Appropriate charger IC or board for single cell LIPO

[boylesg]

If I wanted to include an individual charger for each of these cells inside and enclosure then what would be the most appropriate one to use?

 

[KlausST]

Hi,

As an experienced electronics technician you know that developing a circuit starts with specifications, not with photos.

Therefore find out the specifications for charging these batteries: voltages, currents, charging modes....
Then go to a charger IC manufacturer's internet site and use their interactive selection guide to find appropriate charging controllers.

Klaus

 

[boylesg]

Hi,

As an experienced electronics technician you know that developing a circuit starts with specifications, not with photos.

Therefore find out the specifications for charging these batteries: voltages, currents, charging modes....
Then go to a charger IC manufacturer's internet site and use their interactive selection guide to find appropriate charging controllers.

Klaus

I understand that different manufacturers might have different specifications for rapid charging but surely there are some safe generic charging levels that could apply to all LIPO batteries?

And what of these chargers - they don't specify particular brands of LIPO batteries that can be charged on it. So therefore there must be some reasonable safe charging regimes that can apply to all LIPO batteries.

 

[betwixt]

For cheapness, some LiPO chargers just limit the voltage to a little above nominal (for example 4V for a 3.7V cell) but also limit the current to a low value, say 10mA. They make a compromise between cost, safety and efficiency based on the power being so low that no damage can occur from overcharging or overheating. However, they can take MUCH longer to charge a cell, maybe 24 hours when a controlled charge would take 1 hour. They may not give longest battery life either.

Note the first button on the unit in the photo.

Brian.

 

[boylesg]

For cheapness, some LiPO chargers just limit the voltage to a little above nominal (for example 4V for a 3.7V cell) but also limit the current to a low value, say 10mA. They make a compromise between cost, safety and efficiency based on the power being so low that no damage can occur from overcharging or overheating. However, they can take MUCH longer to charge a cell, maybe 24 hours when a controlled charge would take 1 hour. They may not give longest battery life either.

Note the first button on the unit in the photo.

Brian.

Well that is perfectly acceptable for my application. After all I am not implementing an emergency service drone where time is critical.

In that case it would probably be easy enough to implement a 4V charger with a linear voltage regulator based current limiter wouldn't you say?

And for higher voltage lipo batteries you could surely arrange a circuit where all the individuals cells are in parallel, through the charge balance connector thing, and use the same 4V charger?

- - - Updated - - -

Although I am tossing up where the general risk associated with lipo batteries failing catastrophically is, albeit not all that often, just isn't worth the hassle.

Standard AA or AAA batteries and step down/step up DC to DC converters might be the way to go.

Or possibly the standard 3V lithium camera batteries.

 

[betwixt]

As that is acceptable, I would suggest a regulated 4V supply then each battery individually fed through a resistor. The resistor has to limit the current to no more than a trickle charge rate. For a completely discharged battery to pass 10mA would need a 400 Ohm resistor and a fully charged one about 30 Ohms so you would have to make a compromise of say 330 Ohms. It should be safe but as I pointed out, it will not be optimal for charging or battery life. For best results the current has to follow a profile and the temperature and voltage have to be taken into account.

LiPO should not fail catastrophically if the charge or discharge current is low enough that it can't heat up significantly.

Brian.

 

[boylesg]

As that is acceptable, I would suggest a regulated 4V supply then each battery individually fed through a resistor. The resistor has to limit the current to no more than a trickle charge rate. For a completely discharged battery to pass 10mA would need a 400 Ohm resistor and a fully charged one about 30 Ohms so you would have to make a compromise of say 330 Ohms. It should be safe but as I pointed out, it will not be optimal for charging or battery life. For best results the current has to follow a profile and the temperature and voltage have to be taken into account.

LiPO should not fail catastrophically if the charge or discharge current is low enough that it can't heat up significantly.

Brian.

Thanks Brian - I appreciate the effort you always go to when I post questions.

 

[d123]

Hi,

A couple of short notes on Li Ion charging, enough to give a good idea for the method you want to follow.

View attachment panasonic_precautions_and_safety_notes_for_li-ion_batteries.pdf

View attachment Charging Li Ion VL type AAA4000COL17.pdf

If this is for the irrigation thing, I'd delve into the max. and min. expectable charge/discharge cycles for that circuit, even with a polished charger IC a nominal 1,000 cycles can dip far below 500 - somewhat less than two years life for the battery. Also, if you decide to use a charger IC, pay close attention to how (at what voltage) it resumes charging as that detail can reduce that 1,000 to 500 cycles to something far less adequate, even for a hobby project.

 

[betwixt]

Note that d123's links are for Lithium Ion rather than Lithium Polymer but the two are virtually identical if you follow the method I described earlier.

Brian.