17 replies to this topic

[TKOTC]

I am working on a circuit that will be able to drive a 115VAC half wave vibratory feeder using the Netduino. I attached the circuit diagram to the post. As I am not realy experienced in this I was wonding if someone would be able to have a look at the circuit I designed and provide feedback to ensure that the circuit is sound. I really do not feel like killing my Netduino (or myself) by connecting to mains... I know that I lack fuses in the design as well as values for components, I will calculate those later. Any help with this is much appreciated. Regards

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[Dan Morphis]

I am working on a circuit that will be able to drive a 115VAC half wave vibratory feeder using the Netduino. I attached the circuit diagram to the post.

As I am not realy experienced in this I was wonding if someone would be able to have a look at the circuit I designed and provide feedback to ensure that the circuit is sound. I really do not feel like killing my Netduino (or myself) by connecting to mains... I know that I lack fuses in the design as well as values for components, I will calculate those later.

Any help with this is much appreciated.

Regards

From your schematic it looks like you are using an optoisolator to then switch some stuff to then turn on the mains. Is that correct? If thats the case, you should look at the Arduino relay circuit.

-dan

[TKOTC]

From your schematic it looks like you are using an optoisolator to then switch some stuff to then turn on the mains. Is that correct? If thats the case, you should look at the Arduino relay circuit.

-dan

Your assumption is correct, sorry for the vague-ness of the post. I am planning on using an optoisolator to protect the Netduino from the mains. The IGBT to control the power going to the vibratory feeder, and the diodes to make the 1/2 wave required to drive the vibratory feeder.

I actually had a look at the Arduino Relay circuit but wanted to use an IGBT for cost and efficiency.

As stated, I am still new to this so I might be way off base but by using an SCR doesn't that introduce other issues such as inrush currents, needing to put a freewheel diode on the circut, and mechanical noise from switching, etc..?

For this application I figure a MOSFET or IGBT would be the most appropriate form of controlling power.

Again, I am new to this so I could be off base.

Regards.

[Mario Vernari]

Dan helped me to understand better what are you going to do.
So, you want to switch a particular load by an output from your Netduino, and this load is powered by the 115VAC main.
The circuit of your picture is wrong, because you are working with AC. However, the basic idea to opto-isolate is surely right.
Here is a simple circuit (5th page) that should work. When you want to switch AC, often the solution is the TRIAC.
Hope this helps.

OFF TOPIC:
A question for whom of you is English is mother tongue. Why you say "insulate", then "opto-isolate" (and not "opto-insulate")?
Thanks a lot.
Cheers

[Nevyn]

OFF TOPIC:
A question for whom of you is English is mother tongue. Why you say "insulate", then "opto-isolate" (and not "opto-insulate")?

I think it will be because of a subtle difference between the definition of insulate and isolate. In this case, insulate implies a physical barrier between two or more physical entities. Isolate implies a total separation.

There is no physical connection between the two sides of the circuit so they are isolated.

Regards,
Mark

[Bill E.]

I haven't seen any responses to this post by TKOTC since Aug. 17. I hope you are allright? I am always worried when someone wants to start using the mains AC power from a wall outlet in a project. Call me a worry-wort! I have a relative who is building a "device" that distills fermented stuff (whatever it may be!) into, for the sake of this post, "alternate fuel". Use your imagination and you can figure out what it is. He needed to control a water heater heating element, a 1500 to 3500 watt device, and was looking for advice. I did give him some - reluctantly. He is still with us!! There is available, on the web, a ton of posts about building a "device" for distilling fermented stuff. The majority talk about using a triac, a potentiometer, capacitors, lugs, etc. That is a good way to do it. The problem I had was the lack of warnings and cautions to the reader of getting their butt fried by 220VAC! Or 115VAC for that matter. There was very little warning of using an "isolated tab" triac, et al. So I send this advice with a degree of consternation. An SCR is an ideal device for the half-wave vibrator. You do, however, need a method to "remove" the electrical circuit in order to shut an SCR off. You cannot do it via the gate terminal. You will need an intermediate "switch", or equivalent, to do that. MOSFETs won't work like you think when switching AC. The IGBT is, for lack of arguement, nothing more than a power MOSFET with a bipolar transistor controlling its gate. You could use a triac followed by a rectifier (big enough to handle your load(s)) to run the vibrator. A triac can be turned on and off with its gate. Use the opto-isolator with the netduino. Please, PLEASE be careful!! I cannot scare you enough about working with mains. If you were an electrician, or a disciplined timkerer, well, then you know the way to do this and, possibly, how it feels to get knocked on your keester by mains voltage. But for a beginner, I am "discouraging" you to mess with this without having a CPR qualified partner nearby. I am SERIOUS about this! Mains AC is not to be fooled with! I am speaking from experiene. And, yes, I am CPR qualified. If anyone on this forum disagrees then you are: 1. Lucky 2. Never fooled with mains AC 3. An experienced Electrician that doesn't care about anyone else 4. Misinformed about the pain, physical mutilation, agony from electrical burns 5. Add your own description By itself, a Netduino cannot harm you. You can put your tounge on it and it will only (probably) stop working. No big deal. You won't feel a thing. Playing with high voltage (anything over 32 VAC/VDC is high voltage to me!) will bite you! Bad. And, you do NOT want to experience that. It takes less than (if I remember correctly) 8 ma of current to the heart to stop it. Your mains circuit breaker is normally 10 or 15 AMPS! Enough said. Be careful. BE CAREFUL!! I don't want to hear about anyone, eecially on this forum, being hurt by messing with something that they don't understand. I would like a similar post to ALL members warning about fooling around with household AC. Again, you do not know what you are dealng with if you are an amateur. Bad mojo. Ask a pro or a friend experienced with AC. PLEASE!! All my best regards, Bill

