LiFePO4 batteries

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.

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.

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

The Lithium Phosphate batteries even use your existing chargers.
Jim
********
This is correct. I bought a K2 w/o the BMS this year. I already owned a few Battery Tender Jr. chargers, so I emailed K2 and Battery Tender. Both replied the charger was fine for a K2. I was concerned about the lack of BMS and bought a K2 charger to conduct my own tests, so if anyone wants this $50 charger at a discount, let me know.
~Bruce

On Thursday, October 11, 2012 3:39:55 PM UTC-7, wrote:
The Lithium Phosphate batteries even use your existing chargers. Jim ******** This is correct. I bought a K2 w/o the BMS this year. I already owned a few Battery Tender Jr. chargers, so I emailed K2 and Battery Tender. Both replied the charger was fine for a K2. I was concerned about the lack of BMS and bought a K2 charger to conduct my own tests, so if anyone wants this $50 charger at a discount, let me know. ~Bruce

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?

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?

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.

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.