Julian's Postbag: #65 - A Momentary Lapse of Polarity :(

[@etheroar6312]

Thank you for vhaving the courage to show your mistakes. It would have been easy to scrap the video and we would never know.

[@arfyness]

+1

[@voltlog]

I have never seen power banks with positive spring links, so that is always a sign of polarity unless marked otherwise. Too bad the magic smoke escape but it should be repairable.

[@outaspaceman]

This vid made me feel better after I'd just reverse polarity fried a project. Even experts can get it wrong it seems.

[@Heimbasteln]

Its sad that these chinese things dont have reverse polarity protection

[@AureliusR]

experts...

[@AureliusR]

Walter Boxhead Yeah, apparently. I can't freaking stand this guy. Had to delete my other comments because I didn't even want to deal with the fanboys.

[@DavidWatts]

Ha ha ha, I did the exact same thing last year. That video never saw the light of day :-) Did you see that the micro:bit came out for pre-order?

[@JulianIlett]

Yes, I saw your announcement. I'm going to make my micro:bit video very soon - much more relevant now that people can buy them.

[@robfenwitch7403]

The burnt component is reversed so the lettering you can see is the bottom line so it *might* be the same as the unburnt one.

[@JulianIlett]

Ah, yes, good point - that would be the bottom line - date code or some such.

[@sej7278]

i thought that too. time for a repair video

[@503technics]

+andrew moon 50Ah

[@EscapeMCP]

P.S. Try opening your other power banks from that same manufacturer. They may have the same components in, despite being differing models. If a designer has a preference for a particular circuit layout (and more specifically, a preference for using that chip), he may have used it in one of the other models that you have?

[@John_Ridley]

The MOSFET cooked because they have integral body diodes. It was conducting the entire output of the cell.

[@YouAllKnowBob]

The little battery tester seems to be really accurate. I tested a LG HE2 and the meter showed 2580 mah and the charger said it took 2560 to recharge. And my 'favorite' Ultrafire 3000 may showed 487 to discharge and 470 to recharge.

[@TMS5100]

i have one of those capacity tester devices too :3 i use it to measure capacity on 12V SLA batteries. quite a handy cheap little device. it's good to have constant current DC loads on hand to use with it. the 0.6V bias is probably due to forward voltage drop across a diode.

[@lillydoye7418]

This brightened my day a little. Thank you. Sorry about the bad luck.

[@johannamin2777]

I have the same power bank, QD186-VAX. The logo, as I later found out is actually the stylised Chinese characters 七电 (ChiDian). The mAh counter started in the 15000++ range for me but zeroed out when the batteries ran dry. It then starts counting upwards when you charge it.

[@Ralphgtx280]

I just Tested on mine pressing (+) stops the discharge allows you to change the cut off voltage while running without removing any information pressing (-) clears the memory and yeah you start again. I needed to test ALOT of batteries so I took a cheap power bank curcuit and used that to boost the output to 5V than used that to charge other batteries using a TP4056

[@iamdarkyoshi]

How much to send just the powerbank PCB to america? I am determined to fix it...

[@webchimp]

Thanks to this video, the first thing I did when buying my first power bank was to put little stickers in the bottom with + & - signs on.

[@drkastenbrot]

Nitinol wire makes a very nice load, just wrap it around something fireproof and connect beefy wire to the ends. you can also curl it up and leave it hanging in the air. Its basically cheap high resistance wire (also used in hairdryers) and gives an easy high wattage load without cooling issues.

[@TKomoski]

Julian maybe it's a combination power bank and vaporizer.

[@docgonzodotcom]

The powerbank board is marked KCX-061. Thought I recognized that display from somewhere. They also make USB Doctors : KCX-017 and KCX-045. I have some of them, but never use them any more after watching your YZXStudio video. Got the two you reviewed, and a more recent model. And just bought the latest one from Franky.

[@Ralphgtx280]

my identical looking battery tester remebers stuff if I want to change the termination voltage mid test , not sure why yours cleared it

[@booboyBL]

Kudos to you, Julian for confessing your mistake and not just 'sweeping it under the carpet.' We've all done similar (and worse, well, I have anyway).

