Solenoid & Capacitor values? - Page 1
Forum section: electronics / beginners

author: jingate
author_rank: Contributor
timestamp: February 08, 2018, 09:46:51 am
content: Hello everyone,I'm a total newb around here tinkering with some simple electronics for model kit dioramas and the like and I need a little advice on choosing a solenoid and capacitor.My current project is attempting to activate a small solenoid using a capacitor, powered by a regular 9v(PP3) battery. Basically, I want to press a button, have the solenoid activate for a fraction of a second until the capacitor is empty and the plunger springs back, then when I release the switch, the capacitor charges again so that I can repeat the action. Essentially an electronic trigger that I can repeat activate as often as I want.I know how to set it all up circuit-wise, but am having trouble choosing a suitable capacitor and solenoid, despite having tried to read up on it. (Maybe I started too much "in the middle", my skill level kind of ends with soldering LEDs!) I don't know what values to choose for those two components. The solenoid should ideally have a travel of at least 10mm- the only small ones I've found with that much travel draw upwards of 300-500mA. Can a regular 9v Battery even activate one of those? And if so, what type of capacitor is suitable? (It needs to charge almost instantly and have enough juice to activate the solenoid to fully retract and release. It doesn't have to "hold" it.)If I have to go smaller, what solenoid/capacitor values should I aim for? (I've found a couple solenoids rated at around 130mA but they have very little travel.)Here is one solenoid I've been looking at. (It's rated at 500mA current draw at 9 volts, 700mA at 12v and has a passive resistance of 15.6 ohm).https://www.amazon.com/TOOGOO-Frame-Solenoid-Electromagnet-ZYE1-0837ZP/dp/B00UBOMN3C/ref=pd_sbs_147_1?_encoding=UTF8&pd_rd_i=B00UBOMN3C&pd_rd_r=9ZA88QYRABK9GRKY69Q9&pd_rd_w=eYCKA&pd_rd_wg=hTHWY&psc=1&refRID=9ZA88QYRABK9GRKY69Q9Many thanks in advance for tips!//Joe

author: Rigolon
author_rank: Regular Contributor
timestamp: February 08, 2018, 05:57:19 pm
content: Hi Joe,For starters, I am newb too, so let's if I can help a little.Could you explain how the circuit is going to be set up? I'm not quite getting how this circuit could work with only battery, button, capacitor and solenoid.About the solenoid, if you use one with a higher nominal voltage than your power supply, it can work (within a limit) but won't have the strength it should (0.8N in the one you linked). But you can use a transistor to control the current to get the solenoid to work as strong as it can be.QuoteThe solenoid works as an load, with a multimeter you can measure it's resistance. So from what you said I don't know if this solenoid needs 500mA with 9V to work properly or only that it draws 500mA. In the first case you already know how much current you need on your transistor circuit. In the second case, you can use Ohm's Law V = R x I to find the resistance (R) of the solenoid, use it again to find nominal power P = V2/R. With that you define the current you actually need to use 9V, I = P / V.But be aware, 9V battery can have capacity between hundred or thousand of mAh. Let's say you use a rechargeable Ni-MH battery (usually 250mAh. It means you will be able to use about 30 minutes with the solenoid activated (with 500mA). There are batteries with lower capacity, meaning it will probably activate once and die.For choosing an solenoid can't help to much with choosing one, but I advice to search one with 9V or lower so you won't need the transistors, and watch for the nominal power consumption, so you can choose the right battery/power supply.I can't help with the capacitor without knowing how you planned the circuit.

author: floobydust
author_rank: Super Contributor
timestamp: February 08, 2018, 06:55:06 pm
content: You want the smallest solenoid possible and most sensitive mechanics so that you use the least energy possible to move things on the diorama, for long battery life.Your idea is good, to store energy from a small battery in a capacitor, then dump it into the solenoid. Model railroaders use this approach with switchups.But I see a problem- ZYE1-0837ZP is a large solenoid 12V 0.75A; A 9V/PP3 battery just doesn't have the energy to move it many times.Make the mechanics lighter, pick a smaller solenoid, or a larger battery pack.2,200-10,000uF is what I see as a range for capacitors used, if you want to experiment.

