Li-Ion/Charger mismatch question

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As I have admitted in the past I am still pretty new to the Li-Ion/Li-PO battery and its charging so bear with me.

 

I am evaluating a device that uses the following single cell for power:

http://www.tenergy.com/30036-0

 

It's a pretty standard Li-Ion cell, 3.7v/1400maH

 

 

The charging IC that is on the board is this one:

http://ww1.microchip.com/downloa...

 

The actual part number appears to be MCP73831-2, whose regulated output voltage is 4.2vdc and max output current is 500ma, with a 2k programming resistor.

 

Here is where I get a little stuck.....isn't there a minimum current that needs to be injected into the cell, and arent you not supposed to go over the nominal voltage of the cell?  I believe if you do not adhere to these specs the cell goes BOOM!!

 

With the spec of the battery and the spec of the charger IC are these two mated correctly?  Something tells me they are not a good fit, but I feel better asking someone with more knowledge on this.

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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To charge a battery, you need to inject more than the cell's nominal voltage. In this case, you charge with 4.2V. I'm not sure of the minimum current, but you do need to watch the maximum current when charging. You can charge the battery you note at 1.4A (1C) without too much drama. Going beyond that you need to consider the battery heating up. With the ic you mention, the max current is 500mA, so there's no issue there. So I'd say you're good to go.

With a recent project of mine I was lazy so I just used the cheapy tp4056 boards you can get out of China for $1.50 and did the footprint for it on my pcb. I am using a small postage stamp sized battery of 250mA/h, so I changed the charge resistor to only charge at 250mA. Job done.

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Kartman wrote:
To charge a battery, you need to inject more than the cell's nominal voltage.

That much I know.....My issue is that the IC has several variants that go up to 4.5 volts or so.  Hence I was wondering what the rule of thumb for the charge voltage is.  Can I get away with a charge voltage of 4.5vdc and what would be the gain/loss over 4.2vdc for example?

 

Kartman wrote:
I'm not sure of the minimum current,

Makes two of us

 

Kartman wrote:
but you do need to watch the maximum current when charging. You can charge the battery you note at 1.4A (1C) without too much drama. Going beyond that you need to consider the battery heating up. With the ic you mention, the max current is 500mA, so there's no issue there. So I'd say you're good to go.

That is comforting to know.

 

 

Kartman wrote:
With a recent project of mine I was lazy so I just used the cheapy tp4056 boards you can get out of China for $1.50 and did the footprint for it on my pcb. I am using a small postage stamp sized battery of 250mA/h, so I changed the charge resistor to only charge at 250mA. Job done.

Nothing wrong with that.  I use a regulator board from China with the LM2596 on it.  I can buy the board in lots of 25 for about $15.00 fully assembled.  I cannot buy 25 of the IC alone for that price so do the math.

 

Thanks for the fast reply

 

Jim

 

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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For LiIon batteries, the standard charge algorithm is to charge at a constant current (typically C) until the battery reaches some set voltage (typically 4.2), then hold it at 4.2V for some longish period of time, such as an hour. This second part is referred to as the "float phase"". 

 

Additionally, good quality chargers will try a short term lower current charge to verify that the battery will come up above some minimum voltage before it applies full charge current. This is because a damaged cell that is excessively discharged is not safe to charge unless the terminal voltage comes up after some initial charging. Failure to observe this CAN result in explosive consequences but this is not the only possible cause of explosion. Good quality chargers also limit the amount of time for the constant current phase since a battery that does not fully charge is also subject to explosive behavior.

 

I've always used TI BQxxxx chargers, though I am quite sure that there are now good quality devices from other sources.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

Last Edited: Wed. Dec 28, 2016 - 01:36 AM
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I will look at the TI BQxxxx chargers and compare for phase two of the project.  I was not involved with phase one.

 

JIm

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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You can get 18500s with internal low/high voltage cutoff, e.g. http://powertacusa.com/index.php...

But 18650s seem very common nowadays.

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Just looked at the MCP73831-2, it is a very basic charging solution. + I couldn't find a datasheet for the battery as well. Share if you have it.

