50Hz 60Hz Question Again! Battery Charger

I would just get a step down voltage converter....although I might call B&D to see if what recommendations they might have....

http://www.amazon.com/VCT-VTM-150UK-Converter-Products-Chargers/dp/B0014XCK8W

I agree. Using step down transformer is the right way to go.

Mains frequency of 50 Hz / 60 Hz is not a serious problem for chargers that generate DC output voltage as designs are for dynamic range of power frequencies from 45 Hz to 65 Hz as you are never sure if generator runs at exact frequency or not. Frequencies may be critical only for timing circuits, notch noise filters, synchronization circuits etc.

Some circuits sold at Amazon may be highly critical for the DC voltage and may simply get burnt out so be careful not to use higher input voltage else your device may fail forever.

Ni-Cd batteries have one serious drawback that if they get discharged below a certain charge level, then recharging them may be impossible and they may simply get heated and may also bulge. Just keep them charging and that often work fine and are relatively cheaper than Lithium Ion batteries.

You'll never know the difference.

The "on" time compared to the "on charge" time will probably be 5%/95% so it will sit on the charger far more than it will ever be run.

NiCads don't tolerate being on charge as well as newer battery technology, so I saw it won't matter.

Maplin Electronics...http://www.maplin.co.uk/c/batteries-and-power/power-supplies/voltage-converters

Part code RP90X

This appears to be a 230V to 110V transformer 45 watt, 3 pin UK plug on socket side and USA pattern 2 pin socket outgoing.

There may be a smaller rated one.

This is probably a lot less trouble than cutting the lead and attaching it to a 230V/21V transformer (if you can find one), for which you will have to make an enclosure.

Good luck.

67model

For the avoidance of doubt, further to my first post...

The usual way of these cordless vacuum cleaners is for the vacuum to have an internal rectifying diode (to get DC) and ballast resistor. The "plugtop" gives an AC output.

Since you write that the plugtop itself has a rating plate specifying AC output, I am sure this is what you have.

As other posted replies write, the battery will not care.

The only "snag" is that a 60Hz transformer (in the supplied plugtop) driven at 50Hz by its specified 60Hz input voltage gets 60/50 of the magnetic flux density, which may mean seriously increased losses.

If it got too hot to easily hold your hand on it after several hours I would not use it. This kind of gear is left on continuously, unattended, and could be a fire risk if overheated.

67model

67model-

Your battery charger may not have a transformer at all. "Switching power supplies/chargers" do away with the large transformer and use electronic circuitry to eliminate the bulky and relatively heavier power transformer. This type of unit increases the frequency of the incoming power, puts it through what is called a toroid and then rectifies that to obtain the output power. Depending upon the circuitry the output can be higher or lower than the input.

Switching supplies are much more tolerant to voltage input changes and frequency changes. The power supply that you spoke of with the transformer is usually called a "linear" power supply.

If you can see the internals of the power supply find out what type of supply it has. No matter what it has it is best to use the international conversion transformer, a very cheap one, to change the input voltage from 220v to 120v. If it is the switching type supply then don't worry about the 60-->50 hz change. The switching unit will still operate fine and charge the battery.

Good Luck, Old Salt

Dear old salt,

Ref your post #8. I think you misunderstood. The original post question definitely wrote that the "plugtop" rating label specified 21V AC output.

So I did not confuse by reference to DC output plugtops, which might be "switch mode".

We have gone through 3-4 of these cordless vacuums, that I can remember, till the latest, they had the AC output plugtop and lasted until the batteries failed, a good 4 years I guess.

The latest (Dirt Devil, super 12V, high power, and far more expensive than former models) has a DC output "switch mode" plugtop. It has only lasted 2 years. The plugtop gives out 8V DC when it should give 15V - it sits by me at the moment awaiting a solution.

The new complicated electronic design seems less reliable than the old. Perhaps I should have stuck to "Hack and Wrecker, with whose tools in the TV commercials, you can do a lot of damage in a short time" , like the previous ones.

Note that I am "67model" because I finished my training with a telecommunications company in 1967: as a designer of transmission electronics, which was full of ferrite toroidal transformers and pot cores, working at audio frequencies to Mc/s (pre-Hz). Much smaller than iron cores.

