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Looking for special SPDT switches

M

Mike Kaplan

Jan 1, 1970
0
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
 
A

Alexander

Jan 1, 1970
0
Mike Kaplan said:
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.
It probably won't do 15 Amps continues either.

Alexander
 
M

Mike Kaplan

Jan 1, 1970
0
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.
 
M

Mike Kaplan

Jan 1, 1970
0
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
 
J

Jasen Betts

Jan 1, 1970
0
---
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...
 
Mike said:
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.

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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