Re: 10 amps to drive steppers

Mo,

I would be interested in the circuit you are thinking of for an overheat
shutoff for this controller. I currently have no need to push higher amps,
but I like the idea of getting some protection from a fan failure.

Tim
[Denver, CO]

> -----Original Message-----
> From: Mo [mailto:mo@...]
> Sent: Saturday, June 12, 1999 8:02 PM
> To: CAD_CAM_EDM_DRO@onelist.com
> Subject: Re: [CAD_CAM_EDM_DRO] 10 amps to drive steppers
>
>
> From: "Mo" <mo@...>
>
> > know how it goes. The only modification to the board needed to allow
> higher
> > current is to parallel the existing .1ohm sense resistors with another
> .1ohms
> > which will double the adjustment scale to 10 amps.
> >
> > Wish Me Luck!
>
> Matt,
> I wish you luck!
> It is far nicer to explore at the ends of the envelope when you have a
> safety chute.
> Getting the board to run at high Amps is one thing, getting it to run
> reliably for years is another.
> My advice is to analyse and improve your protection system to keep the
> experimenting fun and painless.
>
> Do the units have a temperature sensor on the heatsink for over temp
> protection?(always a good idea when you are relying on forced cooling and
> fan health) If not consider providing a thermistor or other type
> temp temp
> sensor on the heatsink near to the trannys/fets this should be
> used to drive
> the enable/disable pin.
> You may have several of these in key positions. If you need
> simple circuitry
> let me me know.
>
> Use good quality heatsink compound and really go over the top with the
> cooling design. The simple baffles in Tim Goldsteins setup caused a 40F
> drop.
> Many fans are better than one. If one goes then you still have forced
> cooling from the other fan(s) On the subject of fans get the airflow specs
> for the fans you intend to use and go for the highest you can find - I use
> the Minebea Smartfan 4715ML-012P542-P1 12V 0.5A (commonly found in old
> Compaq Servers this has an external thermistor which allows it to run as
> fast as it needs to saving on life, you can replace this with a 5k pot for
> manual setting or with a 1k resistor for an airflow that will have your
> Bridgeport hovering around the shop!
>
>
> Get the max operating temps for the mosfets from the manufacturers
> datasheets or Dan. Run the units for extended periods measuring
> their temps
> and gradually increase the current until you don't feel safe
> going further -
> need more current then add more cooling and continue your tests.
>
> With good cooling you will keep it going well and the attention paid to
> sensing/shutdown areas will be a great security blanket. Dan may
> be able to
> shed some light on these areas.
>
> Mo
>
>
>
>
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