On Sat, 07 Jan 2017 19:56:38 -0800, mike wrote:

On 1/7/2017 1:25 PM, T i m wrote:
On Sat, 07 Jan 2017 11:48:01 -0800, mike wrote:

snip

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,

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).

MIGHT?

Yup.

Sure, he might...

Exactly. ;-)

but he also may catch fire.

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.

Are you feeling
lucky with your daughter's life? house?

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.

the poster child for lithium battery safety.

Didn't know that, thanks.

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

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


How many bad signs do you need before you determine that this is too
risky??

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.

Not at all clear exactly what he's doing.
If he's adding a parallel charging path

If you have followed his idea and see that's exactly what he is doing
then fair enough.

I couldn't tell where on the schematic he put the diode or the type of
diode.

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.

If he had the EXACT tablet as yours,

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

with the SAME hardware version

Or that shared a common circuit design ...

and the SAME firmware version

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

and he disclosed the EXACT connections
on the schematic

Ok.

and we had specs for all the relevant chips, I'd be much
more inclined to give him the benefit of the doubt.

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

If not (and playing devils advocate for a second)
then couldn't it (possibly?) be a nifty / safe solution?
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.

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

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

I couldn't tell where on the schematic he placed the diode.

Ok, that is key information for me.

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.

Ok.

That is
an extremely bad idea.

Agreed.

Do you think he is likely to more about this
than the people who make/use the chip in production?

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? weg

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.

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).

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.

Understood.

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.

Understood.

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.

Understood.

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.

Understood.

THE DEVIL IS IN THE DETAILS. We don't know ANY of the details of the
charging circuit or what his mod does.

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.

But, we can surely guess.

That was why I asked here Mike g. 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! ;-)


thru the unspecified diode,

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

What is a std rectification diode?

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.

How do you know that's what he used?

Because he tells us in the video.

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.

Understood.

(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.

A 1N4001 diode always works, until it doesn't.

;-)

You had the ability to test
the result and determine that the circuit works.

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

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.

Agreed.

Since
it's not your tablet, you'll not be around to notice any telltale signs
of danger.

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

snip

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.

Quite.

Samsung can't even get it right on their second try of the Note 7.

Quite.


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.

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.

This is one of those times.

Ok. ;-)

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).

I don't think you can tell any more. Paying more doesn't guarantee
better stuff.

Exactly.

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.

Yup. ;-(

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?

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.

Even if the designer had it all figgered out, that's still no guarantee.

Ok.

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.

So was I and it was a big eye opener.

Just like your example. "It's just a std. diode." Unless it isn't.

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

I buy almost all my stuff busted at garage sales.

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

I have an electrical engineering degree and 40 years design experience.

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 almost always get it close enough to right.
ALMOST!

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'. ;-)

I once set a laptop on fire while charging the battery.

Not done that ... yet! ;-(

I assumed that
the designers had some common sense.

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

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.

Ah.

The internet is a very dangerous place.

Agreed.

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.

Ok. ;-)

Get your ideas from the web. VERIFY the solution and do your own math.

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

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.

We did indeed.

Are we having fun yet?

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