ZX81 cooling fan

Discussions about Sinclair ZX80 and ZX81 Hardware
Lardo Boffin
Posts: 655
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 cooling fan

Post by Lardo Boffin » Sat Nov 11, 2017 3:44 pm

Moggy wrote:
Sat Nov 11, 2017 12:18 pm

All in all an excellent idea worth pursuing although having thought about it a bit more I feel the opening on the case underside may be a bit restrictive causing some back-pressure, in which case removal of the "slats" would provide an unobstructed airflow at this point but I do understand any reluctance to butcher the case in this fashion.
In my head the gaps underneath the case were bigger than they actually are. Doh! A small amount of surgery may be required. To be fair the case in question is a bit batterer so no big deal.
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

Moggy
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Joined: Wed Jun 18, 2008 1:00 pm

Re: ZX81 cooling fan

Post by Moggy » Sat Nov 11, 2017 3:57 pm

I'm really looking forward to the outcome of this,Lardo especially the thermal camera thing. If this turns out as I hope it does then two of my own cased 81s will be converted to fan cooling. :D

Good luck with this and please keep us up to date.

Regards.

Moggy.

Lardo Boffin
Posts: 655
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 cooling fan

Post by Lardo Boffin » Sat Nov 11, 2017 10:01 pm

I fitted the fan. I covered up the unwanted ventilation slots to help ensure that the air does not recirculate in the immediate area. Good old insulation tape! It also is currently holding the fan in place. Rather firmly! I may need to move the fan one more slot towards the keyboard before it all fits together. Not sure yet.

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I remounted the regulator on a bit of board using angled pins and left two of the pins sticking out at the base to hold the plug for the fan:-

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Here is the fan spinning merrily around:-

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You can just about make out the two pins for the plug:-

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1A0DA35C-D336-4F1B-8C7E-8172D2778715.jpeg (540.71 KiB) Viewed 159 times

Shame I soldered the regulator at an angle but I’m not about to do it all again...

So does it work? Yes I think. It blows a lot of air out of the base of the case. If you point it at your face you can really feel it. In order to blow the air out it must be getting it from within the case (as the vents are taped) and so therefore must be causing air to flow through the case. How much of it comes from the mic / ear / 9V sockets versus the edge connector I don’t know. So therefore how much it will cool the ULA I don’t know. But the air must be moving in there which can only be a good thing.
Hopefully when I can get to the office and borrow the thermal camera I may be able to see the difference with and without the fan.

Is it silent like the sales blurb says? Nope. But then my zeddy doesn’t have feet and it is only held in place by insulation tape at the moment. That said it is not intrusive. But then again my hearing is a bit rubbish. Too many Motörhead and Slayer gigs... You can hear it spin but unless you are in an otherwise silent room I doubt it would annoy.

Once I have finished sorting the zeddy and screwed it all together properly I will recheck the noise level.

Boffin, Lardo Boffin...
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

Moggy
Posts: 1513
Joined: Wed Jun 18, 2008 1:00 pm

Re: ZX81 cooling fan

Post by Moggy » Sun Nov 12, 2017 1:17 pm

Top work lardo top work love pin/plug solution!!

Don't worry which vent the air is coming in from because like I said earlier the vacuum effect will ensure the air over the ULA is moved and also as said earlier you would be surprised at how small the airflow required is, and with the case slats cut away the airflow will be even greater, I would add that some space is required underneath to allow air to escape freely I only mention this as you say this zeddy is footless.

An example I can relate is a customer of mine way back when wanted a 400watt per side stereo mos-fet power amplifier for stage use but insisted on no visible heat-sinks/cooling plates etc, everything internal was the brief. The result? After one hours use all internal wiring and transformer wiring suffered insulation meltdown(high power mos-fets do run very hot). The solution? One carefully placed PC case fan running off a 9v transformer provided a gentle quiet flow of air through the case resulting in one very cool running amplifier,all my stage/guitar amplifiers adopt this same approach.

As for testing I have found that with a normal cased zeddy some time is needed for the case to heat up as it were and a warm/hot spot on the case top-side appears above the ULA after about two hours running more so with the issue threes so perhaps a thermal picture taken of the case top-side without fan after running for this amount of time then one taken with a zeddy booted from cold with fan running for same said couple of hours?

