Re: Cooling Rutex drives

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Chris Baugher
<cbaugher_yahoo@b...> wrote:

>
> Hi,
> Anyone here that is using Rutex servo drives, can you give a rough

idea of

> how much cooling is needed? The instructions say to use a "large"
> heatsink. How large is large? Would a fan directed over the drive

be

> enough?
>
> C|

The amount of cooling depends a lot on several factors. The voltage
of your DC power supply, the total average current of all your motors
and the physical environment you are running in. Which Rutex drives
do you have and tell us the voltage and currents involved and a more
accurate answer can be formulated. The greatest destroyer of solid
state devices is excess heat. Removing heat as all about thermal
conduction (how well a hot object passes its heat to a cooler
object), thermal mass & area, ambient conditions and air flow.
Heatsinks are just large surface area devices folded up to take less
space.

The heatsink has to be able to pass heat from itself to the
surrounding air. Without some airflow the air stratifies around the
object and transfer ratios go way down. Forced air cooling will do a
lot in keeping temps down but you have to have enough surface area in
contact with the air to make moving air work.

My unscientific method of telling if I need more heatsink is to run
the unit under worse case conditions for 15 minutes. If I can hold
my hand on the actual heat producing object without being
uncomfortable then I am satisfied. Although mfg's normally rate
their components to run at 100 deg C that is the internal die temp
and that is not the final external temp.

All that being said, it would be a good idea to plan a custom bracket
for you drives that includeds a heatsink as least as large as the
Rutex open case surfaces with at least .75 inch tall fins. Forced
air cooling is probably in order. If you do not use a fan directly
on the heatsinks make sure the fins are mounted vertically to let
natural convection remove the trapped air between the fins.

A little attention to heat removal and RFI suppression on the inital
design will save you having to redo it in the future.

I have several Rutex units most of which are still in the bubble wrap
waiting to go on my full size mill conversion. I am running one 990
servo drive on a plasma table but the rest of the drives are Gecko's.
I have minimal heatsinking because my servo's only draw 2 Amps each.