DIY battery packs

[divingdingo]

So the deal is that i came accross an old dive rite cannister and torch head. however it was 'sans batterie', mes amis!!

it was thus my challenge to make myself a battery pack which was suitable for the 12v - 20W Halogen Bulb.

so i went off and bought 10x C cell rechargeable nimh batteries so as to solder together in series to form a 12v battery pack. each c cell battery has a rating of 2.6ampHours.

question 1: if each cell has 2.6 AH rating presumable this means when in series the pack has a 2.6 AH rating (not 26AHs)?

question 2: if i wanted to make another battery pack with a higher capacity charge, i.e. a higher Amp Hour rating. does anyone know of some other types of batteries i can use to form a pack? it would still have to be 12v total because of the bulb.

p.s. i'm a cheap bastard so don't go suggesting buying a made pack from divingniknaks !!

and does anyone want to confimr for me that: with a 12v - 20w bulb it will have a current of 1.6amps (yes?) which means with my 2.6aH pack i would get an absolute maximum burn time of 1hr 40mins (approx) ?

or if anyone has their own experiences regarding battery packs please post for those others interested.

cheers

[Woz]

Blimey. Where to start. If you pop the batteries in series you up the voltage and the Ah remains the same. If you do them in parallel you up the Ah but the V stays the same. Parallel batteries must be matched or you'll get an internal discharge.

The discharge characteristics of different chemistries change- some are flat then drop off quick, others are a more linear discharge.

The only way to get more juice into the space is to us Li-ion but watch them as they don't like water much.

Plus you will now need a custom charger. Invariably it's better to buy a commercial one than DIY as with NiMh you need to not overcharge them as it buggers them up.

[uwila]

Q1 - Yes, total capacity 2.6 Ah

Q2 - try buying 6 packs of these 4.5 Ah NiMH C Rechargeable Batteries Up To 4500mAh

To charge the pack, try one of these Ansmann ACS 410P Traveller Battery Pack Charger

I've made my own pack from cells and used an Ansmann charger. Worked a treat and was lots cheaper than buying a manufacturer replacement.

Cheers, Chris

[uwila]

Originally Posted by divingdingo

and does anyone want to confimr for me that: with a 12v - 20w bulb it will have a current of 1.6amps (yes?) which means with my 2.6aH pack i would get an absolute maximum burn time of 1hr 40mins (approx) ?

Indeed that's the maximum time, but in reality you'd struggle to get that, especially if diving in cold water. I'm not 100% sure of the performance of NiMh batteries, but some types hate being totally discharged and one torch I used to own had a limiter which turned itself off as the voltage dropped to protect the cells. I'd assume no more than 70 mins of useful time and be happy if you get more.

Cheers, Chris

[divingdingo]

cheers woz and uwila.

all good, i've actually bought an intelligent charger off ebay that is supposed to do the lot from lith ion, nimh, etc just incase i decide to upgrade the pack in future and it cost around the same. fingers crossed that it will do what they say it will do.

uwila - i wish i had seen those batteries a week ago before i just spent £25 on the ones i have now. still, good link for my next battery set!!

now i just need to solder the batteries in series so that they fit into the canister!

has either of you two used that black shrink wrap stuff to give the packs the professional touch. or do you just use gaffer tape!! where do i get the shrink wrap from, any ideas?

thanks for your help. much appreciated.

[uwila]

Duck tape - a million uses

[divingdingo]

thought as much. that stuff is just too good.

safe, 'en-lightened', diving good man

[turbanator]

Originally Posted by divingdingo

thought as much. that stuff is just too good.

safe, 'en-lightened', diving good man

I look forward to seeing your shutdown drills with burnt fingers!

[divingdingo]

Originally Posted by turbanator

I look forward to seeing your shutdown drills with burnt fingers!

anyone know how to solder? wanna solder 10 batteries together !!!

perhaps i'll just stick 'em together with kitkat foil and some insulating tape. should do the trick!! anyone wanna go caving with my 'new' torch !!!

[uwila]

Originally Posted by divingdingo

anyone know how to solder? wanna solder 10 batteries together !!!

perhaps i'll just stick 'em together with kitkat foil and some insulating tape. should do the trick!! anyone wanna go caving with my 'new' torch !!!

If you didn't get tagged batteries, you might find it hard to solder them together.

I used plastic tubing, split it along it's length if it's too big. Put the batteries in it and then overlap the tubing, mark up the overlap and cut it off. Then you can tape it up to make a battery tube (put the batteries in first). Then you can cut it to length and use metal connectors and a decent spring at each end (more duck tape here!) to get a connection. No solder needed on the batteries!

An Alternative, if there's room in your canister is to buy some of these:
Maplin > C Size Battery Holders

Cheers, Chris