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Mate rang last night asking for something to be designed and 3D
printed and this morning sent me a diagram with vernier caliper
measured dimensions for me to work from.

I designed and started the printing but when I checked a bit later,
expecting to see it all done (as usual), the printer was off and the
head not parked etc? ;-(

Long short, it looks like the 20A x 12V 'open frame' SMPSU has gone
weak?

eg, After some faultfinding it seemed it could power most of the
printer, just not the heated bed and so I have that now running from
my old 13.5V 12A bench PSU that was last used powering my 70 cms
packet radio and TNC.

The heated bed is pulling a good 11.5A (at 13.5V) from the linear PSU
and the SMPSU is 'still' running the extruder, Arduino Mega, RAMPS
display / interface board and 5 stepper motors?

The guy I was helping with the print job is the guy who originally
bought the printer kit on the grounds I built it with him ... and the
PSU was what was supplied in the kit. It's made in China of course and
I'm guessing they may have been reasonably optimistic with it's
ratings? That said, it's done a fair bit of work over a good few years
so owes me nothing.

When (if) this job actually finishes, I'll take the PSU out and have a
look inside and a measure up then find a replacement that's about the
same size, as it fits under the printers bed and there isn't much
room for anything taller or wider.

I still have one of the game console PSUs that I bought after a 'heads
up' from someone here, and a stripped out PC PSU but on that the 12V
is only 16A, and neither will fit under the printer and whilst I
thought it being there wasn't 'a good idea', it actually helps keep
all the power cables short and the PSU within the constrains of the
printer itself without getting in the way.

Maybe two PSU's would be better than one, (similar to how I'm running
it now as the bed heater role can be completely independent of any of
the printer electronics as it's powered though a relay) especially if
they might not like being run close to their advertised ratings? 2 x
12V, 15A better than 1 x 20A (or 25A as it might be the same size)?

Cheers, T i m


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T i m wrote:
I still have one of the game console PSUs that I bought after a 'heads
up' from someone here, and a stripped out PC PSU but on that the 12V
is only 16A, and neither will fit under the printer and whilst I
thought it being there wasn't 'a good idea', it actually helps keep
all the power cables short and the PSU within the constrains of the
printer itself without getting in the way.


Probably me.

The open frame ones are on ebay:
https://www.ebay.co.uk/itm/164357507368
You can also get them in power brick form:
https://www.ebay.co.uk/itm/293813499442

although who knows what the quality is like.

Theo
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On 13 May 2021 17:00:33 +0100 (BST), Theo
wrote:

T i m wrote:
I still have one of the game console PSUs that I bought after a 'heads
up' from someone here, and a stripped out PC PSU but on that the 12V
is only 16A, and neither will fit under the printer and whilst I
thought it being there wasn't 'a good idea', it actually helps keep
all the power cables short and the PSU within the constrains of the
printer itself without getting in the way.


Probably me.


It probably was. ;-)

The open frame ones are on ebay:
https://www.ebay.co.uk/itm/164357507368


Yeah, I was looking at them earlier and on Amazon (for Prime delivery)
but as it did manage to finish the print I have a bit more time to
seek a replacement.

You can also get them in power brick form:
https://www.ebay.co.uk/itm/293813499442


But in 12V form you mean?

although who knows what the quality is like.


And that's the thing. I've taken the original one out and it's top off
and it looks like one of the caps has blown (top right of the group of
4 x 1000u /16V at the bottom):

https://ibb.co/VHYxc88

You can also see that choke has been running pretty hot as the shellac
is dark.

I think there was a fan in there (you can see the remains of the gloop
on the lower side (on the pic) of the txfmr) but it failed and we took
it out as the PSU ran cold (originally).

When I took it out earlier it was quite hot.

Where it is on the printer is open on all 4 sides and not in any way
enclosed.

I wonder if a set of new caps and maybe add a second PSU to split the
load might be a good repair / upgrade?

Cheers, T i m

p.s. From a quick Google it comes up as a 5V x 40A model but I'm
guessing that's something they change in the factory (slightly
different bits but the same mechanics / circuit)?
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On 13/05/2021 17:00, Theo wrote:
T i m wrote:
I still have one of the game console PSUs that I bought after a 'heads
up' from someone here, and a stripped out PC PSU but on that the 12V
is only 16A, and neither will fit under the printer and whilst I
thought it being there wasn't 'a good idea', it actually helps keep
all the power cables short and the PSU within the constrains of the
printer itself without getting in the way.


