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Author Topic: Calling on the !OLD SCHOOL GUYS!  (Read 8089 times)

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I was given a couple of old electric industrial carts a few weeks back,and need a little input from the old school guys here,as I'm only half old school lol.

Anyway,i stripped down one of the PWM that they used back then,and would like some help verifying a couple of thing's. One thing I'm really interested in is what i believe to be very large transistors(PNP TYPE),as the positive polarity is ground in these machines-tipical English design of the times. There was also 3 serious diodes in this PWM as well.

So here is the video of the strip down.

https://www.youtube.com/watch?v=FnxO5KSgGT8

cheers
Brad


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First step is to identify the type of motor. Usually these have separate control of field and rotor currents. Then get an old Westinghouse SCR manual which may have some rudimentary motor control circuits using devices of that period. I'm guessing one of the devices is an  SCR for rotor current, the other controls field current.

I have a GE electric tractor, model E15 that I've maintained for 35 years, but it does not use PWM, rather just resistive control of field and rotor currents so my schematics would not apply.

With a little searching you may luck out and find a schematic for your motor controller.

Westinghouse published app notes on their large current SCR's for DC motor control, maybe still available.

Good luck with your carts, maybe try some golf cart sites also, they publish lots of schematics.


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Lansing Bagnall is now defunct but according to Wikipedia there is a huge archive of material at the Churchill Archives Centre in Cambridge UK.  Maybe worth contacting them.

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Dear Brad.

I had the misfortune to be the works engineer at firm that had one of those Lasnsing Bagnall  fork trucks !!  :)

Those transistors are IMO Thyristors ??  I am working from deep past here !!  If I remember correctly it was called a chopper control circuit ?? As you pressed the throttle, for want of a better word, one of those little modules would start to groan and then rise in pitch as the speed got up. I was lucky enough to have some schematics at the time and was able to keep the old girl going until the battery bank expired and was deemed too expensive to replace.

Each of those coloured modules had a different function, as you will no doubt already be aware, good luck, I found the overall construction was of a high standard and should last you a good while.

Cheers Graham.


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First step is to identify the type of motor. Usually these have separate control of field and rotor currents. Then get an old Westinghouse SCR manual which may have some rudimentary motor control circuits using devices of that period. I'm guessing one of the devices is an  SCR for rotor current, the other controls field current.

I have a GE electric tractor, model E15 that I've maintained for 35 years, but it does not use PWM, rather just resistive control of field and rotor currents so my schematics would not apply.

With a little searching you may luck out and find a schematic for your motor controller.

Westinghouse published app notes on their large current SCR's for DC motor control, maybe still available.

Good luck with your carts, maybe try some golf cart sites also, they publish lots of schematics.
Here is the motor ION.
45 volts-3.3hp-1500RPM-series wound.This is extremely large for a 3.3HP,and very heavy to that of what we have today. I would suspect it could handle a lot more than its ratings.


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Lansing Bagnall is now defunct but according to Wikipedia there is a huge archive of material at the Churchill Archives Centre in Cambridge UK.  Maybe worth contacting them.

Smudge

A little search on that Lansing Bagnall will turn up service manuals and other info maybe close to your model.

Chopper circuits for motor control are described in both GE and Westinghouse SCR (Silicon Controlled Rectifier) aka Thyristor manuals from the 60's and early 70's

With four connections to the motor, it looks like they brought out the rotor and field windings unless I am missing something.

Usually the field polarity is reversed with a relay in order to run the motor in reverse.


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A little search on that Lansing Bagnall will turn up service manuals and other info maybe close to your model.


Usually the field polarity is reversed with a relay in order to run the motor in reverse.
I believe this to be the case,as it had 4 thick cables running from the motor up to the front of the machine,and connected as shown in the video. The two large relay's use to switch over when put into reverse,changing which cables became negative and positive.I'm a bit lost with that throttle box but-seems to be some sort of hall sensor,that sensed the magnetic field around the negative supply cable from the battery box. I'm guessing that the small disk magnet on the swinging arm some how changed the magnetic field the hall sensor received.When you pushed the peddle down,the disk magnet would move away from the hall sensor(if that is what it is),and i would guess that a stronger magnetic field from the cable would be seen by the hall sensor. All guess work here,as i have never seen a setup like this one.


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I'm guessing that the small disk magnet on the swinging arm some how changed the magnetic field the hall sensor received.When you pushed the peddle down,the disk magnet would move away from the hall sensor(if that is what it is),and i would guess that a stronger magnetic field from the cable would be seen by the hall sensor. All guess work here,as i have never seen a setup like this one.

Might not be a Hall sensor, might be a satureable inductor whose inductance somehow influences the pulse width modulation.  The field from the battery cable could be there as some sort of feedback governor for speed.

