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16  Using Arduino / Motors, Mechanics, and Power / Re: DC PID motor controller on: August 21, 2014, 05:08:16 am
On the basis that you get one pulse per revolution (measured variable) and that you have a defined period per revolution (set-point) then you "simply" measure the difference (error -  positive or negative) between the set-point and the measured variable and adjust the speed drive signal to eliminate the error.

The PID algorithm contains 3 elements P (proportional), I (Integral) and D (Differential)

If you aren't too bothered about a small degree of fixed error then only the P element is essential.  The controller produces a correction which is proportional to the error - but it never eliminates the error entirely

If you want to eliminate error then use both P and I where the I factor produces a corrective factor dependent upon how long the error exists

The D factor produces a corrective factor based upon the rate at which the measured variable is moving away from or towards the set-point.  For low inertia systems it isn't required.  A typical use would be where a heater is being used to heat up a large mass.
17  Using Arduino / Motors, Mechanics, and Power / Re: DC Motor Current Goes DOWN When Stalling? on: August 21, 2014, 04:57:35 am
I'm afraid harddrive is wrong with his argument.

A centrifugal blower is the pneumatic version of a centrifugal water pump.

The least loaded condition on this type of device is when there is no fluid being pumped - whether it be air or liquid.

Circulatory fluid within the pump body does produce some load but certainly nowhere near the pump's rated capacity.

The stonewall effect that occurs in large centrifugal compressors when the through-flow is restricted, which results in potentially destructive surge, does not apply to "toy" sized pumps such as leaf blowers - the manufacturing clearances are so wide that pump efficiencies are too low to experience such an effect.

When starting large centrifugal liquid pumps the outlet valve must be closed during the run-up phase, then, when the motor is up to full speed the outlet valve is gradually opened.  Suction valves are not used for this process as the loss of inlet head to the pump would induce cavitation resulting in damage to the impeller blades.

Therefore when you blocked your leaf blower, the load flow through the "pump' reduced, resulting in less load on the motor, a corresponding increase in speed and a reduction in motor current.
18  Using Arduino / General Electronics / Re: What is a calabrating battery type called? on: August 18, 2014, 03:52:49 pm
If memory serves me correctly, (it's over 50 years since) we used to use them on Cambridge Pots/bridges  in conjunction with wet ice flasks (cold junction compensation) for the calibration of thermocouple systems.

At that time all our instrument systems were valve operated and, although maybe now considered ancient, were extremely capable of running a nuclear power plant.

Their voltage was somewhere around 1.018 and their output current capability was zero.  Woe betide the apprentice who failed to balance the bridge so that no load was placed on the cell
19  Using Arduino / General Electronics / Re: Safety match activation energy on: August 18, 2014, 02:38:29 am
Don't you think it would make more sense of you got yourself some fine nichrome wire, a box of whatever type of match you are interested in and a variable voltage DC power supply.  With those you could conduct your own empirical tests.  
Using a sledge hammer to crack a walnut (a metaphor for the video shown) doesn't confirm the energy required, it merely demonstrated that enough was used.

As far as maths is concerned Watts is the product of voltage and current   ---   time does not come into the equation
20  Using Arduino / General Electronics / Re: High current Measuring sensor on: August 11, 2014, 01:15:47 pm
Yes I have used hall sensors and in every case they have provided a perfectly adequate measurement system.

The following is extracted from the ASC712 data sheet :

Noise (VNOISE). The product of the linear IC amplifier gain
(mV/G) and the noise floor for the Allegro Hall effect linear IC
(≈1 G). The noise floor is derived from the thermal and shot
noise observed in Hall elements. Dividing the noise (mV) by the
sensitivity (mV/A) provides the smallest current that the device is
able to resolve.

For the subject device with a +/- 20A range the output is specified as 100mV/A with a nominal noise figure of 11mV.
From the above sheet this gives a minimum resolution of 11/100 = 110mA.  With a 20A range, this gives a possible resolution of just over 0.5% referenced to FSD.

