Solid State Relay - 230VAC; 30 AMP
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Just bought a Harbor Freight 230 volt spot welder - it requires a 30
amp circuit. I'd like to build a timer using a Basic Stamp and a
solid state relay. I think that I can figure out the Basic Stamp
end - I'm guessing that I'll write some code to first allow the user
to select between a .5 second and a 5.0 second pulse time, and then
based on that input I'll power up a pin to trigger a solid state
relay. Unfortunately, that's about the limit of my understanding.
I'm guessing that I'll need a solid state relay that has two
switches (is this called a two pole?) - one switch for each leg of
the 230 VAC circuit. Also, I assume that there is some designation
for "normally open". Finally, I'm guessing that a relay that will
switch two 115VAC legs will also require its own separate power
supply - meaning that the +5VDC of the pin will not be powerful
enough to close the relay.
Specific questions:
1) Am I on the right track?
2) Any suggestions regarding how I would specify the relay I'm
talking about?
3) Suggestions for sources of the relay?
Thanks,
Bob Jacoby
Florida
amp circuit. I'd like to build a timer using a Basic Stamp and a
solid state relay. I think that I can figure out the Basic Stamp
end - I'm guessing that I'll write some code to first allow the user
to select between a .5 second and a 5.0 second pulse time, and then
based on that input I'll power up a pin to trigger a solid state
relay. Unfortunately, that's about the limit of my understanding.
I'm guessing that I'll need a solid state relay that has two
switches (is this called a two pole?) - one switch for each leg of
the 230 VAC circuit. Also, I assume that there is some designation
for "normally open". Finally, I'm guessing that a relay that will
switch two 115VAC legs will also require its own separate power
supply - meaning that the +5VDC of the pin will not be powerful
enough to close the relay.
Specific questions:
1) Am I on the right track?
2) Any suggestions regarding how I would specify the relay I'm
talking about?
3) Suggestions for sources of the relay?
Thanks,
Bob Jacoby
Florida
Comments
You will need more than a 30 amp SSR if the machine requires a 30 amp
circuit.
Welding equipment will give the current draw on the rating plate. Normally
you would go with the next higher service rating. For a 30 amp machine I would
recommend to my customer he use a 45 amp service with Slo-Blo Fuses.
The reason for this is the main transformer in this type of equipment, acts
like a dead short for the first 1/2 line cycle, until the magnetic field has
built up in the transformer. This inrush current can be 300-400% higher, over
100 amps. This will also destroy most 30 amp SSR's.
Ben there, got the brochure.
On the other hand, there should be a trigger circuit to activate the welder.
This will usually be a relay controlled by the Stamp. The relay contacts will
most likely be 1 amp or less. Your manual should specify this.
You power on the machine, the cooling fan(s) run all the time, and when you
close the relay, the machine closes its main contractor and energizes the
transformer, and the welding circuit. I control multiple 1000 amp Plasma Cutters
this way. They are the same as welders, just a higher DC voltage.
If you have any questions let me know. I have not seen a welder that does not
work this way, as a unit that is always on with power would not be safe.
Thanks,
Alan Bradford
Plasma Technologies
www.plasmatechnologies.com
In a message dated 4/6/2004 11:12:15 PM Eastern Daylight Time,
BobJacoby@B... writes:
Just bought a Harbor Freight 230 volt spot welder - it requires a 30
amp circuit. I'd like to build a timer using a Basic Stamp and a
solid state relay. I think that I can figure out the Basic Stamp
end - I'm guessing that I'll write some code to first allow the user
to select between a .5 second and a 5.0 second pulse time, and then
based on that input I'll power up a pin to trigger a solid state
relay. Unfortunately, that's about the limit of my understanding.
I'm guessing that I'll need a solid state relay that has two
switches (is this called a two pole?) - one switch for each leg of
the 230 VAC circuit. Also, I assume that there is some designation
for "normally open". Finally, I'm guessing that a relay that will
switch two 115VAC legs will also require its own separate power
supply - meaning that the +5VDC of the pin will not be powerful
enough to close the relay.
Specific questions:
1) Am I on the right track?
2) Any suggestions regarding how I would specify the relay I'm
talking about?
