0

I am trying to replace the battery of a rechargeable LED torch, but it looks different than most others that I have seen. I was wondering if anyone can help me identify it, so I can try to find a replacement. Otherwise I'm thinking I'll replace it with an 18650 and a TP4056 (mini USB dc charging), but an in-place replacement would be good. It recharges from Mains power, if that helps. I opened a couple of others of different make but similar form, and they all had similar looking batteries.

The yellow caps are kinda like silicone I think, and not solid. The battery voltage is ~3 or 3.5 I think, and the LEDs are very dull. The source of the torch is India. But essentially Mains is 220V.

The battery is very similar to this 4V 0.5Ah lead acid battery

enter image description here enter image description here

Dave Tweed
  • 168,369
  • 17
  • 228
  • 393
Karthik T
  • 167
  • 10
  • This is not a safe project to attempt. Replace the entire light with a properly engineered product of higher quality. – Chris Stratton Aug 04 '19 at 15:30
  • 1
    @ChrisStratton I think replacing the battery AND the charge controller AND the source of light by a properly protected Li-Ion battery, a properly design Lithium charger and switch-mode constant current source, and a white LED would be quite a nice project. But yeah, of this whole thing, the case and the reflector might be salvageable, probably at a cost much higher than that of a new flash light. – Marcus Müller Aug 04 '19 at 15:35
  • What mains voltage ? Mains AC direct to torch? For interest, where are you located. (Massachusetts is one guess :-) ). – Russell McMahon Aug 04 '19 at 16:46
  • @RussellMcMahon the source is an entire planet away in india. I believe mains of 220V is connected to the PCB above the battery which is then charging the battery. – Karthik T Aug 05 '19 at 03:30
  • @RussellMcMahon Im curious, why Massachusetts? :) – Karthik T Aug 05 '19 at 03:52
  • Welcome to EE.SE! This appears to be a reverse engineering, modification, or repair question. Please be aware that such questions must involve specific troubleshooting steps and demonstrate a good understanding of the underlying design of the device being discussed, so that you can ask specific, focused questions that can be answered concisely. Otherwise, the question is far too broad. More information can be found here: [Is asking how to fix a faulty circuit on topic?](http://meta.electronics.stackexchange.com/q/2478/11683). – Dave Tweed Aug 06 '19 at 11:18
  • @DaveTweed I'd consider editing his question if I thought it needed changing to meet your above suggestions. He says he has a torch that has a junky battery. He'd like info on the battery BUT he's happy to change the design to accommodate a superior battery chemistry and charger. These lights would be anachronisms here but are sold in the Indian market. He'll learn something useful about LiIon charging, the dangers of the old power supply, the merits of including low voltage cutoff, or not, ... . ... – Russell McMahon Aug 06 '19 at 12:48
  • ... The IC I mentioned is a (strong) suggestion. Its been around for years and is still popular and has some years of life yet. || It can be seen as a shopping suggestion of sorts BUT in basic form its one IC and some passives on a small PCB. In better form its 3 ics. Building ANY basic LiIon charger from components makes minimal sense in most cases. This adaption path is one that most people willing to learn would follow - even the very hardware keen. If someone wants ideas on LiIon charging I'd hope we can suggest an IC or two ICs and a double FET. – Russell McMahon Aug 06 '19 at 12:48
  • @KarthikT Even Google masters cannot mentat correct answers / locations with 100% certainty. Based on apposite web stalking attempts an Indian location seemed most likely but a photo of similar appearance is used by an Indian (national?) dwelling in Massachusets. Occasm suggested the the US may be slightly more "simple" although the interesting torch did seem most likely to be Indian. I've seen similar in China. || And, not so much of a world away from me as you may imagine :-) ||What city are you in? – Russell McMahon Aug 06 '19 at 13:10
  • @RussellMcMahon: I know that battery-operated lighting systems are "your thing", but SE is simply not the place for a broad treatise on the subject. – Dave Tweed Aug 06 '19 at 13:27
  • @MarcusMüller I am aware enough of the "Captain Cook's Axe" phenomenom here (Make That George Washington's axe :-) ). BUT apart from the tutorial value, which often seems to be appreciated except in questions that I answer, There may will still be merit in this change. This is India. The LA batteries ARE available. They are a few 100 mAh (according to links provided by others) and the capacitor charger is slow but also probably cooks the battery. The TP4056 charger modules are under $US1 (free shipping from China). Any well used 18650 will be an improvement on the LA. ... – Russell McMahon Aug 07 '19 at 06:00
  • ... Charger goes from lethal to any cellphone charger (including the one for your phone. LED replacement is optional. A 33 Ohm LED drive resistor for a crummy LED gives 20 mA at good battery and a graceful fail with most LEDs. Lower R = more I. Overall a workable significant improvement for very little. Labour excepted :-). – Russell McMahon Aug 07 '19 at 06:00

