Replacing battery pack in a hand-vac

[IamMatt]

I have a very old Hoover dustbuster-type hand-vac that will only run about 15 seconds after charging. At its age, I figure the batteries need replacing, so I opened it up and it has a 3-cell battery pack of Sanyo KR-1300SC Sub-C Ni-Cad batteries wired in parallel for a total of 3.6V and 1300 mAh.

The inside of the vac has no electronics related to regulating charging. There is a typical step-down transformer on the power cord that goes from the wall to the vac (puts out 4.5V, 300mAh), but the wiring from the power plug on the vac goes directly to the battery pack with nothing inbetween. Is that typical for rechargeable Ni-Cad stuff, to have no regulating electronics?

Anyway, my first option was to try to find an OEM replacement pack with the 3 cells already wired but that did not come up in my internet search. So I figure I will buy 3 replacement cells and take the tabs from the originals and solder them to the new batteries. There are plenty of places that sell the individual KR-1300SC's.

I am a neophyte so I have a couple of questions I hope someone can help me with.

First, given the lack of any electronics between the power and the batteries, is there a better battery type than the originals that I could use? Maybe Ni-Cad Sub-C's with more than 1300 mAh, or a different type like NiMH (some of them have as high as 5000 mAh)? Would other types work with the power going directly to the battery pack?

Second, is there anything special about soldering tabs on batteries? I have a soldering iron but have not done much soldering since a high-school electronics class 40 years ago, so I am a bit rusty.

Thanks in advance.

 

[Burgess]

Hello Matt --


I'm gonna' take a Wild Guess here . . . .


Gonna' guess that yer' individual cells are not SOLDERED together,

but, rather, they are WELDED together.


Just a guess, you understand, since i haven't actually SEEN it.


Hope this is helpful.


_

 

[IamMatt]

On closer examination, I think you are right. Each tab has two small indentations where it is connected to the battery, and there is no solder visible. So I may be SOL as far as reusing the tabs and connectors, but I can probably get some new ones at an electronics shop.

Any advice on the type of batteries I should/could use?

 

[dave w]

On closer examination, I think you are right.
Any advice on the type of batteries I should/could use?

The batteries are wired in series for you to have 3.6 V. Unless you typically run the vac for long periods I would just stick with good old cheap NiCads. You could go to NiMH for longer run time, and NiMH are less susceptible to developing memory but NiCads in the hand vac application will probably give you longer life span.
http://www.all-battery.com/index.aspx "All Battery" will have cells with solder tabs, otherwise use something sharp and put several heavy scrathes on the top and bottom of the new batteries and you can usually get solder to stick well enough to tack down a wire or the solder tabs ripped from your old cells.

 

[IamMatt]

Of course, the are wired in series, I must have had a brain freeze. Thanks for the input. I will see if I can remove the terminals from the pack so I can plug a new pack into the existing power connections, and just stick with NiCads.