LiFePO4 batteries

On 10/11/2012 7:05 PM, Uncle Fuzzy wrote:
On Thursday, October 11, 2012 3:10:36 PM UTC-7, JohnDeRosa wrote:
On Wednesday, October 10, 2012 9:04:15 PM UTC-5, Uncle Fuzzy
wrote:



"His charging system is a piece of lamp cord cut to a length that
delivers his desired charge current."



Huh? The wire length limits the charge current? I may be dense
but you are going to have to explain this to me a bit more.
Wire has resistance, enough wire (his cord is approximately 30 feet
long)has enough resistance to drop the charge current to his target
10 amps. That's an extrememly mild charge rate for an A123 cell pack
that will happily discharge at 80 amps.

Was that cheaper than buying a charger? Even if the wire was free, I
think it'd be safer and cheaper in the long run to buy a charger that
was smarter than a piece of wire.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

At 22:10 11 October 2012, JohnDeRosa wrote:
On Wednesday, October 10, 2012 9:04:15 PM UTC-5, Uncle Fuzzy wrote:

"His charging system is a piece of lamp cord cut to a length that
delivers
his desired charge current."

Huh? The wire length limits the charge current? I may be dense but you
are going to have to explain this to me a bit more.

How else would you control current other than with an appropriate
length/size of wire? You can if you wish coil it and package it and call it
a resistor.

On 10/13/2012 1:45 AM, Don Johnstone wrote:
At 22:10 11 October 2012, JohnDeRosa wrote:
On Wednesday, October 10, 2012 9:04:15 PM UTC-5, Uncle Fuzzy wrote:

"His charging system is a piece of lamp cord cut to a length that
delivers
his desired charge current."

Huh? The wire length limits the charge current? I may be dense but you
are going to have to explain this to me a bit more.

How else would you control current other than with an appropriate
length/size of wire? You can if you wish coil it and package it and call it
a resistor.

Perhaps he is able and willing to stand by the battery and monitor the
process, but I'd rather buy a charger: it could regulate the current,
measure the amp hours delivered, and shut down automatically when the
battery is fully charged or the time has run out.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)nz

I'm still having trouble with the concept of charging a battery with AC
power. I saw no mention of a rectifier... Maybe he flip-flops the wires 60
times per second?


"Eric Greenwell" wrote in message
...
On 10/13/2012 1:45 AM, Don Johnstone wrote:
At 22:10 11 October 2012, JohnDeRosa wrote:
On Wednesday, October 10, 2012 9:04:15 PM UTC-5, Uncle Fuzzy wrote:

"His charging system is a piece of lamp cord cut to a length that
delivers
his desired charge current."

Huh? The wire length limits the charge current? I may be dense but you
are going to have to explain this to me a bit more.

How else would you control current other than with an appropriate
length/size of wire? You can if you wish coil it and package it and call
it
a resistor.

Perhaps he is able and willing to stand by the battery and monitor the
process, but I'd rather buy a charger: it could regulate the current,
measure the amp hours delivered, and shut down automatically when the
battery is fully charged or the time has run out.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email
me)nz

On Thursday, October 11, 2012 7:25:17 PM UTC-7, wrote:
My K2 w/o BMS has just two terminals just like any Pb acid, so I don't see how a charger can monitor each cell. I also don't know what a balance plug is, so I'll stop commenting. I'm just relaying what K2 and B-T Jr. told me.

Okay, perhaps when they assemble/manufacture these batteries they ensure the cells are very well matched. The typical A123 and LiFe batteries used in RC have a special plug, often a JST-XH/(JR in the case of ElectroDynamics) type that allows the cells to be balance charged when using a capable charger. It is an absolute must in the case of Lipos (for safety)but with Life/LifePo/A123 you can get away without balance charging to some degree.

On Saturday, October 13, 2012 1:17:23 PM UTC-7, Dan Marotta wrote:
I'm still having trouble with the concept of charging a battery with AC

power. I saw no mention of a rectifier... Maybe he flip-flops the wires 60

times per second?





"Eric Greenwell" wrote in message

Okay, now I see your confusion. Based on a lack of information in my post. My mistake. He's connecting his 3 cell LiFePo to a car battery, using the 30(ish) feet of zip cord as a dropping resistor (I just talked to him today, last year he got fancy and added a springwound cutoff timer). I was just trying to point out that the A123 cells are pretty robust, and while using the recommended charger and charge profile will likely lead to the longest possible life of your LiFePo batteries, he's been beating the hell out of the same 3 battery packs for 2+ years now, and has subjected them to more cycles than I would be able to put on a battery used in my glider in 5 years.

...

On 10/13/2012 1:45 AM, Don Johnstone wrote:

At 22:10 11 October 2012, JohnDeRosa wrote:

On Wednesday, October 10, 2012 9:04:15 PM UTC-5, Uncle Fuzzy wrote:



"His charging system is a piece of lamp cord cut to a length that

delivers

his desired charge current."



Huh? The wire length limits the charge current? I may be dense but you

are going to have to explain this to me a bit more.



How else would you control current other than with an appropriate

length/size of wire? You can if you wish coil it and package it and call

it

a resistor.



Perhaps he is able and willing to stand by the battery and monitor the

process, but I'd rather buy a charger: it could regulate the current,

measure the amp hours delivered, and shut down automatically when the

battery is fully charged or the time has run out.



--

Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email

me)nz

On Thu, 11 Oct 2012 17:55:20 -0700 (PDT), wrote:

hmmm, I wouldnt use existing/old style chargers on LifePo or A123. You really should use a balance charger which monitors the voltage of each cell during charge. This will help avoid ruining your nice new battery. I presume the K2 has a balance plug?

the electronics for charge regulation and balancing are built into the
battery case of the SLA replacement sets. So, just two terminals.
That's all

aldo cernezzi