Updated Beeb PSU

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MartinB
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Updated Beeb PSU

Post by MartinB » Mon May 30, 2016 12:03 am

I've previously mentioned the APD DA-45C01 as being a potential replacement for the Beeb PSU and as a background task I've been assembling and testing a complete unit using a second low-current and regulated 5v DC adaptor for the -5v rail. Anyway, I'll post more details in due course but so far, testing is going well, incestuously but ably supported by some I2C self-temperature monitoring! :D
New PSU on-test (s).jpg

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Re: Updated Beeb PSU

Post by MartinB » Tue May 31, 2016 12:15 am

The two replacement PSU's fit very nicely into the form-factor of the original metal frame and the configuration retains the original mains on/off switch, the auxiliary power connector and the motherboard power distribution harness. Indeed, once fitted in a Beeb, it looks no different at all to the original. All the initial tests look good and perhaps not surprisingly, the rails demonstrate better stability and noise performance than the standard unit - for example, the typical ripple on the +5v rail under high load is only around 35mV pp on a very stable 5.1 volts.

I'll fit it properly next and do some more temperature testing via I2C but it does seem to run relatively cool. I suspect the efficiency of even the smallest modern SMPS is very good compared to earlier designs.

Some more pics, not very exciting but they show some assembly detail....
New PSU 1.JPG
New PSU 2.JPG
New PSU 3.JPG
New PSU 4.JPG
New PSU 5.JPG
New PSU 6.JPG
New PSU 7.JPG

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Re: Updated Beeb PSU

Post by paulv » Tue May 31, 2016 1:00 am

=D> =D> =D> =D>

That is cool 8)

Long term though, how serviceable is it compared to the original? Or would it end up needing to be a case of finding a suitable replacement once it fails Vs finding parts for the original?

I guess it comes down to which is more likely to be an issue 5-10 years from now...

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Re: Updated Beeb PSU

Post by MartinB » Tue May 31, 2016 9:00 am

Electronics reliability depends on a few factors, principally quality of components, quality of assembly and importantly, that the majority of the operation of the unit is within the derating envelope of its individual components and within that of the complete assembly. The APD devices are excellent quality, (as are many others I don't doubt, just avoid the unbranded, sparse label types), and the capacity of the 45C01 for example, far exceeds the needs of a Beeb meaning it isn't in any way stressed and will be working well within its designed derating envelope. Viz, it runs relatively cool, is subject to a fairly constant current demand in the Beeb environment and there aren't any stressful capacitive loads to speak of which can lead to upsetting distortions.

The second PSU I have used happens to be a Casio 5v 600mA DC unit (ex-camera maybe?) and so is easily up to the job of supporting the Beeb -5v requirement. The APD is a mains three-pin through-earth device such that mains earth is DC earth but the Casio is intentionally a mains two-pin no-earth (floating) device such that I can connect its +5v output to the DC earth of the APD and the Casio 0v output then becomes -5v.

The mounting arrangement retains the individual mains plugs of both PSU units and using terminal block, although it may look untidy, allows easy re-use of the existing Beeb harness and auxiliary connector, offers high integrity connections and replacement of an individual PSU becomes very straightforward.

In summary answer to your question about reliability then, I guess only time will tell but given the discussion above and my testing to-date, I suspect the unit will be fine for many years.

Incidentally, my push to finally try and assemble a more modern PSU came from my I2C project where I have been running my Beeb for long, very long, sessions whilst experimenting and having fun with things like temperature, humidity and barometric pressure sensors. Curiously, that same motivational I2C interface is now helping with the testing of a PSU to support said interface use.... :)

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Re: Updated Beeb PSU

Post by 1024MAK » Tue May 31, 2016 11:01 am

Any reason why you did not use a DC-DC converter for the -5V supply, as the current demand is small on this rail?

I talked about DC-DC converters here

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Re: Updated Beeb PSU

Post by steve3000 » Tue May 31, 2016 11:54 am

Great write up, I may try something similar (possibly with Mark's suggestion of DC-DC converter for -5v), as I'm repairing an issue 7 beeb with no psu.

Just wondering, as you've selected a 4A psu, what is the current draw from the standard 32k beeb?

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Re: Updated Beeb PSU

Post by MartinB » Tue May 31, 2016 12:26 pm

Regarding DC-DC converters, I am familiar but decided that there was no point in bothering with loose components when regulated 5v floating converters are ten-a-penny. If you don't have a suitable one to hand and you're considering discretes, you can even pull the innards from an old 5v phone charger and float it to -5v as I did. I was taking the path of least resistance (sic) and it does look neat.... :wink:

Steve - I wasn't particularly chasing 4A, just something with plenty of headroom because a more capable unit at low revs will be less stressed and, as I discussed earlier, well within its derating envelope. Not sure on the actual current draw but since I've now got terminal block in there, I can easily measure it which I will do tonight... :)

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Re: Updated Beeb PSU

Post by 1024MAK » Tue May 31, 2016 12:42 pm

:-k Hmm, I have two (different) plug in power meters, and thinking about it, I don't remember ever testing a Model B, or any Masters. I tested just about everything else in the house at the time, but for some reason not any retro computers :?

