Lighter weight replacement for 12v SLA brick battery

[Avatar28]

One of my fellow cavers built a homemade light using a 20W 12v tracklight spot bulb fit into a length of PVC pipe. It is powered by a 12v SLA brick (that JUST fits inside a fanny pack). He loaned it to me awhile back on my last trip but I found that, more than anything, it was extremely heavy and got rather uncomfortable after sitting against my hip for awhile.

That got me to thinking on how that light could be improved upon. I know that battery technology has come quite a way lately. I figure that if anyone knew how to come up with a battery pack that could replace that SLA brick it would be you guys.

So is there a battery pack that I can buy or make that would give me the same or better performance than an old SLA brick or is SLA still going to be the way to go for high current capacity?

 

[scott.cr]

What's the capacity of the battery?

BTW, if you overdrive that lamp you'll get a lot more output and better efficiency at the expense of lamp life. Most of those household-type MR16s are rated at 3,000 hours life, if you overdrive to, say, 16 volts, output will increase by roughly 2.5x and efficiency increases roughly 75%. The lamp will consume more power, but with the increased efficiency you will get more lumens per watt.

Back to the original question...

So what's the budget for the new battery? You could get a lithium polymer pack but that will easily run $150+. But you can get them built to a variety of voltages. Another method is to run a string of 18650s but that can also get expensive. With the 18650s you will also have to keep the "2C" current draw limit in mind; if you are running a 100 watt lamp that means also running a double-stack of 18650s. A four-cell double stack (8 cells total) can be $80 if you buy the $10 LG 18650s.

 

[matrixshaman]

I'm haven't done much caving but I think a lot of people here who do would use a combo of lights and would use some of the new very effecient LED's running from rechargeable batteries like the 18650 to get a LOT of light as well as good runtime. I'd likely carry 6 to 12 of these batteries as backups for my main light and that would still be way less weight than a 12 volt SLA. I don't know right off if any headlamps run from 18650's but at 3.6 volts I'm sure they could be substituted with some fanagling for lights that run from RCR123's.

 

[NeonLights]

It would help to know the weight and capacty of the existing battery. I've put batteries as light as a 6.5 lb AGM battery in a car before. That battery was a "Magnapower" brand that was bought locally at a Meijer store for around $55. Started the car (a Miata) just fine.

 

[Avatar28]

I don't remember the exact capacity, which is why I didn't post it. I believe it was maybe a 5 amp-hour but I'm not certain now.

I don't have a specific budget in mind. At the moment I'm just trying to get an idea what I'm looking at.

Scott, that's a great idea about overdriving the lamp. They aren't that expensive and the increased output would be helpful I think.

 

[jayb79]

Check out this site, http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=869

Lots of lithium options.

 

[VidPro]

yup a regulated lithium series set with proper balancing taps would be lightest for the power weight ratio.
there are 14.4v finished packs for the trailtech HID lights that are regulated down to a perfect 12V for (about) any 12V application
li-ion weighs about 40% less than ni-mhy.


we replaced our BRICK lead acid TRASH with 10X1.2V D cell ni-mhys, and the weight feels about 1/2. but more than the weight reduction the ni-mhys will actuall recharge more than 25times total.
lead acid does NOT like to be deep discharged one bit, and gell cells are pickey weak hunks of boat anchor perfect for emergency lights and UPSes but nothing else.

the ni-mhys dont have to be constantally topped off, last YEARs longer, weigh less, and with a slow dumb charger they can be balanced without balancing taps on it. And the ni-mhys held up under high loads MUCH better without sagging down.
i use 12X2parellel 9-11AMP D cells (24batts) with a 100W video light, and the light runs for a good 1h 45m without drooping like the lead acid did.

as often as we were replacing and loosing gell cells due to time, deep discharge, not keeping them topped off fully, the ni-mhys paid for themselves in more than just frustration and weight. we were having to carry 13Lbs of boat anchor lead acid, and i rarely got the total amperage out of them.

 

[Avatar28]

yup a regulated lithium series set with proper balancing taps would be lightest for the power weight ratio.
there are 14.4v finished packs for the trailtech HID lights that are regulated down to a perfect 12V for (about) any 12V application
li-ion weighs about 40% less than ni-mhy.


we replaced our BRICK lead acid TRASH with 10X1.2V D cell ni-mhys, and the weight feels about 1/2. but more than the weight reduction the ni-mhys will actuall recharge more than 25times total.
lead acid does NOT like to be deep discharged one bit, and gell cells are pickey weak hunks of boat anchor perfect for emergency lights and UPSes but nothing else.

the ni-mhys dont have to be constantally topped off, last YEARs longer, weigh less, and with a slow dumb charger they can be balanced without balancing taps on it. And the ni-mhys held up under high loads MUCH better without sagging down.
i use 12X2parellel 9-11AMP D cells (24batts) with a 100W video light, and the light runs for a good 1h 45m without drooping like the lead acid did.

as often as we were replacing and loosing gell cells due to time, deep discharge, not keeping them topped off fully, the ni-mhys paid for themselves in more than just frustration and weight. we were having to carry 13Lbs of boat anchor lead acid, and i rarely got the total amperage out of them.

