What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Lightspeed Ignition Switch Question

E

ethand

Well Known Member
Have a question about wiring the Plasma 3 Lightspeed for my RV-10

Planned Set-up:
Dual batteries: Odyssey 925 and 680
Dual externally regulated alternators
Vertical Power (Lightspeed will be wired separately directly from battery)

In the Lightspeed wiring diagram they show a dual battery single alternator set-up with a switch to select which battery the ignitions are running from.

Is there a reason a SPDT switch (ON-Off-ON) cannot be used for each Lightspeed to eliminate the selector? This would allow either ignition to be powered by either battery independently via use of the switch.

Am I missing something here?

Thanks in Advance
E
 
I had a similar setup in both my first RV-10 and current one. I was using a "Z-14" setup where the dual alternators/batteries were split and each on their own independent buss. Not sure how you're implementing that with a VPx but...

If you've got dual batteries, just wire each ignition to its own battery. No need for a switch to select anything. They get a permanent (via a CB) hot connection and the unit is turned on/off via the keyswitch (via the LSE keyswitch inputs). If you don't use a keyswitch, you can simply switch the power for each using standard toggle/rocker switches.

The diagram you're referring to is showing a small, dedicated backup battery that is kept charged and when main power drops below some threshold, you manually switch over to that. Not the setup you are describing.
 
Thanks Bob.

This will be separate from the VPX.

If I did this right, the schematic I am considering is below. Each ignition switch receives power from bot batteries thought the required 7.5 amp CB and the pilot can choose which each is set to during operation. I foresee flying with one on each but have the option should something go drastically wrong with a battery in flight.

33bq236.jpg
 
What's your objective? If it's to populate the panel with lots of complicated switches, you could do better. :) If it is to have both ignitions powered whenever the switch is on, regardless of which battery is in what condition, I'd be tempted to do something simpler and easier to manage in an emergency. The switch shown could be DPDT or DPST.

dualpower.png


If a battery shorts or has some low voltage condition, the ignition is still powered. The only thing it really doesn't protect against is an overvoltage condition. That would best be handled by some other circuit (OV sensor that drops the battery contactor, for example) and doesn't rely on you seeing the OV condition and manually switching your now-probably-dead ignition to the good battery. Diodes can be whatever form factor you're comfortable with - I'd use Schottky diodes to keep the heat dissipation down.

Now you just have one ON/OFF switch to worry about. If you really need to kill just one ignition you can pull its breaker. You won't lose either ignition unless both batteries have failed. I guess you could have a diode fail and not know it. It's unlikely but not impossible. Maybe stick an LED and resistor in parallel with each one to indicate a failure, and check them once in a while.
 
KISS

I would do as Bob suggests. If you use your schematic, you will probably pop one of the 7.5A breakers if you try to run both ignitions on the same battery.

One ignition will keep you flying and draw less current if you lose one of your batteries. If there is an over voltage condition on one battery, only one ignition would be affected.

Paige
 
Last edited:
PaigeHoffart said:
I would do as Bob suggests. If you use your schematic, you will probably pop one of the 7.5A breakers if you try to run both ignitions on the same battery.
Click to expand...
Well... no, since there is a CB for each ignition, not one per battery.
 
PaigeHoffart said:
When I said "your schematic" I was talking to the OP...look at his schematic.
Click to expand...
Ah. Gotcha, sorry. You're right about that, of course. Bob's approach is the simplest, and if you're worried about an OV condition it's fairly safe.
 
The engine will run very smoothly on a single LSE ignition. One reason Klaus implemented the LEDs for dual setups is so you'll know that one isn't working!

Bob
 
ethand said:
If I did this right, the schematic I am considering is below.]
Click to expand...

Consider that if one of your Plasmas shorts internally, it should pop the CB, then, not appreciating what just happened, you might switch that ignition to the other battery and pop the other CB.

I have dual plasmas but I keep the two sides separate with no crossover provision. The chances of two separate problems that take out both ignitions is so slim that I don't fret it.
 
DaleB said:
What's your objective? If it's to populate the panel with lots of complicated switches, you could do better. :) If it is to have both ignitions powered whenever the switch is on, regardless of which battery is in what condition, I'd be tempted to do something simpler and easier to manage in an emergency. The switch shown could be DPDT or DPST.

dualpower.png
Click to expand...

