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Which AUX/Backup Battery?

Brantel

Brantel

Well Known Member
I need to purchase my backup battery and need to know what the experience has been with the different makes and models out there.

Planning to use a battery similar to this:

UB1280-F2.jpg


I have been looking at the UB1280 but have seen some negative reviews on the UB???? models.

Whats the VAF knowledgebase say?
 
Brian,

I have been using a Shoria LFX18L1-BS12 (18AH) as my primary battery for the last 6 months. It replaced a PC 680. It only weighs 2.1 lbs.

In my panel redux, I am switching the current battery into the backup role and adding a Shoria LFX27L3-BS12 (27AH) as my primary. Both batteries are actually over sized for their respective roles.

The combination of the two batteries is 6.8lbs. That is still well under the 15.4 lbs of the PC 680.
 
I've always used a 4.5 aH viersion of the one you pictured Brian - but I am ready to swtich to the LiFe Po the next time I need a battery - lighter, way better capacity. I have a neighbor using one in his F-1 as a starting batteyr now.
 
Brian, I've used several of those UB batteries. Not only on MGL's, but also to self-power my guitar pedalboard. They are usually good (heavy though). I have had 2 that went flat soon though. Probably somebody's old stock and they ripped me off. I have a newer one on my pedalboard that will hold charge for a couple months with no input and no loss.
 
My Aux/backup battery is the Panasonic LC-R127R2PG, 7.2 AH with Faston 250 (1/4") terminals. This is interchangeble with the UB1280 you are looking at. Anecdotally, I've heard the Panasonic is more reliable than the universal UB1280, but I've seen no data to back that up. It does cost more. These batteries also come with the smaller Faston 187 terminals, so pay attention to that, if you decide to go this route.
 
Not a problem.....

Used the UB1280 for about three years as a backup battery. It charges anytime the master is on. No problems and easy to get. $19 at Academy sports, or less at most autoparts stores. This is the same battery used in most home alarm systems.

Bill
 
Overcharge a backup battery?

How do you prevent overcharging a backup battery? Do you need a separate voltage regulator? It does not recharge the same as a starter battery does it?

:confused:

CC
 
comfortcat said:
How do you prevent overcharging a backup battery? Do you need a separate voltage regulator? It does not recharge the same as a starter battery does it?

:confused:

CC
Click to expand...

A 12 Volt backup battery charges just fine along with the main battery without a separate regulator. There are a number ways of setting up the electrical system such that it is an isolated battery to avoid voltage drop to the electronics durign start. But it will charge just fine on the main bus.
 
Backup battery needed?

I know this is not the question Brian asked but I ask why do you need one or maybe how many of you have needed one? I only ask because I thought about it and dismissed it. I did however put an alternate switch to a relay with a direct feed from my battery just in case the master switch or solenoid failed. Flip the switch, activates the relay, power to find an airport. What would a back up do for you that my set up will not?

Feed back appreciated.
 
Bob, one reason for a backup battery is for panels with electronic engine monitoring. In this case, you need to turn the EMS on before engine start. If you have just one battery, the starter can momentarily drag down the voltage too much and cause problems for the EMS.

There are other reasons too.
 
comfortcat said:
How do you prevent overcharging a backup battery? Do you need a separate voltage regulator? It does not recharge the same as a starter battery does it?

:confused:

CC
Click to expand...

Most of the smaller batteries have a "Maximum charging rate" limitation to prevent overheating, so some method of current limiting is required for a small BU battery. A search of the forums or google will produce plenty of results on various methods.
 
Here is the proposed wiring diagram for my backup/aux power system:

click for big version:




The backup battery will get charged anytime the master is on. The typical startup work flow will be to close the Aux Battery feed switch first thing to get the EFIS and EMS up and running before start. This switch will remain on till shutdown.

Charge current is limited by the 10ohm 20W resistor. The VP-X Pro takes care of monitoring the backup batteries voltage level.

Distributed overcurrent protection is provided by both inline fuses and the 6 fuse block.

