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Go Back   VAF Forums > RV Firewall Forward Section > Electronic Ignition Systems
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View Poll Results: Do you have a dual Plasma ignition system?
Do you you have an emergency backup battery? 11 64.71%
Do you rely on the aircraft battery only? 6 35.29%
Voters: 17. You may not vote on this poll

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  #11  
Old 01-03-2022, 12:22 PM
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airguy airguy is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
One other comment, if you run dual ship power dependent ignitions I strongly recommend a robust electrical power design. Perhaps they exist but I have not seen a “per instructions” backup battery install that satisfies my risk tolerance. Specifically these backup battery schemes do not provide adequate electrical reserves (should be more that 90 min for me), many do not provide indication of backup battery health during normal operations, and I’ve found some of these backup batteries to be dead in flying airplanes (as in installed a decade ago and forgotten).

It can be done, but hard with just a single ship battery as your base. I suggest there are many advantages to a two identical ship battery design that uses no backup batteries (either for the engine or the panel).

Whatever you do test it! You don’t want to find out if it works or not when you really need it. Make sure whatever switch manipulation are needed (if any) to keep the fan running are clearly documented in your POH Emergency Procedures - and routinely tested.

Carl
This is gospel.

If one or more of a critical ship function requires electrons, make certain you have a solid robust method of delivering them for Plan A, B and C.

As for the poll - it doesn't matter how reliable the electronic ignition system is, if you have a cheap alternator. The chain is only as strong as the weakest link.
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Last edited by airguy : 01-03-2022 at 12:26 PM.
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  #12  
Old 01-03-2022, 08:40 PM
Captain Avgas Captain Avgas is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post

I do not have any data to demonstrate if the Plasma III is more reliable than the II+. Perhaps others can comment.

Carl
I think that they are both quite reliable units but it is most likely that the Plasma 11+ is slightly more reliable than the later Plasma 111. It is my understanding that the longer spark duration of the Plasma 111 puts greater stress on the coils. But the Plasma 111 proved more popular because it had a higher number so everyone just assumed it must be better technology.

It was a bit like the Spinal Tap amplifiers that had a volume control that went to eleven
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Last edited by Captain Avgas : 01-04-2022 at 02:19 AM.
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  #13  
Old 01-04-2022, 12:01 AM
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Tandem46 Tandem46 is offline
 
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LSE Plasma II, 1 Mag. LSE has been FLAWLESS for 1200+ hrs.
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  #14  
Old 01-04-2022, 07:07 AM
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Returning to topic....

Quote:
Originally Posted by Janekom:

I am sure there are many arguments for an emergency backup battery and there are also those who will say it is not needed on a day VFR ship. Your opinions will be appreciated.
It's funny how terminology can change perception. Here the second battery is called an "emergency backup". It's a reasonable perception based on the wiring diagram in the Lightspeed manual, reproduced below. Note the "power select switch" in the power path for IGN2. Although it can be operated either way, the natural perception is that the power select will connect IGN2 with the main battery during normal operation, and be switched to the "backup battery" in the event of alternator, main battery, or main battery supply wiring failure.

The obvious fault with this scheme is the requirement for pilot intervention. For sake of this discussion, eliminate the power select switch. Wire IGN2 directly to the second battery.

Ok, new perception. The second battery is no longer a "backup". Each battery, battery connection, power supply wiring, switch, CDI unit, and ground path are essential elements of an individual ignition system. "Dual" truly become two complete systems.

VFR or IFR? The only difference is the minimum required run time with a failed charging system. In the past, a VFR install might use a second battery smaller than the main, which was mostly a weight saving measure given the installs were lead/acid. Given the low weight of lithium iron phosphate, it's now possible to install two equal, high capacity batteries with no penalty other than cost.
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Last edited by DanH : 01-04-2022 at 08:20 AM.
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  #15  
Old 01-04-2022, 08:02 AM
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Carl Froehlich Carl Froehlich is offline
 
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Looking at the classic Lightspeed diagram for the aux battery demonstrates a key design problem.

