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Dual LSI - Sanity Check

N130WN

N130WN

Well Known Member
My RV-7 project (night VFR, dual AFS 4500 with internal battery, VP-X) has dual Lightspeed plasma II ignitions. I'm weighing my options as far as the electrical system goes, and I find that I like this approach, from the Lightspeed web site:

-Is a back-up battery necessary?
If you are using a battery to start your engine, you have sufficient energy to run an ignition system for several hours after an alternator failure. Therefore, a back-up battery is not required when running a dual electronic ignition system. Once the system is running, less than 5V are required to maintain operation, giving a further safety cushion. At this low power level, most other electrical equipment will have long stopped functioning giving the pilot adequate warning.
Click to expand...

Sounds good to me -- no unnecessary complexity, cost or weight. But, I have never heard of anyone here using this approach. Many projects, even those with only one electrically dependent EI, have backup alternators and/or batteries. Whats wrong with the simple approach above?
 
Lightspeed Battery Backup

My $.02 - If you have a problem with the battery - your in trouble. While not likely I would not be without a backup. According to Lightspeed, a very small backup battery will power the system in the event of a total failure - even a 9 volt batter. My guess is that it would weigh no more than 1/2 pound.......so why not.
 
N130WN said:
My RV-7 project (night VFR, dual AFS 4500 with internal battery, VP-X) has dual Lightspeed plasma II ignitions. I'm weighing my options as far as the electrical system goes, and I find that I like this approach, from the Lightspeed web site:



Sounds good to me -- no unnecessary complexity, cost or weight. But, I have never heard of anyone here using this approach. Many projects, even those with only one electrically dependent EI, have backup alternators and/or batteries. Whats wrong with the simple approach above?
Click to expand...

Are you saying that you have never heard of anyone using a dual LSE setup w/o the use of a backup battery systems to run them? Most are in fact set up this way. I assume that by 'simple' approach you mean no backup battery to run the LSE.

If thats what your asking.... Yes its simple, and yes lots of installations are this way.

As a general rule, adding the complexity of redundancy should in fact address a problem or failure mode that is likely or common enough to justify the added risk of the complexity. You will find that Klaus does in fact recommend no battery back up since as a rule, batteries dont fail. And if wired per his instructions, ie. directly to the battery or very close to it, and having the rest of your systems wired with good practices, well then you have a very reliable rig.
 
Paul Lipps had a backup battery in his Lancair...he designed the Lightspeed systems so if that tells you something....and I understand Klaus something fail and found out the hard way his backup battery wasn't charging.
 
Seems like the most practical, simple answer is one EI and one mag. The advantage of 2 vrs 1 EI's is hardly noticeable. Unless the pilot has an instant alternator failure indication, the battery won't last as long as needed with other stuff sucking it down.

But then we fly with just one prop, crankshaft and cam; why not one source of power for the ignition system?

Actually, that's not right. There are 2 sources of power in every airplane - #1 is the alternator and #2 is the battery. The battery sits in reserve, the alternator does all the grunt work. Hook a load meter up to it and another to the battery and it is the alternator doing all the work at its higher voltage.

Claus's thinking is not all that far out.
 
I don't see anything wrong with a no "back-up" system design, as long as your electical system has been designed and assembled to the highest standards and has proven to be reliable. After 2 years of running with 1 mag and 1 EI, I then switched to dual EI. I added a BUG (back up gen) at that time but that was to provide for redundancy on long cross countries where I may not want to stop or I could continue to the airport of my choice.

As long as you have a good electrical system monitor to let you know when your alternator has quit, and you are prepared to load shed and land soon if that occurs, then I don't see any issue with it.
 
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One of my good friends had the battery contactor fail in flight in his RV7. The coil shorted internally. Total shutdown of the electrical system. As he was diagnosing the problem, he shut the alternator off and it wouldn't come back on due to the field wire requiring battery power to energize. The alternator I use does not require battery power to excite. I tested this in my -6.

A few years ago I had a battery in my Jeep fail shorted. Instantly shut everything down. I doubt this is very likely in an AGM-type battery but probably is still possible.

All it takes is a small 4-5aH battery isolated with a diode and a resistor or mosfet to limit charging current to have some insurance.
 
