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Starter Solenoid fuse blows, ideas?

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mdharfst(at)comcast.net
Guest

Posted: Sat Jul 07, 2007 2:42 pm Post subject: Starter Solenoid fuse blows, ideas?

I have had a small nagging problem for several years since I started flying my plane. All my attempts to mitigate the problem have not solved it but have decreased the frequency. The basic problem is that the fuse that controls the firewall mounted starter solenoid occasionally blows. Since the fuse is under the glareshield it is a pain to change.  Basically I am looking for ideas of what might be causing this to happen and how to test to see if that idea is the cause. 



This is a detailed description of my system. An O-320 engine with a Skytec lightweight starter, two Slick mags, B&C 40A alternator and B&C voltage regulator, a 17AH RG battery and master solenoid (S701-1) on the aft side of the firewall, a B&C starter solenoid (S702-1) on the forward side of the firewall, and a fuseblock under the glareshield. The big cables are #4 welding cable. The battery is 12" from the master solenoid. The master to starter solenoid cable is about 10" through the firewall. 

The plane is wired based on Bob's Z-11 drawing with the starter solenoid circuit set up like Z-22.  I use the rotary keyed mag/starter switch from ASSC.   



Here is a description of the exact problem.

I have a fused wire leading to the bat terminal of the keyed switch that activates the firewall mounted starter solenoid. The fuse is a 7.5A fuse. Occasionally the fuse blows during starter cranking and then has to be replaced. The first few times I replaced the fuse with another 7.5A fuse. The fuse would blow every couple of months, and might occur two or three times in a row when it happened. Also, it is tough to know exactly when the fuse blows. If it happens after the solenoid engages I might get it started but won’t realize it is blown until I try to start it again for the return trip or maybe days later for the next trip. That makes it difficult to pin down associated factors.



Here are a few things I've tried.

Originally I figured the starter itself was sticking and causing the starter solenoid to overload so I put in a 10A fuse. This lowered the frequency of occurrence, to about once or twice a year, but did not totally eliminate it. 



I originally used the small light duty solenoid from B&C (the S704-1) which I thought might not be up to the task. I eventually swapped it out for a heavy duty intermittent duty solenoid and increased the size of the associated wiring to be sure the wire size didn't cause a problem or have an intermittent fault to ground somewhere.  When I changed the solenoid the frequency went down to about once a year. 



Recently this 10A fuse blew and I replaced it with a 15A fuse that I had with me but it immediately blew also when I turned the key. So I hand propped the plane and took it to the hangar. The next day when I checked it the plane had no problem and started right up with a new fuse. Just to check the normal current flowing through this circuit with the plane acting well, I started it with successively smaller fuses until one finally blew when I turned the key. The plane started fine with a 15A fuse, with a 10A, with a 7.5A, with a 4A, with a 3A and finally with a 1A fuse the starter kicked in and started the plane but the 1A fuse blew. This told me that the solenoid normally drew between 1 and 3 amps, just like it is supposed to, when the system is acting normally. It also told me that when the system blows the fuse, the current draw can be as high as 15A momentarily.  That just doesn't make sense, how can a little solenoid pull 15A?



Here are a few ideas that I haven't been able to confirm, but I think might be true. 

If I don't move the prop, after a fuse blows, the next fuse will blow too, probably.

A blown fuse is a little more likely to happen when the engine is hot, but not always. 

It happens easier if I have to crank the starter for quite awhile, I can't tell when exactly it pops though.



Early on I checked the voltage at the switch during cranking and it will drop to 10V before too much cranking. I haven’t checked it for a couple of years. I am on my second battery too.



Also, the possibility exists that the keyed switch is the culprit, but I won’t replace it to test that idea. I would rather rewire to two toggle switches and a starter button. I’m saving that action for later.



I’m open  for suggestions.

Mike Harfst

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rjquillin

Joined: 13 May 2007
Posts: 123
Location: KSEE

Posted: Sat Jul 07, 2007 6:49 pm Post subject: Starter Solenoid fuse blows, ideas?

At 15:35 7/7/2007, you wrote:

 	  Quote: 	
		  I'm open  for suggestions.

Mike Harfst


	


Where, physically, is the fuse located?

What is it mounted in?



I'm wondering if heat and vibration are contributing to degradation 

and early failure.



Ron Q.

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mdharfst(at)comcast.net
Guest

Posted: Sat Jul 07, 2007 8:01 pm Post subject: Starter Solenoid fuse blows, ideas?

Ron

The fuse is mounted in a fuseblock on top of the glove box behind my panel. No heat there, little vibration, none of the other fuses have blown but are all subjected to the same environment and some fuses blow without ever being flown. You may have something there though, I'll put it on the list of things to check.

