Advice Needed - Relay and PSU

[Timmymna]

Hi All

I'm finally going to purchase a decent power supply, I was looking at this CALTEK|PSM3/2A|PSU, LABORATORY | Farnell UK
Does this look like a good supply and at a good price?
I would be happy with the fixed 5V and two variable supplies.

Also I am after some relays so I can switch some things on with a PIC, T5 bulbs, pump and maybe a couple of other things. 240V AC.
I've never used relays but would this do? MULTICOMP|HRS4-S DC5V|RELAY, PCB, SPCO, 5VDC | Farnell UK
They seem rather cheap, not cheapness is a bad thing but is there something I'm not looking for or missing?

Thanks for any help
Tom

 

[Pommie]

The supply looks good but it's a while since I bought one so I'm a little out of touch.

The relay is fine for switching up to 5A (~1kW) but you can't drive it straight from a pic as it requires 100mA. You can drive it via a transistor.

Mike.

 

[richard.c]

Hi,

That sure is one nice PSU - will cost you about £125 inc vat and delivered - so not cheap.

Just wondered why you needed such a beastie like that, or are you doing much more than the typical pic projects ..?

If you are OK with mains circiutry then building you own, good quality, but simpler psu would suffice - but if you don't like mains - then yes go with the Farnells unit - ( Maplin don't seem have anything as good )

As for the relays - you get what you pays for - their datasheets shows they will only handle a couple of amps at 250vac - but for the small stuff you have they sound ok - you will need to interface the pic and relay with a transistor or relay driver chips like the ULN2803


hth

 

[Timmymna]

- Just wondered why you needed such a beastie like that, or are you doing much more than the typical pic projects ..?

TBH I've been using a small 5v power brick for most stuff and has worked well so far.
Lately I have been using different things that require different voltages and I have run into problems trying to supply the different circuits.
I just thought it was about time I bought something proper, I'll get plenty of use out of it and hopefully have it a long time, at that price , as I'm still at Uni and, at the moment, still planning to go into engineering, it should be useful.

Though saying that, if there are some good, proven, designs for power supplies then I could be tempted down that route. I've looked into it before but never really found anything that looked that good.

Any suggestions?

Cheers,
Tom

 

[ericgibbs]

hi Tom,
Its a nice psu, but IMHO an overkill in price for most hobbyists.

The other point is the lowish 2A output, especially if you start PWM motor drive projects etc.

I would buy low cost power supplies, also one that will give about 6A at 15V.

You can always add regulators for lower voltage work.

For Example:

Bench Type | CPC

 

[richard.c]

Hi,

It really depends on what you want to do and what you want to spend.

I would be tempeted to buy a dual secondary 0 -12v or 0- 15v transformer at around 100VA and add on a collection of 5v, 12v pos and neg regulators, and Lm317 variable regulators in a large case, so that you can add extra transformers / regulators for any future heavy current devices like Eric mentioned.
You can add on your own meters and overloads etc as funds permit.

All the regulators come with typical circuits provided in the manufactures data sheet - they are easy enough to make; if thats your interest..

For a really cheap method - I used to make up my own psus with the old fashioned transformers with muti-tapped secondaries - you might be able to find some of these old stock or second hand in some of the surplus electronics shops

Richard