The Schottky diodes take care of ensuring current flow in the correct directions and to power up the Gemini which does not have a built in backup power pin. The G3X system has backup power pins.

I ended up ordering this battery from BatteryMart.com:

alt1-sla-12v7-f2.jpg


They had hundreds of good reviews on this battery and I have ordered from them before with good service. This appears to be a high volume battery for them so hopefully I will get a fresh one....
 
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Brain,

I've been looking into this backup battery implementation a little lately to try and nail down my panel layout and switch requirements. I've been looking at a circuit similar to yours but being a EE I don't like a simple resistor for the current limiting function. That is a separate discussion, and I'm working on a solution for that too.

I too would like to be able to turn on my aux bat for the startup sequence. Ideally I'd like to be able to leave it on and not have to worry about switching over later. But... I'm not sure your circuit is going to work exactly as you intended or at least how I'd like it to work. I have seen others here which have similar configurations so I'm not trying to single you out but I haven't checked those as thoroughly. The problem that I see is that if you leave the Aux battery switch on then your primary and backup battery will discharge at the same rate since they are effectively tied together. Your backup battery may be partially discharged before you notice that the primary is discharged. Then you wouldn't have the full use of your backup battery. On the other hand if you opened the switch during normal operation you would retain the full capacity of the aux battery. The G3X simply diode ORs the power inputs so it will take power from the highest voltage source. Am I missing something here?
 
Nope, your not missing anything.

It works exactly how I wanted it to. It is simple and very reliable which was my goal.

I could have over complicated it with an active charging and switching system since I am an EE as well but I see no need to do that with these sport planes.

If the alternator fails, I am alerted by the G3X and in that failure mode, what I want is capacity so it does not matter to me that the batteries may equally discharge with a similar voltage.

If the main bus fails, I will be notified by the G3X and the backup battery will do its job.

For a seamless failover to the backup power on the devices with backup power inputs, the backup bus must be on all the time...

In all failure modes, the G3X lets me know what is going on and decisions can be made based on the situation.

Super simple and it works great!

That being said, the EE in me has purchased an off the shelf DC-DC converter with current limiting. I plan to play around with this to improve the backup battery charging circuit efficiency.
 
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Ray - for whatever reason (escapes me now) my switch on the backup is on it's output to my essential bus with the charging circuit "live" with the main.

My original opps plan was to throw both main and backup switches before start and leave them. However, I kept thinking the same scenario you describe and so I've had my standard opps to be both on for start and then backup-off after take-off and back on before landing.

If I lost my alternator and main feeds together, I would momentarily lose my essential bus until I turned that switch on. I'm convinced neither case is perfect.

I do have idiot lights on both and the idiot light for the backup is set to a higher voltage than the main. Thus, if the system were drawing down both batteries as you describe, the backup will start blinking at me almost immediately.

Essential bus circuit: http://thesalmonfarm.org/blog/p/3509
Idiot lights: http://thesalmonfarm.org/blog/p/3673
 
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Ok well we all make our own decisions on what is best for each of us. I wanted to make sure I fully understood the situation.

In the arrangement where the aux and primary battery are not connected during normal operation I would think that a low voltage warning of some type could be set with a value that is still sufficient to operate the electronics, but would be low for normal conditions. At that point loads could be shed and the aux battery turned on. I think that is how I'll plan to do it.

I do appreciate everyone's input and their circuits to build my knowledge of these systems. Without this supplemental information it would be very difficult for me and others to make their own decisions.

Now just a comment on the Diode / Resistor current limiting for the aux battery charging circuit. I think this is a simple solution and it probably works fairly well as long at the aux battery is not discharged very far. The resistor value selection is a compromise between charging time and maximum charging current. So if the battery is only slightly discharged it could work great and that probably covers most of the normal usage. If for some reason it became more fully discharged then I don't like this arrangement. I decided I would build a circuit to charge the battery the correct way at a constant current independent of voltage. Yes it will be more complicated but it should cover all of the discharge cases. I'll keep everyone updated on my progress.

