[TriEmbed] Power Supply rail current

[Rodney Radford]

Relays are rated at a specific amperage and as long as that amperage is not
exceeded, you can open and close the contacts while current is flowing so
that is really the best option

Since this was a 1-off private build, for me, I would have checked the
price of the larger capacity relays and if they were too high, I would have
gone for a cheaper relay and just be careful that the current through the
contacts is low at the time they are opened/closed.  That is a pain to do
manually and I was just checking the supply specs to see if it has an
inhibit on the output that can be used to control the supply to prevent it
from supplying current until the relay is energized and it does not.

Given that, just look for a high enough amperage relay - I would push
beyond the 30A - perhaps to 50A for each of the legs.

The supply does have remote sensing and I would recommend running that to
the front panel.  That allows you to connect small wires to the load and it
will measure the voltage at that point and control it to meet the desired
voltage - so any voltage drop across the wires, relay, binding posts, etc
will not be a factor.  Usually these are connected internally to the power
supply outputs already, so you would need to remove that wire (specs don't
say how to do that, but it is usually just a small wire that is cut or
unscrewed) and then connect it to a set of binding posts on the front
panel.  To make life easier for you in cases where you don't really care
that much about exact monitoring, you can provide a front panel switch that
connects the remote sensing back to the outputs on the front panel.  Just
turn that to off and provide the wires to the load when you do care about
exact voltae monitoring in high current situations.



On Wed, Jul 9, 2014 at 8:08 AM, Jeffrey Crews <cruzetti at gmail.com> wrote:

> Asking more for my own education than as a suggestion: could a large
> enough capacitor prevent the arcing across the contacts as the relay opens
> and closes? And if so, how large a capacitance would it take to handle this
> much current?
>
> jsc
>
>
> On Wed, Jul 9, 2014 at 8:01 AM, Adam Haile <email at adamhaile.net> wrote:
>
>> Ok, yeah, that's what I was thinking. I wanted it to be normally open and
>> then energize the relay to close and provide power. That way when I turn
>> the supply on, nothing is connected by default. But I assume I still have
>> to be worried about the contact welding in that scenario since I might
>> already have the device drawing power hooked up (I would rather not have to
>> disconnect it every time I start up the supply).
>>
>> Also, I think I found my power rails:
>> http://www.amazon.com/dp/B000H9JRI0/ref=biss_dp_t_asn
>> 1/8" x 1/4" copper bar stock. My calculations show this should be able to
>> handle WAY more power than I need. And it's pretty cheap. Figure I'd just
>> do a slightly wider than 1/4" trace and then solder this on top.
>>
>>
>> On Wed, Jul 9, 2014 at 4:19 AM, Scott Hall <scottghall1 at gmail.com> wrote:
>>
>>>  On 07/08/2014 05:50 PM, Adam Haile wrote:
>>>
>>> So,  let me make sure I understand this...
>>> When you say have the relays energized, I know you mean energize the
>>> solenoid but do you mean by that that the relay contacts are closed (power
>>> flowing) or open (no power)? I'm guessing you mean don't go from open to
>>> closed while there's power flowing since their will be a temporary arc?
>>> Could I just use a normally closed relay and then use the microcontroller
>>> to open the relay and cut the power if I need to.
>>>
>>>
>>> For safety reasons, you want the relay to disconnect if energizing power
>>> is removed.  An NC contacts will not break the circuit if you have power
>>> control problems to the energizing coil.
>>>
>>>
>>>  Do you have any links to those higher cost relays? I would really love
>>> to actually make it so that I could have a button on the front (hooked to
>>> the uC) that would allow me to, using the relay, turn the power on or off
>>> to any of the outputs. So having one of these nicer relays, if not too
>>> expensive, might be nice.
>>>
>>>
>>> Look up "contactors" for relays designed for high currents and regular
>>> switching.
>>>
>>>
>>> --
>>> Scott G. Hall
>>> Raleigh, NC, USAScottGHall1 at GMail.Com
>>>
>>>
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>>
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