Relay Ratings
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Posts: 46,084
Hello:
My current project is a relay driver and although this question isn't
strictly a stamp based one I was hoping somebody could help me out a
bit. I'm going to use the relays to control a 120 VAC circuit and I
have some great 30 AMP Automotive relays but they were originally
designed for 12 volts. If I put 120 Vac through the contacts will
they have an okay life span.
Thank you
Aaron Nielsen
My current project is a relay driver and although this question isn't
strictly a stamp based one I was hoping somebody could help me out a
bit. I'm going to use the relays to control a 120 VAC circuit and I
have some great 30 AMP Automotive relays but they were originally
designed for 12 volts. If I put 120 Vac through the contacts will
they have an okay life span.
Thank you
Aaron Nielsen
Comments
with little or no problem. The coil must still be run at 12 volts and
this will have to be DC not AC. I must caution you that if a problem
occurs with a fire or some unforeseen because of your design, there may
be repercussions down the road. 12 volt relay's were designed to be
safe at 12 Volts. 120 VAC relays are designed accordingly. Good luck
with your project and if you decide you need some higher power relays,
they are called contactors or motor starters and can be found in
Industrial equipment, sometimes real cheap..
Kind Regards,
Leroy
Aaron wrote:
>
> Hello:
>
> My current project is a relay driver and although this question isn't
> strictly a stamp based one I was hoping somebody could help me out a
> bit. I'm going to use the relays to control a 120 VAC circuit and I
> have some great 30 AMP Automotive relays but they were originally
> designed for 12 volts. If I put 120 Vac through the contacts will
> they have an okay life span.
>
> Thank you
> Aaron Nielsen
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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of the message will be ignored.
>
>
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--
*******************************************************
* Leroy Hall *
* 317 Cherokee Drive *
* Loveland, Ohio - USA 45140-2404 *
*******************************************************
* Phone: (513) 697-7539 *
* Cell : (513) 300-8632 *
* Email: leroy@f... *
* Home page URL: http://home.fuse.net/leroy/ *
* Resume URL: http://home.fuse.net/leroy/resume.htm *
*******************************************************
* Leroy Hall *
* 317 Cherokee Drive *
* Loveland, Ohio - USA 45140-2404 *
*******************************************************
or resistance, *and* the current ratings for the contacts at various
voltages. There are relays with a12-volt coil that are designed to switch
120 volts AC, but the automotive relays are probably not the ones designed
for that.
Original Message
> My current project is a relay driver and although this question isn't
> strictly a stamp based one I was hoping somebody could help me out a
> bit. I'm going to use the relays to control a 120 VAC circuit and I
> have some great 30 AMP Automotive relays but they were originally
> designed for 12 volts. If I put 120 Vac through the contacts will
> they have an okay life span.
relay is designed for 12 volts then it probably has insulation,
creeepage and clearance distances designed for 12 volts and that could
result in problems. Probably would be a better idea to spend $5 and get
a relay that won't risk burning things up. Also with the increased
voltage across the contacts there is the possibility that arcing could
occur with the relay in the open position. This potential for arcing
would vary with humidity and temperature.
On Fri, 10 Aug 2001 20:22:53 -0000 "Aaron" <snazzyguy2@y...> writes:
> Hello:
>
> My current project is a relay driver and although this question
> isn't
> strictly a stamp based one I was hoping somebody could help me out a
>
> bit. I'm going to use the relays to control a 120 VAC circuit and I
> have some great 30 AMP Automotive relays but they were originally
> designed for 12 volts. If I put 120 Vac through the contacts will
> they have an okay life span.
>
> Thank you
> Aaron Nielsen
>
>
> 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.
>
>
> Your use of Yahoo! Groups is subject to
> http://docs.yahoo.com/info/terms/
>
>
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energize the relay coil, which I'm sure you probably realize. I'd say
you'd be okay as long you don't pass any more than 2A or so through
the contacts at 120VAC. I'm not 100% for sure on any of this but if
it were me I'd give it a shot for the hell of it.
Maybe some other people on this list can help me (us) out here on my
2A calculation. 120VAC is somewhere around 170 volts peak I belive
(120 * sqrt2?), 170 volts is roughly 14.2 times higher than 12V,
30A/14.2 = 2A. Does this even apply? I don't know. Maybe someone
can confirm or deny this logic and give some better insight.