Regards,

67model

67model-

My profuse apologies- My answer #8 was not intended directly to you. It was for the original poster and not in any way you. Again my apologies. I am much better at engineering than I am at keyboarding.

But while you are here, I read the original posting to indicate that the input to the battery charger to be AC and the output directed to the vacuum battery to be DC (AC/DC wall wart) or the battery charger was actually a wall plug-in reducing transformer with a switching power supply internal in the hand vacuum This would function as what is also known as a "DC wall wart". Likewise if the complete battery charger were internal the same function could be achieved.

Also, when composing my answer I somewhat doubted the accuracy of the statement that the charger output was 21vac @ 100ma. Since the manufacturer rates the unit as "15.6V HAND VAC" (VAC denoting vacuum and not "volts ac") and the battery would have to be within the hand vac. Also with a hand vacuum weight is a critical item. Why would a manufacturer want to put anything other than the battery in the unit if it could be mounted in a wall wart? Also power supplies for portable tools, and almost all other portable tools, no longer use AC output power supplies most of the time. Costs and space considerations have led them to use DC output supplies. I don't recall any AC power supplies being used for portable tools in the past 20 years or more.

Unfortunately many of the tool brands now concentrate on brand recognition and marketing instead of durability, convenience of use and especially quality. I have had similar experiences with some items such as you have. Being of the somewhat "old school" on this matter I miss some of the old brands such as "Williams", the old "Rockwell", the old "Milwaukee", the old "Porter Cable", the old "Proto", etc. I also find Snap-On to be very good but not at the premium that has to be paid.

Just as you refer to yourself as a "67model" I refer to myself as "Old Salt". The "Old" refers to both my age and what some friends perceive to be intelligence. The "Salt" refers to my infinite love of sailboats and sailing. Fortunately for both of us '67 was only a few years ago, at least in spirit.

Your experience and knowledge in electronics/electrical are certainly to be admired by others. Anyone who has successfully experienced the transition from vacuum tubes to transistors is certainly very knowledgeable in the field as well as respected.

Again, please accept my apologies.

Good Luck, Old Salt

Hi, Old Salt,

A most courteous reply from you. Your score of 1 Good Answers per 10 posts is very good. This post was one where the original post was soon lost in the crowd and it all became confused - so I will leave it now.

I agree that DC output adapters are the norm today. But one has to go with what one is told. If it is a switch-mode AC to DC wart it will not care about frequency, but if it has an iron transfo there could be danger.

You are right that durability has gone on the back-burner for a lot of products. But motor vehicles last far longer, are more efficient and need negligible maintenance.

They are not "Made in China" yet, though!

Good sailing, see you around on CR4,

67model

For switching supply it is easier to rectify the input voltage and store the charge on a capacitor first and then do some high frequency switching with Ferrite core isolation transformer.

If input stage has a transformer for step down then it has to be low frequency iron core to cover 50Hz/60Hz frequency range.

Transformer coil primary and secondary if wound separately then they are much safer due to greater isolation and even in worst case of coil bunt out condition they still remain isolated.

There is some advantage of using just one rectifier diode. You will have only 50Hz / 60Hz ripple. If you use full bridge then ripple frequency doubles.

Current control resistor sure is a good idea with calculated risk of low and high current range already estimated.

Using such circuit, battery charges initially for almost half cycle and then charging time keeps coming down as voltage develops over the battery.

Safety circuit can have a way to stop charging rather than going for minimum continuous charging.

I think you have written 21V 100mA and transformer of much higher power. This 21V if you plug into your system then its voltage will drop drastically if you have switching supply for charging which is very likely. If you use transformer of the same output voltage but of higher power then voltage will not drop down and may behave differently.

There are two possibilities. you can experiment and it may or may not work and there is a chance of getting your charger damaged forever. Why not look into catalog and see minimum and maximum ratings for voltages and desired current levels? With higher power transformer, chances of getting damaged are much higher.

Some charging circuits can even damage the transformer as they may have voltage clamping Zener diode or some other circuit which may not work properly at higher wattage at source.

