[NSRCA-discussion] Reducing the odds...
Earl Haury
ehaury at houston.rr.com
Mon Mar 27 13:07:20 AKST 2006
Jim
I've used the datalogger to monitor in-flight performance quite a bit.
Typically, during a P-07 flight the low voltage stays above 35v (typically
<65A max) and power consumption is in the range of 3000 to 3400 mAh
(depending on wind) for an eight minute flight. I've set the ESC min volts /
cell to 3.0v, but 3.3 would work. These numbers are similar with APC 20x15,
21x14, and 21x13W E props - Hacker C50XL-14 motor.
Be observant of motor heating in the Abbra, I saw some pretty high numbers
with "typical" baffles. Filled the nose with foam (wing core type), bored a
"tunnel" for the motor, and hot wired ducts. Motor stays very cool now.
Earl
----- Original Message -----
From: "J.Oddino" <joddino at socal.rr.com>
To: <chad at f3acanada.org>; "NSRCA Mailing List"
<nsrca-discussion at lists.nsrca.org>
Sent: Monday, March 27, 2006 1:16 PM
Subject: Re: [NSRCA-discussion] Reducing the odds...
> Hi Chad,
>
> I'm about to launch my first electric pattern plane and I'd like to get
> your
> opinion on my logic for setting the cutoff voltage. First of all I'd
> prefer
> that I'd never let any cell get below 3.3 volts per cell. However, I'd
> also
> prefer that the motor never stopped. My plan is to get to know the
> battery
> voltage vs. flight profile to accomplish both. I will set the cutoff
> voltage very low so it will never cut the motor. I will telemeter the
> voltage and current and keep track of the mAh consumed. If I see the
> voltage getting too low (<33V)under max load or use more than 80% of the
> capacity I will land. If I can't get through the pattern I'll probably
> need
> to go to a smaller prop. Once I am confident that the profile is
> consistent
> I can remove the TM system. What do you think?
>
> Jim O
>
> ----- Original Message -----
> From: "Chad Northeast" <chad at f3acanada.org>
> To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
> Sent: Sunday, March 26, 2006 10:45 AM
> Subject: Re: [NSRCA-discussion] Reducing the odds...
>
>
>> Hi Eric,
>>
>> Regardless of cutoff, its the resting voltage that is of paramount
>> importance for good pack life. A 1C discharge with a 3V/cell cutoff
>> will leave you with a very low resting voltage, as compared to a 15C
>> discharge with the same cutoff. Recently there has been a number of
>> discussions about increasing safe cutoff values as the C rates go up
>> since most of the current packs hold voltage so well up until then end
>> when they simply dump everything they have....so 3 v/cell now equals to
>> a much deeper discharge than in the past.
>>
>> Then there is the problem that the ESC is only seeing average pack
>> voltage and not cell voltage...so its entirely possible while under
>> discharge to have a pair of cells at 3.2v (6.4 total) and the third at
>> 9-6.4....or 2.6V, and now your ESC will cut properly...but that one cell
>> is being damaged.
>>
>> If you run a bit higher cutoff (3.1-3.2) and fly so that your open
>> circuit resting voltage is 3.75-3.8 you will have very happy batteries.
>>
>> I agree...there is not enough of this information available without a
>> lot of online reading. There is a lot of this on RC Groups...although
>> it can take a significant amount of time to wade through the BS and
>> gather what is useful.
>>
>> Chad
>>
>> Grow Pattern wrote:
>>
>> >Chad,
>> > The speed controller cuts out at 9V. It actually drops to
>> > about
>> >8.3V under load and then settles back to 9.0V after the motor cuts.
>> >
>> >You know it's not so much that I am reporting what I personally do as
> much
>> >more like I am stating what the system does.
>> >
>> >The voltage cut-off end-user value options on the speed controller are
>> >selectable but still have fixed values. A three-cell pack has to use the
>> >9.0V option. I used my in-line meter to monitor and measure these
> results.
>> >
>> >Once again we are back to the instructions verses acquired knowledge!
>> >
>> >Regards,
>> >
>> >Eric.
>> >
>> >
>> >----- Original Message -----
>> >From: "Chad Northeast" <chad at f3acanada.org>
>> >To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
>> >Sent: Sunday, March 26, 2006 10:30 AM
>> >Subject: Re: [NSRCA-discussion] Reducing the odds...
>> >
>> >
>> >
>> >
>> >>>I now believe that I had a bad cell on the one that blew-up.
>> >>>
>> >>>
>> >>If you were discharging to 3 v/cell as I read it from your data then
>> >>its
>> >>not surprising that you would have bad cells....a 3v/cell resting would
>> >>indicate that you are discharging much below that under load.
>> >>
>> >>shoot for 3.7-3.8 v/cell resting (5-10 minutes) after the flight and
>> >>your batteries will be much happier, and stay in balance all by
>> >>themselves for the most part.
>> >>
>> >>Chad
>> >>
>> >>
>> >>Grow Pattern wrote:
>> >>
>> >>
>> >>
>> >>>First of all thanks for all of the suggestions and advice from the
>> >>>list
>> >>>surrounding the charging of my Lipo's.
>> >>>
>> >>>
>> >>>
>> >>>I have been messing with the big Lipo's since before Jason flew his
> most
>> >>>notable entry at the world's four years ago. This was my first
>> >>>catastrophic
>> >>>failure of a battery pack. I have spent around $7000 on electrics in
> that
>> >>>period of time and have closely monitored their technical development.
