Computer water cooling system for a 40w laser tube?

[jjk.krizzi]

Hi all,

I've received some help on this topic already but would like to receive some more help.

The answers given, although thorough, are of little use due to my lack of providing any information.

We are a group of Architecture students from South Africa, and are busy planning a Lasersaur build. We envision our machine to be able to speed up our model building process. Thus a 40w laser system will be more than adequate. Our biggest dilemma, is the costs involved (obviously) but would like to figure out if a prebuilt or custom build computer cooling system would be able to cool the 40w laser tube, doing MAX 10 hours a day ( I highly doubt it will ever do more than 2 hours a day). 

The kit system we considered is as follows: http://www.zalman.com/global/product/Product_Read.php?Idx=185

Maximum Coolant Capacity	: Max. 1.25ℓ
- Integrated Water Pump	: 6W, DC 12V, 300L/Hr

Alternatively does someone have a BOM (And maybe pictures) for a homebuilt system that would be more cost efficient? 

Thanks in advance for any help! 

[Peter van der Walt (Gmail)]

I have a 40w... Good for engraving and paper cutting. Just a heads up

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[Jacob Kritzinger]

Would it be able to Cut 1mm grey card cardboard/ 3mm corrugated brown cardboard?

Kind regards

Jacob Kritzinger

---

From: "Peter van der Walt (Gmail)" <peter.p...@gmail.com>

Sender: lase...@googlegroups.com

Date: Sat, 7 Dec 2013 06:35:56 -0800

To: <lase...@googlegroups.com>

ReplyTo: lase...@googlegroups.com

Subject: Re: [lasersaur] Computer water cooling system for a 40w laser tube?

[Peter van der Walt (Gmail)]

(: yes. But i also thought that would the max i need to. Once you get one though you find you have lots you also want to cut. Even 3mm perspex is tough.

Ps on the cooling question. In durban in summer and a bucket plus pump keeps the 40 w cool

[Steve Baker]

You shouldn't have trouble cutting cardboard, paper and cloth with a 40W
laser. But acrylic and plywood would be tougher. A 60W laser will cut
6mm (1/4") materials like wood and acrylic - albeit fairly slowly.

Do you really need the large bed size of a lasersaur though? If you
don't, then I think a lasersaur (even with a 40W laser tube) is overkill.
There are systems you can buy from china via ebay that will do what you
need for less than half the price of a lasersaur.

As for cooling...is your workshop air conditioned? Wikipedia says that
your summer temperatures are around 30 C - which is probably too warm to
use passive water cooling.

Assuming the 40W tube is about the same efficiency as the 100W one, it'll
be putting out about 360W of waste heat when it's running on full power
(which it'll be doing most of the time probably).

* 360W is 360 joules/second.
* It takes 4.2 joules to heat one gram of water by one degC.
* The ideal max temperature for the laser tube is around 30 degC

So you have two issues to deal with (maybe three):

1) Flow rate. You need to have enough water flowing from the input to the
output of the laser each second to ensure that the water at the output
isn't over 30 degC.

2) Heat reservoir. Can your water container hold 2 hours (or 10 hours)
worth of water at that flow rate?

3) If the answer to (2) is "NO!" then you need to consider how you can
cool the water down using fans and radiators, ice or refrigeration.

Clearly the answer to all three questions depends a lot on the temperature
of the water at the outset. Buying bags of ice is really painful and
expensive - so it's probably best to assume that the water is at ambient
room temperature...which if you have airconditioning, should be no more
than (let's say) 24 degC.

So if the inlet water is at 24 degC and the outlet is at 30 degC, and the
laser is pushing out 340 joules/second - and heating 360/4.2=85g = 0.085kg
= 0.085 liters of water through one degree every second. Since you have 6
degrees of temperature rise allowed, you can push through 0.085 liters of
24 degC water every 6 seconds and never overheat the laser.

That's 0.014 liters/second 15 liters/minute or 51 liters per hour.

That's 13 US gallons/hour or 11 UK gallons/hour.