 

The standard way to charge LI-ION batteries is as follows :-

 

CC - Constant current

CV - Constant Voltage

 

Two main charging states :- 

 

FIRST :- cell is provided with a CC. The CC charging cycle will keep working till the battery reaches the max charging voltage specified in the battery's datasheet. (In the above diagram it is 4.2V)

SECOND :- After CC charging is done the cell is provided with CV. The cell will keep consuming lesser and lesser current as the time passes. At a threshold the cell's charging current will be too low and at this point we can consider that the battery is fully charged.

 

You need to have Constant current and then constant voltage charging. You might need to add trickle charging stage as well for deeply discharged batteries.. This is to maximize the battery life. 

 

The battery manufacturer will mention the maximum cell charging and discharge rates. Something like 1C or 2C or half C. You can charge your cell at a lower current than what your manufacturer has specified, it is just going to take more time to charge the battery.

 

If you want a part recommendation which takes care of all hassle(Other than TI BQxxxx- they are really good ofcourse) :- Microchip's MCP73871 

This part has pre-charging circuit inbuilt which is useful for deeply depleted cells.

Product page :- http://www.microchip.com/wwwprod...

Demo Board :- http://www.microchip.com/Develop...

MCP73871 Evaluation Board - http://www.microchip.com/Develop...

 

For general information on LI-ION charging read :- http://powerelectronics.com/site...

 

Good Luck

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jgmdesign wrote:
That much I know.....My issue is that the IC has several variants that go up to 4.5 volts or so. Hence I was wondering what the rule of thumb for the charge voltage is. Can I get away with a charge voltage of 4.5vdc and what would be the gain/loss over 4.2vdc for example?

 

DON'T do that!

For every cell chemistry there a very specific cut-off voltage that must never be exceeded and consequently there is no rule of thumb.

The most commonly found cells(both LiPo and LiIon) have pretty exactly 4.2V as maximum. Going to only 4.25V may cause the cell to blow up. And even if it doesn't, it will loose capacity very quickly and those types that are just wrapped in some plastic foil will get puffy.

But you can always charge it to less and enter the previously mentioned CV charge mode earlier. You will however not use the full capacity.

It's always good practice to consult the datasheet or the manufacturers website if available. Which is way too often not the case :(

 

-Patrick

 

 

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

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Good information, thanks

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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So just to clarify, during the initial constant current charge, does the charge algo need to keep current less than max like 1C, AND keep voltage not greater than 4.2, or can it turn the V up to get 1C charging until it gets to max current, THEN it maintains 4.2V? 

 

Imagecraft compiler user

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Ok so the normal procedure is as follows: A discharged battery is connected to a charger. The charger will then deliver a constant current of most usually about 1C. It will do so until these 4.2V are reached. It will continue to deliver this constant voltage until the current reaches zero.

This of course means that any voltage limited constant current power supply can be used as a charger as long as safety features are not needed.

The 1C charging current must no be enforced by higher terminal voltage than the end of charge voltage specified by the manufacturer. Some cells however can be charged at significantly more than 1C, up to 10C is common for high power packs.

 

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

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Its still a little foggy. I have a lion battery that needs charging, rated current is 1A. Lets say it has 2V in it. I hook it up to my bench supply that can go to 30V and 3A. I turn up the volts and at 4.2V I'm only getting .5A so how do I charge at 1A? Only way I can see is to up the volts until I get an amp, and then come back and check the battery volts with charger disconnected every minute until it gets to 4.2, then finish off or maintain at 4.2V. In other words, during constant current charge phase, you can apply more than 4.2V to get 1A charge. Correct? Incorrect?

 

 

Imagecraft compiler user

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Both; it's more that 4.2V before the current regulator.

Adjust the power supply's voltage to the cell's float voltage, adjust the power supply's current limit, standby on the power supply, attach cell, standby off.

