Lithium powered things not charging?

Hi all and HNY.

Daughter recently bought a 'refurbished' Samsumg Galaxy Tab2 10.1" (tablet) and it seemed ok at first. However, the supplier forgot to include the charger. She called them and in spite of requesting a genuine Samsung one, they sent her a generic jobby (and only 650mA).

Along the way (and not helped by the charger thing) she's allowed it to go flat and now it won't charge up again (I've tried various chargers, inc a 2A Samsung one) and after Googling about it looks like this (sort of thing) is a known problem with these Lithium batteries and Samsung tablets (and probably other makes and devices as well etc).

One solution seems to be to pop the back off, pull the battery connector, refit the battery and away it (often) goes but it is also suggested that if you get to that low voltage state again, it will / could lock up again. ;-(

However, one chap on Youtube suggests a more permanent 'fix' by the addition of a small 'bypass' diode and whilst I'm happy to do that (I was a field support guy, years ago and still try to keep my hand in with basic repairs), I thought I'd ask here if it sounds 'sensible'?

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I'm not able to work out where on the diagram he put the diode or if it has any other (negative?) impact. He starts to show the schematics from 4:20 onwards and there are also links to them and the full service manual in the text. Ours is a GT-P5100, as are the manuals he links to but he seems to be discussing the GT-P3100 (the 7" model and may not have the same PCB layout for someone old / simple like me to follow )?

Obviously our first port of call will be the supplier but we didn't want to go though the trouble of sending it back, for them to disconnect the battery and send it back to us, only for it to lock up again later.? ;-(

Basically she was just looking for a 3g 10" tablet that was 'nice' to use and that she could afford and the s/u 10" Tab2 seemed to fit the bill.

Thanks for your time in any case. ;-)

Cheers, T i m

Reply to
T i m
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How long have you left it on charge?

Some items take a surprisingly long time to get enough "initial" charge into them from flat to show any sign of charging let alone being willing to boot ...

Reply to
Andy Burns

A couple of hours (before trying something else). The thing is, the loop it's in (shows charging screen then seems to reboot etc) doesn't seem to be conducive to it even taking any charge? ;-(


Cheers, T i m

Reply to
T i m

You have an unknown source suggesting some vague fix that defeats charging protocols using an unknown "diode" not clearly defined on the schematic to a DIFFERENT tablet made by Samsung, the poster child for lithium battery safety. How many bad signs do you need before you determine that this is too risky??

Not at all clear exactly what he's doing. If he's adding a parallel charging path thru the unspecified diode, I'd suggest that it's a time-bomb. You'd need at least three silicon junction diodes and a series resistor. I would never, ever, suggest that anyone try such a stupid thing.

Another thing that I believe is overlooked. When you modify a device in an unsafe manner, you risk harming yourself and those around you. If you let ANYONE else use it, or steal it, or sell it to someone, you put THEM at a risk that they're not even aware of. If it's sold at your estate sale, all your good intentions to remove the mod are worthless.

Reply to

Seems to me this is best fixed at the software level. Is there a firmware update available, or have you tried contacting Samsung?

Reply to

Potentially yes. He *could* know exactly what he's doing (he looks like he might) but he also may have no idea (so point noted).

Didn't know that, thanks.

Well, to be fair I wasn't going to even attempt anything (if I ever did) until several other avenues had been exhausted but again. I do get your point / caution.

If you have followed his idea and see that's exactly what he is doing then fair enough. If not (and playing devils advocate for a second) then couldn't it (possibly?) be a nifty / safe solution?

Unspecified other than a "a std rectification' diode you mean, or were you still talking about it's roll?

(The other day I fixed an electronic motorcycle speedo for a friend by replacing the remains (through water ingress / corrosion) of some SM diode with a 4001 I happened to have a load of. It seems to work ok but isn't charging a battery of course.)

I do understand your caution so thanks for that.

Understood ... and that's why I asked if anyone could 'vet' what was proposed here. ;-)

Understood ... but I would prefer to see it as 'if' rather that when as not all cases *will* be inherently dangerous (even if they weren't fully considered or technically correct). Like, loads of people have simply unplugged and replugged the battery in such 'non-charging' situations but how do we know if that also isn't potentially bypassing some safety function?

Understood. There are many jobs I could easily undertake but where the thought of something going wrong, even if nothing to do with my input, doesn't bear thinking about ... so I don't. What I call the 'what if' factor.

