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nuckolls.bob(at)aeroelect
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 Posted: Wed Aug 19, 2015 6:54 pm Post subject: Anything 'unique' about incorporating EarthX? |
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| Quote: | | With a B&C overvoltage protection module (nominal trip voltage of 16.2 volts), I could have voltage to the battery greater than the BMS triiger voltage and have loss of battery power supply at the same time I have no alternator electrical source! |
How so? At what voltage and how fast does the BMS
bring the battery back on line? What leads you
to believe that during the interval from onset of
an ov condition, alternator shut down and BMS
recovery . . . that the bus voltage will drop too
low for too long to keep the fan running?
Bob . . . [quote][b]
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blues750
Joined: 06 Jun 2015
Posts: 56
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| Posted: Sat Aug 22, 2015 6:05 pm Post subject: Re: Anything 'unique' about incorporating EarthX? |
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[quote="nuckolls.bob(at)aeroelect"] | Quote: | | With a B&C overvoltage protection module (nominal trip voltage of 16.2 volts), I could have voltage to the battery greater than the BMS triiger voltage and have loss of battery power supply at the same time I have no alternator electrical source! |
How so? At what voltage and how fast does the BMS
bring the battery back on line? What leads you
to believe that during the interval from onset of
an ov condition, alternator shut down and BMS
recovery . . . that the bus voltage will drop too
low for too long to keep the fan running?
Bob . . .
Bob,
That's part of my dilemma, I cannot answer that question yet. Failure characteristics with respect to time onset and voltage ouptut during a failure to an overvoltage output by a generator or regulator of my type I do not know. If I am recalling correctly, I have read that the B&C OVPM reacts within milliseconds to an overvoltage issue. The Earthx BMS starts doing it's thing around 15.5 volts - but that is dependent on a few variables. I have asked the engineer for some time, temp, charge state and charging voltage correlations to try and determine how quickly the BMS will react and protect the cells and simultaneously deprive me of needed power to my busses from the battery. Again, it is my understanding after talking with the engineer at Earthx, that no voltage is available from the battery (nothing allowed in or out) while the BMS is protecting the battery I still need to followup with those questions, if they are indeed the right questions to be asking! (I think so  ) but was trying to get more insight here first. Based on my understanding at this point, I am concerned about a scenario in which the output from the alt and R/R to my battery and busses is somehow slowly rising above 15-16 volts. The BMS decides to act out and take my batteries offline. I can fly on the alternator if necessary though maybe not ideal for some equipment or to what value the voltage may rise. But to get my batteries back, I do need to alleviate the overvoltage presented to them. Ideally, I would notice the overvoltage prior to the BMS getting protective, simply shut down the alternator and proceed to the hangar with my batteries supplying the required voltage as intended. But, having to take my alternator off-line with my batteries off-line simultaneously does not seem like proper design if that is indeed a real possibility.
Appreciate the initial feedback and comments, would gladly welcome any more related to this scenario.
Dave
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nuckolls.bob(at)aeroelect
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| Posted: Tue Aug 25, 2015 5:39 am Post subject: Anything 'unique' about incorporating EarthX? |
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At 01:00 PM 8/24/2015, you wrote:
| Quote: | "With a B&C overvoltage protection module (nominal trip voltage of 16.2 volts), I could have voltage to the battery greater than the BMS triiger voltage and have loss of battery power supply at the same time I have no alternator electrical source!"
I just talked with Kathy at EarthX and mentioned this concern with the OV protection. I am very near making the decision on batteries to use on my project also using the B and C regulator so was very interested in this. She strongly recommended to use one of the new aircraft specific battery designs, ETX680, ETX900, or ETX1200, and that these batteries have the OV protection set at over 19V in order to address this very issue. She said new batteries also have greater redundancy and battery fault warning than their other batteries. |
19 volts? Hmmm . . . wonder how they arrived at
that figure . . . which seems to argue with some
widely circulated 'never exceed' numbers that
are reputed to trash the battery.
It will be interesting to see how the return on investment shakes out for
this new direction in battery technologies. When you're selling Apple
products, there's a market segment that can be depended on to 'need'
whatever new features are offered. That market is a classic demonstration
of "Build it and they will come". A market with little incentive to deduce
what features really improve performance and/or reduce risk.
Speaking of great experiments in "Build it an they will come",
there are many thousands of housing and commercial units built
and supposedly move-in ready. Multiple complete cities standing empty in
another part of the world . . .
[img]cid:.0[/img]
. . . again, a powerful demonstration that encourage folks
to understand the economics . . . the return on investment for
needs versus wants. I am still mystified as to how it's a
'good thing' to add a wad of transistors to a battery just
to achieve a few pounds of weight savings . . . we'll just
have to wait and see.
Bob . . .
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