Mounting base for rotating rectifiers - Aluminum or Copper?
Mounting base for rotating rectifiers - Aluminum or Copper?
(OP)
I have seen many rotating rectifiers (3 phase, bridge type) for generators mounted on aluminum plates, which also act as heat sinks.
Given that copper has a better thermal conductivity, wouldn't it make more sense to use it than aluminum?
Muthu
www.edison.co.in
Given that copper has a better thermal conductivity, wouldn't it make more sense to use it than aluminum?
Muthu
www.edison.co.in





RE: Mounting base for rotating rectifiers - Aluminum or Copper?
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
I have seen american machines with copper base plates while the europeans use aluminum.
Muthu
www.edison.co.in
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
Muthu
www.edison.co.in
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
Long term cooling capacity of a heatsink is mostly determined by airflow and surface area. So, if you have the same surface area on the heatsink then the use of Cu vs Al really makes little difference.
The higher heat capacity of Cu means a smaller piece of copper heatsink can be used in a power electronics application subject to short term overloads or periods of high power output followed by cooling off time. The higher thermal conductivity of Cu is why you might see a heatsink with a Cu center and Al fins. The Cu center helps conduct the heat to the fins a little quicker. Size vs cost vs weight has to evaluated to determine if it's worthwhile in these cases.
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
If you can source suitable copper washers, that avoids machining costs and keeps the mass of copper purchased low.
This may give the best of both worlds.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
This being a rotating unit, no fins can be fixed and surface cooling should be good enough with diodes themselves acting somewhat as a fan pushing the air around.
Muthu
www.edison.co.in
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
As a very simple illustrative example, imagine geometrically identical copper and aluminum bars insulated along their length. On one end, each bar has a constant power source (our power electronic device). On the other end, the bar is in contact with a large reservoir of ice water at 0C.
With the thermal conductivity of copper being twice that of aluminum, the power source device on the aluminum bar will be at a steady state temperature twice as high over 0C as the device on the copper bar providing the same amount of power.
The comparsion is not much different when dissipating to ambient air at, say, 25C.
Curt Wilson
Omron Delta Tau
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
With 4 mm thick copper, the final diode temps were from 58 to 68 deg c and the copper temps (in 4 places) were from 57 to 67 deg C. Cu = 570 gm
With 5 mm thick aluminum, the final diode temps were from 59 to 77 deg c and the aluminum temps (in 4 places) were from 60 to 73 deg C. Al = 198 gm
With 3 mm thick aluminum, the final diode temps were from 59 to 70 deg c and the aluminum temps (in 4 places) were from 57 to 65 deg C. Al = 132 gm
All the diode temps were measured at the point where they were bolted to the base plates. The ambient was around 32 deg C.
Basically, not a great difference between the three. I am going with 3 mm thick Al mainly because of lower weight.
Thank you all for your tips.
Muthu
www.edison.co.in
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
Muthu
www.edison.co.in
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
Thanks for posting the results of your experiment.
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
Copper 3 mm - Plate 1 & 2 - 0.070 & 0.071 mΩ
Aluminum 5 mm - Plate 1 & 2 - 0.071 & 0.071 mΩ
Aluminum 3 mm - Plate 1 & 2 - 0.10 & 0.10 mΩ
With such low values, the I^2R is minuscule in mW.
Muthu
www.edison.co.in
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
I'm curious why you can't fit any fins? Space? I've seen quite a few rotating rectifiers with fins over the years.
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
A pic of the test set up.
Except for the material thickness, all the test parameters are almost identical.
Bill
Yes, the diodes themselves will act like a fan.
Muthu
www.edison.co.in
RE: Mounting base for rotating rectifiers - Aluminum or Copper?
Keith Cress
kcress - http://www.flaminsystems.com
RE: Mounting base for rotating rectifiers - Aluminum or Copper?