Spindle cooling requirement, basics of calculation.

# Thread: Spindle cooling requirement, basics of calculation.

1. ## Spindle cooling requirement, basics of calculation.

Hello,

After reading couple threads about cheap Chinese water cooled spindles I came to conclusion, most people here have no idea how much cooling does your spindle need, so in here we will calculate:
How much water flow do you need?
How large radiator/much air flow you need?

Here we will use school level thermodynamics, so everybody should understand what we discuss.

Here we go, we will analyze how much water flow does a 2.2KW spindle need.

Assumption1 spindle is 80% efficient, so 20% directly goes to heat. Or 0.44KW is needs to be absorbed by water. In reality your spindle is not ruining 100% load all the time, so these are worst case numbers.

Wasted_power = 440W

Water_specific_heat = 4200J*kg/C How much heat does 1kg water need to absorb to rise temperature by 1C.

Water_temperature_rise = 20C We assume that water after spindle heats by 20 degrees. 20C is very conservative, in reality it can be up to 60C

Water_flow = Wasted_power / (Water_temperature_rise * Water_specific_heat * Water_density) =440W / (20C * 4200J*kg/C * 1kg/l )= 0.005l/s or 19l/h so any water flow is enough for this spindle

That is under 20 liters per hours for 2.2kW spindle under FULL LOAD

For a diy machine we will use a cheap 120mm PC water cooling radiator.

Water_temperature_rise = 20C

Air_flow = 100m3/h = 0.028m3/s In reality 120mm fan has air flow similar to 130M3/h, but lets assume that radiator provides some air resistance.

Air_specific_heat = 1000J*kg/C

Air_density = 1.3kg/m3

Air_temperature_rise = 0.5 * Water_temperature_rise = 10C

Power_dissipation = Air_flow * Air_specific_heat * Air_density * Air_temperature_rise = 0.028m3/s * 1000J*kg/C * 1.3kg/m3 * 10C = 360W

A 120mm pc radiator with fan will dissipate 360W of power if you are ok with spindle temperature 20C above room. Or a 120mm pc radiator with fan will cool a 2.2kW spindle, under FULL LOAD, with temperature rise of 25C above room temperature.

In reality 40-60C above room temperature is safe for most spindles.

PS: hope this sticks.

2. ## Re: Spindle cooling requirement, basics of calculation.

Know this is old, but if u r still out there, thanks for this.
(A) The cheap pumps that come with the spindles say 3500 LPH (925 GPH) LOL. Yeah right.
(B) I knew they would in reality require a lot less seeing as some of us never even hook the cooling up. I was about to figure it out, thanks for doing it already.
Given all this, I found a good deal on JUST the spindle and inverter not all the extra junk. Going to get a small pump from HD or Amazon.
Thanks again.....

3. ## Re: Spindle cooling requirement, basics of calculation.

Interesting post.

I did the same as you and did purchase just a 2.2kW water cooled spindle for my "David's New Desk Top Router" build thread.

I used two 80mm radiators in series driven by a small 4.2W (about 400 milliAmp) pump. Plenty of circulation with that tiny pump. The biggest input/output temperature delta I measured was about 18-20 degrees F (about 10 degrees C).

4. ## Re: Spindle cooling requirement, basics of calculation.

I clamped a few turns of 1/8" bore copper tube tightly around the uncooled spindle and used an inexpensive pump from ebay and a large tub of water from the local HW store. No radiator at all. Works fine. Pump was sold as spindle pump for CNC too!

Bit of gal steel and some hose clamps to hold the copper tube tightly in place.
Silicone rubber hose for the water.

Cheers
Roger

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