Charging Li-Ion

[AllenInHouston]

Okay, I have a question. I have 4 of these http://sanyo.wslogic.com/pdf/pdf/UF103450.pdf rectangular Li-Ion coming, and I'd like to know the best/safest way to charge them.

Should I purchase some of the chips that are available specifically for this purpose, use the manual-timing method, or is there an easier/better way that's still safe?

Thanks for any input,
Allen

 

[Doug S]

Originally posted by AllenInHouston:
Thanks for any input,
Allen

<font size="2" face="Verdana, Arial">Allen, What resources to you have?
Equipment and level of electronics knowledge/assembly skills?
Are you looking for something KISS for fooling around on your workbench or do you want more of a stand-alone solution where you can just insert a plug into a charging jack on some mod you wish to design and build?

 

[AllenInHouston]

Well, I guess I wasn't puting much thought into this one. I was thinking "2xAA compartment=3v" - the Li-Ion supplying around 4v slipped my mind. That should simplify that part.

I'm still not sure about the charging circuit - I will probably try some sort of Li-Ion based IC to be safe. Thanks for the help.

Allen

 

[N4aeq]

I have lots of camcorder,cellphone,laptop packs
& I remove the individual li on cells,there 3.6v
each.I bought a rayovac li on universal camcorder
charger off ebay for 10 bucks,it charges 3.6 or 7.2 v any current size.
I just picked out two contacts & soldered jumper
leads,it auto senses if its a 3.6 single or 7.2
double.I charged 500ma cellphone packs to 4000ma
laptop cells and all inbetween with excellent
results all for 10 bucks and shipping.

 

[Entropy]

If you don't trust your bench supply, an adjustable linear regulator would work too.

BTW, I would be careful about 1A/cell. While they can PROBABLY handle it, I think it would be safer to limit charge rate to C/4 or less until you feel very comfortable working with LiIon chemistry.

I think National Semi has an eval board for one of their charge controller ICs.

Does that cell you're using come with protection circuitry?

 

[AllenInHouston]

Doug,
I use to assemble drilling tool sensors, and I have lots of little electronics "stuff", so assembly and soldering aren't an issue. I took a bunch of electronics classes, so I have all of the basic knowledge. I even recently came into an old o-scope and benchtop p/s.

Anyway, it doesn't have to be really simple, but I don't want to get a custom PCB fabbed for it. I have a few perf boards, and I don't mind ordering the charging IC's from Digikey if that's the best way.

One project that I was considering was a rechargable flashlight using this old 2xAA Duracell flashlight where the head pivots out and turns on the light at the same time. If I do a little carving, the Li-Ion cell should fit inside the 2xAA compartment with plenty of room for a charging jack and charging and regulation circuitry (thinking of the MicroPuck/Luxeon Star setup).

This wouldn't be my first mod by far, but it would be my first flashlight project.

Allen

 

[Doug S]

Charging a single cell or multiple cells where they are all in parallel is easy. Use your bench PS set to 4.15 to 4.20V unloaded. If the PS has adjustable current limit, set to no more than 1.5A per cell [to be conservative I would suggest no more than 1.0A]. If the PS does not have an adjustable current limit and can deliver more than 1.5A, insert at least .25 ohm in series with the supply/battery. It may be that your leads alone will have enough resistance. The first time you do this, after half an hour disconnect momentarily and recheck the PS unloaded voltage since some power supplies drift as they heat up.
If the reliability of the supply is unknown and/or you wish to be conservative, place battery on a noncombustible surface such as a Pyrex baking dish.
BTW, for your intended mod I don't think the micropuck is the right choice since it is a stepup. If your intention is to drive a 1W Luxeon, just use the battery and a little series resistance. With this arrangement you don't even need to worry about undervoltage protection for the cell.

 

[AllenInHouston]

The spec sheet doesn't mention anything about protection circuitry, but it does spec a charging current of 1400mA at 4.2v. Seems high to me though; I'll start out much lower than that if I use the p/s method.

I do like the camcorder charger adaptation idea...ebay, here I come.

