[TriEmbed] Power Supply rail current

Wed Jul 9 13:57:59 CDT 2014

I am way out of my depth in this whole discussion, but I did convert a
couple of gas vehicles to 100% electric drive trains a few years ago.  In
both vehicles, I installed relays to cut out in case of impact (driven by
inertial switch de-energizing them). One relay was at the back of the
vehicle and another at the front so that power would be cut even if one
relay was crushed in the closed position in an accident.

I mention it because these relays, while not cheap, were rated beyond 500
amps at around 150VDC, which was the full drive of the PWM controller
running the DC motor that activated the drive train. They controlled arcing
by having permanent magnets installed near the contacts to "bend" the arc
away from the far contact.  One of the relays activated and deactivated
each time I touched or released the accelerator pedal.  Although, that
implies that under normal conditions it was at low current when it opened.
 But it also worked if I turned the car off at the ignition under full
acceleration, or pulled the gear shift to neutral.

Rob.

On Wed, Jul 9, 2014 at 11:42 AM, Shane Trent <shanedtrent at gmail.com> wrote:

> If you are using Remote Sense you may want to connect the on-board sense
> terminal to the output terminal with a 100 ohm resistor at the power supply
> terminals to provide feedback if your remote sense wire becomes
> disconnected. The pdf below has more on remote sense, Fig 6b.
>
> I once had a developer at Borg Warner melt a 24V clutch unit under test
> when the remote sense of their power supply line became disconnected. The
> power supply also toasted my PWM FET module but I melted the unit under
> test before my module failed. They were impress at how much power the PWM
> module delivered before they it died!
>
> http://www.astrodyne.com/wp/wp-content/uploads/AP_Remote_Sensing_AP6.pdf
>
> Shane
>
>
> On Wed, Jul 9, 2014 at 9:24 AM, Rodney Radford <ncgadgetry at gmail.com>
> wrote:
>
>> 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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