Just OOI if I may Mike, do you ever buy any unbranded electronics ... phone chargers, cables, battery packs etc? I ask because I understand some of these sort of things are also not built with the same level of safety in mind that we might assume and pay for in some of the (hopefully) better branded kit? (genuine question).

Thanks for your feedback. ;-)

Cheers, T i m

Reply to
T i m

I prefer that idea, that's for sure but to find out I'll need to get some charge in the battery. ;-)

I can't be 100% sure but daughter may have accepted an update or two when she first got the unit but I'm not sure she's remember what they were if there were.

No, I haven't yet because this being a second user device, I felt my first port of call would be the supplier.

I have read many who have contacted Samsung and if it was in warranty they were sent back and repaired or replaced and if out they suggested the customer bought a new one.

I will get daughter to email the supplier for Monday, possibly requesting a full refund and treat her to the difference on a new Tab A 10.1 (with a 2 year warranty).

Cheers, T i m

Reply to
T i m

Charge initially at a very low rate until the protection circuitry sees a voltage higher than 3V from each cell in the battery, then charge normally. If it doesn't take a charge then it's dead.

Reply to
Wayne Chirnside

I don't think I can do that from the 'outside' as it doesn't seem to accept any charge at all. I will try it again tomorrow (when we are here) and see what happens.

I have an intelligent charger than can do all battery types (charge, discharge / balance) but to do that I'd have to get the back off and the battery out.

The suggestion is that even if the unit was 'recovered' that way, there is a good chance it could lockup again, if left to go flat (that shouldn't typically be flat past std external charger recovery).

I have several tablets and all have at some time or another been left 'on' (standby) for some period, gone flat but recharged ok afterwards (so far anyway). ;-)

We will speak to the supplier on Monday and see what they say and if they offer to replace the unit with another (A1 refurbish) that they allow the replacement to go flat to ensure that one recovers ok.

Cheers, T i m

Reply to
T i m

MIGHT? Sure, he might...but he also may catch fire. Are you feeling lucky with your daughter's life? house?

Unless you've been living off the grid you couldn't escape the hoopla over the Samsung Galaxy Note 7 battery fires.

I couldn't tell where on the schematic he put the diode or the type of diode. We could certainly guess the type of diode. If he had the EXACT tablet as yours, with the SAME hardware version and the SAME firmware version and he disclosed the EXACT connections on the schematic and we had specs for all the relevant chips, I'd be much more inclined to give him the benefit of the doubt.

If not (and playing devils advocate for a second)

Possibly. Are you feeling lucky? I suggest that if it's a widespread problem with a solution that simple, you'd read a lot more about it from verifiable sources.

If your car heater is busted and someone suggested that you should put an open container of gasoline on the front seat and set it on fire, would you try it? I'm quite sure you'd be warmer if you did that.

I couldn't tell where on the schematic he placed the diode. The schematic shows the protection chip, so it looks like he may be defeating some or ALL of the circuitry that controls the charging process, possibly affecting the full charge detection. That is an extremely bad idea. Do you think he is likely to more about this than the people who make/use the chip in production?

Another alternative is to bypass the chip and apply some charge to directly to the battery until it reaches the threshold where the protection chip can take over.

There are two serious problems with this. If you just use a diode, you're gonna supply all the current the charger can supply. Maybe that's two amps? Let's say it's only one amp. If the diode voltage is at the max spec, it might be 1.2V. So, at 1 amp that's 1.2 watts and the diode will melt the solder and fall off, landing who knows where.

Second, it's risky to try to recover a lithium battery that's been discharged below the minimum voltage. If you do, you need to use LOW current. The diode provides HIGH current...very bad.

You fix the current with a resistor in series with the diode. Now, you have to worry about maximum voltage. At nominal 5.000V charger voltage and nominal 0.7V diode drop, that leaves you with 4.3V on the battery. That's not good. I've seen chargers with nominal 5.3V at low current. That puts your battery at 4.6V. That's asking for a fire. If the diode overheated, it may be leaky, making things worse.

If you use two silicon junction diodes and a resistor, you start to get into the range of possibility. Three diodes is even better, but then you run into the possibility that the battery will never reach the voltage needed for the protection chip to take over.

THE DEVIL IS IN THE DETAILS. We don't know ANY of the details of the charging circuit or what his mod does. But, we can surely guess.

