LiFePO4 batteries

There are two versions of the K2 battery, one with (suffix EB) and one without (suffix E) the Battery Management System. From reading the technical literature, it sounds like the BMS is designed to prevent battery damage in high discharge or high charge rate situations. Since in a glider we're only discharging and charging at about 2 amps max, can do without the BMS? Or have I got it wrong and would be risking a fire?

-John

On 10/10/2012 1:55 PM, John Carlyle wrote:
There are two versions of the K2 battery, one with (suffix EB) and
one without (suffix E) the Battery Management System. From reading
the technical literature, it sounds like the BMS is designed to
prevent battery damage in high discharge or high charge rate
situations. Since in a glider we're only discharging and charging at
about 2 amps max, can do without the BMS? Or have I got it wrong and
would be risking a fire?

I'd be inclined to get one with BMS, since there doesn't seem to be
anyway to equalize the battery cells without it; however, I can't find
any technical info on their site, so I'm just guessing. In fact, I can't
even find the one you are talking about on their site.

The lack of readily available info makes me bit leery about the product.
Any Li battery that is sold as a drop-in replacement for an SLA battery
should tell me a lot more about it than the price before I would put it
in my glider.

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

On Wednesday, October 10, 2012 5:53:45 PM UTC-4, Eric Greenwell wrote:
On 10/10/2012 1:55 PM, John Carlyle wrote:

There are two versions of the K2 battery, one with (suffix EB) and

one without (suffix E) the Battery Management System. From reading

the technical literature, it sounds like the BMS is designed to

prevent battery damage in high discharge or high charge rate

situations. Since in a glider we're only discharging and charging at

about 2 amps max, can do without the BMS? Or have I got it wrong and

would be risking a fire?



I'd be inclined to get one with BMS, since there doesn't seem to be

anyway to equalize the battery cells without it; however, I can't find

any technical info on their site, so I'm just guessing. In fact, I can't

even find the one you are talking about on their site.



The lack of readily available info makes me bit leery about the product.

Any Li battery that is sold as a drop-in replacement for an SLA battery

should tell me a lot more about it than the price before I would put it

in my glider.



--

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

email me)

I ran across this the other day when looking into these things...(almost) everything you never wanted to know about the K2
http://www.etotheipiplusone.net/?p=1991
and the datasheet...
http://www.houseofbatteries.com/documents/K2B12V7EB.pdf

The takeaway is that the BMS will do balancing so that you can use a normal SLA charger on it, the BMS will also provide output protection for under-voltage or over-current situations (though if your panel manages to pull 24A battery damage is likely low on the worry list). The BMS however, doesn't seem to provide any input current/voltage protection.

I'm no expert on battery charge profiles, so it isn't clear to me whether the BMS will turn random SLA charger output into a proper LiFePO4 profile. My understanding is that an SLA charger should do the job. What I don't know is whether or not it would have an impact on the maximum charge state or cycle lifetime, it'll take someone more knowledgeable about batteries than me to answer that.

On Wednesday, September 26, 2012 8:29:19 PM UTC-7, JS wrote:
TA posted about LiFePO4 batteries a while ago.

Using the Tenergy 10AH batteries, I'm impressed. Lighter, longer lasting.

6 hours of ClearNav, 302, 6201 and TT21 brings two 10AH batteries "down" to 13.1V. The old SLA and AGM stuff I'd been using now seems rubbish.

The Lithium Phosphate batteries even use your existing chargers.

Jim

Just anecdotal... one of my RC flying buddies wanted high capacity in an un-finicky rechargeable battery, so he chose LiFeP04. He uses them in an RC plan that draws in excess of 40 amps at full throttle. He has over 600 cyles on the battery pack so far. His charging system is a piece of lamp cord cut to a length that delivers his desired charge current. His source: battery packs for cordless power tools. His thinking was that if it can handle the current draw of a 10" circular saw, it could handle his RC plane.

I wrote to K2 Energy regarding the Battery Management System used with their LiFePo4 battery. In my e-mail, I gave typical glider battery usage:

1) charging the K2B12V10 batteries inside a home environment with normal SLA chargers at 1.0 A maximum.

2) in-glider average current draw of 1 A, rising to 2.5 A when transmitting and the transponder is being pinged.

3) in-flight use in a 0 deg F to 110 deg F temperature range.

K2's answer was "Purchase the K2B12V10EB (with BMS). It will give you more cycle life and is well worth the extra few dollars. The current draw is no problem. Our battery with BMS is rated for 25A continuous."

Hope this helps someone. The extra weight and flat power delivery aren't big enough problems for me that I can justify spending $180 per battery when a SLA of similar capacity goes for $20.

-John

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.

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?

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.

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.