Ceengland
Joined: 11 Oct 2020
Posts: 391
Location: MS
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 Posted: Mon Oct 18, 2021 9:53 am Post subject: Subject: Re: Lithium Battery and Alternator Failure |
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Excellent joke (and advice), but I suspect that it won't be a 'derating'.
I don't think it will help your situation any, but there is a European regulator made for 'dynamo' style (permanent magnet) alternators that starts out with lower charge *voltage*, and slowly ramps up, which is what you're effectively asking for.
FWIW, 55-60A internally regulated automotive alternators get hammered like that all the time in cars, in much worse temperature environments, and seem to survive just fine. (And you can buy one for way less than $100, too). You'd have to go through the inconvenience of adding $50 worth of external OV protection, of course...
Charlie
On 10/18/2021 11:59 AM, Bill Boyd wrote:
| Quote: | Chris,
I don't know how helpful this input is, but I'd consider de-rating the Plane Power alternator by converting it to a product from B&C. I made the buy-once, cry-once decision based on reliability reports on VAF and haven't looked back.
On Mon, Oct 18, 2021 at 12:46 PM Chris Mullins <mullincl(at)gmail.com (mullincl(at)gmail.com)> wrote:
| Quote: | Thanks to the group for your responses on this problem.
Follow up on questions asked:
Bus voltage before the alternator failed was about 13.8. This was the standard voltage seen with this alternator during it's life. I believe the Plane Power alternators do have overvoltage protection. Battery cell balancing has been accomplished using a Li specific maintainer on the ground. The last capacity check on this battery was June 2021 and it was about 20% reduced from new.
I'm hearing Bob loud and clear that theoretically the alternator should be able to tolerate these conditions without problems. I am understanding Bob to suggest that I keep flying it like it is. But allusions have also been made to lower reliability for these units.
Bob, would you please explain the phrase "failure of process control"? (manufacturing tolerances?)
Also, do you assume this failure was related more to an individual fault in the failed alternator and that it is not likely the replacement will have the same vulnerability?
I'm focused more on the practical side of how to make this less likely to happen again.
Bob made this statement:
The only way to 'smoke' a
normally functioning alternator is to operate
it at near max rated output for extended
periods of time with INADEQUATE cooling.
I am wondering if my installation is creating this exact scenario after startup - max demand (abruptly from 0 to 60amps) and minimal airflow for cooling. Undercowl preheating of the alternator during hot starts could be additive.
The mfgr says his product can't tolerate a Li battery with no BMS, and under the circumstances, I'm inclined to believe him. He has basically asked me to de-rate the alternator after startup until the battery recovers it's baseline charge.
Respectfully, if I end up choosing to modify the system, there were several suggestions to place components in the B lead. This approach would need 'devices' rated to handle the full current and heat energy of the alternator output - big connections, dollars etc.
This is probably a foolish question, but could one accomplish the same thing by restricting the field circuit in some way? (It seems any of these modifications will end up de-rating the alternator under all flight conditions. In my installation I can accept that.)
Thanks again to all for sharing your expertise.
Chris Mullins
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