I am constructing a Velleman Mk111 interval timer and looking to increase the pulse time to 1 min and the pause time to 5min. I have acquired the resistor and capacitor to modify accordingly. The resistor I bought is a 220k 1/8W resistor. The resistors that can with the kit look to be 1/4W resistors. Will I have a problem with burning my resistor up by using a lower power rating resistor?

I am trying to attach a pump to the circuit. The output says MAX 24V / 3A. Does this mean that I am unable to attach an AC current to the relay? I know the relay can handle AC, but not sure about the circuit handling AC current. Any help would be appreciated.

 

The resistor wattage is OK.
However, 24V/3A is the maximum voltage and current that the relay is rated for. You cannot switch a higher voltage or higher current than that, or you will destroy the relay; you will also cause an unsafe condition. Never attempt to apply more voltage to a device than it is rated for.

 

Are there any part numbers or markings on the relay besides the 24v part?

 

15A 125VAC, 10A 28VDC, 10A 240VDC, 10A 28VDC SRU-12VDC-SD-C is printed on the relay. The submersible pump I am using is 23V.

 

I have the same relay in a thermostat circuit. The relay contacts are capable of handling AC (15A @ 125V or 10A @ 240V) or DC (up to 10A @ 28V). However, there may be extra limitations imposed by the circuit board. Mine, like yours, says 24V 3A, and although the circuit tracks look fairly meaty, 3A is presumably the limit set by the board manufacturer. So, your pump would be OK as long as it doesn't draw more than 3A.

I have seen someone use this board to switch 240V AC. Although the relay is up to it, putting a high voltage like this on a board designed to switch 24V max and where the rest of the circuitry is designed for 12V is probably not very sensible!

 

P.S. For "not very sensible", read "barking mad".

 

The Velleman website:
http://www.velleman.eu/distributor/products/view/?country=be&lang=en&id=339209
...the kit assembly manual ...
http://www.velleman.eu/downloads/0/minikits/manuals/manual_mk111.pdf
... and the PCB all state 3A/24V for the relay output.

I do not know offhand what the limiting factor would be, as I do not have one of these kits. However if you exceed the kits' clearly stated ratings, your project is "at risk".

I do not recommend exceeding the stated ratings, as they were not assigned purely by random chance.

 

The submersible pump I am using is 23V.

Maybe I missed the current required by the pump; if it is 3 amps or less, I don't see a problem. I have built a kit or two that use this same relay and the current restrictions often are a reflection of the trace size on the PCB rather than the relay contacts.

Post your question here and you can get an answer straigt from Velleman.

http://forum.velleman.eu/viewforum.php?f=7&sid=1f41c1f8804382a41a1777cd42eb5bc4

ETA: Actually, I see that you have already tried to get an answer from the Velleman forum. I suspect the problem is that they think they answered your question and didn't see your follow-up. Go back to the mini-kits section of the forum and make a new post. State the voltage and current required by your pump and ask if the MK-111 will handle it. Their support personnel sometimes take a day or two to reply, but they always do. Since their primary language is Dutch, it's better to be very clear in your wording of the question.

Second ETA: I see the OP hasn't posted here since January 3; he's probably already solved his problem.