Charging Li Ion Batts With Lower than Spec Voltages?

[bullet308]

Hi: Im working on a project where I have a 4000 mAh lithium ion battery that I am trying to rig a solar trickle charger for. I was planning on using a cheapie USB solar charger intended for cell phone use, but when I wired it up, found that it was only putting out about 1.6v. Normally you charge these batteries at about 4.3v or so. What happens when you pump 1.6v into a 3.7v battery that normally charges at 4.3v? Anything good? Anything particularly bad? If the latter, how does this charger manage to charge cell phones that nominally take 5v in?

Once I asked the dean of the local university EE program about how to charge an obscure Russian night vision scope battery. He stroked his greying beard and mumbled something about battery charging being a bit of a dark art...

TIA

[NiHaoMike]

You'll need a boost converter (with MPPT or at least a duty cycle limit) for it to work. Limiting charge voltage to 4.1V (instead of 4.2V) improves the battery lifetime.

[Flávio V]

The battery will feed the output of the charger...that means than it will discharge and the circuit might get damaged if the ICs aren't protected...

[tom66]

If you do manage to charge it to 1.6V, and it stays there for any longer than a few minutes, it will likely be permanently damaged.

[FenderBender]

If you haven't watched this already...

[IanB]

Hi: Im working on a project where I have a 4000 mAh lithium ion battery that I am trying to rig a solar trickle charger for.

You can trickle charge a lithium ion battery (in other words, charge it very slowly), but you must respect the voltage limits, and you must not charge it above 4.2 V. Safely charging lithium ion cells or batteries always requires electronic charge control between the supply and the battery being charged. You cannot simply connect them to an unregulated power supply, solar or otherwise.

I was planning on using a cheapie USB solar charger intended for cell phone use, but when I wired it up, found that it was only putting out about 1.6v.

Then the charger appears to be broken. Cell phone chargers need to supply about 5 V so that the charging circuitry inside the phone can regulate it down. Are you putting it in bright enough sunlight?

(Note that if you are not charging a phone, you will need to provide your own charge control circuit that otherwise would be provided by the phone.)

Normally you charge these batteries at about 4.3v or so. What happens when you pump 1.6v into a 3.7v battery that normally charges at 4.3v?

You cannot "pump 1.6 V into a 3.7 V battery". This sentence is physically and grammatically in error.

Anything good? Anything particularly bad? If the latter, how does this charger manage to charge cell phones that nominally take 5v in?

The charger doesn't manage to charge any phones if it only generates 1.6 V. It is broken or it never worked.