Ask Chris if CR4 has some insurance cover for free advises here.

'67model-

Don't ever feel lonely if you prefer to use cycles/sec, such as megacycles, mc/s, or kilocycles, kc, or even now gigacycles, gc. There are some of us holdovers that prefer the old way and not the new Hertz, Hz, nomenclature. Makes me think of a rental car every time I say it. Maybe they will come out with a new unit of "Avis" to compete with hertz. This could be a hardness/time unit such as Avis/sec with "We Try Harder".

Good Luck, Old Salt

What ever happened to the "Alamo" rental cars? Did they go the way of the Alamo?

"Yes its 4.5 Alamos on my Meter......"

That franchise was owned by Davey Crockett regretfully. We all know what happened to him at the Alamo. Franchise for Alamo cars and "Rent a Nag" were merged shortly before then so I guess his assistant from "South of the Border", Senor Pepi must have taken over. He always had an explosive attitude while doing business.

The completion of 95 probably left Senor Pepi by the wayside at South of the Border.

Please note: Translation by Google Translate is not available for this message. Translations from American regional dialect to English are available upon request

Good Luck, Old Salt

It is probable that there is no filtering capacitor so the output would be either a fully rectified (120 pulses a second) or semi rectified (60 pulses a second). inputting 50 Hz would out put either 100pps or 50 pps. Check the output with an oscilloscope if in doubt. anyway, I would suggest that it would be okay to just use a step down transformer. Any hobbyist could build a cheap charger for you to run from 240V and 50 Hz. This question does raise the question of when is America going to join the rest of the world and go 240/50?

" when is America going to join the rest of the world"? Probably never. Why would we?

And, why not 87, or 133 Hz?

Or 400Hz?

Why is 50 better than 60?

220/230/240 is available most everywhere.

As one US transformer maker said to me after I complained that his power transformer was beginning to saturate on 50 Hz, "Ah, yes, 60 cycles but 50 hurts".

To the OP I would suggest buying a UK/EU-market replacement power supply from B&D.

Lyn, I recall this from college - 60 hz (my professor used cps - he was an older man) in lighting cannot be visually detected, but some people are bothered with 50 hz. Why not 87 or 133 or 400? I'm not sure from a power generating standpoint, but looking at this from the efficiency side, higher frequency transformers require less iron (if iron core), so you would think it would be better to use higher frequencies. But what about hum? Since higher frequencies can be more of an audible nusiance (60 hz is pretty low). Just a thought ...

The real issue here, that I did not bother to bring up, is the astronomical cost of retrofitting every generator/motor/clock/etc. etc. That's insanity!

Theophilus did, I don't remember where.

I was commenting on the original choice to use 60hz. Since our entire country is using 60hz, I agree that the cost would be horrendously high.

And going to 220 or 240V would also be out of the question. Not to mention that I don't like getting shocked by 115V and I know that 220-240 would be much more dangerous. I don't like messing with the circuit breaker panel with the cover off - that's 230V and I know it'll hurt really badly!

"Check output with oscilloscope if in doubt."

How many people who are self-admittedly not electronics hobbyists nor engineers have an oscilloscope and know how to use it? Are you bluddy kidding?

Your point is taken. I should have said... Get the output wave tested with an oscilloscope .... Most serious hobbyists should have one.

"when is America going to join the rest of the world and go 240/50?"

I thought 50 years ago that America would change to metric within 20-30 years. Now the only thing that has successfully changed are the alcoholic and carbonated (and a few other) beverages.

About 20 years ago there were a few gas stations that started to show liters, and a few road signs showed distances in km. Those have all disappeared.

Since 60Hz magnetic devices are generally more efficient than 50Hz devices, and require less magnetic core, I see no reason to change the frequency. (why do aircraft use 400Hz?)

As far as voltage is concerned, we already have 240V for the higher powered devices in homes, and in industry we commonly use 208, 240, 277, and 480V (and other voltages) 3-phase.

I suspect the answer to your question is: about a century after America converts to metric. The metric conversion should happen, but it won't be in my lifetime...

