very basic questions on mains plugs for rechargable batteries

[electrifying]

I needed replacement plugs for rechargeable batteries (eg from mobile phone devices) and had heard alot of alarming statements (no pun intended) on general related websites, all telling me to avoid third party adapters that had an incorrect or higher output in voltage or current than what a device required, as this could potentially wear a battery out alot quicker if the output does not match the device completely-or even be dangerous. I have some questions that I hope someone out there can help me with:-


1-I needed a replacement adapter for a mobile phone. It is rated at 3.7V 1000mA, yet a popular unofficial mains charger that I bought for it online, is rated as having an output of 5V 1200mA. Is this safe to use? I have been told that the minimum mains output is often usually 5V minimum-is this true?

2-Another rechargable mobile device requires 5.2V 450mA and can also be charged via USB on a computer, but one unofficial mains adapter thats stated to work for it, is found to give out 5V 900mA. Again is this adapter safe with a ever so slightly lower voltage and much higher outputted current?

3-Would an adapter giving a higher voltage to the device, be less safe than one giving a higher current than the device, or does a device with a rechargeable battery for both voltage and current only ever take whats needed? If a mains plug could be dangerous to a rechargeable device, eg giving out a far higher voltage or current, would this difference have to be far greater than what the device required (eg either twice of whats needed)? Both plugs output as dc, for these devices which are also labelled as dc.


Sorry for the lack of knowledge and multiple questions for what may be something of not much importance, but I suppose this is what this forum is for, and would prove to be something worth knowing for future reference. thanks for any help

 

[simpson93]

sorry not the most knolagable guy myslef but pretty sure al these small apliances will have a zener diode to limiting voltage

but i really do have to ask why did you just not buy the ones which you knew would work??

 

[Richard Burns]

I would generally recommend that you keep the supply voltage the same as the original charger, though a slightly lower voltage may work, i would not think it ideal to try to charge a battery significantly above its intended voltage.
The current rating of the chargers are the maximum current they can supply, not the actual current supplied and so when charging the battery the current would be that required by the battery. The only problem you may have is if the battery is very flat the charging current could be very high initially and overheat the battery pack, however this would also overload the original charger so is unlikely.

 

[MarkieSparkie]

Hi, Welcome to the forum. Sound advice from Richard. Mobile phone chargers are usually unregulated and the charge regulation and/or timing controlled by the phone itself but it is dependant on the charger designed for it. If a different charger is used with a high output voltage, that excess voltage will either result in the battery pack getting hotter than it was designed to do and hence a shorter battery life as a result. In extreme cases the battery gets so hot it fries the phone electronics. Or if the voltage is regulated by the phone charge control it will make the charger run hotter than intended, the charger should be protected by a thermal fuse but often cheap units omit this leading to very hot chargers initiating house fires in extreme cases.

 

[electrifying]

thanks for all the replies It sounds like both of these third party replacement chargers should be relatively safe from what everyone has mentioned. My initial concern was with current-the adapter of the second device giving out twice the mA than required, but if all modern devices only ever take what is required, then that adapter should be safe. One website had stated that a mains adapter with a far higher current might wear the rechargeable battery out faster, and that was what got me into posting in the first place.

The first device (3.7V mobile) also has a USB charger lead. Its mains charger gives out a higher voltage (5V), and I think USB also gives out 5V as standard, so just over 1V more than necessary shouldnt be a problem regarding safety if its USB compatible. Im wondering how high a voltage could be before entering any danger zone to damage the product, but I imagine this may vary alot depending on the device type/stability etc.

I will also take into account the one-off chance of a battery possibly being very high in current initially and potentially overheating an empty battery pack, especially concerning the second 450mA mobile using its unofficial 900mA mains adapter. Hopefully the adapter is stable and the initial current wont ever be too high to cause damage to the device or its battery (if the quality of the adapter would be the main link to this ever happening?). Cheers