# Help me make a Solenoid Magnet

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#### reaver26

##### New Member
hello everyone, i'm currently planning to make my own solenoid Magnet as prototype on my project. this will serve as a "magnet lock" for my electronic door with pin code as access.

the reason im asking you experts on electronics its because i nearly burn down our house due to miss calculations on creating one and following various instructions over the web.

things at hand:

28-guage wire (100grams)

i'm planning to make a solenoid magnet that could work on 24volts(prototype only) which will represent as "magnet lock"

any suggestions with the wire that i have right now.. hope you could help me.

#### MrAl

##### Well-Known Member
Hi,

This will save you lots and lots of headaches.

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#### ke5frf

##### New Member
Cost of House: $150,000 Cost of commercially available solenoid:$50.00
Keeping your family and possessions safe: PRICELESS

What Mr. Al said, ditto.

To make what you want to make properly you honestly need a properly tooled machine shop as well as the wire for the coil. Or at least the ability to have it made for you.

Materials and time could EASILY exceed the cost of a prefabricated solenoid.

If you were building some little hobby project, like a small robot or something like that, it might be well worth it to build this type of thing simply because Its use and function would always be under controlled, observed conditions. A door lock would be energized, I assume, during times when you are away from home and asleep.

All of these reasons, along with the fact an insurance company will likely not honor your policy in the event of a fire are reasons to do it the right way.

##### Banned
There are any number of used electronics devices that you can get solenoids from. A toaster being the first one that comes to mind. Most simple toasters have a solenoid wired directly to a thermo couple which pops the lever that causes the toast to come up when it's been heated enough. They'll trigger on extremely low voltages and will provide incredible torque for brief pulses, perfect for a locking mechanism that doesn't need to actuate frequently.

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#### mbarazeen

##### Member

if you work by trial and error method.
you have 28SWG see whats its rating, select 80% of the rating as your design, then calculate the DC resistance of the solenoid to make that rated current.

ie: R= V/ 0.8XRating (only for DC application)

now your winding should have the same R as calculated(wind the coil until you measure this resistance value between terminals). so the flux your solenoid would produce is as number of turnsx current (0.8 rated)

since you have to stick on the resistance of the coil the size and the strength of the magnet may be too big or very small for your need.

in this case you have to slect another size of wire and rating...
repeat as above until you get the correct one to give good result.

to summerise.
the voltage and
the size of the coil decides everything for a particular solenoid.

other method

but in practice we do it in reverse...the 1st selection is the strength required, then the size of the solenoid(ampere turns) , then depends on the voltage the coil is being slected. to work on this you need more accurate information not like the 1st method.

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#### ke5frf

##### New Member
One question that did come to mind about your solenoid project, which is very elementary but could be CRITICAL to your outcome.

Solenoid coils are wound with enamel, resin, or some other insulation material. You mentioned almost burning down your home. Yep, that would happen if you used bare copper wire. Might be a pretty flame for a good bit!

Forgive me if this question sounds like it belittles your intelligence, but believe me we can't take anything for granted!

#### mneary

##### New Member
100g of AWG 28 wire is about 450 feet; and its resistance is about 30 ohms. At 24V, it will carry 0.8 A. It would dissipate 19 Watts, which will make it very hot. In open air, 28AWG should carry 0.2A, and should be derated for a coil.

SWG 28 is slightly heavier, decreasing the resistance accordingly, drawing more current and becoming even hotter.

It will burn your house down again.

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#### Njguy

##### Member
Please don't burn your house down. I would suggest using 21 gauge magnet wire. This wire can take 200 Degree C, give or take depending on the manufacturer. Making one that doesn't overheat too quickly is not hard. The homemade one in the picture uses 21 gauge wire and I used it on a 12v circuit. Never got hot. Felt like one of those heat packs from the pharmacy after an hour. Its not the strongest magnet in the world, but it's not terrible.

Cheap-yes
Efficient-definitely No
Safe-I say yes, but hesitate because you can never make things stupid proof
Gets the job done-yes
Easy to make-not really

Your best bet is too buy one. Picture is just an example, I'm guessing yours would be smaller.

