I recently purchased a solenoid for my car which controls the flow of methanol. After seconds of use it melted. It got so hot that I burned my hand when trying to move it and the solder inside melted with a wire falling off.

I contacted the seller and they told me I had used the solenoid with a controller that was incompatible.

The thing is this is a 12 volt solenoid, rated at 4.75 amps. My original solenoid was only 12v and 1.5 amps.
I do not understand how the solenoid could melt, unless it was defective?

Surely I could connect the solenoid directly to the 12v car battery for 3 seconds and then disconnect it and it would be ok. Wouldn't it only draw the 4.75 amps? That is not what I did, but I don't believe it should melt.

I look forward to hearing peoples thoughts. So we are talking 12 volts DC.

 

Solenoids are not necessarily rated for continuous use.
See the 'Duty Cycle' section here: http://docs-europe.electrocomponents.com/webdocs/001b/0900766b8001b732.pdf

 

Solenoids are not necessarily rated for continuous use.
See the 'Duty Cycle' section here: http://docs-europe.electrocomponents.com/webdocs/001b/0900766b8001b732.pdf

Yes thanks, I do understand that. The solenoid is not supposed to be used more than 15 seconds. My wide open pull was 3 seconds.
I'd expect the solenoid could take 3 seconds at 100% duty. It's a normally closed solenoid.

 

So, unless you hooked it up wrong it has to be defective. The 4.75 is the load current and the coil gets connected to 12 volts when the selonoid is on. I am guessing it's the 12 volt wire that melted ? There isn't a polarity with the 12 volts is there?

 

I recently purchased a solenoid for my car which controls the flow of methanol. After seconds of use it melted. It got so hot that I burned my hand when trying to move it and the solder inside melted with a wire falling off.

When you say, "controls the flow of methanol." Are you calling a solenoid valve just a solenoid? Many solenoid valves require the actual movement of the controlled fluid to cool them when in use. Especially small ones in car systems. So if you just wired the item to a battery it could melt down.

 

So, unless you hooked it up wrong it has to be defective. The 4.75 is the load current and the coil gets connected to 12 volts when the selonoid is on. I am guessing it's the 12 volt wire that melted ? There isn't a polarity with the 12 volts is there?

Yeah the solenoid doesn't care which way round it is wired. Just a 12 volt unit.

 

When you say, "controls the flow of methanol." Are you calling a solenoid valve just a solenoid? Many solenoid valves require the actual movement of the controlled fluid to cool them when in use. Especially small ones in car systems. So if you just wired the item to a battery it could melt down.

so basically the pump comes on and builds pressure. Then the solenoid opens to allow it to flow. Once off it closes and prevents methanol from being sucked out of the tank by the manifold vacuum when not under boost.
The meth was flowing which I can see from fuel trims readings. Gets richer and richer.

I believe the unit was basically defective but I'm checking as the seller doesn't want to refund me the cost of the item.
I'm not an electronics expert but I believe I know enough here.

 

I believe the unit was basically defective but I'm checking as the seller doesn't want to refund me the cost of the item.

Things do fail catastrophically.

I had some solenoid that controlled fuel flow to the carburetor on my riding lawn mower fail while I was mowing. Smoke was coming from under the hood; I shut it off and got off. Luckily, nothing burst into flames. When the fuel pump died because someone kept cranking it repeatedly when it was out of fuel, I stopped using it and parked it under a tree.

 

In automotive use it might see 14 V instead of 12, for a power dissipation of almost 78 W, which is a lot unless there is significant "thermal mass" to the coil. Still, 3 seconds is a small fraction of the nominal allowable ON time.

Can you post a photo or a link so we can get an idea of the physical structure?

 

Yeah the solenoid doesn't care which way round it is wired. Just a 12 volt unit.

If your solenoid has a built-in protection flyback diode, it will definitely care which way it is connected with respect to polarity.

 

If your solenoid has a built-in protection flyback diode, it will definitely care which way it is connected with respect to polarity.

Yes understood but there can't be a diode as both wires are black and exactly the same. Instructions are that it can be connected either way round. The coil simply energises.

I suppose it is possible that it saw 14v when the alternator was on but meth systems are designed for that. It's actually a bit beneficial as the pump runs faster on the higher voltage.

The solenoids are only small

 

Solenoid acts like so:

 

Solenoids don't care which way around they're connected; they always pull "in".

I'd say there was a short in the coil to start with and you just ran a bunch of current into it, melting it. Look at the spec's of the thing and see if they tell you the resistance of the coil. Ohm's law from there...

It's always a good idea to have some kind of current limiting in place for anything connected directly to a battery. A simple fuse would have been of good use here...

Mike Tripoli

 

Without anything for scale, it is a bit hard to tell what the size is, but going by the wires, I'm guessing the ports are 1/8" NPT and the body is about an inch/2.5 cm in diameter.

It is probably rated for 12 volts "actual", so automotive "12 volts" might be pushing to the maximum permissible voltage. Even at exactly 12 volts, 4.75 A, 57 W is an awful lot of power for a coil that size. 5 W continuously would make it quite warm. But once again, even with 14 V, I have my doubts about a 3 second activation being enough to kill it. Is there any chance that the controller that had been used at 1.5 A failed short-circuit and kept it powered for too long? A transistor might fail quite quickly at three times the expected current, and failure mode in transistors is usually short-circuit, at least initially.

That design won't get very much cooling from flow. The end of the coil adjacent to the valve body would get a little cooling, but the other end of the coil would get next to none. In the valves like that that I have seen, the coil is on a bobbin that just slides rather loosely in place and, with the cover, is held there with the nut at then end of the actuator tube.

Is it rated for some very high pressure? That is a remarkably powerful coil for a small valve.

I've seen polarized solenoid valves designed to mount on a manifold plate. There are "latching" types that are polarity-dependent. I've never seen a conventional type in that style that was polarized, but I've only ever seen a couple dozen types up close. A polarized type would not have both leads the same color.

 

Yeah the solenoid doesn't care which way round it is wired. Just a 12 volt unit.

It might be that the solenoid has an internal diode for surge limiting. I once had that problem with relays and it took a long time for the poor service tech to discover the problem. AND, constant duty for a DC solenoid intended to be used with a PWM controller will usually burn them up. 12 volts and 4.75 amps is a lot of watts. In addition, that may have been an AC solenoid. Much lower DC resistance and so they heat up very fast on DC.

 

The solenoid is rated for up to 300 psi. The base of the solenoid is a solid block of aluminium and water and methanol will be flowing through it at about 0.7 litres per minute.
I do wonder if there was a short circuit

 

It may have been defective, although I think that I read a comment where he make claimed an incorrect diver was used. If it required a specific driver then it could have been any sort of drive required. Some solenoids need a very brief full power pulse to operate and then they hold in with far less current.