I think you'll find that it will be cheaper for you to just call this a "lesson learned" and just shell out the £30≈60 for a UK hand vacuum. How much will a suitable transformer cost?

A big thank you to everyone here. I am re-assured and will go for a simple step down transformer whilst keeping an eye on the power supply temperature.

On the side, the only reason I got this model from the states is that it isn't available here and I was impressed by the reviews more than the models that B and D offer in the UK

Hey guys and gals, you have been fab

The standard frequencies were all decided by the technologies available at the time.....the US was slightly later, technology had improved and the frequency was slightly "upped".....

Today, I suspect we would have a far higher frequency than either, but what would be practical and not too expensive, I personally cannot say, but 100 to 120 Hz at least. Naturally 400Hz would probably be more efficient, but might the alternators be too expensive?

It would be good to hear from someone who has studied this in greater detail, with regard to cost and practicality and what frequency would be best.

But let us not kid ourselves, the likelihood of a change today is really tiny.......thats progress for you......like the standard railway rail width of today, that is the same as Julius Caesar had for his chariot wheels (4 feet 8.5 inches I believe!).......I read somewhere......

I personally see no need to address frequency "problems" they can be safely ignored.

I personally would simply supply the unit with either AC or DC (that will get the hounds baying shortly! As none will have thought about it properly!) at 21 volts, as it would appear that the charging "intelligence" is in the unit itself, not uncommon today.

I even have a cheapie LED SWAT flashlight that has the true charging circuits in the unit.....

The only difference between 21 volts AC and DC is that the AC has a higher peak voltage, but the "work done" by both is the same......

Also, we should not forget that as far as I am aware,there are no AC batteries in this world, so the unit internally will convert AC to DC and even DC to DC will be OK........as it will be easier to achieve 21 volts in DC, than searching for a 230 to 21 VAC transformer.....probably cheaper too....

The power input is MOST unlikely to go via a second transformer in the unit, its far more likely to be full wave rectified immediately.

(Furthermore even if a second transformer IS in the unit, no damage will occur and no charging will take place. But it should not be allowed to overheat the second transformer though by hours and hours of connection......)

21 VDC will probably also extend the possible working life of the charger electronics as well, due to the lower "peak" voltage.....just a thought! No need to debate that!!!

These spares are available on the B & D website.

Is that the US charger, e.g. 120 volts?

I think he wants a UK 230 volt version if I remember correctly....

GA!

Its a puzzle to me how you got up that tree! Have you seen them in their native Chile?

Do not connect your 60Hz charger to 50Hz. It will not make it even for a week. One of my neighbour had bought a shaver in US and bought a step down transformer and connected it to 50Hz here. The charger was damaged within few days.

Gajanan Phadte

The problem is not always just the frequency.

1. Some step-down transformers are not 2:1 ratio but include an allowance for poor regulation. I have encountered a 100W transformer with a turns ratio of about 1.8:1 which gave it the correct output voltage only at full load but gave more than 130V off-load with 240V supply. A shaver may be only a few watts and receive much higher voltage than it should.

2. There are some cheap plug-top 'power converters' sold retail as 'transformers' but which are electronic devices of uncertain pedigree and probably have horrible output waveforms to which some appliances may be susceptible.

Good Answer so GA from me.

Many people do not consider checking such output voltages before putting them to use......sadly. Nor do they consider the type or the quality of the unit and how this affects the output.....

In a few cases, I have found enough room in a unit, to remove the original transformer and completely replace it with one (usually of better quality as well) for the voltage currents frequency needed.......if the pins do not line up, stiff copper wire works as does one or two tie-wraps to hold it in place. I have even used hot melt glue for smaller stuff. Put the transformer on its "back" first!!

What I usually do though is not that. I simply leave the original charger as it is and as they are generally, (not in this case though), an AC to DC power supply, I buy on ebay, a charger (really a power supply!) of the correct output voltage, that can supply at least the maximum current needed, or even a bit more......BUT ALWAYS OF THE SWITCHED MODE TYPE! Which are far more accurate in the value of the output voltage than the real cheapos.....

Sometimes these are SM power supplies with switchable/variable voltage output, then I place a label OVER the switch (after selecting the correct output and checking it with a meter) to stop anyone playing with it and also detailing which device it is intended for.....

