Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

LPF Donation via Stripe | LPF Donation - Other Methods

Links below open in new window

ArcticMyst Security by Avery

Charging circuit for micro batteries

Joined
Dec 11, 2015
Messages
1,628
Points
113
Electrical engineering isn't my strong point so I have no idea where to go from here. I've got some tiny li-ions on the way, (<80mAh, one is even 65mAh!) and I'm kinda stumped on how to charge them.

At first I thought of using the TP4056, but then saw on the datasheet that the minimum appears to be 130mA. Ideally I'd like the charging rate to be ~1C, but I'm not dead set on that. Does anyone know an available circuit for charging currents this low, I'd like to not have to use a bench-top power supply.

Thanks for any help.
 





diachi

0
Joined
Feb 22, 2008
Messages
9,700
Points
113
I think either of these ICs would do the job.

http://cds.linear.com/docs/en/datasheet/1734lf.pdf

I don't know what your soldering skills are like, this second one may be tougher to assemble into a finished product given that it uses a QFN type package, meaning you'd be best reflow soldering it. It could be hand soldered but I don't fancy trying that. The first chip is SOT-23 and could be hand soldered without issue if you have a little practice hand soldering SMD stuff. If you don't, pick up a cheap practice board like this (link) and give it a go, with a decent iron, good solder and the correct tips it's a breeze. You'll be doing SMD decently well by the time you complete that board.

http://cds.linear.com/docs/en/datasheet/3552f.pdf
 
Last edited:
Joined
Sep 20, 2008
Messages
17,622
Points
113
Electrical engineering isn't my strong point so I have no idea where to go from here. I've got some tiny li-ions on the way, (<80mAh, one is even 65mAh!) and I'm kinda stumped on how to charge them.

At first I thought of using the TP4056, but then saw on the datasheet that the minimum appears to be 130mA. Ideally I'd like the charging rate to be ~1C, but I'm not dead set on that. Does anyone know an available circuit for charging currents this low, I'd like to not have to use a bench-top power supply.

Thanks for any help.
I just ordered a bunch of those for a project
we are working on in the shop.
We bought from this seller because in his listing
he shows what values of a Resistor on the PCB
that needs to be changed to get the Current
you want.

I'd go that route if you don't want to do too
much SMD soldering.... Just change 1 Resistor...:beer:

10PCS 5V 1A MiniUSB 3.7V Lipo Lithium Battery Cell Charging Board Charger Module | eBay

[EDIT]
Just looked at the data sheet and there is a formula
there to calculate the resistor require for Rprog for
the current you want.

https://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/TP4056.pdf


Jerry
 
Last edited:
Joined
Dec 11, 2015
Messages
1,628
Points
113
Thanks to both of you, although diachi I think that's out of my league. Jerry thanks for that eBay link, I'll use that chart and change Rprog accordingly, thanks. :yh:

Edit: actually might get that practice kit, can't beat the price for the experience. Worth a shot at least, especially for just a loonie :D
 
Last edited:

diachi

0
Joined
Feb 22, 2008
Messages
9,700
Points
113
Thanks to both of you, although diachi I think that's out of my league. Jerry thanks for that eBay link, I'll use that chart and change Rprog accordingly, thanks. :yh:

Edit: actually might get that practice kit, can't beat the price for the experience. Worth a shot at least, especially for just a loonie :D

No problem! For sure, easier to get something ready built.

I got that same kit a couple years ago, can't go wrong for a loonie! There's some others ones out there too, just search SMD practice kit. :beer:
 
Joined
Mar 27, 2011
Messages
504
Points
43
Simply using digital/analog Li-ion charger for button cells would do the trick. (Take this for example)

But if you insist for having a dedicated custom-made circuit for your battery, the IC which mentioned above would do the job ;)
 
Last edited:
Joined
Sep 20, 2008
Messages
17,622
Points
113
Simply using digital/analog Li-ion charger for button cells would do the trick. (Take this for example)

But if you insist for having a dedicated custom-made circuit for your battery, the IC which mentioned above would do the job ;)
That is only for Button Cells and it costs ~$11.00 USD.
As I understand it the li-ion Batteries he is getting are
not Button Cells... I could be wrong..
The above PCB I linked to is only ~$0.70 USD. :yh:

Jerry
 
Last edited:
Joined
Mar 27, 2011
Messages
504
Points
43
That's because of his requirement:

  1. To charge <80mAh (65mAh) battery
  2. To charge with about 1C (charging with current of 60~80mA)

The link that you provided is gonna charge the battery with ~1A,
that would means charging the said battery with more than 16C :eek:
Although the selling page said that you can adjust the current by simply changing resistor (but which resistor??)

