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Member postings for SillyOldDuffer

Here is a list of all the postings SillyOldDuffer has made in our forums. Click on a thread name to jump to the thread.

Thread: Brand Names
15/07/2022 16:02:08

Posted by Peter G. Shaw on 15/07/2022 10:17:37:

... Which is why, nowadays, I go for the recognised brand names, even if it does cost more.

But there are no 'recognised brand names'! The value of a brand name depends mostly on the commercial position of the current owner, who can be almost anyone, plus whatever a bunch of customers choose to believe in, which could be nonsense. Lots of fanboys about!

Many reasons why buying by brand name only is unwise:

  1. Brands don't mean much once products reach commodity status. Generic aspirin is as good as Beecham's Powder etc. (I suspect older folk may not realise just how many manufactured goods are commodities, not requiring trained men to produce them, and made to any price-point the retailer can sell. Most consumers do not want old-fashioned 'quality'. )
  2. Many brands exist to sell overpriced goods and services. To quote the advert, they are 'reassuringly expensive'
  3. Brands vary over time. Old-favourites may have become expensively third-rate whilst a previously notorious brand could have sorted it's act out and become inexpensively excellent.
  4. Brand reputations depend too much on past glories and lazy purchasers. It's what the product does today that matters, not faded memories or wishful thinking.
  5. Many brands are rebadge jobs with no relation to where they were manufactured or by whom or to what specification.
  6. 'Quality' can vary within the same brand when it covers products ranging from cheap and cheerful to designed to last.
  7. Brands are often counterfeited. If Flash Harry offers you a cheap Rolex in a pub car-park, what could possibly go wrong? Rolex are an excellent brand...

I suggest folk should assume nothing and check.

Recent experience of a reputable supplier is a much better guide. In practice, most stuff I buy, which is generally inexpensive, works out well compared with the upmarket gear my mum trusts. My cheapo oven cooked food as well as her expensive one and lasted a year longer. But my choice looks and feels cheap, whereas hers is drop-dead gorgeous. Although her doors open and close with a satisfying quality clunk, it's three times the price and I'd rather spend my money on something else. Be warned, I dress like a tramp too...

Dave

 

Edited By SillyOldDuffer on 15/07/2022 16:03:19

Thread: A bit of bother drilling
15/07/2022 14:17:59

Posted by Chris Murphy on 15/07/2022 10:05:51:

...

sometimes when I try to drill with the tailstock the drill doesn’t seem to go anywhere and the tailstock starts moving back slightly, even though it’s lock in place.

I take it that you drill a pilot hole and then use smaller drill bits until you can use the drill bit for the job in hand. Am I right in thinking this.

...

Blunt drill and/or difficult metal can cause a properly adjusted tailstock to slip. It can be helped by the operator pushing as he turns the handle, but if the drill is sharp and material cooperative, it's time to look to adjusting the tailstock clamp. It may also require cleaning - a clamp soaked in oil and running on swarf is likely to slide.

Run a clean cloth along the underside of the bed where the clamp grips: if it comes out plastered in oil or dirt, consider removing the tailstock and so the clamp can also be cleaned.

If that doesn't fix it, check the adjustment.

Some tailstock clamps are just pulled tight by a nut on a stud; not much to go wrong. However, because having to spanner the tailstock is a time-waster, it's more usual for a lever on the tailstock to cam the clamp tight. Much faster but can come out of adjustment and be fiddly to reset because the mechanism is often on the crude side.

The nuts are adjusted until the cam-lever operates correctly. Loose enough for the tailstock to slide without binding when the lever is off, and tight enough to pull the clamp hard enough to brake the tailstock firmly when the lever is on.  Sounds simple but it may take a few attempts to get right especially at first. The cam may allow the stud to slop from side to side, so be prepared to experiment with the angle as well as how the nuts are positioned. With luck simply tightening the nut a little will be enough, but expect fun and games if the tailstock is removed or the adjustment is way off.

Opinion on the best way to drill larger holes varies. Everyone agrees always start with a good pilot hole, because they reduce wandering. (Twist drills love to wander).

