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Crowbar let the smoke out

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finn.lassen(at)verizon.ne
Guest

Posted: Mon May 25, 2020 12:00 pm Post subject: Crowbar let the smoke out

Happened to turn on master switch (relay) and saw smoke coming from the 

OV circuit. (Made from the AEC9003-14A schematic more than two decades ago.)



I thought that was rather rude of it.



The SCR is the one that fried.



No problems many times before. Must have seen a spike from alternator 

field winding.



But very worrisome that it did NOT pop the 5 amp W23-X1A1G-5 pull breaker.



The schematic specifies 20 AWG wires, and I used thicker -- perhaps 12 

or 14, and very short, about three inches total for ground and + wires.



Maybe that was the problem?



Finn

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nuckolls.bob(at)aeroelect
Guest

Posted: Mon May 25, 2020 2:32 pm Post subject: Crowbar let the smoke out

At 02:56 PM 5/25/2020, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Finn Lassen <finn.lassen(at)verizon.net>



 Happened to turn on master switch (relay) and saw smoke coming from the OV circuit. (Made from the AEC9003-14A schematic more than two decades ago.)



 I thought that was rather rude of it.



 The SCR is the one that fried.



 No problems many times before. Must have seen a spike from alternator field winding.



 But very worrisome that it did NOT pop the 5 amp W23-X1A1G-5 pull breaker. 	


   Yeah, it probably opened the chip

   bonds on the SCR before the breaker

   could even respond.



 

  	  Quote: 	
		  The schematic specifies 20 AWG wires, and I used thicker -- perhaps 12 or 14, and very short, about three inches total for ground and + wires.



 Maybe that was the problem? 	


   Yup. You'll notice that the z-figures

   show crowbar ov modules at the end of the

   feeder to the alternator field switch . . .

   and wire sized more to the task of

   supplying a 3A alternator field. 20AWG.

   The W23 breakers are slower than the

   miniature devices but this isn't a 

   show stopper if you limit the fault

   current with judicious wire sizes and

   lengths.



   This limits trip current to some value

   within limits for the SCR. I've had

   customers install their AEC fabricated

   modules right at the breaker on a legacy

   bus bar . . . they even shortened the

   factory supplied leads. Their modules

   suffered the same fate the first time

   they tripped.



 



 

   Bob . . .

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finn.lassen(at)verizon.ne
Guest

Posted: Tue May 26, 2020 3:09 pm Post subject: Crowbar let the smoke out

Exactly what I did. zip-tied (and       siliconed) it to top of breaker, with very short thick wires to       ground (ring around breaker mounting neck) and to breaker terminal       screw.

       

       

       [img]cid:part1.4C74E486.CF8A9B92(at)verizon.net[/img]

       

       So, shorter and thicker wires is not always better 

       

       This is a 60 - 70 amp alternator, so I figured would need at least       5 amps or approx 10% for field winding?

       

       Not expecting to ever use that much current, but didn't want to       pop the breaker in case of a nearly discharged battery.

       

       So use 22 awg the 30" from breaker to alternator? And a bigger       SCR?

       

       Finn

       

       On 5/25/2020 6:28 PM, Robert L. Nuckolls, III wrote:

     

      	  Quote: 	
		   I've had

         � customers install their AEC fabricated

         � modules right at the breaker on a legacy

         � bus bar . . . they even shortened the

         � factory supplied leads. Their modules

         � suffered the same fate the first time

         � they tripped.

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