Re: Power Draw

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

randall b reynolds wrote:
>  
> HI everyone, I'm at the point in construction where I'm starting to 
> think of wiring and a speed controller. I checked a book out of the 
> library called "complete combat Robots". It has some formulas to figure 
> out Wire size , Amount of amp. draw from a dead stop and running draw. 
> Has anyone done this on their Elec. system, or have you used past 
> experience, maybe ?  Any help would be appreciated.
>                                                                              

When it comes to wiring, you can't make the main power lines too heavy. 
  Ev Warriors can pull over 70 amps -at- 12v when stalled, which is a very 
large current draw.  During normal operations, however, the total 
current draw is less than 30 amps, but that is still worthy of 
heavy-duty wiring.  For that reason, I have doubled up my battery wires, 
using two pairs of 10 gauge, stranded wire. (Stranded wire carries DC 
current much better than solid wire.)  Alternatively, you can use 10 
gauge wire that has twice as many strands as standard stranded wire. 
They sell such wire for high-power audio systems, I think they call it 
monster wire.  If I remember correctly, it has over 40 strands, whereas 
standard wire has less than 20. I also run separate supply wires to each 
side of my speed controller to reduce the current through each wire.

With large current draws, you also need to consider how all the wires 
are connected.  Conventional in-line power connectors, such as the ones 
used on batteries, are usually not rated for such loads, so you have to 
either double them up or connect the wire directly to a terminal strip. 
    Direct connections are best from a power perspective, but whenever 
you change batteries it is easy to hook them up backwards, which can 
lead to some nasty surprises.  For that reason, I use polarized, 
double-up connectors for all batteries and I use large spade terminals 
and terminal strips for the rest of the wiring.

You'll also need to get a cut-off switch that is capable of handling the 
max current draw.  I use a 100 amp key switch that is normally used in 
cars to disable the starter battery.  They are very durable and the key 
is a nice bright orange so that you can easily spot it on the outside of 
the tank.

Finally, you'll want to include a high-amp, slow-blow fuse somewhere 
between the batteries and everything else.  I use an 80 amp fuse that is 
used for high-powered car stereos.  They come in different shapes and 
mounting fixtures, but they all do a good job of safely shutting things 
down if you short something.

        Frank P.