My feeling is it's best to drill the hole full-size in one go because it shares the cutting load across the full edge and big diameter drills are less likely to wander than small ones. But the lathe may not be powerful or stiff enough for this, in which case stepping up is the answer. On the downside, stepping up concentrates wear on the outside of drill tips, and I think using a progression of small drills gives each a chance to decentralise the hole. Twist drills are bendy creatures.  There's always a risk the hole won't be straight, and I've had a few dreadful curves!

Boring is best when it's important for holes to be straight or diametrically accurate. A twist drill is used to make a hole big enough to take a boring bar, which then opens up the hole as required. Slower, but boring cuts on the rotating axis, doesn't wander, and will cut to any diameter. Tailstock not used!

Dave

 

 

Edited By SillyOldDuffer on 15/07/2022 14:23:45

Thread: online upgrades: Is it broken, a disabled feature, or customer gouging
14/07/2022 21:05:00
Posted by Mike Poole on 14/07/2022 19:56:50:

A friend was a service engineer for ICL, he described a service call to install a memory expansion, he moved the link to enable the memory that was installed as standard but not enabled. The customer paid much more than the cost of a service call.

Mike

The ICL1906A I started on had 256k words of core memory installed, but my employer could only afford to pay to have 198k words* switched on. Must have been pricey because this was a machine expensively installed in it's own purpose built building, with a water cooled computer hall and office space for about 200 employees, plus it's own electricity sub-station, six rotary generators, and a 2MW diesel generator set. Originally worked on a 3-shift system, later cut to 2 after software efficiencies and giant 200Megaword disc drives were installed. Seriously expensive to run, but it saved an enormous amount of money, well over a billion in today's terms.

A curious thing I remember was that almost all the peripherals - line printers, card readers, paper tape, magnet tape and disc drives etc each cost roughly the same as an average home. Scary thatt it was more than half a century ago, but not as horrifying as that old bloke I see in my bathroom mirror every morning...

sad

Dave

* words not bytes. Each word contained four 6 bit characters, so upper case only.

Edited By SillyOldDuffer on 14/07/2022 21:05:48

Thread: Very Confused
14/07/2022 19:02:31
Posted by Haydn Callow on 14/07/2022 18:02:21:

I read that quite s few have used brushless 500 watt motors using motors that are available for sewing machines and they come with digital controllers…..can I not get a similar controller and hook it up to my SIEG motor.

I don't know the answer. Motors usually come with a matched controller and without that the repairer has to understand enough detail to make the match.

The 110V brushed DC motor normally fitted to mini-lathes is fairly easy - relatively simple wiring and lots of suitable controllers are sold on ebay and others if you can't find a direct swap for the machine.

Replacing with a 3-phase motor and VFD is fairly straightforward, otherwise it can get difficult.

A recent question about a Wabeco lathe hasn't had a good answer yet because it's DC motor has field winding inputs and a tachometer output, so both it and the controller are unusual enough to be mysterious.

Some other machines are fitted with 2-speed motors, or two or more 3-phase motors. They're a complication I would rather avoid!

Your Seig motor is brushless, details unknown, so although it may be possible to get it going with a sewing machine controller, I doubt anyone on the forum or in the trade knows for sure what to buy. Might get lucky if someone reads this and has done it already. I don't recall anyone reporting having to repair a Seig brushless lathe yet.

Easier to get a brushless sewing machine motor and controller together as a package, because someone else has already sorted out the details. Buying a package avoids the possibility of accidentally causing the dreaded magic smoke, or hitting a wiring puzzle can't be fixed by hard-thinking. As mistakes are expensive, may be better to bite the bullet and buy a replacement motor of the type that's failed - minimal change fitting and reconnecting, so low risk.

Dave

Thread: MAX-T
14/07/2022 15:29:54

As regular readers know I have a low opinion of brand-names; whilst some are carefully protected indicators to well-made products, most are just labels, perhaps entirely symbolic.

Seem to me that MAX-T is just a trading name rather than a manufacturer or a particular product line. Generic manufacturers are happy to provide whatever colour, brand-name, packaging and price point the retailer wants. Anything between top of the range and too cheap.