1 Answers1

1

The following (as edited :-) ) IS good advice.
Whether it is worth following, is up to the original poster or those who come after. Do please note the clear warnings re potentially ** lethal voltages probably present in the original device. These will not be present if a 5V USB type power supply is used, as recommended, in the new design.

The battery is "almost certainly" a two cell "4 Volt" lead acid one.
These are not common but I have seen Chinese made lights using similar.
The design is probably very old (I'd love one), the LED is probably low efficiency and low output and the charger is probably lethally dangerous. If that doesn't stop you, read on.

The battery can probably be replaced with an 18650 or other LiIon single cell battery. These have lower low end voltage than the Pb battery - which may be a problem if their circuitry purposefully drops some voltage using eg series diodes or a voltage regulator with more than a few tenths of a volt dropout voltage. (Use of a regulator is unlikely.
A simple series resistor would probably replace the "electronics" previously used (if any).

Recharging is more problematic.
The mains charger will destroy the liIon battery unless limited to say 4.0V ABSOLUTE MAXIMUM. You can float a liIon cell at 4.0V with some hope of an OK lifetime but NOT at 4.2V.

A good alternative choice is to use one of the many many TP4056 LiIon charger modules available on ebay / AliExpress. These accept 5 to 6V (preferably 5V) and handle all charging aspects.
Modules with an inbuilt output protection/cutoff feature cost little more and are a good idea.

Identifying what sort of charger is currently in use.

There are strong indications from the photo that the existing charger is a dangerous "AC mains input series capacitor" type. This is covered below, but 1st I'll mention the possible alternative.

Low voltage charger: - IF the charger uses a "plug pack" / wall wart" with a low voltage output of say 5VDC to 6VDC it may be able to be used for a LiIon battery - see below. If not, adding one would be (very) wise.

HIGH VOLTAGE AC MAINS INPUT TO TORCH.

If the cord that connects to the torch carries AC mains (110 VAC?) then the following applies.

ASSUME THAT ALL PARTS OF THE TORCH AND CHARGER CIRCUITRY ARE AT FULL MAINS VOLTAGE WHEN THE LIVE CORD IS CONNECTED TO THE TORCH!!!

The markings on the capacitor used indicate that it is a 0.68 uF 400V rated part - indicating that this is almost certainly a mains voltage charger. (Such as part is almost certainly not used in a low voltage charger).
Be aware that IF you input AC mains to the on-body connector then it is almost certainly a capacitor impedance voltage dropper type that will kill you if you let it - consider ALL connections always at MAINS VOLTAGE with that sort of supply.

If it is a mains input charger the best choice would be to change to a regulated 5VDC plug pack (such as used for most modern cellphones) and proceed with the TP4056 advice.

If you MUST try to adapt a lethally dangerous AC mains capacitor charger (Hint: Don't!) then you need to establish Voc and Ichg. Charge current is probably 25 or 50 mA half/full wave on 110 VAC and about double that on 230 VAC. Too low really. I'll not give more advice on that here - ask if still interested in that aspect.