3) Suggestions for sources of the relay?
Thanks,
Bob Jacoby
Florida
[noparse][[/noparse]Non-text portions of this message have been removed]
Alan's note on inrush currents is "spot on" [noparse];)[/noparse] Sorry, I couldn't
resist.(oops.... yet another pun).
The spot welders I used a while back all had 100-amp SCR's on the 30-amp
feed supply. So certainly a "little" 30-amp SSR would be destroyed by the
inrush. If you can find some really big surplus SCRs (C&H Sales has surplus
units), you might build your own SSR using a zero-crossover IC to trigger
your industrial-duty triac. The IC number escapes me, but I used them 20
years ago, so I'm sure there's modern inexpensive ICs that do the same
thing.
Also, be aware that welders generate huge magnetic fields that can couple
into anything nearby. Shielding will be very important, as will isolating
your Stamp's power supply from the AC line.
Mike Sokol
mike@f...
www.fitsandstarts.com
" One should not increase, beyond what is necessary,
the number of entities required to explain anything"...
-William of Occam-
Original Message
From: "jacoby01" <BobJacoby@B...>
To: <basicstamps@yahoogroups.com>
Sent: Tuesday, April 06, 2004 10:22 PM
Subject: [noparse][[/noparse]basicstamps] Solid State Relay - 230VAC; 30 AMP
> Just bought a Harbor Freight 230 volt spot welder - it requires a 30
> amp circuit. I'd like to build a timer using a Basic Stamp and a
> solid state relay. I think that I can figure out the Basic Stamp
> end - I'm guessing that I'll write some code to first allow the user
> to select between a .5 second and a 5.0 second pulse time, and then
> based on that input I'll power up a pin to trigger a solid state
> relay. Unfortunately, that's about the limit of my understanding.
> I'm guessing that I'll need a solid state relay that has two
> switches (is this called a two pole?) - one switch for each leg of
> the 230 VAC circuit. Also, I assume that there is some designation
> for "normally open". Finally, I'm guessing that a relay that will
> switch two 115VAC legs will also require its own separate power
> supply - meaning that the +5VDC of the pin will not be powerful
> enough to close the relay.
>
> Specific questions:
>
> 1) Am I on the right track?
>
> 2) Any suggestions regarding how I would specify the relay I'm
> talking about?
>
> 3) Suggestions for sources of the relay?
>
>
>
> Thanks,
>
> Bob Jacoby
> Florida
>
>
>
>
> To UNSUBSCRIBE, just send mail to:
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the power to stop flowing. However, having said that, this leaves one side
hot. Since it's inside a welder, this may not be considered a problem.
Your call. I haven't seen 2PST solid state relays, but two individual ones
would work fine in your application, one for each leg. Drive the inputs in
parallel.
Note that solid state relays, when running a bunch of power, need a good
heat sink. Bolt them down to good metal, use heat sink grease. Feel the
area nearby after working for a few minutes. If it's very warm, think on
more sinking or air movement.
Look at the ratings on the welder. Though it takes a 30 Amp circuit, it is
possible that it will draw more under bad circumstances. Doesn't take many
over current activities to kill a relay.
A one shot driving the relays might be more simple than a stamp, but either
way, it's fun.
Look at digikey.com for parts. They have a good search engine, web links to
the catalog pages, and links to either data sheets or the manufacturers.
Many solid state relays will turn on from 3 to about 24 Volts, and draw only
milliamps. Check the ratings, but the ones I use, I drive directly with
TTL, and the stamp is TTL compatible.
Good luck<G>.
Original Message
From: jacoby01 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=F_ZSfwWhQsuXm4NVO0Sn1WgNGbOtW4zEAfg-gIFiOWWfABjVoYz2QvEDmocttBRVDqdSHnej_-uwdof01lLOcA]BobJacoby@B...[/url
Sent: Tuesday, April 06, 2004 10:22 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Solid State Relay - 230VAC; 30 AMP
Just bought a Harbor Freight 230 volt spot welder - it requires a 30
amp circuit. I'd like to build a timer using a Basic Stamp and a
solid state relay. I think that I can figure out the Basic Stamp
end - I'm guessing that I'll write some code to first allow the user
to select between a .5 second and a 5.0 second pulse time, and then
based on that input I'll power up a pin to trigger a solid state
relay. Unfortunately, that's about the limit of my understanding.