Probably the only way to find out for sure is to buy a MAX-T tool and test it. If HSS, there's no special magic in the way most of it's made, so it will probably work as well as any other HSS of the same specification. But what specification? Often unstated by small vendors. If it matters, order from an industrial supplier who identifies the exact type of HSS that meets your needs and perhaps certificates it as well. May cost more...

'Quality' is the simple sense of the word probably isn't a factor. For example, M1 and M2 HSS are similar except M1 is the more shock resistant of the two. That's good, unless cutting temperature is the critical issue, because M2 withstands heat better than M1. Which of the two is the highest 'quality' depends on how it's used, not on the material.

The similar T-Max is a registered Sandvik brand-name covering a range of industrial grade carbide products.

Dave

Thread: Rev. Counter
14/07/2022 14:41:44
Posted by Lynne on 14/07/2022 13:18:24:

S.O.D. N.D.I.Y.and others. Read my post. I refer to 'spindle speeds when using my mill' so why introduce things relating to lathes? ...

I did read the post! Perhaps unfortunately I described the magnetic tachometer on my lathe rather than the optical tachometer unhelpfully fitted to my mill. But the machine is irrelevant: magnetic tachometers work the same way whatever they're fitted to: lathe or mill, similar answer.

I hoped I'd answered the question by describing the three things likely to cause a magnetic tachometer to misread RPM. Frequency or other Hall Effect weirdness is unlikely.

My co-defendant is innocent too! NDIY's neon light is the classic way of calibrating the RPM of any shaft; works OK on both mills and lathes. Other methods available, but probably easiest to buy a cheap RPM meter and compare results.

Dave

Thread: Lathe Blowing Fuses
14/07/2022 12:09:02
Posted by Andrew Struth on 13/07/2022 12:23:11:

I have a used CL300 Clarke lathe,it blows fuses EVERYTIME I get the cutting tool jammed.It not often I stress to point out ,but it’s annoying me to the point I’ve become over cautious when cutting.Any answers.

Hard to judge from a distance or if something is wrong with the lathe. Possibly the motor is faulty but stalling puts a severe strain on the motor and electronics; blowing the fuse may be the best option! If the lathe blew fuses during normal cutting, I'd suspect a machine fault, but jamming the tool suggests something else is going on - material and/or operator causing overloads.

I learned to turn on a mini-lathe and found it had a sweet-spot between too light and too heavy cutting. Much depends on the material too. Are you using free-cutting metal or unknown scrap? My early learning was severely slowed because my scrap box happened to be full of difficult metal, and DIY store metal is nearly as bad. An unlucky start, followed by finding the lathe was much better than first thought!

Once I found mu mini-lathe's sweet-spot jamming the cutter and stalling became rare, usually due to mistakes. Certain operations are best avoided: parting off steel was too much for the lathe, and sticky Aluminium was risky too. Also threading under-power: easier to make a crank for the spindle and thread by hand. Make sure the gibs are adjusted tight, but not too tight, lock everything that can be locked, and minimise overhang from saddle to tool-tip to prevent movement. Dipping cutting edges are likely to dig-in.

Same sweet-spot principle applies to my current lathe. Although considerably more powerful and stiffer than a mini-lathe, I still drive it defensively. Roughing out: after making sure the cutter is good and at centre height, I set RPM and feed rate in the right zone for the material and diameter, then adjust depth of cut so the machine sounds as if it's noticeably working rather than idling, but not labouring.

Big lathes, and especially industrial machines, are less fussy about 'sweet-spots' than small ones, but they all work best driven within their design envelope. Mini-lathes aren't ultra-delicate, but they're hobby machines, not metal hacking bruisers.

Over cautious cutting is liable to rapidly blunt tools, so avoid doing it. I learned the dangers of 'pussy-footing' from Andrew Johnson of this forum, along with many improvements from other members. Very often forum advice has to be practised to get the best out of it, so persist.

With luck the lathe is OK,

Dave

Thread: online upgrades: Is it broken, a disabled feature, or customer gouging
14/07/2022 11:09:39

I see it as the usual basic economics.

