Battery comparison for emergency light

[eem2am]

Hello,

We are designing an Emergency LED luminaire, and need to evaluate the battery technologies in terms of cost per mA.hr, size of battery, Cost of charger circuitry given that we have 18 hours in which to recharge, and battery lifetime.

(Emergency Luminaire must suppy 5W for 3 hours.)

We have only had info from SAFT so far, and to be honest, we know of no major competitors to SAFT. Do you know of any?

Also we are having difficulty getting pricing info.

We wish to evaluate and compare..

NiCd
NiMH
Li ion
Li polymer

i've read lots of articles but none seem that concise, wikipeida seems best but we cannot get the comparison from there.

 

[Harald Kapp]

Do you know of any?

How about this list?

but we cannot get the comparison from there

You'll have to specify the requirements in detail, then find suitable batteries and chargers (or charging technologies). Next get quotes for the selected components from major distributors (or wherever you buy) and add them up for each configuration. Lastly compare the results.

 

[KJ6EAD]

SLA (sealed lead acid) will be more economical than any of the battery technologies in your list, but it's not in your list. Why not?

 

[eem2am]

thanks, SLA too big

 

[(*steve*)]

Do you mean SLA is too big, or SLA is too heavy?

 

[eem2am]

Lithium ion batteries...scarce

hello,

For the last 5 hours i have been rummaging over the www to find the price of any Li-ion or Li-polymer battery in AA size with capacity of 2400mAH plus.

..but no luck, -either i am just dumb, or Lithium batteries are just not in the market yet.?

 

[CocaCola]

Don't you already have a thread about this? Of course you do...

https://www.electronicspoint.com/battery-comparison-emergency-light-t254488.html

Seriously, have you read any of Steve's warnings over the last week in regards to your horrible habit of starting a new thread every few hours for the same project?

hello,

For the last 5 hours i have been rummaging over the www to find the price of any Li-ion or Li-polymer battery in AA size with capacity of 2400mAH plus.

Google 'FR6 battery' or 'L91 battery' they are Li-FeS based and about 2900mAH @ 1.5V... *NOTE* not a rechargeable rated chemistry...

Or you can pick up the dime a dozen regular Li-Po 14500 sized batteries at about 900mAH @ 3.7V, and recharge at will...

or Lithium batteries are just not in the market yet.?

Been on the market for about 20 years now and have pretty much become the new standard in rechargeable batteries used in portable devices...

 

[Harald Kapp]

If I enter

Li-ion or Li-polymer battery in AA size with capacity of 2400mAH

in Google I get a whole bunch of hits.

Don't know what you are doing

 

[(*steve*)]

eem2am, I have yet to receive any acknowledgement that you have read my numerous warnings about starting new threads for no apparent reason.

The next time I have to merge two of your threads or close one because I'm too fed up to keep merging them I will ban you for a week.

 

[eem2am]

ok, my apologies, no more unecessary threads now , i promise that.

Regarding lithium, we need 2200mAh plus ....and rechargeable.

Lithium polymer batteries seem unavailable in the standard AAA, AA, C, D sizes.

Our boss want s us to look into Li-polymer for its small size.

Also, i am not sure if emergency lighting batteries have to be "qualified" for that use?

 

[BobK]

I suspect that they do not make LI Ion batteries in those sizes because people would plug them into devices that want 1.5V batteries.

Bob

 

[(*steve*)]

There are several standard sizes in LiPo batteries, there are also a plethora of non-standard ones.

The standard sizes are numbered according to their size. A 18650, or 16340, or 32650, or ... well things like that. You'll also find CR123A size and others.

Check the size and capacity. You can't just "magic" a certain capacity in a certain size -- they're proportional.

Beware of manufacturers claims of capacity. If it sounds to good to be true, ... you know the story.

 

[CocaCola]

Lithium polymer batteries seem unavailable in the standard AAA, AA, C, D sizes.

Did you bother reading my reply? I gave you specific examples, what part of that did you miss? Lithium is most certainly available and easy to find especially in AAA, AA , C and D sizes, you just need to actually apply yourself to looking... Most people go for an alternative flat pack design to get the run time, if run time is important...

Try this go to Ebay or Google and do a search for

'10440 battery' presto a plethora of AAA sized LiPo cells...
'14500 battery' presto a plethora of AA sized LiPo cells...
'26500 battery' presto a plethora of C sized Lipo cells...
'32600 battery' presto a plethora o D sized LiPo cells...

And there are a bunch of fill in sizes for specific applications as well that can be beneficial... The revolution must be lagging...

I suspect that they do not make LI Ion batteries in those sizes because people would plug them into devices that want 1.5V batteries.

They do, and sadly yes many dolts plug them in and then wonder why things don't work anymore... That or the LED flashlight guys brag about how much 'brighter' their flashlights are with those batteries...

One word of caution when doing this, sizes slightly vary from manufacture to manufacture as they have different protection board they affix to the end of the cells, thus the LiPo cells are sometimes a little bit longer then traditional cells, but in most cases will still fit in traditional holders, but not always...

