After a half dozen re-writes, I realize I may be asking
the impossible, but here goes...

What I need to do is supply 100 ADC to a .001 ohm load
and reverse the polarity to this load every four seconds.

jdworley@hiwaay.net> wrote in message news:45C571D1.B1480424@hiwaay.net...

After a half dozen re-writes, I realize I may be asking
the impossible, but here goes...

What I need to do is supply 100 ADC to a .001 ohm load
and reverse the polarity to this load every four seconds.

Why? An explanation would help to focus the answer.

FWIW, have you looked at magnetic blowouts?

What I need to do is supply 100 ADC to a .001 ohm load
and reverse the polarity to this load every four seconds.

jdworley@hiwaay.net wrote:

What I need to do is supply 100 ADC to a .001 ohm load
and reverse the polarity to this load every four seconds.

Is it an inductive load ?

That makes a *big* difference.

Graham

Hi all,

After a half dozen re-writes, I realize I may be asking
the impossible, but here goes...

What I need to do is supply 100 ADC to a .001 ohm load
and reverse the polarity to this load every four seconds.
I'm seeking a (least expensive) solution that can be used in
lieu of multiple relays because I believe most contactor
relays within my budget would be short-lived.

The most desirable characteristics in order of
importance are:

1) Robust design (failure intolerant situation)
2) tolerate 50% duty cycle @ 100 Amps (100% if devices
share the same case/heat sink?)
3) operate at as low a voltage as possible
4) Low thermal loss (lowest switching device saturation
voltage)
5) easily mounted device(s) to facilitate heat sinking
(i.e. TO-220 case style or chassis mountable)
6) easiest and/or most convenient drive requirements

Thus far, considerations have included; 4 3PST contactor
relays, 2 contactor relays + 2 power sources, 4 SCR's, 2
SCR's + 2 power sources, MOSFET(s), and power
transistor(s). IGBT devices were abandoned because I could
not find one with low enough saturation voltage, and DC
SSR's due to cost.

Optional control scenarios included programming the power
source to zero current to turn off SCR's, and in the case of
relay's, additionally firing an SCR across the p/s output to
circumvent contact arcing (might not be possible if o/p
voltage is under 1 VDC?). Obviously, an additional goal is
a favorable MTBF of p/s('s) and component choice(s)... .

I have some junk box parts, consisting of used
contactors that will support 100 ADC with paralleled
contacts (coils are 24VAC, high wattage...), 4 SCR's are on
order to at least try (MITSUBISHI TM200DZ-H's X2, but I
don't expect these to meet characteristic #4 above), a few
SSR's suitable for p/s input or contactor drivers, and
several large heat sinks.

Can anyone recommend alternative device(s)
(manufacturers & part numbers?!) or even a full
switching/control scenario utilizing as much of my on-hand
items as practical - that will generate the least amount of
excess heat without eating up my two used power supplies
that would cost me $4000+ each to replace if I had to do it
during a test cycle... .

Thanks in advance!!!!
Stephen Kurzban

jdworley@hiwaay.net> wrote in message news:45C571D1.B1480424@hiwaay.net...

After a half dozen re-writes, I realize I may be asking
the impossible, but here goes...

What I need to do is supply 100 ADC to a .001 ohm load
and reverse the polarity to this load every four seconds.

Why? An explanation would help to focus the answer.

FWIW, have you looked at magnetic blowouts?

On Sun, 04 Feb 2007 07:43:43 GMT, "Homer J Simpson" <nobody@nowhere.com> wrote:


jdworley@hiwaay.net> wrote in message news:45C571D1.B1480424@hiwaay.net...

After a half dozen re-writes, I realize I may be asking
the impossible, but here goes...

What I need to do is supply 100 ADC to a .001 ohm load
and reverse the polarity to this load every four seconds.

Why? An explanation would help to focus the answer.

FWIW, have you looked at magnetic blowouts?

Albright International have motor reversing contactors with magnetic blowouts
and double-contact break on most of them.

We use their products a lot and have found them to be very reliable.

Carriage/Post might be a cost problem if you are outside the UK, but worth
looking at.

The SW180 is probably the one to look at for single pole switching, but look
through their site and see what suits you:

http://www.albright.co.uk/

Peter

--
Peter & Rita Forbes
Email: diesel@easynet.co.uk
Web: http://www.oldengine.org/members/diesel

Eeyore wrote:

jdworley@hiwaay.net wrote:

What I need to do is supply 100 ADC to a .001 ohm load
and reverse the polarity to this load every four seconds.

Is it an inductive load ?

That makes a *big* difference.

Graham


What rise / fall times can you tolerate? Even assuming a non-inductive
load, it's going to take some time to switch that amount of current.

Note that even a non-inductive load will still have some inductance
simply due to connectivity; very small admittedly on a good set of planes.

