You might like to have a read of a typical 3-phase motor control chip to get a feel for what is involved.
eg <A href='http://www.allegromicro.com/en/Products/Part_Numbers/3936/3936.pdf' Target=_Blank>External Web Link</a>
Personally, I would not attempt getting the PICAXE to do the real time control part. Let a custom chip do the hard part and use the PICAXE to control the driver chip.
Here's an FAQ session that gives an overview of many of the terms and issues involved.
<A href='http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1511' Target=_Blank>External Web Link</a>
BB is quite right.
Proper/good/safe control methods are NOT simple.
Have a Google for yourself and you will see the pwming frequency methods.
If you are a beginner (in electronics and programming) then I reckon you may either take BB's approach or buy a controller.
I don't want to dampen your enthusiasm but this may be a tough project to start with.
I appreciate you advice. You are absolutely
right how complicated this stuff. I though that PICAXE relatively easy to work with microchip.
On one amateur show in Pennsylvania I've seen small controller appr. 5"x5". This controller uses Atmel 2313 chip and through MODBUS capable to drive 3Ph AC motors.
This controller was designed to regulate air flow in Green houses.
I'm interested to have the same type controller for my business.
What would be the best solution to solve this task.
Maybe you should expand on how much/little of this system you want design/create or integrate into an existing system.
I had a very quick look at MODBUS. Although it is a comparitively simple protocol, it would not be a simple task for a novice to take on if you are after interfacing into an existing system.
Are your airflow regulators ready made or do you want to build them yourself? A 3-phase motor is not a simple beast to tame so why not use a single phase device or maybe a stepper motor?
I may have your project intention completely wrong, but if your mission is to "open the windows when it gets hot", then there are plenty of easy to control linear actuators available that could be very easily controlled by a PICAXE. The same PICAXE could also monitor temperature and humidity.
The project could be expanded as your skill improves to include data logging and even radio link back to a central PC.
Start simple then expand. PICAXE is VERY easy to use. It is the 3 phase motor that is complicated to drive.
My point is to pre-program chip in order to
make motors rotate at different speed for different period of time.
- start - reach speed 35Hz in 1 sec
- go for 25 sec at speed 35Hz
- stop for 3 min
- start - reach speed 60Hz in 55 sec
- go for 95 sec at speed 60Hz
- go for 70 sec at speed 45Hz
and so on....
That controller was connected to Mitsubishi 3Hp variable speed drive. The guy explained that MODBUS gives very accurate precision performance for the motors.
I'm wandering if it is possible to do the same with PICAXE.
The point I was trying to get at is which part(s) of the system do you already have and how much do you want to build yourself.
WHY 3 phase motor? Is this because you already have modules controlled by MODBUS?
By the way, MODBUS has absolutely no effect whatsoever on the accuracy, precision or performance of any motor. MODBUS is like a 'language' used to tell a controller what to do. That's a bit like saying USB is a way of getting very good quality prints from a printer.
Whether or not you can get a PICAXE to generate the MODBUS protocol is beyond me. Maybe one of the code/protocol gurus can give you a better answer.
I nave motors 3Hp and 5Hp. To get the VSDs not a problem. I need only controller which
manipulates the motors + several digital I/O. It doesn't really matter for me if it's MODBUS or other protocol. Controller has to be easy programmable. I noticed that PICAXE has graphic programming option. For me it would be the best. I think you understand my point.
From a newbie. Aquarius, do you already have the motor. If not, then why 3ph. What is the size of your greenhouse. If it is large then a commercial inverter is what you need. These will have a 0-5 volt or 4-20 mA input. This can be controlled by a ADC stuck on to a picaxe.
If your greenhouse is small then why not use a few old fans, 12vdc, from old PCs.
Depending on the make and type of vsd and the number of speeds you require you may be able to set up the drive to run different speeds from a preset table within the drive. typically there will be three digital inputs that are used to increment between user programmed values in a table of consecutive registers. If you get/or have such a type of inverter then this would probably be the easiest/cheapest route
have 3Ph motors 3HP and 5HP. The hole idea is to smoothly regulate the speed of motors by using program. Beside the fan motors I need to regulate the speed of pumps.
The Jaka's idea about ADC method looks good to me. How to make it.
Now we know the size of motors.
Do you realize the drives will cost you upto £1000. But it is the only way. Unless you are an electroncs genius, building them yourself is out of the question.
Like erco say's, using the 3 cofigurable inputs to select speed is the simplist way.
0-35Hz in one second, "ramp time" can be set in the drive. I doubt if a fan could do this anyway. Fans can take a while to get up to speed.
A picaxe with enough outputs could control the process. The inputs on the drive would need to be shorted to the drives 24v internal power supply, so you would need slave relays.
If you want more than 3 steps then a picaxe with HWPWM connected to the 0-5 or 1-5 v inputs should work. You would require a suitable RC network to smooth out the PWM.
By the way does anyone know the diference between an inverter and a VSD.