[Mario Vernari]

Wow, Bill, your post is amazing!
I totally agree with you about the danger on working with (relatively) high voltage. I didn't advice that guy on my previous post, and that was a big mistake!

Nothing in contradiction to your long post, just taking advantage to point so considerations...

TRIAC- the most common semiconductor for controlling the main AC is surely the triac, but...it's a *very* long time that the triac is disallowed. Here's why. If you take a look at the resulting waveform (here is the link to the italian page), it is anything but a sine. That did not like at all at the Electric Companies, because creates a ton of huge harmonics along the main wiring. Of course, we should consider thousands of triac in the city...
All that harmonics were wasting a lot of energy, and -if you mean- a long cable carrying the main is much like an antenna, so ton of emissions...
That's because -for example- it's disallowed the traditional rectifier in favor of the most modern switch-mode power supplies.
So, if you were control a simple heating resistor, I would use an on-off techinque via a solid-state relay (which is a triac, but without partialization).

220/115VAC- you know, here in EU we use 230V as AC mains. It's been about 40 years that the 125VAC is totally disappeared, at least in northern Italy AFAIK.
There are two reasons on choosing the 230 over the lower one:

• the current involved along the wiring is about the half, so halved are also the wasted energy (and emissions);
• it seems that the 230VAC is less dangerous than the 110VAC: the higher voltage makes your body react faster, thus your finger leaves the hot point quicker. Don't ask me more because I am not a medic (or whoever knows that).

AC MAINS- it's about 30 years, here in Italy, that in any house/office it must be installed a safety switch. In US that's not mandatory? Basically it is a switch (normally closed), that opens as soon the difference of current between the hot and the neutral are above 30mA. This would be the typical situation when you touch accidentally the hot wire, but all the current flowing through your body is going toward ground. That makes the switch opens.
It works very well, and you almost don't feel anything: too fast to feel the shock.

Cheers

[Dan Morphis]

AC MAINS- it's about 30 years, here in Italy, that in any house/office it must be installed a safety switch. In US that's not mandatory? Basically it is a switch (normally closed), that opens as soon the difference of current between the hot and the neutral are above 30mA. This would be the typical situation when you touch accidentally the hot wire, but all the current flowing through your body is going toward ground. That makes the switch opens.
It works very well, and you almost don't feel anything: too fast to feel the shock.

Cheers

Mario,
We have much the same regulation here, except it doesn't apply to all outlets. Outlets in a wet location (WC/bathroom, kitchen) and exterior are required to be GFCI (the technical name for the "safety switch" you mentioned), or protected by an upstream GFCI or GFCI breaker.

On the one hand they are nice to keep you from frying yourself, on the other hand they can be a complete pain in the butt. I have to replace the exterior outlet I plug my car into in the winter once every year or so because it goes "soft" due to the draw of the block heater on my car.

-dan

[Bill E.]

Thanks for the kind comment, Mario. Yes, I thought very hard about what I wanted to say in that reply of mine. I cannot emphasize enough about being very respectful of household mains voltage. Enough said about that! Dan, I feel your pain! I had to chuckle about the engine block heater! Your bio doesn't say where you are at but I remember well the "dipstick heater" from my youth in Rhode Island! What are they? 100W? Not much good when the temp is at -20 degrees... Good points about the safety switch, aka GFI (or Ground Fault Interruptor). But it only works when the wiring is correct: in the U.S., the AC Neutral to the large, wider slot, the AC Line to the shorter slot, and a GROUND to the half-moon slot. Get the line & neutral reversed and your at risk - even with a GFI. When I lived in Germany, the locations were determined by relative location to the ground lug. It is easy either way to mis-wire by a "do-it-yourselfer". Regards.

[Dan Morphis]

Dan, I feel your pain! I had to chuckle about the engine block heater! Your bio doesn't say where you are at but I remember well the "dipstick heater" from my youth in Rhode Island! What are they? 100W? Not much good when the temp is at -20 degrees...

Good points about the safety switch, aka GFI (or Ground Fault Interruptor). But it only works when the wiring is correct: in the U.S., the AC Neutral to the large, wider slot, the AC Line to the shorter slot, and a GROUND to the half-moon slot. Get the line & neutral reversed and your at risk - even with a GFI. When I lived in Germany, the locations were determined by relative location to the ground lug. It is easy either way to mis-wire by a "do-it-yourselfer".