I'm guessing that I'll need a solid state relay that has two
switches (is this called a two pole?) - one switch for each leg of
the 230 VAC circuit. Also, I assume that there is some designation
for "normally open". Finally, I'm guessing that a relay that will
switch two 115VAC legs will also require its own separate power
supply - meaning that the +5VDC of the pin will not be powerful
enough to close the relay.
Specific questions:
1) Am I on the right track?
2) Any suggestions regarding how I would specify the relay I'm
talking about?
3) Suggestions for sources of the relay?
Thanks,
Bob Jacoby
Florida
To UNSUBSCRIBE, just send mail to:
basicstamps-unsubscribe@yahoogroups.com
from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
Yahoo! Groups Links
> Just bought a Harbor Freight 230 volt spot welder - it requires a
30
> amp circuit. I'd like to build a timer using a Basic Stamp and a
> solid state relay. I think that I can figure out the Basic Stamp
> end - I'm guessing that I'll write some code to first allow the
user
> to select between a .5 second and a 5.0 second pulse time, and then
> based on that input I'll power up a pin to trigger a solid state
> relay. Unfortunately, that's about the limit of my understanding.
> I'm guessing that I'll need a solid state relay that has two
> switches (is this called a two pole?) - one switch for each leg of
> the 230 VAC circuit. Also, I assume that there is some designation
> for "normally open". Finally, I'm guessing that a relay that will
> switch two 115VAC legs will also require its own separate power
> supply - meaning that the +5VDC of the pin will not be powerful
> enough to close the relay.
>
> Specific questions:
>
> 1) Am I on the right track?
>
> 2) Any suggestions regarding how I would specify the relay I'm
> talking about?
>
> 3) Suggestions for sources of the relay?
>
>
>
> Thanks,
>
> Bob Jacoby
> Florida
Hi Bob,
Here is the answer to #1 AM I ON THE RIGHT TRACK ?
Not completely. I think you may be over complicating it a bit.
First, I would warn about altering a product or mixing high voltage
AC loops with low voltage stuff.
Also a plasma/arc can wreak havoc on your logic and low voltage
controls.
Second, I would NOT add external relays to the device. Much like
altering the speed of a car with an anchor, the relay you want to hit
is internal, sized and installed my the equipment manufacturer. I am
thinking of welders with internal logic here and not the ones that
are simple transformers. But, I would look at where the manufacturer
put the power interrupt circuit.
Also, best (simplest) connection would be the hand switch.
A simple solenoid could be used to activate the switch and leave the
unit intact. This could be as simple as a clamp on device that
leaves your main unit factory fresh.
Adding electrical connections to allow an external low power relay to
duplicate the switch functions could be at the switch, or at the main
unit on the same connections as the hand device.
If the unit is one of those portable units ITEM 45690-3VGA, the
power switch is a toggle switch. You can add a solenoid onto that so
the solenoid activates the switch and you do not have to do any
further modifications.
And if you expect any sort of production from the device, consider
replacing the switch with a relay. and this may come full circle.
If the switch is the AC primary, it will be high voltage, low current
(i.e.: probably less than 10 amps) And if the unit is mostly a
transformer and a switch (yes welders can be that simple) then your
original idea of a relay is pretty simple.
now, the circle is complete.... (heavy mechanical breathing)... first
the relay was on the power and now the relay is on the power...
(more mechanical breathing....) Luke...
Question #2) Any suggestions regarding how I would specify the relay
I'm talking about?
For any high AC relay that will be controlled a micro, I would
seriously consider a solid state relay (SSR) the reason is that
electromechanical relays offer different problems. One is that
switching speed is really slow in electrical terms and the state
change creates a spike creating electrical noise.
Also, the unit must be sized, in your case, for production use. That
is to say more than a few times an hour. The relay will get hot as
it activates and heat will shorten the life. For multiple operations
per hour I would consider a relay rating of twice the current draw.
