#0015: Device analysis of an unbranded LED dynamo torch
Preamble
It’s rather hard to provide a useful review of an unbranded product such as this. Since it has no brand, and no model to specify; we can only identify this particular device by it’s general appearance. Unfortunately this can be an issue when it comes to stating anything definitive about the product. This is due to the unregulated variations and derivatives on the market. In other words, just because two of these unbranded devices are outwardly identical, doesn’t necessarily mean that the components (or configuration there of) are also going to be the same. Heck, we don’t even know if any two different units were made by the same OEM (Original Equipment Manufacturer). Consequently, your mileage may (and probably will) vary if you pick up one of these dynamo torches. I can only show you what I have in front of me; and I have a sample size of two.
Device Demonstration
Device internals
Schematics
Torch A
Torch B
Key:
L1: 5 mmØ through-hole LED (white)
L2: 5 mmØ through-hole LED (white)
L3: 5 mmØ through-hole LED (white)
R1: 5.1 ohm resistor
S1: two-state toggle slide switch
V1: dynamo (AC source)
B1: [x3] AG10 / LR1130 button cell battery
Possible modification
- rectifier and capacitor on the dynamo circuit
Key:
DB1: Diode Bridge
C1: capacitor
I think that perhaps some kind of rectifier followed by a capacitor on the dynamo circuit will provide the parallel LEDs with a more constant voltage. Allowing it to stay on with a constant light intensity for a little longer, at the cost of a few initial revs without any light output as the capacitor charges. Is it worth the effort? Not especially. It might just help prevent the sudden light dropout. I’ll need to test it out myself before I say anything definitive here.
As for the rectifier, I would recommend a full-bridge rectifier using four diodes for maximum efficiency. That is if there’s space for it. This is because this configuration inverts the AC negative voltage into positive, before passing it onto the smoothing capacitor. Alternatively, a single inline diode will simply cut the AC in half by passing only the positive voltage. It’ll do the job, but at the loss of the negative voltage of the AC. Although, this is lost anyway at the LEDs, since they’re diodes. With this use-case, I think we need all the efficiency we can get, and a full bridge rectifier may even make the device function a little better. Like I said it needs proper testing, that’s why I stated this as a “possible modification”, rather than my usual “recommended modification”.
EDIT (2021-02-04): On further thought, any benefits of rectifying the dynamo AC will probably be negligible. I believe this is the case due to the low voltage provided from the dynamo (approximately 2V AC) coupled with the forward voltage drop that will occur within the diodes themselves.
The example diodes I have (namely 1N5818) have a really small forward voltage drop of 0.45 volts at 1 ampere. Even this miniscule drop will have a notable effect on any resultant DC.
web link: https://www.bitsbox.co.uk/data/diodes/1N5818.pdf
Still I still think the idea of rectifying a dynamo’s AC to DC would be worth while if for no other reason then to make a generally more useful form of power. Unfortunately, for a dynamo of this output, it’s just not worth it.
Dynamo AC generation demonstration
Gear array and dynamo
A1: Spur rack: 24 mm w/ 11 teeth
B1: Spur gear: 8.5 mmØ w/ 10 teeth
B2: Spur gear: 41 mmØ w/ 81 teeth
C1: Spur gear: 7 mmØ w/ 12 teeth
C2: Latching spur gear: 2 pivoting teeth
D1: Internal spur gear: 26 mmØ (inner diameter) 32 mmØ (outer diameter)
(Please note: when two gears have the same gear letters, it means that the gears are connected.)
Dynamo:
24 mmØ toroidal (doughnut) magnet (with 4 Norths and 4 Souths)
coil consists of:
- dynamo core (magnetic conductors)
- a 920 cm length of 0.1 mmØ gauge copper wire
(wrapped into a coil of ~276 revolutions)
Please forgive any inaccuracies in naming convention for the gears, this is the first time I have actually paid any attention to the subject of gears in general, and it appears to be a deeper subject than initially expected with quite the learning curve involved. The “latching spur gear” and “internal spur gear” are the ones where I hazard a guess as to what they might be called, this is because at the time of writing I was unable to find a named example of what I was looking at. It can be difficult to find something when one doesn’t know the keywords to search.
