ok I have a little circuit that drops 24volts down to 5volts to power my 'duino
it all works a treat even though the regulator gets a bit warm
here is the regulator (A) from rs
I have some neat little heatsinks (B) also from rs
how do I join flange A to sprocket B?
I did buy some heat sinks for my Big Easy Driver from Proto-Pic (SparkFun parts) that came with little double sided sticky pads
I guess they're what I'm looking for - or are they just double sided sticky tape?
Take it back and get one that's drilled and tapped.
Or maybe you have a friend or neighbour with a drill and tap set.
Or find some aluminised two-part epoxy.
24V to 5V is a big drop - and 1/4A output will yield around 5W on the regulator.
You can drill a hole in the heatsink and use a small machine screw and nut.
You can drill and tap a hole in the heatsink and use a small machine screw.
You can use "thermal adhesive" (a thermal conductive glue).
I use machine screws and thermal grease. Just use a little bit of grease and be sure that the heatsink and regulator surfaces are parallel.
runaway_pancake:
Take it back and get one that's drilled and tapped.
Or maybe you have a friend or neighbour with a drill and tap set.
Or find some aluminised two-part epoxy.
24V to 5V is a big drop - and 1/4A output will yield around 5W on the regulator.
hee hee - I'm happy to keep them, just wanted a way to attach them
they're a bit small to drill/tap as there is no space between the fins
I have no choice about input and output voltages
it gets warm, but has been running all day quite happily
johnwasser:
You can drill a hole in the heatsink and use a small machine screw and nut.You can drill and tap a hole in the heatsink and use a small machine screw.
You can use "thermal adhesive" (a thermal conductive glue).
http://uk.rs-online.com/web/c/semiconductors/sockets-heatsinks/thermally-conductive-insulators/?sort-by=P_breakPrice1&sort-order=asc&view-type=List&sort-option=Price
thanks for the link, but it would be cheaper to bin the heatsinks and go with the SparkFun version
pgmartin:
I use machine screws and thermal grease. Just use a little bit of grease and be sure that the heatsink and regulator surfaces are parallel.
nice idea but no room for a screw/bolt
what would happen if I tried
a) spot of Araldite?
b) ordinary double sided tape?
cheap - moi?
thanks peeps
I just saw the type of heatsink you are planning to use.
My solution are :
The regulator in question... I notice it is a 78M05 type. The datasheet say the max current is 500 mA. Not 1 A. The 7805 is.
Just to let you know about that small detail...
it's only powering a duino and an LCD
I just measured it's only drawing 60 mA on the input side
so at 24 volts that should be less than 1.5 watts
since it has thermal protection built in it ought to shut itself down if it starts cooking
it is warm to the touch, but not raising any blisters
it's been on all day just to see if it will let any magic smoke out
no evidence so far
is it worth putting a dropping resistor in series with the input, just to take some of the load?
say 240 ohm which would drop 14 odd volts, so leaving 10 for the regulator to play with
it would need to be 1 watt I guess
mmcp42:
it's only powering a duino and an LCDI just measured it's only drawing 60 mA on the input side
so at 24 volts that should be less than 1.5 watts
since it has thermal protection built in it ought to shut itself down if it starts cookingit is warm to the touch, but not raising any blisters
it's been on all day just to see if it will let any magic smoke out
no evidence so faris it worth putting a dropping resistor in series with the input, just to take some of the load?
say 240 ohm which would drop 14 odd volts, so leaving 10 for the regulator to play with
it would need to be 1 watt I guess
The thing is, you got the wrong heatsink for the part. To use the part you have, as others have recommended, is going to require a bit of machining to remove a fin or two, then drill out the hole (you don't need to tap anything, unless you want/need to use the heatsink as the nut to secure the screw; a small lockwasher and nut will work fine).
What you want for this part is a TO-220 heatsink (of which, RS has several, including ones that clip-on):
http://uk.rs-online.com/web/c/?searchTerm=to-220+heatsink&sra=oss
Also as already noted, you want to use a bit of heatsink grease between the heatsink and the tab on the regulator; not too much (more is not better here!), just a light coating.
is it worth putting a dropping resistor in series with the input, just to take some of the load?
say 240 ohm which would drop 14 odd volts, so leaving 10 for the regulator to play with
it would need to be 1 watt I guess
That might work. I just test it in the simulator - Circuit Wizard ... It work and the wattage across the resistor is 600 mW and I use 220 ohms instead. You don't want to limit the current going inside the regulator.
About the heatsink problem. A small hole between the fins might work and with the right size of screw and nuts, washers.
@cr0sh
yup fair cop - it's not the right part
but I had some in my box-o-bits so thought I'd give it a whirl
I've used heatsink grease before on cpu heatsinks, so quite happy with that side of things
@Techone
yup I would ensure the regulator has enogh volts to let it do it's work without frying!
I may take the heatsink out to the workshop for a one-to-one with my drill
see if I can make it see things my way!
cheers peeps
PS
I tried dropping the input to 12 volts
regulator obviously much cooler
but more importantly, the rest of the circuit (outside the 'duino) still works fine
it's an odd stepper motor with built in controller
paperwork demands 24 volts
but it seems to run just fine at 12 volts
difficult to see why that wouldn't be a better fix all round 
If the regulator is only warm to the touch, don't worry about it. If it's too hot to touch for more than a second or two, use a heatsink. As you say, it has thermal limiting built in. I don't recommend araldite or sticky tape for attaching a heatsink, they don't conduct heat very well. You should use a machine screw or a spring clip.
thanks for the update
now I've dropped to a lower voltage it's just pleasantly warm!