Talk:Recharge mod

From S1MP3 Wiki

don't you risk damaging your batteries if you use this? i allways thought that ni-mh and ni-cd batteries must be fully discharged and then fully charged in order to work properly. this would work with li-ion batteries only... --Codertux 13:30, 22 February 2006 (CST)

This is an interesting USB charger, probably uses the LTC4062 or similar. I always thought NiCd's were prone to a "memory effect" if they don't get deep charge/discharge cycles but it turns out to be something of a myth. There's a shed-load of tiny battery charger IC's & circuit links on this site. --JedOi

http://en.wikipedia.org/wiki/Ni-Cd#Memory_effect about the memory effect... i am living proof that it exists... unfortunately... i have a pair of NiCd's that last for less than half an hour (in a flashlight) while others last a lot more...--Codertux 10:04, 2 March 2006 (CST)

Don't do it!

Please do not attempt the "three diodes" recharge mod!

This modification carries a very real risk of overheating, explosion, and personal injury. It is ill conceived and likely to damage the diodes, any AAA cell installed and the player. It could cause damage to the USB device it is connected to.

How it doesn't work...

The three diodes will drop approximately 3 * 0.65V = 1.95 V. Assuming a nominal 5.0V USB supply that leaves the diodes striving to apply about 5.0 - 1.95 = 3.05 V to the AAA cell and to the player chip. Something has got to give.

The NiMH or NiCd cell, if fitted, will absorb huge amounts of energy if you try to put more than 1.5V across it, so it may well overheat, outgas or even explode.

Alternatively if no cell is fitted, and the modified device were connected to a USB source, then a voltage in excess of 3 V would be applied to the player chips and might cause them to fail, again with overheating being a probable outcome.

It is possible that, with a rechargeable cell installed, the series resistance of the diodes would limit the current to non-destructive values, but there is no guarantee. It is also possible hat the USB source will have its own protection and will limit the current supplied to the cell and/or player, but this varies from USB device to USB device. The current limitation feature may be completely missing from some simple USB devices or "USB" mains adaptors. Even if these effects prevent catastrophic failure they will not prevent over-charging and degradation of the re-chargeable cell.

Is there a way?

The only safe modification would be a three terminal charge circuit specifically designed and engineered for recharging a single NiMH or NiCd cell from a nominal 5V supply while obsering ALL datasheet parameters for the components used and observing the USB specification. This would require a willing and competent electrical engineer. Such enterprise should not be taken lightly, witnessed by the fact that these compact low cost players are not so equipped in the first place.

Hum... shall we give up this mod then, DELETE it or leave it there as a challenge for the future electrical enginner who visit this page ? --Wladston 18:20, 30 March 2006 (CST)

Hi, This 3xDiode charger has real problems. It WILL overload the USB power rail. What happens then depends on a number of factors unique to your computer - it may be fine for some, it may permanently damage your computer or explode the battery on others. There is no guarantee it will charge the battery to full or that it will stop charging when the battery is full (ie battery may leak/explode). Normally with a NIMH battery (Dont use NICAD), a diode and a resistor would do. The resistor is chosen to limit the current. If you set the current to 1/10 of the batteries capacity (ie for a 700mAh Cell you set the current to 70mA) then it can be left on charge indefinately without concern of overcharging regardless of the charge level of the battery. (takes a long time to charge though) The BIG WORRY here is that if the battery becomes disconnected (accidentally or by invisible corrrosion of terminals-which is common) then the charger could power the device with too much voltage. Will this blow it up? who knows - depends on the unit. A simple, safe option is a diode, resistor and voltage regulator but the design is not as easy as it sounds as there are only small voltages available - choice of regulator is critical and charging would still be slow (15hr from flat) . bye Electronic Engineer

This Mod. Charger Is Not Risk For MP3Player -

'"Alternatively if no cell is fitted, and the modified device were connected to a USB source, then a voltage in excess of 3 V would be applied to the player chips and might cause them to fail, again with overheating being a probable outcome. "' It,s not cause DAMAGE ! The 5 Volts go to CI regulator too.

Elias Tapxure Netto.

Try to put a smal resistor of 22R / 1/4w in serie with the diodes. this component will droop about 2v with a charge current of 100mA. try use a AAA cell with internall charger. those cells use a internal circuit that control the charge of cell. I use a rayovac ic3 cell.

ps. sorry for my poor english.

Nagendra Pratap Singh

Please see my addition. This has 2 more diodes (total 5) and a resistor added to it. I have uploaded pictures also. Even if no cell is fitted the voltage is 2.2volts. Experience shows that this player can deal with it. I would rather buy a new player than pay over and over for batteries.