I'm not a battery expert (yet) but i believe charging the Li-ion battery waaay above its C rating can be dangerous, if not it will degrade the battery quickly.
 
Joined
Sep 20, 2008
Messages
17,622
Points
113
That's because of his requirement:

  1. To charge <80mAh (65mAh) battery
  2. To charge with about 1C (charging with current of 60~80mA)

The link that you provided is gonna charge the battery with ~1A,
that would means charging the said battery with more than 16C :eek:
Although the selling page said that you can adjust the current by simply changing resistor (but which resistor??)

I'm not a battery expert (yet) but i believe charging the Li-ion battery waaay above its C rating can be dangerous, if not it will degrade the battery quickly.
:thinking:..If you read the previous posts and my Linked
Datasheet you will see that the PCB/Chip I suggested
has a resistor named Rprog.
By changing Rprog's value using the formula in that
Datasheet you can change the output current to even
less than 60-80mA....

Jerry
 
Joined
Dec 11, 2015
Messages
1,628
Points
113
Yea, they're cylindrical but not standard. Definitely wouldn't fit into a button cell charger unless modified. They're a capacitor-battery hybrid, being a capacitor form factor but a li-ion composition.

34nir09.jpg
 

Encap

0
Joined
May 14, 2011
Messages
6,113
Points
113
Yea, they're cylindrical but not standard. Definitely wouldn't fit into a button cell charger unless modified. They're a capacitor-battery hybrid, being a capacitor form factor but a li-ion composition.

Did you ask the people that sold them to you what charger they suggest or use?

What sizes are they actually?
 
Joined
Dec 11, 2015
Messages
1,628
Points
113
Did you ask the people that sold them to you what charger they suggest or use?

What sizes are they actually?

Yes, they suggested any standard li-ion battery charger of a suitable current, but did not give me a specific model.

Specs are as follows:

4pcs - Capacity: 80mAh Rate: 10C Diameter: 6.5mm Height: 38mm

4pcs - Capacity: 80mAh Rate: 10C Diameter: 7.2mm Height: 30mm

4pcs - Capacity: 65mAh Rate: 10C Diameter: 8mm Height: 25mm
 
Joined
Sep 12, 2007
Messages
9,399
Points
113
The wonderful thing about engineering is there are many "correct" answers. Since I value simplicity, if it were me, I would use one of the dozen standard chargers I have lying around with a resistor in series to limit the current.

I=V/R
.08=(4.2-2.8)/R
R=~18ohms would be fine.
 

Encap

0
Joined
May 14, 2011
Messages
6,113
Points
113
Yes, they suggested any standard li-ion battery charger of a suitable current, but did not give me a specific model.

Specs are as follows:

4pcs - Capacity: 80mAh Rate: 10C Diameter: 6.5mm Height: 38mm

4pcs - Capacity: 80mAh Rate: 10C Diameter: 7.2mm Height: 30mm

4pcs - Capacity: 65mAh Rate: 10C Diameter: 8mm Height: 25mm

OK if the sellers say use a standard Li-ion battery charger then that would be fine--try it out. Most small inexpensive chargers will take something as small as 25mm and if you wanted stronger contact a conductive spacer --small piece of metal bar or whatever could be used.

You could also just attach 2 wires ---one to the charger's + and one to the - terminals and on the other end solder a small magnet to make contact/attach to the battery poles.

If for some reason you wanted to reduce the charge rate then Cyp's resistor solution is an excellent one
 
Last edited:




Top