Primary lithium battery protection and vented gas

[blackrooster]

We are working on preparing a battery powered medical device for FDA and I am currently going through 60601-1. It is a 3V primary LiPo battery that has UL 1620 and IEC 60086-4. We have reverse polarity protection and a fuse on our PCB but there is nothing on the battery itself.

Is it typical that I should be looking into having the battery supplier provide some protection at the battery terminals or is this overkill? I have been trying to read about it but everything seems to talk about secondary rechargeable batteries.

I thought the battery was ok due to the approvals but now I am reading about 15.4.3.5 which basically says to assess the risk of a short between the fuse and the terminals. I tested the short circuit of a couple batteries and they both vented after several minutes. It seems that I need to consider the risk of this gas emission. I don’t know how to mitigate it except to make sure it can never happen which leads me back again to the protection on the battery terminals.

I welcome any comments on expected protection of primary lithium batteries or how to manage the risk of toxic gas from the battery.

 

[Ronen E]

Hi,

I can't help you too much with the specifics, but if you scroll down in this page you'll get to a section titled "similar discussion threads". Those threads might have valueble information for you. I do vaguely remember we had some discussions related to risks associated with battery venting.

You could also use the "search Elsmar" box at the top, to get more relevant threads.

Cheers,
Ronen.

 

[Pads38]

Clause 15.4.3.1 (Housing) would suggest that your battery housing needs to be ventilated and designed to avoid short circuits.

Then, 15.4.3.5 details requirements for fusing and a short circuit test. But if you check the rationale (Annex A) for this clause, it shows that if you provide 2 MOOP between your battery positive and negative (say - on your PCB tracking) then the short circuit test is not needed.

(Single fault condition - SFC - would be a short circuit of one MOOP not 2).

Creepage distance to give 2 MOOP at 3V = 1mm (Pollution degree 2, no altitude factor)

 

[blackrooster]

Ronen,

Thank you for the comment. I did look at a lot of the old threads and there is good discussion but I couldn’t find an answer to my specific questions.

To restate my questions for anyone reading this (hopefully someone else has made a device with a lithium battery):

1) What protection (if any) is typical on at the terminals of a primary LiPo battery? For example, on secondary batteries it is easy to find descriptions of PTC, fuses, or other protective circuitry at the battery terminals. But what about primary batteries?

2) How does anyone deal with the hazard of toxic gas other than prevention? I understand the need to vent the enclosure to prevent buildup, but then isn’t there the risk of inhalation?

 

[blackrooster]

Pads,

Thank you for the reply. I have some more questions if you don’t mind.

I saw the part about 2 MOOP but I get confused about how to apply creepage and clearance as means of protection. I agree with you that the creepage value is 1mm. For this application, the battery has a couple wires terminating in a connector. So as long as the creepage within the connector, header, and traces for battery positive & negative are >=1mm it is considered to have 2 MOOP? Does it count even if the air clearance is not 2mm (looking at table 13)?

Also, let’s assume that I claim 2 MOOP on this part of the circuit but I know that there will be a venting condition if the battery shorts. Is this still something that needs to be covered in the risk assessment? Or is it enough to say that there is no hazard because there can be no short condition?

 

[Pads38]

The MOOP requirements are needed only between your battery and the fuse (or other protection. See the diagram in the rationale, Annex A.

Your required Clearance is 0.8mm - Table 15 (Table 13 is for clearances from Mains parts).

If you meet the requirements for 2 MOOP the fault condition of a short circuit occurring between the battery and the fuse may be assumed to not occur.