Re: [CAD_CAM_EDM_DRO] Re: FS: New 4 axis microstepping driver $45.00 USD

Using a couple of the circuits in the LM78xx datasheet available here:
http://www.fairchildsemi.com/pf/LM/LM7805.html
It would be possible to build a regulator with short circuit protection.
See figures 10 & 13.

Regards,
JJ

On Friday, Mar 19, 2004, at 23:23 US/Eastern, jt4897 wrote:

> I think in this case it is not simply about exceeding the
> manufacturers limits but rather that we are talking about
> home built power supplies and that for the Allegro chip
> 35V cannot be exceeded. I think that Jeff can attest to
> that as an expert.
>
> My power is quite good and my provider (Hydro Quebec) says
> that for a normal 120V supply the voltage can vary between
> 106V and 127V (marginal) and that normal would be between
> 110V and 125V.
>
> Doing some math we can see that at 24VAC x 1.414 = 33.936VDC
> But that would be based on 120VAC in - what happens when
> it jumps to 127VAC? My DC could jump to 35.9156. That's
> about 1VDC more than it takes to blow the drive and yet we
> are still within the acceptable limits of service. Now
> add back EMF.
>
> Personally I'm running a 22VAC transformer and I feel like
> I've pushed the limit (aprox. 32VDC). I think Jeff
> recommends 30VDC as a limit.
>
> There is a circuit around somewhere from Mariss (of Gecko)
> that shunts overvoltage to ground. Great! But most
> users of these drives are probably like me and haven't
> built it. :-( Most of us want to snap the pieces
> together and go, safer to recommend 18VAC or 24VDC and
> leave the limits to those that are more daring.
>
>
> -John
>
> PS: Some UPSs allow you to set out voltage but many
> cheaper UPSs I wouldn't trust to hold it 120V.
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Fred Smith" <imserv@v...>
> wrote:
>> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "jeffalanp" <xylotex@h...>
>> wrote:
>>> Fred wrote:
>>>
>>>> A 24 volt ac transformer is just
>>>> about right for a power source (plus a bridge and a
> capacitor).
>>>> These transformers are readily available in 2-4 amps and
>> contribute
>>>> to a very inexpensive solution for a do it yourself project.
>>>
>>> Please be aware that 24VAC when filtered and rectified becomes
>>> about 34VDC. If the transformer were rated for 110VAC to produce
>>> 24VAC, and you used 115VAC or 120VAC (like I have), then you
> would
>>> surpass the 35VDC *absolute maximum* limit of the A3977SED driver
>>> chip.
>>
>> Jeff,
>>
>> I agree whole heartedly. If local line voltage exceeds 120, it is
>> probably a good idea to consider a step down transformer for any
> CNC
>> equipment, this is very common practice on commercial machinery. I
>> would also recommend a UPS type setup on your computers as a UPS
> will
>> usually have some voltage regulation to maintain supply voltage
>> within a narrow range. Surge protectors at a minimum.
>>
>> It's a good idea not to exceed the manufacturers limits on any
>> electrical equipment.
>>
>>> On Wednesday, Mar 17, 2004, at 17:40 US/Eastern, Fred Smith wrote:
>>>>> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Fred Smith"
>> <imserv@v... wrote:
>>>>>>> We have a limited edition, 4 axis, microstepping driver
>> available.Based
>>>>>> on
>>>>>>> the Allegro A3977 chip. The board is rated at 2 amps per axis
>>>> and
>>>>>>> maximum of 35vdc. This is a promotional item and is subject
> to
>>>>>> prior
>>>>>>> sale. Quantities are very limited.
>>>>
>>>> Info at: http://www.cadcamcadcam.com
>
>
>
>
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