A decent aquarium pump can do about 80 gallons/hour - so it's plenty fast
enough...but a crappy pump might only do 3 gallons/hour which isn't
enough...so you'd better check that!

I very much doubt that a "CPU cooler" will be able to pump 13 gallons per
hour...and that's something you'll DEFINITELY have to check if you plan to
use one of those because if the flow rate is less than 13 gallons/hour
then you'll overheat the laser tube for sure - and that'll reduce it's
life significantly.

Now, clearly if you did want to run for 10 hours, you'd need a 130 gallon
water tank...which is a hell of a lot!

But the water in the tank won't stay hot for 10 hours, so you can
recirculate it...which means you can have a smaller reservoir. How much
smaller depends on how fast the water cools...which is a tough
calculation.

It would be better to have something like a car radiator and a fan (or a
CPU cooling system) that could cool the water so you can recirculate it
with a fairly small reservoir.

So the next question is "How many watts can your cooling system dissipate?"

CPU radiators will typically say how much heat they radiate in watts - and
some of the very best ones will radiate 360 watts...HOWEVER, the
temperature of the water coming out of a CPU core will be up at 60 degC -
and the rate at which a radiator dissipates heat is the SQUARE of the
temperature difference with the air in the room. If the waste water from
your laser tube is only 6 degrees over ambient - and the radiator
dissipates 360 watts with a 36 degrees over ambient water supply - then
it's not going to work worth a damn at cooling your laser.

-- Steve

Peter van der Walt (Gmail) wrote:
> (: yes. But i also thought that would the max i need to. Once you get one
> though you find you have lots you also want to cut. Even 3mm perspex is
> tough.
>
> Ps on the cooling question. In durban in summer and a bucket plus pump
> keeps the 40 w cool
> On Dec 7, 2013 5:01 PM, "Jacob Kritzinger" <jjk.k...@gmail.com> wrote:
>
>> Would it be able to Cut 1mm grey card cardboard/ 3mm corrugated brown
>> cardboard?
>> Kind regards
>>
>> Jacob Kritzinger

>> ------------------------------
>> *From: * "Peter van der Walt (Gmail)" <peter.p...@gmail.com>
>> *Sender: * lase...@googlegroups.com
>> *Date: *Sat, 7 Dec 2013 06:35:56 -0800
>> *To: *<lase...@googlegroups.com>
>> *ReplyTo: * lase...@googlegroups.com
>> *Subject: *Re: [lasersaur] Computer water cooling system for a 40w laser

>> tube?
>>
>> I have a 40w... Good for engraving and paper cutting. Just a heads up
>> On Dec 7, 2013 4:33 PM, "jjk.krizzi" <jjk.k...@gmail.com> wrote:
>>
>>> Hi all,
>>>
>>> I've received some help on this topic already but would like to receive
>>> some more help.
>>>
>>> The answers given, although thorough, are of little use due to my lack
>>> of
>>> providing any information.
>>>
>>> We are a group of Architecture students from South Africa, and are busy
>>> planning a Lasersaur build. We envision our machine to be able to speed
>>> up
>>> our model building process. Thus a 40w laser system will be more than
>>> adequate. Our biggest dilemma, is the costs involved (obviously) but
>>> would
>>> like to figure out if a prebuilt or custom build computer cooling
>>> system
>>> would be able to cool the 40w laser tube, doing MAX 10 hours a day ( I
>>> highly doubt it will ever do more than 2 hours a day).
>>>
>>> The kit system we considered is as follows:
>>> http://www.zalman.com/global/product/Product_Read.php?Idx=185
>>>

>>> Maximum Coolant Capacity: Max. 1.25â„“- Integrated Water Pump: 6W, DC

-- Steve

[Quy Ngo]

You should be able to cut acrylic albeit very slow. http://www.youtube.com/watch?v=l5IzVu7kuNY

I'm not sure how you plan to build a lasersaur if you are skimping out on the cooler. It is pretty expensive when you add it all up.

You might want to look into a 2.x laser. http://buildlog.net/sm_laser/drawings.html

[jjk.krizzi]

Thank you for the detailed response Steve and to all others!

