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  #1  
Old 07-22-2019, 07:04 AM
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humptybump humptybump is offline
 
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Default BMS and you’re failure scenarios (Not an EarthX)

Update: I have never said who the battery vendor is. After a good open discussion of several days, a moderator took it upon themselves to change the title of my thread to add “(Not EarthX)”. I did not request that change.



On a recent flight, on a cruise descent, while about 30 minutes from landing, my engine monitor gave an over voltage warning.

A brief diagnostics determined it wasn’t something I’d resolve in flight.

Background: My plane has one alternator, one main battery, and one “minimum essentials” backup battery. The backup battery is “dumb” while the main battery is newer - (a recent replacement) - and has an integrated battery management system (BMS).

No worries I thought. I’ll switch off the alternator and the main battery is more than enough for the last 30 minutes with plenty of power to spare.

Oops.

It appears the undocumented BMS behavior in my situation is to disconnect itself and shutdown for some unknown amount of time.

I landed with my backup systems without incident.

The moral? My redundant electrical system isn’t as redundant as I had thought. I had assumed an alternator failure would leave me with main and backup batteries. The reality is some basic failure scenarios could immediately remove two sources of power, not just one.

If you have a BMS associated with your battery it’s a good idea to know it’s response to all of the situations it’s design to protect.
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Last edited by humptybump : 07-26-2019 at 10:57 AM. Reason: Clarification that a moderator changed the title without warning
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  #2  
Old 07-22-2019, 01:57 PM
444TX 444TX is offline
 
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Glen,

It would be interesting to know what the indicated voltage was when the overvoltage was alarming. Also what is your overvoltage point in the warning settings.

Now the big question. Did the battery go open causing the overvoltage event or open as result of the overvoltage event?

What type of battery (I assume EarthX), type of alternator/regulator, and type of overvoltage protection.

This incident is a good reminder of the unknown consequences that can result from experimental electrical design. What pilot actions were necessary to activate the essential buss, did everything have to reboot, can the buss be left on and remain isolated from other systems, what is on the essential buss.

A lot can be learned from this.

George Meketa
RV8
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  #3  
Old 07-22-2019, 02:52 PM
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rv6ejguy rv6ejguy is offline
 
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Good post Glen. If you're electrically dependent, be sure your backup power source is available no matter what happens to the alternator and primary battery. We recommend that you can fully isolate these from backup power.
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Old 07-22-2019, 03:06 PM
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Actually,
Rather than assume, please do tell us the battery manufacturer. Not all BMS’s are the same.
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  #5  
Old 07-22-2019, 04:35 PM
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Let me try to get some answers:

My airplane is basic. Dual mags.

My warning is set at 15.0V. I observed 15.3V while I was attempting to diagnose.

It’s unclear when the battery disconnected.

After shutdown, it reset at some point. The next morning the battery showed 13.1V. The “dumb” battery showed 13.7V.

I’m in the middle of correspondence with the manufacturer to better understand the BMS. Once I have a response, I should be able to answer “which came first?”

I agree that not all BMS are the same. If you’re battery has a BMS and it’s not well documented, then it’s a good idea to contact the manufacturer.
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Old 07-22-2019, 04:59 PM
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scrollF4 scrollF4 is offline
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Quote:
Originally Posted by humptybump View Post
I agree that not all BMS are the same. If you’re battery has a BMS and it’s not well documented, then it’s a good idea to contact the manufacturer.
Well said, Glen, I totally agree.
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Sid "Scroll" Mayeux, Col, USAF (ret)
52F Aero Valley Airport, Roanoke TX (home of DR's Van Cave)
"KELLI GIRL" N260KM RV-7A tipper, YIO-360M1B with Danny King “Beautiful Doll’s” old Hartzell CS prop, dual PMAGs, dual SkyView, GTN-650, VPX, EarthX LiFePo4.
Nose Art by VictoryGirl.com. Smoke by Smoke System Helper.
90% done, 90% to go...
www.mykitlog.com/scrollf4/

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  #7  
Old 07-24-2019, 06:57 PM
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humptybump humptybump is offline
 
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Small update:

I’ve attempted to reach out to the manufacturer of the battery I am currently using as my main battery.

Thus far, the manufacturer has not provided any details of how their BMS behaviors - specifically what events will cause the BMS to disconnect the battery from the circuit and how long before it attempts to reconnect.

Until my event, I never thought to ask these questions. I now consider this critical data to have when a BMS is in my electrical system.
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  #8  
Old 07-24-2019, 08:08 PM
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Glen,
It sounds like your main BMS battery is NOT an EarthX but some other brand. Am I correct?
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Sid "Scroll" Mayeux, Col, USAF (ret)
52F Aero Valley Airport, Roanoke TX (home of DR's Van Cave)
"KELLI GIRL" N260KM RV-7A tipper, YIO-360M1B with Danny King “Beautiful Doll’s” old Hartzell CS prop, dual PMAGs, dual SkyView, GTN-650, VPX, EarthX LiFePo4.
Nose Art by VictoryGirl.com. Smoke by Smoke System Helper.
90% done, 90% to go...
www.mykitlog.com/scrollf4/

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  #9  
Old 07-25-2019, 05:19 AM
bobnoffs bobnoffs is offline
 
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i have an electrically dependant system. 2 batteries, independant of each other and fed by an alternator that will run the system without batteries. these are earth x . i had wondered this exact scenario. i had assumed that the battery would go online again as soon as the overvoltage was removed. if this is not the case i guess i have to dig into this before first flight.
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  #10  
Old 07-25-2019, 05:41 AM
sailvi767 sailvi767 is offline
 
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I would love to know if this was a EarthX and if not how a EarthX would handle this situation since I am sonsidering the Surefly ignition system.
G
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