Reviving an LED Lantern

[fridgerova]

Hi there,

Please don't laugh but I might have the dullest idea you've read today. Nevertheless, i'd appreciate any advice you can give me.

I found an old LED lantern that i'd like to revive and make functional again. It is probably at least 5 years old that i picked up from a Canadian Tire store.
It uses a lead acid which I haven't charged in probably good 3 or more years. On top of that, I've lost the power charger to actually charge the lantern.

A few pictures:
Lantern: http://i.imgur.com/aQbgTJm.jpg
Battery: http://i.imgur.com/O6W8XL7.jpg , http://i.imgur.com/NSrpKd7.jpg
LEDs: http://i.imgur.com/Y6rzdV7.jpg

Questions:

1. I used multimeter on the battery and i got 0.666V. Aside from the fact that its telling me its down right evil , is it possible to revive it? Nosferatu battery! I figure I could probably try and find a replacement if it's really dead. But then how would I charge it, which brings me to question #2.
http://i.imgur.com/5Dpo4W6.jpg

2. How can I find out what DC charger it requires? Could I try find a close match 6V, 4Ah? or make my own? I am very new and yet willing in the realm of electronics, heavens help my cause.
The internet is pretty empty as far as finding specs for this cheap, old, forgotten piece of technology
http://i.imgur.com/5aQxf2A.jpg

3. Would using say 2,3 or 4 18650 Li-Ion batteries instead be a good idea? I have 4 spare 2600mAh 3.7V ?
http://i.imgur.com/8Z17Z27.jpg


Again, advice welcome

 

[cjdelphi]

you need 7.5v to charge this battery....

chances are you'll have standard 5mm leds to power..

2 lithiums in series would supply over 8v possibly damaging the circuit, an ldo at 7v might be an option. ..

 

[fridgerova]

Thank you very much for the reply.
Are you saying the battery CAN be charged after all this time and not totally dead?
Also, what is ldo?

 

[cjdelphi]

ok, shake the 6v battery...

if you hear rattling noises, bin it...

if you hear liquid swishing about, then you might be ok, a slow charge of a couple hundred ma over night (as simple as a resistor from 7.5v) first time charge...

it's difficult to say without specialist tools, normally you'd put a decent load on it and measure the voltage drop...

 

[fridgerova]

Thank you, I will try finding some sort of charger that fits that category, though 7.5 sounds pretty specific.
Tried shaking it, no sounds at all haha, its evil!

 

[cjdelphi]

any 12v charger will do, then use an lm2596 or lm317 to fine tune it (lm317 is cheaper but less powerful so to speak .. up to 500ma from 12v is about the limit with a small heatsink...

 

[cjdelphi]

wait..no sound? the electrolyte has dried, you might be lucky enough to get inside to top it up...

stick with the lithium idea

 

[fridgerova]

Heh, I am now not sure whats easier, considering my extremely limited knowledge when it comes to electronics.
Ok, this will sounds ridiculous: lm2596 to solder into the existing circuit?
If I go the lithium route (2x 18650), i'd have to regulate to 7.5 in a similar fashion, correct?

 

[cjdelphi]

the lm2596 is a simple switching regulator which set to 7v would chage your battery nicely... ideally you'd need a current adjust circuit to to prevent the battery getting > 1.5a max current surge on a 6v lead acid...

but since you want to use lithiums, you'd need to keep a nice steady 6v to the lantern, again the lm2596 would do that just fine from lithiums...

basically what i'm saying is there are a lot if options, charging the lithiums may prove tricky too..

2 4.3v cells in series gives 8.6v.. but you can't charge batteries in series you'd need to charge each cell independently ..

i guess it's a question of what you need ...

 

[AnalogKid]

That is an industry standard battery available from Batteries Plus, DigiKey, Mouser, etc. 6V, 4 A h. Without have a datasheet, I'd say the normal max. charging current is C/10, or 400 mA. I would limit the charging current to 50-100 mA to be safe until you know how it is responding. If you are using just a wall wart and a series current limiting resistor, 12 V is too high for unattended operation. But for only an hour, a 12 V ww and a 100 ohm, 1 W resistor should be enough to see if the battery will wake up. Measure the voltage drop across the resistor to determine the charging current.

A series-parallel arrangement of the 4 Li batteries with some diodes will work, but the LEDs will be brighter than with the SLA battery and the current limiting resistors will run hotter. Looking at the amount of air space around the current limiting pc board, it looks ok try. Run the LEDs on the Li batteries for one minute, feel the resistors and see if they take your skin off, then make an evidence-based decision.

Not sure about that sound thing. We use the same battery type made by PowerSonic, and they never squish.

ak

 

[AnalogKid]

Just a moment...just a moment... Let's look at the pc board again. Given the presence of the diodes and the single 330 resistor, here's my guess:

The power jack in the middle of the board is for an AC wall wart, just a transformer with wires. The diodes rectify the AC for charging and prevent reverse polarity operation. 330 ohms is the charging current limiting resistor. With that large a current limiter, the transformer could be 12 V AC output or more, which would be about 30 mA peak current, large enough for slow charging and low enough for a float connection. The 2.4 ohm resistors could imply 5 LED strings, but there are four LED pc boards in the lamp and only one source wire going to them. That implies a parallel connection for 0.48 ohms or some series-parallel combination. This probably is to limit the short circuit current in the wiring up to the top of the lantern where the LEDs are. The LED array could be 28 LEDs each with a current limiting resistor, all in parallel. At 20 mA per LED, that's 0.56 A, so you would get 6-7 hours of operation out of a good, charged battery. Or there's a switching power converter up there for better efficiency.

BTW, great photos. Flip over the pc board for one more.

ak

 

[Alec_t]

If you're new to electronics I'd caution against using the lithium batteries for this or any other project. Unless their charging and discharging are properly controlled they can catch fire or EXPLODE. Take a trip to www.batteryuniversity.com and check out battery charging arrangements for SLA and lithium batteries.

 

[fridgerova]

Wow, thanks so much for such amazing info guys! I am a bit overwhelmed with the information here but I am taking it slow one thing at a time.
I will take the suggestion and not mess with lithium batteries because i am just too new and rather keep my limbs intact haha!
So:

Step #1: Try reviving this existing battery by employing the lm2596 to make it work with a 12V adapter , since i have a few laying around. Though, of course, they all vary in the amp output, so i'd need to limit that.
By the way, I am way over my head here. I can solder 2 wires together, but that's a bout it Yes, it definitely makes me pretty stupid in this field. Again, I am optimistic, reading/learning skill comes in handy.
Step #2: If charging yields no results and the battery is indeed toast, I will invest into getting a replacement 6V 4Ah battery, as suggested, BUT I still need a charger which will be available if I am successful in Step #1

Thanks for bearing with me

A few more pictures of the bottom and top circuit boards:

Bottom
Bottom (opposite side)
Top
Top (opposite side)

 

[cjdelphi]

swish as in you can hear the electrolyte. i've never had a sealed lead acid you can't hear liquid from... unless it's a dry cell?