Test #1 for peltier cooler

[davidpretorius]

Hi,

expected low of 1 degree and with a high pressure system about to park itself over the state, I can finally measure the peltier cooling system.

I hope to have the new one up and running in a couple of weeks, so i can then run the test again.

The current one has only one peltier, there is no perspex insulator and the aluminium cold plate disc is too big to fit inside the mirror cell cavity behind the mirror.

The new one will have two peltiers, a perspex insulator that will seal the base and also the cold plate will fit in behind the mirror.

graphs from 1/2 hr measurements to come.....

[davidpretorius]

13 odd degrees at 6.30pm in the garage and out we go out outside

[davidpretorius]

8pm update

[davidpretorius]

9pm, gamma 2 delphinus was nice even with the fan on

[Photon]

Hi Dave, I'm watching ..... and waiting .... I would have expected the mirror to be diving closer to ambient by now, with the cooler that is, how long does it normally take?
Regards IanG

[davidpretorius]

Hi ian,

this is about right in terms of cooling rate. The system is not efficient ie no insulator like a normal fridge. Soon to be fixed though!!

High cloud coming in from the south east, so we should see some temp changes soon

[davidpretorius]

clouds here and the temp has gone up, as bird says, the heat the earth is releasing has been halted by the clouds and hence, up goes the temp.

the internal air temp between cold plate and mirror is 3.5 degrees.

clouds should disperse soon

[Photon]

Hi Dave,
I'm very interested nice you are giving us a live update! Since 20:00 mirror and ambient are tracking closely, I assume without the peltier the mirror would be much warmer over ambient?
Regards IanG

[davidpretorius]

yup, with a fan only, it would be 1/2 as slow i reckon

clouds must have left at around 10:15 and another batch is on its way

[bird]

hi DP, nice data. I'll be watching for the next couple of hours (also watching nasa tv waiting for atlantis to launch at 12.30 :-))

Transient clouds can really be a pain - the mirror will stop cooling unless you're using peltiers or similar.

cheers, Bird

[davidpretorius]

Hi Bird,

yup more clouds have arrived and up goes the ambient again.

Mirror has stabilised due to ambient still having some effect on it along with the cold air from the peltier. This is really thick cloud now!

[bird]

Peltiers only generate a relative temperature difference between their hot and cold sides, so if ambient air temp goes up by a couple of degrees then the cold plate temp will also go up a couple of degrees.

Normally this is a good thing, as the ambient temp drops through the night then the cold plate temp is always a few degrees colder than it. But when clouds come along like this it can spoil the party unless you can engage more cooling to compensate.

cheers, Bird

[davidpretorius]

yeh, can't wait for the new system to get built, with two peltiers and insulated, then i can really push it along!

[davidpretorius]

well cloud seems to have settled in

the air temp between the mirror and cold plate is now 3.7 degrees

damn clouds!

[davidpretorius]

well he clouds have gone away and now the ambient plummets!!!

this has been a great example tonight in that at no time has the viewing due to tube currents been ideal!!!

[bird]

Yeah, with the peltiers running they can exaggerate thermal currents, cause they are adding a very cold layer of air around the mirror. It seems to take at least 15 minutes with the peltiers turned off before the air and mirror settle down. Just long enough to go and make a cuppa hot milo or coffee at 4am :-)

cheers, Bird

[davidpretorius]

clouds have come in for the last time, scope is now away in the garage!!!

off to watch the shuttle!

[bird]

Looks like a good test.

Bird

[Dennis]

Excellent live broadcast Dave with expert commentary all round. Well done the lads!

Cheers

Dennis

[stringscope]

Fascinating exercise DP. Most instructive to read your commentary and see the plotted ambient temp excursions :eyepop: .

Great stuff! Can't wait to follow Test #2.

Cheers.

[gbeal]

I too found this fascinating DP, but haven't you got a TV? Or a good book?
Can't wait to see the Mk2 model. Gary

[Starkler]

Looks like the ideal is to have a mirror of the lowest thermal mass possible, ie a thin mirror or a conical.

I wonder in the case of GS scopes whether a redesigned mirror cell allowing more of that chilled air to get at the mirror would be worthwhile?

[davidpretorius]

i agree geoff, hence Bird foray with his 13.1"