Would be interesting to see what the results are. I do remember giving up testing low power loads, as they did not give meaningful readings.

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Re: Updated Beeb PSU

Post by MartinB » Tue May 31, 2016 10:58 pm

Steve wrote:Just wondering, as you've selected a 4A psu, what is the current draw from the standard 32k beeb?
Fairly standard, full complement of roms and an Acorn 1772 FDC.....
BBC B +5v current.JPG
So, just over 2.1A with a steady +5v rail voltage of 5.1v at the Mode 7 post-boot screen. I'll leave it connected as above until tomorrow night in case anyone has any additional thoughts on current measurements.

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Re: Updated Beeb PSU

Post by 1024MAK » Tue May 31, 2016 11:05 pm

A measly 10.78 Watts, despite being known as heaters, that's a bit poor. No wonder you get cold in winter... :lol:

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Re: Updated Beeb PSU

Post by 1024MAK » Tue May 31, 2016 11:09 pm

MartinB wrote:I'll leave it connected as above until tomorrow night in case anyone has any additional thoughts on current measurements.
Smoke test, by shorting the +5V rail out? :lol:

< Got to keep the fire fighters in work, BeebMaster has not blown up as many Beeb PSUs recently (or at least, not admitted to it at any rate :P >

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Re: Updated Beeb PSU

Post by 1024MAK » Tue May 31, 2016 11:17 pm

Oh, and while I am munching on a choccy biscuit to take away the bitter taste of the tablets I have been prescribed (don't ask), I have forgotten to say...

Well done Martin =D> =D> =D>

You almost certainly have/are likely to nudge some foke to restore their poorly Beebs back to life. Not every one can repair a failed PSU, especially if it is more than renewing the usual three capacitors.

If there are spelling errors or strange words, I blame the predictive text and spell checker. I have already retyped five words, it's doing my head in #-o ](*,)

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Re: Updated Beeb PSU

Post by BeebMaster » Wed Jun 01, 2016 5:59 pm

This is very exciting!

I couldn't see Econet or Speech interfaces in the test Beeb, can it cope with them as well as ROM/RAM boards and all the new-fangled surface-mount nuclear-reactor-on-a-molecule gubbins that people mount inside the lid and which draw power?

What sort of current is available to the aux power socket? On a Master I (inadvisedly, of course) like to use the aux power to run a host adapter, ST506 controller and Winchester Disc, I wouldn't do it on a BBC B, I think it might be a bit of strain but if a new PSU could handle it, that would be a great advantage.
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Re: Updated Beeb PSU

Post by BeebMaster » Wed Jun 01, 2016 6:00 pm

One more request...a timer set to 10 or 15 years rigged to cause a pop and a smoky discharge flavoured with burnt marmite? It's got to be authentic, remember!
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Re: Updated Beeb PSU

Post by steve3000 » Wed Jun 01, 2016 8:03 pm

MartinB wrote: So, just over 2.1A with a steady +5v rail voltage of 5.1v at the Mode 7 post-boot screen. I'll leave it connected as above until tomorrow night in case anyone has any additional thoughts on current measurements.
Brilliant thanks for posting those results Martin.

I know the actual current will vary with every possible combination of beeb expansion and probably pcb issue, but great to have 2.1A as a start point for reference :)

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Re: Updated Beeb PSU

Post by MartinB » Wed Jun 01, 2016 8:30 pm

No worries Steve, glad to help 8)

( Actually, doing the measurement set me thinking that someone else may have reached a similar conclusion regarding current consumption fairly recently - maybe hoglet Dave ? Or am I dreaming....:-k )

Ian wrote:I couldn't see Econet or Speech interfaces in the test Beeb, can it cope with them as well as ROM/RAM boards and all the new-fangled surface-mount nuclear-reactor-on-a-molecule gubbins that people mount inside the lid and which draw power?
Well Ian, the standard PSU totals +5v @ 3.75A, -5v @ 100mA and +12v @ 1.25A whereas the two PSU's that I've fitted total +5v @ 4A, -5v @ 600mA and +12v @ 2A - i.e. more! In my configuration, the output is parallel connected to the motherboard and auxiliary socket so the combined current drawn from both must not exceed the cited totals available but to be fair, the auxiliary socket was never intended to be used for high demand devices, only for transient load devices such as floppy disc drives. Indeed, to preserve the longevity of the PSU and of the Beeb itself, I always advise powering external devices from an external source because more current from the Beeb PSU = more heat in the Beeb case = shorter Beeb life... :(

It's important to say that I'm not advocating any particular design or configuration here, I'm just showing for technical interest what can be achieved with modern kit whilst retaining a good degree of original authenticity. There are countless DC adaptors available and there is room in the PSU case for two, maybe three (do leave some 'free air' for circulation though) so to some extent, you could select PSUs to suit your bespoke needs. The standard Model B current measurement shows that a +5v 3A unit would be fine with plenty of headroom (I wouldn't recommend going lower) so the APD 4A would I believe happily support a packed Beeb but I can only base that on extrapolation, not actual measurement.

