LiFePO4 chargers

On Saturday, November 10, 2018 at 12:03:42 AM UTC-6, kinsell wrote:
On 11/4/18 3:51 PM, wrote:
On Monday, November 5, 2018 at 8:02:04 AM UTC+10, wrote:
I also have heard the stories about fires while charging, but, as far as I know, most involved a different Lithium chemistry (Li-ion, Li-Polymer etc.) LiFePO4 is supposed to be safer, but by how much I do not know. At any rate, I am pretty much stuck with charging them in the plane, as they are mounted well behind the spar, and it takes a good 20-30 minutes to get them out and put them back in.

Here is an FAA report that supports the assertion that LiFePO4 cells are safer: https://www.fire.tc.faa.gov/pdf/TC-16-17.pdf

In their testing, which they admit had quite variable results, they did not get any thermal runaway with LiFePO4 cells, but did with all the other Li chemistries they tested. Note that the graphs in the above article show 1 cell out of 5 consumed by "thermal runaway" but that was the cell that they were heating externally to try and initiate the runaway.

Not to say that you shouldn't take precautions, all battery chemistries store enough energy to start an electrical fire, even if they are relatively immune to thermal runaway and overcharging.


I would hope they're safer than something like a li-po, model airplanes
using those things routinely put on a fireworks display during a crash.
Fascinating videos on YouTube.

However, "safer" isn't actually the same as "safe", LFP's are quite
capable of burning, despite what the scholarly articles say. There have
been a number of fires, particularly when they're used as starter
batteries. High charge rates and very high discharge rates seem to
cause problems, as homebuilders of small power planes have discovered.
There was also that LFP battery fire in an EB-28 in Finland this summer.

-Dave

Dave, if you look around youtube long enough, you will find that a AAA battery can make a fire. Certainly a 12V lead-acid has enough juice to do that if circumstances are right. The overwhelming evidence of many years of usage of LiFePo4 chemistry in glider batteries suggests that they are as safe as the old gel-cells. Give progress a chance, I'm not saying be a Progressive.
Herb

Mark, When K2 was fairly new on the market I contacted them asking if Battery Tender Jr. is okay and safe, they replied that it is perfectly okay and nearly the same as their charger. I also contacted Battery Tender Jr. with the reverse question and they said the BTJr is fine for LiFePO4. I used the BTJr for years on my K2 with no issues. They're about $25 on internet sites.

On 11/13/18 6:08 PM, wrote:
Mark, When K2 was fairly new on the market I contacted them asking if Battery Tender Jr. is okay and safe, they replied that it is perfectly okay and nearly the same as their charger. I also contacted Battery Tender Jr. with the reverse question and they said the BTJr is fine for LiFePO4. I used the BTJr for years on my K2 with no issues. They're about $25 on internet sites.


Have you measured the amount of charge you're getting into the K2's? It
will be considerably less than the rated amount due to using a lead-acid
charger.

Also, if K2 has cell balancing capability, it won't be used because your
Battery Tender doesn't put out enough voltage to make it work.

On Tuesday, November 13, 2018 at 11:11:52 PM UTC-5, kinsell wrote:
On 11/13/18 6:08 PM, bruce... wrote:
Mark, When K2 was fairly new on the market I contacted them asking if Battery Tender Jr. is okay and safe, they replied that it is perfectly okay and nearly the same as their charger. I also contacted Battery Tender Jr. with the reverse question and they said the BTJr is fine for LiFePO4. I used the BTJr for years on my K2 with no issues. They're about $25 on internet sites.


Have you measured the amount of charge you're getting into the K2's? It
will be considerably less than the rated amount due to using a lead-acid
charger.

Also, if K2 has cell balancing capability, it won't be used because your
Battery Tender doesn't put out enough voltage to make it work.

Many simple lead-acid chargers reach up to around 14.2-14.8 volts. That voltage would suffice to charge an LFP battery to well above 90% capacity if it stays there for a while. If it quickly shifts to "float" at 13.5V or so then it won't do well in charging LFP. So simpler is better in this case. Measure what your charger does. And disconnect it after several hours, don't leave it on "float".

On 11/14/18 9:03 AM, wrote:
On Tuesday, November 13, 2018 at 11:11:52 PM UTC-5, kinsell wrote:
On 11/13/18 6:08 PM, bruce... wrote:
Mark, When K2 was fairly new on the market I contacted them asking if Battery Tender Jr. is okay and safe, they replied that it is perfectly okay and nearly the same as their charger. I also contacted Battery Tender Jr. with the reverse question and they said the BTJr is fine for LiFePO4. I used the BTJr for years on my K2 with no issues. They're about $25 on internet sites.


Have you measured the amount of charge you're getting into the K2's? It
will be considerably less than the rated amount due to using a lead-acid
charger.

Also, if K2 has cell balancing capability, it won't be used because your
Battery Tender doesn't put out enough voltage to make it work.