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For a dissenting voice, let me say that while batteries rarely fail outright, it happens. And it's not just the battery, it's the whole battery circuit (one reason Klaus recommends attaching the EI directly to the battery is to avoid a bus failure ... but that assumes that the direct circuit to the EI won't fail. I note that the dual PIII system I just received included the backup circuit diagram and a zener diode. A small backup battery that lives behind the panel somewhere is cheap insurance. But I agree in principle with Walt; it's not a big deal if you don't have it.
 
Using the backup charging diagram as shown by Lightspeed will eventually cause the backup battery to become damaged. The reason is that the regulator is a device designed to charge a battery and limits charging current based on sensed voltage and temperature. Since the main battery is of much lower impedance when it is in a discharged state the backup battery will overcharge. I talked to Paul about this very thing and he agreed and even said that he found this out to be true via the school of hard knocks and designed a circuit using a mosfet to limit current of the backup battery. As I recall his backup battery bulged severely and came close to exploding.

With a dual battery setup current limiting is not required individually because the batteries have identical impedance, or close to it, and because they're larger, are more tolerant of improper charging.
 
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rocketbob said:
One of my good friends had the battery contactor fail in flight in his RV7. The coil shorted internally. Total shutdown of the electrical system. As he was diagnosing the problem, he shut the alternator off and it wouldn't come back on due to the field wire requiring battery power to energize. The alternator I use does not require battery power to excite. I tested this in my -6..
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If he would have had a "standard" Z-11 with an E-bus design this would have been a non issue.. good design and implementation is very important. As noted in the EI diagrams everything is bypassed and the EI is directly hooked to the battey via swtch and CB, so again the above situation would be irelevent to the EI

rocketbob said:
A few years ago I had a battery in my Jeep fail shorted. Instantly shut everything down. I doubt this is very likely in an AGM-type battery but probably is still possible.
Click to expand...

Sure anything can happer but a highly unlikely event with modern AGM batteries, is it possible, sure anything is "possible", but not likely. No more likely to fail than your Napa oil filter :rolleyes:
 
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Consider also your terminals. A dozen back-up batteries are worthless if some itty bitty terminal lug or connector contact serving the ignition decides to fail (in a number of ways). Nearly an axiom in maintenance, if the electrical goodie isn't working, check the connections first.

Lightspeed ignitions are excellent, but power sourcing is why I now use P-mags despite their early problems.

John Siebold
 
rocketbob said:
One of my good friends had the battery contactor fail in flight in his RV7. The coil shorted internally. Total shutdown of the electrical system. As he was diagnosing the problem, he shut the alternator off and it wouldn't come back on due to the field wire requiring battery power to energize. The alternator I use does not require battery power to excite. I tested this in my -6.

A few years ago I had a battery in my Jeep fail shorted. Instantly shut everything down. I doubt this is very likely in an AGM-type battery but probably is still possible.

All it takes is a small 4-5aH battery isolated with a diode and a resistor or mosfet to limit charging current to have some insurance.
Click to expand...

This is a good point. Yes contactors do in fact fail which is why the EI power should be on the hot side of the contactor and as close to the battery as possible to reduce failure modes of contactors, terminals and the like.
 
Contactors do fail, but they usually will show some anomoly prior to totallly failing. For example, I had a master contactor that started not engaging fully when I put the switch on the first time, if I reset it it would engage the 2nd time. The next day that relay was in the garbage and a new one on the way, I didn't wait for it to fail totally.

Good maintenance is listening to your aircraft, it will usually tell you about problems, the hard part for many is to not ignore it, take that cowl off and fix it! Don't ignore the signs of trouble, it usually means impending failure is at hand.

BTW, when I was changing the master contactor I also changed the starter contactor... preventive maintenance.
I also replace my battery every 2-3 years... I don't like problems.
 
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Dual EI's

Dual LSI's Aero Connection Z13-8 architecture with alternator, back up SD-8 alternator and single battery.

Or dual P-Mags.
 
I can, with relative ease, poke quite a few holes in Z11 and describe several single points of failure. Some of them are alarmingly simple. This is why I don't have a Z11-style system in my Rocket.
 
Dual LSI

I'm setting up a dual LSI in my -7 now. Single PC-680 batt, SD-8 back up alt. Not using smaller back up batt as shown in LSI manuals because of the use of SD-8. Both LSI power inputs run to the batt buss that is wired directly to the 680. The SD-8 also comes to the batt buss through a separate terminal other than the batt buss main power feed.