  • Manufacturers are in business to profit by selling stuff
  • Customers want stuff, and have to decide how much they are prepared to pay for it
  • Stuff can be anything people want. Services, software, commodities, machines, or bling. Stuffs value varies with demand and availability.

Adding heated seats and other extras were originally done by car makers as specials; men and machines were diverted off normal production to add them, hopefully at a profit. Modern car factories are heavily automated, volume pushes prices down, making it likely cheaper to install 'extras' as standard and profit by charging the customer if he decides to pay for them. Not price gouging, because there is no obligation. Nor should the customer expect to be showered with freebies by generous manufacturers: they have to make the business pay in a ruthlessly competitive world.

As the UK and much of Europe is currently suffering a heat wave it's hard to imagine any customer round here wanting to pay at the moment for an extra hot bottom! Presumably, BMW's offer tempts drivers planning for winter or the sort who value a full set of accessories. The offer works because basic economics confirms that a pound in the bank today is more valuable than a pound that might turn up in six months.

Economics is interesting because customers don't behave rationally and their changing behaviour as a mass causes the cost of 'stuff' to vary unpredictably. Price gouging occurs when demand outstrips supply, which is often caused by foolish customer behaviours like panic buying. (Remember the toilet roll crisis when COVID kicked off?)

Once we've been fed and have a roof to live under, we tend to loose the plot in another way by spending money on fads and fancies. Good fun, but it does lead to unwise expectations, perhaps assuming god or politics will guarantee our personal wealth irrespective of what else is happening across the world. Actually wealth depends on hard-work, innovation and meeting customer needs rather than beliefs or alternative facts.

Customers often see the same situation differently: just as people prefer cats to dogs and vice versa, some of us enjoy paying big money for things others consider ill-judged. Personalised number plates are an example. Putting it politely, large numbers see them as evidence of having 'more money than sense' at best, and a much, much ruder word is commonly applied to drivers who have them! Nonetheless, I see personalised number plates all the time: their owners must have a different world view: I wonder who is right, or are both sides wrong?

Dave

Thread: Oils/grease for mini lathe
13/07/2022 22:46:02

Posted by Andy Chancer on 13/07/2022 22:04:18:

...

Hope I’ve not committed a cardinal sin on here lol!

Nah! I'm not sure a search would find what you want that easily, specially not the top right box which is naff. The one half way down the home page is better,

Mini-lathes aren't fussy about oil and grease. I used white lithium grease and ISO32 hydraulic oil on mine. 20/50 motor oil if the iso32 wasn't handy. May be worth putting Way Oil on the bed: it's sticky and resists being squeeged off by the saddle and tailstock. I have some but usually just splash whatever's to hand: the main thing is to have some lube. I normally apply oil at the beginning of each session and regrease the change gears when I swap them or remember! The hi-lo wheels inside the headstock don't need much attention and the headstock bearings are sealed,

Can I recommend NOT starting with a strip down. Get to know the machine reasonably well first by making several different things. Nothing like cutting metal as a way of finding real problems. Trouble with diving in at the deep end is it's hard to tell the difference between new faults introduced by your inexperienced good self from existing faults, normal limitations, and misunderstandings. Although not rocket science, there's more to reassembling and adjusting lathes than might be expected. Materials matter too and operator skill makes a big difference!

Dave

Thread: Myford ml7 toolpost bolts
13/07/2022 19:40:29
Posted by roy entwistle on 13/07/2022 19:28:40:

TPI ?

Roy

Like it, makes sense, ta!

Aren't all BSW 1/4" bolts 20 TPI? If so could explain why many websites don't bother stating it.

Dave

Thread: New motor for wabeco lathe
13/07/2022 19:33:53
Posted by Robert Atkinson 2 on 13/07/2022 19:26:40:

A motor with brushes, a commutator (segmented rotor contacts) and a wound stator (not permanent magnet) will run on AC or DC. For this reason they are often called a "universal" motor...

Doh, is it that simple? In my defence, the spec says it's a 1.4kW motor, which I assumed is too big to be a Universal. Don't know why though, except I've only come across Universals on sewing machines and small power tools up to about 250W max.