Oh yeah I was just trying to figure out what switches I wanted on my panel. Yikes another side project.
 
rapid_ascent said:
In the arrangement where the aux and primary battery are not connected during normal operation I would think that a low voltage warning of some type could be set with a value that is still sufficient to operate the electronics, but would be low for normal conditions. At that point loads could be shed and the aux battery turned on. I think that is how I'll plan to do it.
Click to expand...

Ray, I agree. My idiot lights give me that low voltage warning. The extreme case I was referring to is a sudden 100% failure of both my main battery and alternator.

I'll be interested in what you come up with for a charging circuit.
 
Just something to think about...

If you have a panel full of modern glass avionics and you lose your main bus for a millisecond or two without the backup bus powered and your gonna get a total reboot. (Excluding devices with their own built in battery)

This could leave you in the dark so to speak until your system boots and reorientates itself.

There are a quite a few reasons you could lose your main bus even with a fully charged main battery.
 
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rapid_ascent said:
Now just a comment on the Diode / Resistor current limiting for the aux battery charging circuit. I think this is a simple solution and it probably works fairly well as long at the aux battery is not discharged very far. The resistor value selection is a compromise between charging time and maximum charging current. So if the battery is only slightly discharged it could work great and that probably covers most of the normal usage. If for some reason it became more fully discharged then I don't like this arrangement.
Click to expand...

I know what the theory is telling you but in reality this is not really an issue. Sure the further the battery is discharged the longer it will take to get it back to full charge but in reality under normal use, these backup batteries don't see much of a drain on their capacity. At least that has been my experience over the past year of flying mine.
 
rapid_ascent said:
I decided I would build a circuit to charge the battery the correct way at a constant current independent of voltage. Yes it will be more complicated but it should cover all of the discharge cases. I'll keep everyone updated on my progress.
Click to expand...

I have one of these that I bought and I am going to test it soon to see if it will do the job. I potted most of it with E6000 to make it more durable.

It looks and feels like it will be the perfect solution for a cheap and effective backup battery charger.

While it is imported from China and the specs are a little hard to read, it looks like it should work fine.

http://tinyurl.com/lb72wqp

ezodfr.png


Another advantage is that it should allow the battery to be charged to its full rated capacity. Something that is not possible with the simple passive system and the isolation diode.

The only fear I have is that the oscillator may induce unwanted noise in the audio/radio system.
 
Brian,
Have you seen this device? http://www.bluesea.com/products/7610/SI-ACR_Automatic_Charging_Relay_-_12_24V_DC_120A

I have been using this with a pc925 and a pc680 as the aux batt. It effectively will limit the charging current by not allowing charging of a battery that falls below 9.5 volts. The combining is automatic and does not induce the voltage drop of a diode and a current limiting resistor.

I am also feeding a backup alternator through the aux battery with the field normally powered down unless I need it. The nice thing about the 7610 is it does not care which battery has the charging source applied. Also, I monitor the aux batt volts directly through the G3X. If the VPX fails I still have a voltage and current monitor.
 
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I know what the theory is telling you but in reality this is not really an issue. Sure the further the battery is discharged the longer it will take to get it back to full charge but in reality under normal use, these backup batteries don't see much of a drain on their capacity. At least that has been my experience over the past year of flying mine.
Click to expand...

I agree that normally your aux battery is going to be almost fully charged. That is the case where the diode / resistor works as desired. Low charging currents are sufficient to maintain the battery near full charge.

The diode if the proper one is selected is not really the issue that I have. At low currents when the battery is charged the voltage drop as low as a couple of tenths of a volt. For a more expensive diode ($5-$6) it could be only even as low as tenth of a volt.

The problem is the selection of the "correct" resistor value. The battery discharge voltage will be fairly flat until a fair amount of capacity has been lost. That would mean you could just allow for a small voltage drop across the resistor. Let's say 1 volt. With a 10 ohm resistor that is only a charging current of 0.1 amps when the battery would normally be charged at about 2 amps. This will take 20 times longer to charge the battery. Oh, and then as the battery charges its voltage goes up and the charging current continues to go down. This is of course a problem with any of the resistor/diode solutions. If you say its only 0.2 volt low which is more likely if your start time was very limited. Then only putting 0.02 amps back into the battery at the start of the charge cycle.

