Re: Batteries

[Frank Pittelli <frank-at-rctankcombat.com>]

Aahz. wrote:
>>Unless you've lots of money you'd like to invest in your tank, you
>>probably want to stick with Sealed Lead Acid/Gel Cell batteries.
> 
> How much are we talking here? Since I was using DeWalt motors I was
> considering using the batteries they make too but really hadn't looked into
> the cost yet. 
> 

Gel Cell:  The batteries in the Tiger-1 are 12v -at- 26Ah and they cost $45 
dollars at the local battery warehouse (we bought 10 at a time and got a 
reasonable discount).

Nicad:  Tower Hobbies sells 7.2 v -at- 1.5Ah nicad batteries for approx $8 
each in quantity.  Basic maths says that you'd need approx 30 of those 
batteries to equal the storage capacity of the gel cell listed above, 
for a total of $240.  Of course, Nicads *can* be fully drained without 
damage and they handle heavy loads better than gel cells, so you really 
only need half as many Amp hours for the same effective performance, or 
$120 worth of nicad batteries.  (This comparison is based on my personal 
experiences using both kinds of batteries in combat conditions).

If you are a surplas purchasing god, such as myself, you can find 
acceptable nicad batteries for about $1 per 1.2v -at- 2Ah cell.  Wire 
roughly 65 of them together and you have the same nicad solution for 
about half the Tower Hobbies price at $65.

If you're really lucky, you can find some military surplus nicad packs 
with really large cells (e.g., 10Ah each).  Usually, they are "wet" 
cells, which require routine maintenance, but they are very robust and 
are generally well-suited for our tanks.  I used to see them a lot 10 
years ago (even bought a few myself to try in a battleship) but haven't 
seen them lately (although I haven't really been looking either).

So, my general rule of thumb is that Nicads cost about twice as much as 
Gel Cells for the same storage levels required for our tanks.  Nicads 
have some nice advantages (dump energy quickly, can be charged quickly, 
and are less dense), but they also have some disadvantages (cost more, 
more complicated charging and have more connections).

And, keep in mind, the more cells ... the more chance of failure. 
Larger cells are better than smaller cells, which gives Gel Cells the 
advantage.

        Frank "Still Waiting For Cheap Fuel Cells" Pittelli