Higher voltage DC power supply

Hi John, @itinerant-john

  I haven't the foggiest idea whether it will work, but AliExpress (and probably others), are offering a boost converter that claims up to 50V out, with an input of 5V-32V, for about US$1

https://www.aliexpress.com/item/1005006379907883.html

Maybe, use a 'wall wart' to produce a 'safe dc voltage' from 230V ac mains, and feed it to this to the boost converter. Perhaps an obsolete mobile phone charger?

I would expect the bell to produce a high back emf voltage, which may destroy any unsuspecting electronics, so you will probably need at least some overvoltage suppression and filter capacitors, between the converter output and the bell.

Of course, responsibility for staying safe, any losses. etc. is completely down to you.

Good luck and best wishes, Dave

@davee @itinerant-john One thing to note, the mentioned boost converter is spec'd at a max of 50VDC. The OP said 50 to 70 so that could be an issue, and in my experience these devices often don't quite reach the max.

However, I am sure there will be a 70VDC version out there someplace.

Hi Ron @zander,

 I noticed the 50V - 70V, but also "I'm looking for some way of creating ~50V DC", which I focused on.

 A higher voltage version would give a better margin, and I am sure there will be something somewhere.

 As I am sure you realise, specifications are tricky things, especially when they are not in a formal document. Is 70V a maximum, that shouldn't be exceeded, or minimum that is needed for a 'reluctant' bell?

I thought, for about a US$1, it might be worth giving it a try, and it was an example of the kind of thing to look out for, but perhaps I should have explained that.

Clearly, my answers are getting too short. 🤨 

Best wishes, Dave

@davee NOOOOOO your shorter answers are spot on!

Again, I think we North Americans understand your UK English differently. When he said 50 to 70 then later mentioned only 50 I ignored that and stayed with the 50 to 70 as the requirement. I did that because over here we tend to take shortcuts and liberties with language, and I also suspect that he might think that if 50 to 70 is ok, then 50 is ok. You and I know that 50 to 70 is the possible range and each bell will 'work' at some voltage in that range. Some will work at 50, and others only at 70 with the vast majority somewhere in between. That is why it is specified as a range. This is ancient tech so it is not surprising about the range.

The Boost converter I found had the 50 to 70 range mentioned so should work for any of them in the 50 to 70 range.

Thanks for that @davee but as you say, I'm sceptical when it comes to claimed performance characteristics on AliX products.  On the other hand, at ~US$1 a piece, I won't be crying in my beer for too long if the magic smoke comes out ... 😉

After watching something on Youtube last night, what are your thoughts on using a pair of these boost converters and, forgive my description, inverting the output from one to give +25V and -25V, or a 50V potential difference?

Your caveats are duly noted ... 👍 

Hi John @itinerant-john,

 If you buy for a $1, then yes, it is a gamble, and whilst I have bought a lot of small things through that channel, every delivery has its surprises - some good ... some not so good.

As Ron (@zander) has pointed out, the 50V-70V specification is also a bit of an 'unknown'. If it turns out your bell needs 70V, then 50V is not going to be enough.

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The simple answer to your two boost converters query is a 'may' work, and if you could get an 'up to +35V' and a 'down to -35V', to work nicely together, that would be better still. 

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Sorry, but it is not an easy case to give a definite answer.

First, these cheap boost converters (and buck converters for reducing the voltage) do not usually have any isolating transformers ... and hence the '0V' line may be the '0V' line out, or it may have a low value resistance joining the 0V in and '0V' out for current control. This is the kind of thing that may only be apparent if you have the board in your hand, and you also have enough experience to figure out exactly how it works etc. There will not be a handy manual, etc.

In the latter case, you would probably need two power input sources that were isolated.

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And also, some care will be needed to absorb the back emf from the bell.

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I also assume, you are aware and know the risks of electrical shocks, as 50-70V is starting to get into an area which the Health and Safety world often considers hazardous.

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So, sorry I will not take the risk of recommending it as a course of action, although with care and expertise, it might work.

Of course, any action you decide to take, is totally your responsibility.

I wish you all the best. There may be other boards that give a slightly higher voltage than 50V ... I just saw the advert for that one, and provided it as an example of the kind of thing you might consider. As you know, AliExpress is an Aladdin's Cave ... anything might turn up.

Best wishes, and please take care, Dave

BTW, You cannot just swap the wires to get -25V, because of the common 0V line I mentioned. I thought you meant two different boards, one giving +25V and the other -25V, as their design specifications.

@itinerant-john Why do you need to try something as tricky as +-25v when you can buy a 50V boost? I showed you a 70V adjustable which would be much better.

As far as your comment re ALi, did you know that a large number of Amazon parts come from Ali.