If I was going to do the diode/resistor approach and assume that the battery won't be discharged very much. I think I would use a much lower resistor say 2 ohms maybe even a little smaller. Then with a 0.2 volt drop I would be putting 0.1 amps into the battery. For a 1 volt drop I'd be putting 0.5 amps. Well let's say the voltage drop is 3 volts, still fine, the charging current is only 1.5 amps. Battery is probably dead at this point. Just add a fuse to take care of the extreme case of battery discharge its probably of no use at this point anyway.

I was just thinking this through as I wrote this and maybe its not so bad with a resistor, but I think it needs to be a small value. I'd still prefer a constant current charger.
 
Well I wanted to give everyone an update on what I've been doing.

First of all let me respond to Brian on his DC-DC converter find. This is close to what you want but not quite the full solution. With current limiting and a voltage set to approximately 14.7 V you can fully charge the battery. However the next phase of recommended charge is to maintain a float voltage at a voltage of approximately 13.6V. So its close, but not quite what I want.

So its with this in mind I went off looking for a solution for my circuit that I planned to build. It turns out its not that easy to find a part that will do the full recommended charge sequence. I did eventually come up with a design that should do it. I just sent the PCB out for fabrication so soon I should know whether it will work as planned or not.

I fell in this rabbit hole so hopefully I can get back to my panel design. Oh then Garmin releases a new G3X. Well at least its not cut yet.
 
Well not too much yet. I have the PCB boards that I layed out and I'm just ordering parts to build up a couple to test.

The board that I designed has the battery charger and a pair of "ideal diodes" to combine the power from the Main Bus and the Aux Battery to the Endurance bus. The charger and the diode functions are separate but they are both required for what I decided to call an Aux Battery Controller. Nothing really wrong with the simple diode solution, but this solution will burn a lot less power and hopefully not require any heatsinking. I decided I would add the diode function on since I was creating a new PCB anyway.
 
I have elected to give the EarthX Lithium ETX12A battery a try for my new panel as a backup battery. I originally purchased a Power Sonic PS-1290 9 AH battery but after receiving it I decided I didn't want to add that much weight (approx. 7 lbs vs 1 lb for the Lithium!). I went with the standard diode/resistor combo (1.5 ohm) for a charge circuit. We'll see how it works.

BTW: Customer service from EarthX is outstandanding :D
 
Hmmm... even their smallest battery, the ETX6A, ought to power avionics for a little while. I'm mostly wanting a solution for keeping the G3X Touch powered up during engine start. This $129 battery could be just the ticket. :)
 
I have tested my Shorai LFX18 batteries with a West Mountain CBA IV battery analyzer with a 7A essential load. That will give me 50 minutes on one battery in the event of an alternator failure before it reaches 11V.

I considered 11V a safe voltage to test without the possibility of deep discharging the battery and potentially damaging it.
 
Update to my setup.

I switched to a 1.5ohm 25watt wire would with aluminum case resistor.

I also put the charge circuit on one of the VP-X pins so I could see what was going on in flight.

Happier with this value since I get faster recovery.

My Shottky drops almost a volt at these voltages and currents. It was the best one I could find to fit the need.

I built a charger with two back to back Mosfets, current limiting and stuff but it could not handle the voltage drop of a discharged battery so I tossed that idea and went back with the simple solution.
 
I found Walt's diode on both Digikey and Mouser. About $18.

Regarding diodes... Probably too optimistic, but since there are 2 diodes in this package, what would happen if you wired them in parallel? Less voltage drop or would it just not work?
 
I meant the resistor, not the diode... :)

"I switched to a 1.5ohm 25watt wire would with aluminum case resistor."

Thanks,

-Dj
 
grayforge said:
I found Walt's diode on both Digikey and Mouser. About $18.

