solenoid keeps burning  - Page 1
Forum section: electronics / projects

author: pete1111
author_rank: Contributor
timestamp: August 01, 2022, 11:51:55 am
content: I have a 12v solenoid. I have it built into my car door so when I trigger a relay with a switch that connects to ground. The relay sends 12v to the solenoid that in turns pulls the cable in the door and opens the door.this is very brief action. All was working fine till otherday my car was filled with smoke. Turns out the solenoid has completly burnt. I don't understand how this happened as no voltage was going to the solenoid. If it did my door would be open. I have since replaced the solenoid and relay and all wires and 2 weeks later its happened again. I have added a fuse that did blow in the end. Can anyone help? I'm going to use a diode across the solenoid this time. And run a ground wire thought the door to the solenoid then to shassi of the car. Incase its bad ground.Can anyone else recommend me add anything else to it?On a side note. The other door has been fine yet its setup exactly the same as the otherside.

author: wraper
author_rank: Unknown
timestamp: August 01, 2022, 11:56:19 am
content: Likely relay contacts welded together. Inductive loads are much worse than resistive.https://www.hw-group.com/cs/podpora/how-not-to-destroy-a-relay

author: CaptDon
author_rank: Super Contributor
timestamp: August 01, 2022, 01:08:46 pm
content: It is obvious the solenoid must have been energized. Leakage current causing your relay to not release? Leakage current path to your solenoid, not enough current to release the door but enough to burn the solenoid? Once your car goes up in flames maybe the insurance company can help you figure it out? If you can build all of this circuitry into the door you are surely not too physically handicapped to just open the door using the normal method. Is this for someone else?

author: pete1111
author_rank: Contributor
timestamp: August 01, 2022, 01:24:08 pm
content: My insurance is aware of all modifications to the vehicle. It is also only third party so won't cost them anything if it does go up in smoke.Don't understand why your trying to pick a fight with me. I'm only looking for help from more experienced people.

author: david77
author_rank: Frequent Contributor
timestamp: August 01, 2022, 01:54:25 pm
content: Good start!

author: wraper
author_rank: Unknown
timestamp: August 01, 2022, 02:06:48 pm
content: Add thermal protection to solenoid. Get a thermal fuse like thishttps://www.tme.eu/en/details/tz-d-110/thermal-fuses/proffuse/, connect it in series with one wire of the solenoid and put it on top of the solenoid winding. Then wind heat resistant insulating tape over it to fix it in place. It will protect things from burning even if relay gets stuck in ON position.

author: madires
author_rank: Super Contributor
timestamp: August 01, 2022, 02:17:10 pm
content: A freewheeling diode is a good start for an inductive load. Is the relay rated for the load?

author: pete1111
author_rank: Contributor
timestamp: August 01, 2022, 02:47:48 pm
content: Thermal fuse is a really good idea I like it. Will add that on. Here is the wiring diagram picture attached. The relay is rated at 40amps.https://www.ebay.co.uk/itm/383890351244?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=2563ijqrsz6&sssrc=2349624&ssuid=akPLwrbvSw2&var=&widget_ver=artemis&media=COPY

author: madires
author_rank: Super Contributor
timestamp: August 01, 2022, 05:00:00 pm
content: No freewheeling diode in the diagram. And 40A for those small automotive relays?

author: Seekonk
author_rank: Super Contributor
timestamp: August 01, 2022, 06:09:45 pm
content: I love PTC fuses. Any time I've had a problem in a car electrical system one of them gets installed. I've used 4A ones in place of 40A fuses as they do have quite a delay.Another trick is to use a resistor in series with the solenoid. Solenoids take a third less energy once they pull in. Size resistor to get half current. Place several thousand uF across the resistor to provide short term pull in current.

author: inse
author_rank: Super Contributor
timestamp: August 01, 2022, 06:51:41 pm
content: A PTC or Polyfuse is definitely a good idea to prevent a catastrophe in case of failure, the trick is to select the right type.The next step is to find out why the solenoid burned off, for sure there must have been current flowing longer than specified.Many years ago, I retrofitted automatic locks in my car and made a circuit that only applied a specified pulse length to the actuator, independent of the control signal.

author: pete1111
author_rank: Contributor
timestamp: August 04, 2022, 12:27:26 pm
content: Here is what I come up with from all your help. See image attachedI have done a continuity check on the solenoid and it's shorted. So my guess there has been voltage stored in the solonoid and its over heated. Melted wires internally and when shorted burnt the fuse.. hsre as the Soleniod only revices 12v for about 1 second to pop the door open. Hopfully the diodes added should protect from this now?And a resistor to lower the voltage a little to the solenoid

author: inse
author_rank: Super Contributor
timestamp: August 04, 2022, 12:51:23 pm
content: A solenoid cannot store voltage, unfortunately you are on the wrong path here.The windings can only overheat if the actuator is powered for extended time.

author: mikerj
author_rank: Super Contributor
timestamp: August 04, 2022, 12:53:26 pm
content: The diode across the solenoid is the wrong way around! The other diode doesn't appear to be doing anything useful.

author: pete1111
author_rank: Contributor
timestamp: August 04, 2022, 12:54:52 pm
content: Maybe the relay got stuck ON and over time over heated the solonoid. However if the relay got stuck on the door would not stay closed. As the solonoid would be constantly pulling the door latch.