Gear system in action
Pushing force on the handle moves the spur rack against spur gear B1. B1 then rotates clockwise. This in turn rotates the conjoined spur gear B2 clockwise. B2 interfaces with spur gear C1, and rotates spur gear C1 counter-clockwise. Which in turn rotates it’s conjoined latching spur gear (counter-clockwise).
The swivel teeth within the latching spur gear are designed to lock into the teeth of the internal spur gear D1. Although this happens only when they rotate counter-clockwise within D1. In doing so they rotate D1 and it’s toroidal magnet. This rotation causes a flux in the local magnetic field. This is picked up by the magnetic metal of the “dynamo core” and transported via this core to the copper coil winding. Where it induces an alternating current that powers the LED lights.
Once the handle is fully pressed in, with the spur rack (A1) at the end of it’s track. The operator’s pressing force is removed. At which point the spring in the handle pushes the handle back out; and forces the spur rack to move back to it’s start position. In doing so it rotates spur gear B1 counter-clockwise this time, this rotation is passed on to spur gear B2. Which rotates spur gear C1 clockwise. This rotation is passed to the 2 tooth latching spur gear C2. Which in turn spins clockwise freely and allows the gear system to reset position. Then the process repeats as the operator pushes on the handle. And so on.
The device as a consumer product
Build quality
This is probably the cheapest dynamo torch on the market. If not in price, then certainly in build quality. The main body of the torch is made up of two separate mouldings that sandwich together. This configuration clips into the grey plastic ovoid that houses the LEDs, batteries, and the light guide/reflector. Add to this one or two (depending on version) small self tapping phillips screws to keep the device together.
The phillips screws for the housing are set into thin moulded standoffs that seem prone to either splitting at the screw thread or cracking at their base. The cracks on the base of these standoffs I believe are caused by the general mechanical stress incurred by the gear and spring system. Both in action: when the dynamo mechanism is being used, with the spring loaded handle being vigorously pumped back and forth; and at rest, because the spring that pushes the handle back out puts a constant stress on the gears that are set into these flimsy standoffs.
I have had these two torches in safe storage for a few years, I was surprised to find out that one of the two had broken it’s standoffs, well off. Considering my storage solution (think sealed plastic tub in a garage), this may have been caused if not exacerbated by temperature variations, in addition to the stress of having a coiled spring pushing against them. But basically, I put the thing away fixed, and found it broken. Considering that one of the use-cases the online retailers advertise this thing for is camping, I don’t think that the temperature swings of the mild british weather should have caused this.
Something positive. The internal components I generally have little problem with; from the LEDs, to the Dynamo, and nylon gears. They are all very inexpensive components, but there is nothing especially wrong with them. They are all basically fit for purpose. Even the dynamo, although unfortunately, it’s delicate hair thin wires extend out the dynamo coil and into the device proper: towards the switch and LEDs. This makes the device far more likely to suffer a breakdown, as these wires are far too thin and delicate to be used for general device circuitry. Especially when in the presence of an unshielded gear-system. Look at the pictures to compare the dynamo wire (~0.1 mmØ) to the LED (~0.4 mmØ) or switch (~0.5 mmØ) terminals to understand just how thin the dynamo coil wire is. Please note: inaccuracies in recorded measurements are due to the pictured calipers used … and me.
False advertisement claims
I have seen this torch (and it derivatives) in multiple online stores. I have also seen a lot of false advertising around this product across multiple vendors. Including Ebay, AliExpress and especially Amazon. This is predominantly due to the seller’s lifting the product descriptions from each other, in some cases they’re literal copy-pastes.
There are many claims on these store pages that made me chortle. These included: “High tech ultra bright LEDS” when referring to the 3 bottom market 5mmØ through-hole LEDs; or the sentence “perfect for outdoor use” when describing an electronic product that is about as watertight as the average kitchen sponge.
