[NSRCA-discussion] Reducing the odds...
Nat Penton
natpenton at centurytel.net
Mon Mar 27 14:08:32 AKST 2006
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.
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>>
>>> >>>_______________________________________________
>>> >>>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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