Re: 10 amps to drive steppers

Let me chime in. On some units that I sold to people that live in very hot
climates like india, I included some thermal cutoff switches. I simply
mounted one rated at 135F on each heatsink. I wired them into the Vin to the
controller. Thermal switches are available from www.meci.com for about
$1.30 ea.
Dan
-----Original Message-----
From: Tim Goldstein <timg@...>
To: CAD_CAM_EDM_DRO@onelist.com <CAD_CAM_EDM_DRO@onelist.com>
Date: Saturday, June 12, 1999 8:27 PM
Subject: Re: [CAD_CAM_EDM_DRO] 10 amps to drive steppers

>From: "Tim Goldstein" <timg@...>
>
>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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>
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