What is a std rectification diode? How do you know that's what he used? He did suggest removing a random diode from another tablet/phone. If it's a schottkey diode, the voltage is lower and might have significant effect on how it works...maybe...we don't know.

A 1N4001 diode always works, until it doesn't. You had the ability to test the result and determine that the circuit works. I suggest that you haven't the knowledge or equipment to validate a lithium battery charger mod...or you wouldn't have asked the question. Since it's not your tablet, you'll not be around to notice any telltale signs of danger.

Wouldn't be the first time that something seemingly simple and impossible to screw up caused a major screw up. Won't be the last either. Samsung can't even get it right on their second try of the Note 7.

This is one of those times.

I don't think you can tell any more. Paying more doesn't guarantee better stuff. The name is no longer sufficient. Most everything these days is bought from the cheapest bidder. The seller slaps his label on it and charges big bux. The next one you buy from the same vendor may be completely different.

If you treat the tablet and charger as a system, you can save money by leaving out some parts. The manual probably says, "don't ever use any charger other than the one supplied." How many of us heed that warning?

Even if the designer had it all figgered out, that's still no guarantee. I've had situations where purchasing decided unilaterally to change a part to save a few cents. I didn't learn about it until the production line shut down. Just like your example. "It's just a std. diode." Unless it isn't.

I buy almost all my stuff busted at garage sales. I have an electrical engineering degree and 40 years design experience. I almost always get it close enough to right. ALMOST! I once set a laptop on fire while charging the battery. I assumed that the designers had some common sense. I was wrong. The charge current limit was in the external charger, not anywhere near the battery. Label says

19VDC, but if you apply 19VDC, you let the smoke out.

The internet is a very dangerous place. It's a great place to get ideas, but implementation is often lacking. Most people who post stuff haven't a clue. They take a narrow view of the problem/solution. Often it doesn't matter. Sometimes, it sets you on fire.

Get your ideas from the web. VERIFY the solution and do your own math. Implement what you can verify and/or test. Even if you think you know what you're doing, it's extremely difficult to test for stuff you never anticipated or couldn't simulate. We learned that from the design of the Hubble Space Telescope.

Are we having fun yet?

Reply to


Exactly. ;-)

True, but it might not. My point is that unless we know *exactly* how his mod works we can't determine if it is a potentially safe or dangerous one.

The thing is (and subject to the thoughts above), there could be loads of things we use that are inherently dangerous, like tumble dryers or any other battery or charger so it needs to be taken in the right perspective.

Ah that, sure (a mate had one on order but it was cancelled by Samsung).

Well I can do the latter as he tells us in the video. It's a general purpose, SM (ideally for the small size) 2A rectification diode, as typically found on phones and tablets etc. We could certainly guess the type of diode.

Or a tablet from the same manufacturer and series ...

Or that shared a common circuit design ...

It may not be firmware dependant but I do get your points etc ...


Well I believe we have the former as he references the service manual and schematics for the exact same model I have.

Well yes, and such may be out there but how many people are up for opening their devices *and* soldering stuff in?

I think that may be a slight over-exaggeration Mike. ;-)

Ok, that is key information for me.



Are you suggesting that no manufacturer hasn't ever price engineered a solution or made a mistake with the design? Have you never seen hand re-mapped circuit boards, cut tracks or components that were obviously never designed to fit that board? Have you never heard of a product make or model that was known to be unreliable and/or be recalled for safety reasons? Did you hear about the Note 7?

Yes, but as he says, that may not prevent the same thing from happening again (the next time the tablet is allowed to go flat).





Well, my general understanding is that the diode mod 'bypasses' (his words) a part of the circuit that allows for a battery to be recovered from an over-discharged state. Now, it may do so by using the existing charging circuitry but kick starting the detection stage, rather than passing the actual charge itself.

That was why I asked here Mike . In the past people have been able to look at a photograph of a PCB that I have presented and work out exactly how it worked! ;-)

A general purpose device to be used in a known environment. So, if we are talking about a Tablet then we won't be needing a device able to handle 600 volts or 100 GHz.

Because he tells us in the video.



As our guy in the video did ... and all those who also did as he suggested and fixed their tablets?


In this case daughter still lives with us so I probably would.



Ok. ;-)


Yup. ;-(

Well, I'd say we try to because I have been involved with 'electronics' for over 50 years I have probably a better understanding of the rules and risks than many 'ordinary folk' and do take notice of the charger volts and current capacity etc. I have also been playing with rechargeable batteries for nearly as long and still have a road going electric car and designed, built and raced an electric motorbike (raced as it was more 'endurance / range' than racing as such).