Probably me.

The open frame ones are on ebay:
https://www.ebay.co.uk/itm/164357507368
You can also get them in power brick form:
https://www.ebay.co.uk/itm/293813499442

although who knows what the quality is like.

Theo


'Meanwell' PSU's seem to be pretty good quality and value. Lots on eBay.

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Cheers
Clive
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On 13/05/2021 18:07, T i m wrote:
On 13 May 2021 17:00:33 +0100 (BST), Theo
wrote:

And that's the thing. I've taken the original one out and it's top off
and it looks like one of the caps has blown (top right of the group of
4 x 1000u /16V at the bottom):

https://ibb.co/VHYxc88

You can also see that choke has been running pretty hot as the shellac
is dark.

I think there was a fan in there (you can see the remains of the gloop
on the lower side (on the pic) of the txfmr) but it failed and we took
it out as the PSU ran cold (originally).

When I took it out earlier it was quite hot.

Where it is on the printer is open on all 4 sides and not in any way
enclosed.

I wonder if a set of new caps and maybe add a second PSU to split the
load might be a good repair / upgrade?

Cheers, T i m

p.s. From a quick Google it comes up as a 5V x 40A model but I'm
guessing that's something they change in the factory (slightly
different bits but the same mechanics / circuit)?


That's an odd place to put the fan.

https://ibb.co/3FZYMPP

Sure looks like there's been some cooking and boiling !

PA



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T i m wrote:
Mate rang last night asking for something to be designed and 3D
printed and this morning sent me a diagram with vernier caliper
measured dimensions for me to work from.

I designed and started the printing but when I checked a bit later,
expecting to see it all done (as usual), the printer was off and the
head not parked etc? ;-(

Long short, it looks like the 20A x 12V 'open frame' SMPSU has gone
weak?

eg, After some faultfinding it seemed it could power most of the
printer, just not the heated bed and so I have that now running from
my old 13.5V 12A bench PSU that was last used powering my 70 cms
packet radio and TNC.

The heated bed is pulling a good 11.5A (at 13.5V) from the linear PSU
and the SMPSU is 'still' running the extruder, Arduino Mega, RAMPS
display / interface board and 5 stepper motors?

The guy I was helping with the print job is the guy who originally
bought the printer kit on the grounds I built it with him ... and the
PSU was what was supplied in the kit. It's made in China of course and
I'm guessing they may have been reasonably optimistic with it's
ratings? That said, it's done a fair bit of work over a good few years
so owes me nothing.

When (if) this job actually finishes, I'll take the PSU out and have a
look inside and a measure up then find a replacement that's about the
same size, as it fits under the printers bed and there isn't much
room for anything taller or wider.

I still have one of the game console PSUs that I bought after a 'heads
up' from someone here, and a stripped out PC PSU but on that the 12V
is only 16A, and neither will fit under the printer and whilst I
thought it being there wasn't 'a good idea', it actually helps keep
all the power cables short and the PSU within the constrains of the
printer itself without getting in the way.

Maybe two PSU's would be better than one, (similar to how I'm running
it now as the bed heater role can be completely independent of any of
the printer electronics as it's powered though a relay) especially if
they might not like being run close to their advertised ratings? 2 x
12V, 15A better than 1 x 20A (or 25A as it might be the same size)?

Cheers, T i m


If it's a 12V supply, you can use an ATX supply for that.
The modern ones are double forward conversion, and the 12V
section is separate from the 3.3V/5V section and the other
sections don't need a load particularly (should have better
cross-load characteristic than the old single-transformer ones).

ATX supplies can be very efficient, so less waste heat to remove.

If it's a 13.5V supply, then you're looking at some other
form factor, like ham radio supplies (some of which are linear
and lower RF noise, some of which are SMPS with a bit of hash
on the wires). Now the efficiency can be poorer (like on the
linear), and fan cooling is required for a good result. The SMPS
ones will be more compact, because less heatsink is needed.

I think the very best ATX I've seen, was somewhere around
97% efficient at mid-load. This is state of the art stuff.

https://seasonic.com/pub/media/wysiw...s/Titanium.png

seasonic prime fanless tx-700

+3.3V @ 20A,
+5V @ 20A,
+12V @ 58A,
-12V @ 0.3A,
+5VSB @ 3A

That's not an endorsement, but it shows what is possible. I'd
still want some air movement through the poor thing.

