Sealed lead acid batteries.

[Nygie]

Hi all, new to the forum. Been reading loads and alot of is somewhat over my head to be honest. I have a basic knowledge of electronics (school stuff mainly).
I have a couple of the P7 led torches that run on the 18650 cells.
From what I have gleened from the specs and posts here is that the LED emitter is 2800mA at 3.6V. Driven by an LED driver that is probably limiting the current draw on the battery.
Having searched and not really found many simple external packs to extend runtime.
I was thinking of a simple pack using a 6V 7Ah (or 10Ah) sealed lead acid ((heavy I know) I'll shed a few pounds to compensate lol ) battery with a 3A limited voltage regulator.
I know most use the Li-Po and various other types.
Is this the right approach apart from the sealed lead acid battery lol.

Basically I want a pack that I don't have to strip down to charge, I don't have to incorporate failsafes or charging circuits and most of all is unlilkely to burst into flames whilst charging.

What a waffly first post.
Let the lead acid flaming commence.
Cheers

 

[bluecrow76]

:welcome:

I made this little light box out of some spare parts and run it off of 12V SLA batteries. It's actually my bed light and served well as a room light during hurricane Gustav a couple years back.

 

[poguy]

Why would anybody flame? SLA works fine for applications that are not too weight/size sensitive. And you can get slightly used ones cheap at hamfests and the like. Keep them charged and they last for years.

Back to the P7 question. I haven't seen P7 drivers from KD or DX that would take the 13.6 volts put out by a fresh 12V SLA. There are some that go up to 8.4 (2*18650) and you could use a 6 volt SLA on it.

It would be possible to find a switching converter from 12 to 5 volts, but that's too much money and added complication. If someone ever comes up with a P7-able driver that takes from 6-18 volts, I'm in.

 

[rmteo]

SLA's are fine for your application if weight is not an issue. To put things in perspective, an equivalent LiPO will be about 25% the weight of an SLA - or less.

 

[csshih]

well heck, bluecrow.. that is cool! I wish I had the skill to make one of those.. I have a SLA sitting idle :naughty:

 

[Nygie]

Thanks for the replies guys, I was joking about the flaming.
I may have found more about SLA but I never thought about searching the abbrev. term!

I was thinking of using the original LED driver in the torch and just making a small regulator circuit to get the battery output somewhere near to the prerequisites of the driver. Using something similar to this http://www.maplin.co.uk/Module.aspx?moduleno=46055

 

[Nygie]

SLA's are fine for your application if weight is not an issue. To put things in perspective, an equivalent LiPO will be about 25% the weight of an SLA - or less.

Where would I find such rated Li-PO packs? Or is it something I would have to put together myself?

Cheers

 

[rmteo]

Check out the packs used by the R/C guys. I have a 3-cell, 5000mAH (11.1V, 55.5WH, 20C discharge rate) pack that weighs around 12.6oz. and is about 5.6x2.0x10in. I'm guessing that a 6V, 10AH (60WH) SLA is going to be about 60oz.

The key to safe/efficient use of these packs is proper equipment and common sense - a balancing charger is highly recommended.

 

[Nygie]

WOW them Li-Po packs are EXPENSIVE £60 at model power.
I did find these ... 1.2 Volt 10,000mAh Vapex NiMh D Cell's.
Would I be OK using 3 of these to give me 3.6V using the standard driver?
It would be sooo simple if that would work.

 

[rmteo]

3x 10000mAH NiMH cells (in series) should substitute for a 18650 in your application. I'm just guessing here - all of the stuff I do involves Lithium chemistries only.

 

[Lightcrazycanuck]

Where would I find such rated Li-PO packs? Or is it something I would have to put together myself?

Cheers

http://www.maxamps.com/


lovecpf

 

[balou]

Yes, just 3 NiMH cells in series should work as a 18650 replacement.

edit: oops.. I just see that somebody already answered. Well.. I already typed it, so here goes my mouse to the submit button

 

[Nubo]

Where would I find such rated Li-PO packs? Or is it something I would have to put together myself?

Cheers

LiPo are voted "most likely to burst into flames", so don't seem to match your initial objective. Not saying that lots of people don't use them successfully, but they do have certain care and feeding requirements to stay "happy".

You don't mention what your application is. Your mention of weight loss to compensate leads me to suspect bicycle lighting? SLA will certainly work there; depends on how you feel about the weight.

NiMH is a pretty good compromise, imho. Saves some weight over SLA, flatter output curve, and less fussy charging requirements compared to lithium chemistries. But to use effectively a smart charger is still recommended, whereas SLA can be reasonably charged with dumb-charger low-current "wall wart" charges as long as you take care to limit the duration of the charge cycle to prevent overcharging.

 

[rmteo]

LiPo are voted "most likely to burst into flames"

 

[Nygie]

You don't mention what your application is. Your mention of weight loss to compensate leads me to suspect bicycle lighting? SLA will certainly work there; depends on how you feel about the weight.

You are correct, the application is for the mountain bike. Going to make a pack for a mate who is pretty much a technophobe and fussy charging requirements would definitely not be his thing, nor mine to be fair.

Thanks for the info.