[@DeeegerD]

Glad you are getting your packages from China - some of mine are taking 3+ months if they show up at all in Canada.

[@jellyfishjelly1941]

You could just try to to bridge over the battery protection circuit or just over the burnt part and it should work, just keep an eye on voltages.

[@TonyLing]

4.0 * 1.7 is the size OD and ID (mm) of the input connector

[@ChipGuy]

That 358 marked devices are LM358, from Japan Radio Corporation ;) Or the chinese manufacturer that puts on any brand you want.

[@cmj20002]

The power bank, being so expensive you would think it had reverse polarity protection. So if you buy one make sure the batteries are in the correct way. It is to bad because I was thinking of getting one, so I wanted to see a review of it first. Did you get a new one? If so can you do a review on it.

[@reggiebacci]

Protection diode on the MOSFET forward biased, saturated and released magic smoke?

[@YouAllKnowBob]

Those MOSFETs SHOULD be the same. I was just looking at a DW01 setup and the two MOSFETs face different directions. One is overcharge protection and the other over discharge protection.

[@CezaryAkakios]

Seems to me like it was the body diode that fried. That seems plausible if the controller turned off the 'discharge' MOSFET and turned on the 'charge' MOSFET, creating a high current path through the on MOSFET and the body diode of the off MOSFET.

[@TheChipmunk2008]

4.0*1.7 probably gives the dimensions of the plug required? 4.0mm outside diameter, 1.7mm pin?

[@Gameboygenius]

So the cells are just connected in parallel. That could be a bit problematic if the cell charge isn't fairly well matched when you put them in.

[@fatpo888]

the AXXXX IC is a silergy 5V boost converter , very high efficiency

[@arfyness]

11:04 "Ooh I was about to put that in back to front I think... "

[@arfyness]

I hope you find a good candidate replacement part, and make a video of that bit. I commend you for posting the embarrassment of it all. And hey, did you test the switch for continuity? It might be okay. You might have sent current through with an errant press of it, in your haste to stop the smoke.

[@classicmacintosh]

If it can't handle incorrect battery installation then IMHO it's junk. There is no excuse for a lack of polarity protection in these kinds of products. Junk.

[@AJB2K3]

Did it go pop due to the mystery chip being installed the wrong way around?

[@maicod]

Hi Julian, I love your meticulously explained videos. What I wanted to know is do you buy the stuff in the postbags yourself or do companies sometimes also send items for reviews ? I ask it cause you sometimes seem so surprised when you find out what is inside a postbag :)

[@tonylock7657]

As you were putting the battery in, I was thinking that the spring is usually the negative end and you'd said it was positive - I thought you were reading markings on the plastic. Then we see the magic smoke. Good on you for fessing up though. It's a mistake many viewers will not now make because you did it for us!!

[@fatpo888]

the burned is 8205, u can replace it with ao8810

[@DeeegerD]

The smoke made me burst into laughter - thanks for the chuckle! Chinese never heard of reverse polarity protection I guess.

[@oskimac]

Hi Julian, can you implement a way to capture the screen (is really easy)? because have it recorded on cam give these moire effect and bad contrast. maybe someone can suggest a good free software. I know you maybe want to keep it simple and you may need to edit the video but please consider it.

[@stefflus08]

How are you supposed to run a 5w 8ohm resistor load on a 12v battery? In my head, internal resistance aside, the 5 watts would be in the 6v range?

[@marc6340]

The corner of the PIC looked a little bit like it was blistered as well.

[@helloworldstein]

Anybody know what the name of the USB flashlight thing he plugged into the battery pack to test it was? Ebay searching is so far unsuccessful.

[@xanataph]

It's difficult to implement reverse polarity protection with current flows in different directions for charge and discharge cycles when connecting to batteries. We have all done these buggery things on occasions. Actually just yesterday I did a reversal on the charge controller I was fixing. Fortunately no harm whatsoever, but certainly was stressful and forced extra checking so still rather annoying. Why don't you just scrap all the circuitry in there and put some new stuff in of your own taking advantage of the case & battery connexions at least?

