Question on Relay rating..
- Thread starter sputz
- Start date
Sputz.
Have a look at the datasheets for these 12 volt relays.
http://www.rapidonline.com/Electronic-Components/Relays-Solenoids/PCB-Relays/20A-PCB-Power-relay-SPST/34921
http://www.rapidonline.com/Electronic-Components/Relays-Solenoids/PCB-Relays/High-sensitivity-subminiature-DPDT-1.25A-relay/29512
Both need 12v to operate, but the "loads" vary.
Have a look at the datasheets for these 12 volt relays.
http://www.rapidonline.com/Electronic-Components/Relays-Solenoids/PCB-Relays/20A-PCB-Power-relay-SPST/34921
http://www.rapidonline.com/Electronic-Components/Relays-Solenoids/PCB-Relays/High-sensitivity-subminiature-DPDT-1.25A-relay/29512
Both need 12v to operate, but the "loads" vary.
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Sputz, make it a HABIT to get the DATA SHEET on the product you are interested in or just-about-to-use.
There can sometimes be mistakes/ambiguities/etc on catalogue pages. And even confusions in terminologies.
DATA SHEETs should be your first place to look after getting excited looking in the catalogue (careful!).
There can sometimes be mistakes/ambiguities/etc on catalogue pages. And even confusions in terminologies.
DATA SHEETs should be your first place to look after getting excited looking in the catalogue (careful!).
Mycroft2152
Senior Member
Sputz,
When using relays to switch high currents, you need to consider arcing between the contacts. The arcing will degrade the contact surfaces and I've even seen the contacts welded together.
Myc
When using relays to switch high currents, you need to consider arcing between the contacts. The arcing will degrade the contact surfaces and I've even seen the contacts welded together.
Myc
westaust55
Moderator
Additionally, relay contacts can have several rating:
1. Lower curernt at higher voltage and (of course) higher current of lower voltage
2. Higher current on ac than on dc
3. Higher current on ac and dc (it is harder to extinguish the arc when contacts open on dc as ther is no zero volt crossing to act as an arc extinguising point
4. Higher current with resistive loads than with inductive and capacitive loads.
So it is definitely as case of READ THE DATA SHEET.
1. Lower curernt at higher voltage and (of course) higher current of lower voltage
2. Higher current on ac than on dc
3. Higher current on ac and dc (it is harder to extinguish the arc when contacts open on dc as ther is no zero volt crossing to act as an arc extinguising point
4. Higher current with resistive loads than with inductive and capacitive loads.
So it is definitely as case of READ THE DATA SHEET.
There you go Sputz, several reasons (and there are probably several more if we tried hard enough to bore you) for you to download and read and absorb the Data Sheet.
This really does apply to any/every component you use.
And the bonus is that by reading up you will learn.... so much quicker than leaping to the Forum
[Of course, if you've bought some anonymous cheap thing without any documentation from an Ebay supplier then tough).
This really does apply to any/every component you use.
And the bonus is that by reading up you will learn.... so much quicker than leaping to the Forum
[Of course, if you've bought some anonymous cheap thing without any documentation from an Ebay supplier then tough).
Dippy, you must be one crazy mind reader! That's exactly what I did. Well I haven't received it yet... here's what the description said: RELAY - DPDT - 12V DC COIL - PC MOUNT - 2 FORM C.
Should've asked *before* buying! So I guess I can't use this with the Picaxe then...
Intention was to control some 6V motors using relays instead of the darlington or the motor driver chip.
Thanks a bunch for the advice guys... will be useful since I haven't worked with relays before.
Mycroft, I'm sure I won't run that risk running some hobby motors, but I'm curious, what is the solution to prevent/minimize arcing?
Well the "12V DC Coil" should give you a hint as to the rating of the coil eh
Many relays have a similar footprint so you may be able to get a clue as to the pinouts* and check with a multimeter.
You'll be safe with low voltage / Lowish current stuff on the contact/switching side. But, I'm sorry to bang on about it, buying cheap stuff can be a false economy or you can strike lucky.
I'm sure it'll be fine in your low-power app.
*Have a look at websites like Farnell and RS and various others which have a wide range of relays made by proper manufacturers. Those cheapie Chinese (or whatever) will be copies, sorry, I mean designed to a high standard and pin-compatible.
You can buy contact arc suppressors (usu a Res+Cap).. maybe even from Ebay.
Many relays have a similar footprint so you may be able to get a clue as to the pinouts* and check with a multimeter.
You'll be safe with low voltage / Lowish current stuff on the contact/switching side. But, I'm sorry to bang on about it, buying cheap stuff can be a false economy or you can strike lucky.
I'm sure it'll be fine in your low-power app.
*Have a look at websites like Farnell and RS and various others which have a wide range of relays made by proper manufacturers. Those cheapie Chinese (or whatever) will be copies, sorry, I mean designed to a high standard and pin-compatible.
You can buy contact arc suppressors (usu a Res+Cap).. maybe even from Ebay.
I know! That's why this forum posting! Was hoping against hope it means maximum voltage! Oh well, how else will I learn!Well the "12V DC Coil" should give you a hint as to the rating of the coil eh
"Was hoping against hope it means maximum voltage!"
- eh? Don't really understand.
If you look at Data Sheets for relays you will see the range of voltages at which it will work. A 12V coil may work OK between 9 and 14V or whatever, depends on the relay.
But I can't see it working at 5 or 6V.
Funnily enough, for 5 or 6V operation you should choose a relay with a coil rated at 5 or 6V....
Even if you'd looked at ANY Data Sheet for just about ANY relay you'd have discovered that. Real basic stuff.
Well, it won't rot so you can save it for your next project and I guess it only cost pennies.
- eh? Don't really understand.
If you look at Data Sheets for relays you will see the range of voltages at which it will work. A 12V coil may work OK between 9 and 14V or whatever, depends on the relay.
But I can't see it working at 5 or 6V.
Funnily enough, for 5 or 6V operation you should choose a relay with a coil rated at 5 or 6V....
Even if you'd looked at ANY Data Sheet for just about ANY relay you'd have discovered that. Real basic stuff.
Well, it won't rot so you can save it for your next project and I guess it only cost pennies.
Yeah, ok, ok! My mistake! If I post again without reading datasheets looks like I might get beaten up!
But seriously, thanks guys! The info gathered here has always helped and your inputs are greatly appreciated. Yep... didn't see the datasheet. All I had to look for was 'operating voltage range'! Yes most 12V relays have a range starting from 7.5v (after reading so many replies, quickly opened up some datasheets!
) ...still high for 6V ... plus as you point out, relays are available for 5/6v. Well, certainly a good learning experience.Sputz.
This might be useful, one day.
http://www.forward-relays.com/product/product_images/p/en_p__85.pdf
e
This might be useful, one day.
http://www.forward-relays.com/product/product_images/p/en_p__85.pdf
e
BeanieBots
Moderator
I'll reply on Mycrofts's behalf.
The use of snubber networks. Usually just a simple R & C in series across the contacts.
As we are all showing off about our relay knowledge, here's one that not many will know.
Relay contacts also have a MINIMUM switching current.
Yes thats right, a MINIMUM current.
If the current is too low during switching, the contacts start to oxidise. Normally, the arc vapourises any oxides but if it is too small, the oxide builds up quicker than it is removed. In MOST applications this does not matter. However, in precision analogue circuits, the change in contact resistance can be a problem. One way around it is to use mercury wetted contacts but that's not very "green" these days.