May 09, 2010 by treymd I bought a solenoid online and it turns out it came from Hong Kong. I'm having a tough time tracking down a datasheet. is there a way using ohm's law to calculate the current needed to drive the solenoid? Can I simply measure the resistance of the coil with a multimeter and do the math or is there something more I would need to do? I have a really good track record at finding datasheets. Please post a picture and describe any information on it, I'll see what I can find (might be a few days). BM Cool boba... tracking this stuff down can be a nightmare. the label is scratched up pretty good (it came airmail and I have witnessed airport personnel using the bottom of their boots to cram things in to a plane as tight as they can get it.) ZH is on one line followed by missing label DC is on the next line also followed by missing label. it is a 12V 1/2" solenoid and here is the source: and doh... they have the current listed now, or perhaps they did before and I missed it, 250mA. Sorry to waste your time =( it's a nice cheap water valve to play with though, link: http://www.virtualvillage.com/12v-dc-1-2-solenoid-valve-for-water-train-air-pipeline-001540-024.html I would like to know if I could simply measure the resistance of the coil though, I'm curious! You could measure the resistance but it would probably not help much. You would have to know the wire gauge the coil is made from as well. there is a table for the various wire sizes, lengths and voltages for things like relays and solenoids. I'll see if I can find it. That's OK mongo, I have seen the tables, I think even wikipedia has that. Why do you need to know the wire gauge? I thought ohms law, V=IR would give you current if you knew the resistance and the voltage? Wire gauge matters when you don't have the other numbers. Different sizes have different resistances per a given length. If you have the number of turns, (length), you can also figure out the rest. I make it seem complicated but there are so many ways, and they are really pretty simple. Another factor is wattage necessary for it to function properly. Bigger solenoids at the same voltage rating will certainly have a lower resistance. Mostly because of the larger wire gauge. With that, the current and wattage goes up too. Bear in mind, that since you're dealing with an induction coil, you aren't dealing with just resistance. You're dealing with reactance, too. However, you can get a pretty good idea about it by using the basic equations. ``````E = 12VDC I = 250mA P = 12 * .250 P = 3 Watts R = 12/.250 R = 48 Ohms `````` An observation- Note the low amperage. This is NOT a very powerful valve. Light duty. The price also tells you something about it :P -- Again, very light duty. Very low pressure. BM Thanks, guys, I was looking for the science and you gave the answers. FYI this experiment is for automating my wife's chickens. We have about 15 of them, because we can. And they make great robotics test subjects because they just don't care too much! This Solenoid will be used to autofill their water and I'll soon deck out the chicken house with sensors to check their food level, ambient temperature, and whatever else I dream up. Expensive chickens, but I'm entertained! Oh I also want to use a stepper to automate the door to let them in and out every morning/evening. Mongo, yeah I'm paying attn to wire gauge and type and number of turns very closely. I live on the eastern shore of lake Ontario where wind is in abundance. When I get the safety worked out, I WILL be erecting a wind turbine. Or 10. It's the batteries that kill you. I suppose I can crack this thing open and figure out the wire guage and count the turns, and I may very well do that with another one, but this one has a job. I also understand it's a light duty valve but I did the conversion from bar to psi and it suits my needs. 0.5 MPA ~ just over 72 PSI. Your average household is 60PSI or below. I'm not using her to launch potatoes out of a tube. Or replicate the water show at the Bellagio in Vegas (though maybe someday I will) I also ordered a thermocouple from the same source at the cost of about 3 bucks. 0-800C K type with a 1000mm (1m) whip, that'll get installed in a toaster oven for my SMD experiments! Loving my nerdkits! OOOOHHH!!! Wind turbines!. One of my favorite topics! The battery part for me was easy. Got a couple of prototype turbines put together... Just no !@#\$ WIND. My wife happened across this the other day because she's trying to steer me away from wind... http://www.thesolarplan.com/articles/your-own-solar-panel-collector.html But solar is not needed where you have wind, and National grid is building wind farms all around us, I want one too! Hey treymd, I liked reading about your chicken experiments, it sounds pretty fun. The solenoid reminded me of the flipper coils on pinball machines. Most have 2 windings, 1-lower wrap for power stroke and another smaller gauge one for 'holding' the flipper without burning the coil out. I think the newer MPU ones just have the one coil and limit the current to it during the 'holding' time. That was my thought that you don't overdrive it for too long to heat it up. About the stepper for the door, personally I would go with a solenoid there too. You could have a 'dark detector' start an algorithm that could scan the nesting boxes with IR sensors to do a head count and if all are in, slam the door. Yeah, ain't this cool? Have fun, Keith hrm that's a good idea 59, I was trying to convince my wife we need to fit them all up with RFID tags, I'll have to research what is cheaper... rawr.. yeah this is fun!