On the other hand.....
You may wish to consider using an optoisolated module like the ones
sold by Opto22 (http://www.opto22.com, take a look at their G1 or G4
models). These devices will interface to your stamp nicely since they
are controlled by a low current 5V source. Quick, easy, fairly cheap.
If you use your automotive relays you'll have to somehow step up your
stamp output from 5V to 12V at a much higher current output. This
will obviously require more circuitry, headaches, etc. I always
prefer the easier and less complex method that's easy to work on/fix
later as opposed to saving a few bucks.
--- In basicstamps@y..., "Aaron" <snazzyguy2@y...> wrote:
> Hello:
>
> My current project is a relay driver and although this question
isn't
> strictly a stamp based one I was hoping somebody could help me out a
> bit. I'm going to use the relays to control a 120 VAC circuit and I
> have some great 30 AMP Automotive relays but they were originally
> designed for 12 volts. If I put 120 Vac through the contacts will
> they have an okay life span.
>
> Thank you
> Aaron Nielsen
can handle 10A then it'll handle 10A at any voltage, so long as the
insulation is enough for said voltage.
I've used automotive relays before without any trouble, but never for
permanent installations, so I can't be sure of their longevity.
Jason
tbanez@h... wrote:
>
> Like someone else mentioned before, you'll still require 12V to
> energize the relay coil, which I'm sure you probably realize. I'd say
> you'd be okay as long you don't pass any more than 2A or so through
> the contacts at 120VAC. I'm not 100% for sure on any of this but if
> it were me I'd give it a shot for the hell of it.
>
> Maybe some other people on this list can help me (us) out here on my
> 2A calculation. 120VAC is somewhere around 170 volts peak I belive
> (120 * sqrt2?), 170 volts is roughly 14.2 times higher than 12V,
> 30A/14.2 = 2A. Does this even apply? I don't know. Maybe someone
> can confirm or deny this logic and give some better insight.
>
> On the other hand.....
>
> You may wish to consider using an optoisolated module like the ones
> sold by Opto22 (http://www.opto22.com, take a look at their G1 or G4
> models). These devices will interface to your stamp nicely since they
> are controlled by a low current 5V source. Quick, easy, fairly cheap.
>
> If you use your automotive relays you'll have to somehow step up your
> stamp output from 5V to 12V at a much higher current output. This
> will obviously require more circuitry, headaches, etc. I always
> prefer the easier and less complex method that's easy to work on/fix
> later as opposed to saving a few bucks.
>
> --- In basicstamps@y..., "Aaron" <snazzyguy2@y...> wrote:
> > Hello:
> >
> > My current project is a relay driver and although this question
> isn't
> > strictly a stamp based one I was hoping somebody could help me out a
> > bit. I'm going to use the relays to control a 120 VAC circuit and I
> > have some great 30 AMP Automotive relays but they were originally
> > designed for 12 volts. If I put 120 Vac through the contacts will
> > they have an okay life span.
> >
> > Thank you
> > Aaron Nielsen
>
> 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.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
--
_______________________________________________
Jason Lavoie
jlavoie@e...
jlavoie@o...
ICQ#:10604243
Electrical Engineering III, Carleton University
usually measured in tenths (.01) of an ohm or less. What's more
important here is the speed at which they open when commanded to open
and the speed at which they close. Also, it's important as to the
distance the contacts are open to. I would expect a contact rated for
120VAC might be several thousands wider when open to prevent arcing when
controlling an inductive load. So there is a little more to what
happening here than just ohm's lam.
Kind regards,
Leroy
tbanez@h... wrote:
>
> Like someone else mentioned before, you'll still require 12V to
> energize the relay coil, which I'm sure you probably realize. I'd say
> you'd be okay as long you don't pass any more than 2A or so through
> the contacts at 120VAC. I'm not 100% for sure on any of this but if
> it were me I'd give it a shot for the hell of it.
>
> Maybe some other people on this list can help me (us) out here on my
> 2A calculation. 120VAC is somewhere around 170 volts peak I belive
> (120 * sqrt2?), 170 volts is roughly 14.2 times higher than 12V,
> 30A/14.2 = 2A. Does this even apply? I don't know. Maybe someone
> can confirm or deny this logic and give some better insight.
