OT, any electrickery experts out there?

[guest18]

Quick question for the electrical experts...

I'm aiming to replace a knackered ni-cad battery pack in a lightweight hoover for Mrs HS(told you it was OT!)
Currently (geddit) it has four 1.2v 1300mAh sub C cells wired in series.
Am I better to use 8 x 1.2v 1700mAh Duracell AA nicads from Tesco wired series parallel to give me the required 4.8v and a larger 3400mAh,
or,
Should I buy four of the original type from somewhere like here and replicate the original pack ?( http://www.batteriesplus.co.uk/acatalog/1.2V_NiCd_Sub_C_Rechargeable_Tagged_Batteries.html )

The wallwart charger for it incidentally pushes out 7.5v and 150mA

Advice? 

[themoudie]

Aye Smudge & Mrs HS,

Delighted to read of the good news!  Kat and I hope all goes well.

As for the battery, not a clue mate!

Slainte, Bill.

[JOOLZ]

No problems replacing them for the larger capacity batterys it will take longer to charge but will run for longer too

[guest18]

Cheers Bill 
I should know the answers but it's a wee while since I was at college and I've forgotten 99.9% of the theory stuff I learned for my ham licence! 

Joolz, Thanks, will the AA's survive a (relatively) heavy draw, given their greater AH rating or will their smaller physical size work against them? Also any ideas how I work out the length of time they need to charge for?

[guest40]

All good if you have a home for 8 AA batteries. Why not go whole hog and use the 2400 Ah ones. Try and get a 500ma or more charger. If you think about it you could even hook up one of those 6volt sealed lead acid batteries and create a real bruiser.

PS Hint, its cheaper to replace 1 off AA than a C . Not all 4 or 8 AA's will die together at the same time. Have you checked the C's as only one could be dead.

PPS.. change over to NiMH as they dont suffer the same memory effect as the NiCads. If you do, make sure you change the charger too. You can get chargers that do both types.

PPPS  NiCads have a service life of around 3 years if charged daily, have you checked the old ones for memeory effect?

[guest1380]

I'd go with Kurt on this one and only add a question. Have you checked for dry solder joints because that really messes with NiCads.

If you really want to go crazy get some racing 'C' cells from your local RC model shop. Made mods to the Black and Decker vacuum where I used to work with a old set of racing cells and a highly modified RC racing motor.

I wouldn't go that far again though as it only lasted three months before melting the casing!!