Thanks,

Mike



 	  Quote: 	
		  >> Where, physically, is the fuse located?

        What is it mounted in?
	




        I'm wondering if heat and vibration are contributing to degradation 

        and early failure.<<<<

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hooverra(at)verizon.net
Guest

Posted: Sun Jul 08, 2007 3:32 am Post subject: Starter Solenoid fuse blows, ideas?

Mike,

When the fuse blows what does it look like? If the element looks like it 

melted and sagged until it parted you have a consistent slight overload. 

If it the element is vaporized and black it was a large overload. I 

suspect that if it is blowing 10A fuses consistently but at long 

intervals and it operates on a 3 amp fuse for long periods of time you 

may have an intermittent fault to ground. The solenoid pull in current 

should not change with the load on the solenoid. The current required to 

pull the solenoid is greater than the hold current so I suspect that 

voltage drop while cranking is not the problem. You mentioned that you 

do not know when the fuse blows. Does the starter drop out while 

engaged? Does the solenoid start to move, click and drop out? Is it just 

dead while no problem was noted on the previous start? Do you have a 

snubber diode across the solenoid coil?



-- 

Ralph C. Hoover

RV7A 

hooverra at verizon dot net

mdharfst(at)comcast.net wrote:



 	  Quote: 	
		   



 I have had a small nagging problem for several years since I started flying my plane. All my attempts to mitigate the problem have not solved it but have decreased the frequency. The basic problem is that the fuse that controls the firewall mounted starter solenoid occasionally blows. Since the fuse is under the glareshield it is a pain to change.  Basically I am looking for ideas of what might be causing this to happen and how to test to see if that idea is the cause. 

 (snip)

 I’m open  for suggestions.

 Mike Harfst

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nuckollsr(at)cox.net
Guest

Posted: Sun Jul 08, 2007 9:28 am Post subject: Starter Solenoid fuse blows, ideas?

At 10:35 PM 7/7/2007 +0000, you wrote:



 	  Quote: 	
		  



I have had a small nagging problem for several years since I started 

flying my plane. All my attempts to mitigate the problem have not solved 

it but have decreased the frequency. The basic problem is that the fuse 

that controls the firewall mounted starter solenoid occasionally blows. 

Since the fuse is under the glareshield it is a pain to change.  Basically 

I am looking for ideas of what might be causing this to happen and how to 

test to see if that idea is the cause.



This is a detailed description of my system. An O-320 engine with a Skytec 

lightweight starter, two Slick mags, B&C 40A alternator and B&C voltage 

regulator, a 17AH RG battery and master solenoid (S701-1) on the aft side 

of the firewall, a B&C starter solenoid (S702-1) on the forward side of 

the firewall, and a fuseblock under the glareshield. The big cables are #4 

welding cable. The battery is 12" from the master solenoid. The master to 

starter solenoid cable is about 10" through the firewall.

The plane is wired based on Bob's Z-11 drawing with the starter solenoid 

circuit set up like Z-22.  I use the rotary keyed mag/starter switch from 

ASSC.


	


    Z-22 describes a boost relay for the purpose of

    utilizing the starter's built in solenoid while

    isolating the relatively fragile starter push button

    or key-switch from the ravages of starter solenoid

    inrush currents. See:



http://aeroelectric.com/articles/strtctr.pdf

 	  Quote: 	
		  Here is a description of the exact problem.

I have a fused wire leading to the bat terminal of the keyed switch that 

activates the firewall mounted starter solenoid. The fuse is a 7.5A fuse. 

Occasionally the fuse blows during starter cranking and then has to be 

replaced. The first few times I replaced the fuse with another 7.5A fuse. 

The fuse would blow every couple of months, and might occur two or three 

times in a row when it happened. Also, it is tough to know exactly when 

the fuse blows. If it happens after the solenoid engages I might get it 

started but won't realize it is blown until I try to start it again for 

the return trip or maybe days later for the next trip. That makes it 

difficult to pin down associated factors.


	


   Starter solenoid? If you have a boost relay installed, the the

   firewall mounted contactor goes away.

 	  Quote: 	
		  Here are a few things I've tried.

Originally I figured the starter itself was sticking and causing the 

starter solenoid to overload so I put in a 10A fuse. This lowered the 

frequency of occurrence, to about once or twice a year, but did not 

totally eliminate it.


	


   The "STARTER" fuse on the main bus powers only the coil

   of what ever device is expected to operate when the start

   contacts are closed. If you're using an S702-1 style Starter

   Contactor



http://www.aeroelectric.com/Pictures/Contactors/s702-1l.jpg



   then the current draw through this fuse is limited to about

   5A max and a 7.5a fuse will handle this task indefinitely.

