[NSRCA-discussion] Reducing the odds...
J.Oddino
joddino at socal.rr.com
Mon Mar 27 10:16:45 AKST 2006
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
> >>>
> >>>
> >>>
> >>>
> >>>
> >>_______________________________________________
> >>NSRCA-discussion mailing list
> >>NSRCA-discussion at lists.nsrca.org
> >>http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
> >>
> >>
> >>
> >
> >_______________________________________________
> >NSRCA-discussion mailing list
> >NSRCA-discussion at lists.nsrca.org
> >http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
> >
> >
> >
> _______________________________________________
> NSRCA-discussion mailing list
> NSRCA-discussion at lists.nsrca.org
> http://lists.nsrca.org/mailman/listinfo/nsrca-discussion
>
>
> --
> No virus found in this incoming message.
> Checked by AVG Free Edition.
> Version: 7.1.385 / Virus Database: 268.3.2/293 - Release Date: 3/26/2006
>
More information about the NSRCA-discussion
mailing list