Bill,
I live in Anchorage, Alaska, USA (Yes, some people forget we are part of the US :{). Normally temps get down to about 20F, but at times to -20F.

The way I remember how to wire up an outlet is "B2B - Black to Brass." All the outlets I've dealt with all have a brass and an aluminum side corresponding to hot (or black) and neutral (or white).

-dan

[Bill E.]

Dan, I am humbled. Anchorage, eh? Makes my winters in R.I. seem like the Bahamas. On my bucket list I have "trip to Alaska". I hear many good things about your beautiful state. I will get there someday. You are spot-on on the colors. "Black-on-Brass" "White-on_silver". When wired corerctly WHITE & GREEN cannot kill you. But, Never trust the colors. Am I being a PITA about this subject? Regards, Bill

[Dan Morphis]

Dan,
I am humbled.
Anchorage, eh? Makes my winters in R.I. seem like the Bahamas.

On my bucket list I have "trip to Alaska". I hear many good things about your beautiful state. I will get there someday.

You are spot-on on the colors. "Black-on-Brass" "White-on_silver". When wired corerctly WHITE & GREEN cannot kill you. But, Never trust the colors.

Am I being a PITA about this subject?

Regards,
Bill

We aren't that much different than the lower 48. We just have longer winters and shorter summers. Winter typically starts mid September and runs till mid April Oh, and its dark here, at the winter solstice the sun comes up around 10:30 and sets around 3:30 .

When you come, come in the summer time. June is a good month, not to hot, its usually pretty sunny. August is the worst time, it rains almost every day. In fact, last year it rained every day for 36 days in a row

As to being a PITA on the mains issue, I don't think you are. People need reminders sometimes that the mains can hurt you :-)

-dan

[Bill E.]

We aren't that much different than the lower 48. We just have longer winters and shorter summers. Winter typically starts mid September and runs till mid April Oh, and its dark here, at the winter solstice the sun comes up around 10:30 and sets around 3:30 .

When you come, come in the summer time. June is a good month, not to hot, its usually pretty sunny. August is the worst time, it rains almost every day. In fact, last year it rained every day for 36 days in a row

As to being a PITA on the mains issue, I don't think you are. People need reminders sometimes that the mains can hurt you :-)

-dan

[Bill E.]

Hi Dan. June, eh? I will remember that. Everyone else got that? I still see no response from TKOTC. I sure hope he didn't try out his circuit! When I built an "arc furnace" with, get this, D-cell battery carbon rods (from the inside of the batteries), a salt-water "rheostat" (now THAT was smart!) and a clay flower pot as the "containment vessel" (search arc furnace, science project, etc.) AND of course the 115VAC mains, back in, ohh, 1965(?) when I was young and stupid, (Oh My GAWD!!! I found the plans here! : http://redneckfabric...php?topic=486.0 ) I was very lucky to survive that one! Us kids in the 60's got away with so much!! My Dad found out what I was doing & freaked OUT (he was an EE)!! Especially when the house lights dimmed and the power meter went beserk! I thnk I caused the, was it 1964? "Great Blackout" on the east coast with that! That was, I have to admit, really fun and radical. I can use that excuse to explain that I am the way I am today because of ... Still on-topic: my point being I was really lucky! And think what I could have done with a Netduino!! Regards.

[Mario Vernari]

@Dan: aren't you scared about the quake? I guess the your's in one of the most dangerous areas for the quakes! I have seen some of medium/high intensity here in Italy, and I must confess that's horrible! Anyway, despite this dark page, my wife loves to visit those places! Cheers

[TKOTC]

Thanks for all the replies, albeit most were just amusing as opposed to helpful. I had put this project to the side in lieu of other work. Looks like SCR is going to be my method of choice on this project. Thanks all

[Richard Crowley]

I recommend against "rolling your own" power mains switching circuit unless you have adequate experience working with lethal power. A plug-in solution would be a PowerSwitchTail which can be operated directly from a Netduino output pin. Or at least a Solid-State Relay (SSR) which can also be operated directly from a Netduino output pin. http://powerswitchta...om/default.aspx http://www.futurlec.com/RelSS.shtml (and many other sources of SSR) It would be beneficial to take into consideration the power load (amps, watts) of the vibratory motor, and whether it is an inductive load or not.

[Dan Morphis]

@Dan: aren't you scared about the quake? I guess the your's in one of the most dangerous areas for the quakes!
I have seen some of medium/high intensity here in Italy, and I must confess that's horrible!
Anyway, despite this dark page, my wife loves to visit those places!
Cheers

Mario, I missed your reply until today :/

The quakes don't bother me one bit. You get used to them after 26 years :-) Only one had me concerned, and that was a magnitude 7.9 quake. Usually, the ones we feel are in the magnitude 4 to 5 range.

-dan