Primary lithium-thionyl chloride battery in a sealed enclosure - Hazards?

[nub12]

We're working on a project that will have a D cell lithium-thionyl
chloride primary cell sealed up in a small IP67 enclosure.


I was wondering if enclosure venting was needed in case of catastrophic
failure of the battery. As I understand it these primary cells are well
behaved and don't present a risk.

Thoughts?


If it matters its a 3.6V Saft LSH 20 D-size spiral cell.

Thanks

[Allan Herriman]

I've had multiple designs with lithium-thionyl chloride cells get through
UL (and various other compliance) tests.
Mine were smaller though; 2/3 AA vs your D. Also, the enclosures weren't
sealed.


The impression I got from the tests was that basically they didn't care
as long as a few conditions were met:

1. There must be a reliable way of making sure the charging current is
never greater than the datasheet max value (assume 0.0uA if one isn't
specified).

2. The maximum discharge current is limited. I think that might be more
related to temperature rise rather than current per se.

3. The temperature range was limited.

4. There is no chance of mechanical penetration.


Note that those tests may be performed with a specified number of faults
(typically one) active.

Example 1. You need to meet the reverse current spec with your reverse
current protection diode shorted out.

Example 2. If you have a DC/DC converter on the board (it might be
unrelated, but still thermally coupled), give it a reasonable current
limit, which will control temperature rise when a short circuit happens.


Also, if using e.g. current limiters, using ones that already have UL
recognition may make your own approval process easier.


Your test lab may have different ideas. Talk to them.

Regards,
Allan

[nub12]

Thanks for the detailed response Allan. There's some good feedback there
for me to work on.

[Mikko OH2HVJ]

Hi,

nub12 <nu...@null.com> writes:

> I was wondering if enclosure venting was needed in case of
> catastrophic failure of the battery. As I understand it these primary
> cells are well behaved and don't present a risk.

> If it matters its a 3.6V Saft LSH 20 D-size spiral cell.

In my experience the LSH20 is extremely stable, I've only seen a few failures
while running a few billion hours with these cells. These required
rather extreme circumstances to happen, though.

What kind of environment (temperature range, any moisture ?) and load
profile do you expect ?

--
mikko

[nub12]

Dry environment inside a small IP67 ABS enclosure.
Temp range could be anything from -10C to +60C

Most of the time its asleep drawing microamps, when it wakes it may draw
100mA or so for 10 to 20 seconds.

[jrwal...@gmail.com]

I worked with similar cells some years ago and came across one issue. If
the cell has been "sleeping" for a long time and is then suddenly called
on to deliver a lot of current the internal resistance may initially be
higher than usual.

John

[Mikko OH2HVJ]

nub12 <nu...@null.com> writes:

>> What kind of environment (temperature range, any moisture ?) and load
>> profile do you expect ?
>
> Dry environment inside a small IP67 ABS enclosure.
> Temp range could be anything from -10C to +60C

Sounds safe, our problems have been mostly with even hotter cells
getting some mechanical shocks with high power load.

> Most of the time its asleep drawing microamps, when it wakes it may
> draw 100mA or so for 10 to 20 seconds.

Sound like a long lifetime application. Take care of the cell
passivation, the voltage can drop quite a bit if you have long
inactivity period if the load comes online fast.

--
mikko