relay or???

hjl4

Member

• Sep 10, 2007

• #1

Which is more suitable? In my circuit, I have a PIC 12F675 acting as a 2.5hr timer(running thru delay), and when the (delay)/timer has run out, the pin GPIO2 goes low. But during the time that the pin is high(2.5hr), I have 24 vdc going to a set of batteries, thru a relay, or a transistor. No more then 2 amps.
Which would be more efficient? The relay or the transistor? You must of figured out already, that the PIC is running the relay or transistor.
I hope this is clear enough.

 

Nigel Goodwin

Super Moderator

Most Helpful Member

• Sep 10, 2007

• #2

Depends entirely on what you're trying to do?, you don't give enough information!.

 

hjl4

Member

• Sep 10, 2007

• #3

Hey Nigel, think of it as the PIC gives a signal (high) to either a relay or transistor to keep a valve open. The valve is held open until the timer runs out. What I want to know is which uses the least amount of power to actuate the valve, The relay, or the transistor.
Thanks

 

audioguru

Well-Known Member

Most Helpful Member

• Sep 10, 2007

• #4

For 2A you could use a TIP31A transistor. At a collector current of 2A its base current should be 200mA but it will work (not good) if the base current is only 100mA.

A 2A relay needs a coil current of about 40mA at 12V.

A Mosfet doesn't need any current to turn it on very well.

 

hjl4

Member

• Sep 10, 2007

• #5

OK Audio, It's what I thought, but again just double checking to make sure.
I thought for sure a Darlington transistor would use less energy to keep the flow of current going from collector to emitter, instead of a relay mechanically latched and held that way to do the same thing.
I guess a Mosfet can also do.
Just needed to be clear on this, as relays are expensive.
Thanxs

 

audioguru

Well-Known Member

Most Helpful Member

• Sep 10, 2007

• #6

Use either a darlington transistor or a logic-level Mosfet.

 

hjl4

Member

• Sep 10, 2007

• #7

Ok Thanks Audioguru, I appreciate the help.

 

blueroomelectronics

Well-Known Member

• Sep 10, 2007

• #8

If you want really low power use a latching relay.

 

hjl4

Member

• Sep 10, 2007

• #9

I see what you mean blueroom, but trying to keep cost low as possible. I will go with Darlington, and see what gives.
Thanks for input.

 

blueroomelectronics

Well-Known Member

• Sep 10, 2007

• #10

Depending on what you're switching the relay might be the cheapest option. Why does it have to be cheap? How cheap under $10?

 

hjl4

Member

• Sep 10, 2007

• #11

Yes under $10. I checked Digikey, and cheapest was $15 from OMRON(Latch Relay).
The whole board has to be under $10. A PIC, a Darlington and a few resistors and caps, and that's it.
I should acheive that no problem with a darlington transistor.
I hate these budget projects from the company I work for.

Anyways, Thanks.

 

K

kchriste

New Member

Forum Supporter

• Sep 10, 2007

• #12

The IRLZ34NPBF-ND FET at DigiKey costs $2.12 CDN and will switch up to 30 Amps. It has a max RDS on of 0.06hm: at 14 Amps with a gate-source voltage of 4V. As long as you can switch the (-) side of the solenoid, this should work fine. I'm sure if you browsed DigiKey longer than I did that you could find one that would work for even cheaper. Don't forget the catch diode!

 

Last edited: Sep 10, 2007