To answer some of the other questions, we've already minimized the size of "our" Lasersaur ( Can't quite call it a Lasersaur anymore but it is our main pot of gold for ideas) to our standard paper and cardboard size (A1), thus cutting some costs. We've also found alternative suppliers for many of the parts which has saved on costs but also provided better shipping options to South Africa. We have combined ideas from many sources, mainly the 2.x , Lasersaur, and Blacktooth system but including some variations of all of those by other enthusiasts. Our machine stands at roughly $2100.00 at present costing and now only needs a cooling solution before all the bits and bobs get ordered. 

As for the cooling, I think we'll just have to find the best way of getting a proper cooling system, home made or not. Even though our workshop is kept at 18 degrees C, we would rather not suffer the pains of broken tubes unnecessarily early. 

**To ask an unrelated question Steve, about you mentioning the Chinese machine, do they actually work? I have only, and I mean ONLY seen videos and blogs where they are referred to as large paper weights, unless completely retrofitted with new components. I speak of the $800-$900 systems, as anything above $2500 is out of our price range. Open source/D.I.Y seems to be our only option because of the very awkward price jump from the $800 machines to massively expensive machines, only made even more unaffordable by the shipping costs. 

Thanks once again for all the info and support everyone, I will liaise with our design/funding group and try convince them of using a 60w+ laser system. I'm sorry for the half-assed answers and information, but I will provide more details as the build actually starts to take place and all the parts are sourced from the various corners of the globe...

[Steve Baker]

The problem with the Zalman contraption is that the specifications only
tell you what the flow rate is.

That tells you that *IF* the coolant input temperature is at least about 5
degrees cooler than the Laser tube's maximum safe temperature then you're
OK.

HOWEVER, a $20 aquarium pump can do that.

The real problem is how the warm waste water coming out of the laser gets
cooled back down again before it's recirculated. It clearly claims to do
that - but nowhere in any of the specifications does it say how many watts
of heat energy it can dissipate.

If it's not enough then that reservoir of coolant will get gradually
warmer and warmer until the laser is being fed warm water instead of cold
- and it's not getting cooled anymore.

So unless you know for 100% sure that this unit will dissipate 360 watts
of heat - it's no good.

Worse still (as I explained before), the amount of heat a simple passive
radiator can remove is dependent on the relative temperature of the
coolant and the air. Imagine a cup of boiling water sitting on your desk.
It'll drop from 100C to 90C very quickly - but it takes a very long time
to drop from 35C to 25C because the rate of cooling depends on that
temperature difference.

Since CPU's run at 65 C or more - the waste water is relatively hot - so
it's easy to cool it down dramatically by blowing 25 C air across it. But
the laser is chucking out 30 C water - and blowing 25 C air across it
doesn't do much good.

People will tell you "Yes, my laser works just fine with such-and-such
cooling system" - but they really don't know that until they've put enough
hours onto their system.

According to RECI (who make the tubes), the userful life of the tube is
dramatically shortened by running it hot. So if you have (say) a 3,000
hour tube and you run it too hot, you won't know until it starts to lose
power after (say) 1,000 hours. Also, it only loses power fairly gradually
- so it's not like people recognize a sudden failure.

So I'd want to be sure that the outlet temperature of the laser stays
around 30 C.

From what I've been reading, it seems unlikely that a CPU chiller will do
the job - although a large enough bucket of water and an aquarium pump
might work pretty well.

But everything depends on the temperature of your workshop with the laser
running and how that liquid reservoir is cooled.