2V is low for safety so trickle charge the cell before proceeding with high rate charging.

bobgardner wrote:
I hook it up to my bench supply that can go to 30V and 3A.
0 to 24V, 0 to 3A :

http://cds.linear.com/docs/en/lt-journal/LTJournal-V24N2-02-df-BenchSupply-Szolusha.pdf

25mv to 36V, 0 to 3.5A :

PowerStream Technology

DC/DC converter constant-voltage or constant current for battery charging, supercap charging, LED control, laser diode power, magnet control, PST-DCCP.

http://www.powerstream.com/Product3.htm

 

"Dare to be naïve." - Buckminster Fuller

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Incorrect. These batteries are (usually) built by coiling up two metal sheets with the electrolytes and active layers in between. So if you apply current to it, it will spread along these foils, causing a voltage drop along its path because the metal foil doesn't have zero resistance.

If you now apply more than 4.2V, the portion of the cell close to the terminals sees almost the full voltage because the there has not been much voltage drop yet as the current path was short. And this portion will quite certainly cause trouble.

 

Also, the battery should draw a lot more than 1A if the quiescent voltage is only 2V and you enforce 4.2V at the terminals. It should have only little more than 2V at terminals at 1A (if it is a 1Ah battery) because lithium batteries have very little internal resistance.

I suspect your battery is at the end of it's life or you have significant resistance in the current path. Because it's got only 2V quiescent voltage, I assume it's dead. A lithium battery with 3.7V nominal should never be discharged below about 2.8V, better not below 3V.

You can try to get it back on it's feet by charging it rather slowly. I'd go for about 0.1A until it reaches 4.2V. But do so only in a fireproof environment, it might catch fire in the process!! And until you charged it more than maybe two or three times from now, I wouldn't trust that thing anymore.

And don't expect it to still have it's full capacity if it should work.

 

Edit: The incorrect in this post refers to bob's question, not gchapman's post. Just so I don't anger anyone or come off as condescending.

 

2nd Edit: @gchapman: what is with these product recommendations? If I understood correctly, bob already has a power supply. I mean it's really nice of you to direct people to good deals, but why bother?

 

-Patrick

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

Last Edited: Mon. Jan 2, 2017 - 06:58 PM
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Some great information.

 

In another thread Simonetta posted some links to the Li-Ion cell I am using and I was surprised at the wide range of cell capacities for the 18650 there is...from 1400maH all the way up to 6000maH. 

 

THis one here:

 

http://www.ebay.com/itm/50PCS-58...

 

Seems too good to be true, but for teh price i may order a box just to try it.

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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Jim,

 

I don't know that I would want to test each one to prove its claimed 5800mAHr capacity just so you could demand a refund... maybe you have more spare hours than me. cheeky

 

HNY,

 

Ross

 

 

 

Ross McKenzie ValuSoft Melbourne Australia

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LOL.  No, I have some time on my hands, but not in that capacity(pun intended)

 

The thing is that I may need a large supply of these cells and for $35.00usd it might be worth buying a box of 50 and do a random test batch to see what the run time with a load of say 1 amp would be....even a 80% would be great.

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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@jstampfl

Check your PM's please.

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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Great video.  Goes to prove that if it looks to good to be true  It probably is.

 

I am guessing though that if one stays in the 3000maH and under you should be able to get some decent performance from most cells, but purchasing a few and doing some real world testing tells the tale.

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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Anything above 3600mAh for a 18650 cell is a lie. No respectable manufacturer has ever claimed to be able to do more than that, so these cheap Chinese things won't ever keep what they promise. Usually, these cells stem from old notebook or power tool battery packs. That means not even the seller or the guy re-branding them knows in what shape they are.

If you're lucky, you might just find one that still has a decent capacity. If you're not, these batteries might go up in flames when you try to charge them. I'd be very careful with this stuff.

But if you get them really cheap, it might just be worth the risk. Just charge them in a fireproof environment.

 

"Some people die at 25 and aren't buried until 75." -Benjamin Franklin

 

What is life's greatest illusion?"  "Innocence, my brother." -Skyrim

 

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And make sure that if you do buy them, you pay via Paypal and then demand a refund. Eventually the seller will lose at least on the postage and maybe then be driven from the marketplace. Do the crime, do the time!