 	  Quote: 	
		  I originally used the small light duty solenoid from B&C (the S704-1) 

which I thought might not be up to the task. I eventually swapped it out 

for a heavy duty intermittent duty solenoid and increased the size of the 

associated wiring to be sure the wire size didn't cause a problem or have 

an intermittent fault to ground somewhere.  When I changed the solenoid 

the frequency went down to about once a year.


	


    Now I'm really lost. The S704-1  is a 30A plastic

    relay suggested as a stand-in for panel mounted

    switches that do not do well controlling the starter

    contactor/solenoid assembly directly -OR- for the

    prevention of Starter Engagement Run-on phenomenon

    common to PM motor starters. See notes on Figure Z-22

    on page Z-5 of



http://aeroelectric.com/articles/Rev11/AppZ_R11J.pdf

 	  Quote: 	
		  Recently this 10A fuse blew and I replaced it with a 15A fuse that I had 

with me but it immediately blew also when I turned the key. So I hand 

propped the plane and took it to the hangar. The next day when I checked 

it the plane had no problem and started right up with a new fuse. Just to 

check the normal current flowing through this circuit with the plane 

acting well, I started it with successively smaller fuses until one 

finally blew when I turned the key. The plane started fine with a 15A 

fuse, with a 10A, with a 7.5A, with a 4A, with a 3A and finally with a 1A 

fuse the starter kicked in and started the plane but the 1A fuse blew. 

This told me that the solenoid normally drew between 1 and 3 amps, just 

like it is supposed to, when the system is acting normally. It also told 

me that when the system blows the fuse, the current draw can be as high as 

15A momentarily.  That just doesn't make sense, how can a little solenoid 

pull 15A?


	


   We're wrapped about some semantic axles here. The S704-1

   is a power relay, the S702-1 is a starter contactor (BIG

   relay) and a solenoid is that hunk of stuff bolted to the

   side of your starter that pushes the pinion gear out to

   engage the ring gear. Further, the back end of the solenoid

   is fitted with a contactor that closes power to the starter

   motor only after pinion gear engagement is achieved.



   If your starter switch contacts on the key-switch are driving

   an S704-1 relay, then this coil needs just over 100 milliamps

   of operating current. Your experiment with the 1A fuse confirms

   this. If you're blowing fuses, then some transient fault condition

   exists in either the wiring between starter switch and boost

   relay or within the starter switch itself. Instant blowing

   of the 15A fuse you cited is a good confirmation of this.

   Your STARTER fuse should function well with 1A driving a

   piece of 22AWG wire that runs through the BAT terminal of

   your keyswitch to the starter boost relay illustrated in

   Figure Z-22.



   I'm mystified about the "firewall mounted" starter

   solenoid . . . are you speaking about the S704-1

   relay here? If, when you installed the S704-1 relay

   you eliminated a firewall mounted contactor as Z-22

   suggests, then we can zero in on the transient fault

   that is taking the STARTER fuse to ground and causing

   it to open.

 	  Quote: 	
		  Here are a few ideas that I haven't been able to confirm, but I think 

might be true.

If I don't move the prop, after a fuse blows, the next fuse will blow too, 

probably.

A blown fuse is a little more likely to happen when the engine is hot, but 

not always.

It happens easier if I have to crank the starter for quite awhile, I can't 

tell when exactly it pops though.



Early on I checked the voltage at the switch during cranking and it will 

drop to 10V before too much cranking. I haven't checked it for a couple of 

years. I am on my second battery too.



Also, the possibility exists that the keyed switch is the culprit, but I 

won't replace it to test that idea. I would rather rewire to two toggle 

switches and a starter button. I'm saving that action for later.


	


    It does suggest an experiment. Wire in a temporary

    push button of any size with a new 22AWG wire from the

    fuse block through the push button and out to the S704-1

    relay. Use a 5A or less fuse in the fuseblock. See how

    this runs for awhile. If the fuseblowing event goes away,

    all this leaves is the keyswitch and wires downstream of

    the keyswitch that you've eliminated by the experiment.



    Bob . . .

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mdharfst(at)comcast.net
Guest

Posted: Sun Jul 08, 2007 9:04 pm Post subject: Starter Solenoid fuse blows, ideas?

Thanks for the responses.

Ralph wrote:

 	  Quote: 	
		  >When the fuse blows what does it look like? vaporized and black?<<< 

The blown fuses are vaporized, like a overload would cause. I do have all the diodes installed in the circuit.

Todd wrote:	

 	  Quote: 	
		  >>Chaffing at the firewall feed-though, Chaffing ONLY occurred when the engine was running!<<

Hmmmm, that could be a source of an intermittent fault. I don’t have a fat wire going through the FW. It is a custom made, through connection. I will go over all the other wiring again though just to make sure.

