Li-ion & Nimh (long)
Jerry Budd
jbudd at QNET.COM
Sun Dec 15 20:35:38 AKST 2002
Hi all,
Someone a few postings back on this thread asked what the advantages
of Li-Ion batteries were. Well, here's my story. I switched to
Li-Ions early last summer to try and get the Gator Giles G-202 I was
flying at the time under the 5kg weight limit for the Nats. I had
been using a JR 1400 mAh Extra NiCad pack that weighs 4.8 oz and
which only gave me 3 flights max in Masters before I needed to fast
charge (yeah I know that's substandard capacity but I had two of
these JR Extra packs that gave nearly identical performance and I
just wasn't interested in buying any more NiCads). I briefly
considered NiMh batteries as I could use my existing Sirius charger
but it didn't look like the weight savings were going to be that
significant over NiCads (I didn't know at the time that NiMh packs
consistently exceed their rated capacity by about 40%). I also
didn't consider the old DuraLites (Li-Metal) as I was aware of a
growing realization among their users that they had a shelf life
problem and would die after something approaching a few hundred
flights (if even that), not to mention that they were also way too
expensive for my liking. For many of the same reasons I also decided
against the new Li-Ion Duralites (questionable reliability, cost,
etc). I don't usually have many competition ready pattern airplanes
in my stable (unfortunately, most of the time you can count them on
one finger) so I tend to be pretty picky about critical function,
single point failure components.
The batteries I settled on are the 2000mAh 2-cell Li-Ion pack from
Bern Furgang at http://www.superbatterypacks.com/ in Simi Valley,
CA. It's $32 for the pack, it weights 3.2 oz (the JACCIO regulator
added ~0.3 oz if I remember correctly), and I get about 8-10 flights
with a full suite of JR digitals. The charger is a modified 12v cell
phone charger ($28) that appears to be constant current output.
According to Jim Oddino, the modification Bern made was to add a
trimming pot to the circuit to fine tune the output voltage to
something around 8.4 volts. The only way I can see this charger
overtemping the batteries due to charging (which is usually the
expected significant failure mode), is if the battery pack was fully
shorted out to begin with (i.e. dead), and in that case I think the
3A fuse in the charger would open and halt the process before
anything significantly bad happens.
I have been using this pack/charger setup since late June, Jim
Woodward since March, and Jim Oddino a lot longer than that (Jim
Oddino is very familiar with this company's charger - he bought a set
and then took it apart to see how it worked... typical Oddino! : ).
The concensus among our small group seems to be that we are all
pretty happy with this battery/charger system. Other opinions may
vary. BTW - Bern also sells NiCad and NiMH packs, and at very
reasonable prices too.
I think the issue here (if I understand it correctly) is that Li-Ion
cells fail due to overtemping from overcharging in a much different
way than either NiCad or NiMH packs (open flame out the vent hole for
the Li-Ions vs simple outgassing with NiCad/NiMHs) which almost
guarantees a fire if/when it happens. That is a very legitimate
concern, and well worth passing on to the masses for their
consideration. That particular characteristic makes the design and
fail-safe functionality of the charger of critical importance when
charging Li-Ion packs.
I do not have any reason to think that there is any significant
difference between the cells that Bern uses and the cells used in the
new Duralite packs (I suspect that the cells are in fact the same).
Obviously there is a substantial difference in the charger systems
and how they are used and/or perform. Based on the latest
information at hand it would seem that the Li-Ion battery
charger/system being marketed by Duralite has (or had, maybe they've
been fixed?) some problems that need addressing.
One last point, in case someone is wondering - I am only sponsored by
myself so my reasons for stating the above are neither political nor
financial, only technical and (to a much greater degree) safety
driven. Back in Sept I was asked by Eric Henderson to consider
writing an article for publication in the K-Factor or Model Aviation
on this subject. I didn't commit to it at that time, but may do so
once I get around to validating my observations with some solid
engineering quality data.
Sorry this posting ran so long, but some topics just can't be fully
discussed in a couple of paragraphs.
Thx, Jerry
FWIW - For reference here's an exchange of eMail's on this subject
posted to the list back in Sept '02 on this topic:
------------------------------------------------
At 9:38 AM -0700 9/11/02, Woodward James R Civ 412 TW/DRP wrote:
>I spoke with Bern via email about potential problems regarding Li-ion pack
>overheating to such an extend as to cause a fire, or if ANY of his packs
>have been involved in fires, or any other type of catostrophic event. Any
>news or word of this sort is troublesome. Bern reported back that NONE of
>his packs have been involved in any type of fire or melt-down. Furthermore,
>had stated that he had been contacted by persons who have experienced severe
>problems with other manufactorers li-ion packs. Bern did not say anything
>about who, or what other batteries have been tied to serious overheating or
>fire. His charger utilizes an "electric balance" type of operation (just
>like Jerry B. described in another post), and is very safe. Thus, this
>brand/design of Li-ion packs and equipment is free of incident.
