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Solid State Relays

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Thu Jul 16, 2009 7:56 am Post subject: Solid State Relays

Saw these  http://www.futurlec.com/RelSS.shtml

 and  for $20 they look like possible replacements for the common electro-mechanical  relays that we now use. These are light, compact, and very reliable. But I  don't know if there are gradations of MOSFETs or if they're just basic building  blocks. The cost of these is about 1/8 of an almost identical Teledyne unit and  I wonder if "you get what you pay for" is appropriate to apply here? Or is  Teledyne just passing on the costs of marketing, regulatory environment,  lawyers, pensions, etc?

  

 The only obvious downside that is evident from the  data sheet is that the load capability starts falling off at about 60 deg C,  so installation in an engine compartment is off the table without a  blast tube and heatsink.

  

 One of these has a load spec of 240VAC (at) 70A  and another specs 100VDC (at) 40A. I'd rather have more amperage  capacity. Do solid state relays care whether the load is DC or  AC?

  

 What think you all? 

  

 John

  

  

   [quote][b]

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jonlaury

Joined: 06 Nov 2006
Posts: 336

Posted: Thu Jul 16, 2009 8:41 am Post subject: Solid State Relays

OK, I should've gone to the archives BEFORE I  posted this thread.

 But the objection 11/2 yrs ago was a voltage drop  of 1.5 (at) 12v. These claim .35v (at)30V. Did the earlier versions claim a similarly  low V drop?

 I guess the only way to be sure is to buy one and  test it.

  

 JB

   [quote][b]

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mprather(at)spro.net
Guest

Posted: Thu Jul 16, 2009 9:20 am Post subject: Solid State Relays

If I read the data correctly, it appears these relays are only rated at 3A

continuous which even fairly small switches can handle.  Not sure why

you'd pick the relay over a switch unless you wanted to use a micro-micro

switch to control something.



Also, a few other issues:



 - It's rated for AC.  Not sure how it will perform controlling a DC load.

 - The forward voltage drop seems like it might be large - up to 1.5V at

peak current.  Not only is that a bit of a performance hit, it will

generate some heat.  The app notes specify to provide adequate

ventilation.

 - Don't know what behavior you might see if the load tried to drive the

source - might not be bidirectional.

Regards,



Matt-



 	  Quote: 	
		   Saw these

 http://www.futurlec.com/RelSS.shtml

  and for $20 they look like possible replacements for the common

 electro-mechanical relays that we now use. These are light, compact, and

very reliable. But I don't know if there are gradations of MOSFETs or if
	


they're just basic building blocks. The cost of these is about 1/8 of an

almost identical Teledyne unit and I wonder if "you get what you pay

for"

 	  Quote: 	
		   is appropriate to apply here? Or is Teledyne just passing on the costs

of
	


 	  Quote: 	
		   marketing, regulatory environment, lawyers, pensions, etc?



 The only obvious downside that is evident from the data sheet is that

the
	


 	  Quote: 	
		   load capability starts falling off at about 60 deg C, so installation in

an engine compartment is off the table without a blast tube and
	


heatsink.

 	  Quote: 	
		  

 One of these has a load spec of 240VAC (at) 70A and another specs 100VDC (at)

40A. I'd rather have more amperage capacity. Do solid state relays care
	


whether the load is DC or AC?

 	  Quote: 	
		  

 What think you all?



 John

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retasker(at)optonline.net
Guest

Posted: Thu Jul 16, 2009 9:53 am Post subject: Solid State Relays

I think you may have looked at the wrong part.  You have to go down to 

the bottom of the page to find the high amp rated DC units.



That said, see my previous email.



Dick Tasker



Matt Prather wrote:

 	  Quote: 	
		   



 If I read the data correctly, it appears these relays are only rated at 3A

 continuous which even fairly small switches can handle.  Not sure why

 you'd pick the relay over a switch unless you wanted to use a micro-micro

 switch to control something.



 Also, a few other issues:



  - It's rated for AC.  Not sure how it will perform controlling a DC load.

  - The forward voltage drop seems like it might be large - up to 1.5V at

 peak current.  Not only is that a bit of a performance hit, it will

 generate some heat.  The app notes specify to provide adequate

 ventilation.

  - Don't know what behavior you might see if the load tried to drive the

 source - might not be bidirectional.

 Regards,



 Matt-

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retasker(at)optonline.net
Guest

Posted: Thu Jul 16, 2009 9:53 am Post subject: Solid State Relays

The 0.35V drop only applies to the low voltage assemblies which are not 

listed at Futurlec.  They only show the 100V and 200V for sale and they 

have a much higher voltage drop at a lower current.



The 30V versions look very attractive with the 0.007 milliohm on 

resistance at 50A.



However, they say nothing about reverse voltage, so I would have to 

assume that these are only good for supplying power to a load and not 

good for use where there could be a reverse voltage on them - such as 

what would occur if you were trying to use two of these to switch two 

different batteries to a common load.



Dick Tasker



John Burnaby wrote:

 	  Quote: 	
		   OK, I should've gone to the archives BEFORE I posted this thread.

 But the objection 11/2 yrs ago was a voltage drop of 1.5 (at) 12v. These 

 claim .35v (at)30V. Did the earlier versions claim a similarly low V drop?

 I guess the only way to be sure is to buy one and test it.

  

 JB

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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