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Re: Updated Beeb PSU

Post by MartinB » Fri Jun 03, 2016 12:35 am

I was on with properly fitting the re-worked PSU when I remembered that I had a miniature 12v fan going spare and since it only draws 60mA, I thought I might as well throw it in there just to move some air around a little which is never a bad thing with PSU's. (I actually added a small series resistor too because even though the fan is very small, it's a lively little thing and I didn't need it to be quite so racy...)
Fan.JPG
Fan fitted.JPG
Anyway, all refitted, everything happy and you'd virtually never know I'd been in there.... :)
New PSU fitted.JPG
I'll do more I2C thermal measurements over time (I've instrumented the PSU with a sensor :wink:) and report back if there's anything of note temperature-wise....

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Re: Updated Beeb PSU

Post by johnkenyon » Fri Jun 03, 2016 6:09 am

MartinB wrote:I was on with properly fitting the re-worked PSU when I remembered that I had a miniature 12v fan going spare and since it only draws 60mA, I thought I might as well throw it in there just to move some air around a little which is never a bad thing with PSU's. (I actually added a small series resistor too because even though the fan is very small, it's a lively little thing and I didn't need it to be quite so racy...)
Either run it off the +5v rail, or connect the fan to the 12v (+ve wire) and 5v (-ve wire) rails and run it at 7v.
Whichever way you choose, you don't end up with the ironic configuration of a cooling fan being driven by a warming resistor...

The 7v approach is the one I've used several times in the past.

The best way of reducing noise through is to use a larger fan, running at a lower speed - in this case, impractical and it means spending £...

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Re: Updated Beeb PSU

Post by MartinB » Fri Jun 03, 2016 6:37 am

Thanks John - I did consider the 7v option but given that the two rails are from different PSU units, I wasn't sure whether sinking 60mA (or a bit less at 7v) from the APD into the low-current Casio was a good choice. At 5v, the fan is technically below the required start-up voltage and at that low speed with the Beeb re-assembled, it would be impossible to tell if it had stalled. The 150 ohm half-watt series resistor only generates about 0.3W and doesn't even feel warm in the scheme of things so I went with that option.
To be honest, a fan isn't really needed, it was literally just one lying around that I thought might as well be doing something useful and that faint shushing noise you get as you switch on seems to make the Beeb feel like a real computer.... :)

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Re: Updated Beeb PSU

Post by johnkenyon » Fri Jun 03, 2016 6:57 am

Going off at a tangent...
MartinB wrote:Thanks John - I did consider the 7v option but given that the two rails are from different PSU units, I wasn't sure whether sinking 60mA (or a bit less at 7v) from the APD into the low-current Casio was a good choice.
I reckon the most likely behaviour would be that the Beeb would sink the current, and the problems would either be that the 5v rail is lifted up too high, or more likely that the fan would inject noise onto the 5v rail (which would probably affect nothing more than the already noisy speaker...)

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Re: Updated Beeb PSU

Post by MartinB » Fri Jun 03, 2016 7:38 am

I'm sure you're right John and it was just that very thought of there being the potential for various (possibly unpleasant) side-effects from using a differential approach that made me cut to the safe route of employing a limiting resistor. As I said earlier, because it is such a small fan, the resistor really doesn't generate any noticeable heat 8)

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Re: Updated Beeb PSU

Post by topcat96 » Fri Jun 03, 2016 6:37 pm

Watching this thread closely ...

[-o< for a replacement power supply
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Re: Updated Beeb PSU

Post by MartinB » Sat Jun 04, 2016 10:28 am

topcat96 wrote:Watching this thread closely ...
[-o< for a replacement power supply
Ah, watching in what way? I wasn't ever planning on taking this to a build-and-supply conclusion I'm afraid, I was just doing the usual posting for technical interest and for others to follow if it floats their boat... :wink:

If you're after a replacement original PSU, maybe a post on the Wanted area...?

