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A complicated question about LiFePO4 batteries, - and switching.



 
 
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  #41  
Old July 24th 18, 05:43 AM posted to rec.aviation.soaring
Andy Blackburn[_3_]
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Posts: 608
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.


John (OHM),

Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.

My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.

If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.

Andy Blackburn

9B
  #42  
Old July 24th 18, 03:09 PM posted to rec.aviation.soaring
Chris
external usenet poster
 
Posts: 25
Default A complicated question about LiFePO4 batteries, - and switching.

Thanks John OHM for putting this presentation together and for keeping it current!
  #43  
Old July 24th 18, 03:31 PM posted to rec.aviation.soaring
Dan Marotta
external usenet poster
 
Posts: 4,601
Default A complicated question about LiFePO4 batteries, - and switching.

In my last experimental glider I used two rather stout SPST toggle
switches to control my two LiFePO4 batteries.Â* At some point of the
flight I would switch the second battery on and then switch the first
battery off.Â* I don't think it was really necessary given the longevity
of these batteries compared with the SLAs that I used previously, I
simply switched about half way through the flight so that both batteries
would get some use.Â* I like John's idea with the MOSFETs.

On 7/23/2018 10:43 PM, Andy Blackburn wrote:
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.

John (OHM),

Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.

My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.

If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.

Andy Blackburn

9B


--
Dan, 5J
  #44  
Old July 24th 18, 04:31 PM posted to rec.aviation.soaring
2G
external usenet poster
 
Posts: 1,439
Default A complicated question about LiFePO4 batteries, - and switching.

On Tuesday, July 24, 2018 at 7:31:44 AM UTC-7, Dan Marotta wrote:
In my last experimental glider I used two rather stout SPST toggle
switches to control my two LiFePO4 batteries.Â* At some point of the
flight I would switch the second battery on and then switch the first
battery off.Â* I don't think it was really necessary given the longevity
of these batteries compared with the SLAs that I used previously, I
simply switched about half way through the flight so that both batteries
would get some use.Â* I like John's idea with the MOSFETs.

On 7/23/2018 10:43 PM, Andy Blackburn wrote:
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.

John (OHM),

Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.

My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.

If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.

Andy Blackburn

9B


--
Dan, 5J


Here is a demo circuit board you can buy that does pretty much everything:

http://www.analog.com/en/products/mo...-evaluationkit

Tom
  #45  
Old July 24th 18, 05:05 PM posted to rec.aviation.soaring
OHM Ω http://aviation.derosaweb.net
external usenet poster
 
Posts: 147
Default A complicated question about LiFePO4 batteries, - and switching.

On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
In my last experimental glider I used two rather stout SPST toggle
switches to control my two LiFePO4 batteries.Â* At some point of the
flight I would switch the second battery on and then switch the first
battery off.Â* I don't think it was really necessary given the longevity
of these batteries compared with the SLAs that I used previously, I
simply switched about half way through the flight so that both batteries
would get some use.Â* I like John's idea with the MOSFETs.

On 7/23/2018 10:43 PM, Andy Blackburn wrote:
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.

John (OHM),

Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.

My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.

If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.

Andy Blackburn

9B


--
Dan, 5J


Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?

I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.

For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).

On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".

YMMV. Be careful out there.

- John OHM Ω
  #46  
Old July 24th 18, 05:13 PM posted to rec.aviation.soaring
[email protected]
external usenet poster
 
Posts: 465
Default A complicated question about LiFePO4 batteries, - and switching.

On Tuesday, July 24, 2018 at 12:05:18 PM UTC-4, OHM Ω http://aviation.derosaweb.net wrote:
On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
In my last experimental glider I used two rather stout SPST toggle
switches to control my two LiFePO4 batteries.Â* At some point of the
flight I would switch the second battery on and then switch the first
battery off.Â* I don't think it was really necessary given the longevity
of these batteries compared with the SLAs that I used previously, I
simply switched about half way through the flight so that both batteries
would get some use.Â* I like John's idea with the MOSFETs.

On 7/23/2018 10:43 PM, Andy Blackburn wrote:
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.

John (OHM),

Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.

My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.

If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester).. I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.

Andy Blackburn

9B


--
Dan, 5J


Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?

I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.

For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).

On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".

YMMV. Be careful out there.

- John OHM Ω


With two SLA batteries that are in good shape it probably won't blow any fuses. The danger is if one battery goes bad, e.g., one of its six cells shorts out, so it effectively becomes a 10 volt battery. This happens fairly often in SLA batteries that are quite old. Then the good battery will keep sending current into the bad one, wasting its energy, and potentially causing the bad one to burst. You can minimize the chances of problems by only using fairly new batteries (say under 4 years old) and only as a matched pair of the same size/brand/age. LFP batteries typically have protection circuits built in that would prevent major issues like that, but why take chances? Schottky diodes are cheap enough.
  #47  
Old July 24th 18, 05:48 PM posted to rec.aviation.soaring
John Godfrey (QT)[_2_]
external usenet poster
 
Posts: 321
Default A complicated question about LiFePO4 batteries, - and switching.

