is it safe to use the player while it is charging???
 

is it safe to use the player while it is charging or will it lose battery life in general?

man_utd , general battery care would advise against using the battery power whilst it is charging.

Personally i feel it does not really matter that much. Since the player is not a high-drain equipment, the amount of power drawn is relatively little. And thus insignificant effects on the battery or player.

man_utd, I agree with "lattesurf" and usually do run my players while charging and seem to have no ill affects. If you are watching video though the charge will take longer than usual.

as an electronics student..o advice that you may use the player when charging, only if the player's battery has the right amount of charge in it..so if the player is completely drained and charging you may want to wait at least 30 mins for you to use because using it immidiately will lessen the battery life in the long run..you may not notice it but actually the battery life will be much longer than expected..l..the point is the battery must not be stressed while using it..

Re: is it safe to use the player while it is charging???
 

There would be no harm in charging the battery and using the player at the same time. In fact, it would actually be better for it.

Lithium-ions have no charge memory and no scheduled cycling is required to prolong the battery's life. They also have a low self-discharge rate meaning that they can set on the shelf for a long time without losing charge. Many batteries (dry cell, lead cell, nicad, NiMH) have a cell voltage of 1.5 volts or less. This means that you have to use several cells in series to get enough working voltage. Lithium-ions have about 3.6V per cell. This means you only need 1 cell for many mobile devices including these players. They are also not as environmentally toxic as other batteries are.

However, they are not a deep cycle battery (full charge to no charge to full charge). To prevent this, a protection circuit is built into the battery pack. The protection circuit limits the maximum voltage of the cell during charge and prevents the cell voltage from dropping too low on discharge. I have not taken a player battery apart to see if it has the circuit in there or not. I just assume that it is since this should be standard practice. The circuit could be on the player's circuit board also. The maximum charge and discharge current on most packs are limited to 1C on smaller batteries (ipod, cell phone, etc.). 1C does not relate to temperature. C is the C-rate (Charge rate).

C-rate explained

The battery on mine is 250ma.
This means that it can supply 250ma for 1 hour. That is a 1C.
It could supply 125ma for 2 hour. That is a .5C
If it could supply 500ma for 1/2 hour, that would be a 2C rate.

However, if the protection circuit is designed correctly, it should limit it to only 1C. This works as a current regulator for the battery and prevents it from being discharged too quickly causing deterioration of the battery.
Once the battery can no longer supply the required amount of current, the voltage starts to drop. I don't know if the protection circuit detects low voltage or low current, but the result is the same; the battery gets shut down to prevent it from being totally discharged. This probably also protects the firmware too. Low power could cause who knows what to happen to it. The firmware must detect low power before the protection circuit does because the player will shut itself down instead of just dying when the protection circuit kicks in.
If this is the case, then the battery's protection circuit may not be needed for low power and some sort of current limiter could be on the player board to stop high current charging. I have not looked for something like that and I don't feel like taking the player apart now.

All this protection and 1C stuff also applies to charging (which was what this topic was about in the first place).
The 1C protection should not allow a charge current greater than 250ma in this case.
My wall charger says 200-300ma output, which would make sense.
The amount of current supplied by the usb gets a bit more complicated. The usb specification says that 500ma is the max output for a usb port coming from your computer. The usb supply (on the mobo) also has a protection circuit which trips around 700ma - 850ma depending on the design and will try to reset in about 100ms.
Software can also cut power to the usb. XP will shut down the port and pop up saying that the usb port is overloaded.

If you put a non-powered hub on your usb port, each device connected to it will no longer get a max of 500ma. They will only get 100ma max (I believe that is regulated by the hub). However, if your hub is plugged into an external power supply (wall wart), the hub should be able to deliver 500ma to each of the connected devices.

Just because it can supply 500ma does not mean that the battery has to use all 500ma. Your house may have 100 Amp electrical service going to it, but that does not mean that your house has to use all 100 Amps. It only draws what it needs just as your player and battery do.

With these precautions in place, the possibility of metallic lithium plating occurring to the battery (which would be a bad thing) due to overcharge is virtually eliminated.

If the player shuts down due to low power, it can be powered back up as soon as the usb connection is made. The usb can supply at least 100ma and maybe as much as 500ma, which is more than the player needs to operate, so the player runs totally off the usb with power left over to charge the battery.
We know this because we can see the charge level go up even when the player is being used, but it may charge more slowly depending on the max current that the usb can supply.
Some rough math says that if a player will run for 3 hours with a 250ma battery, then 250 / 3 = 83 or 83ma would be the current draw of a running player. Of course the number varies depending on what the player is doing (video, music, volume, display on, etc.)

The slower a battery is charged, the better it is for the battery.

This brings us back to my opening line: Then again, I could be totally wrong. :lol:
More about Lithium-ion batteries.
More about C-rate

Re: is it safe to use the player while it is charging???
 

A very informative read, thanks. It gave me a lot of useful info I was needing to know about these types of batteries. It also raises a couple of questions:

People have reported the cheap chargers that come with their mp4 players have melted their batteries. If the Li-Ion batteries have built in limiters, why would this happen?

For USB charging, does the 500mah limit mean you can't full charge Li-Ons with a capacity greater than 500mah via the USB? Are you for any reason better charging your player via the electrical outlet than the computer's USB?

michiganjfrog , as the name suggests, cheap chargers and cheap batteries sometimes do not come with a cut-off circuit. And continues to charge the battery even when it is fully charged. Thus causing an over-charge.

