ABOUT APPLE-1 TRANSFORMERS AND FUSES

13 posts / 0 new
Last post
Offline
Last seen: 4 min 50 sec ago
Joined: Apr 1 2020 - 16:46
Posts: 552
ABOUT APPLE-1 TRANSFORMERS AND FUSES

I often get asked about hooking up transformers for the Apple-1 PSU and sometimes about fuses, despite everything can be found in the datasheets of the transformers. I'm still reluctant to give any detailed wiring instructions because it's a test: if you can read and understand the transformer datasheets, then it is likely, but not guaranteed, that you have the level of electrical expertise to hook them up correctly to the Apple-1 and to the line voltage ("mains") without killing yourself or your loved ones or setting the house on fire. See, I do not have the "License To Kill" from the Government like those manufacturers of the "vaccine" have got (yesterday I heard about 1400 victims in Colorado Springs alone, from a gentleman who got a blood clot in his leg, and then a piece of the clot broke off and caused a mild stroke, and his doctor told him the number of victims, and that he can't sue, and that he may not survive, nice deal !), and unlike these big pharma crooks, I have no blanket immunity against any liability either. I would LOVE to have a "License To Kill" and that blanket immunity against prosecution and getting sued. This world would be a much better place if I had that. But since I don't have that, I can't bite off a huge piece of liability by telling you things you should better not know to try out. But as far as the transformers/fuses issue goes, I can regurgitate some of the info in the datasheets of the transformer and fuse manufacturers and add a little bit higher safety margins. Still, use all this information in this post at your own risk only ! I assume no liability, for any incidental or consequential damages arising for the use or misuse of this information.

 

LET'S DEBUNK SOME MYTHS FIRST 

      

There are a lot of myths and misconceptions about fuses out there, and some relate to fuses on transformers. Let me debunk a few of them:

 

1. Myth #1: A 110V fuse won't protect a 12V circuit. You have to use 12V automotive fuses for that.

 

Untrue. The voltage rating of a fuse specifies the maximum AC voltage it can safely disconnect when open. This boils down to arcing, isolation and spacings of its connectors. A 110V rated fuse can protect a 12V circuit, but not the other way around.

 

2. Myth #2: A 110V (or 220V) fuse will open slower when running from a lower voltage, such as the secondary of a transformer.

 

Untrue. A fuse blows by melting of its filament. The melting of the filament is done by the current alone, and not by the voltage. The filament has no idea about the voltage in the circuit until it opens ... see Myth #1.

 

3. Myth #3: A transformer can be protected by a single fuse on its primary winding.

 

Untrue for transformers with multiple secondary windings (including center tapped ("CT") windings). But it is true for a transformer with a single secondary winding. After all, a transformer transforms the currents by the winding ratio for each pair of windings. If you draw 1A out of a 12Vac secondary winding, the primary winding running at 120Vac (not a typo) will draw 0.1A, and so a single fuse on the primary winding can protect both the primary winding and the secondary winding of the transformer from overload conditions.If the transformer has multiple secondary windings, a fuse on the primary winding will protect the primary winding, but may not protect the secondary winding if that secondary winding is overloaded.

 

4. Myth #4: One fuse in the primary feed can protect a multitude of transformers connected to it.

 

Untrue with a few exceptions. If you have two transformers of the same power rating and don't want to run them at their limits, one fuse in the primary feed may be able to protect both (but observe the explanation at Myth #3). This may even be used as an advantage as one overload condition would disconnect both transformers from the mains, and so all voltages into the load(s) will be gone, which may be beneficial for some loads which don't like some voltages being present and others being gone. So by using this concept, you can save a lot of components for additional protection circuits. But in the general case, you can't protect two transformers with a single fuse, especially if one of them has a lower power rating than the other. The fuse will not blow when the little guy is overloaded and starts smoking and dies. This is the case with the Apple-1 PSU in its original form, as shown in the Apple-1 manual.

 

HOW TO DO IT RIGHT

 

1. Use a fuse with appropriate voltage rating for the highest voltage you will ever use it. Automotive fuses are perfectly fine for the secondary side of transformers if their voltages are below 30V or so but you will find out that despite automotive fuses are dirt cheap, the fuse holders are expensive. The most economical solution is to use 220Vac rated, 5x20mm fuses, which you can find, buy and use all over the world.

 

2. How quickly a fuse opens depends on its speed class. To protect transformers from thermal overload, "slow blow" or "time-lag" fuses are the best choice. They allow you to use a lower current rating for the fuse which helps protect the transformer better. Quick acting fuses are not recommended as they tend to blow during the power-on surge unless they have a current rating that may be too high to protect the transformer from long but weak overload conditions.