 

[(*steve*)]

but in most cases will still fit in traditional holders, but not always...

Quite often the difference in length between "protected" and "unprotected" cells makes the difference.

In some cases the protected ones are a little too long for other than a *very* tight fit, and occasionally the unprotected ones are a tad short. I've heard of people buying come of the very thin disc shaped rare earth magnets as spacers in this case!

In your case, I'd probably recommend you get protected cells. It sounds like you don't have the skills to ensure correct charging. Whilst the protection won't stop you over charging or over discharging the cells, it will help prevent you from straying too far in this direction, and hopefully prevent a fire.

 

[eem2am]

Thanks, With your help, Li-ion batteries is not a problem now, and i have found loads as you said.

However, the boss has specifically asked for "Lithium Polymer" to be looked into.

I can find almost nothing on this.

The cell that we currently have is this one....(6V NiCd 4000mAh)

http://www.batterymasters.co.uk/Pro...h,-Emergency-Lighting-Stick-W-Leads_1919.aspx


...however, its very bulky, and the boss thinks that Lithium polymer (more so than lithium ion) is the way forward. This is the only lithium polymer one that i can find thats anywhere near our requirement, but it actually has too much capacity (we only need 3Ah at 7V4) so its not very good.............->

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

So it is the elusive lithium polymer situation which is racking our brains....we can find nothing.

Do you have any ideas?

 

[(*steve*)]

OK, now we are getting into the area of conflicting requirements. LiPo cells are generally flat rectangular things, not the cylinders that your boss also wants.

Another option is LiFePO4 which are slightly lower capacity than LiPo, far safer, and come in the package you want. They will apparently smoke, but not catch fire in situations where other Li technology would have you running for an extinguisher.

 

[CocaCola]

...however, its very bulky, and the boss thinks that Lithium polymer (more so than lithium ion) is the way forward. This is the only lithium polymer one that i can find thats anywhere near our requirement, but it actually has too much capacity (we only need 3Ah at 7V4) so its not very good.............->

I have to be blunt and asked, really... Seriously? How hard have you actually tried looking? As I eluded to above most people go to 'flat packs' for applications like this, and just like the cells you were asking for a few hours ago, there is a plethora of them to be found, even in lower mAH ratings, finding 2500-3000mAh is trivial easy... That is if you actually spend a few minutes trying to find them... I would give you links but at this point I feel that you simply want everyone else to do your job while you collect the paycheck...

 

[eem2am]

Thanks Steve, i'm glad you confirmed that, i did notice that i kept seeing low volume Lipo's but with large++ suface area due to flatness.......not what we want at all.

Coming back to Li-ion, i think we can appease the boss with this offering...

http://www.all-battery.com/li-ion18...rypackwithpcbprotectionandhitecconnector.aspx

....its actually too much capacity, but still the size is 70 x 55 x 18, much smaller than our NiCd solution (above).

One thing thats really foxing me is that this Li-ion pack actually works out cheaper than the NiCd solution we already have (above)......and i thought Li-ion was supposed to be expensive?

Anyway, regarding charging for this Li-ion pack, (it does have overvoltage circuitry in the pack), i am wondering if we can get away with constant current charging at 244mA?
...we'll continuously monitor the terminal voltage with a microcontroller and when it gets to 12V (4V per cell), we'll turn the current source off.

.....we are told that we loose 20% of the capacity by undercharging in this manner...however, the capacity of this pack is enough to be OK even if we are using only 80% of it.

....so do you think our charging regimen is ok?.....i dont want to explode the Li-ion pack.

 

[(*steve*)]

Charge them from a current limited, fixed voltage source (this is appropriate for anything except *really* flat cells).

Preferably get a pack that has circuitry to level the cells.

Having the microcontroller monitor the charge is a problem if it ever crashes. You'll end up with either over-discharged cells, or overcharged cells. Both are bad news.

If you're employing a watchdog timer and you're a good programmer, then the risk is less. However the basic charging circuitry is even simpler if you're not concerned with deeply discharged cells or the fastest possible charge.

 

[eem2am]

Preferably get a pack that has circuitry to level the cells

...i was worried to hear this.....i doubt that kind of circuitry is in most of these cell packs.....i hope we don't need it?.......is it more of a problem with Li-ion than NiMH and NiCd? (i.e. unequal voltages across the different series cells in a series pack)

Charge them from a current limited, fixed voltage source

.......that's going to be something of a problem in our set-up....there is no fixed voltage source........the 'maintained' LED current, and the battery charging current, are just constant currents supplied from current sources.......we can switch off (or rather divert into a short) the charger current, for when the battery is fully charged.

However the basic charging circuitry is even simpler if you're not concerned with deeply discharged cells or the fastest possible charge.

.........yes , we're definetely not interested in fast charging, we have 18 hours to re-charge the cells and intend to use all of it, with as low as possible (<C/10) charging current, ...thats why i am hoping we can get away with very simple on/off charging current source and simple uC voltage monitoring?