Dave

Thread: Myford ml7 toolpost bolts
13/07/2022 19:20:28
Posted by Chris Murphy on 13/07/2022 18:17:16:

Hi,

Ive been searching around for these bolts but can’t seem to find the right ones anywhere .

I’ve seen some on Amazon, but most don’t say what the tip is, mine are 20 tip.

...

What do you mean by '20 tip' Chris?

Dave

Thread: New motor for wabeco lathe
13/07/2022 19:01:37

Here's the circuit diagram from the manual:

d3000circuit.jpg

Assuming the problem isn't confirmed by magic smoke from a cooked control board!

The manual says the brushes should be sanded down every 100 hours and the commutator cleaned. Plus advice to check in the event of a stoppage that the plugs and sockets haven't vibrated loose. If that's been done, I'd check the usual other mini-lathe weak-spots before rushing to change the motor or board:

  1. Check the safety cut-outs are all allowing power to reach the board:
    • S10 - switch on chuck guard closed
    • T2 - thermistor on motor closed
    • S1 - Emergency cut-off reset, not popped open
  2. Confirm the speed control potentiometer is working - they often fail by going open circuit. A squirt of switch cleaner might get it going, or replace

The manual says the motor is single-phase, and the circuit shows 8 connections:

  • Pair to Thermistor, disconnecting the mains if the motor gets too hot.
  • Pair from Tachometer to board providing speed regulation. If this failed would the motor run fast, slow or not at all?
  • Pair to K1 and K2. I guess these are the field winding and may be fused. If fused, this pair may be the main power input. Check for fuses - I don't recognise the circuit symbol, but it could be an inline fuse. I can't see anything else that might be a fuse,
  • Pair to W1 and W2. I guess these feed the armature and are fed a control voltage from the power board.

The claim to be a single-phase motor might make sense if this was a simple triac triggered speed control circuit, but I don't understand what the brushes are for. They suggest a DC motor, or is there a type of AC motor with brushes?

Dave

Thread: Rev. Counter
13/07/2022 17:21:19

On my lathe the Hall Sensor is mounted perilously close to the magnets, of which there are four. They sit in shallow milled cavities about 3mm diameter.

Suggestions:

  • The new sensor isn't mounted close enough to the spindle, or the magnet(s) don't pass directly underneath and it isn't being triggered reliably.
  • One or more magnets has been lost (assuming more than one), causing a miscount.
  • If a magnet was dislodged in the accident, maybe it's been replaced upside down (wrong pole facing the sensor)

Dave

Thread: Myford ml7 toolpost bolts
13/07/2022 17:02:56
Posted by Sandgrounder on 12/07/2022 15:10:34:
Posted by Mike Poole on 12/07/2022 14:04:35:

My first choice would be to hunt down some square headed screws but that may not be so easy, remember that 1/4 UNC is often a passable alternative to 1/4 BSW and in this application will not be critical

Mike

Why are square headed screws used anyway and not hexagon headed? I've always thought the latter are easier to obtain and use with more spanner positions available, especially if using a bi-hex wrench. is it just historical?

John

I'm sure no-one on the forum insists on hitting a spanner extender with a big hammer in order to guarantee tightness, but some folk find the temptation irresistible! Hex heads are begging to be wrenched! And they take up more space on the tool-post than other types.

My guess is square-headed screws are provided with a matching T-handle to discourage ignorant overtightening. Allen screws have the same characteristic: the amount of torque that can be applied by a Gorilla high on Steroids is automatically limited by the arm length of the Allen key.

My mini-lathe had Allen cap-screws and it's bigger replacement has squared nuts. No problem using either.

Dave

Thread: What is acceptable chuck run out?
13/07/2022 16:28:54

Measured with the 15mm diameter length of Silver Steel I use as a test bar, the chuck supplied with my Chinese lathe has run-out averaging 0.04mm (worst 0.05) . I measured the run-out 50mm away from the chuck jaws.

Not sure why the run-out varies, could be a mix of the scroll not tightening evenly, faulty micrometer technique, and perhaps the Silver-Steel rod is imperfect; it's diameter is on the small size and it might be slightly bent. Nonetheless the values are within expectations - average run-out 0.04mm is somewhere between 1 and 2 thou.

