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  #1  
Old 05-25-2018, 09:17 PM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
 
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Default Earth X Battery Questions

Pertaining to recent questions in another thread on backup system auto switching points, I wanted to gather some more info on Earth X batteries so we can make some informed decisions regarding setup of switching points when people fit our devices in conjunction with these batteries.

I've never used one of these so have zero first hand experience with them.

It seems like the ETX900 series is the most popular being fitted to RVs. What other models are people using?

I downloaded the manuals for these batteries and saw this in the literature:
" An over discharged battery typically has a voltage less than 11.5V."

Is there some auto shut off below this voltage? Not clear to me from the literature.

In the specs, they list cold cranking tests down to 7.2V so it would seem that they can continue to function down to this level?

Appreciate feedback from users and Earth X reps.

Thanks
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 422 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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  #2  
Old 05-26-2018, 05:26 PM
VNS VNS is offline
 
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Location: New Zealand
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Default EarthX Aircraft Battery Management Syatem - BMS

These batteries will not die a slow and painful death like a lead acid battery. The BMS will disconnect the load if it is drained to less than 5% remaining
charge (an over-discharge condition). The voltage at which this happens will depend on the variables like temp and load but generally will occur at a voltage below 11.5 volts. A battery in this condition has not been damaged and can be recharged to full health. The risks with over discharge and short circuit are managed by the BMS. Running a Lead Acid under 11 volts is probably not ideal either
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  #3  
Old 05-26-2018, 06:36 PM
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Can you tell me what voltage the BMS cuts off at on the low end?
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 422 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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  #4  
Old 05-26-2018, 07:28 PM
VNS VNS is offline
 
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The voltage will vary. The load will disconnect when the capacity reaches the 5% level. The capacity is a product of Voltage by amperage. If you use high amps - crank your engine until it stops - the voltage may get as low as 7.2 volts. If you walk away and leave your master on it may get to 5% capacity while showing 11.5 volts. The recommendation is if you are showing 11.5v AND ARE NOT CHARGING, you need to consider implementing your backup process.
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  #5  
Old 05-27-2018, 09:38 AM
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Thank you. In light of this, we'd have to revise switching points on our CPI2 when using Earth X batteries as either primary or backups. We'd have to pick the 11.5V figure to be sure, which might leave a lot of capacity on the table.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 422 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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  #6  
Old 05-27-2018, 04:46 PM
VNS VNS is offline
 
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Agree, I would like to see the EFIS manufacturers provide a battery 'capacity sensor' (perform the Watt/hr remaining calculation in real time) as DJI do in their Drone software where you can command an action at a preset capacity.
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  #7  
Old 05-27-2018, 10:43 PM
Bicyclops Bicyclops is offline
 
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If keeping the engine running til there is absolutely nothing left in the back up battery is the goal, the EarthX is probably not the right one to use. There would be no real hazard in running a Lithium battery right down. The hazard would be if you try and recharge it afterward. If it got you to a safe landing, a new battery would be worth it to buy. The EarthX will protect itself by shutting down before it is irreversibly damaged, delivering its rated amp hours, (assuming it is healthy to begin with) and could be recharged. That won't help you if the engine quits, though.

As a primary battery, it would shut off and your CPI would see 0 volts. That would be a good time for the backup to come on line even if the engine quit for a second or two. The ignition would come back on, right? If the ignition were set to go to backup battery at 10 or 10.5V, which is about dead for a lead acid battery, a primary Li battery would have already damaged itself or shut itself off to protect itself. What about a dip switch or jumper to set the ignition for battery chemistry?

The ETX series are, I believe, the only batteries that EarthX makes with the protection circuit. The ETX 680 weighs 3.9lb and shows a discharge curve of better that 2 hours at 6.2Amps. Seems like you could run your fuel out with that. What will the CPI2 draw, 2 or 3 amps? Maybe 4 hours of endurance? Where in the lower 48 can you not find an airport with services in two hours or so at nearly 200mph? Not a cheap battery, though.

Ignitions aren't the only thing that most newer airplanes need to supply electrons to. We need to have a plan to keep our EFIS alive to the airport, also radio, transponder, etc. Substantial primary battery capacity and some sort of back up supply is in order - 'nother battery and/or a second alternator.