There was a time, when some of these SMPS were only 60% efficient
and the heat used to pour out of them, requiring
a stout fan and associated noise. They've come a
long way since then.

Paul
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On 13/05/2021 22:39, T i m wrote:
On Thu, 13 May 2021 16:53:30 -0400, Paul
wrote:

Do you know what they mean by 'single rail'?

https://www.scan.co.uk/products/600w...-psu-black-psu


One +12v rail offering a lot of current as against two. That's how they
started out until someone decided that so much demand on +12v meant that
two +12v would be a better idea. Lower currents per rail. OK, but
loading the two rails correctly didn't work out for some systems. So
some have returned to a single, many ampere, rail.

I think that this really kicked off when all the PCIe connectors were
loaded onto the same +12v rail of a two-rail PSU.

PA

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On Thu, 13 May 2021 20:37:35 +0100, Clive Arthur
wrote:

On 13/05/2021 17:00, Theo wrote:
T i m wrote:
I still have one of the game console PSUs that I bought after a 'heads
up' from someone here, and a stripped out PC PSU but on that the 12V
is only 16A, and neither will fit under the printer and whilst I
thought it being there wasn't 'a good idea', it actually helps keep
all the power cables short and the PSU within the constrains of the
printer itself without getting in the way.


Probably me.

The open frame ones are on ebay:
https://www.ebay.co.uk/itm/164357507368
You can also get them in power brick form:
https://www.ebay.co.uk/itm/293813499442

although who knows what the quality is like.

Theo


'Meanwell' PSU's seem to be pretty good quality and value. Lots on eBay.


Thanks Clive, they do seem to be a step above the basic offerings, or
should do by the price of some of them. ;-)

The only one SP-200-12that looks like it's the same width as the
existing is only 200W / 16A, and that's a bit less than the 20A of the
original. However, the chances are the Meanwell is a real 16A versus
the cheapo and given *that* lasted for a good 5+ years ... ?

We know the 3D printer heated bed draws ~10A (on 12V) but can also run
on 24V and so would be nearer to 5A on 24V. If replacing the caps
(ordered) doesn't sort the old PSU, I was thinking I could use a
SP-200-12 for the 12V stuff and a 24V (10A indicated, assuming it's
only 7) PSU for just the Bed Heater.

Originally is was being driven by a Mosfet on the main board but the
FET got very hot so I used the FET to drive a 12V 40A automotive relay
and that seems to have worked ok (bang-bang). That means I could
easily set the heated bed up for 24V and use the same relay (still
driven by 12V on the coil).

I tested all 4 caps and they all came out ok (on my little component
tester) but I'm wondering if it might be different under real load /
voltage (or why would one cap be bulged and the PSU not working
properly)?

Cheers, T i m
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On 13/05/2021 22:46, T i m wrote:
On Thu, 13 May 2021 21:27:03 +0100, Peter Able wrote:

snip

That's an odd place to put the fan.


Agreed.

https://ibb.co/3FZYMPP

Sure looks like there's been some cooking and boiling !


Yeah, that ferrite was quite warm and one cap bulging but the caps
tested out similarly, eg, VLoss ~1.8%, Cap ~1150 uF and ESR ~ .1?

Cheers, T i m


Your tests were when it was cool? Closest to the toroid? Missing the fan?

PA

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On Thu, 13 May 2021 16:53:30 -0400, Paul
wrote:

snip

If it's a 12V supply, you can use an ATX supply for that.


I do have one I've taken the main output wires from and just left the
power on lines, with the idea of using it on the printer. And that
would be a bonus as the setup can actively drive a PSU that powers the
bed and extruder heaters and so shut them down in the event of a fault
/ overheat.

The modern ones are double forward conversion, and the 12V
section is separate from the 3.3V/5V section and the other
sections don't need a load particularly (should have better
cross-load characteristic than the old single-transformer ones).


OK.

ATX supplies can be very efficient, so less waste heat to remove.


Noted.

If it's a 13.5V supply, then you're looking at some other
form factor, like ham radio supplies (some of which are linear
and lower RF noise, some of which are SMPS with a bit of hash
on the wires). Now the efficiency can be poorer (like on the
linear), and fan cooling is required for a good result. The SMPS
ones will be more compact, because less heatsink is needed.


