Topics

Heatsink issue #ubitx #homebrew


edoardo marchetti
 

Hi everybody!
I am near to finish the enclosure of my v5 ubitx and I projected to add 2 new heatsink. The problem is that one of the mosfets is exactly on the pcb center and this forbid me in drilling a hole for the transistor mounting. 
The question is, can I desolde the two mosfets and connect a little piece of cable in order to put theme in a better position without create electrical problem? I would like to stack both at the center of the two heatsink.
Thanks for reading
IU6DBK


Jonas Sanamon
 

Hi Edoardo,

No, I don't think You can do that without creating instability or other issues for the PA stage. 
I would do either
1) Use just one of the 2 heatsinks (which ought to be enough anyway unless You are feeding the PA with 30v and using it for WSPR or FT8). Use a FAN running very low speed (= no noise) if necessary.
2) Get a bigger heatsink.

Either way: You *MUST* isolate the IRF510s from the heat sink electrically, otherwise the smoke will come out...
(Hint: use special TO-220 isolation pads)

Regards
Jonas - SM4VEY

Hälsningar, Jonas


Den ons 14 okt. 2020 kl 15:54 skrev edoardo marchetti <mentorade@...>:

Hi everybody!
I am near to finish the enclosure of my v5 ubitx and I projected to add 2 new heatsink. The problem is that one of the mosfets is exactly on the pcb center and this forbid me in drilling a hole for the transistor mounting. 
The question is, can I desolde the two mosfets and connect a little piece of cable in order to put theme in a better position without create electrical problem? I would like to stack both at the center of the two heatsink.
Thanks for reading
IU6DBK


edoardo marchetti
 

Thanks for replying so quickly, I m wondering if the only 15 x 10 cm x 1 mm thick aluminium sheet could dissipate enough power. If my option was too much heavy for the 10 watt output maybe the direct connection of both transistors to the aluminium enclosure could be a sufficient solution.
What do you think about it?
Thanks
IU6DBK

On Wed, 14 Oct 2020, 16:16 Jonas Sanamon, <sanamon@...> wrote:
Hi Edoardo,

No, I don't think You can do that without creating instability or other issues for the PA stage. 
I would do either
1) Use just one of the 2 heatsinks (which ought to be enough anyway unless You are feeding the PA with 30v and using it for WSPR or FT8). Use a FAN running very low speed (= no noise) if necessary.
2) Get a bigger heatsink.

Either way: You *MUST* isolate the IRF510s from the heat sink electrically, otherwise the smoke will come out...
(Hint: use special TO-220 isolation pads)

Regards
Jonas - SM4VEY

Hälsningar, Jonas


Den ons 14 okt. 2020 kl 15:54 skrev edoardo marchetti <mentorade@...>:
Hi everybody!
I am near to finish the enclosure of my v5 ubitx and I projected to add 2 new heatsink. The problem is that one of the mosfets is exactly on the pcb center and this forbid me in drilling a hole for the transistor mounting. 
The question is, can I desolde the two mosfets and connect a little piece of cable in order to put theme in a better position without create electrical problem? I would like to stack both at the center of the two heatsink.
Thanks for reading
IU6DBK


Evan Hand
 

Edoardo,
I have not done that myself, however, I have seen others do just that: attach the IRF510s to the back of an aluminum enclosure.  You still need the insulators as the tabs on the IRF510s are at the drain (12volt) potential.  I have also seen where the fins are added on the other side of the aluminum mounted with the screws for the transistors.  You can always add a fan if it gets too hot for the IRF510s.

73
Evan
AC9TU


Jonas Sanamon
 

Hi Eduardo,

Unless You have feeding the PA with more than 13.8v, I am sure that using that aluminum plate will be enough. Remember that the heat sinks supplied by HF Signals are probaby used by a lot of uBitx owners around the world, so as long as you have a larger surface area than the original heat sinks you should be fine.  If you are using an aluminum enclosure, mount them to that and you should be fine. That also makes it easy to monitor the temperature of the heat sink, just use your hand :-)

But like I said before, you *need* to use insulating tab + plastic "washer" to isolate the IRF510s from the metal:
image.png
image.png
Regards
Jonas - SM4VEY


Den ons 14 okt. 2020 kl 21:48 skrev edoardo marchetti <mentorade@...>:

Thanks for replying so quickly, I m wondering if the only 15 x 10 cm x 1 mm thick aluminium sheet could dissipate enough power. If my option was too much heavy for the 10 watt output maybe the direct connection of both transistors to the aluminium enclosure could be a sufficient solution.
What do you think about it?
Thanks
IU6DBK

On Wed, 14 Oct 2020, 16:16 Jonas Sanamon, <sanamon@...> wrote:
Hi Edoardo,

No, I don't think You can do that without creating instability or other issues for the PA stage. 
I would do either
1) Use just one of the 2 heatsinks (which ought to be enough anyway unless You are feeding the PA with 30v and using it for WSPR or FT8). Use a FAN running very low speed (= no noise) if necessary.
2) Get a bigger heatsink.

Either way: You *MUST* isolate the IRF510s from the heat sink electrically, otherwise the smoke will come out...
(Hint: use special TO-220 isolation pads)

Regards
Jonas - SM4VEY

Hälsningar, Jonas


Den ons 14 okt. 2020 kl 15:54 skrev edoardo marchetti <mentorade@...>:
Hi everybody!
I am near to finish the enclosure of my v5 ubitx and I projected to add 2 new heatsink. The problem is that one of the mosfets is exactly on the pcb center and this forbid me in drilling a hole for the transistor mounting. 
The question is, can I desolde the two mosfets and connect a little piece of cable in order to put theme in a better position without create electrical problem? I would like to stack both at the center of the two heatsink.
Thanks for reading
IU6DBK


Don - KM4UDX
 

Hello edoardo! 

You are giving us all heat sink envy!  Hahah.  But, as others have observed, the kit heat sink's are fine except in some unusual operations:
- more than 13v to the finals
- full power FT8 or WS
- zero free air movement. 

In 95% of cases, just drill some holes for air movement, and/or install a small & slow fan. 

I do 20v on the finals and WSPR 24/7 when I don't do psk/Hellschreiber.  And I use a fan on a thermal switch.


edoardo marchetti
 

Thank you for your reply, I finally chose two smaller cpu cooler instead of the first. I'm happy to know that the original ones were enough but, until I saw how hot was the 7805 connected to the raduino board, I have started to doubt about the ubitx cooling in general. In fact I added a small heatsink for it too.
73
IU6DBK

On Thu, 15 Oct 2020, 19:12 Don - KM4UDX, <dontAy155@...> wrote:
Hello edoardo! 

You are giving us all heat sink envy!  Hahah.  But, as others have observed, the kit heat sink's are fine except in some unusual operations:
- more than 13v to the finals
- full power FT8 or WS
- zero free air movement. 

In 95% of cases, just drill some holes for air movement, and/or install a small & slow fan. 

I do 20v on the finals and WSPR 24/7 when I don't do psk/Hellschreiber.  And I use a fan on a thermal switch.