Sounds good. On our market similar drives(VSD) Mitsubishi, Hitachi,e.t.c. cost appr.
750USD. Not a big deal.
I'll remind you, the controller I've seen doesn't connect to VSD's digital or analog inputs. Simple connection by Ethernet plug in VCD and using MODBUS protocol. Though if PICAXE can send commands via digital or analog signals it's OK. But speed regulation has to be smooth.
The modbus interface you Describe can probably do a whole lot more than regulate the speed of the drive (it could probably overwrite most of the read/write registers of the drive). However bear in mind that in motion control applications (as far as i know) still use an anologue signal to the drive, but here we are talking absolute precision (in common industy terms) surely far beyond what is needed to control a ventilation fan?. You may even be able to find a drive that can communicate directly with the picaxe serout but before you decide which way to go just do a sense check on what what you want to achieve and the consequences of a failure of any items that you implement. That said most of the inverter drives that I have seen seem to be masters of all trades (open loop,vector,and servo mode), I think I may have heard of dedicated fan controllers (may be termed VSD's) which may offer a cheaper soluotion.
Aquarius. As erco say's, more info is required.
ie. what is your knowledge of electronics/progamming etc.
Are you serious about using a picaxe. I have been playing with them for a few months and only just getting to grips with then. That was after spending 3 years with the BS.
Sorry about the £1000, I was looking at UK MRRP. Also I was thing of kW not hp.
One more thing, these are pretty big motors for fans. You must have a huge green house.
Please ask what kind of information do you need.
I'm newbie with PICAXE, but I have an experience in C programming and able to do not a complicated electronic project.
I'll clarify more about the motors, 3HP for the fans and 5HP for the pumps. Greenhouses are 110m x 18m.
Again if PCAXE can handle this task I will stick with the idea to use it for manipulating motors speed .
Is the application up and running now without control?. Depending on how many fans and the spread of air they shift you may be able to have the fans dol or star/delta and just poll them sequentially as required. As for the pumps How many are there,what type of pump and what are they pumping?
Aquarius. Ok I don't know too much about horticulture so I will take your word.
Pleased to see you are going to take the simple approach. Modbus would only be an advantage if you wanted some sort of remote control or indication.
By trade I am an electrical engineer who specialises in installing control gear for pumping plant for 30 years. I'm the guy who nails it to the wall and gets it working in basic form. Any more than this I call the scada guys in. But I have picked up a lot in this time. Don't know too much about fans except that the torque settings can be lower.
Somethings you need to be aware of. Some motors do not like inverters because they can run hotter and the the cooling of the motor fan will not blow enough air across the motor cooling fins. Not so much a problem with the fan motors of course. You would need to consult the manufacturers regarding this. As you mention Hp and not Kw they could be old motors so trial and error will come into play. In any case, I suggest you fit temperature sensors to the windings. Connect via relays to the picaxe and program to shut down untill cooled. These can be retrofitted. I'v done it many times with success.
With pumps make sure that the min speed setting from the picaxe will still allow the pump to pass water. Use the min statement. This will stop the seals/packing from getting hot and leaking. The norm is not to go below 10% of the best efficiency point of the pump "BEP".
Also the cable to the motors are best sceened. They can emit harmonics that would cause havoc with TV's etc. Don't know about the US, but in Europe you would fall foul of the emc regulations.
You may have to fit chokes to reduce interference back down the supply, the manufacturers of the inverters will supply them. Most people install the minimum, then wait untill someone complains.
Do you mean a induction motor or series motor as found in drills, vaccum cleaners etc. Series motors have brushes and change there speed with load.
Series motors are easy to control manualy, plenty of drill speed circuits about, even light dimmers (probably becoming scarce in your part of the world) would work on a small motor.
You would need to figure out some way of replacing the pot with a signal from the picaxe. PWM->optocoupler->dimmer could work.
They rely on detecting the zero crossing point of the mains supply sine wave, so NO DIRECT CONNECTION. Look for subjects like "simple circuit using triacs". I have a little paperback called 101 things to do with a thyristor, it is a wealth of information.
Induction motors can be controlled by this method but over a very limited range. You need to alter the frequency. All the inverters I have used are 1ph input up to 1.1-2.2kW with 3ph output, and 3 ph input above this.
Trying to alter the speed of a single ph motor would incur lots of problems. Start and run capacitors would need to be different values at different speeds for a start.
Guys, I'm kind of layman in this field and you are gurus.
There is a simple connection:
Program or Soft + Controller + Variable Speed Drive + 3Ph motor.
I need your advice how to arrange programming and control. With PICAXE or other microcontroller it doesn't matter. It has to be smooth and flexible.
Regarding software. The guy, I've seen on the show, had notebook (with software program) connected to the controller (appr. 5"x5". Controller was connected to the electrical panel, electrical panel was connected to the motor.
He was able to change motor speed and other parameters like time,time delay,e.t.c.