All Ali is is a bunch of small sellers using the Ali infrastructure. They buy their products from the same factory as everyone else. Are there occasional fakes on Ali, yes, but also on Amazon. Here is one of the results searching Amazon for 18650 5000mAh (there is no such thing)

https://amzn.to/4ddYTGL

@itinerant-john Here is the Amazon link to a boost converter that is adjustable up to 70V.

https://amzn.to/3xRXsh2

Posted by: @itinerant-john

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Some time ago, I found a beautiful old telephone repeater bell system in a junk shop and it followed me home.

However, the part of the project that makes the bells ring has had me stumped, as there's not too much space within the hardwood box for something that will provide the required 50-70V DC required to operate the ringer system, and I would like the power supply to be 'compact'.

Obviously, the required current to drive the ringer is going to be low, so I'm looking for some way of creating ~50V DC from 230V AC at the wall.

Once you've helped me sort out the how to get the ringer working, I've got a few ideas for why I might want to ring the bells, but that's a question for another day.

TIA

John 

Hi John,

I would use a bench supply to get the bell to ring and measure the current required. I am not so sure the bell used DC voltage. If this is one of the old wall phones from around 1900, as I recall it used an AC signal to ring the bell. This was generated by a hand crank generator as I recall. If it is indeed AC, then you might be able to use an H-bridge FET arrangement with a DC supply to create the signal. Once you are certain how to make the bell ring, then look at the DC-DC converters available online in the right voltage and current (or power) range. You can google H-bridge for ideas on how to configure it if needed. If it is just a pulsed DC signal, then a single FET should do the trick. The reason I suspect it is AC is that it is probably a solenoid type device and if you apply DC it might make the bell ring once but repeated application of DC will cause the iron to magnetically saturate unless the polarity is reversed to reset it magnetically. If the iron magnetically saturates, then the current on the next pulse will be exceedingly high.

Thanks @zander, the 50V figure is something that I've seen mentioned elsewhere as a mid range figure, so I'm using that as a starting point.  

Given that the device is quite old, and the tech behind it is even older, I'm not going to get too hung up on precise values, especially given that the current carried by the telephone lines so will have losses.

Thanks @bbutcher85, I'm embarrassed to say that I hadn't considered using a bench top supply to see if I could get the solenoid to give the hammer the necessary kick and come up with a plan for the power supply from there ... 🙄 

However, you are correct that the ringer will require the polarity of the supply to reverse, but the frequency is in the 20hz range, so I thought mentioning AC might confuse folks.  However yes, I was already thinking of using an H-bridge to get the ringer to function.

Thanks, your suggestions they have given me plenty to think about.

As an aside, you mention 1900 in passing, but New Zealand is a very, very young country, and the first exchange  didn't open until October 1881, so it would have been a very rare device here in the early part of the 20th century 😎 

Posted by: @zander

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@itinerant-john Here is the Amazon link to a boost converter that is adjustable up to 70V.

https://amzn.to/3xRXsh2

@itinerant-john I can still remember my great grandmother cranking the phone to make a call. When the operator answered she asked for her party by name, no numbers back then. They had one of the first phones in Hamilton. The Hamilton exchange was opened on June 20, 1877, the first in Canada.

My memories are of roughly early 1950's.

They never owned a car, had a wood burning stove, and an ice box refrigerator.

They were married over 75 years and both lived to about 90.

Their great grandson has not owned a landline for over 7 years now.

Thanks for the memories.

Posted by: @zander

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@itinerant-john I can still remember my great grandmother cranking the phone to make a call. When the operator answered she asked for her party by name, no numbers back then. They had one of the first phones in Hamilton. The Hamilton exchange was opened on June 20, 1877, the first in Canada.

My memories are of roughly early 1950's.

They never owned a car, had a wood burning stove, and an ice box refrigerator.

They were married over 75 years and both lived to about 90.

Their great grandson has not owned a landline for over 7 years now.

Thanks for the memories.

Thanks Ron,

Your memories pre-date my arrival on this blue pebble by over a decade, though I can beat your cousin's landline free timeline by a similar margin, as I've been cell phone only since the latter part of 2007.

Back on topic, I do actually have a telephone magneto that I could use to generate the required voltage, but I think that's straying a little too far into Heath-Robinson / Rube Goldberg territory for this project ... 🤣 

Though I was watching a Usagi Electric video on YouTube last night, where he was building a 555 IC with vacuum tubes (valves for us Brits), running at 24V, and every possible logic gate can be produced by wiring up the necessary group of tubes/valves appropriately ... but that's definitely a rabbit hole for another day ... 🤣 

Usagi Electric on YouTube ... for those oddballs like me, who enjoy vintage computing, amongst other things ... 🙂