Since these claims made are subjective, you can’t say that they are technically wrong, because that’s just like your opinion man. These are (in my opinion man): just examples of product puffing or marketing wankery. Something that I honestly have come to expect at this point in my life. Whenever I go to buy something, I will inevitably have some to sit through at least some marketing bullshit, because apparently every single product ever made, is as great a sliced bread, and should get you as excited as the second coming of our lord and saviour. Or else there is clearly something wrong with you.
Moving on. Something else that I have come to expect, and let’s be honest here – enjoy: is Chinglish. And there are some great examples of this within these product descriptions. My favourite is “Works on a new technology of pressing handle with your hand.” Hey, it made me smile. Here’s another doozy for you: “LED torch adopt advanced technology of LEDs emitting level of 3 fluorescence tube”. What the actual fuck are they trying to say?! If internet scholars ever decrypt this product claim, you can probably safely bet that is it some form of bullshit.
Which nicely brings me to the real issue that I have with these product ads. It is the genuine examples of outright falsehoods. The main two claims that I have issue with, are: 1) That the dynamo action charges the batteries, and 2) That the product doesn’t include batteries in the first place.
For the first example I have an ebay advert that uses the keyword “charge” in it’s description and makes mention of the 3 disposable AG10 coin batteries that come in the unit. Although it doesn’t mention that they are single charge disposable units. Hence the assumption that the average consumer is likely to make is that the dynamo charges these batteries. Another amazon ads states the claims “No batteries required, Eco and rechargeable”, to make the customer think that it comes with some kind of componentry that either enables the device to charge without batteries (e.g. capacitors), or that the device comes with built-in rechargeable batteries.
Unfortunately neither are true. A cursory look at the above schematic for either unit A or B will show you that at no point does the dynamo charge the batteries. They are on two separate loops. Also, where is all the charging circuitry? The bridge rectifier, voltage regulator, and smoothing capacitors involved in converting the alternating current that the dynamo would produce into a fixed voltage direct current for the batteries. Additionally, even ignoring those facts: let’s say after reading this paragraph someone still isn’t convinced of my claim that the dynamo does in fact not charge the batteries; then why does this torch ship with disposable (non-rechargeable) alkaline AG10 coin batteries then? It’s because this claim is provably false.
Now onto the next false claim. This was the one that I took notice of initially, and actually inspired this rant. The claim of these torches not having a battery to begin with. The disproving evidence of this claim in some cases is in the bloody product description itself. I have even seen adverts that claim that it doesn’t have batteries, to then make the contradictory claim of a 15 minute running time at full charge.
Closing thoughts
I honestly never intended to talk this much about this budget torch. However the more I looked into the item the more I found to say. To sum it up for you: everything from the build quality, to the false claims: make this thing is absolute dreck.
I think the main reason as to why these types of products can make outlandish claims and still sell is because of their price. They are so inexpensive, that returning them may cost more in unreimbursed postage costs, than the refunded price of the product. For example: a torch costing approximately £2.50, will cost £3.10 (at time of writing) to return via a Royal Mail UK only “small parcel”. This is of course assuming that the customer bought the product from a UK distributor.
If it was bought from China, then a return is basically not financially viable. The international postage is only cheap one way; and that’s due to bulk export shipping from China. Consequently, I have had experiences with seller’s who have contacted me offering a full refund with no return if I removed a (well deserved) negative review I have given for the product. That’s likely the main reason why they have such high reviews (4/5 star average on amazon); because they buy off the negative ones; like mine.
As for my final word on the torches themselves: I think that they are basically designed to be factory fresh e-waste. They will go from the factory, to the seller, to the customer, and to the bin faster than should be acceptable. This due to their own shoddy nature and little else. They are a good testament to the saying: “you get what you pay for”. One could also use the saying “buy cheap, buy twice”, that is if a person actually intended to use these torches for their advertised use-cases. Good luck camping with this piece of hot shit in your back pocket.
Thank you for reading.