Falconry Lure Machine

Thread Starter

Icarus1977

Joined Aug 4, 2014
91
Hi all,

I have noticed on the test circuit for the LM3524 that there is a pin called "Shutdown" do I use it to actually turn off the chip?

Only I am curious as to how best to turn on/off the PWM and ultimately the Motor? do I utilise this pin as shown in the test circuit or do I just turn off the power to the LM3524?

I was thinking of using a separate 12V power source, for the control circuit so that the bike battery only runs the lure motor...

The initial plan of attack is to build the test circuit for the LM3524 and take it from there...

Will this do the job IRS2109, as it looks like a single input mosfet half bridge driver with Yet again a shutdown option and the price is bang on what I wanted with plenty of available stock should things go wrong...
 
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Thread Starter

Icarus1977

Joined Aug 4, 2014
91
IRS2109 - IC, MOSFET DRIVER HALF-BRIDGE 8DIP
Device Type:MOSFET
Module Configuration:High Side
Peak Output Current:600mA
Input Delay:750ns
Output Delay:200ns
Supply Voltage Range:10V to 20V
No. of Pins: 8
No. of Outputs:1
Offset Voltage:600V
Output Current:120mA
Output Current + Max:120mA
Output Current - Max:250mA
Output Voltage:620V
Output Voltage Max:20V
Output Voltage Min:10V
Power Dissipation Pd:1000mW
Supply Voltage Max:20V
Supply Voltage Min:10V
Termination Type:Through Hole
 

shortbus

Joined Sep 30, 2009
10,045
I may be wrong about this, but... If your using a car starter motor for power, you only need a low side switch for the PWM/speed control. Low side means between the motor and ground. A Ford style solenoid switch between the battery and motor would control the power on and off.

A car starter motor will only turn in one direction unless you insulate the motor case from the battery negative side. So a half bridge driver is not needed just a low side driver.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
Just to add, a P.M. type motor will reverse with a change of supply polarity, if a series starter motor, the fields have to be brought out and reversed for each direction.
Max.
 
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Thread Starter

Icarus1977

Joined Aug 4, 2014
91
Mine is a series wound motor...

Didn't realise you could do it that way... I was going positive side so thought it had to be 67A
 

Thread Starter

Icarus1977

Joined Aug 4, 2014
91
So am I right in thinking that I am switching the load to the motor positive side or should I be switching the negative side?

Would there be any difference, as wouldn't the negative side also be a high current path returning to ground? or is it dissipated through the motor so no real load on ground connection?
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
Usually with electronic device switching, the negative side is switched due to the more economical source of the devices.
The load current through the pos and neg side of the supply is the same either way, if relay switching, it can be done in either conductor.
A full bridge controller switches both.
Max.
Max.
 
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Thread Starter

Icarus1977

Joined Aug 4, 2014
91
Just placed an order for the IRS2109 hope it's the correct part, I searched for single input half bridge mosfet driver...

Now what Mosfet's should I be looking for should they individually handle 67A or combined?

How many should I be using 2 or 4

Would this be suitable?

NXP, PSMN2R7-30PL, MOSFET, N CH, 30V, 100A, TO-220AB
 
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MaxHeadRoom

Joined Jul 18, 2013
28,617
I have never spec'ed in for that much current, but somehow especially if you bring the revs up gradually, I don't see you hitting that much current for that application, series motors are used because of their very high initial (current) torque under load, but yours seems to be taking advantage of the very high RPM capability, if you have a manual rpm controller of some kind, it may be best when the power is initially applied with a manual setting, the control has to return to zero first before it will run, taking a leaf out of the Treadmill method.
Max.
 

Thread Starter

Icarus1977

Joined Aug 4, 2014
91
Help...

Sorry for the delay had some personal problems...

Got the lm3524 working but I am struggling to calculate a 20khz output, I have it sat at 66khz with a resistor value of 10k and a capacitor value of 820p...

How can I drop it lower as I am unable to mentally work it out...

Are we using 1 over 2piRC
 

Thread Starter

Icarus1977

Joined Aug 4, 2014
91
Basically I have built the test circuit as specified in the LM3524 guide (page 5), I have on pin 6 a 10K resistor and on pin 7 a 820pf capacitor this is giving me an output on pin 12 & 13 of 65.8KHz

but the output voltage is inverted as I have not yet used a 2k pull up resistor to Vin...

