Controller Board Getting Very Hot / Allegro A3977

[Lee Roberts]

Hi, I’ve been in contact with Roy over at diycnc.co.uk about these drivers and this is what I got back:

Thanks,
Roy
P.S The Heat sink stuck to the top of the chip is not effective. The heat should conduct down the legs into the copper on the PCB. That’s why I use 2oz copper on my boards. Allegro do not mention using a heat sink stuck to the top in their data sheets.

Where he makes reference to the heat sink, that’s with regards to the drivers that routoutcnc make, they use heat sinks on their units. I personally think and in my experience of 12 years building computers have never seen a PC that doesn’t have a heat sink on the CPU. Granted there is a difference between the 2, I ask the question of: “do we want heat going back into the PCB?”, and I answer with NO WE Definitely DONT!

Why would you ever push heat back into the PCB when there is an option to pull heat away from the unit via heat sinks, how is it logical to go about things in that way. Your post actually falls in nicely with emails going back and forth from Me, Mike (routoutcnc) and Roy over at (diy cnc) as I’ve asked them both a few questions about each of their units.

I personally think that a heat sink would only but help, why Roy chose’s to not use one I don’t know, the fact that mike dose use them on his units can only be a positive thing. I am currently looking at building my own drivers using the Allegro A3977 chip, so I will be asking the “Heat sink” question to someone I know who has also worked with the chip allot, and I know for a FACT that his site suggests the use of a Heat sink by a member of his site and user of his drivers, I think the best option for you is to get hold of some old heat sink way back from yester-year and mount it to your drivers and see if that helps.

I’m going to ask Mike & Roy to read this thread and give us their inputs as I think they will have better understanding as to why they have both done things differently.

I will also ask the person who has worked with the Allegro A3977 to join us as well.