author: pete1111
author_rank: Contributor
timestamp: August 04, 2022, 12:57:14 pm
content: I added the diode near the relay as some car relays have them built in. So iv added one incase my relay does not have one.

author: Circlotron
author_rank: Super Contributor
timestamp: August 04, 2022, 01:13:21 pm
content: The diode across the solenoid should "point" toward the positive side. The second diode that is across the battery does absolutely nothing. What is the DC resistance of the solenoid? From that, work out the DC current that will flow in it with 14 volts applied. That same amount of current will flow in the diode across the solenoid for several milliseconds when the solenoid is released. Doesn't need to be a 1000V diode. 100V is plenty for this. Also, put a 1uF film cap directly across the relay contacts. That will greatly reduce the arcing of the contacts.

author: pete1111
author_rank: Contributor
timestamp: August 04, 2022, 02:10:44 pm
content: I will remove that diode then. Think this should all work OK now.hopfully no more burnt solonoids

author: Circlotron
author_rank: Super Contributor
timestamp: August 04, 2022, 11:41:05 pm
content: One more thing - having a diode across the relay coil is a bit of a mixed bag. You definitely need one if the coil is switched with a transistor, but not needed if it switched with a simple push button or other mechanical switch. The benefit of not having that diode across the coil is the relay releases faster and so the contacts separate quicker, further reducing arcing and particular, minimising the chances of sticking. The sudden jerk on the contacts serves to separate them better if they are microwelded, which is more common than you might think.

author: wraper
author_rank: Unknown
timestamp: August 05, 2022, 08:25:07 am
content: Quote from: Circlotron on August 04, 2022, 11:41:05 pmWell, the button experiences the same issue as relay contacts when driving an inductive load such as solenoid. So some sort of snubber is advisable, diode is just not the best one as it slows down relay release time significantly and thus may cause more contact wear due to arching. But you can use bidirectional TVS diode (or unidirectional + diode in series) with something like 20 or so volts clamping voltage. It will protect the button contacts but not affect relay release time significantly.

author: pete1111
author_rank: Contributor
timestamp: August 05, 2022, 11:21:58 am
content: Tha k you for your help. I do have this relay. It's for motorbikes to give the starter motor 12v .would this be much better than using a regular 40a relay?STARTER RELAY SOLENOID SOLONOID Fit For Suzuki SV650 LTF250 VL1500 LTZ250 VZ800

author: inse
author_rank: Super Contributor
timestamp: August 05, 2022, 11:52:08 am
content: First of all: noA relay contact has a problem with switching a capacitive load due to inrush current.There contact welding may occur.Switching off an inductive load will only create a high voltage, but the current does not exceed the static current.The spark only wears off the contacts, but the stored energy is very small.

author: wraper
author_rank: Unknown
timestamp: August 05, 2022, 12:01:36 pm
content: Quote from: inse on August 05, 2022, 11:52:08 amEnergy stored is not that small at all. Hence for inductive loads contact rating is reduced several times.

author: Circlotron
author_rank: Super Contributor
timestamp: August 05, 2022, 01:29:46 pm
content: Quote from: pete1111 on August 05, 2022, 11:21:58 amIt would be very useful if you could tell us the DC resistance of the solenoid. That way we can know how much current the relay has to handle.

author: madires
author_rank: Super Contributor
timestamp: August 05, 2022, 01:31:20 pm
content: Quote from: wraper on August 05, 2022, 08:25:07 amMore alternatives: RC snubber or MOV

author: pete1111
author_rank: Contributor
timestamp: August 05, 2022, 02:17:42 pm
content: Hopfully iv done this right?Also with engine on. Voltage be 14v engine off 12v

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 05, 2022, 02:22:28 pm
content: If OP used an similar product, somewhat in the region of 0,8

author: pete1111
author_rank: Contributor
timestamp: August 05, 2022, 02:22:44 pm
content: 5.0k

author: pete1111
author_rank: Contributor
timestamp: August 05, 2022, 02:24:04 pm
content: 5 ohmQuote from: Uunoctium on August 05, 2022, 02:22:28 pm

author: pete1111
author_rank: Contributor
timestamp: August 05, 2022, 02:27:20 pm
content: These are the solonoid I'm using STARTER RELAY SOLENOID SOLONOID Fit For Suzuki SV650NI wonder when I use thees when engine on. 14v this is the problem.

author: Circlotron
author_rank: Super Contributor
timestamp: August 05, 2022, 10:38:48 pm
content: 0.3 ohms is pretty low resistance and part of that reading may be from the meter leads. Starter solenoids often have a low resistance winding to provide a strong initial pull in and then switch to a higher resistance winding once fully in.Edit —> is that 0.3 ohms for a good solenoid or after you say it shorted?

author: Circlotron
author_rank: Super Contributor
timestamp: August 05, 2022, 11:34:04 pm
content: Another thing you could try is putting a car light globe, maybe a headlight globe, in series with the solenoid winding. The cold globe will allow almost full current to flow until the globe lights, then back off by a factor of 6 or 7. That should still be enough to keep the solenoid energised while giving a good deal of protection.

author: pete1111
author_rank: Contributor
timestamp: August 07, 2022, 03:30:59 pm
content: Could I connect a 5a switch to the relays coil negative to trigger the relay? Relqy coil draws just under 3 amps when activated.And just have the 12v permanently on into the coil with a 5A fuse. The bog solonoid draws 9A