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#### mneary

##### New Member
Heavier wire helps with the current handling capability but you need a lot of it to have a resistance that keeps the current drain reasonable. Lower voltage helps, too.

For example, a solenoid with AWG 21 wire which draws 500mA from 12V, weighs almost 1kg.

##### New Member
Determine your needed resistance that will
keep the coil cool (from whatever gauge wire),
and then according to your size limitations,
pick the smallest gauge wire and use the amount
of it (length) that the ohms per length matches.
This will give you the same current draw as any
other larger gauge wire, take less space and
cost less, as well as allowing it to short & break
without it first heating up an incredible amount.
You'll be much less likely to get to the point of
the wire actually sparking.

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#### reaver26

##### New Member
One question that did come to mind about your solenoid project, which is very elementary but could be CRITICAL to your outcome.

Solenoid coils are wound with enamel, resin, or some other insulation material. You mentioned almost burning down your home. Yep, that would happen if you used bare copper wire. Might be a pretty flame for a good bit!

Forgive me if this question sounds like it belittles your intelligence, but believe me we can't take anything for granted!

insulated wire. currently i was able to make my improvised solenoid under 12volts but still its not enough to run my goal "magnetic plunger"

#### reaver26

##### New Member
update on my project:

ive created a SOLENOID LOCK using a #25 magnet wire(150grams) enough to sustain heat even under 24hrs of use. under 220volts(AC)
- i used the idea of a magnetic conductor of machine which it has a movable core

ive use #28 magnet wire(100grams) for my buzzer

#### mbarazeen

##### Member
calculation for AC solenoid are different from DC, for a same voltage AC requires less number of turns.

#### MrAl

##### Well-Known Member
update on my project:

ive created a SOLENOID LOCK using a #25 magnet wire(150grams) enough to sustain heat even under 24hrs of use. under 220volts(AC)
- i used the idea of a magnetic conductor of machine which it has a movable core

ive use #28 magnet wire(100grams) for my buzzer

Hi there,

Sounds very interesting. I wouldnt mind seeing a photograph of that
construction. What did you use for the core and the plunger?

#### reaver26

##### New Member
update on my project:

ive created a SOLENOID LOCK using a #25 magnet wire(150grams) enough to sustain heat even under 24hrs of use. under 220volts(AC)
- i used the idea of a magnetic conductor of machine which it has a movable core

ive use #28 magnet wire(100grams) for my buzzer

Sorry for the CLAIM:

its still doesn't work.

materials used:
10mm in diameter bolt (steel bolt)
250grams of AWG
220AC power source

it gains very high temperature in less than 2mins. the bolt(plunger) is very hot also(steel)

any suggestions?

thank you

#### shortbus=

##### Banned
Double the length of the wire.

#### mneary

##### New Member
Decrease the wire diameter.

This sounds counter intuitive, but an equal length of thinner wire has a higher resistance, and carries less current as a result. The power decreases as ((I^2)*R). If R doubles, then I*2 decreases by a factor of 4. The net result is double the resistance = 1/2 the power.

If you use the same amount of wire (by weight) then the resistance increases even more.

#### MrAl

##### Well-Known Member
Hi again,

Can we see a picture of this thing? Thanks.

#### reaver26

##### New Member

thank you for the suggestion but here in the philippines its really hard to find a commercial one.

im hoping to create this kind of solenoid which it can either be PUSH or PULL
motion or BOTH

like this one:
https://music.columbia.edu/~douglas/classes/motor_mania/sol4.jpg

here is a photo of my homemade solenoid plunger(still not working as it planned)

i hope someone can help me make a solenoid plunger with either PULL or PUSH action or much better BOTH.

thank you

materials used:

10mm diameter 6inches Steel Bolt
aluminum (the magnetic wire is turned)
#25 AWG 250grams

problem arises:
core taken so much heat at lesser time
Coil conducted heat which it should not be

options: going to use a insulation spray and baked it 12hours or more
or any suggestions.

goal:
to be able to create a soleniod plunger either PUSH or PULL action or BOTH
can last more than 24hours working and wont heat up to the limits

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