In article ,
Ignoramus17647 wrote:

How long are your mechanical switches going to last at 60
operations/second? If you can get 1 million operations, that is 277
hours, or 11 days. I'd suspect a mechanical switch will not last
even that long at such a rate.

This is an excellent question. I am thinking, that what I want to do
is similar to "brushes" on electric motors with brushes, and these
last a long enough time. Maybe I can use same sort of brushes.

Igreatly appreciate your input, please do not hold back!

Ya know, instead of switches, you could mount a few magnets on the
wheel and whizz 'em past little coils. Then use that induced current to
switch your transistors. Might have to set up a cascade of transistors
to step up from the wee induced currents to something that could drive
your big transistors cleanly.

--
B.B. --I am not a goat! thegoat4 at airmail dot net
http://web2.airmail.net/thegoat4/

Hey Pete,

Worked OK for me, so here is one of the Item numbers, then do a search
for Sellers Other Items.

3875488109

or maybe just try the lathe.....

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=97230&item=3875488 109&rd=1&ssPageName=WDVW

Take care.

Brian Lawson,
Bothwell, Ontario.

XXXXXXXXXXXXXXXXXXXXXXXXX

On Fri, 18 Feb 2005 13:55:35 -0600, "B.B."
u wrote:

In article ,
Ignoramus17647 wrote:

How long are your mechanical switches going to last at 60
operations/second? If you can get 1 million operations, that is 277
hours, or 11 days. I'd suspect a mechanical switch will not last
even that long at such a rate.

This is an excellent question. I am thinking, that what I want to do
is similar to "brushes" on electric motors with brushes, and these
last a long enough time. Maybe I can use same sort of brushes.

Igreatly appreciate your input, please do not hold back!

Ya know, instead of switches, you could mount a few magnets on the
wheel and whizz 'em past little coils. Then use that induced current to
switch your transistors. Might have to set up a cascade of transistors
to step up from the wee induced currents to something that could drive
your big transistors cleanly.

WHOOPS....SORRY....thais was supposed to be a reply to another post.

XXXXXXXXXXXXXXXXXXXXXXXX
On Sat, 19 Feb 2005 08:00:05 -0500, Brian Lawson
wrote:

Hey Pete,

Worked OK for me, so here is one of the Item numbers, then do a search
for Sellers Other Items.

3875488109

or maybe just try the lathe.....

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=97230&item=3875488 109&rd=1&ssPageName=WDVW

Take care.

Brian Lawson,
Bothwell, Ontario.

XXXXXXXXXXXXXXXXXXXXXXXXX

On Fri, 18 Feb 2005 13:55:35 -0600, "B.B."
. ru wrote:

In article ,
Ignoramus17647 wrote:

How long are your mechanical switches going to last at 60
operations/second? If you can get 1 million operations, that is 277
hours, or 11 days. I'd suspect a mechanical switch will not last
even that long at such a rate.

This is an excellent question. I am thinking, that what I want to do
is similar to "brushes" on electric motors with brushes, and these
last a long enough time. Maybe I can use same sort of brushes.

Igreatly appreciate your input, please do not hold back!

Ya know, instead of switches, you could mount a few magnets on the
wheel and whizz 'em past little coils. Then use that induced current to
switch your transistors. Might have to set up a cascade of transistors
to step up from the wee induced currents to something that could drive
your big transistors cleanly.

By the way, you can't build an inverter with SCRs. An SCR can only be
turned on, not off, on command. Once you turn it on, it will not shut
off until the current through it goes to zero. For building an
inverter, you want power devices that can switch on _and_ off in the
kHz range in order to PWM all the phases you are trying to drive. SCRs
are fine for dimmers and heaters, and if you look at designs for those
you will see that they rely on triggering the SCR at a variable phase
angle, but it is always variable moving back from the zero crossing.

So you want to be using IGBTs probably, although you can also do it
with FETs. As other people have mentioned, there are _lots_ of details
to take care of in this seemingly simple system. Try building a good
variable speed DC motor controller first, since that is sort of like
1/3 of what you are eventually going to get to.

-Holly

Holly,
Maybe someone "lost the recipe" since SCR circuits have been used ever
since they were invented with commutation circuits. There are even
application notes on using SCR drives for DC motors driven from
batteries. My brother used to have an inverter that took 24 volts and
generated 240 volts AC and the active devices were in fact just two
SCR's.
That was his power source in the Alaskan wilderness. It had to be
reliable.

Now, in todays modern world, there are much better solutions, but don't
believe that they can't be used for inverters or commutated once turned
on.

Pete