Francois Robbertze wrote:

>
> If I use a 250Volt 20Ampere relay together with a IT615(600V 15A) triac
> (with a small heatsink). Will this be OK?


I think it will work very well. For switching once every
5 minutes you may need only a tiny heatsink for the triac.



> According to Peter L Peres this relay will also be hot after 30 minutes...Is
> it a better option to look at bidirectional power MOSFET modules then?

I think the relay will stay quite cool. Coil power
for that size relay will probably be about 0.5w to 1w,
very little heat compared to your 30w from just the triac.
The contacts will heat a couple of degrees over ambient,
but this won't matter as the contacts are rated for
20A and you are drawing 12A max, they are fine for
continuous use. Since you are using the triac to
do the initial switch on, you can parallel the relay
contacts safely. (which is normally bad!) I would
choose a 20A dual contact relay, so really it
is a 40A relay. Very rugged!


> I must also say that the ambient temperature is sometimes relatively hot
> (30 - 50 deg C) and can affect the efficiency of the heatsink.
>
> Space is not the main consern but the thing must be very reliable and it
> must last for years...I also don't want the project to consist of 99%
> heatsink if I can prevent it and the cost must be preferrably as low as
> possible.

Definitely go for the most rugged relay you can get
in your price range. The relay contacts are your
weak link. It should be very reliable if you allow
good surge and spike protection.

-Roman

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.