I used the word 'played' there because I wouldn't see / offer myself as an expert in any of it.


So was I and it was a big eye opener.

Yes, true, except in those situations where it really doesn't matter as long it 'works'.

We don't have them over here (Uk) but we do have boot sales (Trunk sales?) and Freecycle and the like.

And that's why I am happy to defer to you and many of the 'experts' here because whilst I did 'design' some of my own circuits, I would generally just be following the component datasheets or borrowing bits from similar circuit designs.As a component level bench and field

*support* tech, I was fine as long as I had the schematics, scope, iron and test gear. ;-)

I like to do similar and hence why I often ask advice from those who know. Whilst my version will often work, it may not be the most efficient design. That said, I have provided feedback to others (who were designers) who have consequently modified their designs because of my input (the last was a 4 way battery charger switcher where a failed relay could allow two 12V to become connected in parallel. My design mod meant that it would always fail 'safe'. ;-)

Not done that ... yet! ;-(

What do they say about 'assumption' Mike. ;-)



Ok. ;-)

Yup ... that's exactly what I was doing here. ;-)

We did indeed.

I think so, and learning / reinforcing stuff at the same time. ;-)

I spoke to daughter when she came in last night and I will probably contact the supplier with her on Monday and start the returns ball rolling. In light of this 'issue' I think (as I mentioned) offer to put the difference towards a brand new tablet for her, as at least our investment would be protected for the next two years.

Cheers, T i m

Reply to
T i m

All the books are telling me that there's a critical minimum discharge voltage that going under damages the cell.

Anything worth having should have a UVLO circuit to prevent that happening - I'd take it back and tell them its not fit for purpose.

Refurbs usually only have 90 day warranty - so get your skates on.

Reply to


And most good devices do of course, however, they may only be protected from everyday full discharge conditions, not being left uncharged indefinitely (battery self discharge)?

That was the plan but there is now an update (and some egg on face).

Recap: Daughter ordered the refurb Tab2 after my suggestion because of the cost, and there wasn't much about that was also 3/4G ready (and network unlocked).

It arrived very quickly and when she unpacked it it *appeared* they had just sent the tablet, charging / data cable and the two pin Uk charger plug adaptor, not no charger itself.

So, because it came with some initial charge she was able to play with it and confirmed it would do what she needed. It seemed to accept some charge using other USB chargers (we have many) and that was that.

She didn't want to take it out till she had a decent case so put it to one side and ordered an Otterbox defender that took a while to go though. She mounted it in the case, tested that it still worked and put it aside again.

In the meantime she had contacted the supplier re the missing charger and they quickly sent a generic (only 650mA, not the Samsung 2A) one though.

I tried the charger but only saw the charging loop issue (and it was too flat to turn on by now) and no other charger seemed to make matters any better, including a genuine Samsung 2A one that came with a Samsung phone.

Then I did some Googling and posted here, assuming the tablet had gone into what appears to be a known under voltage / loop state.

I then contacted the supplier, went though what we had done so far and they emailed her a courier collection / returns document and I went to pack it all up ready for collection. As I picked up the Samsung box, I felt something moving inside that felt heavier than the Uk plug adaptor pins but when I opened it up there was nothing (other than said adaptor) to be seen, however, when I lifted up the blow moulded layer I found the genuine Samsung (5V 2A) charger underneath!

So, I plugged it into the Tab and lo and behold it started charging properly (the gold battery icon stayed on screen for a good time), however, the plug didn't seem to seat fully?

Upon close inspection it looked like there was something laying across the bottom of the socket and I carefully removed it it appeared to be a 5mm length of softish plastic that could have come from the Otterbox or been there all the time (and part of the issue)?

So, at this time we are keeping the tablet 'under observation' and will discharge it completely to make sure it continues to recover ok (although if it recovered from the previous depth of discharge there is no reason it shouldn't ... *unless* it's an intermittent problem.

Anyway, I thought I'd relay what actually happened in case it helps anyone else and thanks to all who replied. ;-)

Cheers, T i m

Reply to
T i m

Try it with a genuine charger for the tablet.

An iPhone charger may not charge an iPad.

iAnythings seem to shut off before going totally flat. I don't know about others though.

--- sam

Reply to
Samuel M. Goldwasser

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