>> >>>
>> >>>
>> >>>
>> >>>Right now I am working on sport type or sport level electrics. Not the
>> >>>foamy
>> >>>type or super light type of models, but the alternatives to 40 sized
> glow
>> >>>motor powered models.
>> >>>
>> >>>
>> >>>
>> >>>I particularly like the HIMAX offerings where they sell a motor, a
> motor
>> >>>mount, a matching speed controller and a prop all in one box. This
> saves a
>> >>>lot of guessing and previous trial and error on the part of the buyer.
> You
>> >>>are left with the choice of what battery pack and what plane to put it
> in.
>> >>>
>> >>>
>> >>>
>> >>>Which brings us back to the exploding Thunderpower 4400 pack. I had
> been
>> >>>using my Astroflight 109 chargers with great success. I have 4 of
>> >>>them.
>> >>>This
>> >>>was before the little add-on balancers were available. They charged a
>> >>>bunch
>> >>>of different packs up to and including the big 4S3P packs with no
> problems
>> >>>etc. I am familiar with their warning etc. In particular, it states
> that
>> >>>it
>> >>>is not recommenced to charge a fully charged pack, (note: not
> forbidden).
>> >>>It
>> >>>further states that the charger will shut down the charge after about
>> >>>4
>> >>>minutes if you actually try and do this.
>> >>>
>> >>>
>> >>>
>> >>>Now we get to the 3S pack in question. I was not satisfied with the
>> >>>knowledge of what happened and the comfort of how to prevent it
> happening
>> >>>again. I did not have another pack, or at least I was not going to
>> >>>risk
> an
>> >>>old friend's second and last pack. I did a couple of things.
>> >>>
>> >>>
>> >>>
>> >>>I measured the each cell of my 3600 mAh Tanic's using the voltage taps
>> >>>that
>> >>>are part of the assembled pack.
>> >>>
>> >>>
>> >>>
>> >>>CELL UP CELL DOWN
>> >>>
>> >>>I 4.18 3.01
>> >>>
>> >>>II 4.18 3.00
>> >>>
>> >>>III 4.19 3.01
>> >>>
>> >>>
>> >>>
>> >>>Charging the pack when at 9.2V gave-
>> >>>
>> >>>
>> >>>
>> >>>CELL UP
>> >>>
>> >>>I 4.18
>> >>>
>> >>>II 4.19
>> >>>
>> >>>III 4.18
>> >>>
>> >>>
>> >>>
>> >>>Charging the pack when fully charged caused the charged to read it as
>> >>>3
>> >>>cells. It went through the 3 minute determination pause. Charged for
>> >>>about
>> >>>a minute and said "I'm done!" did this with two different 3600 mAh
> packs.
>> >>>The charger did what it said it would do.
>> >>>
>> >>>
>> >>>
>> >>>Then just as an FYI, I flew the model with both packs wired in
> parallel.
>> >>>One
>> >>>pack was giving me 5 minutes of flight at full throttle. I needed more
>> >>>air-time on the sport plane. (World models Sky Raider). I now had 10
>> >>>minutes
>> >>>plus and the flight did not run out of steam.
>> >>>
>> >>>
>> >>>
>> >>>The two packs were fully charged and the plane flown for about seven
>> >>>minutes.
>> >>>
>> >>>
>> >>>
>> >>>This created a 3S2P pack. The readings were very encouraging.
>> >>>
>> >>>
>> >>>
>> >>>PACK-A
>> >>>
>> >>>CELL UP CELL PARTIALLY DOWN
>> >>>
>> >>>I 4.18 3.68
>> >>>
>> >>>II 4.18 3.68
>> >>>
>> >>>III 4.17 3.67
>> >>>
>> >>>
>> >>>
>> >>>PACK-B
>> >>>
>> >>>CELL UP CELL PARTIALLY DOWN
>> >>>
>> >>>I 4.18 3.68
>> >>>
>> >>>II 4.19 3.68
>> >>>
>> >>>III 4.18 3.67
>> >>>
>> >>>
>> >>>
>> >>>The cells were discharging and charging nice and equally.
>> >>>
>> >>>
>> >>>
>> >>>My charging practices have been upgraded to.
>> >>>
>> >>>1. Test voltage of each cell before each charge.
>> >>>
>> >>>2. Monitor the charge initiation.
>> >>>
>> >>>3. Place pack on 1/2" metal plate on table outside of van. (Deep Cycle
>> >>>marine 12V is in back of van).
>> >>>
>> >>>4. Check reading periodically.
>> >>>
>> >>>5. Test voltage of each cell after each charge.
>> >>>
>> >>>
>> >>>
>> >>>I now believe that I had a bad cell on the one that blew-up. I also
> would
>> >>>not charge the TP pack without the after-market device. In fact I now
> do
>> >>>anything to reduce the odds of another accident.
>> >>>
>> >>>
>> >>>
>> >>>Just looking at the display on the 109 charger tells you a lot. The
> number
>> >>>cells, the voltage during initialization and during charge, must be
>> >>>correct,
>> >>>or at least in range. Putting the pack in a fire safe place is
> paramount.
>> >>>
>> >>>
>> >>>
>> >>>Regards,
>> >>>
>> >>>
>> >>>
>> >>>Eric.
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>_______________________________________________
>> >>>NSRCA-discussion mailing list
>> >>>NSRCA-discussion at lists.nsrca.org
>> >>>http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
>> >>>
>> >>>
>> >>>
>> >>>
>> >>>
>> >>_______________________________________________
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>> >>http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
>> >>
>> >>
>> >>
>> >
>> >_______________________________________________
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>> >
>> >
>> >
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>>
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