author: jingate
author_rank: Contributor
timestamp: February 08, 2018, 07:08:03 pm
content: Hi and thanks for the input!I managed to find the passive resistance of the solenoid in the link above: 15.6 ohmI was planning on using a regular alkaline 9v which seem to be around 500mA.This is how I'll connect it all (note that I DON'T know the mH of the solenoids I have looked at... seems it's never listed):The capacitor will be needed either way, since the solenoid is only supposed to be active for a short time, maybe a few milliseconds... basically as soon as it hits bottom it should deactivate and spring back. The idea is that every time I press the "trigger", the solenoid will click and release.Finding a suitable 9V solenoid is proving difficult they are usually either 12v (with the stroke I need) or 5-6v (too short stroke). I first bought one to test, but realized afterward that it drew 1.4A at 9V and 2A at 12v, so when I connected a 9v (admittedly not absolutely new and fresh) to it, absolutely nothing happened! (Told you I'm a total newb haha.) But the new one I've got coming in (linked in the OP) is rated lower.Since capacitors are so inexpensive, I can get a few in those ranges and do some testing. As long as the 9V can move the solenoid maybe a couple hundred times it should be enough IF I can't find a suitable smaller one. (Again, the problem is that the stroke on all the smaller ones that I've found is too short- usually 3mm and I need at least 10-11.)

author: Rigolon
author_rank: Regular Contributor
timestamp: February 08, 2018, 07:51:30 pm
content: Hi again Joe,When i finally figured out how the circuit should be I came to see that you answared with the circuit I thought it should be.It should be quite easy then.For this solenoid, nominal current should be 12V/15.6= 0.76A approximately the 0.75A floobydust said.With this circuit it will only draw about 0.58A, so it won't work full force, perhaps it won't have enough strength to pull/push the plunger. But i think it will be sufficcient as long the plunger don't need to use a lot of force. Just test it out.As I see your main problem is the battery, batteries also have a limitation with the amount of current it can supply at once. So even if your battery has 500mAh capacity, it could be limited to supply 750mA at maximum without damaging it (These values are random, just for example).Now, for the capacitor, as Floobydust said you will have to use big capacitors.As I said, the solenoid can be viewed as a resistance (so the inductance value won't matter here). The time for a capacitor charges/discharge is called RC time constant, and as the name says it's a simple multiplication of R x C. RC is the time it takes to charge/discharge 63% of it's power.So let's say you want the solenoid to be active for 100ms, you will need a RC time bigger than 100ms. It's not a linear charge/discharge so it's hard to get an absolute value. Try use RC = 500ms, this should give you 100ms with voltage of 9V to 7.2V (See capacitor charging/discharging graph).For the equation: RCtime= R x C therefore C = RCtime/R = 500m/15.6 = 32mF or 32,000 uF. Crazy big capacitors and quite expansive ones (probably using 3 10,000uF in parallel should be cheaper).Sorry for the long awnser, or if it's confusing (english is not my first language), but i wished to explain the details so you will know how it works properly.

author: jingate
author_rank: Contributor
timestamp: February 08, 2018, 08:42:51 pm
content: Thanks again for the help.Hmm... I might have to rethink it a little. I looked into larger capacitors and there's no way I can fit one that large into the space I need, along with everything else. And a charge time of 500ms will probably be too long.Maybe I can go with a smaller 5-6v solenoid instead and increase the actuation with a fulcrum. It doesn't have to be strong, just move a piece of plastic that weighs a few grams a suitably long distance.I've found one that might be suitable:Movement: 4.5mm (specs say 6mm, but apparently it's only around 4.5, but a lever can double that easily enough)5V4.5ohm1.2W (240mA)ZHO-0420S-05A4.5Guess I might have to go with 4 AAA instead of a 9v or use a suitably large resistor?

