Author Topic: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply  (Read 27898 times)

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Offline EEVblog

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How to safely charge Lithium Ion & Lithium Polymer batteries with a bench power supply.

« Last Edit: September 02, 2016, 09:40:06 pm by EEVblog »
 
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Offline PeterL

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #1 on: September 02, 2016, 06:18:23 am »
At 10:15 you say you can compensate for the voltage drop across the wires by tweaking the max voltage. But I think that is a bad idea.

Most charging is done in CC mode, at which point the set voltage doesn't matter. Once it goes in CV mode the current will drop quickly, and so will the voltage drop across the leads. If you had set your PS to 4.230 volt then by the time the cell is full you would in fact have charged it to 4.23V.



 
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Offline Dr. Frank

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #2 on: September 02, 2016, 06:26:29 am »
Nice and instructive video about charging LiPos.

Anyhow, if the max. voltage has to be < 1% of 4.2V, it is no good idea at all to increase the CV setting due to cable voltage drop @ 1.7A in the CC mode.
In this case, that would have been about 34mV, which is already 0.8% of 4.2V.

As soon as the current drops, going from CC to CV mode, the cable voltage drop also decreases quickly, so the battery would see these 34mV 'overvoltage' sooner or later.

Due to this later decrease of the charging current, it also makes no sense at all to give the charging voltage a threshold for this initial voltage drop.

Frank
 

Offline Chipguy

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #3 on: September 02, 2016, 06:30:27 am »
Nice and very helpful advice there  :-+

In 2007 I designed a product that uses this battery:
http://shop.lipopower.de/850-mAh-37V-Einzelzelle-1C-38mm-breit
That battery is pretty much what people would have had in their non-smart Nokia phones back then. Like a Nokia BL-5C battery.

Before deciding to use them I did some extensive testing on those batteries that also involved an ELV intelligent battery charger:


This thing can do charge and discharge cycles and log the data on a PC.

So I did cycle some batteries for weeks and found one interesting thing:
1) I set it to 1C and 4.200V and left it for 2 weeks, the battery lost x% of it's capacity (can't remember the figures)
2) I set it to 1C and 4.100V, also left it for 2 weeks, the battery only lost 1/10 of the capacity it was loosing before.
Of course the battery was only charged to about 85-ish% of it's rated capacity, but that was still good enough for me.
The test was done with 4 batteries at the same time. They all showed the same aging effect.

I am sure the mentioned cutoff voltage given on LiPos is that voltage where they have the highest capacity.
So my advice to those who have a less precise power supply would be: Set the cutoff voltage to that value where the tolerance of your power supply would not exceed the 4.200V.
As Dave said in the video: You can terminate charging anytime.

And to those who want a longer lifetime out of your LiPos: Charge them only up to 4.100V.
This is what the product does and about 7 years after release the first and oldest ones started to trickle in for battery replacement. That is very good for Lithium based batteries. Only about 730mAh are used of the 850mAh but the longer lifetimes is worth it.

The supplier I use sort of confirmed my findings, they charge the batteries to about 3.95 V.
That is supposed to be the ideal voltage to store these batteries, so I have been told.

In the meantime there was a design change and the new battery can now be replaced by the customer.
I was never really happy with the built in solution but back then availability was not that good as today.
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Offline lwatts666

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #4 on: September 02, 2016, 06:36:13 am »
How to safely charge Lithium Ion & Lithium Polymer batteries with a bench power supply.

If you have the monitor option for the DP832, you can set the '<CURR' monitor to sound the buzzer and turn off the output once the charge current drops below the monitor's trigger current.  No need for a timer...
 

Offline EEVblog

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #5 on: September 02, 2016, 07:22:50 am »
At 10:15 you say you can compensate for the voltage drop across the wires by tweaking the max voltage. But I think that is a bad idea.
Most charging is done in CC mode, at which point the set voltage doesn't matter. Once it goes in CV mode the current will drop quickly, and so will the voltage drop across the leads. If you had set your PS to 4.230 volt then by the time the cell is full you would in fact have charged it to 4.23V.

Yes, good point.
 

Offline EEVblog

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #6 on: September 02, 2016, 07:24:00 am »
If you have the monitor option for the DP832, you can set the '<CURR' monitor to sound the buzzer and turn off the output once the charge current drops below the monitor's trigger current.  No need for a timer...

As mentioned, I deliberately didn't use any programmable capabilities as most people will not have this.
 

Offline EEVblog

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #7 on: September 02, 2016, 07:26:58 am »
And to those who want a longer lifetime out of your LiPos: Charge them only up to 4.100V.
This is what the product does and about 7 years after release the first and oldest ones started to trickle in for battery replacement. That is very good for Lithium based batteries. Only about 730mAh are used of the 850mAh but the longer lifetimes is worth it.

There is a lot of research out there on this, but it can vary a lot depending upon the type and manufacturer of the cell and their particular process technology.
But generally, yes, a lower CV value will give a longer life. Well worth it for lots of apps.
 

