Hubert,
Here is a web site that shows the schematics for the FC350BJ controller
http://anivo.com/reed/G8689_cont/g8689_cont.htm
The main difference between it, and mine (FC250J), is that the FC250J
has a low speed reverse function that prevents the spindle from turning
more than a couple hundred RPM's in reverse.
I am currently building a mini lathe out of a Homier 7x12 that was
given to me. It is currently spread across my bench in a couple dozen
pieces, and I just (yesterday) got the electronics working by replacing
the power mosfets.
BUT... I've been wondering, instead of taking a PWM signal from the
computer, converting it to +10v, and then having the controller convert
it back to PWM, to drive the mosfets, why can't the mosfets be run via a
opto-isolator from the computer, with a encoder wheel on the spidle to
handle speed/position feedback?
I drew up a very simple circuit a couple of weeks ago, to do just
that, 2 DPDT relays, one for spindle on/off, with a power resistor on
the NC side, and the second for FWD/REV, and a opto-isolator powering
two mosfets.
I bought 2 extra mosfets, a 40 tooth encoder wheel, and a
opto-interrupter from LMS, and I have most of the other bits, but, I'm
still trying to figure out which opto-isolator would be the best to use.
It will be a several weeks before I could begin trying to test this
idea, but I don't see why it won't work. If anybody else has tried
this, please, I would like to know.
Gene, I see you and I have the same idea for a spindle brake, but, is
10 ohms enough?? I was originally thinking of a pair of 50 ohm 10 watt
resistors in parallel (since I already have them). I could always throw
another 1 or 2 on, to decrease the ohm's.
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On 10/10/2009 11:02 PM, Hubert Bahr wrote:
> Peter
> The SX3 or Super X3 sold by Grizzley (G0619) does use the digital
> control. The X3 sold by Harbor Freight and also Grizzley (G0463) use a
> speed potentiometer. My first attempt will be to use the VFD outputs of
> the Gecko G540 which provides an opto isolated pwm to analog reference.
> In its case it is limited to 12 volts so my first job is to determine
> the safest place to measure the voltage across the pot and then measure
> it. I was a radar technician in the mid 60's and then went back to get
> my BSE. So I am very leery of floating references. As you say these
> voltages may be anywhere from 7 to 15 volts. I can probably use the
> G540 pins as long as they are between 5 to 12 volts. I will post my
> findings. Physical inspection of the control boards in the two machines
> reveals different animals in types and quantity of components.
> Hopefully I will not have to reverse engineer them to get them to work.
>
> Hubert
>
> Peter Homann wrote:
>
>> Hi Hubert,
>>
>> You need to be careful connecting to the pot inputs of a lot of these type of
>> speed controllers. The usually put a DC voltage of anywhere between 7V to 15V
>> across the potentiometer. The kicker is that this voltage is generated via a
>> zener shunt regulator and the control voltage is actually 7V-15V below the
>> mains voltage.
>>
>> You need to ensure that any pc control connection to this is isolated. I
>> have
>> a number of products including the DC-03 that take a pwm signal from the PC
>> and convert this into an isolated dc control voltage that is suitable for
>> controlling many types of DC motor controllers and VFDs.
>>
>> http://homanndesigns.com/store/index.php?main_page=product_info&cPath=1&products_id=21
>>
>>
>> As to the X3, I thought it used a brushless motor and the speed controller
>> was
>> digital with buttons for speed up/down and not suitable for accepting an
>> analog control input that replaces a manual speed potentiometer.
>>
>> Cheers,
>>
>> Peter
>>
>>
>> Hubert Bahr wrote:
>>
>>
>>> Just some thinking out loud!! Is it possible to put a rotation detector
>>> on a spindle, use it as an input to EMC and then have EMC drive some
>>> type of digital to analog converter to change the speed until it agrees
>>> with the desired setting? Based on some past discussions on the list,
>>> I believe the answer to be yes. If so, what type of rotation detection
>>> is needed? What is the best way to convert the EMC output to be a
>>> control force for the spindle?
>>> I am talking about a spindle on the X3 Seig Mill. I am planning to
>>> convert the current gear drive to a two range belt drive, and since the
>>> current controller appears to use a pot to adjust the speed and a switch
>>> to change direction I believe I could use some type of control voltage
>>> and a relay to replace the pot and switch. I would appreciate any
>>> suggestions as I explore deeper.
>>>
>>> Hubert
>>>
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