One thing to keep in mind, this design has a single point of failure.

If the S1 switch fails, you lose both ignitions. To me, the loss of panel space taken up by one additional SPST switch is greatly made up for by the added redundancy.
 
NovaBandit said:
One thing to keep in mind, this design has a single point of failure.

If the S1 switch fails, you lose both ignitions. To me, the loss of panel space taken up by one additional SPST switch is greatly made up for by the added redundancy.
Click to expand...

True. To be fair, it would have to be a "sudden and total" switch failure, which is pretty unusual if you pick a decent manufacturer. Two SPST toggles would indeed be slightly more reliable, at least in theory.
 
Configuring

Reviving this because I have a question, I have dual lightspeed ignitions, will be putting a breaker on each ignition module. Is the keyed switch sufficient for switching with two batteries?

Dave Ford
Cadillac, Mi
 
bcondrey said:
The engine will run very smoothly on a single LSE ignition. One reason Klaus implemented the LEDs for dual setups is so you'll know that one isn't working!

Bob
Click to expand...

Agreed.

I have dual LSE ignitions on my RV10. I get about 50RPM drop during "mag" check at ~1800 RPM, but in flight, you can't tell any difference when you shut down one of the ignitions. The LEDs are the only way you'd know.

I have a dedicated TCW backup battery for only one of my ignitions. The other only get's ships power.
 
The key switch doesn't actually switch battery power - the LSE ignitions have separate inputs for keyswitch and power. If using the "keyswitch option", the power to the ignitions is always hot and the keyswitch makes them act exactly like a mag - when pin 1 on the Output connector is grounded the ignition is off (just like a mag p lead) and the ignition doesn't draw any current from the battery.

You can wire them either way - a switch for each ignition to simply turn their power on/off or power is wired direct to battery and omit the keyswitch entirely. Alternately, use a keyswitch and per notes in the LSE manual, don't also use a switch for power if using the keyswitch option.
 
bcondrey said:
The key switch doesn't actually switch battery power - the LSE ignitions have separate inputs for keyswitch and power. If using the "keyswitch option", the power to the ignitions is always hot and the keyswitch makes them act exactly like a mag - when pin 1 on the Output connector is grounded the ignition is off (just like a mag p lead) and the ignition doesn't draw any current from the battery.
Click to expand...

Pin 1 for the Plasma II and III - if you've got the old-school original box like I do, it's Pin 9 that disables the spark when grounded.
 
So I'm thinking battery through individual breakers for each source to modules; then keyed switch to control active modules, would this be a recommended way to connect and operate? According to lightspeed manual he recommends limited switching, hooking directly to battery.

Dave Ford
Cadillac, Mi
 
Sounds like exactly what LSE recommends - power direct through a CB and no power switch(es) if using a key switch.

Bob
 
Kent Ashton said:
Consider that if one of your Plasmas shorts internally, it should pop the CB, then, not appreciating what just happened, you might switch that ignition to the other battery and pop the other CB.

I have dual plasmas but I keep the two sides separate with no crossover provision. The chances of two separate problems that take out both ignitions is so slim that I don't fret it.
Click to expand...

I'm with Kent....two entirely separate power supply leads with a quality ON/OFF toggle for each is a very reliable setup.

I wouldn't even use the circuit breakers, as doing so requires running an unprotected power lead from each battery to the circuit breaker panel. Consider an inline fuse holder or a fuseable link located at the positive battery terminal.
 
Last edited:
Klaus has said that there is an overvoltage module in his ignitions that will blow the specified breaker in an OV event. If fused, much harder to reset. I ran a fusible link from the battery to the breaker and then on to the switch. I'm betting that the fusible link will outlast the breaker.

I've also got a OV module built into the B&C voltage regulator. Who knows which would pop first, but one would hope that the alternator gets taken offline before the ignitions have time to react to the OV condition and blow their own breakers.

Ed Holyoke



[/QUOTE] I wouldn't even use the circuit breakers, as doing so requires running an unprotected power lead from each battery to the circuit breaker panel. Consider an inline fuse holder or a fuseable link located at the positive battery terminal.[/QUOTE]
 
You must log in or register to reply here.
Back
Top