Offline Faith

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #8 on: September 02, 2016, 08:06:08 am »
Video taken down? Can't seem to view it over here and it doesn't appear on the YouTube channel list either >,<"...
<3 ~Faith~
 

Offline ez24

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #9 on: September 02, 2016, 08:07:11 am »
Slowly I am switching all my battery uses to 18650s.  I have gotten rid of all my C and D cell flashlights and my next item will be a radio that uses 18650s.

I got real excited on a previous post because someone wanted to charge 20 of them in parallel.  It turned out he wanted to charge 20 batteries  :-DD :-DD  and bought a 6 cell charger.  There was a discussion of what "parallel" meant.  Did it mean wires or time.

After all if 18650s are good enough for Tesla, they are good enough for me and I am glad to see Dave do a video on one of them.  Wish there were more videos on them, ie on large packs and chargers.
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Offline RGB255_0_0

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #10 on: September 02, 2016, 08:15:20 am »
Looks like a big hassle over using a TP4056.
Your toaster just set fire to an African child over TCP.
 

Offline Smokey

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #11 on: September 02, 2016, 08:24:29 am »
Looks like a big hassle over using a TP4056.

If I can't get it at Digikey (or at least someone on findchips), I'm probably not going to design it in.  It would be interesting to see how engineers from different parts of the world think about sourcing parts.

And ya, can't watch video.  Private.
 
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Offline skoven

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #12 on: September 02, 2016, 08:27:54 am »
what about protection diode when using the Rigol power supply to charge batteries?

/s
 

Offline hwj-d

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #13 on: September 02, 2016, 09:03:14 am »
Looks like a big hassle over using a TP4056.
Why, if you already have a DP832 ;)
But, yes, got a bunch of these board's and housings cheapest from china warehouse.
Input is parallel, battery output goes to each cell separately, +output for sensing 1,45A together. Load curve works fine, doesn't matter which housing got a cell.
Works fine for me. :-+
« Last Edit: September 02, 2016, 09:07:13 am by hwj-d »
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Offline salviador

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #14 on: September 02, 2016, 09:51:45 am »
Why ??????

 

Offline b_force

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #15 on: September 02, 2016, 11:10:40 am »
As for a timer, I would use one of these wall plug/mains timer units.
They are cheap, and good enough to switch off your power supply.
"If you can't explain it simply (or at all), you don't understand it well enough." A. Einstein

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Online mcinque

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #16 on: September 02, 2016, 11:23:19 am »
What about the issue that PSUs are two quadrant devices and can't sink current/voltage so connecting a battery to their ouput can damage them? I was always instructed to use a diode and to compensate his loss in voltage. Even Rigol suggest this with a safety note.
I'm basically still a rookie and because of this, even with the best intentions, I often say bullshits
 

Offline Brumby

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #17 on: September 02, 2016, 11:29:55 am »
What about the issue that PSUs are two quadrant devices and can't sink current/voltage so connecting a battery to their ouput can damage them? I was always instructed to use a diode and to compensate his loss in voltage. Even Rigol suggest this with a safety note.

If the battery voltage is less than the PSU voltage (which is the only logical scenario) then that isn't going to be an issue.
 

Offline crispus

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #18 on: September 02, 2016, 11:38:56 am »
Why ??????
For a couple of hours it was private. I received an email notification in the morning and only at noon was available
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Offline Zbig

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #19 on: September 02, 2016, 12:01:07 pm »
Dave, at 11:24, you meant "switch to constant voltage" but you said "switch to constant current".
 

Offline ja4

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #20 on: September 02, 2016, 12:06:23 pm »
"How to safely charge Lithium Ion & Lithium Polymer batteries"

 I would not use the word "safely" without measuring (and taking measures against overheating) the temperature of the battery during charging.
 

Offline Zbig

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #21 on: September 02, 2016, 12:07:03 pm »
Why ??????
For a couple of hours it was private. I received an email notification in the morning and only at noon was available

I did not notice Dave's remark that you could just dial the PSU voltage up a bit to compensate for the cable voltage drop. It was pointed out here that this reasoning was flawed and Dave agreed. Probably he's pulled the video for a while to edit this bit out.
 

Offline woox2k

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #22 on: September 02, 2016, 12:09:41 pm »
Video thumbnail has UltraFire 18650 on it but in the video it's not explained that these are deathtraps and should never be used! People might get the wrong idea and start buying those unprotected/sand filled/reused laptop cells 6000mAh 18650's that may blow up at one point.
I have personally seen some of them overheat when charging to a point where my charger cut them off. With this bench supply setup there is no temperature monitoring. After taking the labels off those overheated batteries i saw they were just some old trash picked and very rusty unknown laptop cells that had new caps and UltraFire 4000 mAh label stuck onto them.
« Last Edit: September 02, 2016, 12:15:20 pm by woox2k »
 

Offline Barny

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #23 on: September 02, 2016, 12:17:17 pm »
Its always a good idea to charge lithium cells within a fireproof container.
 
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Offline firewalker

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Re: EEVblog #919 - How To Charge Li-Ion/LiPo Batteries With A Power Supply
« Reply #24 on: September 02, 2016, 12:29:25 pm »
Can you charge it lower C rating? E.g. C/10?

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