Terry

Yes, the solenoid from Skytec on the starter motor itself could be the problem. I may have to swap it out. I did a solenoid replacement early on with a rebuilt solenoid when I accidentally stripped a copper bolt on the original. Skytec may have given me a slightly faulty replacement part. I’ll put this on the list. 

Bob N

I am sorry for any confusion, maybe some of my terminology is not exact.

I originally wired my plane based on Z-11 (an earlier version/number really) with the starter circuit based on the original Z-22. I used an S704 relay mounted on the front of the firewall. When that relay failed after 160 hrs I went over the schematic carefully. I think I understand the schematic, in fact I’m the guy that had several off-list emails with you that resulted in the revised Z-22 drawing published in June 05 with all the right diodes in the right places. Anybody can pull up the archives from June 05 to read the discussions in greater detail. 

In those emails I proposed using a heavier duty contactor/relay/solenoid to replace the S704. Your response was: “You COULD replace the S704 with a HEAVIER duty still device like a starter contactor, but it's not necessary. Try the NEW Z-22 and see what it does for you.” Since I live close to Van’s I already had their starter relay version by the time you replied so I went ahead and used it. In their catalog this is referred to as a “Starter Solenoid, intermittent duty relay for the starter motor” and in my installation it is on the firewall. I am not referring to the big honking monster that is on the Skytec starter motor. Again, I apologize for any terminology confusion.

I like the idea of jumping around the keyswitch with a starter button to test the keyswitch. Unfortunately with a frequency of once or twice a year it will take a long time to know for sure. I know your feeling about keyswitches and I’m beginning to feel the same way. Maybe what I need to do is come over from the dark side and rewire to a couple of toggles and a pushbutton. That will probably be a winter project. What I am doing in the short term is to put a 30A fuse in the fuse block position and wire a 15A CB in series with the fuse. Now I can see when the CB blows and just reset it. In a month or so I’ll replace the 15A CB with a 5A CB and see what happens. 

There are some good suggestions here, thanks everyone. Any others to add to the list?

Mike Harfst

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bakerocb

Joined: 15 Jan 2006
Posts: 727
Location: FAIRFAX VA

Posted: Mon Jul 09, 2007 5:43 am Post subject: Starter Solenoid fuse blows, ideas?

7/9/2007



Hello Terry, You wrote: "C-1's job is to energize C-2. The fuse that blows 

feels the draw from both C-1 and C-2."



I am a bit confused by these two sentences.



I thought that coil C-1's job, when the starter switch is closed, is to move 

the slug that then closes the main contacts of that contactor. Then the 

electricity flowing through that contactor's main contacts is the 

electricity that will flow on through coil C-2 and cause its slug to move 

and both engage the starter pinion gear and close its main contacts to 

provide electricity to turn the starter motor.



See Figure 6  here    http://aeroelectric.com/articles/strtctr.pdf



If my thinking is correct then the fuse that blows would not feel the 

additional electrical draw from coil C-2 because that draw is coming through 

the main contacts of the contactor served by coil C-1 and not through coil 

C-1 itself.



Comment?



'OC' Says: "The best investment we can make is the effort to gather and 

understand knowledge."



Time: 10:01:14 AM PST US

From: "Terry Miles" <terrence_miles(at)hotmail.com>

Subject: RE: Starter Solenoid fuse blows, ideas?

Mike,



I am only a Saturday afternoon mechanic.  Take the following as "off the top

of my head" ideas.



Unless I missed it, you didn't mention about the coil on the starter motor.

Without looking at your system, it is likely your B&C "starter solenoid"

actually uses about 1 amp max to energize another coil that is bolted to the

starter motor. I'll call that second coil C-2 so we are both sure which

component we are talking about.  C-2's job like any coil is to close the big

juice contactors so current at 150 amps maybe can go from the batt to the

starter motor.  C2 is also responsible to throw the pinion gear into the fly

wheel and keep it that way until you let off on the starter button.  C-1's

job is to energize C-2. The fuse that blows feels the draw from both C-1 and

C-2.



Your comment about having to move the prop or it blows a 2nd fuse makes me

want to investigate C-2 the coil on the skytec.  Skytec will sell you

another coil for about $5 if they don't just out and out give you one from

stock.  http://www.skytecair.com/   They are real good about answering tech

questions there too.  If you call have model and serial # ready.



The C-2 casing is held on the starter motor with a couple of screws and the

guts can get swapped out just as easy.  Look around at your ring gear and

the starter gears and see if you see any scoring.  The pinion doesn't thrust

into the gears, or has some other mechanical problem the mech load creates

an amp draw that can eat a fuse--and be a literal roulette wheel like

problem that only happens some of the time.



Hope this leads you to a couple of ideas more.  Good luck



Terry Miles

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