 

3. Use a fuse of the appropriate current rating on each secondary winding on each transformer. Typically, modern transformer manufactureres specify the recommended fuse(s) in their transformer datasheets. For instance, the datasheet for the TRIAD VPP16-1900 transformer I recommend in my "Tips & Tricks", they specify a Littelfuse p/n 313 5.0HXP, 5A 250V, slow blow fuse, or the equivalent from Cooper Bussman, if the secondary windings are connected in parallel, which is the case for the Apple-1. These are 5A fuses for their 3.8A windings (if in parallel, each winding can take 1.9A). Hmm. OK, they supposedly have tested their transformer with that 5A fuse not to start smoking or catching fire. Fine. Remember, this is about UL certification. UL does not care whether the transformer is damaged or dead afterwards. All they want to see is no smoke and no fire before the fuse blows, thus ending the threat.

 

I am always a bit on the safe side when it comes to my designs, so I did not become a rocket scientist / designer as my dad. He told me: "if you design a rocket according to the safety legislation for steam boilers, it will never leave the lauch pad." Hence, you need the lauch crew be safe in thick concrete bunkers. And God bless those daredevils who ride on the machine. Allegedly, one of the early U.S. astronauts asked Wernher von Braun if he would swap the place in the capsule with him, and take the ride to fame. Von Braun shook his head and said: "No, no way. You fly." The astronaut asked" "Why ?". Von Braun answered: "Well, if it explodes, among us two I'm the one who can go back to the drawing board and improve the design." Oh, and the astronaut did fly. I don't remember which one, but it may have been John Glenn. The exact wording may have been different, too. It's from my memory.  

 

OK. Nice anecdote. But I think you get my point: different applications need different safety margins. While the rocket designer wants a machine that can lift off and gets a good payload into orbit, the transformer company wants a competitive power figure while still dodging the wrath of the UL, but we, as hobbyists, want to tinker with our Apple-1 and not fry transformers in the process. So I would recommend a 3A slow blow fuse, and not a 5A slow blow fuse  as recommended by the transformer datasheet. 3A is plenty for the Apple-1.Also keep in my that the LM323K regulator has in internal current limit and thermal protection. So it will limit the current on its output side to levels which the TRIAD VPP16-1900 can easily sustain forever. But what if the LM323K itself fails ? Or one of the rectifier diodes fails (they typically fail as a short circuit) ? Or something else happens on the input side of the LM323K ?

It can happen - I will tell you a story later in this post.

 

As for using a lower rated fuse which would blow at lower currents, there is some deeper engineering reason behind my caution. In the datasheets of the fuse you will find a table which typically goes like that:

 

1.5  In   MIN 1 hr.

2.1  In   MAX 2 min.

2.75 In   MIN 600ms MAX 10 sec

 

 

This was taken from the datasheet of the BELFUSE 5ET series (www.belfuse.com)

 

"In" is the rated current of the fuse. So for the 5A fuse mentioned above, 1.5 x 5A = 7.5A would be needed to blow it, but how long would that take ? The "MIN" value means it won't blow earlier than 1 hour under these 7.5A (Oops !)This is roughly twice the rated current for the transformer secondary (2 x 3.8A = 7.6A) and I don't think the transformer will like that current for such a long time. And note that the fuse does not necessarily blow after 1 hour. It's a "MIN" spec. There is no "MAX" spec. Sneaky, isn't it ? So at 7.5A it may blow never.

 

Whereas, for the 3A fuse, 2.1 x 3A = 6.3A and at that current it will blow in no less than 2 minutes (it's a MAX spec, see). I'm quite sure the transformer will not get damaged if it has to source 6.3A for a mere 2 minutes. It may get hot, though.

 

Along the same lines of thought, for the VPP24-1250 which is rated at 1.25A for each of its secondary windings, you may use a 1A fuse in each of its secondary windings (no fuse in the CT leg, please). Or use 0.75A fuses or even lower. The regulators on the +/-12V also have self protection circuitry, but the same rationale applies as for the LM323K.

