"Ignoramus9394" wrote in message
...
| On 28 Jul 2005 13:00:53 -0700, jim rozen wrote:
| In article , Ignoramus9394
says...
|
| I see. I plan to install a regular household light switch to control
| the contactor. UP means run, DOWN means stop. I will have two
| electrical boxes on the outside of my RPC: one for incoming single
| phase power and the switch, another for outgoing power. I may also
| install a Square D disconnect on the outgoing side of the
| converter. I already bought that disconnect used.
|
| You can use your furnas contactor as a drop-out device.
| You wire it to hold in, using the third contact.
|
| Oh, yes, that's right. How stupid of me not to think of that. I will
| try to dig for a start button and stop button. I think that that's all
| I need.
|
| The other two contacts carry the incoming 240 volt lines
| to the motor.
|
| This way a control circuit (which really should be derived from
| the same incoming 240 volt lines via a 240:120 transformer)
| with two pushbuttons can run the thing, and the buttons don't
| carry the load currents.
|
| Well, I can use a separate neutral just for control purposes.
|
| Anyway, is this start/stop switch just what I need?
|
|
http://www.surpluscenter.com/item.as...tname=electric
|
| thanks
|
| i
That will work, but if you intend to use it, you want to learn how to
work with basic control wiring, as start-stop stations are usually expected
to be set up with a holding contact. What that means is when the start
button is pushed, the starter engages, and an auxiliary contact then
bypasses the start switch, holding it on when you let the start button go.
The stop button is wired in series with the holding circuit, so that when
you push the stop button the circuit "falls out" completely.
Personally, I'd recommend a stop button of the mushroom style as a
better safety function. Anyone can slap the stop button and it shuts down.
There's a specific minimum distance that is required between the stop button
and the machinery, and often there will be more than one stop button, which
complicates the wiring dramatically. I like the simple mushroom with a push
pull. When pushed in, the equipment is unpowered, and when you pull it back
out (or twist it to the left to release it,) it can operate again. Your
call as to where you sit safety wise and all that, since it's obviously not
an industrial application that has to conform to all the same rules. IIRC,
OSHA or some other agency has changed the rules about safety stops, leaving
a lot of old hardware out there.
I'm not sure I read it all correctly, but the mention of a dropout
confused me. A dropout kills specified circuitry when a particular phase
drops out, low voltage exists on any leg, or a few other conditions exist.
You can do just that by simply changing the contactor coil to a 240V coil
and wiring as such. If you lose the leg that isn't providing control power
things will be unsafe although the RPC won't be running, but if the coil is
across both legs, then there's the inherent safety.
I'm not trying to get you to spend more money on a project that you are
obviously proud of. I commend you for whipping it up for so cheap, because
I'd be trying to do it even cheaper if I could. However, seeing as how you
value the lives of your children, and I assume your own, safety to me is
more of an issue at home than at work in this respect. At work I understand
and properly deal with the inherent hazards that I know exist, as I've been
trained to do. I can't expect SWMBO and my kids to understand, nor do I
expect them to instantly know what button to push when they're panicking, as
the victim could be you. The simpler the shutdown process the better. As
long as they know that there is one simple button that can be operated with
an elbow or hand the better. Something like this comes to mind:
http://www.surpluscenter.com/item.as...m=11-2520&catn
ame=electric Not necessarily the source you want (although inexpensive) is
automationdirect.com and if you look at item E22JPLB2B you'll get the idea.
If you want, I will revisit your schematic and see if I can help you
make your control both wiring simple and safer for all of you, although I'm
sure there's folks here more experienced than I in the matter. The best
part is that if you think surplus three phase motors are cheap, you should
see all the gobs of control devices that get tossed regularly! It's cheaper
than trying to salvage them, so usually they hit the trashpile. Your
surplus supplier might have a control box or twenty that has the hardware
you can salvage. Lots of folks think they can save the control boxes, too,
but that's even more specialized than the contents, unless it's more
standard or hasn't been punched out too heavily.
Again, I want to add how much what you've done on a shoestring for many
things has impressed more than just me, I think it impresses a lot of us,
and the fact that you are willing to ask for help and take this overload of
information in and make good use of it without taking too many of us
personally. I just wish you were my neighbor, I wouldn't have to buy or
build all this expensive stuff myself!