Battery comparison for emergency light

[(*steve*)]

If you have a current source then you can get whatever voltage you want. No problems.

Cell levelling (or at least cell monitoring) is only needed if you want reliability and safety from things like battery fires.

 

[eem2am]

Thanks Steve, and since Lithium "cells" are far more sensitive to overvoltage than NiMH or NiCd "cells", i suspect that individual cell voltage monitoring in a series stack is far more important in lihium batteries than in NiMH and NiCd batteries?


...but the problem with NiMH batteries is that its not possible to slow charge them at rates of 0.1-0.3C, as the following describes....

I am baffled at the sixth paragraph down of the following web page from batteryuniversity.com, which states that it is impossible to charge NiMH at slow charge rates...............

http://batteryuniversity.com/learn/article/charging_nickel_metal_hydride

It is difficult, if not impossible, to slow-charge a NiMH battery. At a C‑rate of 0.1 to 0.3C, the voltage and temperature profiles fail to exhibit defined characteristics to measure the full-charge state accurately and the charger must depend on a timer. Harmful overcharge will occur if a fixed timer controls the charge. This is especially apparent when charging partially or fully charged batteries.

.....surely this cannot be right?.......if charge is going in, even if only slowly, then surely the battery is charging up?

 

[BobK]

Yes, surely the people at Battery University know less about it than you do...

Did you read the paragraph above the one you quoted? They can be trickle charged at 0.05C. If you allow about 50% overcapacity, you could recharge at 0.05C in 18 hours.

Bob

 

[eem2am]

Thanks, but "50% overcapacity" sounds like a battery full to the brim and ready to explode?

 

[(*steve*)]

When it comes down to it, LiPo are just easier to manage.

My recommendation would be to get a single large cell. This can be very easily charged (no issues with multiple cells). Then use a boost SMPS to get *exactly* the voltage you require.

 

[eem2am]

so do you think that Lithium Polymer batteries like this, which feature an internal protection PCB, are still not safe from fires?...

http://www.all-battery.com/74volt-5500mahli-polymerpackwithpcb.aspx

 

[CocaCola]

Safer yes, 100% safe no... Tap into some of the revolutionary design knowledge and build a safe design to minimize potential issues...

I would have thought the page you linked was clear... I highlighted a few parts...

Caution:
Improper use like overcharging and over discharging can cause explosion and/or fire. User of the battery is required to have the sufficient Li-polymer charging experience and technical knowledge. Tenergy or All-Battery.com are not responsible for any damage or injury caused by misuse, misunderstanding or abuse of this product.