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Care of Lithium Polymer Batteries


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#1 r4e

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Posted 21 April 2012 - 12:10 PM

I just become the proud owner of a secondhand Salvo 200W HMI lamp with Lithium Polymer battery canister. Unfortunately there was no instructions manual available.

After searching through Google and Wetpixel, I am aware of a number of general Lithium safety concerns and would want to take these into account:

1) Storage of batteries: should not store empty nor fully charged? I have seen recommendations of 60-70% charge for storage and that anything else will seriously reduce lifetime of batteries. Should I now estimate discharge during use, then attempt to charge after the dive to a "60-70%" level, but not full, and, just before the next dive, charge the remainder?

2) Should never over-discharge to less than 10% of capacity? The Salvo has an automatic cut-off function. Is this sufficient or should I attempt to stop using the lamp after 80% burntime?

3) Some sources claim that Lithium Polymer Batteries age quickly and loose 10-20% capacity per year. Some other sources recommend removing from service any LiPo batteries that have lost 20% of their capacity. Before the purchase, I made a burntime test in cold water and achieved 67 minutes at full 200W power, which is within 95% of manufacturer specs. I guess I am safe for atleast a year?

4) I have seen recommendations that LiPo batteries should not be charged closer than 2m from any flammable materials, nor within or close to living spaces and that one should watch the entire charge process and never leave the battery unattended. Seriously? My only option would be to spend five hours of so in the cold basement watching. This is hard to believe. My laptop, mobile phone and camera have also Lithium batteries and I have been fast a sleep whilst charging these.

5) Many sources recommend charging the cells separately because chargers might not identify individual failing cells if they are in parallel or in series. With the one-piece battery canister this does not seem like an option.

Any comments on these? What are your recommendations?

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http://www.cerella.fi for the Underwater Photographer and Videographer

 


#2 Undertow

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Posted 25 May 2012 - 11:42 AM

I've just been reading about LiPo's for a different application due to their low weight.

Indeed LiPo's are in a lot of portable devices. I believe they all have protection circuits built in. I would imagine the Salvo pack should also have one built into the battery pack itself. This will be sufficient to avert over discharging the batteries. A single LiPo cell is 3.7 volts and should never be discharged below 3V. Full charge on a 3.7V cell is 4.2V, but even the slightest over charging will damage the cell. The charge current should not exceed its capacity (i.e. a 2200mAh battery should be charged at 2200mA max). Chargers should be very specifically designed to do all this.

I don't think they're inherently dangerous but they should be kept away from anything flammable. If they do ignite, they simply catch fire, they don't explode. I have read of LiIon batteries exploding (18650 batteries) during charging. However this is a non-proprietary battery with a non-proprietary charger. I think the warnings behind LiPos are conceived around this non-proprietary concept. LiIons are also hard shelled, which could build pressure, but LiPos are soft shelled. If you puncture a soft shell LiPo it will likely catch fire, ive done it before :P

Any manufacturer that builds this battery into their product and includes an appropriate charger (like your laptop) should have enough necessary protection built into the system, including physically protecting the soft battery itself. LiPos are used a lot in the R/C heli & plane world due to their low weight. The issue there is customization, the batteries are not built into the system by the manufacturer, but by the consumer. Therein lies the safety risk as appropriate charging, discharging, physical protection etc is up to the consumer.

I'm not sure where the Salvo would fall in there, it would obviously be designed to work appropriately within the proprietary system, though they're possibly not as fool-proof designs as, say a big laptop manufacturer.

A quick search about storage charge says 3.85V (per cell) is ideal and should never drop below 3.5V (at rest is equivalent to 3V under load). They say store at full charge (4.2V) for no more than 4 days. Cheers,

Chris
D200, Aquatica, 10.5, sig 15, 12-24, 17-55, 60, 105
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#3 r4e

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Posted 28 May 2012 - 05:57 PM

Chris, thanks for the info. The four day max recommendation was an interesting detail.

I am now experimenting with a NATO grenade box for containing the battery whilst charging it. I might still line the inside of the box with some ceramic tiling. This will be a precaution for a long boat trip where there will be no other option than to charge the battery on the deck.

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http://www.cerella.fi for the Underwater Photographer and Videographer