ZOYI ZOTEK ZT-703S fire hazard while charging - Page 1
Forum section: electronics / testgear

author: BRN
author_rank: Newbie
timestamp: April 23, 2025, 08:47:17 am
content: Hi.Did not found this topic so I creating another for this famous tool. I just received and disassembled it. There is battery YANNAI YN25A1 ICR18650-3400mAh (I did not found datasheet by googling. Also ICR type is the most dangerous and unstable). Nominal voltage labeled is 3.7V. Typically all 18650 batteries with nominal voltage 3.6 to 3.7V has charging voltage 4.2V. This meter has unknown charging IC labeled just "4086B". I found datasheet only for "ME4086B" and I think it's right after comparing datasheet with physical connections on PCB.https://www.onwaytech.com/static/upload/datasheet/ME4086ESPG.pdfThis IC can't be configured by resistor value and it's hard coded to charge battery to 4.35V. That high voltage can initiate fire for ordinary 18650 battery.I'm very dissatisfied. Product is working, but dangerous! All 18650 batteries I found works with charge up to 4.2V only. I googled and It's impossible for me to get battery which can tolerate 4.35V here in Europe. Also in datasheet there is also variant "ME4086A" that have the 4.2V charging voltage and solves the issue entirely, which is also impossible to get. I rather replace this IC to be compatible for all 18650 types everywhere, than be dependent on some special battery type I can't get. Can anybody have tip to resolve this?

author: coromonadalix
author_rank: Super Contributor
timestamp: April 23, 2025, 10:13:59 am
content: return your product or redesign the charging circuit as you may intend toand you thread title is wrong, you should wrote a possible fire hazard, seems very alarmist ?as there been one or many since the product launch, have you contacted Zoyi on that matter ?

author: xfint34
author_rank: Contributor
timestamp: April 23, 2025, 12:17:02 pm
content: I suspected this could be a problem. It explains why they ship with a protected 18650. Probably they realized the design mistake after production. So they shoved a protected cell into the regular 18650 holder even though it's longer and causes the holder to deform.Probably an easier way to remedy this than trying to source the chip with 4.2v termination is to get protection modules from aliexpress and make our own protected cells.

author: Heyrst
author_rank: Newbie
timestamp: May 28, 2025, 06:18:05 am
content: It would seem that they have installed the ME4086BSPG, B version of the chip, where the voltage is 4.35V. When they should have installed the ME4086ASPG version, where the voltage is 4.2V.So if you can find that A version somewhere, you could change the circuit yourself to the correct one.I'll probably put CN3163 circuit in it with jumper wires.The same problem exists in the XEAST XE-703S version.

author: OLderDan
author_rank: Regular Contributor
timestamp: May 28, 2025, 06:51:52 am
content: can you post some pics showing the battery being charged to 4.35v please. Does the current drop at the end of charge or remain higher trying to push the 4.2v to 4.35v. I have never heard of any issue of fire with the z703s when charging, and when I opened my case It was clear that the 18650 was the standard size with no sign of the battery holder being stressed, but I didn't check voltage/current while charging and/or at the end of the charge cycle when the red led has stopped 'flickering from solid while charging' to off.

author: Heyrst
author_rank: Newbie
timestamp: May 28, 2025, 07:13:46 am
content: Remove the battery and measure the voltage when you charge. If the voltage on the battery holder is above 4.2 volts, you also have a faulty circuit in the charger. The battery also gets really hot before the battery's own protection circuit disconnects it.It is possible that some devices have the correct A version chip and this B chip only for some devices.Apparently there are also 4.35V charging cells. But at least I have the wrong cell as it gets extremely hot.Examle SANYO UR18650ZTA, LG ICR18650 E1?

author: ajar171
author_rank: Regular Contributor
timestamp: May 28, 2025, 08:10:50 am
content: Just checked my meter, it goes up to 4.45V whithout a battery connected and 4.29V with the battery almost full (did not wait until the charger switches off).They are probably relying on the battery protection circuit cutting off the power to the cell above a certain threshold.My battery (ICR18650-3400mAh 3.7V, YANNAI, YN25A1) does not get warm at all.