#3 sources, Jameco offers SSR relays for a decent price.
Jameco #176719 $19.99, RELAY,SOLID STATE,DC/AC INPT:3-
32VDC,OUT:280VAC@40A
But, remember that 230 VAC as TWO hot lines, not like 120 VAC that
has a hot and a neutral.
Dave
> amp circuit. I'd like to build a timer using a Basic Stamp and a
> solid state relay. I think that I can figure out the Basic Stamp
> end - I'm guessing that I'll write some code to first allow the user
> to select between a .5 second and a 5.0 second pulse time, and then
> based on that input I'll power up a pin to trigger a solid state
> relay.
DANGER WILL ROBINSON! Be extremely careful; You're working with deadly
voltages (and currents) here.
For the low frequencies (2 Hz to .2 Hz) you need you could just use a
conventional (electro-mechanical) relay. You do need to switch both legs so
a double pole single throw (normally open) should do the job as long as it's
rated for at least 30 amps. Connect a BS2 pin to the base of a transistor
that has its emitter grounded and then hook the collector to one side of the
relay coil and the other side of the relay coil to whatever operating
voltage the relay requires. The transistor will have to be able to handle
the holding current of the relay coil (and may require a head sink). You
should also put a diode across the relay to snuff EMF currents for when the
transistor opens.
--
Enjoy,
George Warner,
Schizophrenic Optimization Scientists
Apple Developer Technical Support (DTS)
The timing that is used in large spot welding machines uses quite small
times when the welder is on (welding).
We typically measure times in how many cycles of "heat" that we want.
The welding cycles are further controlled with back to back SCRs that
control the amount of each cycle that current flows. e.g.. 15 cycles at 68 %
heat might be part of a particular weld schedule.
I don't know if small spot welders need this quality of control.
I would hazard a guess that 5 seconds is a very long time to spot weld.
Large welder control cabinets only control one leg of the 480 VAC that we
use, and a 2 pole contactor removes the transformer from the line voltages
after a no weld time out period.
I hope this helps.
Scott
Just bought a Harbor Freight 230 volt spot welder - it requires a 30
amp circuit. I'd like to build a timer using a Basic Stamp and a
solid state relay. I think that I can figure out the Basic Stamp
end - I'm guessing that I'll write some code to first allow the user
to select between a .5 second and a 5.0 second pulse time, and then
based on that input I'll power up a pin to trigger a solid state
relay. Unfortunately, that's about the limit of my understanding.
I'm guessing that I'll need a solid state relay that has two
switches (is this called a two pole?) - one switch for each leg of
the 230 VAC circuit. Also, I assume that there is some designation
for "normally open". Finally, I'm guessing that a relay that will
switch two 115VAC legs will also require its own separate power
supply - meaning that the +5VDC of the pin will not be powerful
enough to close the relay.
Specific questions:
1) Am I on the right track?
2) Any suggestions regarding how I would specify the relay I'm
talking about?
3) Suggestions for sources of the relay?
Thanks,
Bob Jacoby
Florida
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each NO (Normally Open) and NC (Normally Open ) contacts Normally Open ( or
closed) is defined as what state the contact is in (open or closed) when the
relay is in the shelf or de-energized state. Hope this helps.
jacoby01 <BobJacoby@B...> wrote:Just bought a Harbor Freight 230 volt
spot welder - it requires a 30
amp circuit. I'd like to build a timer using a Basic Stamp and a
solid state relay. I think that I can figure out the Basic Stamp
end - I'm guessing that I'll write some code to first allow the user
to select between a .5 second and a 5.0 second pulse time, and then
based on that input I'll power up a pin to trigger a solid state
relay. Unfortunately, that's about the limit of my understanding.
I'm guessing that I'll need a solid state relay that has two
switches (is this called a two pole?) - one switch for each leg of
the 230 VAC circuit. Also, I assume that there is some designation
for "normally open". Finally, I'm guessing that a relay that will
switch two 115VAC legs will also require its own separate power
supply - meaning that the +5VDC of the pin will not be powerful
enough to close the relay.
Specific questions:
1) Am I on the right track?
2) Any suggestions regarding how I would specify the relay I'm
talking about?