Allen

 

[Entropy]

Originally posted by AllenInHouston:
The spec sheet doesn't mention anything about protection circuitry, but it does spec a charging current of 1400mA at 4.2v. Seems high to me though; I'll start out much lower than that if I use the p/s method.

I do like the camcorder charger adaptation idea...ebay, here I come.

Allen

<font size="2" face="Verdana, Arial">1.4 amps is pretty close to a charge rate of C.

Most Li-Ion batteries can handle this (As many Li-Ion devices I've seen charge in an hour or so), but as I said, until you're very comfortable with charging the things I would be very careful.

C/4 is still a pretty decent charge rate.

BTW - If you suspect that the cell has been overdischarged (Below maybe 3.0-3.2 volts or so), LiIons should not be rapid charged when they are in such a severe state of discharge. At that point, you might want to charge at C/10 or even slower until the voltage is a bit higher. I'm not sure about the exact derating used.

 

[Willmore]

Actually, I'd recommend against slow C/4 charge rates for Li-ion cells. Most I've seen really prefer a 2/3 C to 1C rate. Not more and not much less. Keep in mind that the current limited portion of the charge cycle will be about .8 to .85 of C. The rest will soak in at the voltage limit.

Entropy is right. Be religious in your protection of the voltage limits of your cell! Over or under voltage is death to Li-ion cells. I'm not kidding. Abuse them once and they're dammaged for life. They're the least forgiving battery chemestry.

Please be careful.

 

[MrAl]

Hello there,

First, hello to Edison and Bridgewater!
Im one town over from Bridgewater and
maybe two over from Edison 🙂

Just to add a few notes to the other great
posts here so far...

Li-ion charging is nothing more then
a current limited voltage regulator,
usually with zero reverse current drain
should the input to the charger be removed.

The voltage regulator and current regulator
portion are logically " or'ed " so that either
high current *or* voltage over 4.2 volts will
cut back the charging current.

One way to take care of current limiting is
to use a series resistor. The rating has to
be high enough to handle all of the power
of the power source if the battery is defective
or near zero volts.

One way to make sure the output goes to high
impedance if the input source is disconnected
is to use a series diode at the output and
use high value resistors for the voltage
feedback divider. This way if the input
power goes away the battery doesnt drain back
into the charger or destroy the circuitry.

Good luck with it,
Al

 

[Entropy]

FYI, National Semiconductor has some good app notes for Li-Ion chargers, including a schematic for a charger that uses two of their chips to charge a single cell from a USB supply.

 

[Hemingray]

For single LI-Ion cells (and paralleled in groups up to 5 cells) I have been using a simple home made regulated supply (LM317). Adjust to 4.2V,
the current is limited by the chip (and the 12V
wall-wart transformer) to 1.5A.

This may not be the best or most elegant solution, but I am using "free" cells salvaged from dead Lap-Top battery packs.

Balsa Products sells, for a reasonable price, a little pack with two A sized Li-Ions in series (7.4V @ 1500 mA/H) and a small protective circuit board , all wrapped in heat shrink, and brought out to a short "pigtail" cable with a small Molex type connector. For this one, I set the voltage to 9V and let the battery's own protective circuit take care of the housekeeping.
Balsa Products suggestsusing an existing Radio Shack r/c model pack 9.6Volt NiCD-NiMH charger.

For my couple of still "intact" lap top packs, I use an HP voltage and current adjustable lab bench power supply that I have here at work. I'll push it to 3A max, or 1/2C, and have had good results.

We also use this method to charge lap top packs that we use in the R&D lab, so it is a
proven and safe method.

/ed B in NH

 

[LightBright]

Hemingray, how about a web link to the Balsa Products site, I curious to see what they have.

 

[James S]

I just did a quick google search on them and came up with this:

http://www.balsapr.com/catalog/battNCharge/lithView.asp?ProductId=S459758

Unfortunately it's not in stock at the moment, so you can't order it. They really do recommend charging it from any old charger appropriate for the voltage. So the chip in that pack must be smarter than the average.

I'm thinking that pack running a BB750 and a 5 watter would be a spectacular light...