LeafLabs Garden » Topic: Solenoids

LeafLabs Garden » Topic: Solenoids http://forums.leaflabs.com/topic.php?id=719 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:18:30 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://forums.leaflabs.com/search.php gbulmer on "Solenoids" http://forums.leaflabs.com/topic.php?id=719&page=2#post-4370 Tue, 19 Apr 2011 06:05:30 +0000 gbulmer 4370@http://forums.leaflabs.com/ Silntknight - I imagine the diameter of wire of 100 turns of something which had 0.6 ohm resistance is small. what diameter of wire was that? About 30 AWG (0.025mm)? Was it a solid iron core, or was it a hollow tube. That would change the cross sectional area of the coil a lot. Certainly to get a handle on what might work, buy a solenoid. There are usually solenoids in old scrap cars (though the copper is valuable), which might be very cheap. Silntknight on "Solenoids" http://forums.leaflabs.com/topic.php?id=719&page=2#post-4367 Mon, 18 Apr 2011 18:45:41 +0000 Silntknight 4367@http://forums.leaflabs.com/ Yeah, I actually did. Thanks! Unfortunately, I doubt its accuracy because I made a 100 turn solenoid with a 1mm gap and I ran it at 6V. The coil's resistance was .6 ohms so there was a significant amount of current, yet no core movement. So I might just have to buy one. gbulmer on "Solenoids" http://forums.leaflabs.com/topic.php?id=719&page=2#post-4362 Sun, 17 Apr 2011 20:02:24 +0000 gbulmer 4362@http://forums.leaflabs.com/ I imagine you've found this solenoid force calculator: <a href="http://www.daycounter.com/Calculators/Magnets/Solenoid-Force-Calculator.phtml" rel="nofollow">http://www.daycounter.com/Calculators/Magnets/Solenoid-Force-Calculator.phtml</a> Silntknight on "Solenoids" http://forums.leaflabs.com/topic.php?id=719&page=2#post-4253 Sat, 09 Apr 2011 01:36:30 +0000 Silntknight 4253@http://forums.leaflabs.com/ <blockquote>Also, the output drive of the TC4426 is a much higher voltage than logic-levels, and I'd rather not subject an input to that level. </blockquote> I am running an input signal at 12V... The datasheet says that it maxes at +22.3V, so I am still well within safe margins, but there should be no problem with connecting the output to the input. Either way, I agree with using the TC4428. Also, I didn't really realize that I could run the TC442* off of the 3.3V the Maple provides, so I will make another test circuit to try that. If the input signal doesn't need to be the same as the output voltage and it runs fine on 3.3V, then I'd rather run it off 3.3V because my board would be much simpler as a result. About removing the opto, I was asking about that earlier. I think I will keep it as extra protection (this is going to be in an electrically noisy area). Also, I'd rather keep the high voltage (12V) circuits completely independent from the low voltage (3.3V and 5V) circuits. Also, anyone have an theoretical equations for the force provided from a solenoid based on the number of coils? I could pull out my AP physics equation sheet, but we don't cover inductors, so I don't know if I have that equation. Still, if I know the force provided, I can figure out how quickly the inductor should move in a frictionless vacuum. gbulmer on "Solenoids" http://forums.leaflabs.com/topic.php?id=719&page=2#post-4250 Fri, 08 Apr 2011 20:42:53 +0000 gbulmer 4250@http://forums.leaflabs.com/ I'd use the TC4428. It seems tidier, and more symmetric. There should be nearer the same propagation delay to the two outputs on the MOSFETs going through the TC4428. To be honest, that chip is so fast that it shouldn't matter much, but the capacitance into the output MOSFET gates might slow one side w.r.t. the other. Also, the output drive of the TC4426 is a much higher voltage than logic-levels, and I'd rather not subject an input to that level. Finally, once you are happy with it all, you might remove the optoisolator, at which stage I'd prefer not to have a higher-voltage output connected to an input side, just in case I made a mistake wiring or a short happened. But