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Thread: Dual STI build log

  1. #281
    Senior Member JoeRuscito's Avatar
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    Default Re: Dual STI build log

    Do you have any type of short circuit protection between the positive lead on the vertical power and the mater contractor? I see the VP lead goes through your firewall (as does mine), if that grommet chafes I believe it would cause a major short. Also to note, I think the earthx batteries have internal short protection but Im not sure if this is what is relied on to protect the main power runs. The manual states it will reset after a cool down period if about three min. I think that would mean if you had a short it would disconnect, then momentarily reconnect every few min?!?

    To that point if the battery internally disconnects the only backup option for avionics power would be a secondary backup battery, as a backup critical systems bus would not function.

    Any clarity on this would be appreciated and Id love to know what people are doing to protect from shorts on the few connections that go straight to the master contractor.

    Thanks!

  2. #282
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    Default Re: Dual STI build log

    Joe, no short protection on the positive lead from the battery to VPX. Personally I don't think its needed. I think it would be more likely that the fault protection breaker fail versus chafe through the grommet and insulation on the wire. My alternators tie into the vertical power/battery that run through a switch/breaker so they protect the electrical from the charging system. The fault protection on the earthx battery is to protect the lithium battery and to keep a thermal runway from happening which typical happens when overcharging occurs. The fault protection also protects the battery to try and save the cells if the volts get to low. Basically if the volts drop to low it shuts off the battery to save the cells until hopefully soon a charge gets put on it.

    I am not running a backup battery system. The electrical system I would run would be completely different if this where an IFR plane. VFR Day aircraft I am not too concerned if I lose avionics. I will just look out the window which hopefully I already am. The one concern I do have is there is a lot riding on the VPX. If the VPX dies, suddenly I will find myself on short final, with both fuel pumps running through it. I may take a closer look at the VPX pro that has a dual bus system so you can run one fuel pump on each bus or possibly run one fuel pump outside the VPX on its own bus. Of course the biggest concern I have with this aircraft is its engine is a piston engine and there is only one.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  3. #283
    Senior Member aviator79's Avatar
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    Default Re: Dual STI build log

    I don't have EFI (yet), so I'm not quite as dependent on my fuel pumps. Nonetheless, the 914 does have two fuel pumps and I do run one fuel pump through my ACM (sort of equivalent to the VPX), and one on its own dedicated circuit. If (when) I do EFI, I'll keep this arrangement for the reasons you state.

    Also, I used something like this to pass power through the firewall:
    https://www.summitracing.com/parts/s...-red/overview/
    --Brian
    Flying - S7SS

  4. #284
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    Default Re: Dual STI build log

    I contemplated running one fuel pump outside the VPX. Couple reason I didn't. One is the VPX monitors the circuit and if amp draw is outside the set parameters it will alert you. I wanted each fuel pump monitored, but now I am relying on the VPX. The other reason is I was having a hard time wrapping my head around how to run a fuel pump outside the vpx and to do it safely.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  5. #285
    Senior Member JoeRuscito's Avatar
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    Default Re: Dual STI build log

    Quote Originally Posted by Shadowrider View Post
    Joe, no short protection on the positive lead from the battery to VPX. Personally I don't think its needed. I think it would be more likely that the fault protection breaker fail versus chafe through the grommet and insulation on the wire. My alternators tie into the vertical power/battery that run through a switch/breaker so they protect the electrical from the charging system. The fault protection on the earthx battery is to protect the lithium battery and to keep a thermal runway from happening which typical happens when overcharging occurs. The fault protection also protects the battery to try and save the cells if the volts get to low. Basically if the volts drop to low it shuts off the battery to save the cells until hopefully soon a charge gets put on it.

    I am not running a backup battery system. The electrical system I would run would be completely different if this where an IFR plane. VFR Day aircraft I am not too concerned if I lose avionics. I will just look out the window which hopefully I already am. The one concern I do have is there is a lot riding on the VPX. If the VPX dies, suddenly I will find myself on short final, with both fuel pumps running through it. I may take a closer look at the VPX pro that has a dual bus system so you can run one fuel pump on each bus or possibly run one fuel pump outside the VPX on its own bus. Of course the biggest concern I have with this aircraft is its engine is a piston engine and there is only one.
    Hey Dustin, As a follow up talked with Earthx and they confirmed that no fuse is needed to protect the battery. Although another kitfoxer pointed out that the rotax generator still needs to be protected against shorts. Which I believe it is by the 2 30 amp fuses. One on the AMP connector pin 3 and one coming from the start power switch (912is).

    On the subject of back up batteries. Do you have any concern the voltage will drop below the EFIS and engine monitor min voltage on start up? It seems this is a good secondary reason for backup battery. However with lithium (14 volts) and min efis voltage around 9 it seems like you'd have to have a pretty dead battery to have the EFIS drop out on start.

  6. #286
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    Default Re: Dual STI build log

    I have thought of this because it seems a little disconcerting starting the engine with avionics powered up for fear of power cycling things on the start. But with all engine gauges being digital kind of need avionics on for start.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  7. #287
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    Default Re: Dual STI build log

    This is what I decided to do. Master turns on GDU 465 and GEA-24. So I will have engine instruments displayed on the G3X. Have not tried to start yet and see if it power cycles the GDU.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  8. #288

  9. #289
    Senior Member
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    Default Re: Dual STI build log

    Thanks! I was reading the vertical power is suppose to have this built into it. Suppose to keep voltage alive on EFIS for starting. I will report back if it does.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

  10. #290
    Senior Member
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    Dec 2017
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    Mapleton,UT
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    Default Re: Dual STI build log

    Its alive! At least the avionics are. Wiring is done and troubleshooting is done, or until I run engine and find any possible problems. I must have an ADSB antenna in range because I am picking up traffic and weather. Radio checks out and I am able to pickup the local airport and had a plane give me a radio check. Getting ready to start the engine but still waiting on a prop. Troubleshooting went faster than I thought, which is a good thing. I guessed which was signal wire on the egt's so had to switch pins as they where indicating backwards. (I was testing them using a heat gun and they where going down in temp) I had trouble getting the trim to work. Its really frustrating to trouble shoot something to find out its not you its the box. Apparently both safety trim switch boxes went out without a jumper pins internally so I was not getting 12v signal to trim motor. So far I have been impressed with the Garmin G3X. Ipad is also talking with the GTX45R so its receiving traffic and weather via ADSB. Its also talking with G3X so attidue and WASS GPS is being received from the G3X. The Ipad is also talking with the AFR so tuning the engine will be possible. Starting to get excited! (Those with a keen eye, I had selected the wrong manifold pressure gauge, its fixed now and I selected the wrong input for the earthx fault monitor, its fixed also)






    Last edited by Shadowrider; 08-20-2019 at 08:14 PM.
    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
    Garmin
    N33TF......FLYING!
    N53TF......FLYING!

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