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Author Topic: Please evaluate and educate. First post  (Read 1547 times)
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The software side looks non-trivial but definitely feasible. It is the hardware and power side that is uncertain. It's certainly possible to regulate mains voltage AC directly and plenty of resources showing how to achieve this using zero crossing and a triac, but it's not IMO a job for a novice. How much current are you trying to regulate at 240V? In your step-up transformer solution, do you have a smoothed 24 DC supply with sufficient current capability to transform up to that much mains voltage current so that you could generate the AC using an H-bridge? That would seem a lot easier and safer, if it's within the spec of a readily available H-bridge driver.

Trying to apply some lateral thinking to the problem, you may be able to tackle the problem another way and control the delivered weight by careful timing of the discharge without stopping the conveyer. I mean, you will know at any moment how quickly the stored weight is increasing, and you can assume that the time to discharge the complete load is fixed and known, so you could open the discharge gate at the point which would result in the correct weight being delivered at the point you close the gate. If you see what I mean!
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The software side looks non-trivial but definitely feasible. It is the hardware and power side that is uncertain. It's certainly possible to regulate mains voltage AC directly and plenty of resources showing how to achieve this using zero crossing and a triac, but it's not IMO a job for a novice.

I agree with you completely Peter, but when I see advice like this, I hear "Don't cook, leave it up to the chefs!" People learn by doing. Introducing someone to the right concepts points them in the right directions to begin learning. Usually THAT is the step that people are stuck on (just like I was with the PID issue you helped me with.)

I am not saying that you are wrong, I just keep seeing that type of advice here and it is troubling and could easily be perceived as insulting (it would be to me.) I don't consider myself stupid, a newbie, or even a novice simply because I ask a question. Sometimes I just need someone to point in the direction that I need to look to speed up the process of learning, to introduce me to a new concept I wasn't aware of, or to break my tunnel vision. But I know that I will need to go and learn about whatever is new on my own. Just need a nudge sometimes or a fresh perspective.

Personally, I find it much more respectful to approach helping people that way.

There may be cases where we tell someone that a triac is the proper route, and they simply go and plug one in without understanding it, but that is unavaoidable (and hopefully the last time they would try that!) A smart person will instead go and look at how a triac works and all the theory behind it, then either experiment SAFELY or come and ask more questions about parts they don't understand. So, to first assume that they wouldn't go and try to learn about the concept would assume they aren't a smart person.

Everybody is a newbie and a novice at some point. Nobody is born knowing how to connect and control a triac. The best time to learn is when you have something you need to apply it to.

To close off certain information because we assume that someone isn't going to understand it feels a bit arrogant to me. We are here to learn, to teach, and to help, right?

You are always helpful, so please don't think I am assuming that you intend it that way at all. Just would love for people to take a moment and think about how this would come across to them if someone were to say it to them.
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There may be cases where we tell someone that a triac is the proper route, and they simply go and plug one in without understanding it, but that is unavaoidable (and hopefully the last time they would try that!) A smart person will instead go and look at how a triac works and all the theory behind it, then either experiment SAFELY or come and ask more questions about parts they don't understand. So, to first assume that they wouldn't go and try to learn about the concept would assume they aren't a smart person.

Everybody is a newbie and a novice at some point. Nobody is born knowing how to connect and control a triac. The best time to learn is when you have something you need to apply it to.

While your points have do have some merit, I just feel you are making too many assumptions about what a given person of unknown knowledge and experience may go off and do with such advice.

 Because AC mains powered devices and circuits have large safety considerations for risks of possible injury, death, and/or major property damage, I have tried to adapt the rather arbitrary stance of "if you have to ask you probably shouldn't be messing with it".

 I try not to sound abusive or condensery about it and many time just won't post a response at all. But I do cringe at time at some of the suggestions or advice given out to what appears to be pretty inexperienced people.

 The internet and it's anonymity allows one to give out advice and recommendations with not much personal accountability of what it might lead to even with the best of intentions. I ask that people at least consider that.  