I can get some really good SMPSs on ebay, with multiple output plugs, up to 1000ma and switchable polarity, for less than €10. Which is a little over US$12 I believe....

The biggest problem wih these units is that they are in my opinion, seldom sold with possible outputs of 21 volts as required here......

But as I have already mentioned, it usually does not matter if a charger circuit, built in as here, receives AC or DC......it simply does not care as its input circuitry for such a charger is usually a simple full wave rectifier, not another transformer!!!! Why fit two transformers? Makes no sense.... (...then it is not true. Quote from Judge Judy, US TV Court Judge!! )

What is really great are that Laptop replacement power switched mode power supplies are sold with 21 volts DC output......usually a higher max current than needed, but WHO CARES!!!

I just found a great 21v switched mode power supply for the OP, available on both US & UK ebay sites, and its also good for anywhere with 50 or 60 Hz, 110-240 VAC input, here is the UK one for example:-

Switching-Power-Supply-AC-110-240V-DC-12V-15V-16V-18V-19V-20V-21V-

This would be a good permanent fix..........switched mode types are also generally very efficient and basically ONLY use the mains current needed and do not waste power as heat.....up to 90% efficiency is often seen nowadays.....as well as having a very stable output voltage through the whole range of current from 0 to the max allowed.....

Its the way for the OP to go, simple and easy.....

Applying a 21V DC supply of 82 VA, say 4 amps capacity, in place of a 100 mA rating given by the Original Post could destroy the battery and start a fire. I would not do it unless I knew what was in the vacuum. A ballast resistor in the vacuum, of type which will fail on overload without catching fire, might convince me.

67model

Electronics is definitely NOT your strong point, is it? Sorry, but you make it rather obvious I am afraid......

This might (note the might!) be true if the unit has:-

a) a lead-acid battery installed. Super seldom nowadays in such equipment as the size and weight do not have anywhere near the capacity required....

b) No proper charger control circuit between this input and the battery. Only a LA battery can (as many cheap car chargers actually do!) have an "uncontrolled" charging circuit. All other battery chemistries need special circuits to charge properly and accurately, with no possible thermal runaway....

I believe that neither a) or b) are true.....therefore only two points need to be adhered to:-

a) The voltage should not exceed 21v AC or DC as measured on a quality meter. Polarity is unimortant in this application (you do understand why?)

b) The power supply current that can be supplied must be at least that needed for charging.....it can be more, that will not be a problem....it will actually only supply what is needed 100ma you said....not more.

May I inquire as to your electronics and battery charger background, knowledge and where you were taught please? I am nosey as to why you posted.....sorry.

Dear Andy,

When I questioned your proposal I was concerned for the OP. I appreciate you yourself have always "looked inside the box" before modifying the charging system.

I have a couple of Black and Decker "Dustbusters" in the graveyard. The most recent is dated 2008. Both have a plugtop supply with AC output (presumably an iron core transfo, judging by weight). Looking inside each roving vacuum cleaner bit, there is nothing but a diode between the charger connector and the battery. Applying ohmmeter across LV, then HV terminals there is resistance as expected for transfo windings.

It seems that B & D like the KISS principle!

I measured the 2008 version, which has a 4 cell 1500 mAh NiMH battery. The plugtop is labelled 230V 50Hz input, 7V 0.15 amp output. You can see the winding resistances in the theoretical circuit of the image below.

The perfect theoretical transformer in the circuit has a ratio of 240/8.6 volts to fit to the no-load voltage ratio measured on test with a true r.m.s. DVM.

Since an NiMH cell has a voltage of 1.35V charged and charging at 0.1C which is 0.1 x 1500 = 150 mA for the capacity, the charger rating is no surprise. With 4 cells the voltage is 5.4 volts. Since there is one diode, this is a half wave rectifier and, allowing 0.7 drop across the diode, charging current will only flow if the AC input voltage is more than 5.4 + 0.7 = 6.1 Volts on one half cycle.