 

 

Ross McKenzie ValuSoft Melbourne Australia

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I'm not sure I would buy a battery named "UltraFire"!  Sounds like a premonition or is that pre-ignition to me q:-)

 

 

 

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Well back with some more questions....

 

I purchased six NCR18650B 3.7v 3400mAh cells, and a charger off of Ebay.  THe markings and shrink wrapper appear to be exactly like the ones I see in the actual datasheets etc so I am going on the premise that these are the real deal.  SO all questions are based on these being healthy, authentic cells.

 

I have charged the cells with the charger, and removed them when it indicated that the cells were charged.  I plaed one in a holder I also purchased, and placed a one amp load on the cell and measured the voltage.  Open circuit the cell read 4.175v

 

After I connected the load the voltage dropped to about 4.05v

 

After 20 minutes the voltage dropped to 3.7v

 

After 30 minutes the voltage dropped to 3.4v

 

After 60 minutes the voltage dropped to 3.05v

 

From what I have read the voltage where a Li-Ion cell is considered 'dead' is either 3.0v or 2.5v depending on the vendor.  I am thinking the "dead" voltage for this cell is 3.0v from what I read on the datasheets I have been looking at, but I would have figured I should have gotten a better run time of almost 3+ hours before it hits this point of being 'dead'

 

Is this discharge rate I am observing correct?

 

I have also read that it takes several discharge/charge cycles to get the cell to full capacity.  Is this correct?

 

If I measure the voltage of the cell when I take it out of the circuit it jumps back up to 3.7v so I think I am testing this incorrectly.

 

Can someone clear up some of this confusion for me?

 

Jim

 

 

 

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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The datasheet I find for these cells states rated capacity is 3200 mAh, not 3400, and the cut-off voltage for that capacity is 2.5V.

 

Bear in mind, also, that a manufacturer's stated capacity often omits other important specs needed to make sense of the rating.  Capacity is dependent upon load, largely because the higher the load, the greater the thermal losses within the cell, so the lower the capacity.

 

A one amp load is 0.3125 C.  Although there isn't curve on the graph for that rate, there are curves for 0.2 C and 0.5 C, so it would fall somewhere in there.  The 0.2 C curve shows a 3.0 V cut-off at about 3300 mAh, and the 0.5 C curve shows a 3.0 V cut-off at about 3100 mAh, so I'd guess your curve should hit 3200 mAh.  As such, yes I would have expected a bit more than 3 hours at your 1 A load.

 

As for charge-discharge cycle conditioning of Li-Ion cells, I don't know the real answer.  I know that NiMH and NiCd cells experience that, and I can tell you anecdotally that LiPo cells I've used have as well, but not by a factor of 3.

 

Silly question, are you certain your load is only 1A?

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"Read a lot.  Write a lot."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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joeymorin wrote:
The datasheet I find for these cells states rated capacity is 3200 mAh, not 3400, and the cut-off voltage for that capacity is 2.5V.

 

I am not at the PC I was using for the datasheet I had, but the one from the Panasonic site says something slightly different than what you have:

 

http://industrial.panasonic.com/...

 

Ok, so 3000mAh, 3200MaH or 3400mAh not a big deal at the moment.  What is common on the datasheets posted is that the cutoff is 2.5v.

 

My question is which is the way to measure the voltage for cutoff?  Under load, or no load?  Under load I hit 3.0v and when I pulled it from circuit it jumped back up to 3.7.  THe circuit was running just fine when I pulled the cell so hence my question on is the cell dead at 2.5v under load or 2.5v no load?

 

joeymorin wrote:
Silly question, are you certain your load is only 1A?

 

The Fluke 117 displayed 1.09 on the DC amps scale.  YES I had the leads installed correctly too. wink

 

JIm

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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my question on is the cell dead at 2.5v under load or 2.5v no load?

Ah.  It was late and I hadn't clocked that part of your OP.

 

No load.

 

Some battery conditioning chargers and battery test rigs will do the same, alternately apply a load for a period of time, then remove that load, take a measurement, and repeat.

 

Voltage under load is important also, but not directly for measuring or verifying specified capacity.

