-cable box with in-line relays to cut the power when mains is off.

[Halcyon]

Why not just leave the mains power on? They'll stop charging once they are full. Even things like mobile phone won't destroy the battery if left on charge for a long period of time (days, weeks, even months).

For the vast majority of things yeah, the charger won't destroy the battery, it will turn off once the battery is 4.2V and wont turn on again until the voltage has dropped a bit and it needs to be topped up again.
But sitting at 4.2V constantly isn't all that good for the battery long term, but in this case it's probably the best option with the least effort.
Just leave the charger powered on and deal with that tiny amount of battery degradation.

I have come across cheap items where the charging circuit is trash and it absolutely does destroyed the lithium battery in around a month of being left on charge.  I once bought a cheap $20 prepay cellphone as an emergency phone and the battery was trash after around a month on charge.

In this case the equipment Wnef is using is decent quality theater electronics, so it will all have proper charging circuits.
If he does leave the chargers running all the time maybe he should do a one-off check to confirm nothing is getting hot once everything has reached 100% battery. It's a bad sign if there is heat and nothing is charging. Not only because it might be overcharging but because the battery is hot continuously which is very bad.
(I think that's what killed my $20 phone battery, the charging circuit kept the battery hot 24/7)

So I think he should leave it charging unless he want to build some sort of multi usb-cable box with in-line relays to cut the power when mains is off.

Very true. I make that assumption based on reasonable quality gear. Of course if it's some cheap, poorly design crap, different options would need to be considered.

[Wnef]

Hello thanks for all your interest ! I'll answer in order

I was happy of my system until I noticed that some chargers have a green led still on while mains power (220V) is off.

does the light go out if the chargers unplugged from the mains ?as  it sounds like the programmable socket is using a semiconductor instead of a relay and the leakage is enough to power the leds

If the charger is disconnected form mains and device, led is off, as soon as I connect it to the device (still not connecting to mains ) the led turns on

You could easily fit a relay to disconnect the load when no input voltage is present.

thanks for the idea. I think I'm going to roll with it, I kind of feel dumb I didn't think about it on my own !!! 

In this case the equipment Wnef is using is decent quality theater electronics, so it will all have proper charging circuits.

Unfortunatly some of my equipment is not good quality.
I've simplified the context to make it quick, but the full story is that we do theater on water not indoor!
we build and pilot weird boats and act on them !
The device wich has the led still on is a handheld smoke machine, very very made in china.
We have in the past bougth expensives handheld smoke machine ( 10x the price ) but due to water corrosion ( salty water will eat everything ) they don't last long and can't justify their price...
On the side note those cheap ones are not as fast to heat up but definitly do the job for the price point.


So considering your advice I think I'll built a relay station that will cut off the connection while in storage mode

[Seekonk]

Most of these chargers have a TL431 sensing voltage and there will always be some current draw from the voltage divider. You could possibly use an ideal diode.  I haven't checked for current draw with these.  Some may not be aware that an ideal diode has to turn off every third of a second for a short time to recharge its power.  At very low voltage differentials, like charging a capacitor with low load, that off time is quite significant.  Delta V has to be more than 0.8V.

[asmi]

LiPo batteries are best stored long term at 50-80% of capacity, and some smart chargers do that - for example charger for batteries from DJI Mini 2 will automatically discharge fully charged batteries to about 70% if they are left in charger for longer than a certain period of time to extend their life and prevent them from "swelling".

[Psi]

LiPo batteries are best stored long term at 50-80% of capacity, and some smart chargers do that - for example charger for batteries from DJI Mini 2 will automatically discharge fully charged batteries to about 70% if they are left in charger for longer than a certain period of time to extend their life and prevent them from "swelling".

Yeah, I think OP needs them charged and ready to use at a moments notice so can't really do any sort of storage charge.

In my expensive doing a storage-charge is much more important for high C/amp LiPo's used in high drain stuff like RC.
It seems less important for low C cells.
Don't get me wrong, it will always degrade any Lithium cell leaving it at 4.2V constantly.
But for high C LiPo's it trashes them in weeks to months.
At least that was my experience flying RC planes/drones. We always had to do a storage charge at the end of the day if we wanted the cells to last.