Referring to the half sine curve in the image, current will only flow in the shaded part of the voltage half cycle. The current will flow in proportion to the voltage above the A-D-C line, assuming constant resistance in the copper windings.

You will know that the current over the conducting portion will be the shaded area volts x time / resistance. The resistance can be simplified to one on the LV side by transferring the primary value to a secondary value of 2700/[(240/8.6)² ] = 3.44 ohm. That gives a total source resistance of 3.44 + 4.5 = 7.94 ohm, with a source e.m.f. of 8.6V rms.

You will realise that such a source can deliver a maximum of 2.3 watts [into a 7.94 ohm load], according to the linear power transfer theory. Half-wave will reduce to 1.3 watts. It is obvious this limits the power which can be lost in the battery.

The shaded area in the curve can be approximated by the area A-D-B-E which is 6.1 volts x 1/6 cycle, so the mean voltage is 6.1/6 = 1.02 volts. Since this is lost across the 7.94 ohm source resistance, the mean current is 1.02/7.94 = 0.128 amps. Of course, the area under the curve is more, because it is above the dashed line A-B : lets add 10% as guess, that makes 0.14 amps.

It is no surprise that this rough estimate is close to the C/10 charge rate for the battery and the plugtop LV current rating - because this simple circuit is designed to do just that. Of course it will have passed the scrutiny of product safety test, by say UL or TUV.

Finally, the transfo winding resistance will increase as it warms up, say 20% so long term current at high ambients will automatically reduce, to the benefit of the battery.

You propose to connect a 21V DC stabilised 4 amp supply directly to the subject vacuum which . You write the polarity does not matter - but there is no bridge rectifier here, nor is there any limiting resistance.

When conduction occurs (with one polarity) the current limit will be 4 amps with about 1.6 volts/cell on 13 cells.

I would like to understand....

1. Where are the special circuits you write about in "All other battery chemistries need special circuits to charge properly and accurately, with no possible thermal runaway...." for the actual B & D NiMH vacuum I have here with me.
2. how the battery will survive that 4 amps charge.
3. What assurance dumping 4 amps into, possibly up to 21 volts (84 watts) continuously (electronic current limit in laptop type supply) into the battery will not be dangerous.

I appreciate the subject system might have a different charging system, but no post has written they know this B & D product and "what is in the black box".

67model

This can only be in a country like say the USA, as such charger circuits as you describe (assuming for the moment that the diode is ONLY a diode) are simply not allowed here in Europe for non LA batteries, (though some cheap companies still try to import/sell them from time to time, I read about in the newspapers from time to time!).

Correctly designed chargers and the like here in Europe must get a "CE" sticker to identify that it is of an accepted fully tested type and safe for usage in Europe. Similar to the FCC.

Does the FCC REALLY allow such units to be sold????? WOW!!

See here for a short explanation of CE:-

http://electronics.howstuffworks.com/everyday-tech/question135.htm

If what you say is true about this charger, this demonstrates to me personally that B&D are simply not to be trusted to supply well/properly designed equipment. Never again for me personally.

I was a B&D fan for many years till today......

Many thanks for your good explanation.

Obfuscation, Andy. The diode is marked 1N4004. That is a 1 amp 400 V PIV rectifier

made by the million.

These are the labels on the unit of the image I put in my last post...

Note the CE marks. Are TUV not German? I think that GS bit means "Safety Tested".

If the B & D 21 volt AC 0.1 amp plugtop charger with the OP's vacuum follows the same design, then there is nothing in the roving vacuum but a 15.6 volt 13 cell NiMH battery (say 1000 mAh) and a diode.

Speculations, please, on what happens if the OP connects a 21 volt regulated, 4 amp current limit, supply to the terminals of the vacuum cleaner [battery] with conducting polarity.

What could be more reliable than a charger consisting of a transfo with 120 years of field technology testing and a silicon diode with 50 years whose short circuit current and power is limited by resistance? Where is the EMC susceptibility? Will there be EMC emissions of any consequence?

Regards,

67model

I believe you - awful but true!!

67model:


Obfuscation (or beclouding) is the hiding of intended meaning in communication, making communication confusing, wilfullyambiguous, and harder to interpret. I like this word. I found this meaning on Wikipedia.

