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.

[EPAIII]

Re: Relays Between Charger and Battery

The amount of current that an LED uses is very small, probably 10 mA or less. The coils of those relays will consume dozens of mA while they are energized. So, depending on the actual currents and charging times, you may use more power with the relays than without.

A solid state relay may be a better choice. Read the specs.

On the other hand, if you are going to go to the trouble of turning the power off, assumedly by manual action, then why not just use a switch instead of a relay. One double gang switch with high enough ratings to switch the incoming power could also switch the DC output of the charger on a second contact. And there would be no extra power drawn by a relay's coil or a solid state relay's circuitry. On would be totally on, both AC power and DC output. And OFF would be totally off. If you want to completely isolate the DC, you can use a three gang switch.  Win! Win! situation.

If you do implement either the relays or my switch suggestion, please do follow good construction practice. To the greatest extent possible, keep the AC power and the DC as separate as possible in the box. Yes, do use a box. An idea for better separation at the switch would be to use one with another set of contacts. Use the first gang's contacts for the AC. Then connect all of the second gang's contacts to ground. Have a grounded, separator inside the box that is attached to all four exterior faces of the box and that jumps across the switch contacts at the location of the second gang, which is also grounded. That creates two separate chambers inside the box, one for AC power and the other for the DC. A third and possibly a fourth gang of the switch would then be used for switching the DC.

That may be a bit of over-kill, but it would certainly provide maximum safety. Something similar could be done if a relay is used. Coil connections in one chamber and the DC in another, with a grounded separation panel between them.

Modern batteries can hold a charge for months. They can be put on the charger after being used and taken off the next day. They should then be fully charged. And will probably stay above 95% of full charge for at least a week or two. Monday morning, first thing after getting your coffee, go and put all the charged items on their chargers. Then, when you finish that coffee, go back and take them off. They will be OK for use at any time later in the week.

[Psi]

The amount of current that an LED uses is very small, probably 10 mA or less. The coils of those relays will consume dozens of mA while they are energized. So, depending on the actual currents and charging times, you may use more power with the relays than without.

A solid state relay may be a better choice. Read the specs.

yeah, probably will, but the issue is the LED running the devices battery flat. So a bit extra power draw from the mains when charging is a small price to pay.

A latching relay is also an option, if he can find them for a good price. They tend to be costly from legit sources and the cheaper aliexpress ones would need some testing to confirm they are not trash.
Only need 0.5-2A for USB charging, Unless its a phone or something super modern.  I guess if he's go to the trouble to make this system he'd want to future proof it for newer USB C stuff that might be 24V5A

If OP does use latching relays, make sure they are the two coil type, not the reverse polarity type, damn those are annoying to drive vs having separate on and off coils.

[soldar]

Re: Relays Between Charger and Battery

The amount of current that an LED uses is very small, probably 10 mA or less. The coils of those relays will consume dozens of mA while they are energized. So, depending on the actual currents and charging times, you may use more power with the relays than without.

A solid state relay may be a better choice. Read the specs.

On the other hand, if you are going to go to the trouble of turning the power off, assumedly by manual action, then why not just use a switch instead of a relay. One double gang switch with high enough ratings to switch the incoming power could also switch the DC output of the charger on a second contact. And there would be no extra power drawn by a relay's coil or a solid state relay's circuitry. On would be totally on, both AC power and DC output. And OFF would be totally off. If you want to completely isolate the DC, you can use a three gang switch.  Win! Win! situation.

If you do implement either the relays or my switch suggestion, please do follow good construction practice. To the greatest extent possible, keep the AC power and the DC as separate as possible in the box. Yes, do use a box. An idea for better separation at the switch would be to use one with another set of contacts. Use the first gang's contacts for the AC. Then connect all of the second gang's contacts to ground. Have a grounded, separator inside the box that is attached to all four exterior faces of the box and that jumps across the switch contacts at the location of the second gang, which is also grounded. That creates two separate chambers inside the box, one for AC power and the other for the DC. A third and possibly a fourth gang of the switch would then be used for switching the DC.

That may be a bit of over-kill, but it would certainly provide maximum safety. Something similar could be done if a relay is used. Coil connections in one chamber and the DC in another, with a grounded separation panel between them.

Modern batteries can hold a charge for months. They can be put on the charger after being used and taken off the next day. They should then be fully charged. And will probably stay above 95% of full charge for at least a week or two. Monday morning, first thing after getting your coffee, go and put all the charged items on their chargers. Then, when you finish that coffee, go back and take them off. They will be OK for use at any time later in the week.

I am not sure I understand what you say because it makes no sense to me.

A simple relay solves the problem.  The contacts disconnect the load. The coil is activated by the primary side of the charger. When there is no supply on the primary side of the charger the load (battery) is disconnected. It never takes any current from the battery.

[Psi]

I think he was just meaning that it will use more power than it saves, which is true but isn't a problem.
I don't think he understood the issue being solved.