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Old Aug 16, 2004, 08:50 AM
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I hadn't realised you were planning on leaving the hardwired series connection in place for parallel charging. A much simpler method is outlined below where the multi-pin connector is used to configure the pack as either series or parallel so that the ESC lead will have a series supply while the charger can operate on parallel cells.

Take the example of a 3 cell pack using 6-pin connectors. The cells would each have a + and - pin to themselves on the 6-pin connector. For the charge lead all three +'s would be soldered to one lead and likewise with the -'s. So charging would be a parallel operation. The six pins on the flight lead to the ESC would be soldered differently. 1 + and 1 - (from different cells) would be wired to the ESC with the other 4 pins joined in 2 pairs connecting the + of one cell to the - of the next to create a series configuration.
So charging is parallel and ESC supply is series. No modifications to the charger or ESC required. Just the connectors. Unforunately this would require you to assemble your own packs as the cells would each need a short length of wire to the connector but I think this is the easiest and most sensible approach - am I missing something.

Aidan
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Old Aug 16, 2004, 09:16 AM
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Quote:
Originally Posted by Aio_1
... Unforunately this would require you to assemble your own packs as the cells would each need a short length of wire to the connector but I think this is the easiest and most sensible approach - am I missing something.

Aidan
You aren't missing anything - it's what we have been doing, e.g:
http://www.rcgroups.com/forums/showthread.php?t=236246

We were hoping to avoid the custom pack construction and extra wire per cell, that's all.

- RD
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Old Aug 16, 2004, 09:31 AM
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Thanks for the clearing up the salt water resistance discrepecies TjCooper. I did some more coffee cup testing using higher voltage (12 volts) and checked current flow. The resistance as measured with my DVM in a similar setup as before was about 400 ohms. When I hooked up a 12 volt battery to the probes and put a current meter in series, I saw lots of bubbling, and current flows of about 150 MA. The impedance of the solution changed from about 400 ohms with the low voltage put out by the meter to about 80 ohms with 12 volts across the electrodes. The current of a LiPoly pack thrown in salt water should be considerably less because of the small surface area of the conductors in contact with the water, but even 150 ma would be a safe discharge rate.

Dan
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Old Aug 16, 2004, 09:40 AM
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Thanks RD,

I hadn't seen the other thread.

Aidan
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Old Aug 16, 2004, 09:40 AM
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Quote:
Originally Posted by Aio_1
The multiplex connectors are commonly used on <20A power systems. To do this they are usually soldered up with 3 pins for - and 3 for +. If we wanted to use them for individual cell connections on 3s packs we would be limited to about 6A - 7A per cell. They'd be perfect for these applications though.

Aidan
Aidan, I'm not sure how much wattage (better than simple amperage rating, IMO) the Multiplex connectors can stand. luc has had a lot of experience with them - I'll ask him to comment.

In general, higher-rated connectors, such as Semos, have to be used for high-output packs. I started out using them before luc pointed us in the direction of multiplex plugs:
http://www.rcgroups.com/forums/showthread.php?t=154208

That thread also contains other plugs and connection systems.

- RD
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Old Aug 16, 2004, 11:04 AM
luc
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well, I use the mpx (3 pins together) till 43A, and I think I am close to the max....
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Old Aug 16, 2004, 12:43 PM
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Aio_1 wrote:
Quote:
A much simpler method is outlined below where the multi-pin connector is used to configure the pack as either series or parallel so that the ESC lead will have a series supply while the charger can operate on parallel cells.
Aidan, very true, when I asked about multiple-pin connectors earlier this is what I had in mind.

However, it would be very convenient to not have to use 6-pin connectors on a 3S, with all pins identical and able to take the full discharge current. I was daydreaming about a charger that would be able to charge the cells individually in parallel while they were still left series-connected - this would require fewer pins on the connector, only four pins for a 3S. Better yet, the two middle pins would never carry anything more than the 1C charging current, opening the door for using two connectors - one heavy-duty 2-pin one, and a second light-duty 2-pin connector used only for charging. That would let me continue to use my current Deans Ultra plugs, merely adding something like a JST to the between-cell taps...