-- Steve

jjk.krizzi wrote:
> Hi all,
>
> I've received some help on this topic already but would like to receive
> some more help.
>
> The answers given, although thorough, are of little use due to my lack of
> providing any information.
>
> We are a group of Architecture students from South Africa, and are busy
> planning a Lasersaur build. We envision our machine to be able to speed up
> our model building process. Thus a 40w laser system will be more than
> adequate. Our biggest dilemma, is the costs involved (obviously) but would
> like to figure out if a prebuilt or custom build computer cooling system
> would be able to cool the 40w laser tube, doing MAX 10 hours a day ( I
> highly doubt it will ever do more than 2 hours a day).
>
> The kit system we considered is as
> follows: http://www.zalman.com/global/product/Product_Read.php?Idx=185
>

> Maximum Coolant Capacity: Max. 1.25â„“- Integrated Water Pump: 6W, DC 12V,

> 300L/Hr
>
> Alternatively does someone have a BOM (And maybe pictures) for a homebuilt
> system that would be more cost efficient?
>
> Thanks in advance for any help!
>

[Steve Baker]

jjk.krizzi wrote:

> **To ask an unrelated question Steve, about you mentioning the Chinese
> machine, do they actually work? I have only, and I mean ONLY seen videos
> and blogs where they are referred to as large paper weights, unless
> completely retrofitted with new components. I speak of the $800-$900
> systems, as anything above $2500 is out of our price range. Open
> source/D.I.Y seems to be our only option because of the very awkward price
> jump from the $800 machines to massively expensive machines, only made
> even more unaffordable by the shipping costs.

The chinese systems are tricky. Some people get them, plug them in and
have nothing but good things to say about them. Other people say they
arrive with not one single nut and bolt tightened up, with cables not
plugged in or tied down, etc, etc.

If you are good with a wrench and have a tolerance for doing work on your
system (which you do if you're building one from scratch) - then perhaps a
cheap chinese machine is the right anwer for you.

But if you're a commercial user who expects to plug the machine in and be
running for hundreds of hours and to get quality customer support when
needed...forget it!

The people I know who bought these things replaced the controller boards
first so that they could use better control software. That seems like a
good idea.

Personally, I bought into the lasersaur because I wanted a LARGE bed and a
100W laser - even from a Chinese supplier, that would have been a $20,000
to $30,000 machine. If I had wanted a smaller bed and smaller laser, then
I'd have bought a Chinese laser cutter instead.

-- Steve


>
> *Thanks once again for all the info and support everyone*, I will liaise

>> <jjk.k...@gmail.com<javascript:>>

>> wrote:
>> >
>> >> Would it be able to Cut 1mm grey card cardboard/ 3mm corrugated brown
>> >> cardboard?
>> >> Kind regards
>> >>
>> >> Jacob Kritzinger
>> >> ------------------------------
>> >> *From: * "Peter van der Walt (Gmail)"

>> <peter.p...@gmail.com<javascript:>>
>>
>> >> *Sender: * lase...@googlegroups.com <javascript:>

>> >> *Date: *Sat, 7 Dec 2013 06:35:56 -0800

>> >> *To: *<lase...@googlegroups.com <javascript:>>
>> >> *ReplyTo: * lase...@googlegroups.com <javascript:>

>> >> *Subject: *Re: [lasersaur] Computer water cooling system for a 40w
>> laser
>> >> tube?
>> >>
>> >> I have a 40w... Good for engraving and paper cutting. Just a heads up
>> >> On Dec 7, 2013 4:33 PM, "jjk.krizzi" <jjk.k...@gmail.com

>> <javascript:>>

>> >>> Maximum Coolant Capacity: Max. 1.25ℓ- Integrated Water Pump:

>> 6W, DC
>> >>> 12V,
>> >>> 300L/Hr
>> >>>
>> >>> Alternatively does someone have a BOM (And maybe pictures) for a
>> >>> homebuilt system that would be more cost efficient?
>> >>>
>> >>> Thanks in advance for any help!
>> >>>
>> >>> --
>> >>> You received this message because you are subscribed to the Google
>> >>> Groups
>> >>> "lasersaur" group.
>> >>> To unsubscribe from this group and stop receiving emails from it,
>> send
>> >>> an

>> >>> email to lasersaur+...@googlegroups.com <javascript:>.

>> >>> For more options, visit https://groups.google.com/groups/opt_out.
>> >>>
>> >> --
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>> > You received this message because you are subscribed to the Google
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>>
>>
>> -- Steve
>>
>>

-- Steve