 

So with three cheap fuses, 1 x 3A and 2 x 1A, you can mitigate disaster and protect your transformers. An appropriate fuse holder looks like this:

 

 

 

WHAT MAY HAPPEN WHEN YOU USE NO FUSES

 

Well, this is probably OK if you keep your Apple-1 under adult supervision all the time when it is powered on, no exception, not even a bathroom break. See, if anything bad happens and an IC dies, or a short circuit occurs, the Apple-1 will not just continue to run happily, but it will crash the running program or show some other symptoms of distress, such as smoke or stink. Now, if you see a program crash and the usual RESET/CLR SCREEN does not bring remedy, or you see or smell smoke, SIMPLY TURN OFF THE POWER IMMEDIATELY ! And do not touch the possibly hot parts. You may use your contactless IR thermometer as discussed in post #5 of this thread:

 

https://www.applefritter.com/content/apple-1-clone-ic-temperatures

 

to try find out which IC ran too hot and died, before everything has cooled down again. Note that most dying ICs will not get hot and smoke. These are more difficult to find.

 

Now, suppose you have plugged in your Apple-1, and it powers up correctly, and you have loaded a program, and then take a bathroom break. A few minutes later, approaching the Apple-1 again, you can already smell it (and I don't mean the bathroom stink you left behind, I mean a BURNING smell, as in "FIRE" !). Then you find your Apple-1 does not run the program anymore, and the transformer looks like this:

 

 

How did it happen ? Well, it was late in the evening and the light was poor, and when I plugged in the J1 connector I plugged it in by one pin offset. So the poor VPP28-1060 transformer had to source the full current load of both the +5V side and the +/-12V side. It did its best, a glorious struggle, until it gave up the holy smoke. Dead. Another hero which died on Uncle Bernie's electronic battlefield. No medal granted, though. Thanks to the good transformer designers at TRIAD there was no open fire (according to their datasheet they use bobbin materials with a flame retardent that exceeds UL requirements). But there was an awful stink in the living room which lingered for days despite I had immediately ventilated the whole house. This was the first power supply I had built for the Apple-1 and of course it had no fuses because I would never let it run unsupervised. Except for that one incident of plugging it in wrongly and that one bathroom break immediately afterwards, so I could not see the catastrophy unfolding before it was too late. Like with airliner crashes, most catastrophies are not being caused by one sole point of failure, as the designers have foreseen them. But any combination of two or three failures may be too much, and then no trained procedure may be able to save man and machine.

 

In the case of the transformer, three cheap fuses would have prevented this dire outcome. It's not so much the $15 or so for the transformer, it's feeling stupid and then on top of this psychological punishment having to spend hours to build a new power supply. This time with fuses, of course, I promise !

 

Comments invited !

Offline
Last seen: 1 day 2 hours ago
Joined: Feb 11 2021 - 05:22
Posts: 83
Thanks for that. I have a

Thanks for that.

 

I have a related question: Living in Germany, there is 230 V coming out of the outlet. I use a transformer to reduce it to 110 V to make my Apple-1 power supply work which I have bought online. My question is: What transformers would I use if I wanted to create a 230 V "compatible" power supply for the Apple-1?

 

Best

 

Armin

CVT
CVT's picture
Offline
Last seen: 1 hour 58 min ago
Joined: Aug 9 2022 - 00:48
Posts: 328
You can rewind any

You can rewind any transformer for 110V and make it for 220V by replacing the primary winding with a wire that has half the cross-sectional area and twice the number of turns. Of course for 230V it's not exactly twice, but closer to 2.1 times.

 

Online
Last seen: 23 min 19 sec ago
Joined: Jul 5 2018 - 09:44
Posts: 1559
Wouldn't it just be easier to

Wouldn't it just be easier to buy a transformer with the right number of windings to begin with?  I'm assuming what retroplace_1 is looking for is part numbers for transformers that will work with an Apple-1 with 230V 50Hz power and look roughly like the ones normally used back in the day?

 

I don't know if Triad, Hammond, Stancor, etc, make transformers that look period correct that will produce the right outputs or not.

 

 

 

Offline
Last seen: 1 day 2 hours ago
Joined: Feb 11 2021 - 05:22
Posts: 83
Yes, indeed, ideally I would

Yes, indeed, ideally I would be looking for a transformer that works just like the "original" ones …

Online
Last seen: 23 min 19 sec ago
Joined: Jul 5 2018 - 09:44
Posts: 1559
Maybe the Hammond 186D10

Maybe the Hammond 186D10 which is supposed to be 115/230V AC in, 10V AC 3A  out and the 186D28 which is 115/230V AC in, 28V AC 1A out? 

 

https://www.mouser.com/ProductDetail/Hammond-Manufacturing/186D10?qs=mc7aZrK7NcqxkmPTuLD%2F2A%3D%3D

https://www.mouser.com/ProductDetail/Hammond-Manufacturing/186D28?qs=mHL17HKVUJC06rtkzrH9WQ%3D%3D

 

There are data sheet links on those pages.

