LiFePO4 Batteries on sale.

On Saturday, November 28, 2015 at 4:04:29 PM UTC-8, Soartech wrote:
I agree on the protective circuit BUT it will not protect higher voltages for extend periods of time.


Hmmm, sounds like a poorly designed protection circuit. It should recognize the charge voltage is too high and disconnect it from the battery.

I agree about the protection circuit, but will take the advice of both Bioenno and Stark Power not to use higher voltage chargers.

Richard
www.craggyaero.com

On Saturday, November 28, 2015 at 4:13:26 PM UTC-8, Richard wrote:


I agree about the protection circuit, but will take the advice of both Bioenno and Stark Power not to use higher voltage chargers.

Richard
www.craggyaero.com

A good idea.

However, there's a difference between charging a 12 volt battery with a capable 24 volt battery charger and connecting a relatively low power solar panel to that same 12 volt battery - even if the PV panel has a higher Voc (as all the panels we are talking about do).

A typical 36 cell panel, intended for 12 volt systems, might have an Voc (open circuit voltage) of +- 20 volts. But connecting that PV panel to the battery doesn't mean the voltage in the system would be bumped up to 20 volts.. Ever. The PV panel voltage will be instantly "clamped" to battery voltage - and then charging will occur which would slowly raise system voltage, but only if current output of the PV panel is more than the system avionics load is consuming. Normally, with load applied and the small PV panels we are using, there is no net charge to the battery as long as avionics are on.

So, in flight, no issue, even with no solar charge regulator, as long as the avionics continues to use more current than the solar panel output - which again is the case in most current glider PV panel installations. Using a solar charge controller intended for lead acid batteries? Sure, also no problem as long as the glider isn't left in the sun with avionics off and the PV panel still charging.

If planning to leave it parked in the sun with avionics off, then it's important to make sure the solar charge controller max output voltage will not exceed the battery max charging voltage. On my LFP batteries that's 14.2 volts.

That said, it's best to use a solar charge controller intended for LFP batteries. And plan on occasionally using a recommended LiFePO4 battery charger to do a cell balance charge if that's the mfg's recommendation.

On Sunday, November 29, 2015 at 11:10:07 AM UTC-8, bumper wrote:
On Saturday, November 28, 2015 at 4:13:26 PM UTC-8, Richard wrote:


I agree about the protection circuit, but will take the advice of both Bioenno and Stark Power not to use higher voltage chargers.

Richard
www.craggyaero.com

A good idea.

However, there's a difference between charging a 12 volt battery with a capable 24 volt battery charger and connecting a relatively low power solar panel to that same 12 volt battery - even if the PV panel has a higher Voc (as all the panels we are talking about do).

A typical 36 cell panel, intended for 12 volt systems, might have an Voc (open circuit voltage) of +- 20 volts. But connecting that PV panel to the battery doesn't mean the voltage in the system would be bumped up to 20 volts. Ever. The PV panel voltage will be instantly "clamped" to battery voltage - and then charging will occur which would slowly raise system voltage, but only if current output of the PV panel is more than the system avionics load is consuming. Normally, with load applied and the small PV panels we are using, there is no net charge to the battery as long as avionics are on..

So, in flight, no issue, even with no solar charge regulator, as long as the avionics continues to use more current than the solar panel output - which again is the case in most current glider PV panel installations. Using a solar charge controller intended for lead acid batteries? Sure, also no problem as long as the glider isn't left in the sun with avionics off and the PV panel still charging.

If planning to leave it parked in the sun with avionics off, then it's important to make sure the solar charge controller max output voltage will not exceed the battery max charging voltage. On my LFP batteries that's 14.2 volts.

That said, it's best to use a solar charge controller intended for LFP batteries. And plan on occasionally using a recommended LiFePO4 battery charger to do a cell balance charge if that's the mfg's recommendation.

So could you put the solar panels in parallel with the batteries through some diodes to eliminate the sitting on the grid with the avionics off scenario? That is pretty common. Sure you'd never charge the batteries, but that's not really the purpose anyway.

9B

In a word, YES.
In the ASW27 that is currently Sergio's, the Strobl charge controller is on the master bus before the avionics master. runs in parallel with whichever battery is selected. We wired it that way before LiFePO4 technology. Used it later with LiFePO4s.
One sunny day at Cal City I noticed after removing the batteries that the ClearNav was still running. At that point it was in "power save" mode. As soon as I touched the stick controller, the CN drew more current which dropped the voltage and it shut down.
The Strobl charger has a lower charging voltage than LiFePO4s want, so won't actually charge to full but will maintain. Like a sustainer versus self-launcher.
Jim


On Sunday, November 29, 2015 at 4:25:06 PM UTC-8, Andy Blackburn wrote:

So could you put the solar panels in parallel with the batteries through some diodes to eliminate the sitting on the grid with the avionics off scenario? That is pretty common. Sure you'd never charge the batteries, but that's not really the purpose anyway.