The old linear supply was just so I could finish the print job for my
mate Paul. Even though it did get fairly warm after the 90 min print,
the duty cycle was probably 1:10 (after the bed had initially got to
temperature).

I think the very best ATX I've seen, was somewhere around
97% efficient at mid-load. This is state of the art stuff.

https://seasonic.com/pub/media/wysiw...s/Titanium.png


That's good.

seasonic prime fanless tx-700

+3.3V @ 20A,
+5V @ 20A,
+12V @ 58A,


Wow. Shame it's EOL. ;-(

-12V @ 0.3A,
+5VSB @ 3A

That's not an endorsement, but it shows what is possible. I'd
still want some air movement through the poor thing.


Quite, and the printer isn't exactly quiet with 3 other cooling fans
running. A 120mm thermally controlled fan would probably not be
noticed. ;-)

There was a time, when some of these SMPS were only 60% efficient
and the heat used to pour out of them, requiring
a stout fan and associated noise. They've come a
long way since then.


Yup, many of my PC's are passively cooled, as has my WHS been for
about 10 years now. ;-)

Do you know what they mean by 'single rail'?

https://www.scan.co.uk/products/600w...-psu-black-psu

I think I only need 300W on 12V and with the 600W PSUs running around
45 (new), it's quite a bit more than a straight enclosed SMPSU. ;-(

I need to look back of the spec of this console PSU as I think that
was pretty high power and could be switched remotely.

Cheers, T i m


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On Thu, 13 May 2021 21:27:03 +0100, Peter Able wrote:

snip

That's an odd place to put the fan.


Agreed.

https://ibb.co/3FZYMPP

Sure looks like there's been some cooking and boiling !


Yeah, that ferrite was quite warm and one cap bulging but the caps
tested out similarly, eg, VLoss ~1.8%, Cap ~1150 uF and ESR ~ .1?

Cheers, T i m
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Peter Able wrote:
On 13/05/2021 22:39, T i m wrote:
On Thu, 13 May 2021 16:53:30 -0400, Paul
wrote:
Do you know what they mean by 'single rail'?


https://www.scan.co.uk/products/600w...-psu-black-psu



One +12v rail offering a lot of current as against two. That's how they
started out until someone decided that so much demand on +12v meant that
two +12v would be a better idea. Lower currents per rail. OK, but
loading the two rails correctly didn't work out for some systems. So
some have returned to a single, many ampere, rail.

I think that this really kicked off when all the PCIe connectors were
loaded onto the same +12v rail of a two-rail PSU.

PA


On ATX, they dabbled with a few ideas.

You could get some idea, from the length of some of the
ATX PSUs. Two dimensions are standard, the third dimension
(length) is variable.

A few supplies, really did have independent outputs. One
PSU was really long (would have bumped into the DVD drive),
and it had four transformers for 12V. There would be ATX12V1
and 12V2, and a couple rails for PCI Express connectors. The
hardest part of using those, was finding the wiring diagram,
so you could figure out how to load the thing (not overload
any one transformer.

But the idea of doing that, quickly died, and they don't tend
to do that any more.

Now, there's one huge transformer with 12V on it. What should
happen, is sections of the +12V loom, are protected by
current limiters. The main transformer might be 60A, but
there will be three current limiters installed, each connected
to the main output. The output wires then feed some part
of the system (like, just the motherboard). The limiter
might not be 20A, it might be a bit higher. It's there,
to ensure a 20A rated wire, doesn't have 60+ amps flowing
through it :-)

It's also possible they're selling some "let 'er fry" ones,
where there is the 60A transformer, but only the 60A limit
is checked, and maybe it can make some 12V wiring glow
with the heat. Generally, the documentation is negligent,
in that it does not give sufficient detail about the
sections of the loom and what limits are in place. The
marketing people want the message "it's got 60 amps, kids",
to get through, and any other level of detail would be
a distraction. Telling people there was a current limiter
for sound reasons, would only elicit a customer response
of "but I paid for 60 amps!" :-)

Since all the 12V current comes from the same transformer
winding, joining some 1x4 Molex to some other pins, should
not cause loop currents to flow. Loop currents would be
a consideration on the supply with the four transformers.