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...
  #48  
Old July 24th 18, 05:52 PM posted to rec.aviation.soaring
John Godfrey (QT)[_2_]
external usenet poster
 
Posts: 321
Default A complicated question about LiFePO4 batteries, - and switching.

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...
  #49  
Old July 24th 18, 06:28 PM posted to rec.aviation.soaring
kinsell
external usenet poster
 
Posts: 546
Default A complicated question about LiFePO4 batteries, - and switching.

On 07/24/2018 10:05 AM, OHM Ω http://aviation.derosaweb.net wrote:
On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
In my last experimental glider I used two rather stout SPST toggle
switches to control my two LiFePO4 batteries.Â* At some point of the
flight I would switch the second battery on and then switch the first
battery off.Â* I don't think it was really necessary given the longevity
of these batteries compared with the SLAs that I used previously, I
simply switched about half way through the flight so that both batteries
would get some use.Â* I like John's idea with the MOSFETs.

On 7/23/2018 10:43 PM, Andy Blackburn wrote:
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.

John (OHM),

Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.

My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.

If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.

Andy Blackburn

9B


--
Dan, 5J


Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?

I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.

For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).

On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".

YMMV. Be careful out there.

- John OHM Ω


In one of the many previous incantations of this discussion, the same
claim was made about huge currents flowing between a charged and
discharged SLA. At my urging, the claimant actually tried doing that
with an ammeter. Didn't see even a flicker of the needle.

You know how you have to apply 14 volts to charge up a 12 volt battery?
A charged battery sitting at probably 12.6V has basically no capability
of charging a moderately discharged battery.

Switching to lithiums, maybe they have current limiting, maybe they
don't. RIchard P shorted one out, the terminals got hot enough to melt
the case in that area. Doesn't sound like much current limiting going
on to me.

Talking to a pilot who just switched to lithiums, he was touting how
great the current limiting feature was. I asked if he ever shorted the
terminals on purpose to test it? Well no. Would he be willing to try
that? Again no. If you really believe you have limiting, then go ahead
and put the wrench across the terminals just to satisfy yourself. Film
it for use on YouTube, just in case.

-Dave

  #50  
Old July 24th 18, 10:10 PM posted to rec.aviation.soaring
Dan Marotta
external usenet poster
 
Posts: 4,601
Default A complicated question about LiFePO4 batteries, - and switching.

Thanks John,

These were lithium batteries and, yes, they were fused at the battery.Â*
As I recall, I used 5 amp fuses, no diodes, and never blew a fuse.Â* Read
these words out loud:Â* On, Off.Â* That's how long it took to switch
batteries.Â* I know that's not best practice, but it worked...Â* That was
on my previous glider which was experimental. My current glider has
Standard certification and it has a factory installed toggle switch
which is labeled:Â* Main and Aux.Â* I don't know if it's a make before
break switch but I've never had any electronics waver during switching.

On 7/24/2018 10:05 AM, OHM Ω http://aviation.derosaweb.net wrote:
On Tuesday, July 24, 2018 at 9:31:44 AM UTC-5, Dan Marotta wrote:
In my last experimental glider I used two rather stout SPST toggle
switches to control my two LiFePO4 batteries.Â* At some point of the
flight I would switch the second battery on and then switch the first
battery off.Â* I don't think it was really necessary given the longevity
of these batteries compared with the SLAs that I used previously, I
simply switched about half way through the flight so that both batteries
would get some use.Â* I like John's idea with the MOSFETs.

On 7/23/2018 10:43 PM, Andy Blackburn wrote:
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.

John (OHM),

Yup, I have one of Shaun's (on your recommendation) and some of the anti-revere-irrigation ones. I haven't installed either.

My current install uses the Schleicher rotary switch to select: Battery 1, Battery 2, Battery 1+2 (through diodes), Battery 3 (tail). I use a bank of capacitors connected through a power resistor to energize the circuit when the switch is between batteries.

If I had to do it again I would use ideal diodes (though as others have mentioned this is really not nearly a necessary with LiFePO4 batteries since they go through voltages below 11v quite quickly on my battery tester). I would also separate the batteries to individual switches to eliminate the switch as a single point of failure.

Andy Blackburn

9B

--
Dan, 5J

Dan - Do you have diodes in this circuit to prevent cross-charging of the batteries?

I will repeat something I said above that (without diodes) putting the batteries in parallel can cause a large current to flow from the "high" battery to the "low" battery. Effectively one battery is charging the other.

For dumb SLA batteries this will almost certainly blow the fuse on your batteries (you do have a fuse right at your battery's positive terminal, right??).

On lithium batteries, which probably have intelligent current limiting electronics inside, this should not be an issue. But notice the words "probably" and "should".

YMMV. Be careful out there.

- John OHM Ω


--
Dan, 5J
 




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