9B

On Tuesday, November 24, 2015 at 8:33:37 AM UTC-6, wrote:
bioennodepot.com is offering 15% off LiFePO4 glider batteries.

12V 9A only $85.00 bucks

If your old "Sealed Lead Acid" (SLA) needs replacing, here is an opportunity to get a 12 Volt 9 Amp hour LiFePO4 battery. I have been using these for several years and would never go back to SLA's.

Lots of RAS threads on LiFePO4 if you need more convincing.

These are a direct drop in replacement to your old 12V 7A battery but weigh only 2.6 pounds. Here's the link.

http://bioennodepot.com/bioenno-powe...lf-1209ws.html

Here is a note from one of the LiFePO4 manufactures, Bioenno Power, on their recommendation for storing LiFePO4 batteries.

You will want to charge the batteries every 8 weeks or so (put them on the charger, let the battery charge up for about 4 to 6 hours) and then disconnect them from the charger. It is not an issue for storage, as LiFePO4 batteries do not have any memory effect. You can keep them in room temperature (like a closet), no problem. No need for a refrigerator.

OK, but why does the rest of the world recommend to store at 50% charged?

On Thursday, December 3, 2015 at 4:11:15 PM UTC-6, wrote:
OK, but why does the rest of the world recommend to store at 50% charged?

Ueli, you may confuse the advice given for LiPo batteries. They are much more aggressively optimized for capacity and discharge rate and are charged to higher voltages. My experience with LiFe batteries is different, they are very tolerant to being kept fully charged.
Herb

No I'm not confusing them with LiPos. Automatic chargers with a "storage" mode will charge/discharge a LiFePo to 50%. In the german gliding forum this is agreed to be correct. However I googled this again and found a lot of guys have also made the experience that it doesn't really matter a lot. Some even stored LiFePos for months at 0% without any problems.

On Saturday, December 5, 2015 at 10:23:01 AM UTC-8, wrote:
No I'm not confusing them with LiPos. Automatic chargers with a "storage" mode will charge/discharge a LiFePo to 50%. In the german gliding forum this is agreed to be correct. However I googled this again and found a lot of guys have also made the experience that it doesn't really matter a lot. Some even stored LiFePos for months at 0% without any problems.

It's nice that they are so tolerant of being stored "as-is" since that's what a lot of us would prefer. It's also really nice that the prices have come down a bit, for the rest of you at least. ;-)

9B

On Sunday, November 29, 2015 at 2:45:24 AM UTC+8, Richard Pfiffner wrote:
On Saturday, November 28, 2015 at 9:52:42 AM UTC-8, Soartech wrote:
On Tuesday, November 24, 2015 at 12:15:55 PM UTC-5, Richard wrote:
On Tuesday, November 24, 2015 at 8:38:46 AM UTC-8, Jonathan St. Cloud wrote:
Any idea if I had a solar panel for charging would I need some sort of controller to charge these LifePO4 batteries?

If your old "Sealed Lead Acid" (SLA) needs replacing, here is an opportunity to get a 12 Volt 9 Amp hour LiFePO4 battery. I have been using these for several years and would never go back to SLA's.

Lots of RAS threads on LiFePO4 if you need more convincing.

These are a direct drop in replacement to your old 12V 7A battery but weigh only 2.6 pounds. Here's the link.

http://bioennodepot.com/bioenno-powe...lf-1209ws.html

Craggy Aero also offers the same discount.

http://www.craggyaero.com/lifepo_battery.htm

Richard
www.craggyaero.com

Jonathan,

Yes it is absolutely necessary to have a controller specific to the LiFePO4 batteries. If you charge at the higher voltage that solar panel outputs you will fry the battery.

Richard
www.craggyaero.com

You will not "fry" the battery because the battery has protection circuitry built-in.
From the specs:
"Includes built-in PCM (protection circuit module) which provides balancing of internal cells, and protection from overcurrent, undervoltage (overdischarge), and overvoltage."

If the voltage is too high it will simply prevent it from charging. All that is required is a simple regulator like an LM317 to keep the voltage from the solar cell at ~15 Volts. Most solar cells rated for 12V will put out around 18 Volts in strong sunlight.

Soartech,

I agree on the protective circuit BUT it will not protect higher voltages for extend periods of time.

I had a LiFePO4 vendor send me the wrong charger 24 volts instead of 12v. Fried 3 LiFePO4 batteries. They got big and leaked. You would not want this happening in your nice glider with solar panels. Solar panels can deliver 22 to 24 volts. Please use chargers that also have the protective circuits and around 12 to 14 volts. That is what is recommended by the manufactures of the LiFePO4 batteries.

Richard
www.craggyaero.com

I agree about the necessity of a charge controller / regulator. I have been using this one for a number of years now with no problems:

http://www.jaycar.com.au/Ecotech/Sol...anels/p/AA0348