 

CVT
CVT's picture
Offline
Last seen: 1 hour 58 min ago
Joined: Aug 9 2022 - 00:48
Posts: 328
softwarejanitor wrote:Wouldn
softwarejanitor wrote:

Wouldn't it just be easier to buy a transformer with the right number of windings to begin with? 

...

 

It's definitely easier, but some Apple I reproducers are fanatical when it comes to authenticity. I know a guy who got a hold of F-31X and F-40X Triads and rewound them.

Offline
Last seen: 4 min 50 sec ago
Joined: Apr 1 2020 - 16:46
Posts: 552
About Transformer choices for builders outside of the USA

In post #2, retroplace_1 wrote:

 

"What transformers would I use if I wanted to create a 230 V "compatible" power supply for the Apple-1 ?"

 

Uncle Bernie answers:

 

In Appendix 9 of my current "Tips & Tricks" pdf for builders of my famous IC kits,  transformer choices are discussed.

 

Here is an excerpt:

 

HAMMOND Transformers

 

These can be bought at distributors like Digikey. Like the STANCOR ones they come with wires, but unlike theSTANCOR ones, the Hammond 266 series have a split primary winding, so they can be configured to run off110Vac and 220Vac line voltages, same complication as with the TRIAD transformers. Hammond has quite animpressive product line, see here:

 

https://www.hammfg.com/electronics/transformers/power/266

 

End of May 2022, Digikey had 5 of the 266J24 in stock ($22.82) and 3 of the 266J16 ($38.34). Of the somewhatcheaper 166 series they had the 166M8 ($31.04) which is a 8.5 Vac 3A secondary type. But it's 110 Vac primaryonly, and the only benefit from that is less opportunity to make a deadly mistake when hooking them up.The Hammond transformers which come closest to the TRIAD transformers I have listed in Tip #14 from theabove pdf are 266L16 (secondary 8V 4.4A) and 266J24 (secondary 2 x 12V 1.0A) or 226J24B (secondary 24 VC.T.), all these have the same (or a higher) power rating as the STANCOR transformers specified in the Apple-1manual. For a bare-bones Apple-1 with just the ACI card the 266J16 and 266G24 might be powerful enough,but despite these are smaller, and less powerful, they are not cheaper. So go for the 266J16 and 266J24.Like with the TRIAD transformers, their split primary and secondary windings must be properly connectedin series or in parallel for the desired line voltage on the primary and the desired voltage(s) and current(s) on the secondary windings. This is an advantage but also a complication, and it must be done right, otherwise there isdanger, and the transformer may go up in smoke, even with no load attached. Like with the TRIADtransformers, I recommend you to download the datasheets (and any other appropriate information) from themanufacturer or distributor website for instructions on how to connect those split windings.

 

For EU builders:

 

ELMA Transformers

 

Builders in the EU can find these 220 Vac transformers at Conrad Electronics (www.conrad.de). I did not testthem myself (it would be too expensive to ship them over the pond), but several EU based builders have toldme they used them with success. These are:

 

Conrad #514268, ELMA TT1Z57, 8Vac 3.0A secondary, 20 Euros.

Conrad #514764, ELMA IZ59, 10-12-15 Vac 1.2A secondary, 26 Euros.

 

The latter is really cool – literally – because you can try to use the 10 Vac tap of the secondary windings to runthe +/- 12V regulators even cooler – but this will work only if the primary (line) voltage really is on the highside, which however is the case in many European countries (up to 240 Vac are seen). It looks to me as if theyincreased the line voltage to be able to transport more power over the grid without putting any more moneyinto the grid infrastructure. The normal use case with adequate headroom for the regulators would be the useof the 12 Vac taps. Do not mix voltages – otherwise the higher voltage secondary winding will bear almost all ofthe load. And you need to figure out the proper series connection of the windings to make the “Center Tap” or“CT” node. Since I don't have such a transformer I can't tell you exactly how. But if the phase is right is easy tocheck with a multimeter in the “VAC” setting: the series connected windings must give twice the AC voltagethan each end to the CT, so for the 12 Vac windings expect 24 Vac at the ends – and keep in mind that atransformer with no load produces a somewhat higher output voltage than the rated voltage, so don't getconfused. If I dare an educated guess from the transformer datasheet (downloadable from www.conrad.de),you should make the CT connection by connecting node 8 and node 10 of the secondary windings. Try it out,measure it, and tell me the voltage you measure between secondary nodes 2 to 13. With no load it should be atad above 24 Vac. If it's less, something is wrong. Contact me before you go any further. Don't experiment. Inany case, I assume no liability for incidental or consequential damages for this “free” tip (see disclaimer onin first post of this thread for further information).