[@TKomoski]

Maybe a new video category Postbag, Teardown and Repair.

[@karlfell3768]

I love to see the magic smoke every so often lol. Made for an interesting twist to the video, we are only human after all. Keep them coming. Karl

[@juncusbufonius]

It would seem that an 18650 bank without reverse polarity checks is not that good when they often have no indication on the battery. It was also noted below; the springs on both ends only lends itself to duping people. Poor design?

[@AlAmantea]

It looks like the corner of that PIC is damaged as well.

[@Peter_A1466]

Did this video eventually cover the cost of that power bank? 🤔

[@huss987huss]

Please Do more of these! I LOVE THEM :D

[@DavidFowlerEngineer]

If you do buy another, you can get the part number for the smoked chip from it, maybe get the part to fix the one you burned.

[@RichardT2112]

Nice to see I'm not the only one that attacks packages from eBay with all the glee and intensity of a young lad at Christmas.

[@DOMTHESAUSAGE]

hey julian how would the layout of 15 xmlt6s be in a torch if the driver is putting out 15 volts to the leds would it be 5 sets of 3 series leds

[@DOMTHESAUSAGE]

Hahah doc

[@ratbag359]

i would desolder the mosfet and bridge the drain and source. those mosfets are identical the number u were reading was upside down.

[@kyoudaiken]

The Powerbank was bought alongside with 6xNCR18650Bs! -> Total 56,48 EUR... Why don't you just buy another of these protection chips? Should be still cheaper than buying a new unit, even if you can only get a big quantity of these chips.

[@JUANKERR2000]

I watched in mounting horror as you offered the cell up correctly and then turned it around; we've all done it!

[@YouAllKnowBob]

Are you sure they are not both the same chip, one facing one way and the other reversed?

[@intel1538]

Don't feel bad Julian, even though it does suck, I bet you will find suitable mosfets and replace them. Try and get slightly higher current ones though⚡️. This has happened to us all at some point ! One such time was when I very excitedly opened my package from Adafruit. I ordered MANY goodies for a project that used the 3G FONA SHIELD. I was bench testing without my Arduino hooked up and watching in glee as the FONA connected to my local cell tower. The shield requires separate power as the Arduino cannot handle GMRS due to the load. It was time for a real test. I put a small auto dialer in the program to call my cell and hooked everything up. Immediately the shield went black, no fancy blinky lights & I smelled the acrid smell of burned semi conductors 💥 My FONA Board was dead with no obvious signs of damage other than the fact it 's been bricked !!Unbelievably, AWESOME Adafruit is sending me a new one !! This the only time I've had a replacement board sent out to me 👍🏻

[@valentinocolaon6060]

maybe ask the manufacturer to send you a model number of that Q1 mosfet? or at least a detailed photo of the circuitboard..

[@DreStyle]

I have the same annoying problem with those battery holders... Another really annoying problem is the extremely thin wires... Even when you have lager holders you would expect some thicker wires... Does anyone knows a seller that sells better quality holders? I've bought a uni-holder recently.. Maybe I'll do a review on it.. They state I can ramp up to 10 amps

[@CZDrMike]

These mosfets seem to be in back-to-back configuration so they skould be the same.

[@aerotro]

I would suggest buying some Poly Fuses to protect against future disasters :p

[@JanAndHenk]

I only understand about 10% of what Julian is explaining, love to watch this though, very relaxing in a way.

[@SproutyPottedPlant]

What vape was your nephew charging? I wonder if it was a squonking mod!

[@vedranlatin1386]

If you killed one of cell protection mosfets (and you should verify that with schematic for DW01 circuit before continuing) you can just short it's drain and source. You'll loose protection (overcharge or overdischarge) but it should still work. Just leave the gate unconnected to avoid killing DW01 as well :) If you like the charger, you can order a new mosfet from Digikey and replace it later. I believe both mosfets should be identical N channel types.

