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Breaker Sizing

AviatorJ

Well Known Member
I'm to the point now where I'm splitting my harness power wires for installation into the VPX. I had previously set up my VPX CB size using their Planner tool and have made adjustments to that over the years. The harness I received from Stein has the power leads labeled with a Amp number on them as well. However the Stein info isn't lining up with the VPX Planner info or the Garmin G3X installation manual.

Here's an example; GSU 25 (ADAHRS) in the VPX Planner is set as .2A actual draw with a CB size of 1.0A, On the Stein label it's labeled as 2A, and the Garmin doc it's listed as .2 as well. Maybe Stein meant, .2 but for the GEA 24 (EIS) Garmin docs have .43A max but Steins label says 5A.

My thought is obviously use Garmin documentation to ensure proper sizing, plus a 20% margin. I just wanted to make sure I'm not missing anything.

I'm also going to have to combine some items as well as put a few items on a fuse block. When I combine them, like say the Autopilot stuff, GMC 507 and three GSA 28, what is the best way to size that?
GMC 507 .2A
GSA .36 (Typical), 1.8A (Max), 2.8A (Max with 1 Amp trim motor at full load). Multiplied by 3 it's - 1.08A, 5.4A, 8.4A.

So do I take the highest load possible at 8.6A, add the 20% for at least a 10A CB? OR is it typical load, 5.6A with a CB of 7A rounded up?
 
Fuses and CB's are sized to protect the wire, not the device(s). You can downsize based on connected load, or if the device installation instructions state something smaller to be placed inline.
I would follow Steins labeling. He has done this a few times before ;)

Ganging devices is ok, just make sure you size to protect the wire and add in protection or a separate circuit if the device calls for it.

Hope that makes sense.
 
Going to have to rework some of my VPX stuff. I get that breakers are there to protect the wires but with the VPX you?re limited somewhat on breakers of various sizes. So if I can get away with using a 5 amp vs a 10 amp that helps me out.
 
I did what you mentioned - I put some of the "less critical" devices with low draw and not much need to "monitor" with the VPX on a fuse block - like the GDL52R, the CO monitor, etc. Super easy to do, and with the current EFIS screens access to the fuse block etc is wide open and easy to get to.

[not to say the CO monitor isn't important ... but it has its own status light]
 
Going to have to rework some of my VPX stuff. I get that breakers are there to protect the wires but with the VPX you?re limited somewhat on breakers of various sizes. So if I can get away with using a 5 amp vs a 10 amp that helps me out.

The breaker/fuse size may be to protect the wire, but if a specific wire is protected by a 10A breaker, that same wire will be equally protected by a 5A breaker, whether it is inside a VPX unit or a stand-alone panel item. :)

In my case I'm planning to go with the VPX numbers and the manufacturers current (amps not time) data.
 
The breaker/fuse size may be to protect the wire, but if a specific wire is protected by a 10A breaker, that same wire will be equally protected by a 5A breaker, whether it is inside a VPX unit or a stand-alone panel item. :)

In my case I'm planning to go with the VPX numbers and the manufacturers current (amps not time) data.

I've been digging around a bit in more detail. Stein was right about the G5 and the 245 (Audio Panel). Garmin suggests 5 amps breaker on both these. So I'll go with that.

I just have a lot of stuff, using up all my 10-15 amp breakers. I'm going to give it another hard go through and see what I can combine, or move to the 15A fuseblock I'm using.
 
Need some help now working through my logic. When I run into issues of uncertainty I hyper focus until I resolve them. So I spent last night and this morning making a spreadsheet, doing some pivots and running amp tests in my garage.

Here's the crux of my issue, I have 10 items right now that are listed as needing 10 or greater circuit breaker. The problem being the VPX pro only has 9 10-15A pins available. So I need to shed one of the big ones listed below, somewhat in order of importance;

  • GTN 650 Comm 8A (Has to use a 10)
  • GTN 650 Nav 10A
  • Comm#2 8A (using a 10)
  • Pitot/AOA 15A
  • Boost Pump 10A
  • Strobes 15A (Might be able to use a 10A)
  • Landing Light Left 10A
  • Landing Light Right 10A
  • IBBS 10A
  • AccBlock 15A

I can't really touch the GTN, the GTR 20 (Comm#2), Pitot or Boost pump.

Getting into the lights the Strobes use a 10-15, I'll go with a 15 and walk it down if I can in the VPX. But AeroLED manual basically says give 5A to each light, 2 wings and 1 tail. Each Landing light is drawing 5.20 per my test in the garage. I really want the VPX to control Wig-Wag/Recog for the Vspeed feature so each light needs a 10A pin. Changing this would free up several pins but then recog becomes a manual process. It's doable just want to avoid it.

Here are the two items I think I can mess with, the IBBS and my accessory block. Now the IBBS utilizes a 10A pin for essentially charging since I'm not doing any pass-through power. That being the case would it make sense to add this to the 15A accessory block and use a 10A fuse blade?

