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A complicated question about LiFePO4 batteries, - and switching.



 
 
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  #31  
Old June 21st 18, 08:26 PM posted to rec.aviation.soaring
Benedict Smith
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Posts: 28
Default A complicated question about LiFePO4 batteries, - and switching.

At 08:16 21 June 2018, krasw wrote:
On Wednesday, 20 June 2018 20:15:06 UTC+3, Benedict Smith

wrote:

John,
You can connect a 12v led indicator in parallel with the fuse, it

will
light up if the fuse blows, regarding fixing them in flight, I

would
want to know why it had blown before replacing it, not easy to
diagnose electrical faults and fly safely at the same time!
Ben.


Fuse blows it there is a short in wiring. You would like to

continue
supplying current via LED to shorted wires, so you can see that

fuse was
blown?

Yes, 3-5ma through an LED and it’s dropper resistor is not going
to cause any problems, it’s not like I suggested using a car
headlamp bulb!!
I would be interested to know why you think that it would be a
problem.
Ben.

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  #32  
Old June 22nd 18, 12:12 AM posted to rec.aviation.soaring
SF
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Posts: 196
Default A complicated question about LiFePO4 batteries, - and switching.

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
  #33  
Old June 22nd 18, 05:30 AM posted to rec.aviation.soaring
jfitch
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Posts: 904
Default A complicated question about LiFePO4 batteries, - and switching.

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.
  #34  
Old June 22nd 18, 08:18 AM posted to rec.aviation.soaring
krasw
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Posts: 423
Default A complicated question about LiFePO4 batteries, - and switching.

On Thursday, 21 June 2018 22:30:06 UTC+3, Benedict Smith wrote:
At 08:16 21 June 2018, krasw wrote:
On Wednesday, 20 June 2018 20:15:06 UTC+3, Benedict Smith

wrote:

John,
You can connect a 12v led indicator in parallel with the fuse, it

will
light up if the fuse blows, regarding fixing them in flight, I

would
want to know why it had blown before replacing it, not easy to
diagnose electrical faults and fly safely at the same time!
Ben.


Fuse blows it there is a short in wiring. You would like to

continue
supplying current via LED to shorted wires, so you can see that

fuse was
blown?

Yes, 3-5ma through an LED and it’s dropper resistor is not going
to cause any problems, it’s not like I suggested using a car
headlamp bulb!!
I would be interested to know why you think that it would be a
problem.
Ben.


I would be very interested to know why this excellent feature cannot be found in any airplane.
  #35  
Old June 22nd 18, 01:20 PM posted to rec.aviation.soaring
Martin Gregorie[_6_]
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Posts: 110
Default A complicated question about LiFePO4 batteries, - and switching.

On Fri, 22 Jun 2018 00:18:42 -0700, krasw wrote:

I would be very interested to know why this excellent feature cannot be
found in any airplane.


Because there are very few panel mount fuse holders available with built-
in LED indicators?



--
Martin | martin at
Gregorie | gregorie dot org
  #36  
Old June 22nd 18, 02:19 PM posted to rec.aviation.soaring
[email protected]
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Posts: 338
Default A complicated question about LiFePO4 batteries, - and switching.

Because there are very few panel mount fuse holders available with built-
in LED indicators?


How many do you want?

https://www.ebay.com/sch/i.html?_fro...h+LED&_sacat=0
  #37  
Old June 22nd 18, 02:22 PM posted to rec.aviation.soaring
[email protected]
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Posts: 338
Default A complicated question about LiFePO4 batteries, - and switching.

Because there are very few panel mount fuse holders available with built-
in LED indicators?


How many do you want?

https://www.ebay.com/sch/i.html?_fro...h+LED&_sacat=0
  #38  
Old June 22nd 18, 05:02 PM posted to rec.aviation.soaring
Martin Gregorie[_6_]
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Posts: 110
Default A complicated question about LiFePO4 batteries, - and switching.

On Fri, 22 Jun 2018 06:22:27 -0700, markmocho53 wrote:

Because there are very few panel mount fuse holders available with
built-
in LED indicators?


How many do you want?

:-)

I was curious, never having seen any, if indicator fuse holders were
available So I did a bit of searching on the local electronics suppliers
(RS, Farnell and Rapid Electronics) websites for individual LED indicator
equipped 5 x 20mm fuse holders and didn't find any. I looked for that
type because those would be direct replacements for the in-flight
accessible fuse holders in my glider.

I did see indicator fuse blocks and individual indicator holders for auto-
type fuses and rather more with neon indicators, but none of the latter
worked at 12v - they're all for 90-240v circuits.

I'm somewhat surprised that LED indicator holders for 5x20mm fuses aren't
available - it wouldn't be hard to fit an LED in the cap of these
holders.


--
Martin | martin at
Gregorie | gregorie dot org
  #39  
Old June 23rd 18, 05:42 AM posted to rec.aviation.soaring
jfitch
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Posts: 904
Default A complicated question about LiFePO4 batteries, - and switching.

Glass fuse holders are kind of 20th century aren't they? If you were replacing them, going to a circuit breaker which is both resettable and indicates that it has been tripped, might be the direction to go?
  #40  
Old July 24th 18, 04:59 AM posted to rec.aviation.soaring
2G
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Posts: 477
Default A complicated question about LiFePO4 batteries, - and switching.

On Wednesday, June 20, 2018 at 6:27:33 AM UTC-7, OHM Ω http://aviation.derosaweb.net wrote:
Andy,

I have used the ideal diodes mentioned by Shaun McLaughlin (http://re-voltage.eu/ US$27 each) as I was given a pair to test with. They do what they say with minuscule voltage drops across them. Full disclosure, I am currently using two 1N5821 Schottky diodes in my panel right now (page 74 of my presentation) - small, simple, cheap, plentiful, robust, and easy to mount..

That being said - the availability of inexpensive ideal diodes has exploded in recent years mainly for use in systems like solar panel arrays. See https://www.ebay.com/sch/i.html?_fro...es%29&_sacat=0. I also like the increasing range of mounting styles available allowing for placement options behind our increasingly cramped panels.

One other comment: If you use diodes* (of any type) you can run two batteries in parallel safely. The danger was always been that without diodes, and with two batteries at different voltage output levels, that one battery could cross-charge the other. This could potentially happen without any current limit (!) until they equalize voltages. On a single bus with two batteries and diodes, the battery with the greatest voltage level would power the bus by itself until the separate battery's voltages equalized.

- John OHM Ω

* Teaching Moment - A diode only allows current to flow in one direction. In our case current will be limited to flowing from the battery to our avionics. As current flows through a diode there is a small voltage drop across the input to the output. We want to avoid, or limit, this voltage drop in our glider based power systems as we have no generating power source as found in airplanes.


I drew up a zero-loss battery switching circuit in a few minutes. It is based on 2 power p-channel mosfets. A dual opamp compares two battery inputs and selects the higher voltage by turning on its mosfet. Transient suppressors protect the circuit from voltage spikes. The total component count is 12 (16 if you want LED indicators). Send me a private email if you want a copy of the circuit.

Tom
 




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