A complicated question about LiFePO4 batteries, - and switching.

On Wednesday, June 20, 2018 at 10:23:41 PM UTC-4, wrote:
Are the angels on the pin all the same size?

Scholars have spent considerable time debating this question, but likely not as much time as some of the arguments and discussions on the R.A.S. !

But seriously, Angels are pure intelligence and don't occupy space. And for a more thoughtful answer one would really need to know if it is the head of the pin you are referring, or the sharp point, it could make a difference.

John - my Libelle still has the original contest letters on it - QT

Mark Guay

I still think the core issue is whether the count is represented in Arabic or Roman, and in what base. The "head" of the pin is generally agreed to be the "not pointy" end, but I will defer to St. Thomas and the Talmudic scholars for final guidance. Angels can change state as proven by the Large Haydron Collider experiments.

I loved that Libelle, if you ever want to sell it please let me know.

QT

I started off with two K2'S I charged RIPthem in parallel, discharged them in parallel. No issues. Then one of the cells died in one of the batteries. Ran them in parallel on the test rig current meters on both. The good battery ran the load until the voltage dropped and then the battery with the bad cell started sharing the load until I stopped the test when the voltage dropped under 11V. There was never current flow from one battery to the other. It was all 0 current or current supplied to the load.

Now running two starks in parallel, discharge and charge. No issues in 2 years now.

Fuses on each battery, separate switches for each, each battery's connection to the bus is also fused.

Don't need to make this complicated. But you can if you want to.

SF

On Thursday, June 21, 2018 at 4:12:09 PM UTC-7, SF wrote:
I started off with two K2'S I charged RIPthem in parallel, discharged them in parallel. No issues. Then one of the cells died in one of the batteries. Ran them in parallel on the test rig current meters on both. The good battery ran the load until the voltage dropped and then the battery with the bad cell started sharing the load until I stopped the test when the voltage dropped under 11V. There was never current flow from one battery to the other. It was all 0 current or current supplied to the load.

Now running two starks in parallel, discharge and charge. No issues in 2 years now.

Fuses on each battery, separate switches for each, each battery's connection to the bus is also fused.

Don't need to make this complicated. But you can if you want to.

SF

The way you would have a problem is if the batteries are in a very different state of charge when they are paralleled. If always charged and discharged in parallel, this can't happen under normal use. If one suddenly developed an internal short, then the other would dump current into it.

On Monday, June 18, 2018 at 9:22:24 PM UTC-4, wrote:
Another question regarding the above battery type! There are variety of techniques used when switching between batteries - on/off/on switches, good switches with a cut out between the movement, two batteries with a diode to prevent flow between both batteries, etc.
The question I have concerns an older glider with limited battery space (Libelle), previously using SLA batteries and and a simple switch between the two. I will be upgrading with a new panel, likely LiFe batteries and want a back-up as well. While I understand the function of the diodes in the switching circuit, is there any reason to be concerned about their use with the LiPo battery and the internal Battery Management System? Imagine two LiFePO4 batteries that have equal charges, only one is discharging at a time until some threshold is reached and they switch over as determined by diodes outside the internal battery system. Is there a reason to question this type of circuit with the use of this new battery technology and the Battery Management System within?
While I love these new batteries, I don't want to bring on any new problem in the air, being quite aware that the wiring is only to contain smoke.

Thanks ahead, Mark

Just to add an angel to the pin, a rotary switch is a single point of failure...

On Monday, June 18, 2018 at 9:22:24 PM UTC-4, wrote:
Another question regarding the above battery type! There are variety of techniques used when switching between batteries - on/off/on switches, good switches with a cut out between the movement, two batteries with a diode to prevent flow between both batteries, etc.
The question I have concerns an older glider with limited battery space (Libelle), previously using SLA batteries and and a simple switch between the two. I will be upgrading with a new panel, likely LiFe batteries and want a back-up as well. While I understand the function of the diodes in the switching circuit, is there any reason to be concerned about their use with the LiPo battery and the internal Battery Management System? Imagine two LiFePO4 batteries that have equal charges, only one is discharging at a time until some threshold is reached and they switch over as determined by diodes outside the internal battery system. Is there a reason to question this type of circuit with the use of this new battery technology and the Battery Management System within?
While I love these new batteries, I don't want to bring on any new problem in the air, being quite aware that the wiring is only to contain smoke.

Thanks ahead, Mark

Just to add an angel to the pin, a rotary switch is a single point of failure...