3) Suggestions for sources of the relay?
Thanks,
Bob Jacoby
Florida
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[noparse][[/noparse]Non-text portions of this message have been removed]
Just reading the responses for this project, I will offer my 2 cents worth.
First you are working with large DC Currents. They can kill you faster than
an equivalent AC RMS jolt. DC makes your muscles contract, and you may not be
able to let go from the circuit. With AC you can get a second chance..DC you
usually do not.
Remember it only takes 150 Microamps through your heart to stop it.
Now that the lawyers are happy.....
If this was purchased from Harbor Freight, it is most likely a low duty
cycle, hobbiest/small fabricator type machine. The unit will most likely burn up
if
put into a production environment that exceeds the designed for duty cycle.
Most welders and plasma cutters of this type are 20% duty cycle or less. That
means for every 2 minutes of operation you need to cool it for 8 minutes. I
have not delt specifically with spot welders, so check the information that came
with it. It will tell you the duty cycle and period. It may be 5 seconds on
and 20 seconds off. There usually is a temperature sensor in the transformer to
shut it down if it gets too hot. This is a cheap Bimetal device that is one of
the finest sensors you can buy for a Nickel. Usually the machine overheats
long before the device opens up, then it will short cycle until it has fully
cooled down (Usually a few hours)
There is most likely a Start/Stop contact closure or Switch input. I would
use this to trigger the unit. Drive a mechanical relay from a transistor
connected to the coil. I use Opto-isolators or small Solid State relays to drive
the
mechanical relay. This also isolates the Stamp power from the switching
circuits.
The contacts of the relay will connect to the Start input or across the Start
switch. If in doubt about how to do this, consult the manual and schematics.
Usually the schematic is inside a cover if it is not in the manual.
If you do have to switch the input power, unless you use a 100 amp or larger
SSR, you will blow it in short order..Been there and have the burnt tee shirt
to prove it. The inrush spikes will hammer away at the triacs in the relay. If
you spec a 1200 volt or higher Unit you may be OK. Use a mechanical contactor
rated for 40-50 amps. You can get cheap ones from
Automationdirect.(www.automationdirect.com) Around 20-30 bucks. I use them all
the time and in this type
of application it should last many years. The contacts have a special silver
coating that resists the pitting from the arcing when making/breaking. And they
are cheaper than the larger SSR's and require no heat sinking or cooling.
Hope this helps you.
If you have any questions let me know.
Thanks,
Alan Bradford
Plasma Technologies
www.plasmatechnologies.com
In a message dated 4/6/2004 11:12:15 PM Eastern Daylight Time,
BobJacoby@B... writes:
Just bought a Harbor Freight 230 volt spot welder - it requires a 30
amp circuit. I'd like to build a timer using a Basic Stamp and a
solid state relay. I think that I can figure out the Basic Stamp
end - I'm guessing that I'll write some code to first allow the user
to select between a .5 second and a 5.0 second pulse time, and then
based on that input I'll power up a pin to trigger a solid state
relay. Unfortunately, that's about the limit of my understanding.
I'm guessing that I'll need a solid state relay that has two
switches (is this called a two pole?) - one switch for each leg of
the 230 VAC circuit. Also, I assume that there is some designation
for "normally open". Finally, I'm guessing that a relay that will
switch two 115VAC legs will also require its own separate power
supply - meaning that the +5VDC of the pin will not be powerful
enough to close the relay.
Specific questions:
1) Am I on the right track?
2) Any suggestions regarding how I would specify the relay I'm
talking about?
3) Suggestions for sources of the relay?
Thanks,
Bob Jacoby
Florida
[noparse][[/noparse]Non-text portions of this message have been removed]
> Just bought a Harbor Freight 230 volt spot welder - it requires a
30
> amp circuit.
I've looked at the HF website and found 4 spot welders. Two were 230
volt models.
ITEM 45690-3VGA is 2.5KVA @50% duty cycle and that would calculate
out to only 10 Amps AC (primary) although the spec listing call out
6.75 amps. The operating current at the lower voltage at the
electrodes might be higher.
Also, the on-line manual did not seem to make any references to the
required AC limits or breakers.
Dave