Regarding diodes... Probably too optimistic, but since there are 2 diodes in this package, what would happen if you wired them in parallel? Less voltage drop or would it just not work?
Click to expand...

Less voltage drop? No, diodes do not work that way. More current capacity? Yes, but only if the diodes are identical and in good thermal contact. Otherwise, the warmer one will grab more of the current, making it even warmer, so it will grab more current, get warmer,....
 
grayforge said:
I found Walt's diode on both Digikey and Mouser. About $18.

Regarding diodes... Probably too optimistic, but since there are 2 diodes in this package, what would happen if you wired them in parallel? Less voltage drop or would it just not work?
Click to expand...

It may help but I doubt you would see much/any difference with such low currents. And even though theory would lead you to believe they would split the current equally in reality diode junctions vary so one diode would likely carry all or most of the current.
 
Thanks, guys. Bear with me here for a bit. If the resistor is rated to handle up to 25 Watts, and we have a 12v system, does that mean it will only handle up to 2 amps flowing through it?

P=IE, so 25 watts = X Amps x 12v, so X = 2.08 Amps?

Would that imply that the total load on the backup/power buss (as shown by Brantel on page 2 of this thread) should not exceed 2 amps?

Thanks,

-Dj
 
deej said:
Thanks, guys. Bear with me here for a bit. If the resistor is rated to handle up to 25 Watts, and we have a 12v system, does that mean it will only handle up to 2 amps flowing through it?

P=IE, so 25 watts = X Amps x 12v, so X = 2.08 Amps?

Would that imply that the total load on the backup/power buss (as shown by Brantel on page 2 of this thread) should not exceed 2 amps?

Thanks,

-Dj
Click to expand...

In real life the voltage drop across this resistor will be much less than 12V unless something is really wrong and in that case you need to provide overcurrent protection for the circuit.

In reality you should not see more than 4 volts across this resistor and only then if the backup battery is dead and then it will only be that much for a few seconds till the battery voltage starts to rise.
 
Brantel said:
In real life the voltage drop across this resistor will be much less than 12V
Click to expand...

Ah! I see my mistake. It is the voltage drop across the resistor that I need to look at, not the voltage of the system as a whole.

So, what is the highest amperage that this resistor will safely handle to feed the items on the backup buss? At 4v it looks like 6.25 amps.

-Dj
 
The resistor does not feed the backup bus.

The resistor is between the main bus and the aux battery and is there to limit the charge current.
 
Brantel said:
The resistor does not feed the backup bus.
The resistor is between the main bus and the aux battery and is there to limit the charge current.
Click to expand...

Ok, please help me to understand this.
I am looking at this diagram that you posted earlier:
http://oi47.tinypic.com/28qt1zq.jpg

I am assuming that "Aux Volts VP-X J2-12" is power monitoring on the VP-X, and not a power source. In this circuit, I believe there are two power sources, the aux battery, and the feed coming from the main buss through the resistor and diode.

Both of these are feeding the backup bus, correct? Whichever one presents the higher voltage will be the preferred source? At some point the battery and the power coming through the diode will be roughly equal?

For the sake of discussion, if for whatever reason the aux battery became disconnected, what is the highest current that can safely flow through the diode and resistor to feed the aux bus?

I am trying to get a clear understanding of how the resistor comes into play as I design my electrical system. I have a preliminary design that has a small battery to prevent brown-out at engine start, and provides power to my essential bus from either a feed from the main buss through a diode, and/or from the backup battery, but I hadn't taken into consideration limiting the charge to the aux battery, and want to understand so I can add this if needed.

Please excuse the crudeness of my hand-drawn circuit:

http://deej.net/glastar/pics/electrical/Electrical-Rev-3.jpg

-Dj
 
deej said:
Ok, please help me to understand this.
I am looking at this diagram that you posted earlier:
http://oi47.tinypic.com/28qt1zq.jpg

I am assuming that "Aux Volts VP-X J2-12" is power monitoring on the VP-X, and not a power source.
Yes correct..