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Looks like the large one is a transistor of the WT4300 series. All dimentions are exact to the diagram.

http://pdf.datasheetarchive.com/indexerfiles/Scans-003/Scans-0079950.pdf


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The data sheet is from 1980 so yes, they did have high current transistors then. What is the vintage of your cart? I thought it might be from the 60's or early 70's which is why I said "Thyristor".


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The data sheet is from 1980 so yes, they did have high current transistors then. What is the vintage of your cart? I thought it might be from the 60's or early 70's which is why I said "Thyristor".

Seems i was wrong in the last post. This seems to be an SCR,as once triggered,it stays on. Also current will only flow in one direction,so i dont think it is a triac. Now the problem is,the only way i can get it to switch off again is by either disconecting the load,or shorting between cathode and anode. this means that what ever switches it off has to be able to carry the same(if not more) current as the SCR it self.This is most unhelpful. Any ideas as to how to turn it off again?

Here is the video.

https://www.youtube.com/watch?v=gUSD36srBNg


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TinMan,

If you are still puzzled about the throttle control here's my thought on it....

I'm pretty sure it is something called and ITS (inductive throttle sensor), not the same thing as an ITS on a carburetor.

The coil (red block) is the coil which determines the on-time (pulse density) in the PWM wave going to the motor. The position of the magnet has the effect of changing the coil's inductance. I suspect the coil's core is extended to the path of the magnet by the flange-like pieces through which the magnet passes.

The heavy motor current carrying cable bolted to the coil has a similar effect as the magnet except its purpose would be to prevent sudden acceleration. How much it prevents jerky starts is probably controlled by the thickness of the shim.

I remember troubleshooting a similar looking Cushman a very long time ago.

I'm pretty fuzzy on the above as my mind was on other things in those days >:-)

Oh... the Westcode SCR will turn off at the end of each PWM pulse.
   

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TinMan,

If you are still puzzled about the throttle control here's my thought on it....

I'm pretty sure it is something called and ITS (inductive throttle sensor), not the same thing as an ITS on a carburetor.

The coil (red block) is the coil which determines the on-time (pulse density) in the PWM wave going to the motor. The position of the magnet has the effect of changing the coil's inductance. I suspect the coil's core is extended to the path of the magnet by the flange-like pieces through which the magnet passes.

The heavy motor current carrying cable bolted to the coil has a similar effect as the magnet except its purpose would be to prevent sudden acceleration. How much it prevents jerky starts is probably controlled by the thickness of the shim.

I remember troubleshooting a similar looking Cushman a very long time ago.

I'm pretty fuzzy on the above as my mind was on other things in those days >:-)

Oh... the Westcode SCR will turn off at the end of each PWM pulse.
I believe you are right WW. I messured the resistance across the two terminals on the block,and got 5.6 ohms. I have been doing a lot of reserch on this setup,as i like to learn that of what i dont know. Im hoping to use those large SCR's to make a PWM to drive an electric gocart(in the making now),and i think im getting some where now.-See next post.


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After much research and tracing wires on the still together unit, i believe these carts use a class D-LC switching circuit(as seen in pic below). I believe this because the drive circuit uses 1 large SCR,1 small SCR,caps,diodes and inductor hooked up as shown in the picture. The load of course is the motor(resistor/inductor in the pic). Do you guys think this is correct?

The next thing i would need is a switching circuit for the gate's of both SCR's-but what kind?. Dose it just have to adjust the pulse width of the main SCR -or both. How dose cap size effect the pulse width,frequency etc ?. There seems to be many variables that will effect the way this circuit operates-EG,motor size,supply voltage etc.

The goal here is to make a speed controller for a 48v dc brushed motor(as what was in the machine),but without all the parts used in the original setup,and a much smaller/more compact motor ( http://www.evworks.com.au/motenergy-me0708-48v-dc-motor-6-12kw ). As it takes very little voltage and current to turn on the SCR's,i was hoping to use something like a 555 timer to drive the SCR's-or similar.


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OK so they are SCR's

Attached is a schematic of a Jones Chopper Circuit for Battery Vehicles from my copy of the GE SCR Manual 3rd edition @1964.

If you google Jones Chopper, or Morgan Chopper, you will probably find a lot of information.  Also read about methods to commutate SCR's. In some circuits one SCR commutates the other to the off condition via a capacitor and an inductor facilitates turnoff. Similar to the circuit you posted.

e.g. http://books.google.com/books?id=0_D6gfUHjcEC&pg=PA496&lpg=PA496&dq=jones+chopper+circuit&source=bl&ots=NxppYyBuQW&sig=gaI5ep5coByZT_vx-x7sstM9s0o&hl=en&sa=X&ei=JuE7VNTgCJPGsQTn84L4BQ&ved=0CCAQ6AEwAA#v=onepage&q=jones%20chopper%20circuit&f=false
« Last Edit: 2014-10-13, 16:03:13 by ION »


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"Secrecy, secret societies and secret groups have always been repugnant to a free and open society"......John F Kennedy
   
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