Low voltage charger

If adding one, use a 5VDC one rated at up to 1A.

If the existing input is low voltage DC (unlikely)

  • Measure the voltage O/C (open circuit) from the inbuilt charger.

  • If OC voltage is >= 5V and under about 6V or maybe 7V it will operate the TP4056 Ok.

  • Loaded it should be 5V optimum and not over 6V for thermal reasons. The modules are resistor programmable for charge currents of <= 1A.

  • If Voc is > about 7V it will need to be regulated or resistor loaded to bring it under 7V OC.

TP4056 chargers:

ebay TP4056 charger search

Avoid this style - only $2.99 for 10! BUT does not have battery cutoff feature - battery output only - no separate load terminals.

Aim for this style

Note separate Out-/Out+ and Battery - / Battery + connections.
Vin can be via microUSB connector or +/- terminals on other side of it.

enter image description here

Here is an SE EE question related to the TP4056 modules.

TP4056 circuit with and without low voltage battery cutout protection.

This is a typical module circuit diagram:

The simpler modules omit the DW01-A protection IC and the FS8205A back-to-back MOSFET switch and connect B- to Out-.

Simple module: Relatively complete LiIon charger with up to 1A output current.
More complex module: As per simple module but adds a battery over-discharge protection function.

Given the very small difference between the modules, use of the module with output protection is by far the best choice.
The battery connects to B+ and B-. The load connects to Out+ and Out-.
That's it ... .
TP4056 IC datasheet here.

A web page on TP4056 charging performance under various conditions here

enter image description here

Russell McMahon
  • 147,325
  • 18
  • 210
  • 386
  • This is bad advice. The device cannot be safely repaired or re-engineered by the asker with a lithium battery and it is irresponsible to suggest that they could. – Chris Stratton Aug 04 '19 at 15:27
  • @ChrisStratton Your cautions are noted. "Cannot" and "safely" are such strong words :-). I've upgraded my already non-trivial safety warnings, and "very highly recommended" [tm] that a 5V USB plug pack and TP4056 module be used. || At that stage he has a clunky torch with old LED, probably. It may or may not be an attractive mod. It can be done and its safe. – Russell McMahon Aug 04 '19 at 16:40
  • I actually do own a TP4056 already, and I was considering using it here. I prefer the option to charge via USB, and it is safer as well in my mind. – Karthik T Aug 05 '19 at 03:31
  • The torch has a pop out plug which plugs directly into the mains, so no transformer other than what is on that circuit board. The back of the plug is visible in the top right part of the images. – Karthik T Aug 05 '19 at 03:36
  • Marking as the answer because the identification seems right.. I was able to locate it, https://www.aliexpress.com/item/32860027654.html – Karthik T Aug 05 '19 at 03:42
  • Can you point to any resources which contrast the two types of charger boards and the right way to wire them up? All i found earlier was using the out pins to power an LED or something. – Karthik T Aug 05 '19 at 03:45
  • @KarthikT See additions at end re TP4056 module. – Russell McMahon Aug 06 '19 at 12:38
  • @ChrisStratton As the downvote appeared at about the same time as your comment I assumed it was from you. Maybe not. If so, care to remove it? - please see Q&A as they now stand. – Russell McMahon Aug 07 '19 at 08:25
  • @RussellMcMahon thanks for your additional help, Decided to convert to 18650, was successful. Also, from bangalore, working in Singapore as you asked earlier – Karthik T Aug 20 '19 at 02:35
  • @KarthikT Closest I've been to Bangalore is Chennai - and the train to Pune :-). Singapore I've passed through a few times. I assume the lights are sold in India - or are they in Singapore? What did you use for a charger? I mention TP4056 but the hardly costlier TP5000 and TP45100 allow up to 18V in (using switch mode). I have not yet seen a module with the TP5xxx and BMS. You MUST charge/manage the 18650 properly! – Russell McMahon Aug 20 '19 at 07:00