A VPX alternator question

[JurgenRoeland]

This may seems like a trivial question but I didn't find any answer in manuals. it's vpx related and not directly Skyview. My skyview is running well so far and I'm very happy with it. My excuses upfront but I'm not strong in electrics stuff. I've been able to get my vpx and basic circuits running and starting FFW work now.

I was wondering if the alternator field switch controlled by the VPX (J12-11) has any logic in it to be off when the battery master is off.
My master switch is installed as per the manual using a switch input that controls the battery master contactor. The VPX is on the switched side as per Vans manuals.

I read somewhere that if the battery is off and only the alternator would be operating, high voltage spikes may occur and irregular power distribution can happen and that the alternator should only be on when the battery master is on (like with the dual knob red switches on cessna's).
I have a regular on/off SPST input switch for the master contactor and had planned another simple ON/OFF SPST for the alternator switch.

In my current temporary setup, the VPX switches off when I turn the master switch down because the battery gets disconnected and the VPX goes off as I haven't got the alternator installed yet.
But will the same thing happen if the alternator is installed and providing power by the engine ? The alternator is on the switched side and still powering the VPX,
I assume only the battery is disconnected then but the VPX probably continues to be on as the alternator still gives power to the VPX.
If that is the case, is there any logic in J12-11 that would switch off also the alternator if the master is off.
The manual of vpx talks about overvoltage protection on the J12-11 Field line but it's not saying anything about the fact if the alternator is controlled by the VPX

thanks for any hint in the right direction

 

[jradtke]

The VPX provides the field power to the alternator. If the VPX is offline, then there should be no power going to the alternator field; this should cause the alternator to also be offline.

 

[wilkersk]

I started to answer this post yesterday. But, after reading the VP-X and PPS manuals, I'm a bit confused also.

It would make sense to me that you should be able to isolate the battery (battery rocker off) and still have the alternator powering the buss system (VP-X or conventional). But, there's one sentence in the PPS install manual that says if the battery is turned off, VP-X will not be powered on. And it makes no mention of whether the engine is running or not. So, I think I'm gonna ask the Vertical Power people, unless there's someone out there already flying this setup that will chime in...

 

[n144sh]

I started to answer this post yesterday. But, after reading the VP-X and PPS manuals, I'm a bit confused also.

It would make sense to me that you should be able to isolate the battery (battery rocker off) and still have the alternator powering the buss system (VP-X or conventional). But, there's one sentence in the PPS install manual that says if the battery is turned off, VP-X will not be powered on. And it makes no mention of whether the engine is running or not. So, I think I'm gonna ask the Vertical Power people, unless there's someone out there already flying this setup that will chime in...

I don't think you want the alternator connected to the bus and energized without a battery. The battery besides providing surge power serves and important role of stabilizing the voltage.

 

[JurgenRoeland]

The last response of n144sh is what I had in mind having a double switch to make sure there are no surge powers. but I read also in the VPX manual that the VPX field wire does protect against over voltage. That's what keeps me unsure how to wire.
The vpx manual looks pretty clear on having to wire J12-11 to the field. Since vpx connects behind the master switch on the switched side, the alternator would keep the vpx running even with the master/bat solenoid switched off. If the alternator would be switched of with a double rocker switch, the vpx would go down by switching off the master/bat switch. But then what is the function of the J12-11 and it's overvoltage protection. You could as well have the field wire not hooked up to the vpx and through a regular switch.
Would indeed be nice as wilkersk says to hear about it from people that fly with it. I assume there are hundreds so let's hope for someone to share his experience or setup

 

[Foxlees]

Ok I have VPX in my aircraft that I installed, I have also built a panel using a VPX system for another owner, the reason the Alt switch is connected to J12-11 is so the VPX can control the Alternator in case of over voltage by controlling the Field wire to the alternator.
if the engine is running and the Alternator switch is on which in turn is enabling the alternator field circuit the alternator will continue to produce voltage 14V to the BUS if you turn off your Master and nothing else, the engine will continue to run, and therefor the VPX would continue to be powered, and everything else would remain powered, this would be limited to the amount of current that is being drawn from the Bus and the amount of current the Alternator is producing at the time. If you turn your Alt switch off the VPX and everything else would turn off the Engine will continue to run, until your powered it down via Mixture of L/R Mags.
Hope this helps.

 

[JurgenRoeland]

Ok I have VPX in my aircraft that I installed, I have also built a panel using a VPX system for another owner, the reason the Alt switch is connected to J12-11 is so the VPX can control the Alternator in case of over voltage by controlling the Field wire to the alternator.
if the engine is running and the Alternator switch is on which in turn is enabling the alternator field circuit the alternator will continue to produce voltage 14V to the BUS if you turn off your Master and nothing else, the engine will continue to run, and therefor the VPX would continue to be powered, and everything else would remain powered, this would be limited to the amount of current that is being drawn from the Bus and the amount of current the Alternator is producing at the time. If you turn your Alt switch off the VPX and everything else would turn off the Engine will continue to run, until your powered it down via Mixture of L/R Mags.
Hope this helps.

clear explanation, thank you. so I take away from this that your 2 switches for master and alt work independently from each other and can be just simple SPST switches and both can be on regardless of the position of the other. Off course both is the normal operation mode but in case of problems, the battery can be switched off with the alternator still producing power without destroying any valuable equipment thanks to the overvoltage protection on J12-11