>
>Jim W.
>
>
>-----Original Message-----
>From: Henderson,Eric [mailto:eric.henderson at gartner.com]
>Sent: Wednesday, September 11, 2002 5:28 AM
>To: 'discussion at nsrca.org'
>Subject: Li-ion and NiMH Battery from Bern Furgang
>
>
>I have three of these chargers. One in the house and two in the car. The
>house one has a wall unit that gives 12v from a cigar lighter receptacle.
>They behave like Jerry stated. I would add that I use C-Volt meters on the
>planes so you can see the voltage under servo load. You can charge them at
>any time with no battery memory issues.
>
>I also use the I4c load meter with .5, 1 and 1.5 amp load options. to check
>the packs. Interestingly enough they will not take a charge after only one
>flight. Seems that around 8.2v, no load, will not get an LED color change on
>the charger.
>
>So far (8 Months of flying) the Li-ions from Bern Furnang have had no
>problems in operation or charging. I have them in six different planes. With
>digital pattern type set up's I get a good solid 7 flights before I stop
>(7.4V with the plane turned on). With regular servos I see 7.8V after 10
>flights. A fully charged pack shows 8.4v. I have used all my existing, but
>different, regulators with no problems, e.g. no extra or excessive heat etc.
>
>As far as the NiMH packs. they give power like Nicads, charge with my
>overnight chargers like Nicads but hold their charge like Li-ions and don't
>have memory problems either. They are just great in TX packs (8 x 1830's),
>Kavan starter-packs (10 x 3000's) and Radio South glow drivers (4 x 3000's).
>You really do get twice the duration.
>
>What I enjoy the most is their ability to not run down on their own. They do
>lose charge but VERY slowly. One starter-pack I left in the car for six
>months, fully charged. when I went to use it, it worked all day as if it was
>freshly charged.
>
>Hope you all have a strong day and that we all get through this tough time
>with the capability to still love those who don't love us yet.
>
>Eric.
>
At 9:53 AM -0500 9/11/02, Ron Van Putte wrote:
>Jerry Budd wrote:
>
>>I know that the DuraLight folks are putting some circuitry into
>>their battery packs to eliminate overcharging as an issue.
>>However, that extra circuitry introduces additional failure modes,
>>which may be what we are starting to hear about on this (and other)
>>lists. I personally don't think it's really necessary, and in fact
>>it may actually cause more problems than it solves.
>
>
>Jerry is partially correct. The Duralite Plus Li-Ion battery packs
>do have a voltage cutoff device. However, the Duralite Plus Li-Ion
>chargers also have a voltage cutoff device. The charger's is set at
>8.4 volts and the one in the pack is at 8.7 volts. This is a safety
>feature, so one will cut off if the other doesn't. It's unlikely
>that both will fail at the same time.
>
>Ron Van Putte
>
>
>=====================================
>X-Sender: jbudd at mail.qnet.com
>Date: Tue, 10 Sep 2002 23:00:18 -0700
>To: discussion at nsrca.org
>From: Jerry Budd <jbudd at QNET.COM>
>Subject: Re: Li-Ion packs
>Reply-To: discussion at nsrca.org
>Sender: discussion-request at nsrca.org
>X-Spam-Status: No, hits=-1.0 required=5.0 tests=IN_REP_TO,EXCUSE_3
>version=2.01
>
>Hi Verne,
>
>There is an indicator light but it operates a bit differently than
>what most people are used to.
>
>It appears that the charger is a constant voltage charger, which
>means that the amount of current flow into the battery pack is
>proportional (but not linearly proportional) to the difference
>between the voltage level of the battery pack vs the set (more
>likely requlated) voltage put out by the charger. The greater the
>voltage difference, the greater the current flow into the battery
>pack. Initially there is a relatively high current flowing into the
>battery which decreases as the voltage of the pack increases.
>Eventually (about 2 hours for a fully discharged pack) the voltage
>of the pack (given the pack is healthy) rises to the same voltage
>output level of the charger, at which point there is ZERO current
>flow into the pack, and you are done.
>
>As far as how to tell when the pack is fully charged? If you
>connect a pack that has had some amount of usage, the indicator
>light (really a diode) on the charger will glow red. As the pack
>voltage comes up, the current flow tapers off somewhat, and the
>indicator light changes to a red-yellow hue, then to a yellow color,
>then to a yellow-green hue, and then finally it goes completely
>green (indicating no current is flowing and a fully charged battery
>pack).