For non-scientific applications I would have thought this was more than adequate.

But it's up to each to use what they wish
21  Using Arduino / General Electronics / Re: High current Measuring sensor on: August 11, 2014, 07:19:16 am
Why would you not want to use a hall sensor which provides a simple and reliable method of accurate current measurement and effective electrical isolation with minimum number of components (ie 1)

Erm, because they are much noisier than a shunt or transformer sensor?  Unliklely
to matter for this application.

On what basis do you make that statement.   Transformer unsuitable for DC current sensing so not relevant to the topic
22  Using Arduino / General Electronics / Re: High current Measuring sensor on: August 11, 2014, 02:56:06 am
Why would you not want to use a hall sensor which provides a simple and reliable method of accurate current measurement and effective electrical isolation with minimum number of components (ie 1)
23  Using Arduino / General Electronics / Re: What is a jack plug on: August 02, 2014, 04:05:20 am
The 'male' part is the jack (or plug) the 'female' part is the socket.  (Biology and electronics combined)

If the jack is on the end of a flying lead it is a "free" jack  if it is part of a surface or board mounting it is a "fixed" jack

Similarly if the socket is on a flying lead it is a "free" socket and if it is part of a surface or board mounting it is a "fixed" socket

I once had to explain the difference between male and female threaded components to my secretary - she was rather embarrassed when the penny dropped.
24  Using Arduino / General Electronics / Re: battery mAh tester on: July 31, 2014, 05:46:39 pm
Presume you mean 7000mAH per battery.
Forget the theory and all the fancy gizmos.  If you want to know how long your batteries will last under mains failure conditions then the simplest (and most realistic) test is to turn off the mains and monitor the actual discharge voltage as the batteries supply current to your system.   When voltage has dropped to your predetermined minimum (say 11v) then the time it took to get there is the true application capacity.  OK that takes time, but do you want a truthful answer or an answer that makes you feel good.
25  Using Arduino / General Electronics / Re: LM2575 7.4V to 5V (i don't understand the circuit diagram) on: July 07, 2014, 01:30:11 pm
I recommend you use the charger that came with the phone !!
26  Using Arduino / General Electronics / Re: how fast can the arduino switch a transistor? on: June 27, 2014, 06:19:32 am
Can you get a solenoid valve to open and close that fast ?
27  Using Arduino / Motors, Mechanics, and Power / Re: 3VAC on coil side of relay. What's going on? on: June 25, 2014, 03:58:38 am

You will get about 6V between the mains neutral and ground and you can use that voltage for free, it does not get metered. Although you will possibly get put in prison if the electricity company catch you doing it.


Come, come Mike you really shouldn't encourage this sort of behaviour.

If a neutral feeder fault (open circuit) occurs anywhere in the domestic distribution side between the substation and the home then the neutral line within the house could rise to line voltage.  Not a happy scene for anything using neutral-ground potential as a power supply.
28  Using Arduino / Motors, Mechanics, and Power / Re: Cheap power supply? on: June 22, 2014, 01:09:16 pm
On the basis that you have to plug your mains lead into a wall socket then why not buy a suitable wallwart which outputs 12volts (or whatever) and instal a suitable socket on your case for the wallwart DC lead to plug into.  That offers the advantage of solving your space problem and keeps the mains AC voltage away from your low voltage electronics.
29  Using Arduino / Motors, Mechanics, and Power / Re: Cheap power supply? on: June 22, 2014, 05:27:30 am
I'm not suggesting smps are junk, they are generally excellent at what they do; it's just that the one you have would appear to be.  If a device alters its output from the design DC voltage to a much higher AC one when you load it, then it is obviously of questionable use to power a microprocessor based system.  But at the end of the day, it's your choice.
30  Using Arduino / Motors, Mechanics, and Power / Re: Cheap power supply? on: June 22, 2014, 03:06:47 am
With a 400v rated capacitor onboard it is almost certain to be a switched mode power supply.  Your best bet is to cut your losses, throw the heap of junk away and buy a decent supply rated to do what you wish.
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