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  #1  
Old 09-05-2018, 07:47 AM
steve murray's Avatar
steve murray steve murray is offline
 
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Default Firewall Starter Relay Needed?

I have my finish kit and FWF kit on order and was reviewing plans and product specs.

The plans have a starter relay mounted on the firewall and the Skytec website states the 149-NL starter has an "internal solenoid" ? Is the firewall relay redundant, needed?
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  #2  
Old 09-05-2018, 08:08 AM
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Carl Froehlich Carl Froehlich is offline
 
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Yes - you need to install the starter solenoid.

Carl
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  #3  
Old 09-05-2018, 08:09 AM
Electrogunner Electrogunner is online now
 
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Default Starter

Yes the firewall starter relay is needed as usual. I have the same starter.
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  #4  
Old 09-05-2018, 08:14 AM
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Quote:
Originally Posted by Electrogunner View Post
Yes the firewall starter relay is needed as usual. I have the same starter.
Thanks for the quick response from you & Carl. Can you guys help me understand why it is still needed?

Also, does the relay come in the Finish kit or FWF kit?
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  #5  
Old 09-05-2018, 09:28 AM
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An NL can be re-wired internally to operate without a separate start contactor. You may still wish to use a relay between the NL's internal contactor windings and any low amp switch used to control it.

Aircraft traditionally incorporate external start contactors for two reasons. First, it means the big power cable running from the firewall mounted contactor to the starter is dead while in flight. It cannot short to ground because the vibrating engine wore through the insulation. The opposing argument revolves around really good cable routing and fixation.

Second, back in the dark ages a lot of starters didn't have an internal contactor, just a solenoid to drive the pinion out.
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  #6  
Old 09-05-2018, 09:55 AM
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To add to Dan's comment. There is a significant voltage drop across a normally operating external solenoid which degrades performance.

At some point someone decided this was better than common sense. Support the starter cable properly and this is not an issue.

Many older aircraft such as Cessna 150's with pull-start contactors operate safely with an always-hot cable without an external starter solenoid, so the problem having a second solenoid attempts to solve is overblown.

And having a second solenoid is just another failure point.
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Last edited by rocketbob : 09-05-2018 at 09:57 AM.
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Old 09-05-2018, 10:22 AM
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Carl Froehlich Carl Froehlich is offline
 
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As has been pointed out you can just run a start wire to the starter mounted solenoid, and a hot #2 or so cable to the starter.

But - the starter mounted solenoid is no toy. You will need a big boy start switch to handle the current. If not, then you will need to have a control relay in line. Just what you are trying to avoid.

So the traditional starter solenoid becomes the simple, cheap approach. The plus side, as pointed out, is your #2 starter wire is dead other than for engine start. Id use the starter solenoid for this reason alone.


Carl
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  #8  
Old 09-05-2018, 10:30 AM
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Quote:
Originally Posted by Carl Froehlich View Post
But - the starter mounted solenoid is no toy. You will need a big boy start switch to handle the current. If not, then you will need to have a control relay in line. Just what you are trying to avoid.
Carl
This is not correct. The internal solenoid is just another solenoid, with the same current requirements as an external one. They work fine with normal pushbutton switches. Instead of the jumper on the starter wiring to the big terminal of the starter, you remove the jumper and wire the small terminal to a starter switch.
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N678X F1 Rocket, under const.
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  #9  
Old 09-05-2018, 10:55 AM
lr172 lr172 is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
As has been pointed out you can just run a start wire to the starter mounted solenoid, and a hot #2 or so cable to the starter.

But - the starter mounted solenoid is no toy. You will need a big boy start switch to handle the current. If not, then you will need to have a control relay in line. Just what you are trying to avoid.

So the traditional starter solenoid becomes the simple, cheap approach. The plus side, as pointed out, is your #2 starter wire is dead other than for engine start. I’d use the starter solenoid for this reason alone.


Carl
I agree with Bob, they should require similar current. You should understand that the external starter contactor that most use also requires "big boy" start switch, depending upon what you mean by "big boy." That ext contactor that most use draws almost 5 amps. Several start switches listed by ACS fall well short of that rating. I have no idea of the rating of the key switches, as I don't use them.

To the OP, note that you will still need a flyback diode to protect the switch, even if you skip the ext contactor.

Larry
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Last edited by lr172 : 09-05-2018 at 10:58 AM.
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  #10  
Old 09-05-2018, 12:45 PM
BillL BillL is offline
 
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Default Inrush current . . .

Quote:
Originally Posted by rocketbob View Post
This is not correct. The internal solenoid is just another solenoid, with the same current requirements as an external one. They work fine with normal pushbutton switches. Instead of the jumper on the starter wiring to the big terminal of the starter, you remove the jumper and wire the small terminal to a starter switch.
Bob, I don't have the specs and my testing was with the XL starter, but - I wanted to test my starter solenoid for low voltage tolerance. I hooked up a variable voltage 25 amp power supply to activate the solenoid, starter wire removed. It blew the internal current limiter almost every time.

Maybe a standard switch/button is fine due to short term inrush current. It also may have been a super fast acting limiter since the power supply is a switching type supply. So - just a data point, that might not be applicable.

My firewall solenoid was the culprit, BTW, a loose part inside had intermittent contact to activate the starter solenoid. I took it apart to find out why it failed. 20 hours flight time. (it is repaired now, reassembled and ready as a backup part)
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