Paul
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On Thu, 13 May 2021 22:24:15 +0100, Peter Able wrote:

On 13/05/2021 22:46, T i m wrote:
On Thu, 13 May 2021 21:27:03 +0100, Peter Able wrote:

snip

That's an odd place to put the fan.


Agreed.

https://ibb.co/3FZYMPP

Sure looks like there's been some cooking and boiling !


Yeah, that ferrite was quite warm and one cap bulging but the caps
tested out similarly, eg, VLoss ~1.8%, Cap ~1150 uF and ESR ~ .1?


Your tests were when it was cool?


Yup ...

Closest to the toroid?


Not when they were off the PCB and I was testing them. ;-)

Missing the fan?


They may have been. ;-)

But all the above are why I have already ordered some replacements and
*if* they allow it to function again, may offload some of the load
onto an additional PSU as well (for the 24V heated bed). ;-)

I just was ready to see the one with the bulge show very different
results (even cold) but it didn't?

Cheers, T i m

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I'd check any capacitors in the unit, since one usually finds that depending
on the design, these can be critical for its efficient operation.
Brian

--

This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"T i m" wrote in message
...
Mate rang last night asking for something to be designed and 3D
printed and this morning sent me a diagram with vernier caliper
measured dimensions for me to work from.

I designed and started the printing but when I checked a bit later,
expecting to see it all done (as usual), the printer was off and the
head not parked etc? ;-(

Long short, it looks like the 20A x 12V 'open frame' SMPSU has gone
weak?

eg, After some faultfinding it seemed it could power most of the
printer, just not the heated bed and so I have that now running from
my old 13.5V 12A bench PSU that was last used powering my 70 cms
packet radio and TNC.

The heated bed is pulling a good 11.5A (at 13.5V) from the linear PSU
and the SMPSU is 'still' running the extruder, Arduino Mega, RAMPS
display / interface board and 5 stepper motors?

The guy I was helping with the print job is the guy who originally
bought the printer kit on the grounds I built it with him ... and the
PSU was what was supplied in the kit. It's made in China of course and
I'm guessing they may have been reasonably optimistic with it's
ratings? That said, it's done a fair bit of work over a good few years
so owes me nothing.

When (if) this job actually finishes, I'll take the PSU out and have a
look inside and a measure up then find a replacement that's about the
same size, as it fits under the printers bed and there isn't much
room for anything taller or wider.

I still have one of the game console PSUs that I bought after a 'heads
up' from someone here, and a stripped out PC PSU but on that the 12V
is only 16A, and neither will fit under the printer and whilst I
thought it being there wasn't 'a good idea', it actually helps keep
all the power cables short and the PSU within the constrains of the
printer itself without getting in the way.

Maybe two PSU's would be better than one, (similar to how I'm running
it now as the bed heater role can be completely independent of any of
the printer electronics as it's powered though a relay) especially if
they might not like being run close to their advertised ratings? 2 x
12V, 15A better than 1 x 20A (or 25A as it might be the same size)?

Cheers, T i m




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On 13/05/2021 16:31, T i m wrote:

snipped

Long short, it looks like the 20A x 12V 'open frame' SMPSU has gone
weak?


snip

I'd check the rectifier bridge. One of the four diodes blown and it
becomes a half-wave rectifier.


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Cheers
Clive


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On Thu, 13 May 2021 23:20:16 -0400, Paul
wrote:

Peter Able wrote:
On 13/05/2021 22:39, T i m wrote:
On Thu, 13 May 2021 16:53:30 -0400, Paul
wrote:
Do you know what they mean by 'single rail'?

https://www.scan.co.uk/products/600w...-psu-black-psu



One +12v rail offering a lot of current as against two. That's how they
started out until someone decided that so much demand on +12v meant that
two +12v would be a better idea. Lower currents per rail. OK, but
loading the two rails correctly didn't work out for some systems. So
some have returned to a single, many ampere, rail.

I think that this really kicked off when all the PCIe connectors were
loaded onto the same +12v rail of a two-rail PSU.

PA


On ATX, they dabbled with a few ideas.

You could get some idea, from the length of some of the
ATX PSUs. Two dimensions are standard, the third dimension
(length) is variable.

A few supplies, really did have independent outputs. One
PSU was really long (would have bumped into the DVD drive),
and it had four transformers for 12V. There would be ATX12V1
and 12V2, and a couple rails for PCI Express connectors. The
hardest part of using those, was finding the wiring diagram,
so you could figure out how to load the thing (not overload
any one transformer.