I am very conservative. Silntknight on "Solenoids" http://forums.leaflabs.com/topic.php?id=719#post-4239 Fri, 08 Apr 2011 13:07:33 +0000 Silntknight 4239@http://forums.leaflabs.com/ First, I did have a pull-down resistor connected to the MOSFET driver gate, which I forgot to illustrate for some reason. Second, I will either take the suggestion of taking out_1 and connecting that to in_2 or just get the TC4428. I was able to redesign the circuit last night to incorporate that kind of change. I am thinking of getting the TC4428, but what are your opinions? I know either will work, but one is likely to be better for some reason. As for getting more signals, that would add a lot of complexity and require more time than I have. I understand that it is ideal, but this solution should work with the one signal. Thanks. gbulmer on "Solenoids" http://forums.leaflabs.com/topic.php?id=719#post-4235 Fri, 08 Apr 2011 04:50:58 +0000 gbulmer 4235@http://forums.leaflabs.com/ <blockquote>... I am not sure about how much delay I will be adding by taking the output of a MOSFET driver and splitting the signal. </blockquote> The TC4426 and TC4428 both contain two MOSFET gate drivers. The suggestion is to use each drive output to drive a MOSFET. Further there is no need for an inverter. Using mikep's suggestion of driving TC4426 input 2 from output 1, or using a TC4428, the inverter goes away, so the circuit area is smaller. As mikep explains, the optoisolator emitter signal should be connected to ground via a resistor. I think, if you can get another signal in their, and control the energising of the two coils seperately, there would be more flexibility to control the valve movement. Silntknight on "Solenoids" http://forums.leaflabs.com/topic.php?id=719#post-4234 Fri, 08 Apr 2011 00:24:31 +0000 Silntknight 4234@http://forums.leaflabs.com/ 1. I agree. I am thinking of using only NMOS at this point. 2. I was able to make the transistor-based solution work. I am not sure about how much delay I will be adding by taking the output of a MOSFET driver and splitting the signal. 3. The cost of the drivers isn't an issue (shipping will cost more than the parts...), but the problem is space. I'd really rather not redesign the board again. Although, I guess it might be the best solution over all. If nothing else, I did learn a lot about sanity checks when I was building test circuits. gbulmer on "Solenoids" http://forums.leaflabs.com/topic.php?id=719#post-4225 Thu, 07 Apr 2011 18:32:33 +0000 gbulmer 4225@http://forums.leaflabs.com/ I'd like to add a couple of extra points to mikep's comments. 1. First, as explained at wikipedia ... For a center-tapped coil, you don't need complementary (P-channel and N-Channel) MOSFETs, N-Channel is enough. They are both sinking current to ground, neither is connected to the high-voltage rail, so there is no need for P-Channel MOSFETs. (mikep was probably reading the circuit this way) 2. If you put the output of the TC4426 into a MOSFET gate via an inverter, you will lose many of the benefits of using a TC4426, such as of the current source, protected outputs. It would be better to use drive the inputs of TC4426's, then use the outputs to directly drive each N-Channel MOSFET gate. The TC4426 inputs could be driven directly and via an inverter (of some form). 3. Better yet, I see that a TC4428 has one inverted and one non-inverted output, so it would drive the two MOSFETs in anti-phase, which is what you want, if you can only spare one signal to drive the solenoid coils. I'd think more about having overlap or a dead time between energising the two coils. (Edit: Sorry if this seems out of order, I wrote it after mikep's first post.) Silntknight on "Solenoids" http://forums.leaflabs.com/topic.php?id=719#post-4224 Thu, 07 Apr 2011 18:19:16 +0000 Silntknight 4224@http://forums.leaflabs.com/ With the opto cathode connected to +3.3V (positive lead indicated first): Vce = 6.58V, Vin_1 = 0V, Vout_1 = 6.68V, V(op amp inverting) = 4.12V, V(op amp out) = 1.62V, Vled_2 = 2.41V (across cathode/anode, lights up), Vled_1 = 0V (across cathode/anode, doesn't light up), Vds(led_2) = .03V, Vds(led_1) = 4.93V. *Note, during the test, LED_1 suddenly lit up. Pushing the MOSFET around causes it to light... It would appear the tabs are electrically "hot" even though the datasheet did not say that, and that when LED_1 lit up, it the MOSFET tabs were touching... With the opto cathode connected to Gnd (positive lead indicated first): Vce = .03V, Vin_1 = 6.67V, Vout_1 = 0.03V, V(op amp inverting) = 2.14V, V(op amp out) = 4.25V, Vled_2 = 0V (across cathode/anode, doesn't light up), Vled_1 = 1.75V (across cathode/anode, doesn't light up), Vds(led_2) = 4.99V, Vds(led_1) = 4.92V. The LEDs are green. The MOSFETs are FDP12N50-ND. They have a gate saturation of 3V min, 5V max. Both MOSFETS turned on with a test voltage of 3.3V, so I'm not sure that is the problem. For the suggestions: 1. I did not show this (I forgot) but I have a 22K pull-down resistor connected to In_1. 2. I need that output for another NMOS pair. I am trying to control both NMOS with a single control signal. I am going to try using a transistor-based inverter instead of the op amp and see if that makes a difference. mikep on "Solenoids" http://forums.leaflabs.com/topic.php?id=719#post-4223 Thu, 07 Apr 2011 17:20:07 +0000 mikep 4223@http://forums.leaflabs.com/ What is the voltage on "Out_1" in both cases? Also, what color is LED 1? If you measured 4V across the drain and source of the MOSFET it means it is not fully ON, the gate voltage might not be high enough to fully saturate the MOSFET. With a 6V supply voltage and 4V across the MOSFET that leaves 2V for the LED + Resistor, and some LEDs (green or blue) need more voltage than that (that's why the question about the color). In any event, you want to make sure your MOSFETs are fully conducting, not more than 1V across source/drain in the ON state and 6V across source/drain in the OFF state. A couple more suggestions: 1. put a 10k or so resistor from the emitter of the optocoupler to ground so that the TC4426 input is pulled low when the Optocoupler LED is off. 2. you can just connect OUT_1 of the TC4426 to IN_2 of the TC4426 and use OUT_2 to drive the second MOSFET directly. That way you can save the OpAmp and the transistor, since the TC4426 is already an inverter. Silntknight on "Solenoids" http://forums.leaflabs.com/topic.php?id=719#post-4221 Thu, 07 Apr 2011 16:53:48 +0000 Silntknight 4221@http://forums.leaflabs.com/ Going back and looking at it, it is incorrect. I was hoping to not need more Zeners, but adding more is only a minor problem. I actually built a test circuit like what you specified, but I don't have an inverter, so I used an op amp without any gain. In the final design, I might go with using a transistor. If so, it would be placed where the op amp is currently (and connected like in the diagram, but such that the output is inverted). <a href="http://i1221.photobucket.com/albums/dd470/Hari_Ganti/TestNMOSCircuit.jpg" rel="nofollow">http://i1221.photobucket.com/albums/dd470/Hari_Ganti/TestNMOSCircuit.jpg</a> *I am having a problem with this circuit. I am not sure why, but for some reason LED 1 does not light up when the opto cathode is grounded. I checked the voltage across the drain and source with the LED connected, and it read 4V, so the LED should have turned on. I am not sure why it didn't. LED 2 reacted correctly. Placing Zeners across the load would be difficult because this is an automotive application, so the fuel injector and solenoid are close to the engine and far from anywhere I'd be placing a PCB. I understand that they are usually placed there, but it would be more difficult to do so. mikep on "Solenoids" http://forums.leaflabs.com/topic.php?id=719#post-4216 Thu, 07 Apr 2011 15:04:41 +0000 mikep 4216@http://forums.leaflabs.com/ I think the schematic for the second solution is wrong. You have basically both Solenoids connected to each other and both MOSFET Drains connected to each other. You need to have it like