Where is a good place to purchase good D-cell rechargeables and what charger would you suggest as none of my current ones will charge them. I want true D cells, not the AA in a D sized wrappers since I think that would be good for running in our florescent lanterns and portable fan (can't sleep without it) when we go camping. 8 D cells get expensive and I'm afraid to run it very much, especially on high.

 

[jayb79]

http://www.batteryjunction.com/nireba.html

http://www.batterystation.com/nicads.htm

http://www.batteryspace.com/index.asp?PageAction=VIEWCATS&Category=217

Look at the amp hour rating of the cells and if it not more than 4ah for nicad or 7ah for ni-mh then it is not truely a D cell. You will want button top cells. Nicads have less capacity than nimh but are much more tollerent of abuse and they are also cheaper. Running the fan all nite and waking up to dead ni-mh batteries will most likely mean one or more ruined cells. Nicads will recover with little to no effect.

 

[Fallingwater]

Six 18650 cells in a 3s2p configuration will give you 12.6 to 11.1 volts (as the cells discharge).
You could use eight in a 4s2p configuration to overdrive the light, but at full charge voltage you'd get 16.8 volts, which is likely to be too much for the bulb.

 

[VidPro]

Where is a good place to purchase good D-cell rechargeables and what charger would you suggest as none of my current ones will charge them. I want true D cells, not the AA in a D sized wrappers since I think that would be good for running in our florescent lanterns and portable fan (can't sleep without it) when we go camping. 8 D cells get expensive and I'm afraid to run it very much, especially on high.

what he said ^ right below that, ni-cds will handle more abuse, but heck anything can handle more abuse than a gell cell

a 1Amp 12v wall wart that maxes out unloaded at 15v will dumb charge a ni-?? pack, the same way it will a gell cell pack.
not a regulated or switching wall wart, but an old transformer style. it takes 12+ hours to recharge with that, but wont ever cause a problem.

only other charger types would be a very high priced triton or shultz charger , which could properly do a fast charge, SERIES fast charging requires a very special alogrythm and cant be taken lightly.
the other way is to put the D cell in racks or holders, that way you can remove them (seperate to singles) and fast or slow charge with any Dcell type "smart" charger.
any FAST charger without a VERY GOOD alogrythm for charging will just be a disaster for SERIES charging. so its cheapest , and works just fine to have a Dumb power source, that Tapers off at the charge end, when the voltage goes up and the voltage differentials get smaller.
If you can seperate the cells they can also be cycled individually, checked individually, and balanced by doing individual charging.

you dont want to completly depleate the cells in a series set, of about any series set, i find that its better to have ENOUGH capacity that complete depleation isnt ever done at all, recharge after things dim or wane down in power, or you get reverse charge.
by having 2X the capacity you need (even instead of ni-cds) you dont depleate the thing to 0, and you dont incurr reverse charge in anything ni-cds or ni-mhy. replacing a GellCELL can mean almost 2X the power, used the SAME WAY you did when you have a gell cell, you should not be discharging completly anyway.

Sanyo Ni-cds and sanyo ni-mhy are very good, even if they are slightly less capacity total, CTB or whatever that was are overrated cheap stuff that works ok. MAHA i donno, wont try them again because of AA longevity performance.

most of the 12v gell cell chargers will charge a 10x1.2 ni-??? in similarity to what it did with the gell cell, it just takes time.

 

[mdocod]

Personally, I would consider the following:


1. complex expensive lithium-ion/poly setups are out of the question, they are too expensive, and too difficult to charge,
2. A large li-ion/poly failure in a CAVE would likely kill anyone you are caving with with deadly toxic fumes. NIMH is the better solution.
3. NIMH is cheaper and easier to charge.

so...
I would personally step down to Sub-C size cells, which are available up to 4500mAH, but use more of them in series, like 14-15 cells, in conjunction with a lower wattage, smaller reflector style lamp... (10W MR-8). Runtime would be around 4 hours, overdrive would put it at ~18W, (and even brighter than the 20W you were using, as the bulb will be operating much more efficiently). Easiest way to do this is just order up a pair of RC packs (one 7 cell and one 8 cell) and rig up some plugs and wires to put em in series, along with a a switch somewhere. With a little MR-8 you could probably even come up with a helmet mount method. Or order a custom 15 cell pack if so inclined.