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555 monostable timer question.

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Eddie6775

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Hello all, On a 555 one shot, I understand it only takes a pulse to trigger the "timing" sequence. What happens if the trigger is held down for a long time? Will the circuit reset it's self and cycle again?

I realize this it a trivial question, but my bread board is occupied with another circuit at the moment or otherwise I'd tinker with it. :rolleyes: I am SUCH a newb....
 

jpanhalt

Well-Known Member
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Eddie6775

New Member
Hmm. okay, I sort of understand. I'll have to try it. I guess I should explain what I'm trying to accomplish.

I want to operate a small starter motor for a sterling engine. in short my finished circuit would sense when the hot side of the engine is at operating temperature and give the fly wheel a spin. The thing I was afraid of was having the starter motor engage after the engine has already started running. I need it to be hands free because this motor in question will be enclosed. having to spin the fly wheel would be a royal pain.

Thank you jpanhalt!
 

jpanhalt

Well-Known Member
Most Helpful Member
Can you post your whole circuit or planned circuit? There are several members on ETO who are very good at doing simulations with LTSpice. Even I can hobble along a little with it. That may save you a lot of time and effort on the breadboard.

As for the 555, information about triggering is in most of the datasheets, but there is an application note from Philips that I usually go to, because it is easy reading. It also has a few little tidbits that are not in many datasheets. The note is AN170, but last time I checked, Philips had taken it down from its site. I uploaded it to ETO here: https://www.electro-tech-online.com/attachments/555an-pdf.52952/
If you are still concerned about continuous triggering, then you can AC couple your trigger as shown in Figure 3 of that note:
upload_2013-12-27_13-40-44.png


How big is your Stirling engine going to be? I used to belong to a Yahoo group, but it seemed mostly talk and demonstration. Very few people made engines that could do work. That was a few years ago. Has anyone gotten to 1/2 HP or more with a reasonable size?

Sorry to go a little OT, but I do find heat engines interesting.

John
 

large_ghostman

Well-Known Member
Most Helpful Member
Stirling engines are amazing, when I am older and my metal work skill's match my ambition, I would love to make one! Good luck with this, please keep us updated
 

Eddie6775

New Member
Hi, I'm glad I'm not the only one interested in Stirlings here! I haven't built the engine yet, but I plan on a simple alpha type like the one in the link.
https://www.ohio.edu/mechanical/stirling/engines/engines.html
I'll be using the cnc router that I'm almost done building to make some of the wooden patterns for the foundry work so....gotta finish the machine first..lol

As for the circuit, I was going to use a thermistor/resistor voltage divider and comparator to trigger the 555 one shot. I later talked to the guy at the little electronics store near me and he showed me over to a rack of parts I hadn't thought of using and made life simple, so my plans changed. Ill bread board it tonight and post; but here's the theory....

On the hot side of the engine, there will be mounted a normally open electric disc thermostat. for tinkering purposes I bought the 180F part (They come in several different temperature ranges). When the hot side of the engine reaches it's pre determined operating temperature, (in this argument 180F) the thermostat closes, and becomes the switch to the 555 one shot it's self I believe it's pin 4.(?). no need for a comparator circuit! And since the 555 mono stable will only discharge once per trigger, it wont reset until the engine has cooled down and heated back up again. I plan to put a push button switch in the circuit as well in the event of a false start. I'm also experimenting with different capacitors to delay the start time in the event that say....the operating temperature is higher than 180. The delay would give the hot side more heat up time. On the out put side of the 555, I plan to trigger a relay witch in turn will power up a small bendix type starter motor and thus give the engine that spin you normally have to be present for. Now, I've not done my homework on wich relay to choose yet, but that's the general idea of the circuit.

I hope this is making sense, I'm a machinist and a mechanic by nature but electronics is still kind of a mystery to me.

I'm always open to suggestions!

As a matter of the off topic interest: Once this engine in question is running, I hope to kill some of my power bill with it and maybe supplement my hot water. I'm also tinkering with auto tracking solar collectors as a heat source for the engine and water ;)
 

jpanhalt

Well-Known Member
Most Helpful Member
Pin 4 is "reset." It is usually held high; although, some retriggerable designs use it. This is where posting a schematic becomes really important. Once you get something bread boarded, please post it.

