Re: Braking

[Bryan Andersen <bryan@visi.com>]

Bryan Andersen wrote:
[snip]
> As an example, a 2200W 240VAC finned strip heater has an active
> finned length of 19" with 2" x 1.375" fins and an overall length
> of 23.25".  Smaller and larger sizes are available.  I chose this
> size as a single $3 IGBT can switch it easily.  Even placing them
> two deep in an array one ends up with a rather significant sized
> box if one wanted to dump 200A.  The overall box would end up about
> 24" long, 16" wide, and 4" deep + whatever one needs for fans, say
> an additional 3".  Maybe not quite practical, but an idea.  The
> maximum temperature of the elements is 600F.  If one had suitable
> air flow one could easily go deeper than the two deep I used.
> Going 4 deep gives a box size of 24"L x 8"W x 11" deep.

Seeing a couple people commented on dumping 30+kilowatts.

The one I outlined above is a little over 48 kiloWatt at 240V.  

   240 V * 200 A = 48,000 W.  design goal.
   22 elements * 9.167 A = 201.7 A.
   240 V * 201.7 = 48,408 W

If the voltage of the pack is less one can generally assume that 
the amps would proportionally decrease with voltage drop.  That 
means this design would dump about 17.4 kiloWatts at 144V.

   144 V / 240 V = .6
   201.7 A * .6 = 121.02 A
   121.02 A * 144V = 17,426 W

I think it might be better to use different heating elements than 
the ones I picked.  I only designed with the first elements I found 
that could take a corrosive environment.  McMaster-Carr also has 
some bendable round elements that can be used in corrosive 
environments and will take up to 1400F.  If one put them into a set 
of fins like a radiator has I bet one could make it more compact 
and long term durable.  My guess is one could easily make it half 
the size and still have reasonable exhaust air temps.  

If one needed higher voltages one can use 3 120V, or 2 240V elements 
in series.

Anyways, it's an idea and like everything it has it's own associated 
cost benefit ratios.  I could easily see going for it if I lived in 
a hilly area, but living here in the relatively flat midwest it 
isn't as useful.

-- 
|  Bryan Andersen   |   bryan@visi.com   |   http://www.nerdvest.com   |
| Buzzwords are like annoying little flies that deserve to be swatted. |
|      "Linux, the OS Microsoft doesn't want you to know about.".      |
|   -Bryan Andersen                                                    |