How to drive a DC solenoid - Page 1
Forum section: electronics / beginners

author: mrwebb
author_rank: Contributor
timestamp: July 03, 2012, 05:33:58 am
content: OK Guys, new kid on the block and a total newb so go easyI'm a software developer by day and recently started tinkering around with the hardware/arduino/beaglebone/etc stuff.I am trying to wrap my head around solenoids as I have a couple projects in mind where I could use them.I bought one from adafruit:https://www.adafruit.com/products/413I got it and thought I would just try and get it to work before wiring up a circuit to fire it using arduino. But I am stuck.I have an adjustable ac/dcwall power supply. Goes from 1.5-12 volt, docs say it delivers 500mA max, I put it on the multimeter and it is actually more like 14v at 300mA.Now, this solenoid claims it can handle 9-24v and needs about 250mA to work.When I touch the positive/negative leads to the power supply positive/negative I would expect it to fire, but so far I have been unable to get it to actually fire. Am I oversimplifying things, or should I be able to just power this thing direct from the wall ac/dc adapter?

author: TerminalJack505
author_rank: Super Contributor
timestamp: July 03, 2012, 06:53:59 am
content: That's pretty much how it should work.Maybe you need to reverse the wires. Or maybe your power supply isn't up to snuff.The quoted 250 mA may be for a 24V supply. In which case a 12V supply would only provide half the current.Measure the coil's resistance and use Ohm's law to see if the 250 mA jive's with 24 volts or some other voltage.

author: mrwebb
author_rank: Contributor
timestamp: July 03, 2012, 07:43:05 am
content: Hey TerminalJack, thanks for the tip!Resistance is 42.2 ohms * .250 amps, means it should go at about 10.55 volts if my math is correct?So I just measured and from the wall I am getting 14.2v DC and 313mA, seems that sucker should fire. I tried to flip the wires to no avail. I just opened up the package and cant believe it would be DOA. Adafruit doesnt have a spec sheet, but the label says: TUA-1040T u:24V r:43(ohm)If my math is right on those numbers, 24/43=558mA, does that mean that 9/43=209mA?? Seems like it would need more current the lower the voltage, not less?Times like these I wish I had a benchtop supply so I could test the higher voltages/amps. I was looking at this one earlier tonight? Any ideas of if this one is a solid option?http://www.amazon.com/Mastech-TRIPLE-LINEAR-SUPPLY-HY3005F-3/dp/B004ISD7T6/ref=pd_rhf_gw_p_t_3

author: G7PSK
author_rank: Super Contributor
timestamp: July 03, 2012, 07:45:58 am
content: The inrush current will be greater and may be that is pulling down the voltage on your supply, try the solenoid with a car battery or a couple of those six volt lantern cells.

author: mrwebb
author_rank: Contributor
timestamp: July 03, 2012, 07:50:18 am
content: @G7PSK, interesting, is there a way to safely measure what the voltage is being pulled down to? I do notice that when I hit the solenoid that the LED on the wall power supply dims quite a bit.

author: T4P
author_rank: Super Contributor
timestamp: July 03, 2012, 08:25:05 am
content: With a min/max or peak min/max feature on your meter it will be very useful,there's a difference between min/max and peak min/max hold, peak min/max hold tracks much quicker then min/maxAnd some people think the UT61E lacks the min/max ... bitch please they implemented a better versionWith peak min/max you can see what min/max can't seeIt must be said that peak min/max pushes the meter to it's ultimate limits

author: BloodyCactus
author_rank: Frequent Contributor
timestamp: July 03, 2012, 04:10:52 pm
content: I'm familiar with larger pinball solenoids, but not the ones from adafruit.does the link/plunger move smoothly in the solenoid? it should be friction free, works with a cushion of air. does it have a diode? most solenoids I have, have diodes, if yours has one you might want to test it.maybe your solenoid has lost its magic smoke. it happens sometimes.

author: PA0PBZ
author_rank: Super Contributor
timestamp: July 03, 2012, 06:14:40 pm
content: Just put your multimeter on the output of the power supply and measure the voltage when you connect the coil, I guess it will be quite low.You can also measure the current to the coil with the multimeter to see what's happening.Since it is designed to work on 24 volt the 9 volt they give seems a bit optimistic.24 volts, 43 ohms will give you 560 mA, that times 24 volts is just over 13 Watts.when you do the same at 9 volts it's not even 2 Watts, so that is a big difference...(yes, U2.R - I know)

author: G7PSK
author_rank: Super Contributor
timestamp: July 03, 2012, 09:21:37 pm
content: Another thing to check is does the unit have two winding's some have a pull down coil and a separate hold coil switched internally so that it will draw a larger current while pulling in and then stay held on a much lower current, often found on diesel fuel stop solenoids.

author: T4P
author_rank: Super Contributor
timestamp: July 03, 2012, 09:29:31 pm
content: Common solenoids have nothing more then a single coil ...I have the similar ones that adafruit sells and they can get quite hot ... mine was much larger and draws 600mA at 12V

author: amyk
author_rank: Super Contributor
timestamp: July 04, 2012, 09:04:39 am
content: Quote from: mrwebb on July 03, 2012, 07:43:05 amDid you mean TAU-1040T? Buying one from the source is a lot cheaper (like 2-3x):http://chaocheng.en.alibaba.com/product/433202763-0/Solenoid_TAU_1040T_.html...and the spec there shows you likely have the 10W/100% duty cycle model. 10W is relatively high for a small wallwart to supply. See if removing the spring makes any difference; if it's working but just needs more current, the armature should move without the spring or you should be able to feel it resisting manual manipulation more with voltage applied.

author: mrwebb
author_rank: Contributor
timestamp: July 06, 2012, 09:28:31 am
content: Quote from: amyk on July 04, 2012, 09:04:39 amAs many above suggested, when I hit the solenoid the voltage dropped from 14v to about 6v! One thing that was promising was that I could feed the armature resisting when voltage was applied. So, I think I need to get a new power supply.@amyk would you mind explaining what "10W/100%" means exactly? I saw that on the spec but didnt know exactly what that meant.Also, thanks for the link, nice to know I can get them cheaper if I need some more!

author: amyk
author_rank: Super Contributor
timestamp: July 06, 2012, 10:52:14 am
content: How did you get that 300mA @14V figure? 6V across 42.2 ohms is only 142mA.10W/100% means it can dissipate 10W at 100% duty cycle. They make other models with lower resistance for higher wattage (and force), but they can't be used at 100% duty cycle due to thermal constraints.

author: SeanB
author_rank: Super Contributor
timestamp: July 06, 2012, 03:11:18 pm
content: 10W/100% means if you power the coil with a voltage that results in 10W of power being dissipated in the coil you can do that all day long with no problem. If you overdrive the coil ( to increase pull in torque for example or to make it faster) to say 50W, then you can only apply power for a short time before the coil will overheat and burn out. Generally they give this in a table of say 6 seconds in 60 seconds, or give a derating curve with power and duty cycle as axes.