In this circuit, I believe there are two power sources, the aux battery, and the feed coming from the main buss through the resistor and diode.

The node is common with the battery and the charge circuit.

Both of these are feeding the backup bus, correct?
Whichever one presents the higher voltage will be the preferred source?

What you have to remember is that the loads will always prefer the main bus (when it is on and operating properly) over the backup bus since the backup bus will always be one diode drop below the main bus.

At some point the battery and the power coming through the diode will be roughly equal?

Only if the main bus voltage fails to stay in the normal range, if it drops below the aux bus voltage plus the diode drop, the load will transfer to the aux battery seamlessly.

For the sake of discussion, if for whatever reason the aux battery became disconnected, what is the highest current that can safely flow through the diode and resistor to feed the aux bus?

If the backup battery is disconnected and the main bus is on, the loads will still use the main bus since it is still going to be the higher voltage source. If the backup battery is disconnected and the main bus fails, no power will be available. As for the highest current, that goes back to ohms law. If for some reason the power does start to get sourced thru the main bus charge feed, the limiter is the power dissipation capability of 25 watts. I = sqrt(P/R) ... a little over 4 amps max

-Dj
Click to expand...

............
 
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deej said:
I am trying to get a clear understanding of how the resistor comes into play as I design my electrical system. I have a preliminary design that has a small battery to prevent brown-out at engine start, and provides power to my essential bus from either a feed from the main buss through a diode, and/or from the backup battery, but I hadn't taken into consideration limiting the charge to the aux battery, and want to understand so I can add this if needed.

Please excuse the crudeness of my hand-drawn circuit:

http://deej.net/glastar/pics/electrical/Electrical-Rev-3.jpg

-Dj
Click to expand...

What some people do that have a similar setup to what you are wanting is to add either a cross tie contactor that they can close or a properly rated switch to be able to tie the essential bus to the main bus. This can be done in parallel to the charging circuit.

In your drawing it looks like you have some loads that are exclusive to the essential bus. Some of what I said above in post #45 does not apply to your design.
 
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Back up power

I just wanted to post the actual amp hours per battery, which is also found in our manual on the website, for a quick, easy reference whether you are using it for the main battery or the back up battery. Personally, I would think more is better when you are up in the clouds.....

ETX6A= 2.5ah
ETX12A/B= 4ah
ETX18B,C,F= 6ah
ETX24C/D = 8ah
ETX36C,D,E = 12ah
ETX48E= 24ah

Kathy
 
How do you mount this diode?

Greetings!

Thanx Walt for the time and energy to test this stuff. I'm going with the Schottky Diode and Resistor.

Quick question: Do you need to mount this diode on a heat sink or just an aluminum panel? Also, this is electrically isolated right? Meaning I can mount to a rib.

CC



Walt said:
This is the schottky I am using, the chart shows less than .5v at 2A and Vf goes lower as it warms up.

http://ixapps.ixys.com/DataSheet/DSS2x61-0045A.pdf
Click to expand...
 
comfortcat said:
Greetings!

Thanx Walt for the time and energy to test this stuff. I'm going with the Schottky Diode and Resistor.

Quick question: Do you need to mount this diode on a heat sink or just an aluminum panel? Also, this is electrically isolated right? Meaning I can mount to a rib.

CC
Click to expand...

Yes the diode base is electrically isolated so you can attach it anywhere it's convenient. Mine is right next to the fuse block on the sub panel.
 
I wanted to get back to everyone on my progress. Sorry I got distracted with LED NAV lights for a while, but that's another story and another project.

I just got the board that I designed up and running. I call it an AUX Battery Controller. It includes both a battery charger and two "ideal" diodes for combining the outputs of the PRI battery and the AUX battery for the AUX bus if you want to do that. These diodes are actually MOSFETs with a control circuit. They only have a very small voltage drop of around 50mV so there is no heat even for high currents. I still need to test these under heavy load, but so far so good.

I'm just starting to do the testing of the charger and I should have a my battery by the beginning of the week.

I'll give everyone an update as soon as I know how well it works. More details to follow.
 
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