GEC Gemini Speed Controller - Info required

[SimonD]

I have modified the mach3 spindle tuning to limit the voltage produced.

There is something amiss now, either with the motor or the controller. The motor will not start on it's own, it needs a little shove to get going. It will keep going when it is going but needs a shove to start.
I have looked at the brushes and they seem ok, as does the commutator.

I need to find some info and read up on the trimpot settings on the controller and work out how to optimise the output without blowing fuses.


Simon

[melee]

Hi Simon

A guy called Andy who runs Boxford Retro CNC is going to send me what he had circuit diagram wise when he gets back from holiday.
He should be back tomorrow

As soon as I have that I will share it with you.

If you get the partial schematic from the 125 you asked for in the other topic, let me know also.

I will try to test my transformer and wire up enough to get the spindle running tomorrow and then I will be able to test things properly.

regards

Melee

[SimonD]

I asked Andy too I didn't know he was on holiday!

Thanks
Simon

[melee]

Hi Again

1 step forward 2 back sort of day.

My contactor was 110v, probably run from a leg of the 110v 3 phase used for the servo motors.
It only controls motor rotation so I have replaced it with a 240v single coil one with NC and NO contacts and set it up to default to CCW (the lathe is slant bed so everything bar drilling etc is CCW)

The transformer did not have any shorts, so with fingers crossed powered up.

I had immediate rotation of the spindle, albeit slow and uneven, even though I was not applying any signal voltage .
Then the 'TRIP' LED on the Gemini board came on and it stopped.

Unfortunately after 2 minutes the C2 capacitor started smoking.
They obviously have a limited life because I have read a couple of times about people powering up an old one of these boards and this happening.

I have ordered replacements for C1 and C2 (RIFA PME271M as a replacement for the apparently discontinued RIFA PME261 fitted, both 0.1uf and should be suppression capacitors)  
They are only 51p from Farnells so not much lost if the problem is deeper than an old capacitor with internal breakdown.

If that works OK,  I will try applying a signal voltage across screws 2 and 7.
Given your experience it will be a low one to start with!

cheers

Melee

[SimonD]

One of those capacitors on mine blew too, when replaced mine was ok again.

I look forward to your report!

Thanks
Simon

[SimonD]

While I think about it... Can you take a photo of your speed controller POT settings please, I wonder if mine are all screwed up.
you can e-mail it to simon (at) byte-sized (dot) com

Thanks
Simon

[melee]

Hi Simon,

Photo sent as requested.

I replaced both the 0,1uf suppression capacitors and the board powers up no problem - phew!
Farnells are great, ordered at 4pm yesterday and stuff in the post at 9.30 am today.

I attached a switching DC supply across terminals 2 and 7 and achieved a steady increase in speed between 3v and 7.5v

At 7.5v I would guess it was at about 1800 - 2000 rpm which puts it bang on target for a max of 2500 rpm at under 10v.
Cannot be precise until I get an index pulse set up on the spindle, just going by ear, but certainly not the kamikaze speed increase you experienced at just 4.5v.

I cannot do much more until my other boards etc arrive, but the Gemini board looks to be operating properly with signal voltage input to 2 and 7 and 3 linked to 9 as described previously.

Good luck with yours and thanks for your input

regards

Melee

[angel tech]

ok i've just done a boxford 240 tcl, and my gemini is this way

1. no connection
2. 0-8v
3. connected to 9, connected to contacter (thin grey/black wire)
4. no connection
5. no connection
6. no connection
7. common of 0-8v, connected to 8, ground
8. connected to 7 and 10
9. connected to 3, connected to safety interlock (thick red wire)
10. connected to 8
11. no connection
12. no connection

It looks like the link between 3 and 9 is an overide for the safety interlock that should open this connection between the grey/black wire and the thick red wire, disabling the drive