John
 

Eddie6775

New Member
Can you post your whole circuit or planned circuit? There are several members on ETO who are very good at doing simulations with LTSpice. Even I can hobble along a little with it. That may save you a lot of time and effort on the breadboard.

As for the 555, information about triggering is in most of the datasheets, but there is an application note from Philips that I usually go to, because it is easy reading. It also has a few little tidbits that are not in many datasheets. The note is AN170, but last time I checked, Philips had taken it down from its site. I uploaded it to ETO here: https://www.electro-tech-online.com/attachments/555an-pdf.52952/
If you are still concerned about continuous triggering, then you can AC couple your trigger as shown in Figure 3 of that note:
View attachment 83069

How big is your Stirling engine going to be? I used to belong to a Yahoo group, but it seemed mostly talk and demonstration. Very few people made engines that could do work. That was a few years ago. Has anyone gotten to 1/2 HP or more with a reasonable size?

Sorry to go a little OT, but I do find heat engines interesting.

John
Hi John, I'm not sure of the size yet, but I'm trying for 5 or more horse power. It's probably going to end up pretty big. My intent is to make 6 alpha type engines and join them in tandem. copper coils would deliver heat from large solar collectors and all of this will be enclosed in a 10 x 20 foot green house. I've got room to run here in the sticks.... The reason I'm working on the circuitry first is because its the hardest part to wrap my head around. :$
 

jpanhalt

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Most Helpful Member
5 HP, wow! That would be great. I hope you will put a link here when you get it running. As mentioned earlier, I don't follow that Yahoo group anymore. I need only about 1/2 HP or so of electrical power to run the circulator for my dual-source (outside wood burner + propane) heating system.

John
 

alec_t

Well-Known Member
Most Helpful Member
The thing I was afraid of was having the starter motor engage after the engine has already started running.
Presumably you will also want to switch off the power to the starter motor immediately the engine gets running? Or are you going to keep it powered for a fixed time (set by the monostable) regardless of whether the engine is running or not, and rely on the Bendix over-run?
 

Eddie6775

New Member
5 HP, wow! That would be great. I hope you will put a link here when you get it running. As mentioned earlier, I don't follow that Yahoo group anymore. I need only about 1/2 HP or so of electrical power to run the circulator for my dual-source (outside wood burner + propane) heating system.

John
Yes, I think 5hp although an ambitious undertaking can be had. ....with allot of heat. As for the circuit, I built a monostable as per Tony Vanroon's tutorial to see if it would work and it did but the led on the breadboard only timed out once I dis connected the trigger from ground. And yeah you were rite, Pin 2. :) I'm thinking of ways to over come this, and re checking the circuit for any mistake I might have made.
Here's the circuit I just tested:
upload_2013-12-30_11-47-4.jpeg


This circuit is on his web site.
 

Eddie6775

New Member
Presumably you will also want to switch off the power to the starter motor immediately the engine gets running? Or are you going to keep it powered for a fixed time (set by the monostable) regardless of whether the engine is running or not, and rely on the Bendix over-run?
Hi, what I'm thinking is to engage the motor for just one second and rely on the over run. Stirlings take a couple of minutes to reach full speed so I thing it will work. If not, than I'll have to beat my head into the possibility of using a hall sensor or something similar to "let the starter circuit know it's running". The challenge I've created for my self now is how to send just a pulse from the thermostat instead of a steady voltage....

I could be wrong though, the circuit I built was the first one I found.

I wonder how it would work if I used a circuit similar to a camera flash......Hmm. Google time.
 

Eddie6775

New Member
Ok John, You can tell me you told me so now,:cool:
upload_2013-12-30_13-14-27.jpeg


I built the circuit on the left at first, but the one on the rite is what I wanted. Every time I grounded the 0.1 uf capacitor, my led turned on and off for the same duration weather I disconnected the wire or not. I then used my thermostat as my switch (nte-dtc180) and held a lighter near it until it triggered. Putting a larger capacitor from pins 6 and 7 to ground increased the time the led (in leu of the relay) was on. So now its just a matter of deciding what size capacitor to use in my circuit. That will depend on how the engine turns out. but now I know how to start it and never have to touch it!

More to come, Thanks!

Note, The circuit came from the link above for any one who wants an explanation of the difference.:)
 
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