 

The curve agrees roughly with your results:

 

 

I've roughed in the yellow area to show where a 0.3125 C discharge curve would end up at 3.7 V.  Looks like you've consumed about 1180 mAh.  Compared to the expected 3200 mAh capacity at that load (3.0V cut-off), that's 36.875%.  With a load of 1.09 A, nominally after 60 minutes you would have consumed 34.0625% capacity, so fairly good agreement between experiment and datasheet.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"Read a lot.  Write a lot."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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Jim, the interwebs is rife with stories of dodgy 18650 batteries. A common trick seems to be resleeving old batteries - and the Panasonics seem to be the favourite to clone. I'd suggest you try to source at least one battery through a legit source and repeat your tests.

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It does seem odd that a 0.3125 C load would cause such a large voltage drop.  It does smell a bit like an old used cell.

"Experience is what enables you to recognise a mistake the second time you make it."

"Good judgement comes from experience.  Experience comes from bad judgement."

"When you hear hoofbeats, think horses, not unicorns."

"Fast.  Cheap.  Good.  Pick two."

"Read a lot.  Write a lot."

"We see a lot of arses on handlebars around here." - [J Ekdahl]

 

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jgmdesign wrote:

Open circuit the cell read 4.175v

After I connected the load the voltage dropped to about 4.05v

This equates to about 125 mOhm internal resistance, which is rather high. As far as I've been able to find, the NCR18650B should be around 40-60 mOhm.

Either you didn't load it with 1A, or you got either used or fake cells.

 

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Lithium batteries do not like to be fully charged.

Check with the manufacturer on charging and specifically holding a full charge.

 

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Well for now I think I will place a call with Panasonic on Monday and get the definitive answer on the models they make and an authorized sales vendor and get the right ones

Then repeat the tests and see what happens

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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Thought I would bring this thread back up, rather than start a new thread and be admonished wink

 

Still getting my head wrapped around this Li-Ion/Li-Po stuff and according to Battery University, and some other Google reads, there is no real difference between Li-Ion and Li-Po for the most part other than Li-Po are made up of a more flexible material hence they can be made flat, or in some other form factor, where Li-Ion generally are cylindrical in form factor.

Am I correct n this observation?

 

I am looking at this Li-Po cell:

http://www.all-battery.com/Tener...

 

Spec Sheet says 3.7v/1700mAh with an 'Initial impedance' of <35mOhms..... INITIAL??

 

But when I go to the Tenergy website I look up the model number and I get this:

http://www.tenergy.com/30052

 

100mAh more, but no mention of the 'Initial impedance'  Otherwise specs are the same other than the weight

 

I am sure I can get these cells cheaper somewhere, but I have noticed that you cannot get a consistent specification from two vendors to match for the same Unit.

 

Very confusing....and to some degree disturbing.  Again, am I missing something?

 

None the less this cell fits my needs for the most part, I think I can use the MCP73831/2 to charge it.  I now need to find an IC to monitor the cell to prevent deep discharge.

 

Am I on the right path?

 

Jim
 

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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Since I'm generally lazy, I try to do things the 'easy' way - here's something similar from spark fun but has built in protection. I used a smaller capacity battery recently and the cheapy tp4056 based charger boards modded with the appropriate charge resistor value.
https://www.sparkfun.com/products/8483
Pay a little more and get the extra 'magic'.
I also found the local model shops have an assortment of lipos mainly for rc helicopters. These also will have protection circuits.
I had a giggle when reading the tp4056 datasheet -the Chinese writer used a thesaurus when translating and used an English word i'd never heard of before to describe a flashing led.

Last Edited: Tue. Mar 14, 2017 - 12:24 PM
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Kartman wrote:
I also found the local model shops have an assortment of lipos mainly for rc helicopters.
I was going to suggest that too...

 

https://hobbyking.com/en_us/batt...

 

About 750 to choose from there. The ones used in RC are the best quality LiPo's as the usage made in RC is "savage" compared to "normal" usage. People are pulling the amps at 20/30/40C rates from these things! They also expect to get 1,000's of recharge cycles from them too. If used in a "normal" application (like 0.1C or even a lot lower) these things will likely last forever.

