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Battery and Starter Relays.

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GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Thu Dec 14, 2006 7:23 pm Post subject: Battery and Starter Relays.

I'm doing a firewall forward restoration on a Cheetah.  The relays look 

pretty bad.  One of them has some sort of plastic stuff leaking out.  

Knowing that it's such a pain in the ass to change the relays, I wanted 

to get new ones.  Easier said than done.



I started with the Aircraft Spruce catalog.  Then, the Wag-Aero 

catalog.  Then, the Chief Aircraft catalog.  Not being content with 

accepting what they have, I started researching just what the different 

part numbers mean.



The company that made the relays on our Grummans was bought out by the 

White-Rodgers Division of Emerson Electric Co. in St Louis, MO.  

Getting from their web site to the specifications of, and the 

definitions for the relays wasn't so easy.



What I found out was, the relays we use are Type 70 solenoids.  The 

battery relay is a continuous duty relay.  The starter is an 

intermettent duty relay.  The part numbers break down like this:  70 - 

x xx xxx - x



70:  type of relay

x:    this tells what kind of relay, normally open (1) or SPDT (3).

xx:  This tells the voltage for the relay.

        There is a post in the gg archive for a starter solenoid that 

gives a part number

        starting with 70- 109 xxx - x.  It's wrong.  109 is a 6 volt 

relay.

        - For continuous 12 volt, the number is 11

        - For intermettent 12 volt, the number is 12

xxx:  This gives the coil termination description.  The two we need to 

know about is 225 and 226

       225: is for a coil grounded to the relay case.

                - To activate this one, voltage is applied to the small 

terminal.

        226: is for the coil connected to the battery side of the 

solenoid.

                - To activate this one, ground is applied to the small 

terminal.

x:    the last x tells what kind of a mounting hardware it has.  5 is 

typical.



SO . . . .

   Battery relay:  70-111 226-5    Aircraft Spruce has this one.

                       The Battery relay that Wag-Aero has is 70-111 

225-5.

                      That means it needs voltage applied to work.

                       The Master switch on the AA5x goes to ground so 

it won't work.

   Starter relay:   70-112 225-5    Wag-Aero has this one.



Without that bit of info, the wrong relay could be ordered easily.

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_________________
Gary
AuCountry Aviation
Home of Team Grumman

flyv35b(at)minetfiber.com
Guest

Posted: Fri Dec 15, 2006 7:02 am Post subject: Battery and Starter Relays.

Good info Gary!  This subject has been discussed on the GG many times in the 

past and I'm sure the wrong relays have been installed in the past, 

particularly the starter relay.



I think the starter relay, which is intermittent has a stronger coil which 

draws more current and "sucks" the contacts together with more force and 

quicker than the continuous duty master contactor.  This probably is done to 

minimize the arcing that occurs with the much higher current draw on the 

starter contactor.  I have seen a continuous duty contactor installed for 

the starter relay that apparently had the contacts "welded" together.  What 

was scary was when you turned on the master switch the starter engaged and 

the prop rotated!  Don't ever stand in the way of a prop even when you think 

nothing is going to happen.



Another thing of interest is the current draw with the Skytec Flyweight 

starter, which many people have retrofitted, is considerably higher that 

with the original Prestolite or Skytec's newer in-line Hi-Torque starter by 

about 100 amps!  I feel that this will cause more contact arcing in the 

starter relay and shorten it's life possibly.  The permanent magnet 

Flyweight starter also has a characteristic where it does not disengage for 

a couple of seconds after the engine starts or after the starter button is 

released.  You can hear the gears "grinding" so to speak if you pay 

attention.  I've seen one starter that literally exploded when it didn't 

disengage and was oversped as the engine was revved up.  Because of these 2 

things I prefer Skytec's newer in-line Hi-Torque starter over the Flyweight 

even though it is more expensive and weighs about 1.5 lb more.



Cliff  A&P/IA

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GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Fri Dec 15, 2006 12:04 pm Post subject: Battery and Starter Relays.

I put the in-line Sky-Tec on my plane.  I've wondered about the life of 

the starter relay.  With a weak battery on a hot day with a hot engine, 

I had trouble turning the engine over.  New battery helped a lot.



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_________________
Gary
AuCountry Aviation
Home of Team Grumman

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