this: MOSFET1: - Source goes to ground - Gate goes to TC4426 - Out 1 - Drain goes to Solenoid1 MOSFET2: - Source goes to ground - Gate goes to output of the inverter (and the inverter input goes to TC4426 - Out 1) - Drain goes to Solenoid2 That also means you need 2 protection diodes, one from Drain1 -> Ground and one from Drain2 -> Ground Also, in many circuits I am used to, the protection diode is actually placed across the inductive load (solenoid) itself and not across the MOSFET, but the end effect is the same, it limits the voltage that appears on the drain of your MOSFETs. <a href="http://www.softwareforeducation.com/electronics/notes/AS/mosfet/switch.php" rel="nofollow">http://www.softwareforeducation.com/electronics/notes/AS/mosfet/switch.php</a> BTW, the circuit "Drive a MOSFET from a PIC Chip" in the link above shows how to use an transistor instead of an inverter, to achieve the same effect: - Maple Pin = HIGH --> Transistor = conducting --> MOSFET = OFF (Solenoid OFF) - Maple Pin = LOW --> Transistor = not conducting --> MOSFET = ON (Solenoid = ON), since the MOSFET gate is pulled high through the 10k resistor. Some more general info (Coil guns - yes :)): <a href="http://www.coilgun.info/theoryinductors/inductivekickback.htm" rel="nofollow">http://www.coilgun.info/theoryinductors/inductivekickback.htm</a> Silntknight on "Solenoids" http://forums.leaflabs.com/topic.php?id=719#post-4215 Thu, 07 Apr 2011 14:36:29 +0000 Silntknight 4215@http://forums.leaflabs.com/ I just realized that I could simply use a quad op amp as an inverter for controlling each pair of NMOSs. I'm not sure I understand what you mean when you say that I can get low resistance NMOSs when you are talking about the solenoid inductance. I do not have a way to measure it, but I think I found the answer to my question anyway. Right now I am thinking of two solutions: 1. The drawing I made shows what I am thinking of currently. The MOSFETS would have 400V worth of Zeners anti-parallel to them for back EMF protection. The MOSFET driver goes low when it is off, so they should function as a CMOS. 2. Use only NMOS and an inverter IC. Ironically, I accidentally ordered inverting MOSFET drivers, so this would actually solve many problems. If I do this, can both NMOS in each pair share the same Zener diodes? I'll link a schematic of what I mean. <a href="http://i1221.photobucket.com/albums/dd470/Hari_Ganti/NMOSOnlyInductorSetup-1.jpg" rel="nofollow">http://i1221.photobucket.com/albums/dd470/Hari_Ganti/NMOSOnlyInductorSetup-1.jpg</a> gbulmer on "Solenoids" http://forums.leaflabs.com/topic.php?id=719#post-4197 Thu, 07 Apr 2011 05:09:49 +0000 gbulmer 4197@http://forums.leaflabs.com/ <blockquote>Unless I can get a logic IC that switches two signals (ex. for input pin Vs, one output is Vs and the other is _Vs (Vs with a line above it, inverted)) ... </blockquote> I'm not sure I understand. That is an inverter, or am I missing something? If you don't want to use an ordinary integrated circuit (e.g standard 74xx or 4000 series, or even a 74LVC1GU04DCKTG4), you could make it from two transistors, or two MOSFETs, and a few resistors. <blockquote>While the stepper motor idea would work, it is unideal. </blockquote> The point about the stepper motor link to wikipedia is it explains how to drive a similar electro-mechanical system using only N-channel MOSFETs, i.e. no need for complementary (N-channel and P-channel) MOSFETs. I was not suggesting you use a stepper motor. <blockquote>Assumption 1: I believe you are correct. The only concern I would have is the back emf from polarizing the (essentially) inductor one way, then suddenly reversing it. </blockquote> Why? What is the inductance? Have you measured or characterised it? Depending on budget, MOSFETs with resistances of a few milliohm are available. I think the optoisolator is a useful insurance policy while building a prototype. There is no isolation between a Maple and the host PC, and you may well want to gather data from the Maple while experimenting.