author: Rigolon
author_rank: Regular Contributor
timestamp: February 09, 2018, 12:50:45 am
content: I think you could use 4 CR2477 batteries to get 12V they have 1000mAh. (Never used this type of battery in series, don't know if it works but I believe it does.)When charging the solenoid is disconnected, so you will only have the internal resistances of the batteries and the capacitor wich is m. So the charging time is actually a lot faster, almost instantaneously.I guess there is also the natural time the plunger takes to fall back to it's original place, I guess that only testing it out to figure this part. But since it's a mechanical event, it will take at least a few ms (Even more newb with mechanical stuff here). If this holds to be true, you can take a this few ms out of the time you need your cap discharge.In my previous example I used an RC time 5 times longer the time you needed the solenoid activated. If you use a smaller solenoid and the 9V battery it will be way better. As I said RC time is the time that the cap loses 63% of the charge, so if you have 9V on the cap, after RC you will have 3.33V (which, maybem can still activate a 5V solenoid).So now RC time equals the time you need.To be even more precise. Since you are going over the nominal voltage you could use a small resistor to control the current and therefore needing a smaller cap. I will let you do the math this time.About the 5V solenoid you said, i found this datasheet:https://cdn.sparkfun.com/datasheets/Robotics/ZHO-0420S-05A4.5%20SPECIFICATION.pdfBut some informations doesn't match.It actually draws 1.1A and consumes 5.5W.

author: james_s
author_rank: Super Contributor
timestamp: February 09, 2018, 07:54:23 am
content: Does it have to be a passive circuit like this? It sounds like what you want is a one-shot, you can build one out of discrete components, or using a 555 or any number of other methods.

author: jingate
author_rank: Contributor
timestamp: February 09, 2018, 07:28:23 pm
content: @james_s I want a one-shot that repeats with every trigger press, correct. An electronics store where I was inquiring about solenoids also suggested a 55 circuit and gave me this diagram:http://tinyurl.com/ybmkq92tI've been fiddling around with it and managed to get the pulse short enough (by changing the value of the capacitor near the ground) but other than that I can't really make heads nor tales of it. Again... total novice when it comes to how these things relate to each other. Going to try and read up on how 555 timers work, but I'll probably still struggle with understanding how it all works.The ZYE1 solenoid came in today and a fresh 9v battery happily activated it, so the question is if a 555 circuit can be made to work with with a setup like the one linked?I did also get a copy of the 0smaller ZHO 6v solenoid to play around with, but since that creates the mechanical problem of making a linkage/fulcrum I'd rather see if the larger one can be made to work.

author: jingate
author_rank: Contributor
timestamp: February 09, 2018, 11:21:17 pm
content: OK, what about this setup?http://tinyurl.com/y9k4nyzcThe timing is pretty much exactly what I need. Would I just connect the solenoid between the OUT and ground here?Like this (Note: I don't know the correct inductance of the solenoid)?http://tinyurl.com/yd4x2uv7Did I connect the solenoid correctly? I've read somewhere that a diode is good to have across the solenoid a well? (I actually got one with it but the data sheet stated that is isn't completely necessary.)Also, I don't really understand what the "logic input" in this diagram is (and google isn't helping, lol). I gather it's my push-button "trigger" but between what two components is it connected?

author: jingate
author_rank: Contributor
timestamp: February 10, 2018, 11:50:28 am
content: Another small update. I went out and got a battery holder for 4 AAAs and to my surprise, the 6V easily activated even the heavy 2A solenoid easily. IthinkI can fit those four AAAs in the cramped space.

author: james_s
author_rank: Super Contributor
timestamp: February 11, 2018, 01:16:00 am
content: That's precisely what a one-shot is, also referred to as a monostable multivibrator. Each input trigger you get exactly one output pulse of a defined length, regardless of the length of the input pulse. Not to be one of those "let me google that for you" smartasses, but you can do so and get lots of examples, here's the first one that came up for me.https://www.electronics-tutorials.ws/waveforms/555_timer.html

author: jingate
author_rank: Contributor
timestamp: February 11, 2018, 09:21:42 am
content: I'm looking at the possibility of using a timer chip but from the looks of it, the 555 can't handle the power draw of the solenoid I want to use. It has been suggested that I use a transistor after the 555 to trigger a larger power output but I'm struggling to understand what kind I need.