Of course all of this could fail statistically....right after i get struck by lightning and the random asteroid.
 
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ground strap

Bob, actually no I didn't think of that. Thanks for bringing it up. I was assuming that the braided grd strap would be tolerant of the engine to airframe vibration difference. However, that link could make things interesting if it failed.
 
Another thought: if the SD8's regulator is set to a slightly higher voltage than the main regulator's voltage, it will be supplying ALL the current required to your system, and thus can be easily overloaded. So just make sure its adjusted to be well below the main regulator's output voltage.
 
You've piqued my curiosity

Rocket Bob wrote:

Think so eh? Ever think about what would happen if the ground strap on your engine failed?

This seems like it would be a very rare event, maybe up there with the lightning strike and asteroid hit. (With that said, I probably just insured mine will fail tomorrow).
What else do have on Z-11 that you don't like? Since I used that example on my -6, I'm interested in what you have to add.
It might also be helpful to take this to the Aerolectric List. A good back and forth discussion between knowledgeable folks is a good thing. Maybe you and Bob Nuckolls could have an enlightening conversation for the rest of us.
 
shamer said:
Rocket Bob wrote:

What else do have on Z-11 that you don't like? Since I used that example on my -6, I'm interested in what you have to add.
It might also be helpful to take this to the Aerolectric List. A good back and forth discussion between knowledgeable folks is a good thing. Maybe you and Bob Nuckolls could have an enlightening conversation for the rest of us.
Click to expand...

Pretty simple. An internally shorted battery is going to render the whole thing inoperable. Unlikely? Perhaps. Probably. Until that old Murphy guy makes an appearance. That said, a dual battery/dual contactor setup is going to be a little bit more bulletproof and simpler to implement than the Z11 system. Or a simple backup battery charging/isolation circuit for the ignitions. In other words, there are simpler ways to accomplish what Z11 does with a higher degree of redundancy and a significantly less cost of implementing and maintaining.
 
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Still trying to get my head around this dual EI backup battery/alternator issue.

I stand to be corrected but using the aux battery Lightspeed diagram and assuming that the pilot would quickly recognise and alternator failure, then the only event that the aux battery is protecting against is an internal dead short (low resistance between the terminals) in the main battery :confused:

IF this is correct then the next question would be, is anyone aware of an Odyssey type battery failing with a internal dead short??

It also occurred to me that if the battery failed with an internal dead short in a two alternator/one battery system then both alternators would be useless as neither could operate with a shorted battery :confused:

Finally, can an Odyssey type battery fail in the opposite mode such as an internal open circuit in the battery (very high resistance between the terminals). If this were to happen then I presume the alternator would continue to provide regulated power but the voltage may be more spiky without the dampening effect from the battery :confused:

Please educate me :)

Fin
9A
 
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A friend finishing his Lancair II with dual LSE's and no backup power could not get that setup past the DAR recently. He ended up using the backup battery for his MGL, through a switch, to power one of the LSE's and the DAR was happy.
 
David.....You are kidding me?

That is plain stupid....And I know you would never do that, but could you not talk him into doing it far better than that even? This is a Lancair not a kitfox or something similar.

Cheers

DB
 
Not kidding DB, but maybe I did not make the setup very clear. Both of his LSE's run off ships power normally and one of them has access to the MGL backup battery pack for backup power. Does that make more sense?
 
Aeroelectric Z11M

For what it's worth, the Z11M architecture has the alternator field powered off the main buss, not the e-buss. So you still have the problem of the alternator shutting down in the event of a master contactor failure (assuming your alternator requires battery power to keep the field energized).

You can move the field supply wire from the main buss to the e-buss, but now the e-buss diode/alternate feed has an additional 5 amps (or what ever the field draws) going through it.
 
Lars said:
For what it's worth, the Z11M architecture has the alternator field powered off the main buss, not the e-buss. So you still have the problem of the alternator shutting down in the event of a master contactor failure (assuming your alternator requires battery power to keep the field energized).
Click to expand...

Your assumption is incorrect, the alt will happily supply it's own field current and power the bus with the master relay open.
 
Not all alternators work without the field wire excited by the battery. The ND alternators I use do work fine. But I don't know how stable the output is in that condition.