My example being ten times better than the 0.4mm measured by Bryan suggests something is wrong. Perhaps the chuck is a lemon. However, as always, check everything. The chuck may be last straw rather than guilty party; possibly it's weight causes something underneath to move. Does the backplate measure OK if the table is pressed down hard by hand?

Dave

Thread: HBM 250-550 Lathe Tooling
13/07/2022 10:33:04

The HBM looks similar to the Warco WM250 and other generic Chinese Lathes:

Details vary - they're alike rather than standard - but all have similar capability. They're made by at least two major makers.

Worth browsing the Grizzly website to see if they sell the same machine because manuals for the US market are often more complete than the basic material supplied with British machines. The Grizzly G0602 looks similar, it's manual might be useful,

My lathe is the next size up, and it also can take 12mm tooling. It's the maximum size the lathe will put at centre-height rather than the recommended size, and best approached with caution because not all nominal 12mm tools will shim to centre-height. I mostly buy 10mm tools because they're guaranteed to fit! Shimming up is easier than shaving metal off a toughened 12mm tool!

Larger tooling has the advantage of being stiffer than smaller, usually a good thing, but I often find big cutters too clumsy for what I do. 10mm or 8mm is more appropriate and occasionally 6mm. The choice depends on how much space is available between job, chuck and cutter and the delicacy of the job in hand. 10mm is a reasonable size to learn on, and might be all that's needed. It depends on what the lathe is used for over time, which is why second-hand machines often come with a strange mix of tooling!

Must be possible to adjust the cutter to centre height, and then to reduce vibration, which is usually done by minimising overhang. Reach for a big cutter if a lot of metal must be removed quickly, but bear in mind hobby lathes aren't beefy enough to work at industrial rates and using smaller cutters is a good way of reducing stress and strain caused by over-enthusiastic operating.

Dave

Thread: Filing rest - hardened guides ruining files
12/07/2022 12:56:59
Posted by A Smith on 12/07/2022 12:17:16:

Tempered to achieve a hardness slightly less than that of a file? Seems possible but would require better temperature control than I can manage with a gas ring.

If the Domestic Authority allows it, temper in the oven! Light Straw, which is probably still too hard, is about 200°C, so soaking in an oven at 180°C for half an hour or more should do the trick.

My book emphasises the need for speed. The workpiece must go straight into the oven after being hardened, preferably while the metal is still above about 80°C. Taking a few minutes to sort one's act out before getting the metal into the oven makes it likely it will already be stuck in a hard condition rather than continuing to soften down as required. Tempering done accurately to get to a specific combination of hardness and toughness is quite a slow process - hours or longer. For my needs, I either leave silver steel hard and hope it doesn't shatter, or temper it unscientifically, basically hoping holding it rough and ready at a lower temperature for a bit will be good enough.

If the need for speed is as important as my book suggests, it collides with the ordinary way of judging temperature by looking for straw to blue oxide colour changes as the job is gently heated in a flame. To see them the job has to be cleaned first, which wastes valuable seconds. My book avoids the issue by assuming a thermostatically controlled oven is available, and no cleaning is necessary.

Only used filing buttons a few times and left them soft, ordinary mild-steel. They weren't expected to last and I was too lazy to find silver-steel and harden it! Worked OK for what I wanted, but not much of a test.

Dave

Thread: FORUM DOWNTIME AND RESULTING ISSUES REPORTING
12/07/2022 12:18:29
Posted by Versaboss on 10/07/2022 14:58:29:

As this seems to be the place for all strange things, I present mine here.
Not that it disturbs me much, but strange it is nonetheless.

I am - for more time that I dare to think - a loyal user of Opera. But now, when I open the forum page, I get this:

opera.jpg

whereas, when using Firefox, the page looks like that:

firefox.jpg

But please do not propose to ditch Opera - I will never do that!

Is Opera too fast to find the advertisement???

Regards, Hans

'Is Opera too fast to find the advertisement?' might be the answer! Is Opera's ad-blocking feature switched on? Opera claims speed advantages as a result of not retrieving or displaying any link in a webpage that might be an advert.