 

I like HobbyKing (they are the Sparkfun/LadyAda of the RC world) because they are very keenly priced and now have warehouses in most major economies for (relatively) fast delivery.

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Yep... used a few in my designs also... without Thesaurus... google to the rescue.

 

Ross McKenzie ValuSoft Melbourne Australia

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Revisiting an old thread.............

 

Project was on hold for some time, but now is back on the bench.  I am using this cell for project power:

 

https://hobbyking.com/en_us/turn...

 

And have been evaluating this part for charging:

http://ww1.microchip.com/downloa...

 

Which does work, but the charger/manager input voltage is very finicky.  Cannot get rated charge currents unless I have minimum 5.2vdc input - the max for the device is 6v.  In measuring various 5v plug in wall warts for both general purpose, and cell phone chargers they are not well regulated and typically fall to 4.9v with even the slightest load on them, which causes the charger/manager to malfunction.

 

Some Digikey searching brought me to this one from TI:

http://www.ti.com/lit/ds/symlink...

 

Which looks good and from what I see in the datasheet can hit at least 500ma with a 4.9v supply, but unlike the MCHIP product the TI part does not have separate battery terminal pins, or separate output.

 

The issue here is the input voltage.  The device does connect to a PC via USB and the thought was to use the USB jack for both comms and charging - keeping to a 500ma max charge rate, or .25C of the Li-PO cell.  OR I could add another power input port to the device with a step down switching regulator, which then takes care of the voltage issue, but at the expense of a bigger PCB and BOM.

 

I am looking for suggestions for another part to look at that has the same characteristics of the MCHIP part, but can handle an input voltage of as low as 4.75vdc.

 

Thanks

 

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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LTC4059A has a dropout of 200mV max so for a 4.2V float cell would be just greater than the minimum USB VBUS.

Has a simple circuit to switch between USB (500mA max) and wall wart (900mA max)

http://www.linear.com/product/LTC4059

but does not load share.

LTC4155 will load share but it's a buck SMPS during charging (4.35V min for USB VBUS) :

http://www.linear.com/product/LTC4155

 

Edit : LTC4155

 

"Dare to be naïve." - Buckminster Fuller

Last Edited: Thu. Sep 7, 2017 - 07:30 AM
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Just a little FYI; the MCP73871 is used on AdaFruit's PowerBoost 1000C module.

Could be a convenient little evaluation module.

 

Cheers,

Steve

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@gchapman
Thanks for the tips. I will look at those

@sctevo
I purchased an evaluation module from MCHIP, that's how I confirmed the issues with the chargers.

Jim

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

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"Dare to be naïve." - Buckminster Fuller

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My experience with a cheap phone battery from Aliexpress is that they loose capacity pretty quickly.

After less than a year of usage capacity dropped to < 20% of original. Which basically means it's dead.

 

pawi777 wrote:
Going to only 4.25V may cause the cell to blow up. And even if it doesn't, it will loose capacity very quickly

It probably won't explode if you keep the voltage under 4V3 / 4V4 the they are sensitive to overvoltage.

 

Some (most?) of those batteries start loosing capacity if you charge them above 4V1 and this is always a compromise.

Do you want to charge it to 4V2 and get 1000 cycles out of your battery or

do you want to charge it to 4V1 and get 2000 cycles out of your battery, but at the cost of less chare per cycle.

 

I also remember a story of one of those car companies with an electric motor.

They added some solar cells on the roof because ... of marketing reasons?

Even 2m2 of solarcells is probably hardly worth the effort of dragging it around all day, but I am drifting.

They couldn't use the solar sells to (partly) charge the batteries, because those infrequent small charges would damage the batteries in the long run.

And those car batteries do seem to have a life span of 10 years or more...

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

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Jim,

 

curious as we are using the MCP73832. A colleague designed it in and has fully qualified it.

Now we are not using a wall wart but connect it to the PC, but these can be as bad as a wall wart.

