nuckolls.bob(at)aeroelect
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 Posted: Sat Jan 11, 2020 6:22 pm Post subject: Lithium BMS and 'load-dump' worries (CORRECTION) |
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| Quote: | I have wired an unmodified, internally regulated Nippondenso 40 amp alternator in my single AGM Odessey PC680 battery, two alternator, modified Z-13/8 system. I used Z-24 as a guide but with a Perhelion L-OVP module. On start-up, I switch the battery on with both alternators off and push the start switch. After the engine starts, I switch the ND alternator on.
On occasion, I have forgotten to switch the alternator on and took off. A few minutes later, on climb out with high rpm, I noticed the voltage dropping. Upon troubleshooting, I realized the alternator was off. I didn’t think twice, and switched the alternator on. I had no idea this sequence was at some risk to the regulator. Or was it? |
It is not . .
| Quote: | | Would it be a risk to a lithium battery BMS? |
No . . .
You can generally turn an alternator on/off at any time
without risk to ship's hardware. Z-24 (b-lead
dis-connector) offers some risk to an
INTERNAL regulator IF the alternator is shut off
at higher than idle rpm AND the alternator is heavily
loaded (probably recharging the battery -AND- grunting
ship's loads).
One COULD deliberately create a load-dump
event into the ship's systems by turning
of the battery . . . again while the ALTERNATOR(S)
is/are heavily loaded. This is POSSIBLE in ships
like Barons and Bonanzas where alternator and
battery switches are not interlinked and
alternator only ops are permitted. However,
the regulators I designed for the Beech
ships were pretty docile for gross load
dump . . . I don't recall the figures now
(that was about 1978). I do recall that the
dump-transient did not exceed DO160/MIL-STD-704
limits - that was a design goal imperative.
Load dump risks are limited to UNLOADING
an alternator . . . not turning it on/off
(EXCEPT where Z-24 DOES unload an internally
regulated alternator placing ONLY the
internal regulator at risk . . . if at
all). ALL Z-figures recommend progressive
transfer, two-pole switches for OFF/BAT/
BAT+ALT making it impossible to deliberately
or inadvertently initiate a load-dump event.
The suggested protocol for turning the
alternator on/off just after engine start
and just before shut down has to do with
an orderly organization of check list that
ALSO happens to be Z-24 friendly.
Load-dumps are something of a wil-o'-the-whisp
(swamp gas). You gotta work to create one
and 99% of the time they are harmless when
they do occur.
BTW . . . I don't think PM rectifier/regulators
are even capable of creating a significant
load dump transient. They use a cycle-by-cycle
conduction control philosophy that does not
present gain/phase issues present in the
wound field system.
Whether or not the battery is fitted with
a BMS isn't a component of the load-dump
scenario.
Bob . . .
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