If the outcome is how I hope it to be then I have an H4th zeddy ready for the chop!

pioneering stuff. :D

Lardo Boffin
Posts: 655
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 cooling fan

Post by Lardo Boffin » Sun Nov 12, 2017 5:51 pm

It occurs to me that I should have put the pins underneath the motherboard so that when it is screwed back together it makes plugging the fan in a bit easier.... :oops:

I make these mistakes so you don’t have to! :D
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

Lardo Boffin
Posts: 655
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 cooling fan

Post by Lardo Boffin » Sun Nov 12, 2017 11:16 pm

Following on from the previous post I’m not sure there will sufficient clearance on the underside but I will try to see if it is possible. Having screwed this together a few times now the extra cable is not too much of a hassle unless you have trimmed your keyboard connectors. At which point it becomes a major pain.

Less encouraging is the noise and vibration. I fitted a set of feet and left it running on a flat surface for getting on for two hours. It is somewhat noisy. And the vibrations can be felt through the keyboard.

However :-

1) The fan cost 99p including shipping from China
2) It is only held in place by insulation tape

So I’m thinking:-

1) Put some sort of gasket between it and the case.
2) Screw it very firmly to the case.
3) Investigate higher quality fans.

Regarding point 3 I just bought the cheapest fan I could find in case the idea was a total washout. Assuming the vibrations can be minimised I think this has legs so it will be worth spending more on a good fan.

Having run it for nearly two hours I quickly took it apart and used the finger test for temperature on the ULA.
Barely warm. The Z80 was a little warmer but that was still easily cool enough to touch.

This was done with just the flashing K showing as it turns out the keyboard was not working on this zeddy (I only ever use the motherboard to test chips and practice stuff like this).

Tomorrow I will try to steal the top off another zeddy and load The Gauntlet and let it run for a day. It has a good attract mode and plenty going on.
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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Paul
Posts: 880
Joined: Thu May 27, 2010 7:15 am
Location: Germanys west end

Re: ZX81 cooling fan

Post by Paul » Mon Nov 13, 2017 5:20 am

About the noise a das vibration :
There are rubber connector available instead of screws. Haven't seen them for a while but they work pretty good.
Maybe you can find them.
Kind regards Paul
In theory, there is no difference between theory and practice. But, in practice, there is.

Lardo Boffin
Posts: 655
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 cooling fan

Post by Lardo Boffin » Mon Nov 13, 2017 11:32 am

Thanks Paul. I have had a quick look but not found much yet. I am probably searching with the wrong terminology.

At the moment I have the zeddy running The Gauntlet in attract mode to keep it busy. Two hours in and you can just about tell where the ULA is inside the case. Note that I am not yet using the heat sinked ULA just a normal one.

I downloaded a decibel meter app for my phone. At 1 foot away it is reading around 42 decibels if that means anything to anyone.

One further thought that springs to mind is that the case may need additional venting if you want to have something plugged in the back, e.g. a ‘spand. But that will have to wait for a future test...
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

Lardo Boffin
Posts: 655
Joined: Sat Nov 26, 2016 1:42 am

Re: ZX81 cooling fan

Post by Lardo Boffin » Mon Nov 13, 2017 12:24 pm

With some foam tape underneath the corners there are a lot less vibrations going on but no real change to the volume level.
I wonder if the clearance is insufficient now with the extra height so the fan is labouring to pull air through. Certain the fan area is warmer than the ULA area now.
I have seen some 7.5mm high fans for sale. I may get one of those and a sheet of sorbophane.

For the electronically minded - if we reduce the voltage to the fan will it just reduce the speed a little?
I am wondering whether there will be a good tradeoff between speed (and noise) and cooling ability?
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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1024MAK
Posts: 1799
Joined: Mon Sep 26, 2011 9:56 am
Location: Looking forward to summer in Somerset, UK...

Re: ZX81 cooling fan

Post by 1024MAK » Mon Nov 13, 2017 12:30 pm

A more expensive fan (as in a higher quality fan) will run with much lower noise and vibration levels.

In an environment in which there is a forced air flow, you don't need a heatsink on the ULA. Indeed, even on high power devices, where a heatsink is still needed, it can be a much, much smaller heatsink.

As for your existing fan, if you have some rubber O rings of a suitable size, you could use these. That is what is used on some computer fan mounting kits.

On the clearance, for the amount of air that the fan is moving, I would guess that anything more than 3mm would be fine, as although the gap is small, there is a fairly big surface area for the air to flow around.

Mark

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