Do not confuse the relay coil voltage with the input control voltage. The relay coils are made with many different voltages. 3,5,6,12,24 etc. When they say 'x Volt relay' they are usually referring to the coil voltage not the input control voltage.Learning101 wrote: ↑Sat Feb 10, 2018 10:59 amHi, I'm trying to get a project together and I need to power a 24vac solenoid for short periods.
I understand the easiest off the shelf way is with a relay, (please correct me if I'm wrong)
Would this relay be suitable? https://www.amazon.co.uk/Elegoo-Channel ... B06XK6HCQC
It does say 5v and I know the GPIO is 3.3v but I don't seem to be able to find 3.3V relays! Would it still work?
Any advise greatly appreciated.
Thanks for you help, if it worked without the transistor and resistor, would there be anything else I need to put between the PI and the relay? Or not?pcmanbob wrote: ↑Sat Feb 10, 2018 11:19 pmThe relay board you have chosen may work, some of these 5V relay boards do work with the pi gpio and some don't, it seems to be pot luck as to whether they work or not.
You can always make them work and be active high with a simple transistor & resistor interface for each relay input.
Hi, so the solenoids are salvaged off a Coinco Global 2 coin mech, MDB version.pcmanbob wrote: ↑Tue Feb 13, 2018 11:29 pmIf you know what voltage they operate at then it's a simple thing to if they work on DC as you can use a simple multimeter set to amps to measure the current drawn, but your original post said 24v AC to measure AC amps you will need a clipon ammeter.
You could get estimated current if you know the operating voltage and you can measure the coil resistance using voltage / resistance = Current.
Can you give use any information on the solenoid valve you are using
Make, model, supplier ?
Hi Thanks, what is the best way to supply 6v, would it be with an adapter like this,pcmanbob wrote: ↑Fri Feb 16, 2018 7:38 pmThe problem you face with the solenoids having no markings is that even if the coin mech is powered from 34v DC there is nothing to say the solenoids will also be powered from the same 34v DC the coin mech may have output a different voltage to drive them.
So what you could do is using a digital multi meter set on ohms measure the resistance of the coil., then using different voltages
use the formula voltage / resistance = Current to work out the current that will flow for a given voltage.
if you say the wire is very thin then your probable want a current of maybe 100 -500 ma to flow ( thats 0.1 to 0.5 A )
this way you could get an estimate of the required voltage to operate the solenoid.
I would suggest you try voltages of 6,12,18,24,34V
once you have an idea of the voltage you can but test a solenoid and see if it works, but I would be ready to disconnect the power in the even you have it wrong and things start to smoke, it going to be a case of trail and error so be prepared for failure.
Have you done the calculations I suggested and decided that 6v is the correct voltage to use or are you just guessing ?
Yes the 6v was a guess, I was just checking that I understood what sort of power supply I might possibly need.pcmanbob wrote: ↑Sat Feb 17, 2018 10:32 amHave you done the calculations I suggested and decided that 6v is the correct voltage to use or are you just guessing ?
If 6v is the correct voltage to power your solenoid and the current draw by each is less that 0.5A then yes that would probably do the job.
once you know the current drawn you can put a fuse in the feed to your solenoid to protect it.
Not possible for resistance to be too low for a reading. Though many cheap meters are not accurate when measuring low resistance, the meter should read 0.xxx. Touch the meter leads together to test.
Yes I must have a cheap meter, when I touch the leads together I do get a reading.klricks wrote: ↑Mon Feb 19, 2018 6:11 pmNot possible for resistance to be too low for a reading. Though many cheap meters are not accurate when measuring low resistance, the meter should read 0.xxx. Touch the meter leads together to test.
A '1' displayed usually means infinite resistance or an open circuit OR the scale is set too low.
Thanks for your help, I was being stupid the wire a coating.pcmanbob wrote: ↑Mon Feb 19, 2018 7:10 pmSo I have several meters being an ex sparks.
So my calibrated iso-tech IDM303 which auto ranges.
using fused leads 4.35 ohms when shorted together
using un-fused leads 0.24 ohms when shorted together
when leads not shorted reads .OL
my cheap uni-t ut30b meter only has un-fused leads and if I set it on 200 ohm scale reads 00.4 ohms when shorted together, when not shorted together reads 1.
So to measure resistance of coil first short leads and make a note of result.
then connect meter to coil and note reading if its the same as if you had the leads not connected to anything go up one range on your meter 200 > 2000 and keep doing this till you get a reading other than one, if you cant get a reading then it suggests the coil is faulty and is open circuit..
so for a true reading you should subtract the leads reading from you coil reading but in reality the difference will not be much if you have reasonable leads.
so as an example I have some relays with 5v coils
on 200 ohm meter range reading 84.8
on 2000 ohm range 085
20K ohm range 0.08
if you are not sure what you meter is telling you take a picture that shows the reading and setting and post it here.
Thanks, I have learned so much trying to figure this out thanks to your guys help,
Yes thanks wasn't planning on running it off the PI supply, I have a second PI supply.pcmanbob wrote: ↑Mon Feb 19, 2018 8:51 pmNot a good idea to power it off the same supply as you pi its going to put sudden load on the psu and possible reverse voltage spikes back in to the psu as well.
always better to keep pi on its own psu and things like relays and solenoids on there own psu but controlled by the pi.
but its your kit so if you want to try its that's up to you.