Did you guys see the B&C alternator Rick Gray just sold in the classifieds that was factory repaired? $500 alternator that had the diodes replaced by them for $363. No flippin thank-you.
 
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Walt said:
Your assumption is incorrect, the alt will happily supply it's own field current and power the bus with the master relay open.
Click to expand...

No assumptions, other than the rhetorical your alternator. While my experience with alternators in airplanes is limited, I've had plenty of them in ground-bound vehicles. Some do, some don't. Irritatingly so.

My point was that the Z11 architecture wouldn't have helped rocketbob's friend when his master contactor failed. The Z11 diagram has been on my mind as I am wrapping up my own electrical system, and happen to be using it, more or less. The alternator field source was something I pondered last night. I have a Plane Power alternator, supplied in Van's FWF kit. I'm guessing it can sustain itself in the event of a master contactor failure, but I plan to test that before I fly.
 
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rocketbob said:
Not all alternators work without the field wire excited by the battery. The ND alternators I use do work fine. But I don't know how stable the output is in that condition.

Did you guys see the B&C alternator Rick Gray just sold in the classifieds that was factory repaired? $500 alternator that had the diodes replaced by them for $363. No flippin thank-you.
Click to expand...

I did see that. Had the same thought. On a tangent, I've had great experience, albeit in ground-bound vehicles, with junkyard alternators. Seriously. A rebuilder once told me that finding non-rebuilt alternators from late model vehicles in recycling yards was a good bet because if they were working when the vehicle was wrecked, odds were that they would continue to do so. I found the late model (Ford) alternator in my old truck at a local yard. Brought a few tools and opened up the case to inspect. It was in great shape. $30 later, it went on. That one has 50k of my miles on it now and continues to operate fine, under fairly grueling conditions (due to another hobby of mine).
 
Dual LSI with backup battery

I have a dual LSI setup installed very close to how Klaus recommends, but I elected to run separate supply wires to each ignition to help protect against a connection failure. I keep hearing that I'm going to fry my backup battery over time using Klaus' backup battery diagram. The only thing i have between the main battery and the backup battery is a 10 amp breaker and the Recommended diode..... No resistors,,, nothing. Can someone provide a simple solution that doesn't require me to rewire the entire system? I don't need an exploding backup battery in my baggage compartment.

Thanks Gentlemen,

Chad
 
Backup Battery of Electronic Ignition

rocketbob said:
One of my good friends had the battery contactor fail in flight in his RV7. The coil shorted internally. Total shutdown of the electrical system. As he was diagnosing the problem, he shut the alternator off and it wouldn't come back on due to the field wire requiring battery power to energize. The alternator I use does not require battery power to excite. I tested this in my -6.

A few years ago I had a battery in my Jeep fail shorted. Instantly shut everything down. I doubt this is very likely in an AGM-type battery but probably is still possible.

All it takes is a small 4-5aH battery isolated with a diode and a resistor or mosfet to limit charging current to have some insurance.
Click to expand...

Rocketbob,

Can you suggest the proper resistor to use in Klaus's backup battery charging diagram? I currently have this installed in my Glasair and I'd like to make sure I don't burn up my standby battery. I have the diode installed, but no resistor.

Thanks,

Chad
Plano, TX
 
I recently spoke to Klaus about upgrading to dual Lightspeeds and he did not know of any instance where an Odyssey AGM battery (amorphous glass mat) had failed so quickly and catastrophically in flight that the EI would have stopped working.

So it is likely that for a VFR aircraft with an Odyssey battery and dual Lightspeeds, a back-up battery would be providing redundancy for a situation which is very unlikely to happen.

However, Klaus suggested that I install a stand alone lithium back-up battery switchable to one of the Lightspeeds if needed. This battery would be charged every 6/12 months on the ground from a mains charger. His reasoning is that lithium batteries hold their charge for much longer than other batteries and because they are so light weight, I may as well install one. So I am now thinking I will install a stand alone backup battery such as the 7 amp or maybe the 12 amp Shorai battery.

Fin
9A
 
Finley Atherton said:
I recently spoke to Klaus about upgrading to dual Lightspeeds and he did not know of any instance where an Odyssey AGM battery (amorphous glass mat) had failed so quickly and catastrophically in flight that the EI would have stopped working.