I've got dual lightspeeds right now and dual PC680s to run my ignitions and panel, about 8A worth. The Pb batteries run down faster the more load you put on them, so my current alternator out plan is to isolate one battery and run the other down to 10.5V or so and go to the second battery. However long the first one takes to run down would be my absolute drop dead range with the second and it would be folly to try and run it near that long. I should really be thinking about where I'm going to land when first the alternator quits, it just doesn't have to be super urgent if I know what kind of shape my batteries are in. When these batteries get soft, I'll probably replace them with a pair of ETX 680s or 900s.

Ed Holyoke

Quote:
Originally Posted by rv6ejguy View Post
Thank you. In light of this, we'd have to revise switching points on our CPI2 when using Earth X batteries as either primary or backups. We'd have to pick the 11.5V figure to be sure, which might leave a lot of capacity on the table.
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  #8  
Old 05-28-2018, 04:22 AM
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Quote:
Originally Posted by Bicyclops View Post
If keeping the engine running til there is absolutely nothing left in the back up battery is the goal, the EarthX is probably not the right one to use. ...The EarthX will protect itself by shutting down before it is irreversibly damaged, delivering its rated amp hours, (assuming it is healthy to begin with) and could be recharged. That won't help you if the engine quits, though.
My goal isn't "keep the engine running till there's nothing left in the backup battery". It's "keep the engine running as long as possible on the battery". It's an important distinction.

It doesn't matter what voltage the battery can get down to; what matters is how long the battery can supply the necessary current at a usable voltage. It's a poor analogy, but think of a gas tank... everyone seems so focused on having a gas tank that you can get every last drop of fuel out of. Wouldn't it be better to have a bigger gas tank, even if it holds some measure of unusable fuel, as long as the total amount of usable fuel is appreciably greater?

If battery A will deliver the required amps for 40 minutes till it reaches 7V (where, say, your ignition drops out), and battery B will deliver the required amps for 60 minutes till it shuts off at 11V... which one is "better"? Personally
I'm going with battery B, because it's delivering power for a longer time. Even if I don't get "every drop of juice" out of it, the big pilot-cooling fan should keep turning for longer. And that's what matters.

Now yes, going with battery B means I'd have to set up my low-voltage alarms a little differently than I would with battery A. If I have anything that switches automatically based on voltage, I'll have to choose different setpoints. But you make trades with any system decision.
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  #9  
Old 05-28-2018, 06:23 AM
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rv6ejguy rv6ejguy is offline
 
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The 2.9 AH Powersonic AGM we've chosen for our standard CPI2 backup will fire one coil pack down to around 8.5V and 2 coil packs down to around 9.5V. It's only there for the ignition.

A 4 cyl. CPI2 and coil draws around 1 amp at 2500 rpm.

No battery will deliver enough current to charge the coils and properly run some of the MOSFETs at 5% capacity remaining.
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Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 422 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
http://sdsefi.com/cpi.htm


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  #10  
Old 05-28-2018, 11:05 AM
Bicyclops Bicyclops is offline
 
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So it looks like about an hour and three quarters of juice firing one coil and something less than an hour on both coils. Since it only is used to keep the engine running after all other ship's battery power is exhausted, seems like a reasonable amount of ultimate reserve at low cost.

If I understand it right, your earlier question was, (paraphrasing) "how do I know when to switch to ultimate reserve power"? With the modifier "I don't want to do it too early and lose potential range". The best switchover point, if determined by battery voltage, would be different depending on main battery chemistry and whether it has protection circuitry. Most are running lead acid, but more will be running LiFe in the future, so it would seem that your CPI2 needs to be able to be set for either.

The pilot needs to know approximately how much time he's got left. Is there an indicator that shows the CPI running on backup battery? Voltage of backup battery?

Ed Holyoke

Quote:
Originally Posted by rv6ejguy View Post
The 2.9 AH Powersonic AGM we've chosen for our standard CPI2 backup will fire one coil pack down to around 8.5V and 2 coil packs down to around 9.5V. It's only there for the ignition.

A 4 cyl. CPI2 and coil draws around 1 amp at 2500 rpm.

No battery will deliver enough current to charge the coils and properly run some of the MOSFETs at 5% capacity remaining.
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