 

Which does work, but the charger/manager input voltage is very finicky.  Cannot get rated charge currents unless I have minimum 5.2vdc input - the max for the device is 6v.  In measuring various 5v plug in wall warts for both general purpose, and cell phone chargers they are not well regulated and typically fall to 4.9v with even the slightest load on them, which causes the charger/manager to malfunction.

 

we have not seen any failure, so I wonder what happens. Note that we charge with only 100mA instead of the full blown 500mA that you do, perhaps that is causing problems.

 

The datasheet we have states that you need at least 0.3V headroom for operation, but they also have a couple of cases were they have tested with 1V headroom.

 

 

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meslomp wrote:
we have not seen any failure, so I wonder what happens.

The charger delivers about 75 milliamperes and after several minutes, or up to several hours the error for timer time out/thermal comes on.  I am not using the thermal and I have the Timer disabled by pin strap.

 

meslomp wrote:
The datasheet we have states that you need at least 0.3V headroom for operation,

The datasheet I am reading for mine says 1v above charge voltage required for teh device I am using so maybe yours has better tolerance.  I will check it out

 

JIm

 

EDIT:

I see the difference between the device you called out and the one I am using.  Your device is a battery/cell charger, the device I am using is a charger/controller.  Thats a nice device you are using though, I am thinking of using it in a personal project one of these days.

 

 

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user

Last Edited: Tue. Sep 12, 2017 - 11:28 AM
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Hi Jim, might have missed a bit in the readeing, but you state:

 

The actual part number appears to be MCP73831-2, whose regulated output voltage is 4.2vdc and max output current is 500ma, with a 2k programming resistor.

 

The only difference between the 31 and 32 is the status output pin, that in case of the 31 is an push-pull output and in case of the 32 is an open drain output.

Did I miss a chip change? From what you write it seems to be.

 

from your last description.

charging a 1400mAh cell with 75mA gives a charging time of almost 19 hours.

Might be that although you disabled the timer there still is a safety timer that expires after a while. That timer being based on the cell having to be at least in the constant voltage range within a maximum amount of time.

the 31/32 do not have an error indicator, only an indicator that it either is charging (pin low) or finished charging (pin high). 

note that when charging starts it will always first make the pin low and go to constant current charging. If the cell is full after a short while the cell voltage rapidly will have increased to the 4.2V max at which point the charger switches to constant voltage mode. here the current is slowly decreased until a certain "full" threshold. with a full cell this current will be hit quickly. Then the status pin is made high to indicate the cell is full.

 

 

 

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Meslomp,

 

to address your points:

meslomp wrote:
from your last description. charging a 1400mAh cell with 75mA gives a charging time of almost 19 hours.

And as I wrote in a prior post:

jgmdesign wrote:
Which does work, but the charger/manager input voltage is very finicky. Cannot get rated charge currents unless I have minimum 5.2vdc input - the max for the device is 6v. In measuring various 5v plug in wall warts for both general purpose, and cell phone chargers they are not well regulated and typically fall to 4.9v with even the slightest load on them, which causes the charger/manager to malfunction.

As soon as I hit 5.0 the charge current drops off and when I use the cell phone chargers...the low power ones rated for an alleged 1amp, the input voltage drops to an average 4,8v.  The little Apple chargers hit 4.9v and Samsung hit as low as 4.8.

The high power 2.1amp models are also very dodgy in their performance as well.  The ratings on the label and the real world seem to argue with one another.

 

Datasheet says it all.  My input voltage MUST be 1v higher than my charge voltage for proper operation.  Soon as I hit 5.1 the current went up, and at 5,2 the chip operated as it should.  This does rather stink as I now had to put a second regulator to drop a 12v wall wart input to 5.25v to feed the charger/controller.  I picked 12v because from my testing 12 wall warts seem to be better regulated than 5v ones...and considering where this will be used, one can use a car battery in the bush to charge the device in a pinch.

 

 

I will say this journey has certainly been an education on these things.

 

JIm

If you want a career with a known path - become an undertaker. Dead people don't sue! - Kartman

Please Read: Code-of-Conduct

Atmel Studio6.2/AS7, DipTrace, Quartus, MPLAB user