So it is likely that for a VFR aircraft with an Odyssey battery and dual Lightspeeds, a back-up battery would be providing redundancy for a situation which is very unlikely to happen.

However, Klaus suggested that I install a stand alone lithium back-up battery switchable to one of the Lightspeeds if needed. This battery would be charged every 6/12 months on the ground from a mains charger. His reasoning is that lithium batteries hold their charge for much longer than other batteries and because they are so light weight, I may as well install one. So I am now thinking I will install a stand alone backup battery such as the 7 amp or maybe the 12 amp Shorai battery.

Fin
9A
Click to expand...

Not to start an EI war but the complexity of the installation is the one thing I don't like about the Light Speed ignitions. All those connectors, back up batteries, remembering to charge your backup battery every six to 12 months, etc. are just more failure points. Not to mention sitting there with an electrical failure wondering when the last time I charged my lithium battery and if it was still holding a charge is not a situation I would like to find myself in.

If you install a backup battery, you should add a line in your condition inspection checklist to replace every X number of months / years.
 
Speeddog7 said:
Rocketbob,

It's a CSB 12V 4.5 Ah battery.

http://www.altex.com/CSB-12V-45Ah-SLA-Battery-w-F1-Terminals-GP1245-P139593.aspx

Thanks,

Chad
Click to expand...

Doing some ohm's law calculations... a 7.5 ohm resistor will limit current to 1.4 amps and will require that the resistor be rated for 30 watts.

I'm not real crazy about using a resistor due to the heat it has to dissipate if the aux battery were fully discharged. But that will be a fringe case anyway, and the only one where the charging circuit needs to limit current, so 99.9999~% of the time it will run cool.
 
N941WR said:
Not to start an EI war but the complexity of the installation is the one thing I don't like about the Light Speed ignitions. All those connectors, back up batteries, remembering to charge your backup battery every six to 12 months, etc. are just more failure points. Not to mention sitting there with an electrical failure wondering when the last time I charged my lithium battery and if it was still holding a charge is not a situation I would like to find myself in.

If you install a backup battery, you should add a line in your condition inspection checklist to replace every X number of months / years.
Click to expand...

Back in the early 90's I worked at a defense electronics company. We used to do a lot of heat/vibration/humidity testing and I know what applying heat and vibration does to electronics. They WILL fail. Based on this knowledge I would never want anything electronic to the degree of complexity required for throwing sparks bolted onto my engine. So the simplicity you are advocating introduces its own set of failure points.
 
rocketbob said:
Back in the early 90's I worked at a defense electronics company. We used to do a lot of heat/vibration/humidity testing and I know what applying heat and vibration does to electronics. They WILL fail. Based on this knowledge I would never want anything electronic to the degree of complexity required for throwing sparks bolted onto my engine. So the simplicity you are advocating introduces its own set of failure points.
Click to expand...

Fair enough...

So that trigger board that is bolted to the front of the engine or in the mag hole for the LS will also fail?
 
N941WR said:
Fair enough...

So that trigger board that is bolted to the front of the engine or in the mag hole for the LS will also fail?
Click to expand...

I don't have a Lightspeed, so I have no axe to grind but the LSE board is also not being splashed with 200 degree oil, and only has a few components, certainly nothing as complex as a microcontroller is.
 
rocketbob said:
I don't have a Lightspeed, so I have no axe to grind but the LSE board is also not being splashed with 200 degree oil, and only has a few components, certainly nothing as complex as a microcontroller is.
Click to expand...

I'm with you on the ax to grind thing but each EI has some issues. I was just trying to point out that the vibration thing is a common problem.

As for the 200 degree oil issue on the P-mags, they now have cooling fins to dissipate the heat and don't appear to suffer heat related failures. In fact, since I have the EICommander installed in my plane, I can monitor the internal temperatures of the P-mag and they are nowhere close to 200*. Next time I fly, I will write down the numbers I?m seeing and report back.
 
N941WR said:
Not to start an EI war but the complexity of the installation is the one thing I don't like about the Light Speed ignitions. All those connectors, back up batteries, remembering to charge your backup battery every six to 12 months, etc. are just more failure points. Not to mention sitting there with an electrical failure wondering when the last time I charged my lithium battery and if it was still holding a charge is not a situation I would like to find myself in.

If you install a backup battery, you should add a line in your condition inspection checklist to replace every X number of months / years.
Click to expand...