However I think I have convinced myself that a charger to do this, while technically possible, would be quite complex and expensive. Better to do as you suggest, and simply rig the connector to allow series discharge/parallel charge.

-Flieslikeabeagle
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Old Aug 16, 2004, 12:47 PM
luc
I plant balsa sticks too
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I think the "b" should be out...
here is my classic // or serie multiplug, with 2P packs.
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Old Aug 16, 2004, 12:51 PM
luc
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you can see here 5 2P pack on my converted DR1.
Flies perfectly...here is a small vid
http://lucchevaillier.free.fr/DR1.avi
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Old Aug 23, 2004, 12:59 PM
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Sunnyvale Ca
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current gameplan

RD and others,
I got another "sacrifice pack" this weekend and hope to this week repeat the test of the underwater flame and smoke experiment. In another thread there were questions on my sand, tubes, nomex socks, etc. So I did a quick rundown on what each part contributes to the system:
http://www.rcgroups.com/forums/showt...83#post2544083

I hope this week to do the underwater test. I think to insure that the water does not cool down pack, I will build a little frame out of toothpicks to go inside the ziplock bag. this will insure that the water does not touch the pack until it has flamed (assuming it does not get so hot that it melts the ziplock before going to flames). I will put Pb weights in the bag to keep it submerged in the fishbowl. Lets hope this one works.

BTW, one of my friends had a 4S3P pack go "vent and flames". He described the fireball as like 4 feet tall and lasting for 3-5 minutes as each cell was heated and consumed. Has anyone else had a "huge" pack go to flames? Is there any description of how big is the fireball and how long it lasted. Because if this description is accurate, then for big packs, only the ammo box or firesafe could start to be a good container.
Crazy Ted -- a battery junkie
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Old Sep 06, 2004, 12:51 AM
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results of underwater test

LiPoly users,
Here is a new thread to cover the underwater burning of the LiPoly cells:
http://www.rcgroups.com/forums/showt...17#post2598917

BOTTOM LINE: they do "burn" underwater quite powerfully.
Crazy Ted
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Old Sep 06, 2004, 11:05 AM
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The floating lipo

For those who not belive of that. And the water No have salt.
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Old Jul 12, 2006, 01:00 PM
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Quote:
Originally Posted by raptor22
My question still exists: it burns white. Elemental Li burns white when ignited. Li compounds tint flames deep crimson red if they burn. Why is the flame not red?

--Alex
first, not all Li compounds will burn with a reddish tint, spectra depends on the valence electrons energy and position, and how many there are, because they are excited and then fall back to their previous orbital during combustion or other energy releases. You will always get white flames, because some of the Li ions are reacting, the other colors are anything else included or bonded.

By the way, since Lithium is an alkai metal, it will react freely with water producing hydrogen gas and Lithium Oxide, even when bonded to other materials as we know it's reactive, that's why we make the battery, the reactions creates energy. So it's not stable, to become stable it sheds it's current bonds, releasing energy, some of the energy released accelerates the bond made with free oxygens in the water or the decomposition of the hydrogen oxygen bonds, and you get MORE energy. This is released as heat, which causes flames, explosions, and sparks in differing amounts dependent on composition and the specific amounts of each reaction occuring at a given time.

Adding water to it is just bad as it is with any electrical item, but in the case of an alkali you're asking for trouble, the battery could have literally exploded ask like K (Potassium) Lithium reacts violently with water, causing the release hydrogen gas to rapidly combust, along with other reactions along the way with the now free radicals from the lithium bonded polymers, which remember polymers are carbon chains...everything loves to bond with carbon!
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Old Jul 12, 2006, 01:18 PM
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whoa...blast from the past
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Old Jul 12, 2006, 04:43 PM
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Space Coast
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The manufacturers recommend using water to fight LiPo fires.
There is no metallic Lithium in a LiPo cell.

http://www.sanyo.com/batteries/pdfs/lipo.pdf
http://www.ultralifebatteries.com/do...14-Polymer.pdf
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