 | Home > Off Topic > Solenoids v Relays |
 
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| bm52 Member Since: 04 Apr 2010 Location: Kent Posts: 2189   
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i bet it's cost and complexity vs cheap and easier ! Relay is probably more reliable and cheaper BM52
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3rd Feb 2011 10:05pm |
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| pom Member Since: 01 Jun 2010 Location: Worcester Posts: 1343 |
Size
Pom |
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4th Feb 2011 12:12am |
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| Laurie Member Since: 22 Feb 2008 Location: Sussex, England Posts: 2897  
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A solenoid is an actuator, a relay is a switch.
What do you want it to do? |
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4th Feb 2011 2:04am |
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| leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8581
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Am confused why both solenoids and relays are used in split charging systems!
Also why use solenoids I.e. Alb right solenoids on winch electrical systems? Brendan |
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4th Feb 2011 2:18am |
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| K9F Member Since: 12 Nov 2009 Location: Bournemouth Posts: 9610 
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Solenoids/Relays??? It is all 'play on terminology' as an electrician myself there is no clear cut solution to your question! It can purely depend on how the manufacturer has labelled up the item!
What I can say is that solenoids are usually used where more than one force is required to operate a particular piece of equipment or systems where usually both mechanical and electrical forces are needed! For example a solenoid actuated air valve will need both air pressure and electrical supply to open (or close it). Solenoids usually physically have a visible mechanical operation at source relays normally don't! Hope this all makes sense but after 32 years in the electrical game your question is a very hard one to give a definitive answer to! Ideally whether it's a solenoid or a switch if it's correctly rated, will do what you want it to do, and, is suitable for the environment it is going to sit in - it'll be fine!!! What could possibly go wrong!  If you go through life with your head in the sand....all people will see is an ar5e!!
Treat every day as if it is your last....one day you will be right!! |
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4th Feb 2011 9:05am |
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| pom Member Since: 01 Jun 2010 Location: Worcester Posts: 1343 |
current rating on solenoids is much higher as well. Not sure how much more expensive a similar rated contactor or relay would be but I expect quite a lot.
Pom |
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4th Feb 2011 9:19am |
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| Paul_1978 Member Since: 08 Nov 2009 Location: South Yorkshire Posts: 384 
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Generally speaking in the electrical control world (im a electrical control engineer)
A solenoid would be used on gas / fluid control to operate a valve. A relay would be an intermediate device, a relay would be in circuit to drive a more higher current device from a plc. In more higher current circuits we would use a contactor, so a relay would/could drive a contactor. In the split charge example, the relay would sence an increase in voltage, pulling in the solenoid to close the high current circuit to charge the battery. Clear as mud eh! |
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4th Feb 2011 12:07pm |
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| K9F Member Since: 12 Nov 2009 Location: Bournemouth Posts: 9610
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Beg to differ slightly Pom! Latest RS Catalog page 1-1238 there is a 2 watt 12 volt 'cylindrical solenoid' which equates to a current rating of only 0.16 amps. This debate could go on and on!  If you go through life with your head in the sand....all people will see is an ar5e!!
Treat every day as if it is your last....one day you will be right!! |
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4th Feb 2011 12:59pm |
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| Paul_1978 Member Since: 08 Nov 2009 Location: South Yorkshire Posts: 384
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I think solenoid is just an automotive electrical term, in industury a solenoid operates by means of a moving spool inside a metal tube with magnetics. High current devices generally have contactors or air switches. In a winch solenoid, the solenoid part just operates a contact on the high power side, exactly like a contactor but for DC. DC tends to destroy switching devices due to high arc intensitites, can be seen on magnet control devices. 50/60A @ 220VDC. |
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4th Feb 2011 1:21pm |
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| Glynparry25 Member Since: 16 Feb 2009 Location: Miserable Midlands Posts: 3015  
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Automotive wise you only need relays.... I have only ccome across Solenoids on heavy plant machenery.
I would say that solenoids can carry much bigger current, more reliable but takes more current to activte it. Relays are better for use in drier, lower current aplications. Paul_1978.... I agree with that aplication in a split charge system.... but would rather thenre be more control and accuracy in mine 
K9F..... 2W solenoid... What is the point  but yes they can both be made to do the same job if need be.
Glyn   |
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4th Feb 2011 6:24pm |
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| Glynparry25 Member Since: 16 Feb 2009 Location: Miserable Midlands Posts: 3015
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Just thought of a prime example:
On your land Rover there are loads of relays to control all the every day small current tasks. There is one solenoid........ Starter motor, because a relay to do the same job would be huge. Glyn |
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4th Feb 2011 6:26pm |
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| leeds Member Since: 28 Dec 2009 Location: West Yorkshire Posts: 8581
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Albright solenoids I can understand on winches which can in theory draw up to 4-500 amps under maximum load. Would hate to imagine size/cost of an equivalent relay.
Starter solenoids I understand. Solenoid = actuator = movement Solenoids on split charging systems I do not understand as they are bulkier then the equivalent current rated ones. Solenoids for a tail lift rated at 80 odd amps. Can appreciate that a metal can actuator could be considered to be more robust then a plastic encased relay. Also can understand that a larger can solenoid can have four large stud outlets on and can be more robustly secured as it has two metal tags on. The larger metal can might be beneficial from a thermal point of view A couple of minor questions to our auto electricians. How hot would say a 200 amp relay get in a typical 12V split charging system? Is there any real history of relays failing in this type of system? Brendan |
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5th Feb 2011 9:35am |
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| K9F Member Since: 12 Nov 2009 Location: Bournemouth Posts: 9610
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Brendan, Not an auto electrician but now a marine one....With regards to your first question, absolutely impossible to say, mount it on your roof and not alot! Stick it next to your catalytic converter...  loads! You mount it and I'll pop along with my works thermal imaging camera and tell you accurately how hot it is!!! If you're worried about heat fit a heatsink or move the relay under the bonnet in airflow.
The more current a relay supplies the more likely it is to eventually fail due to potential contact wear/pitting/carbon build up. As previously stated if it is correctly rated, fit for purpose and designed for the environment in which it is expected to work it should give you excellent service! If you go through life with your head in the sand....all people will see is an ar5e!!
Treat every day as if it is your last....one day you will be right!! |
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5th Feb 2011 9:42am |
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| Glynparry25 Member Since: 16 Feb 2009 Location: Miserable Midlands Posts: 3015
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The temperature of a 200A relay on s split charge system would depend on the type/ capacity of battery, how low the voltage has reached, the ampage of your alternator..... also is it a 200A peak relay? My IBS relay has never failed and never gets hot
Glyn |
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5th Feb 2011 9:46am |
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