Assume the aux battery is dead. Unless the pilot opens the breaker before the diode that feeds that battery, the volt meter will read main battery voltage (minus the drop across the diode). So pilot action is needed to know if the aux battery is even there.

I wonder how many of these are flying and the pilot never did this check. I found an RV with this exact setup. The aux battery no load terminal voltage was around 2vdc.

Know how your system works, and verify it works on a routine basis.
Carl
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  #16  
Old 01-04-2022, 08:14 AM
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rolivi rolivi is offline
 
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Can you add a poll answer option for having a standby alternator?
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  #17  
Old 01-04-2022, 08:49 AM
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DanH DanH is online now
 
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Quote:
Originally Posted by Carl Froehlich View Post
Looking at the classic Lightspeed diagram for the aux battery demonstrates a key design problem.

Assume the aux battery is dead. Unless the pilot opens the breaker before the diode that feeds that battery, the volt meter will read main battery voltage (minus the drop across the diode). So pilot action is needed to know if the aux battery is even there.
True.

Most of us have voltage monitoring on an EFIS or EIS, which covers the main battery and charging system. It's easy to wire a simple test system for the second battery (green below), just a relay, a momentary ON button, and a $5 voltmeter display. Pushing the button with the ignition operating displays battery voltage under load.

Also installed a voltage monitor on IGN2 (yellow). If running voltage drops below normal charging voltage (open diode, relay, or wiring) I get an aural tone and a flashing LED. That means pushing the aforementioned test button also checks the voltage monitor.

Test button gets punched on the runup pad, standard left-to-right checklist, after boost pump on.

About $20 total.
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  #18  
Old 01-04-2022, 09:06 AM
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Janekom Janekom is online now
 
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Thank you for all the VERY valuable inputs here. This what this forum is about - to learn from others and not to go and make silly mistakes.

DanH my apologies if my terminology is wrong by calling it an emergency backup battery. I will change it to read just backup battery.

I have also downloaded the manual last week sometimes and the diagram that DanH has attached is what has sparked my interest or rather worry about this.

I could not understand that the the backup battery will only run IGN B.

Whatever one do, one should make sure that your backup battery voltage is really good and that it can take the load.

@ Rovili - I have tried but do not know how to change the poll options.
@ Carl - I have sent you a PM.
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Last edited by Janekom : 01-04-2022 at 09:27 AM.
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  #19  
Old 01-04-2022, 10:00 AM
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Quote:
Originally Posted by Janekom View Post
DanH my apologies if my terminology is wrong by calling it an emergency backup battery. I will change it to read just backup battery.
Jan, that's the point about terminology. Don't think of it as "emergency" or "backup". It's simply the IGN2 supply battery.

Here's another way to look at it. It's common to see one big battery and one small battery, which can lead a person to thinking auxiliary or backup. Reality? The big one is a starting battery. In truth, our inflight battery requirement is limited (the alternator is carrying the load). If it wasn't for the starting load, we could do fine with a pair of identical, relatively small batteries...each independently serving its own ignition system.
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Last edited by DanH : 01-04-2022 at 10:03 AM.
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  #20  
Old 01-04-2022, 11:27 AM
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AlexPeterson AlexPeterson is online now
 
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I've had dual direct crank LS3's since around 2007, replacing the thrice failed Lasar system. I did not wire it as per LS's installation, as I (like Dan) did not want any action on the pilots part to be necessary in the event of a main bus failure. I simply have a smaller battery whose only function is to power ig 2 all the time. It receives its charge through a diode from the main bus. I have both battery voltages monitored and alarmed on the G3X. I check battery 2's voltage prior to startup. Another problem area with LS's instructions are the always hot wires with no protection. Always hot is a good idea for ignitions, but one needs a fusible link at the battery. Both ignitions get their juice right from the battery terminals.

I did have one LS brain box croak last summer. It took a couple weeks to get it shipped out/fixed/returned, so I'm going to actively look for a spare LS3 box.

One large blind spot is not knowing, during flight, if an ignition stops sparking. Perhaps some EE here can design a monitor circuit with something to wrap around one lead from each ignition that detects a fault.
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