They use the formula fosc = 1 over RTCT
fosc = 1 over 10K x 820P
fosc = 1 over 0.0082
fosc = 121

Hence my conundrum, how can I calculate it precisely for a 20KHz output...

Do I need to is another question I put to those of you who are more experienced with this than me?

I wish to use it with a 2109 half bridge driver, but can I?

Any help on this matter would be greatly appreciated...
 
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Thread Starter

Icarus1977

Joined Aug 4, 2014
91
First, how fast do you want the dummy prey to move?

It works like this. The smaller pulley has a smaller circumference - call is Cs. If the big pulley has a circumference of Cb, then the motor speed will be reduced by the ratio of the two - Cs/Cb.
I have the pulley on the starter motor with a circumference of 54mm and the circumference of the drum pulley is 84mm... so this gives me a ratio of 0.64???

So with this can we calculate how fast the drum is rotating?
 

Thread Starter

Icarus1977

Joined Aug 4, 2014
91
Yes it was in mm, otherwise if it was CM it would be a massive pulley to rotate... lol

Probably similar to a bike wheel...

So 0.64 and I clocked the motor running at approximately 5600 rpm... so do I times 5600 by 0.64 = 3584

Circumference of larger pulley = Pi (3.14) times Diameter (C=pD)
Circumference of larger pulley = 3.14 x 84 = 263mm

But how to I convert this to a speed as in theory there is no correlation between RPM and MPH...
 

jpanhalt

Joined Jan 18, 2008
11,087
I have the pulley on the starter motor with a circumference of 54mm and the circumference of the drum pulley is 84mm... so this gives me a ratio of 0.64???

So with this can we calculate how fast the drum is rotating?
Icarus1977 said:
Yes it was in mm, otherwise if it was CM it would be a massive pulley to rotate... lol

Probably similar to a bike wheel...

So 0.64 and I clocked the motor running at approximately 5600 rpm... so do I times 5600 by 0.64 = 3584

Circumference of larger pulley = Pi (3.14) times Diameter (C=pD)
Circumference of larger pulley = 3.14 x 84 = 263mm

But how to I convert this to a speed as in theory there is no correlation between RPM and MPH...
Compare the two bolded statements. You can see why there is some confusion of the units.

On a more practical side, a circumference of 54 mm, will probably not work well with an A-size belt. What size and type of belt are you using?

Finally on the topic of circumference, remember to use pitch diameter, not outside diameter of the pulleys.

As for the linear speed to expect, as a first approximation, you simply calculate the pitch diameter X pi X revolutions per second to get speed in whatever units the ditch diameter is in. If that turns out to be cm/second, then you might want to change your final value to metric too. If you want it in mph, a simple relationship to remember is that 88 ft/second = 60 mph.

John
 

Thread Starter

Icarus1977

Joined Aug 4, 2014
91
No sorry I cannot see the confusion both measurements are in mm...

I therefore presume the ratio would be 0.64mm...

Obviously I am missing something here, not sure what...

The measurement is the OD of the pulley that I have measured, the belt is a "V" belt...

So as for the circuit...

I am outputting from on pins 12 & 13 a frequency of 65.8KHz, and I have a variable mark to space ratio... so I presume this is how we can alter the speed of the motor...

But is 65.8KHz too fast to I need to work on getting it a lot lower?

So if I use the output from either pin 12 or 13 to pin 4 of the IRS2109 then use that to switch the mosfets...
 

Thread Starter

Icarus1977

Joined Aug 4, 2014
91
If we are using a Half Bridge Driver, does this mean that I can use lower current mosfets and add them together...

How can I work this bit out?
 

jpanhalt

Joined Jan 18, 2008
11,087
In the first instance, you said the circumference of the drum pulley is 84 mm; in the second instance you calculate the circumference of the larger pulley to be 263 mm.

How many pulleys are there?

BTW, in calculating the liner velocity, I am referring to the drum on which the cable/line is wrapped and assumed a single wrap.

John
 
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