Experimental sailplane self-launch electric conversion

HomeBuiltAirplanes.com

Help Support HomeBuiltAirplanes.com:

John.Roo

Well-Known Member
Joined
Oct 8, 2013
Messages
329
Location
Letohrad / Czech Republic
So what is your plan in advent of a thermal runaway event?
First - prevention
As reperated many times - we try do not overload the cells. Low discharge "C" means that you can keep the cells not even warm. I am carefully watching temp. on cells to see if there is not temp. increase. 30-40°C is max.

Second - monitoring
You have to know temp. on each battery pack. It means if you have for example 27S 5P you need 27 temp. measuring points. All time monitoring is necessary. When temp. raise above 40°C, you need to know it. Some of my friends are flying with battery temp. arround 50°C and from my point of view that is already a lot. This is valid for discharging as well as for re-charge.

Third - emergency cooling
Of course you can still have problem with damaged battery cell. As prevention try to do not manipulate with batteries unless is necessary. As you can see - I am not a fan of removable battery packs. There is always risc of mechanical damage etc. They are existing high pressurized plastic tubes able to cool down the battery packs. We don´t have this system actually installed, but is under testing. It is emergency system able to give you time reserve to make emergency landing.

From Wiki
Most lithium-ion (Li-ion) cells must not be charged above 45°C or discharged above 60°C. These limits can be pushed a bit higher, but at the expense of cycle life. In the worst case, if cell temperatures get too high, venting may occur, resulting in battery failure or even a cell fire.
 

dog

Well-Known Member
Joined
Dec 29, 2019
Messages
276
also, most thermal runaways happen during charging,many thermal runaways occur after mechanical damage or electrical misuse.
Care will iliminate most problems.
The lithium sulfer and lithium iron batterys are better than the strait lithium ion,when it comes to thermal runaway.
Lithium /titanium is almost imune to this and is the battery of choise in Japan.
The problem of thermal runaway stems from the cell seperators failing,lots of attention there right now.Hardley an insermountable issue.
 

opcod

Well-Known Member
Joined
Aug 28, 2010
Messages
51
Location
Canada
Having a pre-heating module to warm up the batterry before recharge do help to increased the batterry life expectancy.
 

blane.c

Well-Known Member
HBA Supporter
Joined
Jun 27, 2015
Messages
3,848
Location
capital district NY
First - prevention
As reperated many times - we try do not overload the cells. Low discharge "C" means that you can keep the cells not even warm. I am carefully watching temp. on cells to see if there is not temp. increase. 30-40°C is max.

Second - monitoring
You have to know temp. on each battery pack. It means if you have for example 27S 5P you need 27 temp. measuring points. All time monitoring is necessary. When temp. raise above 40°C, you need to know it. Some of my friends are flying with battery temp. arround 50°C and from my point of view that is already a lot. This is valid for discharging as well as for re-charge.

Third - emergency cooling
Of course you can still have problem with damaged battery cell. As prevention try to do not manipulate with batteries unless is necessary. As you can see - I am not a fan of removable battery packs. There is always risc of mechanical damage etc. They are existing high pressurized plastic tubes able to cool down the battery packs. We don´t have this system actually installed, but is under testing. It is emergency system able to give you time reserve to make emergency landing.

From Wiki
Most lithium-ion (Li-ion) cells must not be charged above 45°C or discharged above 60°C. These limits can be pushed a bit higher, but at the expense of cycle life. In the worst case, if cell temperatures get too high, venting may occur, resulting in battery failure or even a cell fire.
This is a good system for you. But what about the starving masses? You are bound to sell, despite an abundance of caution, an aircraft to a complete moron. Despite my personal beliefs in social Darwinism the persons family probably loves the idiot. How does it escape from its own folly? Bail-out? Or?
 

John.Roo

Well-Known Member
Joined
Oct 8, 2013
Messages
329
Location
Letohrad / Czech Republic
You are right - serial production is diferent from homebuilt construction. However most important recommendations (do not overload cells durign charge and discharge and try to avoid mechanical damage) are not that much affecting propulsion price. It is more about technical decissions at the beginning.
Temp. measuring is also not so expensive - only you will not use that many measuring points. By the way - some balancers have temp. measuring feature included and balancers you need anyway.

I am also looking for cheaper solutions - my dream is simple electric one seater, ideally in 115 /120 kg EW category :) But from other point of view I had already enough emergency landings so I try to precede problems - at least already known problems.

Beautifull example - this pilot/designer is using LiFePO cells and solar panels.


The only problem is very limited capacity due to LiFePO weight = high discharge rates during T/O and here is possible result
https://pubs.rsc.org/en/content/articlelanding/2018/ra/c8ra04074e#!divAbstract
Positive is a very low price of cells.

So again.... I can share my experience but finally is choice on the designer/owner/pilot decission (and personal bravery) :)
 

dog

Well-Known Member
Joined
Dec 29, 2019
Messages
276
Beautifull example - this pilot/designer is using LiFePO cells and solar panels.


The only problem is very limited capacity due to LiFePO weight = high discharge rates during T/O and here is possible result
https://pubs.rsc.org/en/content/articlelanding/2018/ra/c8ra04074e#!divAbstract
Positive is a very low price of cells.

So again.... I can share my experience but finally is choice on the designer/owner/pilot decission (and personal bravery)

The data in the link posted are for charge/discharge cycles over 2000 times,with the "damage" becoming significant over 500 cycles,
testing was done on many cycles per day.
Fly a lot?
Also testing strait lithium ion,not the newer variants, with sulfur or iron.
This is significant for a daily flyer but ,meaningless for an ocasional weekender.
Other factors will be more significant to performance and safety.
Personaly I would not buy from any battery "maker" without a very good idea of where the cells come from, have they been load and impedence matched,is the charger capable of sofware updates,have they done TTD testing,and knowing exactly how the "fault" diagnosis determines when to shut the batterys down for "safety",etc,etc, a before buying check list!
 

proppastie

Well-Known Member
Log Member
Joined
Feb 19, 2012
Messages
4,418
Location
NJ
Does % discharge (50 % for example ) effect performance or life?
 

John.Roo

Well-Known Member
Joined
Oct 8, 2013
Messages
329
Location
Letohrad / Czech Republic
Does % discharge (50 % for example ) effect performance or life?
Discharge rate "C" affects life of cells (and safety).
For example... 10 kWh battery and discharge rate C=5 means you take 50 kW of power from battery. In this case you will have probably problem with battery temp.

Capacity 50% can affect available power.
For example....
Fully charged battery give you 50 kW of power.
If you have remaining 30% of battery you may not have available 50 kW but only 30 kW. Very important to know this in case you are on final with low capacity because probably you will have not enough power for T/O. Is good to check how available power drops down with decreasing capacity during ground testing. This is different for different battery size and cells type.
 
Top