author: JoanBS
author_rank: Contributor
timestamp: May 28, 2025, 09:41:27 am
content: I checked my unit, and the charger disconnects when it reaches 4.31V. The battery is the same model, with a built-in BMS, but I haven't been able to find any information about it online.It would be necessary to know the characteristics of this battery to determine how dangerous it could be, although some 18650 batteries don't activate the overcharge protection until they reach 4.325V, as shown in the following datasheet:https://www.nkon.nl/es/amfile/file/download/file/120/product/3890/

author: sleemanj
author_rank: Super Contributor
timestamp: May 28, 2025, 10:17:11 am
content: The ME4086ASPG is available on Taobao from a few sellers, which appear to have recent sales.I recommend Superbuy to buy from Taobao outside of China, it's who I use, here are the top two as Superbuy links:https://www.superbuy.com/en/page/buy/?nTag=Home-search&from=search-input&url=https%3A%2F%2Fitem.taobao.com%2Fitem.htm%3Fabbucket%3D20%26detail_redpacket_pop%3Dtrue%26id%3D743753742476%26ltk2%3D17484270865206iztj6ebkuc6mpqsl1lfyy%26ns%3D1%26priceTId%3D2100c80817484270651002042e08dc%26query%3DME4086A%26skuId%3D5513300660143%26spm%3Da21n57.1.hoverItem.2%26utparam%3D%257B%2522aplus_abtest%2522%253A%25222df1e2c121e7600d096a9e9286105f2b%2522%257D%26xxc%3DtaobaoSearchhttps://www.superbuy.com/en/page/buy/?nTag=Home-search&from=search-input&url=https%3A%2F%2Fitem.taobao.com%2Fitem.htm%3Fabbucket%3D20%26detail_redpacket_pop%3Dtrue%26id%3D867039473991%26mi_id%3DpEcOBohJnDktAhcCq_Ltnh91wcUur6yFCrBZ_m_s9f7PI9k2mPsradXqfTyTcPRtaepw9XoUG6j4pVC8Z2ZkdZdmTivM-ZwSY0tK8Hd15iU%26ns%3D1%26priceTId%3D2100c80817484277756488084e08dc%26query%3DME4086A%26spm%3Da21n57.1.hoverItem.2%26utparam%3D%257B%2522aplus_abtest%2522%253A%2522911537ef917c4c6f9c4c1c251161befa%2522%257D%26xxc%3DtaobaoSearch

author: xfint34
author_rank: Contributor
timestamp: May 28, 2025, 12:49:10 pm
content: Quote from: sleemanj on May 28, 2025, 10:17:11 amIs there a quick rundown on how to use that? Looks like they want me to pay upfront. Is this the final sale price of the items?Then I have to pay again to forward the packages to me? Is this right? How much is does shipping typically cost? And what shipping methods are available?

author: pascal_sweden
author_rank: Super Contributor
timestamp: May 28, 2025, 01:09:27 pm
content: It would be nice to inform the company that designed this device, as it is in everybody´s interest that this safety issue gets fixed ASAP!

author: indman
author_rank: Super Contributor
timestamp: May 28, 2025, 01:39:38 pm
content: Recall the entire lot of 703S back to the manufacturer's plant. And the manufacturer should pay those who bought their device moral and material compensation.

author: Heyrst
author_rank: Newbie
timestamp: May 28, 2025, 09:42:28 pm
content: I went through those heated YANNAI 3400mAh batteries that came with XEAST and ZOTEK.There was something strange in their protection circuit. The capacity test reject them below 1A current. I took off the protection circuit. There were no opposing charge and discharge protection fets, but only one fet.Tested capacity on the cell was 1100mAh.When I took off the last protective sleeve, a completely rusty cell was revealed.If you have the slightest doubt about the battery, replace it with a better protected one.

author: sleemanj
author_rank: Super Contributor
timestamp: May 28, 2025, 10:05:08 pm
content: Quote from: xfint34 on May 28, 2025, 12:49:10 pmYes that is correct, you pay first for the product and china domestic shipping, superbuy purchases the item and it is sent to them, they take photos and store in the warehouse, it appears in your warehouse area of your account, you select the item(s) in your warehouse you want sent out to you, the system gives you a variety of options, you choose and pay for the option, superbuy packs and ships.They have a shipping estimate calculator on the site (https://www.superbuy.com/en/page/query/freight/). It would not cost much for just some ICs.

author: Heyrst
author_rank: Newbie
timestamp: July 26, 2025, 08:47:11 pm
content: Now that I finally remember commenting.The Superbay order came and I changed the right component. Easily succeeded with an 8018LCD heat blower and using a lot of Flux. Now the charging voltage is limited to 4.2 volts.Indeed, there will be more fees on the Superbay. First, when purchasing the product and its shipping cost. After that, Superbay has processing costs, shipping costs and still the customs of your country. However, the prices did not become unreasonable.If anyone in Finland happens to need that same circuit, there were several left over from the 10-piece quantity. Shipping in Finland is almost the same as what came from Superbay, but if you're scared, order it yourself.

