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new small relay breaks 300A at 400V

S

Spehro Pefhany

Jan 1, 1970
0

400V *DC* Yes, that's quite impressive, even though its operation life
(in the 100's of operations only) is rather limited.

Note the strange operating current specification-- 40-45W for 100msec
then it drops down to 4W (for the high current version only). I wonder
what's *really* in there- not just a coil, I'll wager.


Best regards,
Spehro Pefhany
 
J

John Larkin

Jan 1, 1970
0
400V *DC* Yes, that's quite impressive, even though its operation life
(in the 100's of operations only) is rather limited.

Note the strange operating current specification-- 40-45W for 100msec
then it drops down to 4W (for the high current version only). I wonder
what's *really* in there- not just a coil, I'll wager.

Probably one of those boosted solenoid things, with a power coil and a
holding coil and a limit switch, like the overdrive solenoid on an
Austin-Healey.

John
 
J

Jim Thompson

Jan 1, 1970
0
Probably one of those boosted solenoid things, with a power coil and a
holding coil and a limit switch, like the overdrive solenoid on an
Austin-Healey.

John

An arc-sweeping "magnet" is mentioned. Maybe it's an electromagnet?

...Jim Thompson
 
C

Carl Smith

Jan 1, 1970
0
400V *DC* Yes, that's quite impressive, even though its operation life
(in the 100's of operations only) is rather limited.

I wonder what its life would be if it was seldom switched under
load.

You might ask, what good is a 300A relay if you never switch a
load with it...

In a previous life I designed motor control electronics at a
forklift company. The forklift had a 600 amp main power
contactor that switched power to the motor controllers. But
under normal operation the main power contactor was never opened
or closed with the motors powered. In the software, the motor
controllers were all shut off first, then the contactor was
opened. So the contactor only opened in an error situation
where the software determined there was something wrong, such as
a failed motor controller.
 
S

Spehro Pefhany

Jan 1, 1970
0
Probably one of those boosted solenoid things, with a power coil and a
holding coil and a limit switch, like the overdrive solenoid on an
Austin-Healey.

John

It could even be an electronic switch of some kind-- they say it
doesn't need any external snubbing (snubbering?) so maybe they had to
add something internally.

They also warn against using a simple diode on the lower-current
version, for the usual reasons.


Best regards,
Spehro Pefhany
 
J

John Larkin

Jan 1, 1970
0
An arc-sweeping "magnet" is mentioned. Maybe it's an electromagnet?

Arc quenching happens in the turnoff direction, so that can't be it.

John
 
J

John Larkin

Jan 1, 1970
0
I wonder what its life would be if it was seldom switched under
load.

You might ask, what good is a 300A relay if you never switch a
load with it...

In a previous life I designed motor control electronics at a
forklift company. The forklift had a 600 amp main power
contactor that switched power to the motor controllers. But
under normal operation the main power contactor was never opened
or closed with the motors powered. In the software, the motor
controllers were all shut off first, then the contactor was
opened. So the contactor only opened in an error situation
where the software determined there was something wrong, such as
a failed motor controller.


I did something like that. It's a power amp for MRI imaging. There's a
BIG 3-phase transformer with multiple secondary windings and
rectifiers to give, basicly, floating bipolar power supplies of 100,
50, and 25 volts. A bunch of smallish relays switch power supply
sections in and out, so we wind up with a dual 3-bit DAC, 25 volts per
LSB, 100 amps max. The relays are selected to set the power amp
voltage rails, depending on the expected load. To keep the relays from
exploding, the firmware makes sure they're switched at zero current.

There is an aux supply to precharge the filter caps so the relays
don't see the surge. It's the world's dumbest switcher: transformer,
rectifier, mosfet, and a big power resistor, with the uP turning the
fet on/off as needed.

This all works great, and when, rarely, something goes wrong, we get
smoke and stuff.

John
 
W

Winfield Hill

Jan 1, 1970
0
Carl Smith wrote...
You might ask, what good is a 300A relay if you never switch a
load with it...

In a previous life I designed motor control electronics at a
forklift company. The forklift had a 600 amp main power
contactor that switched power to the motor controllers. But
under normal operation the main power contactor was never opened
or closed with the motors powered. In the software, the motor
controllers were all shut off first, then the contactor was
opened. So the contactor only opened in an error situation
where the software determined there was something wrong, such
as a failed motor controller.

Resulting in... what exactly, an explosion?
 
G

Graham Holloway

Jan 1, 1970
0
John Larkin said:
Probably one of those boosted solenoid things, with a power coil and a
holding coil and a limit switch, like the overdrive solenoid on an
Austin-Healey.

John

It's to run a compressor that blows the spark/arc out.

Graham Holloway
 
J

John Larkin

Jan 1, 1970
0
It's to run a compressor that blows the spark/arc out.

Aren't there actually explosive things to do that? And I think I've
seen tanks of freon or SF6 or something that are used to blow arcs
out.

John
 
C

Carl Smith

Jan 1, 1970
0
Carl Smith wrote...

Resulting in... what exactly, an explosion?


I should have said "So the contactor only opened under load in
an error situation"

The result was just a bit of a spark. The contactor could
switch the full load of the motor controllers, it just makes a
spark and causes wear on the contactor tips. Older electric
forklifts, such as those that use the GE EV1 controller, switch
the contactors under load in normal operation. But it is a
regular maintenance item on these forklifts to replace contactor
tips.
 
P

Phil Hobbs

Jan 1, 1970
0
FChoquette said:
About 3$ per switch cycle :)


Francois Choquette
Nah, in the forward direction it's rated >10**3 cycles, so it's a mere
30 cents per cycle.

Contact erosion in DC relays is asymmetrical.

Cheers,

Phil Hobbs
 
P

Paul Hovnanian P.E.

Jan 1, 1970
0
John said:
Aren't there actually explosive things to do that? And I think I've
seen tanks of freon or SF6 or something that are used to blow arcs
out.

Compressed air most likely, if you are thinking about utility type
transmission breakers. The SF6 (and other exotic gasses) are sealed
systems, so while there might be some arc-blowing going on within the
switch, replenishing the gas isn't a big problem requiring large
tankage.
 
W

Walter Harley

Jan 1, 1970
0
Paul Hovnanian P.E. said:
Compressed air most likely, if you are thinking about utility type
transmission breakers. The SF6 (and other exotic gasses) are sealed
systems, so while there might be some arc-blowing going on within the
switch, replenishing the gas isn't a big problem requiring large
tankage.

From the '70s until he sold it a few years ago, my dad ran a business
rebuilding those compressors (among other electric utility related stuff).
They're pretty nifty devices - designed to run in very remote locations
under severe environmental conditions, so they do things like periodically
change their own oil (every 'X' hours of operation). The air is compressed
to around 2000psi, if I remember, and of course has to be very dry.

But I think that SF6 is becoming more common even for the run-of-the-mill
utility breakers, except in locations too remote for routine restocking. A
couple of tanks of SF6 is cheaper than trying to keep a fancy compressor
running.
 
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