Many simple lead-acid chargers reach up to around 14.2-14.8 volts. That voltage would suffice to charge an LFP battery to well above 90% capacity if it stays there for a while. If it quickly shifts to "float" at 13.5V or so then it won't do well in charging LFP. So simpler is better in this case. Measure what your charger does. And disconnect it after several hours, don't leave it on "float".


Hate to break this to you, but at $24, the Battery Tender Junior is one
of the cheapest chargers on the market, and is fully featured with a
float mode.

14.2 volts wouldn't begin to charge an LFP to "well over 90%" as you
claim. If you found a charger that delivers 14.8 volts under load, then
it would overcharge an SLA and would be considered defective.

If you're going to spend big bucks for an LFP, you ought to get a proper
charger for it. Still waiting to hear just how much charge the K2's got
in them from a BTJ.

-Dave

On Wednesday, November 14, 2018 at 2:56:35 PM UTC-5, kinsell wrote:
On 11/14/18 9:03 AM, moshe... wrote:
On Tuesday, November 13, 2018 at 11:11:52 PM UTC-5, kinsell wrote:
On 11/13/18 6:08 PM, bruce... wrote:
Mark, When K2 was fairly new on the market I contacted them asking if Battery Tender Jr. is okay and safe, they replied that it is perfectly okay and nearly the same as their charger. I also contacted Battery Tender Jr. with the reverse question and they said the BTJr is fine for LiFePO4. I used the BTJr for years on my K2 with no issues. They're about $25 on internet sites.


Have you measured the amount of charge you're getting into the K2's? It
will be considerably less than the rated amount due to using a lead-acid
charger.

Also, if K2 has cell balancing capability, it won't be used because your
Battery Tender doesn't put out enough voltage to make it work.

Many simple lead-acid chargers reach up to around 14.2-14.8 volts. That voltage would suffice to charge an LFP battery to well above 90% capacity if it stays there for a while. If it quickly shifts to "float" at 13.5V or so then it won't do well in charging LFP. So simpler is better in this case. Measure what your charger does. And disconnect it after several hours, don't leave it on "float".


Hate to break this to you, but at $24, the Battery Tender Junior is one
of the cheapest chargers on the market, and is fully featured with a
float mode.

14.2 volts wouldn't begin to charge an LFP to "well over 90%" as you
claim. If you found a charger that delivers 14.8 volts under load, then
it would overcharge an SLA and would be considered defective.

If you're going to spend big bucks for an LFP, you ought to get a proper
charger for it. Still waiting to hear just how much charge the K2's got
in them from a BTJ.

-Dave

That's the conventional wisdom, but see experimental results he
https://www.powerstream.com/lithium-...ge-voltage.htm
- well above 90% capacity even at a bit lower than 14V!

A cheap dumb 14.x volt fixed-voltage source with limited current output (and perhaps aided by the battery's BMS) would charge an LFP just fine. I'm not saying that's the ideal charger, but in a pinch it would work well enough. I am not happy with the several chargers I have that push SLAs well above 14V (even above 15V), but they may be handy for LFPs.

kinsell wrote on 11/14/2018 12:55 PM:
On 11/14/18 9:03 AM, wrote:
On Tuesday, November 13, 2018 at 11:11:52 PM UTC-5, kinsell wrote:
On 11/13/18 6:08 PM, bruce... wrote:
Mark, When K2 was fairly new on the market I contacted them asking if Battery
Tender Jr. is okay and safe, they replied that it is perfectly okay and nearly
the same as their charger. I also contacted Battery Tender Jr. with the
reverse question and they said the BTJr is fine for LiFePO4. I used the BTJr
for years on my K2* with no issues. They're about $25 on internet sites.


Have you measured the amount of charge you're getting into the K2's?* It
will be considerably less than the rated amount due to using a lead-acid
charger.

Also, if K2 has cell balancing capability, it won't be used because your
Battery Tender doesn't put out enough voltage to make it work.

Many simple lead-acid chargers reach up to around 14.2-14.8 volts.* That voltage
would suffice to charge an LFP battery to well above 90% capacity if it stays
there for a while.* If it quickly shifts to "float" at 13.5V or so then it won't
do well in charging LFP.* So simpler is better in this case.* Measure what your
charger does.* And disconnect it after several hours, don't leave it on "float".


Hate to break this to you, but at $24, the Battery Tender Junior is one of the
cheapest chargers on the market, and is fully featured with a float mode.

14.2 volts wouldn't begin to charge an LFP to "well over 90%" as you claim.* If
you found a charger that delivers 14.8 volts under load, then it would overcharge
an SLA and would be considered defective.

If you're going to spend big bucks for an LFP, you ought to get a proper charger
for it.* Still waiting to hear just how much charge the K2's got in them from a BTJ.

Bienno Power has a $25, 12V/4A LiFePO4 charger. I'd trust that over a BT Jr, and
it's the same price.


--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to email me)
- "A Guide to Self-Launching Sailplane Operation"
https://sites.google.com/site/motorg...ad-the-guide-1
- "Transponders in Sailplanes - Dec 2014a" also ADS-B, PCAS, Flarm

http://soaringsafety.org/prevention/...anes-2014A.pdf