While some of the manufacturers make good 1N4004 to 1N4007 series, sometime they come with bad characteristics and they do get spoiled. Some people used a small ceramic capacitor parallel to the diode and some limited current through diode and some used both schemes.

What if diode fails? Yes, that is a very good question. Diode often short circuits and that means AC to the charging circuit or battery charges and discharges through current limiting resistor. Very likely that battery will get damaged too even though it may take some time.

You should never use 21V DC regulated high current sourcing charge source as that could over charge the battery as load is not continuous.

Best design means both charge injection control and also Battery status monitoring to decide on charge injection.

What may happen to the Battery may be the one to spell out the amount of danger exists in this case.

Greetings, Shyam.

I agree all manufacturers are not equal and sometimes a product has got a problem when a component has been changed to a different [usually cheaper] make. However, B & D make power tools which are frequently driven to their limits and beyond - but survive, so I expect they only source from reliable suppliers.

If there is an RF emission caused by the diode "reverse recovery", a capacitor in parallel with the diode is often a solution. But a capacitor may just change a resonance frequency to give greater amplitude at a more troublesome frequency for the emission limits - adding a series resistor to capacitor, to reduce "Q" & burn-up the energy of the resonance may be needed.

International Rectifier application note AN-989 Fig.12 gives an interesting comparison of recovery currents of different types of diode in the same application - "Brand B" looks to have alarming HF generation!

Reducing the diode current will reduce the "stored charge", but for a simple "resistive load" power supply it is decided by the current required.

I cannot find any reliability or safety fault with the B & D transfo-diode supply. I can only fault its watts energy efficiency.

Even with a short-circuit battery the diode peak current is only about 1.5 amp [half-wave] in a diode with a 1 amp rating, which in the typical application is pushed to near its 30 amp turn-on surge rating [and to its peak inverse voltage rating] by a reservoir capacitor and high voltage source [in the supply I have the 400V diode is working with < 10V rms supply]. You will note that the transfo has a 130'C fuse symbol, so it is protected against sustained short-circuit.

If the diode should short-circuit, the 4.5 ohm transfo secondary resistance limits the current to about (12 volts + 4.8 volts)/4.5 Ω ~= 4 amps peak. I am sure the transfo can easily have a fusible wire included to protect against this.

Greetings, 67model.

I thought that 130'C has something to do with the maximum operating temperature. I did notice that.

Diode short circuit must have been taken care either in the transformer primary winding or through some kind of fuse. I think few cycles of shock battery can take but there is a chance of it getting heated and then it may get badly damaged thereafter.

I often use 1N4007. We test these for reverse leakage current @1uA and associated voltage and slightly higher breakdown current of <100uA. We get parts from various manufacturers from market and also from some top manufacturers. I found that good manufacturers have 1200V to 1600V range for 1uA reverse current. Bad manufacturers had anything from just few Volts to 1200V as breakdown voltage and some were dead to start with. That was a bit funny as they put all these on paper rolls without even testing them and just ship them.

We even test transformers for primary to secondary isolation voltage. For some of them if breakdown current exceeds 100uA then they are permanently damaged. I restrict tests @1uA leakage current. I have a test setup for from 0V to 15kV DC between primary and secondary and with voltage and current monitoring and over current trip.

I know there is this wastage of power in old generation designs but they are somewhat rugged and work for ages. Most of the switching circuit fail and also kill next stage as they may dump too much voltage as high voltage shock.

I have been seeing those RC network around diodes to kill resonance oscillations. I wonder how they will be different in Schottky Diodes. I rarely use them as they have too much of leakage current.

In diodes like 1N914 and 1N914B the later version had lower leakage current. These I used for amplifier protection purpose and sometime used 1N4148. For smaller current and at low voltages I used them in power supplies also for very low current need.

I am thinking of a design to power low power amplifier, ADC and uC boards and aiming at 2.7V to 5V operating range with about 30mA maximum current and power down to <10uA. I am working on to select the Batteries as application needs 3A.hr rechargeable cells. I am going to use isolated switching circuit in the charger as cost is not a primary goal but size and efficiency sure is.