Cheers

PeteS

Hi all,

After a half dozen re-writes, I realize I may be asking
the impossible, but here goes...

What I need to do is supply 100 ADC to a .001 ohm load
and reverse the polarity to this load every four seconds.
I'm seeking a (least expensive) solution that can be used in
lieu of multiple relays because I believe most contactor
relays within my budget would be short-lived.

The most desirable characteristics in order of
importance are:

1) Robust design (failure intolerant situation)
2) tolerate 50% duty cycle @ 100 Amps (100% if devices
share the same case/heat sink?)
3) operate at as low a voltage as possible
4) Low thermal loss (lowest switching device saturation
voltage)
5) easily mounted device(s) to facilitate heat sinking
(i.e. TO-220 case style or chassis mountable)
6) easiest and/or most convenient drive requirements

Thus far, considerations have included; 4 3PST contactor
relays, 2 contactor relays + 2 power sources, 4 SCR's, 2
SCR's + 2 power sources, MOSFET(s), and power
transistor(s). IGBT devices were abandoned because I could
not find one with low enough saturation voltage, and DC
SSR's due to cost.

Optional control scenarios included programming the power
source to zero current to turn off SCR's, and in the case of
relay's, additionally firing an SCR across the p/s output to
circumvent contact arcing (might not be possible if o/p
voltage is under 1 VDC?). Obviously, an additional goal is
a favorable MTBF of p/s('s) and component choice(s)... .

I have some junk box parts, consisting of used
contactors that will support 100 ADC with paralleled
contacts (coils are 24VAC, high wattage...), 4 SCR's are on
order to at least try (MITSUBISHI TM200DZ-H's X2, but I
don't expect these to meet characteristic #4 above), a few
SSR's suitable for p/s input or contactor drivers, and
several large heat sinks.

Can anyone recommend alternative device(s)
(manufacturers & part numbers?!) or even a full
switching/control scenario utilizing as much of my on-hand
items as practical - that will generate the least amount of
excess heat without eating up my two used power supplies
that would cost me $4000+ each to replace if I had to do it
during a test cycle... .

Hi all,

After a half dozen re-writes, I realize I may be asking
the impossible, but here goes...

What I need to do is supply 100 ADC to a .001 ohm load
and reverse the polarity to this load every four seconds.
I'm seeking a (least expensive) solution that can be used in
lieu of multiple relays because I believe most contactor
relays within my budget would be short-lived.

The most desirable characteristics in order of
importance are:

1) Robust design (failure intolerant situation)
2) tolerate 50% duty cycle @ 100 Amps (100% if devices
share the same case/heat sink?)
3) operate at as low a voltage as possible
4) Low thermal loss (lowest switching device saturation
voltage)
5) easily mounted device(s) to facilitate heat sinking
(i.e. TO-220 case style or chassis mountable)
6) easiest and/or most convenient drive requirements

Thus far, considerations have included; 4 3PST contactor
relays, 2 contactor relays + 2 power sources, 4 SCR's, 2
SCR's + 2 power sources, MOSFET(s), and power
transistor(s). IGBT devices were abandoned because I could
not find one with low enough saturation voltage, and DC
SSR's due to cost.

Optional control scenarios included programming the power
source to zero current to turn off SCR's, and in the case of
relay's, additionally firing an SCR across the p/s output to
circumvent contact arcing (might not be possible if o/p
voltage is under 1 VDC?). Obviously, an additional goal is
a favorable MTBF of p/s('s) and component choice(s)... .

I have some junk box parts, consisting of used
contactors that will support 100 ADC with paralleled
contacts (coils are 24VAC, high wattage...), 4 SCR's are on
order to at least try (MITSUBISHI TM200DZ-H's X2, but I
don't expect these to meet characteristic #4 above), a few
SSR's suitable for p/s input or contactor drivers, and
several large heat sinks.

Can anyone recommend alternative device(s)
(manufacturers & part numbers?!) or even a full
switching/control scenario utilizing as much of my on-hand
items as practical - that will generate the least amount of
excess heat without eating up my two used power supplies
that would cost me $4000+ each to replace if I had to do it
during a test cycle... .

Thanks in advance!!!!
Stephen Kurzban

Mercury Relay.

Hi all,

After a half dozen re-writes, I realize I may be asking
the impossible, but here goes...
snip

How about mercury relays.
Four spst NO relays will work.
These relays have very good overload capabilities.
They will emit a lot of RFI when they open on an inductive load.

However, by
the time you get to their higher current product lines (where they
would support the 100 Amps I need, mostly with all contacts in
parallel), they are actually de-rating the contacts at DC. Not sure
why.

Can anyone recommend alternative device(s)
(manufacturers & part numbers?!) or even a full