author: OLderDan
author_rank: Regular Contributor
timestamp: July 27, 2025, 09:53:01 pm
content: Quote from: Heyrst on July 26, 2025, 08:47:11 pmMay I ask how much in terms of the cost of the 703s did it cost?

author: BRN
author_rank: Newbie
timestamp: August 03, 2025, 12:13:22 pm
content: Can someone explain this? I bought ME4086A IC's from LCSC.com which should be legit. Particularly 50pcs of them to eventually fix more devices, but I ran into wall with that. I changed ME4086B to 'A' version successfully. This job was trivial to me because I usually work on much difficult jobs. But! Before, the charge voltage was 4.35V and now it should be 4.2V, but it is over 4.5V? WTF??? I changed the IC again for another 'A' version and same thing. Then I tried to, just in case, minimize temperature by not solder on IC by air. I manually soldered each leg of third 'A' version IC individually with low melt solder (138*C). So way lower temperature stress that manufacturer recommended, but same 4.5V charging voltage. As battery, I used capacitor to remove fire hazard. I tried 10mF capacitor to simulate battery and later tried also with two 2.7V, 1000F super capacitors in series. Supercaps was charged to 3.8V on lab. PSU and charged those through ZT-703S and ME4086A. The charging red LED was on about 10 minutes until 4.12V was reached. Then, I noticed that after 4.12V, the voltage on supercaps started to raise much slower than before, but after about another 20min, voltage was 4.4V and counting. So even worse than with old IC which is already dangerous. Damn it.Dear 'Heyrst', can you test your 'A' version IC in your device with capacitor? 10mF for example works fine. No super caps needed. It behave the same. If you do successfully have 4.2V maximum, I want one IC from you. I'm within EU.

author: Heyrst
author_rank: Newbie
timestamp: August 03, 2025, 12:29:54 pm
content: Without a battery, the voltage is ugly and jumps every where. Some spikes well above 4.2V. I thought it might be because it's not a linear circuit but a switch mode. And its stability is a complete mystery.I measured it directly using a battery with a protection circuit and the voltage settled at around 4.2V. I checked the charging cycles a few times and it worked. The battery I used was a Samsung INR18650-35E 3400mAh 19milliohm 8A to which I added a trusted protection circuit.The internal resistance of the capacitor can be a problem if the circuit is not stable. But..I also wonder if the bottom of the chip is soldered to the circuit board. That pin is the only GND pin. So it must be soldered. Too high a voltage can also be caused by a poor GND reference. You can't really do that with a regular soldering iron, you need an air-blowing soldering iron.

author: kloetpatra
author_rank: Regular Contributor
timestamp: August 03, 2025, 01:39:30 pm
content: Quote from: BRN on August 03, 2025, 12:13:22 pmThe job of checking what you buy before hitting the buy button is too trivial sometimes.ME4069ASPG ≠ ME4086ASPG

author: bingo600
author_rank: Super Contributor
timestamp: August 03, 2025, 04:42:25 pm
content: Outch .....The 69 pinout isNOTeven like the 68...https://lcsc.com/datasheet/lcsc_datasheet_2203311630_MICRONE-ME4068ASPG_C2835845.pdfhttps://lcsc.com/datasheet/lcsc_datasheet_2003112035_MICRONE-ME4069ASPG_C494946.pdf

author: BRN
author_rank: Newbie
timestamp: August 03, 2025, 10:40:37 pm
content: Oh shit. Thank you guys. The error I made was in googling where I search for right IC and google offers similar from lcsc.com because lcsc.com does not have the right one. Maybe this error happen to 'bingo600', right?Nobody mentioned ME4069However thanks to you two kloetpatra and bingo600. I noticed that and made change with circuit. Now, I'm happy because everything works and now I'm charging to 4.136V which is little lower than 4.2V, but definitely safer and with prolonged battery lifeBtw I'm shocked that with incompatible pinout I was able to somewhat charge and without damage anythingBtw I made other improvements which I want to share. I dremel out half of the stupidly strong and long battery spring to release pressure on battery and also soldered battery case. Also I did cut several places on button rubber to soften that inconveniently stiff buttons (I marked the cuts on photo). Feel isn't ideal but definitely better.

author: xfint34
author_rank: Contributor
timestamp: August 05, 2025, 01:41:15 am
content: I guess it turned out to be a happy mistake. Good to know there's other options.I know I asked about this SuperBuy thing earlier but I didn't spend the money because sudden health issues. I'm fresh out of funds.

