Oddities with Surefly ignition, hidden fuses, carrying spares...

[DXB]

Surefly questions. The lead from the battery to the unit is direct, bypasses the master, and has a low power draw from the battery at all times.  It seemed strange that they had a fuse in this lead right next to the battery and not a breaker on the panel for such a critical component, but I now gather that they wanted to minimize the distance between the battery and the fuse to negate the risk of a catastrophic short in that segment of wire.  

Questions:

1. Anyone know the correct 10amp fuse type for the SIM4N?  Oddly it's not specified in any of their literature, and I just failed to get through to their tech support. Specifically anyone know if its supposed to be a fast blow or slow blow fuse?  The one that blew for me was a Bussmann 4GC 10A (fast blow) fuse, but I'm wondering if someone put the wrong one in after the last time it blew.

2. Also any idea why it always seems to blow when we work on the right (conventional) mag??  It's now happened twice in that context. Luckily I'm on the ground and discover it after a difficult start followed by a failed left mag check.  That's the only time I've had the issue in a couple hundred hours of flying with it.  It would suck for it to happen in flight so I'm trying to understand why it blows.  

3. It was pointed out to me that we have to carry spares for all fuses in our planes per the regs, and I now vaguely recall this from studying for the PPL, so it's time to start doing this, particularly since the Surefly fuse seems to like to blow.  Any other hidden fuses in my '68 M20C that I'm not aware of?  The panel is completely redone so some may have been removed. I can't find anything in the service or parts manual about fuses.  BTW I already know about the fuse in the hookup for my battery minder.

[Igor_U]

Good point,

I didn't think about this.

Surefly document just calls for a "10amp fuse" so I would go for a slow blow. I would also try to figure out whey it blows when you work on a RH mag. you might have some ground issues or you shorted the power wire when working in the engine compartment. Is it insulated with the rubber terminal nipple?

I am aware of couple inline fuses under my panel; this are all marked now... one is for Brittain Autopilot and other escapes me... I should look up the values and carry the spares besides a box of 10a fuses in my repair kit.

Good luck.

 

[Ragsf15e]

9 hours ago, DXB said:

Surefly questions. The lead from the battery to the unit is direct, bypasses the master, and has a low power draw from the battery at all times.  It seemed strange that they had a fuse in this lead right next to the battery and not a breaker on the panel for such a critical component, but I now gather that they wanted to minimize the distance between the battery and the fuse to negate the risk of a catastrophic short in that segment of wire.  

Questions:

1. Anyone know the correct 10amp fuse type for the SIM4N?  Oddly it's not specified in any of their literature, and I just failed to get through to their tech support. Specifically anyone know if its supposed to be a fast blow or slow blow fuse?  The one that blew for me was a Bussmann 4GC 10A (fast blow) fuse, but I'm wondering if someone put the wrong one in after the last time it blew.

2. Also any idea why it always seems to blow when we work on the right (conventional) mag??  It's now happened twice in that context. Luckily I'm on the ground and discover it after a difficult start followed by a failed left mag check.  That's the only time I've had the issue in a couple hundred hours of flying with it.  It would suck for it to happen in flight so I'm trying to understand why it blows.  

3. It was pointed out to me that we have to carry spares for all fuses in our planes per the regs, and I now vaguely recall this from studying for the PPL, so it's time to start doing this, particularly since the Surefly fuse seems to like to blow.  Any other hidden fuses in my '68 M20C that I'm not aware of?  The panel is completely redone so some may have been removed. I can't find anything in the service or parts manual about fuses.  BTW I already know about the fuse in the hookup for my battery minder.

I haven’t had this happen yet but haven’t worked on the right mag.  How did you start it if the left mag was dead?  Did it actually die during/after the start? Or did it start on the right mag when you let off the “start”/push on the key?  The right mag is grounded during start but sometimes it’ll start after letting off the starter…

[DXB]

29 minutes ago, Ragsf15e said:

I haven’t had this happen yet but haven’t worked on the right mag.  How did you start it if the left mag was dead?  Did it actually die during/after the start? Or did it start on the right mag when you let off the “start”/push on the key?  The right mag is grounded during start but sometimes it’ll start after letting off the starter…

Exactly that - won't fire in start position which only drives the TDC retard breaker points on the left (or whatever equivalent the surefly does), then fires up on the right with a hard jolt due to the advanced right timing once you switch back to both to keep from frying the starter - a sure sign the left has failed.

[PT20J]

I just took out the fuse that came with it and went to the auto parts store and bought a 5 pack of Buss fuses with same number and rating.

I’m pretty sure the thinking was to have the least stuff possible between the SIM and the battery, hence the direct wire run. The fuse is simply to protect the wire. To blow out a 10 A fuse would take something like a direct short to ground. 

Is your installation a 28V system with the power conditioner and large capacitor near the SIM? If so, I think there are a lot of places to accidentally short it out when working around the back of the engine. It’s really hard to see how the other mag would be involved.

Skip

[Will.iam]

I had the A&P install the fuse by the battery but also a 10 amp circuit breaker on my panel so when i am at an out station i can pull the breaker to keep the surefly from draining the battery. This would inly be necessary when the plane is going to sit for more than a few days not on a battery minder. Even thou, when i got my avionics relay replaced  with a circuit breaker switch, some time during that repair the hotwire from the surefly found ground and blew the fuse instead of popping the circuit breaker. The engine fired up but was idling rough and I didn’t know why until i went to do a mag check and found the surefly was not running at all so my engine started up on the mag as well. I now have a spare fuse next to the fuse holder for in case the fuse gets blown and I’m away from home. 

[N231BN]

This question regarding a CB used to say no, I'm glad they changed it. It is still very important to use the fuse close to the battery to protect the wire. Also, make sure to use terminal nipples or even electrical tape if you must to prevent any short from happening.

[PT20J]

Well, technically, the STC references the AML which references the Installation Instructions that allow ONE circuit protection device located at the battery. I don't know what the standby current is, but it's probably similar to a clock. It's worth asking.

Skip

[N231BN]

I don't know what the standby current is, but it's probably similar to a clock. It's worth asking.
Skip

Exactly

[jetdriven]

I think the installation instructions say 1ma.  

[DXB]

18 hours ago, PT20J said:

I just took out the fuse that came with it and went to the auto parts store and bought a 5 pack of Buss fuses with same number and rating.

I’m pretty sure the thinking was to have the least stuff possible between the SIM and the battery, hence the direct wire run. The fuse is simply to protect the wire. To blow out a 10 A fuse would take something like a direct short to ground. 

Is your installation a 28V system with the power conditioner and large capacitor near the SIM? If so, I think there are a lot of places to accidentally short it out when working around the back of the engine. It’s really hard to see how the other mag would be involved.

Skip

It's a simple 12V system.  Yeah I should trace everything forward of the fuse to the SIM to make sure there's nowhere it could short.  I'd wondered if it had something to do with clipping the buzzbox to the right mag to time it and then turning the ignition switch to unground it, which might unground left momentarily as well - I don't think so, but I ain't too sharp in my understanding of how electrons flow around.