The accessory block is a 12 place fuseblock that I'm hanging a bunch of random stuff off. For the most part low power items like oil damper, cowl flaps and things of that nature. The only items that could potentially max out the amps are the USB ports. I ran a test, seems an iphone uses about .7A and an Ipad uses about .9A, so if I had 4 Ipads plugged in I'm pushing about 3.6A. If I had 4 devices plugged into all the USBs at once with power, all while working the cowl flaps, ram air, oil damper and all the lights on... So 15A might be over kill here. Maybe I make this a 5A and control what's getting plugged into the USBs and when.

My other thought is hang the two USB chargers off the Pass-through power on the IBBS, this would allow me to easily make the AccBlock a 5A circuit.

So I guess what it comes down to is do I put the IBBS on the AccBlock or do I work through the reduction in Accblock size by pushing some stuff through the IBBS pass-through? (Leaning heavily towards putting the two dual USB Chargers off the IBBS Pass-through)
 
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I haven't look at amps requirements for lights but those seem high; have you looked into using lights that are more efficient?
 
I haven't look at amps requirements for lights but those seem high; have you looked into using lights that are more efficient?

In too deep on those lights. I've already done the wingtip mod for the VX's and have the lights sitting in my garage. I thought it seemed high as well but when I put some current through them and metered them out it was 5.2A each. So a 6 amp would have worked but the VPX goes 5-10A so I'll have to use a 10A and bring it down to 6ish.
 
Acc block

Hi Justin,

Why not run your fuse block off the main vpx lug, and not out of a power pin? Just bypass the VPX entirely for the items on fuses..
 
Looking for comments regarding my IBBS - VPX wiring diagram. Will it work? Is there a better way? Thanks.

https://drive.google.com/file/d/19kc6Y6fw7---4Tq8xjj_xjCtZYKa8ZDX/view?usp=sharing

I struggled with the want/need to hang the GPS and/or a Comm off the IBBS. In the end I went with the standard TCW drawing showing just the PFD/MFD/ADAHRS/EIS hanging off it, keeping it under the 10 amp fuse size of the battery.

Hi Justin,

Why not run your fuse block off the main vpx lug, and not out of a power pin? Just bypass the VPX entirely for the items on fuses..

Hey Nick. I have a 60 amp ANL between the contactor and the VPX. So my concern would be blowing that out if I hang too much stuff off the power lug. My solution was to basically remove my two USB chargers from the accessory block and bumping it down to 5a. Here's the latest planner-

http://planner.verticalpower.com/printable/share/2722

I am however going to hang some stuff off the input side of the ANL such as the AC compressor, AC evaporator, airhorn and maybe the USB Chargers. I also am going to go ahead and put two shunts in since the harness you guys made already has those leads. Don't want them going to waste, so that will give me a better picture along with the VPX of power being used.
 
Hi Justin,

Why not run your fuse block off the main vpx lug, and not out of a power pin? Just bypass the VPX entirely for the items on fuses..

Want an on/off avionics switch. By running through the VPX I can configure all avionics (excepting main power for the MFD) to a switch. The power pins for the IBBS will be part of the configuration. Seems I have a bit more flexibility through the VPX.
 
IBBS Voltage to VPX

Running pin 2 (Batt Info) from IBBS to J2 pin 12 (Aux Batt Volt) on the VPX. IBBS says to in stall a 100k Ohm resistor. VPX says to install a 1k Ohm resistor. Has anyone done this? If so, which resistor did you use?
 
Want an on/off avionics switch. By running through the VPX I can configure all avionics (excepting main power for the MFD) to a switch. The power pins for the IBBS will be part of the configuration. Seems I have a bit more flexibility through the VPX.

Does this mean you have the VPX and an Avionics Master switch in series? If so, does this translate to two potential single point failure components in series?

I never design in an Avionics Master switch and perhaps I just don?t understand VPX. If so, sorry for my stupid question.

Carl
 
Does this mean you have the VPX and an Avionics Master switch in series? If so, does this translate to two potential single point failure components in series?

I never design in an Avionics Master switch and perhaps I just don?t understand VPX. If so, sorry for my stupid question.

Carl

VPX actually does the component switching.
 
So if either the physical avionics switch connected to the VPX, or the VPX itself failed you still have avionics?

Can't speak for 'OldGuy', but in my case I would have to flip the back up battery switch to power my two G3X screens, EIS and ADAHRS... now if all that takes a dive then I have my G5.
 
IBBS VPX

So if either the physical avionics switch connected to the VPX, or the VPX itself failed you still have avionics?

Yes. Here?s the rationale: After engine start I flip the Avionics/IBBS Enable switch (DPDT). I then check the IBBS voltage on the MFD to verify the IBBS is fully charged. Let?s assume the IBBS is fully charged and I am flying. At this point if the IBBS Enable switch has a disconnect it will disable the IBBS. However, the avionics connected to the IBBS continue to function since the IBBS is not the source of power. It is a pass-through portal for the power, the actual source for which is the VPX. Now if the VPX does a Lewinsky the IBBS will sense the voltage drop (under 11 volts) and provide power to the connected devices. So, as I see it the only avenue of failure is to have both the IBBS and the VPX go TU, which i consider highly unlikely?
 
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