Hello,
Yesterday i got one of those wireless charger add-ons that you add to your phone.
The coil plugs into the USB port and the coil part sits flat against the underside of the phone. When the coil gets close to the transmitting plate, the phone beings to charge. The spec was 15 watts but it only charges at about 9 watts max, but that's not the real problem.
The real problem is that the coil never stops drawing current even when the phone is fully charged. The current stays at about 300ma. That means the coil is being heated with about 1.5 watts of power which means it gets warm. I would say it even gets very warm and stays that way all night long. The silicone phone case acts as a heat insulator too so the heat mostly goes into the phone back, where the battery is. Needless to say, it keeps the battery warmer than it should be when not being charged.
The problem seems to be with the thickness of the case material. The case is silicone about 1/16 inch chick, which unfortunately ends up between the coil and the charging plate. That means it adds distance between the transmit coil and the receive coil. Distance is very important in magnetic circuits, and even this small distance makes a difference.
If i take the case off and allow the receive coil to rest right on top of the charge plate the current will drop to around 90ma which isnt to bad even though the phone only draws 30ma or so with the regular wall wart (no wireless). If i add two or three index cards between the charge plate and the receive coil the current goes up. This confirms that the reason for the current is because the case keeps the receive coil too far from teh charge plate top.
At first this doesnt sound too bad, but when you feel the back of the phone you can note that it should not be that warm. Sure if you are in a cold environment that could actually help the battery, but with normal room temperature it is not good because any extra heat shortens the life of the battery and also increases the self discharge. How much is hard to tell, but the warming of the battery is not good and besides that it also eats up power when it should not require any power or very little.
But even still that' not the only problem.
This other problem is somewhat secondary but could be very important depending on how the phone USB port is to be used in normal operation. The problem is that once you plug in the receive coil, it takes up the only USB power on the phone, so you can not plug in a USB drive or keyboard or mouse or anything else. If you think you can just unplug the receiver coil to get the USB port free again, guess again. Once installed it is difficult to unplug the coil because the case cover it so you would have to take the case off first, then very carefully try to grab the USB connector of the coil to pull it out, and that is not easy because they designed it so that it is nearly flush with the bottom. That's very good if you never intend to remove it, but bad if you do because it takes time and effort to get it out.
I could probably put up with the loss of the use of the USB port but i cant put up with the extra heat. The batteries on new phones are not removable (or at least not easy at all) so it is harder to replace once it goes bad.
My guess is that when the designed the receive coil they tested it when it was on the back of the phone but with no case. The only way to get that to work is to glue the receive coil to the back of the phone, or use tape. That really puts the USB port out of use forever, but if you dont need it you would be ok and the extra heat would be minimal (almost no heating).
So in conclusion, you may be able to use one of these but only if you dont use a case and dont need the USB port for anything else.
A question that comes up is, could there be something wrong with the transmit charge plate? Perhaps it just can not sense the charge cycle is over and therefore keeps supplying current.
If anyone else here uses one it would be good to ehar from you.
Thanks and take care.
Yesterday i got one of those wireless charger add-ons that you add to your phone.
The coil plugs into the USB port and the coil part sits flat against the underside of the phone. When the coil gets close to the transmitting plate, the phone beings to charge. The spec was 15 watts but it only charges at about 9 watts max, but that's not the real problem.
The real problem is that the coil never stops drawing current even when the phone is fully charged. The current stays at about 300ma. That means the coil is being heated with about 1.5 watts of power which means it gets warm. I would say it even gets very warm and stays that way all night long. The silicone phone case acts as a heat insulator too so the heat mostly goes into the phone back, where the battery is. Needless to say, it keeps the battery warmer than it should be when not being charged.
The problem seems to be with the thickness of the case material. The case is silicone about 1/16 inch chick, which unfortunately ends up between the coil and the charging plate. That means it adds distance between the transmit coil and the receive coil. Distance is very important in magnetic circuits, and even this small distance makes a difference.
If i take the case off and allow the receive coil to rest right on top of the charge plate the current will drop to around 90ma which isnt to bad even though the phone only draws 30ma or so with the regular wall wart (no wireless). If i add two or three index cards between the charge plate and the receive coil the current goes up. This confirms that the reason for the current is because the case keeps the receive coil too far from teh charge plate top.
At first this doesnt sound too bad, but when you feel the back of the phone you can note that it should not be that warm. Sure if you are in a cold environment that could actually help the battery, but with normal room temperature it is not good because any extra heat shortens the life of the battery and also increases the self discharge. How much is hard to tell, but the warming of the battery is not good and besides that it also eats up power when it should not require any power or very little.
But even still that' not the only problem.
This other problem is somewhat secondary but could be very important depending on how the phone USB port is to be used in normal operation. The problem is that once you plug in the receive coil, it takes up the only USB power on the phone, so you can not plug in a USB drive or keyboard or mouse or anything else. If you think you can just unplug the receiver coil to get the USB port free again, guess again. Once installed it is difficult to unplug the coil because the case cover it so you would have to take the case off first, then very carefully try to grab the USB connector of the coil to pull it out, and that is not easy because they designed it so that it is nearly flush with the bottom. That's very good if you never intend to remove it, but bad if you do because it takes time and effort to get it out.
I could probably put up with the loss of the use of the USB port but i cant put up with the extra heat. The batteries on new phones are not removable (or at least not easy at all) so it is harder to replace once it goes bad.
My guess is that when the designed the receive coil they tested it when it was on the back of the phone but with no case. The only way to get that to work is to glue the receive coil to the back of the phone, or use tape. That really puts the USB port out of use forever, but if you dont need it you would be ok and the extra heat would be minimal (almost no heating).
So in conclusion, you may be able to use one of these but only if you dont use a case and dont need the USB port for anything else.
A question that comes up is, could there be something wrong with the transmit charge plate? Perhaps it just can not sense the charge cycle is over and therefore keeps supplying current.
If anyone else here uses one it would be good to ehar from you.
Thanks and take care.