Battery pack - a few problems!

SirJMD · Oct 14, 2009

Im about to mod my old halogen-searchlight. It uses a 6V 55W bulb.

I ordered a slim 35W ballast and a 35W 6k HID bulb. Now i need to figure out a battery pack that will deliver at least 12V.

The standard battery is a 6V 4Ah SLA. Its dimensions are 70 x 48 x 102mm. That should big enough to fit 4s2p with 18650 batteries. I might even be able to fit 4s3p - with the batteries i found at ebay (3.7v and 2800 mAh), that should give me 89 Wh or 124 Wh. Should be good for close to 2-3h runtime?

Next problem.. if i buy such batteries and solder them together.. how the h*** am i gonna recharge them?

Im open to any suggestions!

effulgentOne · Oct 14, 2009

The problem with Li-Ion packs is that a good charger is rather expensive. They're also potentially dangerous if you don't know what you're doing, especially if you want to solder them. I'm not saying you can't do what you want to, but you should make sure you fully understand what you're getting yourself into.

If this were me, I'd use NiMH instead. While they have lower energy density, they're safer, much cheaper, and much easier (and cheaper) to charge. Unfortunately, the space you have to work with doesn't lend itself well to any standard pack sizes i can think of, but if you're not averse to soldering you could make your own (batteries with tabs would be easier to solder). You could probably fit 12 Sub-C cells (like these maybe, though I haven't used any of them personally), for 14.4V and around 4.5Ah, so about 65Wh. Then you can buy a 14.4V capable pack charger for around $20-30 and be all set.

Just my $.02

SirJMD · Oct 15, 2009

effulgentOne said:
The problem with Li-Ion packs is that a good charger is rather expensive. They're also potentially dangerous if you don't know what you're doing, especially if you want to solder them. I'm not saying you can't do what you want to, but you should make sure you fully understand what you're getting yourself into.

If this were me, I'd use NiMH instead. While they have lower energy density, they're safer, much cheaper, and much easier (and cheaper) to charge. Unfortunately, the space you have to work with doesn't lend itself well to any standard pack sizes i can think of, but if you're not averse to soldering you could make your own (batteries with tabs would be easier to solder). You could probably fit 12 Sub-C cells (like these maybe, though I haven't used any of them personally), for 14.4V and around 4.5Ah, so about 65Wh. Then you can buy a 14.4V capable pack charger for around $20-30 and be all set.

Just my $.02

I know what im doing with batteries, dont worry

I have a rather expensive charger somewhere, that can monitor the batteries while charging.

Those batteries at batteryjunction looks great - i actually looked at such batteries in danish stores, but the price were.. ocuh. The cheapest ones were $10 each (if you didnt want 1500 mAh ones).

Thanks for the reply.

EDIT: With a tiny bit of cutting, i will be able to fit 12x C batteries in it. Im gonna order batteries when ive recieved the ballast, so i know how much space it takes up.
Any idea how hot the ballast gets?

yellow · Oct 15, 2009

Such a power from other than Li-Ion (Li-Po) makes for a huge battery pack, imho there is no other option.

Why not get Camcorder Batteries - easily available, cheap, protection included - and wire 2 of them in series.
Get "charging cradles" and conntect them with wires, so the packs remain original.
Canon BP945 is one thing to look at, together with a charger for them.

Just a guess: what will the HID draw from a 12-14.4 V source in use?
35 W, say 3-4 Amps? lets calculate with 4

10 Ni-Mh in series = 12 V, 4000 mA per cell, with that draw: 3000 can be used.
--> 45 mins from 10 Sub-Cs

Camcoder pack (=6* 18650 in 2 rows with 3 cells): 6600 mAh (?)
--> 2 BP945 packs: 1 hour 45 mins

(PS: 2*BP945 are smaller than 10 Sub-Cs)

SirJMD · Oct 15, 2009

yellow --> Great idea! I actually have one of those canon batteries.
I just need to find a way to recharge them, without having to take the entire flashlight apart (you screw reflector + glass off, then remove some electronics, and at the bottom you have the batteries).

I just looked at the dimensions for the mentioned battery pack: 70 x 40 x 60mm.
The old battery in the flash light, was 70 x 48 x 102mm.

Seems like it isnt possible to fit two BP945 packs in it

bstrickler · Oct 15, 2009

SirJMD said:
I know what im doing with batteries, dont worry I have a rather expensive charger somewhere, that can monitor the batteries while charging.

Those batteries at batteryjunction looks great - i actually looked at such batteries in danish stores, but the price were.. ocuh. The cheapest ones were $10 each (if you didnt want 1500 mAh ones).

Thanks for the reply.

EDIT: With a tiny bit of cutting, i will be able to fit 12x C batteries in it. Im gonna order batteries when ive recieved the ballast, so i know how much space it takes up.
Any idea how hot the ballast gets?

If you get these: http://www.batteryjunction.com/onepiofsc38m.html

be VERY VERY CAREFUL! And make sure to order extra's!

I was making a battery pack, and didn't notice there was a bare spot under the + lead, and I let it touch the side of the battery, with my thumb on it. The thin strip of metal turned into an instant red-hot fuse! :poof:

That resulted in me getting a 3rd degree burn, because of my thumb being on the tab of metal when it was shorting.

On top of that, the reason for ordering extras is because sometimes you'll get a dented battery (I got one with my order from allbattery), but if you're nice, you can talk to them, and they'll replace it. It'll be a good idea to check them before you open the packaging they're in, as well.

~Brian

SirJMD · Oct 15, 2009

That doesnt sound good Brain, but.. im aware of that

The center at the top of the battery, is the positive, while the edge is the negative - bad stuff happends if you connect those two directly with eachother

I hope the ballast arrives today (friday now, in my time zone), so after a bit a meassuring, i should be able to determine which batteries that will fit.

SirJMD · Oct 25, 2009

Okay.. i killed my battery pack.. so.. i need a new one

Found a site that sells a custom made 14.4V 3.3Ah for just $45, and a 14.4V 4Ah for $63. Quite fair price in my opinion!

SirJMD · Oct 30, 2009

There we go.. ordered a 14.4V 5000mAh battery pack. That should deliver enough power for at least 1h runtime.

Battery pack - a few problems!

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