Lefty
« Last Edit: April 13, 2013, 10:51:34 am by retrolefty » Logged

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There may be cases where we tell someone that a triac is the proper route, and they simply go and plug one in without understanding it, but that is unavaoidable (and hopefully the last time they would try that!) A smart person will instead go and look at how a triac works and all the theory behind it, then either experiment SAFELY or come and ask more questions about parts they don't understand. So, to first assume that they wouldn't go and try to learn about the concept would assume they aren't a smart person.

Everybody is a newbie and a novice at some point. Nobody is born knowing how to connect and control a triac. The best time to learn is when you have something you need to apply it to.

While your points have do have some merit, I just feel you are making too many assumptions about what a given person of unknown knowledge and experience may go off and do with such advice.

 Because AC mains powered devices and circuits have large safety considerations for risks of possible injury, death, and/or major property damage, I have tried to adapt the rather arbitrary stance of "if you have to ask you probably shouldn't be messing with it".

 I try not to sound abusive or condensery about it and many time just won't post a response at all. But I do cringe at time at some of the suggestions or advice given out to what appears to be pretty inexperienced people.

 The internet and it's anonymity allows one to give out advice and recommendations with not much personal accountability of what it might lead to even with the best of intentions. I ask that people at least consider that. 

Lefty

That's because I am not anyone's mother. Their safety is THEIR concern. If they do not have concern for their own safety, absolutely nothing I say is going to save them. I think mentioning it may be dangerous is simply good enough and move on. But we are talking here about an example where no matter what, the user is playing with mains voltage. There is risk, period.

It's not as if I am telling him to plug one end of the mains voltage into pin 2 and the other into pin 4. There isn't enough information given to even harm himself because he will need to go research how to hook it up in the first place.

Honestly, I am not making any assumptions at all. I am giving information. They can do with whatever they want, including ignoring it completely. The only assumptions being made are assuming the person has a lack of common sense, skill or intellect, and honestly.... that is just arrogant.

I would completely disagree that just mentioning that a triac is the right tool for the job is dangerous in any way, shape, or form.

We need to really stop trying to be people's mothers around here. I'm sorry, but that really irritates me. It is condencending by its very nature whether that is intentional or not. The offered solution seems to be holding out information to people simply because we *think* they might be stupid enough to just jam a triac into an outlet because some guy on a forum mentioned the word? Seriously... think about it.

Where do we stop? Should we not talk about scissors because people might cut themselves? Maybe we should tell them that they need to hold the plastic end, not the metal end?
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Where do we stop?

Where we start and where we stop is a personal subjective choice we all make for ourselves, lets leave it at that.

Lefty
« Last Edit: April 13, 2013, 11:59:22 am by retrolefty » Logged

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Where do we stop?

Where we start and where we stop is a personal subjective choice we all make for ourselves, lets leave it at that.

Lefty

Fair enough smiley My personal and subjective choice is to give people the information they are asking for and leave it up to them as to what they do with it and not to assume the audience is incapable unless they tell me that they are.

If I give the wrong information, please correct me. I certainly don't know everything and I am not always right. But please don't tell me what information is safe to give or not. Is that fair to ask?
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Just need a nudge sometimes or a fresh perspective.

With respect, I think that's what I've given. I've named the technologies which would be needed to implement the solution, and warned that they are not easy to use. Anyone determined enough to press on anyway is now in a position to google the terms, get some reassurance that they are indeed a feasible way to solve the problem, and start researching how to use them. They might even go across to the Motors, Mechanics and Power section for practical advice to get it working. I've also suggested some possible alternative approaches which avoid the difficulty and dangers.