[@-yeme-]

I did the same thing today :( fortunately the power bank I murdered was filthy cheap. its weird tho, the cell I put in wrong was the last of three and I dont think it shouldve blown up because the board would still have seen the right polarity across its terminals because of the other two cells. I can understand the battery spring wire getting red hot and melting itself into the plastic, which happened, but I still think dont think its fair that the power bank was fried. but it was definitely working before and now it isnt

[@jlucasound]

I don't have the capsity to compresend that. At least not in a wireless manner.

[@Darool]

You could also send the seller an message asking which chip it is ;)

[@ProdigalPorcupine]

High Hopes of getting it fixed?

[@lezbriddon]

. Black sharpie / DVD marker, and colour in the neg end of the cells!

[@tanyees]

I bought the QiDian 4cell version after watching your review of it. They are real good quality. I hacked it to use 12cells. Served me well until my mom placed batteries in reversed polarity. Then I bought this 6-cell version because of the display showing current draw, output voltage when in use, battery voltage with no load. Only mah and mWh which I don't usually bother because I hack again to install 12cells which I charge separately.

[@GeorgeK356]

We're all screaming "Julian, don't do it" here, as you inserted that cell :(

[@DreStyle]

BTW.. Did they filled the left down screw with a solder? Why?

[@JulianIlett]

It's just filled with metal - a manufacturing defect I presume

[@JohnnyMotel99]

I don't know much about power banks, but should not li ion batteries be balance charged and I don't see any thing like this.

[@stewartlove2397]

If the positive spring terminals didn't stick out beyond the case tabs, reverse polarity wouldn't be possible

[@rexdoran2051]

I bought one of the battery testers. It only seems to work with the resistor disconnected. Err4 with the resistor. I am going to try different resistors.

[@webchimp]

That's the issue I'm having, the resistor that came with mine was the 5E7.5JR that matches the pic. Does it actually do any discharge at all with the resistor removed? What resistor did you settle on?

[@rexdoran2051]

Yes it discharged with the resistor removed but at a very low rate. I tried a 5W8OhmR which made no real difference, The tester works fine on smaller batteries.

[@webchimp]

Bugger, I bought it specifically to test my 18650s.

[@rexdoran2051]

They are so cheap I bought another one. It works perfectly with 18650s. Where are you from? Bugger is a word I do not hear that much anymore. Kiwi living in the States. If you want a laugh look up "Toyota Bugger Commercial".

[@iceberg789]

this is why you don't turn it on ! you take it apart ! - those words worth a thousand $s.

[@rickyreynolds17]

sounds like a crazy Australian

[@jamescollins6085]

Sounds like EEVBlog.

[@fd1150]

I'm glad other people do this too. At least you have a nice flashy-onie-offie thingy.

[@lmorrison17]

"oh crikey"' Sorry Julian but i couldn't help laughing at your expense.

[@billywhizzy]

I started screaming before you put that battery the wrong way round :(

[@louisfinlayson5844]

You must have so many power banks. You seem to get at least one in every episode of postbag :)

[@MrLordBaer]

maybe mark a "+" on the positive end cells to negate having this happen again

[@modanistas]

Ah well, makes me feel better about the laser printer that I plugged into a 240v supply without checking the label.. Yep, it was a 110v one.

[@joruss]

They both may be UCC2801PWG4 (you're reading secondary marking as the second one is flipped 180 degree) link to pdf: www.ti.com/lit/ds/symlink/ucc1801.pdf

[@MrLordBaer]

they saved money by leaving out a simple polairtiy protection diode

[@maffysdad]

Can you have a reverse polarity protection diode on this device which has a charging circuit?

[@hackeritalics]

Hmm... I think you should be able to. Certainly there must be charge control chips that allow for voltage sensing via a resistor network with the junction voltage taken in to account that flat out block reverse polarity..

[@pauls0416]

Well, the good news is, at least your lithium cell didn't explode, especially while you were holding it.

[@rayreese2]

Glad to know I'm not the only one to reverse batteries.

[@ShannonWare]

Holy smokes! At least you took the battery out quickly. "Not reverse polarity protected"... it should have been.

[@paparoysworkshop]

Reverse polarity protection circuitry would have been nice in its design.

[@poptartmcjelly7054]

Don't buy a new one, just replace the MOSFET and the switch.