But the idea of doing that, quickly died, and they don't tend
to do that any more.

Now, there's one huge transformer with 12V on it. What should
happen, is sections of the +12V loom, are protected by
current limiters. The main transformer might be 60A, but
there will be three current limiters installed, each connected
to the main output. The output wires then feed some part
of the system (like, just the motherboard). The limiter
might not be 20A, it might be a bit higher. It's there,
to ensure a 20A rated wire, doesn't have 60+ amps flowing
through it :-)

It's also possible they're selling some "let 'er fry" ones,
where there is the 60A transformer, but only the 60A limit
is checked, and maybe it can make some 12V wiring glow
with the heat. Generally, the documentation is negligent,
in that it does not give sufficient detail about the
sections of the loom and what limits are in place. The
marketing people want the message "it's got 60 amps, kids",
to get through, and any other level of detail would be
a distraction. Telling people there was a current limiter
for sound reasons, would only elicit a customer response
of "but I paid for 60 amps!" :-)

Since all the 12V current comes from the same transformer
winding, joining some 1x4 Molex to some other pins, should
not cause loop currents to flow. Loop currents would be
a consideration on the supply with the four transformers.

Interesting, thanks both.

I have 'converted' a few PSU's to 12V (mainly) PSUs over the years,
the last for a 12V electrolysis tank (that worked very well).

If I already had a know suitable PC PSU that wasn't in use that
offered at least 20A on the (single) 12V rail I might consider
converting it for use with my 3D printer and having it free standing
beside it (as it wouldn't fit underneath and I can't raise it easily
as the filament spools sit on top and there is restricted height above
it). I could mount it on the frame where it would be out of the way
of the bed / extruder but it would end up requiring all the (heavy
current) cables being longer (and potentially restricting access for
maintenance of the printer etc).

So, a 'decent' replacement of the main 12V PSU to run the printer,
controller and extruder and a second, probably 24V PSU for the bed
heater. Higher voltage = lower current and so even easier to extend
slightly (to the other side under the print bed).

http://mylinux.net.my/blog/2014/05/3...t-3-completed/

My printer is one of those (Mendelmax) and my 'eiectronics' are where
his are, my display / SD card are at the top of the front on the same
side and my PSU is underneath the bed in the same corner, meaning
everything sits inside the main footprint and the power leads are as
short as they can be.

Cheers, T i m

p.s. The whole thing is both quite heavy and has fairly fragile
components on it (axis position sensors) meaning that you have to be
fairly careful when moving it, especially re catching any of
sticky-out-bits on anything or putting any stress / strain in the
wrong places. That said, the whole design is very rigid (one of the
key criteria when I was advising what printer we should build back
then) and unlike many of the simpler 3D printer designs, requires no
re-calibration after being moved (see above for cautions when moving
it) or even if it's only sitting on two feet etc.
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On Fri, 14 May 2021 09:39:49 +0100, Clive Arthur
wrote:

On 13/05/2021 16:31, T i m wrote:

snipped

Long short, it looks like the 20A x 12V 'open frame' SMPSU has gone
weak?


snip

I'd check the rectifier bridge. One of the four diodes blown and it
becomes a half-wave rectifier.


Understood and I (just) checked it (in circuit, diode test on my DMM)
and it seems ok (10 ways). ;-(

I would have preferred to find something, rather than just 'hoping' it
was a cap drying out etc?

That said. We have probably been working it fairly hard over a good
few years, given it's 20A capacity may be fairly optimistic?

The heated bed draws ~10A, all be it with only a 1:5 duty cycle once
up to temp (60degC), the extruder is either 20 or 40W (I can't
remember now, assume 40) so another ~3.5A (worst case whilst at 100%
when warming then maybe 50:50 once running (PWM)), 5 x stepper motors
running at about 1A each plus whatever the Arduino Mega, the RAMPS
interface board + display and 3 small fans may draw, lets guess
another couple of amps:

So that's worst case 10+3.5+5+2= 20.5A (246W). ;-( [1]

ITRW, the extruder heats up pretty quickly, the bed takes a bit longer
and only *after* that was done would the motors initialise ('holding'
current etc), so I don't think we would ever see that 20.5A as such
and certainly not for a prolonged period. And it has run for many
years now and even after the PSU fan went noisy and failed, we checked
the PSU temp and it was never much past warm?