 

(no, I didn't try these ELMA transformers myself because shipping them over the pond would cost more postage than the transformers are worth. Clown world !)

 

I've been pondering for a long time to design and publish a PCB which would allow builders to build a safe TRIAD transformer based power supply, configurable for 110Vac and 220Vac by just plugging in the right line cord, with fuses and the interlock circuit (all voltages turned off when one fuse blows) and all the design work (except for the PCB is done), but so far worries about liability issues have prevented me from finishing this work. Some people may be offended by the "modern looks" of these TRIAD transformers, too.

 

Comments invited !

 

- Uncle Bernie

 

 

 

Online
Last seen: 23 min 19 sec ago
Joined: Jul 5 2018 - 09:44
Posts: 1559
CVT wrote:softwarejanitor
CVT wrote:
softwarejanitor wrote:

Wouldn't it just be easier to buy a transformer with the right number of windings to begin with? 

...

 

It's definitely easier, but some Apple I reproducers are fanatical when it comes to authenticity. I know a guy who got a hold of F-31X and F-40X Triads and rewound the

 

I don't know. To me that doesn't seem "autthentic" at all.  That's probably NOT what an Apple-1 owner in Europe would have done in 1978.  They'd much more likey have bought the 230V transformers than have bought 115V transformers and re-wound them.  That would have been a stupid lot of work back then.  Next more likely thing is they would have built it with 115V transformers and used a 230V->115V step down ahead of both of them.  Actually the latter may have been more common, I don't know.  I have little idea how many of the few Apple-1 sold back then even made it across the pond to original owners.  I suspect most of what is there now were 2nd hand and originally owned by someone in the US, which means 115V transformers.  Re-winding, like repainting a classic auto...  afects "originality" and thus value.

 

Also if someone were really wanting to be "authentic" to what the Apple books say they would have bought the Stancor transformers rather than the Triad F-31X and F-40X.  The reason people use those today is they are still available from places like Mouser, although the new ones come in a box marked "Made in China".  Weird thing though...  the actual stickers on my Triad transformers I've bought recently say they were made in the Phillipines, even though the boxes say China.  Not sure which to believe.

 

Offline
Last seen: 4 min 50 sec ago
Joined: Apr 1 2020 - 16:46
Posts: 552
Don't try to rewind transformers !

In post #9, softwarejanitor wrote:

 

"They'd much more likey have bought the 230V transformers than have bought 115V transformers and re-wound them.  That would have been a stupid lot of work back then."

 

Uncle Bernie comments:

 

Forget re-winding of transformers. At some point in the 1960s it became common practice to dunk the coils into some kind of resin and then, after putting in all the E core metal pieces (left-right-left-right ... see why transformers are so expensive !) and the screws were tightened, the whole transformer was dunked into the resin again.

 

You can't hope to disassemble and re-wind these transformers. Everything is glued together by the resin. It even gets worse with those where the E core pack was welded. No way to ever disassemble that.

 

Offline
Last seen: 6 hours 31 min ago
Joined: Feb 27 2021 - 18:59
Posts: 275
apocrypha

The von Braun story may be apocryphal, but it's adjacent to another episode, retold in The Right Stuff, of Mercury astronauts' insistence that the capsule have explosive bolts and a means to blow them from inside in case of emergency. The von Braun / Operation Paperclip people, maybe a little less attuned to the individual human life, were going to seal the capsule shut from outside like they did when sending monkeys into space.

CVT
CVT's picture
Offline
Last seen: 1 hour 58 min ago
Joined: Aug 9 2022 - 00:48
Posts: 328
softwarejanitor wrote:I don't
softwarejanitor wrote:
I don't know. To me that doesn't seem "autthentic" at all. 
...

Personally I don't see anything authentic when the motherboard was made 2 weeks ago in JLCPCB, but I guess different people have different views on the subject.

 

UncleBernie wrote:

Forget re-winding of transformers. At some point in the 1960s it became common practice to dunk the c

 

The modern chinese Triads that they sell on Digi-key just have a laminated core that comes in two pieces, so it's easy. Even more authentic!

Offline
Last seen: 1 day 2 hours ago
Joined: Feb 11 2021 - 05:22
Posts: 83
Because I do not dare to

Because I do not dare to build transformer-driven power supplies myself, I am now in contact with a German electronics shop that looks into building a small series of 240V compatible power supplies for me. If all goes well, I should hear back from them in the next couple of days and we will take it from there.

 

Updates will follow.

 

 

Log in or register to post comments