Looking for special SPDT switches

M

Mike Kaplan

Guest
I'm looking for 2 SPDT toggle or battery switches. The switches'
parameters:

24v
85 Amp
Break before Make

The switches will reverse current to a motor. I don't want to use
relays, solenoids or contactors - I want a mechanical switch.

The two switches will provide Forward, Reverse and a third option where
the motor leads are shorted together to provide resistance to rotation
- braking.

I could use a standard battery switch except the battery switch
provides a fourth option that connects both "throws" to the single
"pole". The intention here is to connect two batteries together, but in
my situation this would be catastrophic.

A household 3 way switch is basically a SPDT switch rated 15 Amp at
120v. I don't know if this rating is sufficient for 85 Amps at 24v but
I suspect not.

Any ideas?

Thanks.

Mike
 
"Mike Kaplan" <mkaplan@kapcom.com> schreef in bericht
news:1130341807.915116.49440@g14g2000cwa.googlegroups.com...
I'm looking for 2 SPDT toggle or battery switches. The switches'
parameters:

24v
85 Amp
Break before Make

The switches will reverse current to a motor. I don't want to use
relays, solenoids or contactors - I want a mechanical switch.

The two switches will provide Forward, Reverse and a third option where
the motor leads are shorted together to provide resistance to rotation
- braking.

I could use a standard battery switch except the battery switch
provides a fourth option that connects both "throws" to the single
"pole". The intention here is to connect two batteries together, but in
my situation this would be catastrophic.

A household 3 way switch is basically a SPDT switch rated 15 Amp at
120v. I don't know if this rating is sufficient for 85 Amps at 24v but
I suspect not.

Any ideas?

Thanks.

Mike

The household switch is not suited for 85 Amps.
Click to expand...
It probably won't do 15 Amps continues either.

Alexander
 
I should add that the switches will not be opened or closed while
current is flowing. After the switch is in position, then current will
flow, so my main issue is whether the switch can handle 85 Amps at 24v
without arcing or heating.
 
On 26 Oct 2005 09:51:17 -0700, "Mike Kaplan" <mkaplan@kapcom.com>
wrote:

I should add that the switches will not be opened or closed while
current is flowing. After the switch is in position, then current will
flow, so my main issue is whether the switch can handle 85 Amps at 24v
without arcing or heating.
Click to expand...
---
Maybe I'm a little thick this afternoon, but with a single battery,
a motor with two leads coming out of it, and two SPST switches to do
the controlling I don't see how you'll be able to accomplish
reversing _and_ braking. Maybe two batteries? If you go that way
ISTM that you'll need a SPDT switch with a center-off position and
that the other switch (for braking) will only need to be SPST.

In any case, knife switches seem to me to be a pretty good option.

--
John Fields
Professional Circuit Designer
 
John,

Thanks for your response.

I thought about knife switches but couldn't find them on the internet.
Can you tell me where to find SPDT knife switches that will handle 85
Amps at 24v?

My post refers to SPDT switches. You questioned my use of SPST
switches, but I'm not considering SPST switches. I'm looking for SPDT
switches.

A sketch would be the best way to describe the configuration of the
switches, but here goes:

Each switch has three connections, a common and two terminals labelled
A and B. On each switch terminal A is connected to 24+ and terminal B
is connected to ground. The common terminal on switch 1 is connected to
one motor lead; the common terminal on switch 2 is connected to the
other motor lead.

There are 4 possibilities:

Switch 1 A, Switch 2 A - Motor is shorted to 24+.

Switch 1 A, Switch 2 B - Motor runs forward.

Switch 1 B, Switch 2 A - Motor runs reversed.

Switch 1 B, Switch 2 B - Motor is shorted to ground, provides braking.

Mike
 
On 26 Oct 2005 11:13:40 -0700, "Mike Kaplan" <mkaplan@kapcom.com>
wrote:

John,

Thanks for your response.

I thought about knife switches but couldn't find them on the internet.
Can you tell me where to find SPDT knife switches that will handle 85
Amps at 24v?

My post refers to SPDT switches. You questioned my use of SPST
switches, but I'm not considering SPST switches. I'm looking for SPDT
switches.

