Solenoid with 555 timer question

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ketem13
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Solenoid with 555 timer question

Post by ketem13 » Tue Jan 12, 2021 6:08 am

Question regarding the schematic I drew:
solenoid 555.jpg
While tested and seems to work fine, I wanted to ask if it make sense to seperate the power of the solenoid (+12V) from the power of the 555 IC (+9V) - I only connect the Ground of both powers.

It seems the solenoid become pretty hot after a while - does it happen usually ?
any advice what to do with the cv pin of the 555 timer (pin 5) ?
would you add/change some of the components ?

Thanks

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Re: Solenoid with 555 timer question

Post by guest » Tue Jan 12, 2021 6:18 am

looks good. seperating the powersupplies is a good idea, as the soleniod will put a lot of noise on whatever rail its on, so some form of isolation helps. the CV pin of the 555 usually gets a 0.1uF cap, buts not strictly necessary. and solenoids do tend to get warm after a while, some more than others. you can check the datasheet for your solenoid to see if its rated for continuous use.

youll want another diode across the solenoid itself.
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Re: Solenoid with 555 timer question

Post by ketem13 » Tue Jan 12, 2021 6:21 am

guest wrote:
Tue Jan 12, 2021 6:18 am
looks good. seperating the powersupplies is a good idea, as the soleniod will put a lot of noise on whatever rail its on, so some form of isolation helps. the CV pin of the 555 usually gets a 0.1uF cap, buts not strictly necessary. and solenoids do tend to get warm after a while, some more than others. you can check the datasheet for your solenoid to see if its rated for continuous use.

youll want another diode across the solenoid itself.
Thanks, I will add another diode across the solenoid.
I bought a few of those solenoide from ebay and I did not find any datasheet. I do remember it was rating to work with 9v-12v supply...
btw - the solenoid lugs have a polarity ? does it matter which lug goes to +V and which to the collector lug of the tip120?

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Re: Solenoid with 555 timer question

Post by guest » Tue Jan 12, 2021 6:29 am

no, the generally dont have a polarity. i seem to recall there are some latching kinds that due, as they use magnets instead of just a lug of steel, but the regular sort work either way. there are also AC and DC solenoids, and an AC type might get overheated if run off DC. but, in general, they do get warm, and its fine, as long as its not hot to the touch. if you can hold it in your hand indefinitely, then its not too hot. if you cant, then you might want to back the current down a bit, or not run it as often.
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Re: Solenoid with 555 timer question

Post by ketem13 » Tue Jan 12, 2021 6:31 am

guest wrote:
Tue Jan 12, 2021 6:29 am
no, the generally dont have a polarity. i seem to recall there are some latching kinds that due, as they use magnets instead of just a lug of steel, but the regular sort work either way. there are also AC and DC solenoids, and an AC type might get overheated if run off DC. but, in general, they do get warm, and its fine, as long as its not hot to the touch. if you can hold it in your hand indefinitely, then its not too hot. if you cant, then you might want to back the current down a bit, or not run it as often.
backing the current is mean to add a resistor between the +12V and the solenoid?(1k?)

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Re: Solenoid with 555 timer question

Post by ketem13 » Tue Jan 12, 2021 6:41 am

btw - I just try the solenoid with the most simple 40106:
Screen Shot 2021-01-12 at 1.41.10 PM.png
Seems to work great as well!

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Re: Solenoid with 555 timer question

Post by guest » Tue Jan 12, 2021 6:45 am

if you need to reduce current, then a resistor in series will help (probably on the order of 100ohms or less), or going to a lower supply voltage. if you use a resistor, it might get hot as well.
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Re: Solenoid with 555 timer question

Post by Don T » Tue Jan 12, 2021 4:49 pm

Sometimes adding a capacitor to the "powered end" of the solenoid, going to ground, is helpful as well. See these for info:

https://electronics.stackexchange.com/q ... id-circuit

A variant with a good explanation for why:

https://www.electronicdesign.com/techno ... uff-anyhow

Now, most of the solenoid driver circuits I have seen that use caps were for solenoids in AC circuits, or circuits that were using really massive solenoids with heavy currents involved.

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