>
> 2A calculation. 120VAC is somewhere around 170 volts peak I belive
> (120 * sqrt2?), 170 volts is roughly 14.2 times higher than 12V,
> 30A/14.2 = 2A. Does this even apply? I don't know. Maybe someone
> can confirm or deny this logic and give some better insight.
It doesn't apply to the contacts themselves, but it does apply to the
load. If you had a 120W resistive load it would require 10A at 12V
but 1A at 120V and you could select a relay accordingly.
Where you can run into lifetime issues is not having enough current
going through the contacts. Different material is used for different
current levels and a minimum (wetting) current is required to keep
the contacts free of oxidation and other build-ups that add
resistance. Assuming your load is more than say 100mA, you
probably don't have to worry about that in this case.
The voltage rating does matter though.
An automotive relay is designed for an environment where the
normal operation is 12V and an expected fault situation (ie. surge)
is < 100V. A mains rated relay environment is normally 120VAC
and an expected fault situation is >1000V. The relay must be
constructed with that voltage in mind, particularly from the contacts
to the coil. So if you use the automotive relay, all will be fine until
you get a power surge. Then you have a high voltage looking for
somewhere to go and your low voltage circuitry is within its reach
because there isn't much insulation between the contacts and the
coil.
Regards,
Steve.
======================================================
Steve Baldwin Electronic Product Design
TLA Microsystems Ltd Microcontroller Specialists
PO Box 15-680, New Lynn http://www.tla.co.nz
Auckland, New Zealand ph +64 9 820-2221
email: steveb@t... fax +64 9 820-1929
======================================================
about 20 amps of current running through it, by only using five volts from
the stamp.
Original Message
From: Aaron <snazzyguy2@y...>
To: <basicstamps@yahoogroups.com>
Sent: Friday, August 10, 2001 3:22 PM
Subject: [noparse][[/noparse]basicstamps] Relay Ratings
> Hello:
>
> My current project is a relay driver and although this question isn't
> strictly a stamp based one I was hoping somebody could help me out a
> bit. I'm going to use the relays to control a 120 VAC circuit and I
> have some great 30 AMP Automotive relays but they were originally
> designed for 12 volts. If I put 120 Vac through the contacts will
> they have an okay life span.
>
> Thank you
> Aaron Nielsen
>
>
> 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.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
A relay has three ratings typically. AC, DC and inductive.
If you know the DC rating you can use ohm's law to determine the
current carrying capability of the internal wires. Don't worry as
much about the contacts as they are much larger than the wires from
the contacts to the connectors.
There will be a bounce in the contact closure so watch for a dirty
signal if used for signal purposes.
It is this bounce that will erode the contacts and char them with
carbon as the relay is used.
Higher power contacts have heavier plating to protect from multiple
uses. If your project is critical, or safety related, don't scrimp,
get a use rated device and save yourself any headaches. if you're
just being a hobbyist, go ahead and have fun with the parts you can
scrounge. (washing machine solenoids make great water valves for
sprinklers and such)
Also you may find that you are pennies different from totally silicon
when you are done. you will need a transistor to power the coil on
the relay so you will need to power and control that unit with almost
the same resistors and caps you would need to power an AC line rated
transistor.
There was a mention of commercial silicon relays, (solid state)
these are essentially what you will be building to control the
mechanical relay, only using less power.
If you plan on high rates of on and off look into a transistor of
some sort, a Triac or SCR will allow you to vary the output like a
dimmer, a switching transistor will be an on/off device. A little
supporting circuitry and you can switch pretty much whatever you want.
Check out http://www.americanmicrosemi.com/tutorials.htm it will
offer a simple overview of the silicon methods of switching.
Dave
--- In basicstamps@y..., "Aaron" <snazzyguy2@y...> wrote:
> Hello:
>
> My current project is a relay driver and although this question
isn't
> strictly a stamp based one I was hoping somebody could help me out
a
> bit. I'm going to use the relays to control a 120 VAC circuit and I
> have some great 30 AMP Automotive relays but they were originally
> designed for 12 volts. If I put 120 Vac through the contacts will
> they have an okay life span.
>
> Thank you
> Aaron Nielsen