Hi guys. I have a device driven by 3xAAA batteries but would like to use a rechargable lithium battery instead. I really don´t want to open up the device every now and then changing batteries. So, what are my options here? I can´t seem to locate a 4.5V Lithium ion battery anywhere. Can I use a bigger battery maybe and then have some sort of module that keeps the output voltage around 4.5? I´d also like to have some charging/full charge LED indicator. Help much appreciated //Quizz
Rachargable NIMH will only be at 4.5v for a very short time once charged. A single cell lipo when charged is 4.2v Care should be taken when charging though.
It will be 3.6V, and it's plenty. His device probably ACTUALLY consumes 3V. If it consumed 4.5v, then rechargeable batteries wont' even works, as they are 1.2v
Hmm... The device uses regular AAA so I guess It can work with less than 4.5V Do you have other suggestions? I don´t want to open the device everytime the batteries runs out EDIT: It would also be great if I could charge the device though USB
Ok, i might do that. Can you explain why Lithiums are such a pain? Also, I´ve never used NiMh before. Should I go for an 4.8V(closest I found) battery then maybe? And can you add an charge/fully charged indicator somehow? //Quizz
I'm by no means an expert (TBH, I know ****all), but Li-ion batteries are very complicated and require constant balancing otherwise they will last a very short time. Fine if you want to buy a pack yourself, but if you want to make a battery of cells or modify them in some way then it's going to be very difficult. NiMH are a bit heavier and suffer from the memory effect (also, I've just read they have quite a high rate of self-discharge) but are simpler and safer.
You can get low self discharge NiMH such as Sanyo Eneloop. A 4.8v NiMH will be 4 normal cells in series, which will of course show over 5v when fully charged. If the current of the circuit is low enough you could use a zener diode as a regulator to prevent too much voltage being presented to your device. Charging NiMH is much easier than Lithium cells as Lithium cells tend to blow up if not charged properly.
Thanks for the info! So NiMHs shouldn't be charged unless almost completed? How do I know if the current of the circuit is low enough? Another thing. Let´s say I have a NiMH 4.8v 220mah battery, would it be possible to charge it from a USB port?
Ideally you'd have a bit more voltage headroom to charge four cells so the 5v of a USB connection would not be sufficient for four cells in series. It would be ok for charging two in series twice. You still have to be careful that you restrict current as USB current will kill batteries if not turned off once the batteries are fully charged. I doubt you need to worry about voltage regulation as devices do allow a range of voltage and half a volt here or there will unlikely be a huge issue. Also if you are only thinking of powering with a 220mAh battery you'd better hope your device doesn't draw much. Chargers will ideally be constant current until their voltage rises to a certain point and then switch to contant voltage. You can do both with LM317 but as for how to set a circuit up you'd have to check up on that. Using the device while charging could be problematic too. 220mAh is a very small capacity battery. That's in the region of a 9v PPM battery capacity. 4x AA cells would give >2000mA in comparison.
We carry a couple of products that would help, specifically for LiPos really. The Li-po riders are battery charge management boards with boost outputs, so you can use it as a USB charger with up to 5V output. Don't know if they'll do what you need but as another option http://www.phenoptix.com/products/l...-manager-and-power-booster-for-solar-projects