That said, I think I'd prefer some margin and hence why a single 12V /
300W might be more suitable (but don't think I can find one to fit
(100mm wide by 50mm deep worst cases), or a 200W for the heated bed
(set to 24V) and another for the rest (12V)?

Cheers, T i m

[1] Given you can 'manage what you measure', I have a second bench PSU
and given I already know what current the heated bed draws from 13.5V
(11.5A), I can power the rest of the printer though my 20A range DMM
with peak hold and see what worst case *actually* is. ;-)
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On Fri, 14 May 2021 09:39:36 +0100, "Brian Gaff \(Sofa\)"
wrote:

I'd check any capacitors in the unit, since one usually finds that depending
on the design, these can be critical for its efficient operation.


There was one that had a budging top Brian that seems to test out the
same as the others on my little automatic component tester but because
of the bulge and the PSU not working properly, I've ordered Panasonic
replacements and will test it again once done.

Luckily I also have a load tester that I use for testing batteries
that I can put on it once the caps are replaced and test it at it's
twenty amp rated load.

Cheers, T i m
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On Fri, 14 May 2021 09:39:49 +0100, Clive Arthur
wrote:

On 13/05/2021 16:31, T i m wrote:

snipped

Long short, it looks like the 20A x 12V 'open frame' SMPSU has gone
weak?


snip

I'd check the rectifier bridge. One of the four diodes blown and it
becomes a half-wave rectifier.


I replaced the 4 output caps because of the blown one and sorta as
predicted it doesn't seem to have fixed it.

I can go round all the passive components and check the smaller
transistors but there are a couple of big devices underneath (TO220
but bigger style cases), one 3 pin (FET / Transistor) and a 5 legged
one (SMPSU controller device)?

I can probably check for the 400V or so on the input caps (and any AC
voltage present, suggesting those caps had gone dry?) but there is
little point spending too much time (or money) on components, other
than for the fun of possibly repairing it.

After changing the caps and powering it up with no load, I saw a
'weak' (fluctuating) 12V on the DMM but it wouldn't power up with a 5A
load attached (it crowbarred).

Any thoughts?

Cheers, T i m
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T i m wrote
Clive Arthur wrote
T i m wrote



Long short, it looks like the 20A x 12V
'open frame' SMPSU has gone weak?


I'd check the rectifier bridge. One of the four diodes
blown and it becomes a half-wave rectifier.


I replaced the 4 output caps because of the blown one
and sorta as predicted it doesn't seem to have fixed it.


I can go round all the passive components and check the
smaller transistors but there are a couple of big devices
underneath (TO220 but bigger style cases), one 3 pin (FET
/ Transistor) and a 5 legged one (SMPSU controller device)?


I can probably check for the 400V or so on the input caps (and
any AC voltage present, suggesting those caps had gone dry?)
but there is little point spending too much time (or money)
on components, other than for the fun of possibly repairing it.


After changing the caps and powering it up with no load,
I saw a 'weak' (fluctuating) 12V on the DMM but it wouldn't
power up with a 5A load attached (it crowbarred).


Any thoughts?


More likely now that it's the main controlling ic that has gone flaky.


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On Mon, 17 May 2021 04:52:22 +1000, cantankerous trolling geezer Rodent
Speed, the auto-contradicting senile sociopath, blabbered, again:



More likely now that it's the main controlling ic that has gone flaky.


You mean like your senile "brain", senile sociopath?

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cretin's pathological trolling:
https://www.pcreview.co.uk/threads/r...d-faq.2973853/
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On 16/05/2021 10:51, T i m wrote:
On Fri, 14 May 2021 09:39:49 +0100, Clive Arthur
wrote:

On 13/05/2021 16:31, T i m wrote:

snipped

Long short, it looks like the 20A x 12V 'open frame' SMPSU has gone
weak?


snip

I'd check the rectifier bridge. One of the four diodes blown and it
becomes a half-wave rectifier.


I replaced the 4 output caps because of the blown one and sorta as
predicted it doesn't seem to have fixed it.

I can go round all the passive components and check the smaller
transistors but there are a couple of big devices underneath (TO220
but bigger style cases), one 3 pin (FET / Transistor) and a 5 legged
one (SMPSU controller device)?