Bill,

Are you sure you are not trying to start an EI war?:rolleyes:

If I was building again I would certainly consider going dual P Mags, however when I ordered my engine, P/E Mags where having reliability issues so I went with the proven Lightspeed and a conventional mag. Now that I am going to dual EI it is much cheaper for me to add an extra Lightspeed than go with dual P Mags and the required drive gears.

I can't say which is the "better" system. Certainly P Mags are easier to install and are self powered but the Lightspeeds have a hotter spark and with the Plasma III the spark duration is longer. (20 degrees). Whether this makes any practical difference, I don't know.

I stand to be corrected but as far as I am aware there are no P Mags available for 6 cylinder engines which means Lightspeeds or something similar for those with 6 cylinders wanting EI.

I anticipate charging my stand alone Lithium Shorai battery once a year at the periodic annual inspection - hardly an onerous task and yes it will be on my periodic inspection checklist.

I concede your point about the added complexity but a stand alone back-up battery is pretty simple to wire up. Having said that I will now contradict myself as I will be adding complexity by installing an extra voltmeter (mini) connected via a switch to the aux battery. SOP will be to check the aux battery voltage before the first flight of the day during the pre flight checks and then switch off the mini voltmeter so there is no draw on the aux battery.

Fin
9A
 
rocketbob said:
Doing some ohm's law calculations... a 7.5 ohm resistor will limit current to 1.4 amps and will require that the resistor be rated for 30 watts.

I'm not real crazy about using a resistor due to the heat it has to dissipate if the aux battery were fully discharged. But that will be a fringe case anyway, and the only one where the charging circuit needs to limit current, so 99.9999~% of the time it will run cool.
Click to expand...

Thanks Bob! I'll get er' done!

Chad
 
rocketbob said:
Doing some ohm's law calculations... a 7.5 ohm resistor will limit current to 1.4 amps and will require that the resistor be rated for 30 watts.

I'm not real crazy about using a resistor due to the heat it has to dissipate if the aux battery were fully discharged. But that will be a fringe case anyway, and the only one where the charging circuit needs to limit current, so 99.9999~% of the time it will run cool.
Click to expand...

Bob, Will this work for my application? Also, I assume it will be fine if its mounted near the aux battery?

http://www.talonix.com/shop/item.aspx?itemid=11689
 
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rocketbob said:
Using the backup charging diagram as shown by Lightspeed will eventually cause the backup battery to become damaged. The reason is that the regulator is a device designed to charge a battery and limits charging current based on sensed voltage and temperature. Since the main battery is of much lower impedance when it is in a discharged state the backup battery will overcharge.
Click to expand...

Bob,

Not doubting your expertise but I can't get my head around the quote above.

I did a test with an old somewhat discharged 12V battery (I'll call it the main battery) and a fully charged 12V battery (I'll call it the aux battery) and connected them with a diode as per Lightspeeds Aux battery charging diagram. With no external charging applied the measured voltage of each battery was the same as when the batteries were not connected by the diode.

So, I would have thought that if the main battery was discharged and the aux was fully charged (high voltage) then current from the alternator/regulator would flow to the main battery but little current would flow on to the aux battery as there is little voltage potential between the regulator output and the aux battery.:confused:

Fin
9A
 
Two things. The aux battery has to be much smaller than the main battery and it also has to be at a very low state of discharge for the possibility of charging damage to occur.
 
rocketbob said:
Two things. The aux battery has to be much smaller than the main battery and it also has to be at a very low state of discharge for the possibility of charging damage to occur.
Click to expand...

OK. I misunderstood your statement, "Since the main battery is of much lower impedance when it is in a discharged state the backup battery will overcharge" to mean the main battery was discharged rather than the aux battery.

So, would this be correct? Provided the smaller aux battery is not allowed to go flat then the Lightspeed charging system should not overcharge the aux battery as it will not accept a large charge current? Also the Lightspeed diagram includes a 10 amp breaker that would limit the aux battery charge current. Presumably a lower amp breaker could be used to lower the maximum aux charge current further. Of course then there may be an issue of the breaker tripping with a flat aux battery but at least the battery would not overcharge.

I guess if the aux battery ever got flat then good practice would be to charge the aux battery on the ground with a mains charger before further flight.

Fin
9A
 
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