A normal USB port can supply a maximum of 500mA, lesser if you use a USB hub. mA (milliAmpere) and mAh (milliAmphere hour) are different, a battery with example 700mAh capacity simply means that it is able to supply full 700mA of current in 1 hour. This does not mean that the USB is unable to charge the full 700mAh capacity.

Re: is it safe to use the player while it is charging???
 

After I did my last post I thought of something. If you have a brand new player with a battery that has no charge at all on it and it was connected to a non-powered usb hub, it might need to be charged a bit to stop the player from turning off since the player would detect a battery which is too low because the hub could not put out enough power at the start of the battery charging. However, I would like to believe that in the factory they would have had it running and charging for a while to test the player and put the demo files on it. If they didn't at least fire the player up, how would they be able to format it and put that wonderful memory hack in it? When I got my player, it was near a full charge.

The current draw of a charging battery starts off high and decreases as the battery becomes more charged.
You can charge a battery with a capacity larger than 500mah off the usb. Probably much larger. However, if the battery tries to draw more than 500ma during charge, it would cause the usb port to be shut down by windows or the protection circuit for the usb might just trip and then reset over and over again, limiting the current. If this were to happen, placing a current limiting resistor between the usb and the battery would fix the problem.
A charging source always has to have a higher voltage than the battery has. It's sort of like the current falls downhill from the higher voltage charger to the lower voltage battery. If the charger voltage is less than or equal to the battery voltage, the battery can't get charged (no current flow). A battery on charge will draw the most current when you first start to charge it. As it gets charged, the current demand will decrease.
The wall adapter is soooo cheap that I don't think it has any current shut down protection circuit in it other than RF1 which is explained later on. So if the battery wants more current than it can provide, it will cause the charger's output voltage to drop. As the voltage drops, so does the current demand of the battery. Once the current demand decreases to a point that the charger can supply, the voltage stabilizes. Over time, the current demand will go down and the voltage will start to climb back up to a normal state.
So yes you can charge a large battery, it just takes longer. A 1000mah battery will take 4 times as long to charge as a 250mah one. This assumes that the same charger was used to charge each battery and that the charger was able to put out as much current as the battery wanted. Otherwise it would take longer than 4 times.

Could be urban legend, coincidence or cheap chargers.
I assume that the battery has some sort of current limiting protection. I did not verify this.
The chargers are a cheap POS. I found one like mine for $3.82 http://www.pchub.com/uph/laptop/480-...rger-Kits.html
I took it apart to see what was in there. It comes open by removing one screw under a sticker between the folded down ac prongs (mine is a US model so I don't know what other countries' look like).
Before you go taking yours apart, make sure you have it unplugged. If it is plugged in, there is enough power to knock you on you butt.

As I suspected, it contained a switch mode power supply. You could use a linear power supply (like a wall wart), but that would be more expensive and as we know, they want to make these things as cheap as they can. A linear supply would also be bigger and heavier.

I found a schematic for a supply which is fairly similar to our type.
http://www.coilws.com/images/Switch%20Mode/3R6W_ckt.gifThe way it works is the AC power comes in on the left side. As you can see, it doesn't really matter if it is 110 or 220. No modification needed for different countries equals bonus cheap.

RF1 (called R1 on my board) is a resistor that is used as a fuse. If too much current goes through it, it will get smoked and kill the power to the rest of the charger. My resistor is 4.7 ohms. I would not say that it is in anyway a max charge limiting device. Rough calculations show that the charger would have to put out 1300ma for it to smoke. I doubt that there is any way that it could actually put out that much power. It looks like R1 would only get toasted if a "catastrophic" failure occurred within the charger.

The next part of the circuit, from RF1 up to C2, is the rectifier and filter circuit. It converts the AC to DC.
Not low enough for our China men. The coils L1 and L2 are eliminated. They are filters. Coils are relatively expensive parts so they got left out. Note: The maker of the schematic is the supplier of L1, L2 and T1.

U1 is a small semiconductor chip which uses the DC to run as an oscillator. It produces high frequency energy which goes through T1 (a transformer), since it is high frequency and low power, T1 can be very small, light and cheap. As the power comes out the right side of T1, the voltage is now lower.

D5 converts the AC back to DC. (Yes, we have gone from AC to DC to AC to DC.)
L2 (not in mine), C5 and C6 are filters to condition the DC power.

U2 is an optocoupler semiconductor which is used to send a feedback signal to U1. This works with the oscillator and helps to regulate the charger.
Like the coils, U1 and U2 are relatively expensive. So let's not use them. Yes, you heard me. They saved money by replacing them with two really cheap transistors.
With the money they saved, they splurged and put on a red and green LED. They never told us what they mean, but they look cool.
The schematic doesn't have the LED's or the resistors that go along with them.
Even though my board has those extra 4 parts, it still has less parts and cheaper substitute parts than the schematic has.

If I made an actual schematic of my board, I could tell a lot more, but making them is a pain so I choose not to.

Is this the worst charger in the world?
Not really. It's pretty typical of this kind of charger. Your computer power supply, tv, monitor and many other things use switch mode power supply circuits. They just put out more power and have better filtering and regulation.

If I had my choice, I would rather use my quality computer power to charge the battery than a $3.82 POS.

jctoad is right about the lithium charging process..i was talking aboput lower end batteries..and the circuit is good..actually it is using a FET as a regulator/protection.

well one more thing,,the charger i have has a red and green LED..well the red one simply says the charger is plugged and the green LED is well lit when the player is almost drained and dimmer if almost charged..well my charger is different from you and my charger doesnt go too warm but charges fine..guess what it was china made..he3