[NSRCA-discussion] Reducing the odds...
Jerry Budd
jerry at buddengineering.com
Mon Mar 27 19:06:28 AKST 2006
Earl,
How far back does the foam extend? To just in front of the rear
motor support bracket?
Any pics?
Thx, Jerry
>Nat
>
>Fill the fuse nose with foam (wing core type) & spot glue. Cut a motor
>"tunnel" about 1/4" dia. larger than the motor (1/8" air gap). Hot wire
>(wire loop on a soldering gun) ducts from the cheek / chin cowl openings.
>
>Earl
>
>
>
>----- Original Message -----
>From: "Nat Penton" <natpenton at centurytel.net>
>To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
>Sent: Monday, March 27, 2006 5:08 PM
>Subject: Re: [NSRCA-discussion] Reducing the odds...
>
>
>> Earl
>> Can you provide more detail on the ducts ? Nat
>>
>> ----- Original Message -----
>> From: "Earl Haury" <ehaury at houston.rr.com>
>> To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
>> Sent: Monday, March 27, 2006 4:07 PM
>> Subject: Re: [NSRCA-discussion] Reducing the odds...
>>
>>
>>> 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.
>>>>> >>>
>>>>> >>>
>>>>> >>>
>>>>> >>>
>>>>> >>>
>>>>> >>>
>>>>> >>>
>>>>> >>>
>>>>> >>>
>>>>> >>>_______________________________________________
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>>>>> >>>NSRCA-discussion at lists.nsrca.org
>>>>> >>>http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
>>>>> >>>
>>>>> >>>
>>>>> >>>
>>>>> >>>
>>>>> >>>
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>>>>> >>
>>>>> >>
>>>>> >>
>>>>> >
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>>>>> >
>>>>> >
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--
___________
Jerry Budd
Budd Engineering
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