Ad-blockers usually allow advertising hosted directly by a website and only strip material hosted by an external website, especially those known to vend adverts. The Chronos ad in the top banner today comes from 'servedbyadbutler.com', so an obvious target. Possibly Opera removes it, whilst Firefox doesn't. (Ad-blocking is a Firefox add-on, which has to be specifically installed by users and activated.)

Ad-blocking isn't entirely trouble free. Normally adverts are removed seamlessly, or they leave a harmless blank space, but stripping them out sometimes disrupts the format of legitimate content, causing odd side-effects like overlapping text and/or images.

Dave

Thread: LED lamp help please
11/07/2022 10:49:59

I wouldn't worry about the resistance of the diodes; for a circuit like this it's usually enough to confirm the resistance is high on one direction and low in the other, showing the device is working. Measuring the actual resistance requires an experimental set-up measuring amps whilst the volts are accurately varied over a range. As semiconductors don't obey Ohm's Law, the result is a curve on a graph, not needed in this case.

How well or badly Glyn's circuit behaves depends on the properties of the components:

  • The Solar Cells deliver 2W at 5V, that is a maximum of 0.4A each, 0.8A total.
  • BAT41 diodes support a maximum of 100mA. Therefore diodes are at least eight times too small to cope with the maximum output of the solar cells, which is a risk
  • An AA-size NiMh cell has a capacity of about 1900mAh. Three of them in series (4.6V) will charge reasonably well from a 5V solar cell so that's OK.
  • The power requirement of Glyn's flickering yellow LED is unknown, but the small tea-light type run for a claimed 100hours on a CR2032 cell. As the capacity of a CR2032 is about 230mAh, the current drawn by the LED might only be 2.5mA. It would run for about 760 hours on a NiMh AA.

So, if Glyn is using a small LED, and the AA batteries are fully charged at the outset, there's a good chance in normal service that the batteries will never discharge to the point that the solar cells will exceed 100mA output.

All good, unless 'normal service' doesn't happen. If the NiMh batteries go flat in storage, or deteriorate with age, then their resistance will drop massively, causing the Solar Cells to deliver a heavy current, with a high risk of popping a BAT41. (Cells don't obey Ohm's Law either!)

The component values really depend on the current drawn by the flickering LED. In the good old days, LEDs rarely consumed more than a few tens of milliamps, but modern devices can be much more powerful. It would help to know how much current in drawn by Glyn's LED.

From a 'common-sense' perspective the circuit is reasonable, but the operating conditions need to be defined and the sums done. Here common-sense has delivered a solution likely to work, perhaps for years, but - assuming a small LED - there's risk of failure depending on how it's operated. For example, the diodes are likely to fail if the batteries go flat in storage and the unit is suddenly exposed to bright sunlight. Or they might survive if the solar cell output is limited by weak sunshine and the batteries recharge slowly. As always common-sense relies too much for comfort on luck - real engineers work to requirements, do the maths, and set specifications!

Doesn't matter for Glyn's purposes, but - again assuming the LED is small - on the face of it the Solar Panels and Battery are both over-engineered; bigger and more expensive than needed to do the job.

A professional designing a commercial product like this would start from the current requirement of the Lamp, from that decide the capacity of the battery (perhaps assuming long Scottish nights and short winter days rather than Florida), and derive the size of the solar panels needed to charge the battery in the target conditions. The diodes would probably be rated to take the maximum charging current drawn by a completely flat battery from a Solar Panel at peak output.

For cheapness, diodes are fine, but if the device requirement included long-life, then a more or less clever recharger of the type recommended by Bruce Edney would be used. They extend battery life considerably by matching charging volts and amps to the batteries ideal recharge cycle. A requirement for long-life, say the light on a life-jacket, would trigger a bunch of other specifications, such as water-proofing, liable to push the price up considerably. Daft to pay safety-critical equipment prices for a garden ornament, or to expect a garden novelty to last forever!

Dave

 

 

 

 

Edited By SillyOldDuffer on 11/07/2022 10:53:40

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