A sketch would be the best way to describe the configuration of the
switches, but here goes:

Each switch has three connections, a common and two terminals labelled
A and B. On each switch terminal A is connected to 24+ and terminal B
is connected to ground. The common terminal on switch 1 is connected to
one motor lead; the common terminal on switch 2 is connected to the
other motor lead.

There are 4 possibilities:

Switch 1 A, Switch 2 A - Motor is shorted to 24+.

Switch 1 A, Switch 2 B - Motor runs forward.

Switch 1 B, Switch 2 A - Motor runs reversed.

Switch 1 B, Switch 2 B - Motor is shorted to ground, provides braking.
Click to expand...
---
The SPST was a trypo, but of course you're right about the circuit.
Thick is right, I completely missed it...

Anyway, here's a link to some nice looking knife switches, and
Google will get you a lot more hits.

Also, BTW, you'll get braking whe both of the switches are in either
the 24V _or_ the ground positions.


--
John Fields
Professional Circuit Designer
 
On 2005-10-26, John Fields <jfields@austininstruments.com> wrote:
On 26 Oct 2005 09:51:17 -0700, "Mike Kaplan" <mkaplan@kapcom.com
wrote:

I should add that the switches will not be opened or closed while
current is flowing. After the switch is in position, then current will
flow, so my main issue is whether the switch can handle 85 Amps at 24v
without arcing or heating.

---
Maybe I'm a little thick this afternoon, but with a single battery,
a motor with two leads coming out of it, and two SPST switches to do
the controlling I don't see how you'll be able to accomplish
reversing _and_ braking. Maybe two batteries? If you go that way
ISTM that you'll need a SPDT switch with a center-off position and
that the other switch (for braking) will only need to be SPST.

In any case, knife switches seem to me to be a pretty good option.
Click to expand...

+---------------------+-- +V
| |
+-o-_ + _-o-+
~-o--(M)--o-~
+-o 0-+
| fwd rev |
+---------------------+-- 0V


braking by shorting the motor...

--

Bye.
Jasen
 
On Mon, 31 Oct 2005 20:20:25 +1300, Jasen Betts
<jasen-b@free.net.nospam.nz> wrote:

On 2005-10-26, John Fields <jfields@austininstruments.com> wrote:
On 26 Oct 2005 09:51:17 -0700, "Mike Kaplan" <mkaplan@kapcom.com
wrote:

I should add that the switches will not be opened or closed while
current is flowing. After the switch is in position, then current will
flow, so my main issue is whether the switch can handle 85 Amps at 24v
without arcing or heating.

---
Maybe I'm a little thick this afternoon, but with a single battery,
a motor with two leads coming out of it, and two SPST switches to do
the controlling I don't see how you'll be able to accomplish
reversing _and_ braking. Maybe two batteries? If you go that way
ISTM that you'll need a SPDT switch with a center-off position and
that the other switch (for braking) will only need to be SPST.

In any case, knife switches seem to me to be a pretty good option.


+---------------------+-- +V
| |
+-o-_ + _-o-+
~-o--(M)--o-~
+-o 0-+
| fwd rev |
+---------------------+-- 0V


braking by shorting the motor...
Click to expand...
---
Yes, that was the circuit described by the OP quite some time ago.

Maybe it's just me, but it seems like a lot of your posts appear
quite some time after the solution has been presented and then
merely echo the solution. Don't you bother to read the thread before
you post or are you plagiarizing someone else's work?

--
John Fields
Professional Circuit Designer
 
Mike Kaplan wrote:
I'm looking for 2 SPDT toggle or battery switches. The switches'
parameters:

24v
85 Amp
Break before Make

A household 3 way switch is basically a SPDT switch rated 15 Amp at
120v. I don't know if this rating is sufficient for 85 Amps at 24v but
I suspect not.
Click to expand...
Not for very long, no.

Why not use copper washers? Theyre an easy way to make 1 pole 2 way
switches, and are press button as well.

You have 3 copper washers, all threaded loosely over a thin bolt. The
middle one is bolted to the bolt, the outer 2 fixed to frame with a
small gap between them and the middle moving one. Now, add a spring to
push the plunger upward. To use, press bolthead down (add knob since
you dont want to come into contact with those inductive kickbacks). The
one I had had washers around 2cm across, handled around 200A, and
lasted about 15 years.


NT
 
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