author: Eosander
author_rank: Newbie
timestamp: February 11, 2018, 09:55:32 am
content: Hi, I may have created a solution that you are looking for;https://www.eevblog.com/forum/beginners/circuit-and-pcb-design/In the lower part of my circuit drawing, I have a NE555 driving a transistor for the relay coil current.The important part here is that the transistor collector current (Ic) has to have a higher value than the calculated coil current;

author: jingate
author_rank: Contributor
timestamp: February 11, 2018, 06:01:24 pm
content: After reading up a lot on this stuff, I realized that I might've been digging too deep a hole for myself prematurely, so decided to dispense with the theoretics and do some testing.Here are a couple results.Large solenoid with 9v and about 3000uF in capacitors:https://youtu.be/M-9FzBsEjP0Small solenoid with 6V and 6800uF:https://youtu.be/lqcxXQAZT5sIt works surprisingly well, even with the larger one (which I would prefer to use). I'm going to get some capacitors between 3K-15K uF and test different combos. Feels like I'm close to getting this to work as needed.Thanks again for the advice everyone!

author: james_s
author_rank: Super Contributor
timestamp: February 11, 2018, 09:56:54 pm
content: Yes, you will need to use a transistor, that is trivially easy. Search for "using a transistor as a switch", I would suggest using a NPN transistor as a low side switch, it's an extremely common application. Very basic Electronics 101 type stuff.

author: jingate
author_rank: Contributor
timestamp: February 11, 2018, 10:41:29 pm
content: Well, at this point I've put the idea of using a 555 timer on the shelf, and just go with using a single capacitor (as in the videos) since that worked fine, so I will not be needing a transistor after all.My remaining questions now are just finding the most suitable capacitor in the range 3.3-22mF, either 6.3 or 10 volts (I'll have to experiment) and choosing a protection diode (if I really need one in parallel to the solenoid).

author: james_s
author_rank: Super Contributor
timestamp: February 12, 2018, 12:17:33 am
content: That's a bizarre way of going about this but I guess if it works then whatever.The protection diode is to protect a transistor from spikes generated by the solenoid. With no transistor the diode is not necessary.

author: Audioguru
author_rank: Super Contributor
timestamp: February 12, 2018, 12:25:45 am
content: You might have destroyed the 555 by using it to try to output a current that is 10 times its maximum output current rating.

author: jingate
author_rank: Contributor
timestamp: February 12, 2018, 08:36:43 am
content: @Audioguru, yeah I know, which is why I never actually tried it even though the 555s cost next to nothing. : )@james_S, which is bizarre- using a single capacitor to give the solenoid a single, short pulse with ever trigger press or using a timer chip to do the same thing? Seems like the first solution, which was the initial idea, in this case is preferable since it works great (in testing at least) and is a lot less complex than the other. As for the diode, I've seen several mentions, when looking at the first option, of possibly needing a diode connected in parallel over the solenoid, I assume to protect the capacitor from backward voltage spikes.

author: floobydust
author_rank: Super Contributor
timestamp: February 13, 2018, 02:22:45 am
content: I think you are not really testing how strong the solenoid pulls, looking at movement of the plunger alone.When you put a mechanical load on the solenoid, that is a better test I think. Be sure to check it with your mechanical stuff connected, to avoid no joy.

author: jingate
author_rank: Contributor
timestamp: February 13, 2018, 10:02:49 am
content: The videos show only the first test. I've since tested them with weight, and while it isn't strong, it'll be enough for what I need. (It's only going to move a small plastic block that weighs a couple grams.)From the looks of it I am going to settle on a 10V 3300 or 4700uF capacitor powered by a 9V battery. Stronger capacitors hold the plunger for too long. (The 15000-22000uF variants I tested held it for an entire second or two.)So, unless something new develops: problem solved. : )Thanks again to everyone for the input!

author: floobydust
author_rank: Super Contributor
timestamp: February 14, 2018, 12:10:37 am
content: We wanna see the diorama, when you're finished