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Re: Updated Beeb PSU

Post by tricky » Sat Jun 04, 2016 11:47 am

I've looked at these a couple of times as possible replacements for beeb PSUs, but not being familiar with PSUs and any gotchas, and with them coming from the states, I was wondering what you though?
Image
65W Triple Output Switching Power Supply

CH1: 5 Volts @ 5.5 Amps
CH2: 12 Volts @ 2.5 Amps
CH3: -5 Volts @ 0.5 Amps

Features:
Universal AC input/Full range
Low leakage current<0.5mA
Protections: Short circuit / Overload / Over voltage
Cooling by free air convection
100% full load burn-in test
Fixed switching frequency at 65KHz
2 years warranty

Input Voltage (VAC): 90 to 264
Input Frequency: 47 to 440
Maximum Input Current (A): 1.5
Product Type: AC to DC Power Supply
Efficiency (%): 76
Minimum Isolation Voltage: 3000V
Operating Temperature-Min (Cel): -10
Operating Temperature-Max (Cel): 60
Length (inch): 5
Width (inch): 3
Height (inch): 1.7

The holes aren't quite in the right places, but they look like they would fit and not be too out of place.

EDIT: it looks like they are available from Taiwan http://www.ebay.co.uk/itm/1pc-Switching ... SwiCRUgelq
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Re: Updated Beeb PSU

Post by topcat96 » Sat Jun 04, 2016 12:57 pm

MartinB wrote:
topcat96 wrote:Watching this thread closely ...
[-o< for a replacement power supply
Ah, watching in what way? I wasn't ever planning on taking this to a build-and-supply conclusion I'm afraid, I was just doing the usual posting for technical interest and for others to follow if it floats their boat... :wink:

If you're after a replacement original PSU, maybe a post on the Wanted area...?
I'm being a nosey so and so ... seeing how you are making an updated and stable supply - following your diary of events with me making a potential future replacement of my own based on your pioneering work . Floating my boat? you betcha! :mrgreen:
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Re: Updated Beeb PSU

Post by MartinB » Sat Jun 04, 2016 1:10 pm

topcat96 wrote:...based on your pioneering work.
Ha, not sure about pioneering :lol:

( Still, if we're on pioneering, how is RAMagic?... :wink: )
tricky wrote:I've looked at these a couple of times as possible replacements for beeb PSUs, but not being familiar with PSUs and any gotchas, and with them coming from the states, I was wondering what you though?
I'm permanently on the lookout for capable triple rail SMPS that would fit in the Beeb box but managed to miss those. On the face of it, they seem pretty good, I'll have a closer look later as I'm sure will others.

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Re: Updated Beeb PSU

Post by topcat96 » Sat Jun 04, 2016 1:15 pm

MartinB wrote:
topcat96 wrote:...based on your pioneering work.
Ha, not sure about pioneering :lol:

( Still, if we're on pioneering, how is RAMagic?... :wink: )
Hey ... take the credit damn you! lol

RAMagic is still working great - it's plugged into my first BBC B which in turn has 2 of Sprow's 3.5" drives attached. Your little add-on hasn't skipped a beat since the day I bought it.
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Re: Updated Beeb PSU

Post by MartinB » Sat Jun 04, 2016 7:36 pm

tricky wrote:I've looked at these a couple of times as possible replacements for beeb PSUs, but not being familiar with PSUs and any gotchas, and with them coming from the states, I was wondering what you though?
Just noticed that it's a Mean Well which are generally known as good kit. I've actually bought some for use at work a few years ago and they're still going strong (although a different model) but when I've looked before I never managed to dig out a suitable triple rail model for our world. The basic tech specs seem good, the efficiency of 76% can be bettered these days but I don't think that will create excessive heat in a Beeb. Just needs confirming that It will fit in the Beeb PSU frame and think if it does, I'd be prepared to give one a punt - that seller seems to have been around for a while.
I'm away for a few days soon so I won't be able to do any more in the short term but I'd say that was a good spot Richard... =D> 8)

Here's some more info on the item in question if anyone else has any thoughts...

PT-65.jpg
PT-65-SPEC.PDF
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Re: Updated Beeb PSU

Post by MartinB » Sat Jun 04, 2016 10:47 pm

I wrote:Just needs confirming that it will fit in the Beeb PSU frame...
I know you've already done this Richard but to confirm, volumetrically the PT-65A module is slightly smaller than the Beeb module although interestingly, height-wise they're both 42mm!
PSU size comparison.jpg
(The caption should say PT-65A not AT-65A...!)

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Re: Updated Beeb PSU

Post by BeebMaster » Sun Jun 05, 2016 10:50 am

MartinB wrote:I wasn't ever planning on taking this to a build-and-supply conclusion I'm afraid, I was just doing the usual posting for technical interest and for others to follow if it floats their boat... :wink:
Aaaahhh...I fear the container lorry containing my 157 fire-damaged Astec PSUs is already on the way to the MartinB residence...
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