I can probably check for the 400V or so on the input caps (and any AC
voltage present, suggesting those caps had gone dry?) but there is
little point spending too much time (or money) on components, other
than for the fun of possibly repairing it.

After changing the caps and powering it up with no load, I saw a
'weak' (fluctuating) 12V on the DMM but it wouldn't power up with a 5A
load attached (it crowbarred).

Any thoughts?

Cheers, T i m


There looks to be a preset potentiometer, bottom right, in your photo.
Might be worth noting its current position, rotating it from end to end
of its range a few times, then restoring it to the original position. A
spurt of switch cleaner before the above might help, too.

PA

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On Mon, 17 May 2021 10:19:44 +0100, Peter Able wrote:

snip

After changing the caps and powering it up with no load, I saw a
'weak' (fluctuating) 12V on the DMM but it wouldn't power up with a 5A
load attached (it crowbarred).

snip

There looks to be a preset potentiometer, bottom right, in your photo.
Might be worth noting its current position, rotating it from end to end
of its range a few times, then restoring it to the original position. A
spurt of switch cleaner before the above might help, too.


Good (simple) check / suggestion and nothing to lose. ;-)

I believe that pot is just a trimmer allowing you to tweak the voltage
around the nominal 12V so I don't even have to mark it and would
re-set it under load.

I'm not particularly hopeful it will do anything as even if it was
'noisy' and was allowing the voltage to fluctuate around it's entire
range, I would have thought it should still have been able to drive
the 5A load, even if also whilst fluctuating? I wonder though if that
only depends on if the PSU still works at all with (worst case), no
voltage on the wiper of the trimmer?

I'll let you know how I get on. ;-)

Cheers, T i m
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On 17/05/2021 12:10, T i m wrote:
On Mon, 17 May 2021 10:19:44 +0100, Peter Able wrote:

snip

After changing the caps and powering it up with no load, I saw a
'weak' (fluctuating) 12V on the DMM but it wouldn't power up with a 5A
load attached (it crowbarred).

snip

There looks to be a preset potentiometer, bottom right, in your photo.
Might be worth noting its current position, rotating it from end to end
of its range a few times, then restoring it to the original position. A
spurt of switch cleaner before the above might help, too.


Good (simple) check / suggestion and nothing to lose. ;-)

I believe that pot is just a trimmer allowing you to tweak the voltage
around the nominal 12V so I don't even have to mark it and would
re-set it under load.

I'm not particularly hopeful it will do anything as even if it was
'noisy' and was allowing the voltage to fluctuate around it's entire
range, I would have thought it should still have been able to drive
the 5A load, even if also whilst fluctuating? I wonder though if that
only depends on if the PSU still works at all with (worst case), no
voltage on the wiper of the trimmer?

I'll let you know how I get on. ;-)

Cheers, T i m


We all like the intellectual challenge of a difficult fault - and yet it
often ends up being a simple mechanical contact failure !

PA
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On Tue, 18 May 2021 08:20:15 +0100, Peter Able wrote:

snip

I'm not particularly hopeful it will do anything as even if it was
'noisy' and was allowing the voltage to fluctuate around it's entire
range, I would have thought it should still have been able to drive
the 5A load, even if also whilst fluctuating? I wonder though if that
only depends on if the PSU still works at all with (worst case), no
voltage on the wiper of the trimmer?

I'll let you know how I get on. ;-)


We all like the intellectual challenge of a difficult fault - and yet it
often ends up being a simple mechanical contact failure !


On that then, I did give the pot a good working up and down and it
didn't make any difference, but as it was simple enough to do, worth a
try (so thanks).

I have the question open elsewhere and am being guided by folk who
seem to to be fairly intimate with SMPSU's and I'm following a logical
path.

I've since measured the voltage across the two large input caps (both
showing 166V DC) and checked that there is little ripple. The next is
a couple of small electrolytic caps and an opto coupler and then what
may be a rectifier in a TOxxx package.

I think I'm understanding the working principles a bit better as well
so that's a good thing. ;-)

I also have a couple of new / better PSU's on their way so I can get
my 3D printer up and running and if I get this working I can either
keep it as a spare, put it back into use on the printer heated bed
(very basic role) or as a low voltage / high current adjustable bench
PSU with one of the eBay PSU front ends. ;-)

Cheers, T i m
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