Re: [CAD_CAM_EDM_DRO] Clarifications needed -

Weyland wrote:

>On Friday 12 September 2003 09:34 pm, Tim Goldstein spake:
>
>
>
>>>My concern is over the 80 VDC limit for the
>>>Geckos. (G210s marked with "90IFX" on the covers.)
>>>
>>>
>>What happens when your power company lets the voltage float high?
>>According to Mariss (and he should know) the number 1 cause of blown
>>Geckos by a large margin is over voltage.
>>
>>
>
>mmmHmmmm... I hadn't thought of that. Thanks.
>But wouldn't the UPS (if used here) help there, as well?
>(Assuming that I used the right one, that had
>over-voltage protection as well as under-voltage)
><...like a SmartUPS...>
>

Most UPS's do not regulate the line. If the 120 V line goes above, say,
150 V
RMS, they will switch to UPS power. There are "on-line" UPSs that
regenerate
all power internally at all times, but they are usually in the several
thousand $
range.

>
>
>
>> Suggested caps are listed on the
>>instruction sheet.
>>
>>
>
>What causes them to get hot? (just curious)
>Okay, just saw the 470uf callout...
>

The switching action of the PWM output causes large, fast, current
transients
to be drawn from the power supply. If a bank of large capacitors is near
(by wire length) to the Geco units, they will absorb those current pulses.
If not, then the much smaller capacitors inside the Gecko drives will have
to absorb it, and they have much less surface area to radiate the heat.

>
>
>
>>>Third - the +5V.
>>>Assuming that I want to work with what I have right now and
>>>not need to
>>>spend more money, do I get that +5V from the computer power supply
>>>or does it come from somewhere in the parallel port?
>>>
>>>
>>There is no +5 on the parallel port. Get it from the computer power
>>supply or from a game port or from a USB.
>>
>>
>
>I always get confused here, so I'll ask what the majority common practice is -
>
>Use the ground of the parallel port, or +5V
>off of one of the computer power supply leads?
>I've built the controller enclosure to house everything, so picking off of one
>of the power wires isn't a problem; I just need to get the right direction to
>head in. I'd like to understand *why* as well...
>

The chips used in the PC parallel port chips are designed to mimic the
operation
of the LS TTL chips, used years ago in the first PCs. These chips had a
capability
of sinking current to ground of about 16 mA, but a sourcing current
capacity of
about 1.5 mA. So, providing a source of +5 V, going through the
opto-isolator
in the Gecko drive, and then having the parallel port driver chip sink
the current
will provide the current drive needed by the Gecko's inputs. Most
parallel ports
will not source the 5+ mA needed by the Gecko to "see" the condition as
"signal
present".

>
>
>
>>>And Fourth, I'm planning on using a UPS for the controller,
>>>and wanted
>>>to know people's thoughts on using it for the motor's power
>>>supply as well.
>>>
>>>
>>The startup surge could be enough to fry the UPS depending upon the size
>>of your power supply. I put my controller computer on a UPS, but run the
>>motor power straight from the mains.
>>
>>

Yup, that's true, the momentary draw when the motor power supply is turned
on will be high. And, a UPS that produces "modified sine wave" which means
something that looks much more like a square wave :


________ ________
| | | |
| | | |
| | | |
| | | |
______| |_____ _____| |_____
| |
| |
| |
| |
|_________|


This will cause transformers to run very hot, it is designed to make
electric
drills and computers with switching power supplies happy.

Jon