[@Ncky]

you watched video but forgot to turn on brain. did he said the cant find what is that mosfet and maybe its new component. he cant find it. :/

[@petti78]

Should not be too hard to figure out what the pins are and just whack any old mosfet of the same type (P or N) in there and have it work just fine. I'm pretty sure it will work with any reasonable part and does not require this particular product of the shenzen market last tuesday's fake component of the week.

[@poptartmcjelly7054]

N!cky It connects to the negative rail so it's an N-CH mosfet, logic type since it's most likely driven by the micro. It's just so simple, any mosfet that has a saturation at Vgs of lower that 3.3v will work and you can clearly see by the traces where to connect the leads, a bodge it might be but it would be an order of magnitude cheaper than 20 bucks. I'd say Julian got a bit lazy.

[@Ncky]

Poptart McJelly yes in basic theory but you can connect mosfest anyway. n channel can go on posivtive and on negative. i think that one mosfet is for charging and one for load. load mosfter is maybe n channel and charging one is p channel.

[@alexzirnea]

+Poptart McJelly you can find those type of mosfets in almost any cellphone battery protection board(they're under those plastic cap) most of the time they come in dual mosfets in a single package.

[@KarlMarklund]

Julian, did you ever rebuy the powerbank? I just received it today in the mail.

[@JulianIlett]

No, I never did buy a new one - maybe I should.

[@jay7264]

i cant find this powerbank anymore. i bought one but had to be refunded due to it not getting past customs. could you gave me a link

[@KarlMarklund]

I bought mine from kakasell8: www.ebay.com/itm/181896628836?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[@jay7264]

KarlMarklund I tried its out of stock. I can't find it anywhere

[@raykent3211]

I think they could protect against polarity error for one cell by taking the supply through a fast-blow fuse, and then putting a diode to the other supply line. In proper use the diode would be reverse biased and do nothing. If the polarity is reversed the diode conducts and breaks the fuse before anything else fries. I don't know whether a polyfuse could be used. Any thoughts? Anyway, you have my heartfelt sympathy, I think we've all done this! Why isn't there a law forcing battery makers to mark the negative end with spring symbols all around?

[@KennethTanFotografie]

That's why they invented sharpie's

[@zerog2000]

... a law that the Chinese 5000mA UltraFire battery manufacturers would adhere to?

[@barrygiblett5823]

Its ok mate, lot of fun and smoke, for less than the price of a bottle of wine, and the only pain is you kicking yourself, no hangover today... we all do shit like that..

[@yottavolt758]

Test this thing aggain and try to find other dead things whith your thermal imaging cam i think that the mosfet isnt the only blown thing..... and it is really only for some other things. Maybe the resistance also is higher than normal and the thing is shorted out but has a higher resistance what causes the main processor to reboot because of the voltage droop and switches off the output.

[@MrLordBaer]

4.0*1.7 may be the tip size

[@fatpo888]

358 is a dual op-amp IC

[@DOMTHESAUSAGE]

can anyone help with my problem my driver in my torch shit itself and im trying to find 1 im running it now on 4 18650 with no driver and it pulling 2.5 amps would this be safe 4 now or do i 100% need a driver

[@FlyingShotsman]

Inappropriate place to ask your question. Try an electronics forum: electronics.stackexchange.com/ or forum.allaboutcircuits.com/ or try a flashlight forum: www.candlepowerforums.com/

[@DOMTHESAUSAGE]

Sorry obama

[@DiyEcoProjects]

hi Julian... that fried charger. You got a nice battery holder there, why not put a £2 charge controller in the cavity space, and make your own one lol

[@RAPXZibit]

What about asking seller of photo of brand new PCB with normal components? Buy another and resolder it

[@ShaneMatthews27]

You would think that for the price it would be protected.

[@PartTimeRonin]

Is there any removable 18650 powerbanks that support QC2.0 or QC3.0 yet?

[@BillySugger1965]

Julian, don't beat yourself up. Reverse polarity connection comes under the heading of foreseeable misuse and really should be protected against. If you can PM me good photos of both sides of the board (preferably with that dead part removed with a hot air gun), I'll try to source you a replacement.