I don't agree that the right thing to do is to answer every question at face value. It is very common to get questions asking how to make the wrong solution work. The best advice then is to use a different solution. There are also plenty of people who ask for help on projects that they are clearly not competent to complete, and who show no sign of recognising the extent of the problem they're tackling. In that case I sincerely believe that the most helpful response is to warn them that they're opening a can of worms. And of course there are also people who tackle safety-critical projects and give no sign that they're competent to manage the risks. In that case I will make a personal judgement call that I'm not willing to be responsible for encouraging them to do something that is likely to put themselves or others in danger. I don't mean to imply that all these factors apply to this thread, I'm just trying to explain why there will often be situations where I could answer a question more directly, but choose not to.

You may not agree with that approach, but at the end of the day it is up to me to decide what advice or help I give, and you must do the same.
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You may not agree with that approach, but at the end of the day it is up to me to decide what advice or help I give, and you must do the same.

Absolutely. I apologize for getting snippy earlier. In general I was irritated with that sort of attitude (and I still stand by it) but looking at it later, I don't think your post was a good example of what irritated me. So, my apologies, Peter. I just managed to get my knickers in a bunch, that's all.

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Firstly thank you everyone for all your ideas.
I could just go buy something that does exactly what I want, it's a commercial thingI wish to achieve, I own the business! It's just much more rewarding to understand what's going on. Learning stuff when you are older.
I am very comfortable with high voltagJue, well not comfortable, scared would be better, but I have built a lot of HT supplies, up to 600v,  less than an amp of current tho.
Pretty sure that the conveyor will require very little current, way less than 2 amps. It looks like a big smoothing choke. I don't need 240v mains, that's what the variac is for. I60 is flat out and it will transport very slowly down  to about 10 volts.
Any way thanks got lots of ideas, I have even been considering the duct tape idea.
Thanks. Great first post experience
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"Increasing the strength of the vibration will only make your nuts bounce higher on the belt. Controlling the speed (frequency) of the vibration will increase the energy, which will make the nuts move along faster"

Actually I think that is backwards. The nuts don't go up and down. The pulse makes them jump. But also drives the bed forward. Up to a point, the higher they jump, the more forward the bed is when they land. Same thing for HZ, how often they "jump".
I just want them to jump less or lower for the final 10%. I have occasionally "tuned" it with a hammer, it doesn't seem a very demanding bit of gear. Currently controlled by what must be the first PLC in Australia. I will take a photo and post it. Size of a bar fridge and looks like someone thru a couple packs of spaghetti inside. Wires everywhere
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Controlling the high voltage AC as you're planning does seem the obvious approach, but if you aren't familiar with high voltage AC electronics you would have quite a learning curve (and all the associated safety issues to deal with).

Is it practical to just step the voltage down to give you a (constant) slower speed that you can select for the last little bit? I'm thinking of crude electrical solutions such as putting a mains voltage lamp or a rectifier diode or something in series with the driver coil to cut the speed right down, and shorting that out with a relay to go to full speed. Or switch the variac off and leave the coil driven by some other lower voltage transformer, or connect to a different tap on the variac, or something like that to enable you to select different supply voltages. I think trial and error is the only way to find out.
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OK.I have built a H bridge, switching 24v that is stepped up to 240v, to feed my conveyors. I am starting to get my head around "code". I am nearly 50!
I have some stuff i found that is similiar that switches the mosfets in push pull to look like 50/60hz,and I am waiting on a load cell amplifier, so in the mean time i want to get an idea about the code. this is the circuit I am using, it also has the switching code, with lots of other stuff i don't need
http://www.bristolwatch.com/ele/arduino_power_inverter.htm
 #define and int has me a bit confused (tho i "think" i understand now)
I am waiting on the load cell amplifier chip so i would like to substitute A pot for the load  cell. Same thing really but i cant understand how to do it.
Please take pity and show me how. Basically, use the pot to vary the interval  switching between MOSFET 1 and MOSFET 2 (pin 9 and 10).
then hopefully i will get a clue how to intergrate the loadcell.
I would be very greatfull for help with the code. The hardware side works, its the software side that I suck at.
I find lots of blinking led sketches but nothing for process control. I dont want to "walk before I crawl " but this seems a fantastic solution if some one can help me and my analogue brain
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