>
>The only flaw in the system is that when the charger is connected to
>a 12v power source, the light glows green, whether a battery pack IS
>CONNECTED OR NOT! Why? There's no current flowing through the
>diode to make it change color. Obviously this creates a concern as
>to how can you tell that you actually have a good connection between
>the charger and the battery pack. What I do is make sure that I see
>the diode change color when I connect the charger to the charge
>jack. If I don't see a color change, I either have a battery which
>is still fully charged (not likely - check it with a digital
>voltmeter with a 0.5 to 1 amp load), or I don't have a good
>connection. If I see the diode change color as described above I
>know it's charging.
>
>Now, can you leave the charger hooked up to the battery pack
>indefinitely? In theory, yes. In practice, maybe (you still need
>to exercise the pack once in a while). Bern suggests NOT to leave
>it hooked up. I have left mine on for as much as a week or more
>with no effect (as far as I can tell). Your mileage may vary.
>
>The cool part of all this is that the charger is essentually a fast
>charger in that it initially puts out a lot of current at the
>beginning, and then tapers off to a trickle, without any really
>fancy circuitry involved. This is a good thing as simpler directly
>translates into increased reliability (assuming reasonably high
>quality components are used). The drawback is that if you have a
>"bad" battery pack, the voltage of the battery pack MAY NOT come up,
>causing the current flow to remain high, and you could "cook" a set
>of batteries (and maybe an airplane). I think this type of failure
>mode is extremely unlikely. A more likely scenario is that the
>(compromised) pack never does quite reach peak voltage, the charger
>continues to put out a small amount of current (which probably
>doesn't cause much of anything to happen), and you (hopefully)
>notice that the charge light never quite reaches a full green color
>(which tells you something is not right). You then check the pack
>voltage with that 1 amp load VOM I mentioned, and realize the pack
>is maybe not doing so well. I think that's a pretty graceful
>failure mode, and it's certainly one I can live with.
>
>I know that the DuraLight folks are putting some circuitry into
>their battery packs to eliminate overcharging as an issue. However,
>that extra circuitry introduces additional failure modes, which may
>be what we are starting to hear about on this (and other) lists. I
>personally don't think it's really necessary, and in fact it may
>actually cause more problems than it solves.
>
>Jerry
>
> >Bob,
>>Did you get his charger? If so, are there indicator lights on it to let you
>>know it's fully charged?
>>
>>Verne
>>
>>
> >----- Original Message -----
>>From: "Bob Pastorello" <faipatrn at msn.com>
>>To: "NSRCAMail" <discussion at nsrca.org>
>>Sent: Tuesday, September 10, 2002 9:49 PM
>>Subject: NiMh Battery from Bern Furgang
>>
>>
>>> I received the 1680 mah recommended by some on this list, and have to
>say
>>> that Bern was very prompt to send the battery, and provided great
>>> information about charging, cycling, etc.
>>> The battery cycled at 1680, and I flew tonight with it...it weighs
>the
>>> SAME as my 1100mah NiCad exactly, and gives about 35% more mah.
>>> Sure means I won't be field charging as much....really great
>product,
>>> great service!!
>>>
>>>
>>> Bob Pastorello, NSRCA 199, District 6
>>> El Reno, Oklahoma
>>> faipatrn at msn.com
>>>
>>> You Gotta at least TRY....
> >> http://www.rcaerobats.net
> >>
>>
>>----- Original Message -----
>>From: "Jerry Budd" <jbudd at QNET.COM>
>>To: <discussion at nsrca.org>
>>Sent: Friday, September 06, 2002 2:00 PM
>>Subject: RE: Li-Ion packs
>>
>>> >Thanks Jim.
>>> >
>>> >Ive been curious what a discharge curve looks like for
>>> >these batteries, anyone seen one?
>>>
>>> My experience is that it's pretty constant (but not level), similar
>>> to a lead-acid battery (which makes it very predictable). As far as
>>> I can tell (and I've run my Li-ion packs from Bern Furgang at
>>> http://www.superbatterypacks.com down to slightly less than 6.6v) it
>>> stays pretty linear with no discernable change in slope.
>>>
>>> I eMailed Bern about this and he replied with, "I would not go below
>>> the 6V threshold as you could loose the pack. 7.2V is a very safe
>>> low end. If you are at 6.6V you are OK."
>>>
>>> Before I purchased the Li-ion pack/charger I consulted with Jim
>>> Oddino as he had some experience with them. He indicated that he was
>>> favorably impressed. I purchased the bx & charger in late June, and
>>> at this point, I am too.
>>>
>>> Jerry
--
___________
Jerry Budd
mailto:jbudd at qnet.com
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