Go Down

### Topic: battery charging... (Read 2119 times)previous topic - next topic

#### cjdelphi

##### May 05, 2014, 04:15 am
To simplify thing.... I'm wondering if this method has been used before..

If say you charge a 4.2v lithium battery, if you kept a constant .5v above it's charge level, that voltage differential causes current to flow into the battery, as the battery's voltage rises, the current begins to dip, every 2 seconds or so, charging ceases, voltage stabilizes and voltage taken by the arduino...

The new voltage is now the new voltage of battery + .5v

This should give interesting pulse charge swings to the battery...

I'd apply this to a lead acid battery not a lithium. ...  any thoughts?

#### mauried

#1
##### May 05, 2014, 07:23 am
What do you mean by 0.5v above its charge level?
How are you going to measure the charge level whilst charging?

#### cjdelphi

#2
##### May 05, 2014, 07:53 am

What do you mean by 0.5v above its charge level?
How are you going to measure the charge level whilst charging?

#### nixiebunny

#3
##### May 05, 2014, 07:57 am
Lithium-ion batteries are supposed to be charged with a constant current charger. You are assuming that the internal resistance of the battery will make a 0.5V rise with a suitable current. That is not a safe assumption to make, as it depends on a lot of variables over which you have no control.

You can buy Li-ion charging chips for fifty cents that are designed to do the job safely. Best to use one of those.

#### Paul__B

#4
##### May 05, 2014, 08:45 am

Lithium-ion batteries are supposed to be charged with a constant current charger.

Constant-current, constant voltage.  Or more correctly, current limited, voltage limited.

Indicators can show "mostly" charged when switches from constant current to constant voltage and "fully" charged when current declines to a particular low level.

#### cjdelphi

#5
##### May 05, 2014, 10:59 am
I made a kick ass 5v liom battery charger with arduino safely enough..
Arduino will monitor current and voltage..
Question remains, even if it's 2v above, arduino would modify the voltage based on the battery's voltage after it settles..

In short  just by modifying voltage on the fly, it should allow you to control the charger's current?

#### nixiebunny

#6
##### May 06, 2014, 09:00 am
If you can guarantee that the voltage won't exceed 4.2V per cell and the current won't exceed the safe charging current for that battery (~1/2C), then it should work. I can't pass judgement on your circuit without seeing it, and even then I wouldn't give it a seal of approval. I wouldn't trust software to safely do that work. spend the \$.50 on the chip!

#### cjdelphi

#7
##### May 06, 2014, 11:10 am
I can't pass judgement on your circuit without seeing it, and even then I wouldn't give it a seal of approval. I wouldn't trust software to safely do that work. spend the \$.50 on the chip!

Would not trust software? What do you think runs on dedicated charger chips? :p

#8
##### May 06, 2014, 04:56 pm
See page 5
http://datasheets.maximintegrated.com/en/ds/MAX1811.pdf
Looks like analog control to me.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

#### michael_x

#9
##### May 06, 2014, 05:13 pm
MAX1811 looks fine, but does not look like 0.50 \$

#### nixiebunny

#10
##### May 08, 2014, 04:45 am
It's true that software is used to control some charging applications in consumer electronics. However, that software has a lot of error-checking and testing applied to it before it ever leaves the development lab.

For a person making a one-off gizmo, using an analog charging chip that's guaranteed to work is a safer bet than writing software that may or may not behave properly in some weird condition that you didn't anticipate.

But it's your house that may burn down, not mine.

#### nixiebunny

#11
##### May 08, 2014, 04:56 am

MAX1811 looks fine, but does not look like 0.50 \$

Then use the Microchip MCP73812T-420. \$0.65 in onesies, \$0.40 in quantity.

#### cjdelphi

#12
##### May 08, 2014, 06:14 am
Why would it? I trust my circuit and programming.

It will not charge if under 1.5v or over 4.2, the circuit supplies 160ma.. but that's not what this question is about!

I should be able to control the current by varying voltage on the fly with an arduino... I'll have to try and see

#### tsunamy_boy

#13
##### May 08, 2014, 03:17 pm
Sometimes you should trust another IC instead of using the arduino itself.
Remember that you for some reason make a delay in time, or your IC freezes, or it goes into deep sleep mode, that might be a reason to explode with your battery (because there will be no monitoring).

#### cjdelphi

#14
##### May 08, 2014, 04:12 pm

Sometimes you should trust another IC instead of using the arduino itself.
Remember that you for some reason make a delay in time, or your IC freezes, or it goes into deep sleep mode, that might be a reason to explode with your battery (because there will be no monitoring).

I'm not sure how to argue something that is yet to happen and it runs 24/7 for weeks on end, I trust it more than a smart charger...

Go Up

Please enter a valid email to subscribe