Hello,

I'm planning to build a basic variable power supply from the following plans: http://my.integritynet.com.au/purdic/power4.htm

Although the site mentions using metal as an enclosure, I was hoping that I could build one out of wood instead. Can anyone think of any potential issues this would cause? All I can think of is that

a) wood might thermally insulate the supply to the point of overheating (though I can always add a fan or some air vents)

b) metal may be required to shield the circuitry from electromagnetic fields. Would this affect a basic power supply?

Any comments or suggestions would be greatly appreciated! Thanks!

 

Hello,

I'm planning to build a basic variable power supply from the following plans: http://my.integritynet.com.au/purdic/power4.htm

Although the site mentions using metal as an enclosure, I was hoping that I could build one out of wood instead. Can anyone think of any potential issues this would cause? All I can think of is that

a) wood might thermally insulate the supply to the point of overheating (though I can always add a fan or some air vents)

b) metal may be required to shield the circuitry from electromagnetic fields. Would this affect a basic power supply?

Any comments or suggestions would be greatly appreciated! Thanks!

If you are planning on pulling 2 A from the LM317T, it will need a heat sink and the heat sink will need access to air to carry the heat away.

Metal shielding is not required for this circuit.

A wooden box (assuming the wood is dry) is as good as plastic and should pose no real problems.

 

Thanks!

Yes, I am planning on using a heat sink for the LM317T (I assume that thermal grease should be applied — correct?). Would you recommend adding a small fan, or would a few vents provide enough airflow?

 

As to air flow, depends. In general you can never have to much cooling, with the down side it is becomes a dust bunny incubator. If the heatsink is smooth (and the part) thermal grease is not a major requirement.

If I was any good with woodwork I would use more wooden enclosures.

 

Wood would be fine, just keep the heat sink away from the wood. Perhaps some small drill holes above the heat sinked part and some on the sod of the enclosure would do O.K.

 

Some sort of internal metalwork to hold the major components together might not be a bad idea. It could improve the mechanical strength, as well as helping with heat sinking and shielding.

It might even be convenient to build the supply entirely on a metal chassis, so that the wooden box would simply be an enclosure. Building the supply, as well as setting it up and testing it may be easier this way. You would also avoid having to make too many unsightly drillings in the box.

This type of construction would of course involve extra metal working, and the finished result would be heavier.

 

you haven't indicated what your AC supply will be. If it includes mains and a transformer, I would recommend a metal chassis to at least mount the fusing, transformer, and mains strainrelief. The chassis then acts as your bond and an AC shorting bar to drain off any wayward AC, and to contain the mains power away from the rest of your circuit.

 

you haven't indicated what your AC supply will be. If it includes mains and a transformer, I would recommend a metal chassis to at least mount the fusing, transformer, and mains strainrelief.

To avoid messing with the mains (as I'm not very experienced), I've purchased a separate AC adapter to step down the voltage to 16 VAC:

http://www.mouser.com/Search/ProductDetail.aspx?R=XF-1620virtualkey50700000virtualkey507-XT1620

Thanks for the suggestions! I'll let you know how it turns out.

 

To avoid messing with the mains (as I'm not very experienced), I've purchased a separate AC adapter to step down the voltage to 16 VAC:

http://www.mouser.com/Search/ProductDetail.aspx?R=XF-1620virtualkey50700000virtualkey507-XT1620

Thanks for the suggestions! I'll let you know how it turns out.

Although it's probably a good idea to buy a stepdown transformer, you should be aware that the one you have chosen has a rated output of 1.21 amps. So, on the schematic shown in your first post, the 3 A fuse between the transformer and the rectifier circuit is too large. 1 A would be a better choice, which means that the maximum current out of the PS would be considerably less than the 2 A shown on the schematic.

 

Although it's probably a good idea to buy a stepdown transformer, you should be aware that the one you have chosen has a rated output of 1.21 amps. So, on the schematic shown in your first post, the 3 A fuse between the transformer and the rectifier circuit is too large. 1 A would be a better choice, which means that the maximum current out of the PS would be considerably less than the 2 A shown on the schematic.

Although your suggestion makes total sense to me, the plans I'm using do actually utilize a 1.25 amp transformer... I think the "0-2 A" you're referring to is the range of the ammeter, not the max output current.

However, now that you've pointed it out, I don't see why a 3-amp fuse would be used. Perhaps the circuit initially draws more than 1.25 amps when it first powers up? In which case the fuse was added only to prevent a full short-circuit?

Any ideas?