author: DiddlyJackSquat
author_rank: Contributor
timestamp: August 06, 2025, 01:31:45 am
content: Probably because it was intended to ship with 4.35v lipos (see fnirsi's similar looking scopeDMM)but the Zoyi and ANENG AOS03 end up with 18650sThey look different but their hardware is largely fairly similarI prefer the the 2C53T now...

author: kloetpatra
author_rank: Regular Contributor
timestamp: August 14, 2025, 05:25:09 pm
content: I replaced it with ME4086ASPG and now charge termination is at 4.158V. It is lower than 4.2V due to the trace and contact resistance. At the chip it is bang on 4.2V.I have some spare parts left. If you're interested send me a PM. Total cost (1 part + shipping) is 6.51 € world wide, paypal only.

author: swalayan
author_rank: Newbie
timestamp: August 17, 2025, 07:28:30 am
content: lucky me, i'm always charging 18650 using external charger, i can't find me4086a ic in my country, but i already order me4059a, its have different pinout but i think it will work. for now, i just lift up the pin 4 (Vin). you cant charging anymore, but at least is safe to use when connected usb c to pc.

author: Heyrst
author_rank: Newbie
timestamp: August 17, 2025, 09:42:23 am
content: Earlier I mentioned that another option is to use 4.35V 18650 cells.When you put in a SANYO UR18650ZTA or LG ICR18650 E1 cell, you don't need to make any changes to the meter.I would have ordered SANYO cells, but the shipping cost would have been 16€. So changing the circuit was cheaper and you won't accidentally do any damage later if you forget that you should have a cell with a higher charging voltage. If you can find those cells with cheaper shipping costs, that's the simplest thing to do.The manufacturer should actually offer us these cells instead of recalling the device.

author: edisitaru
author_rank: Contributor
timestamp: August 19, 2025, 04:28:19 pm
content: https://www.aliexpress.com/item/1005009303293303.html

author: metehoca
author_rank: Newbie
timestamp: August 20, 2025, 09:31:09 am
content: Just asked zoyi about this issue. Here's the reply;Quote

author: OLderDan
author_rank: Regular Contributor
timestamp: August 22, 2025, 11:29:22 pm
content: So anyone who doesn't read this thread, and changes the battery for a higher capacity standard 18650 is at risk?

author: bc888
author_rank: Regular Contributor
timestamp: September 02, 2025, 03:37:35 am
content: Quote from: OLderDan on August 22, 2025, 11:29:22 pmYes. I think that there are 2 points worth reviewing. 1st) If what you are calling a "higher capacity standard 18650" is a battery that has 3000 Mah (higher capacity), BUT it terminates at 4.20 V as do most 18650, then you will have a huge issue. Suggest keeping the fire department on speed dial if anyone decides to stuff the battery in there regardless.If, however, your new 18650 battery has a higher capacity of 3000Mah BUT it terminates it's charging at 4.35V, you're fine. Apparently Zoyi made the poor choice to have the 4.35V battery termination and put the battery inside to accomodate that choice, somehow believing that no one would later stuff a 4.20V (the most common version) inside!!Bad dog Zoyi, no bisquit!

author: SammysHP
author_rank: Newbie
timestamp: September 02, 2025, 07:17:50 am
content: Whatever Zoyi told you, I checked the datasheet of the included battery and it is clearly rated for 4.20V, not for 4.35V.If the status LED is blinking after charging, it means that it triggered the battery protection circuit, stops charging, waits until the protection circuit resets and then continues to charge again.

author: Paul T
author_rank: Regular Contributor
timestamp: September 02, 2025, 10:40:17 am
content: If you have a source of used laptop batteries (Dell, hp, Lenovo), the OEM ones often contain LG/Samsung cells which have a termination voltage 4.30 or 4.35. You can usually find out what this voltage is by carefully reading the label, and using google convert if some of the text is in a different language. Take the highest voltage listed and divide by 3 (or 4).Once you get a window into the cell bay, look for the part number printed on the sides of the cells. You can use the following resource to search (ctrl-F) and find what the specs are.https://docs.google.com/spreadsheets/d/1fYjDxxCJXfm2wdpGWCaOUGq8V8TOEgsnplHQa4YQpRQ/htmlviewThe reason for the higher voltage is to squeak out every last W*h they can from the available capacity cell. They reach a higher voltage by way of the chemistry of the cell plates.Some charge chips, namely SW family of powerbank controllers, have a VSET resistor option which enables user selection of termination voltage.Do not try changing the termination voltage using a resistor or diode. I believe bigclive did a test of this and it just drove the charger crazy.