Re: (ET) 48 volts

["Bob Murcek" <rmurcek geisinger edu>]

Anyone consider the possibility of a low-cost solid-state controller to 
drop the 48V to 36 for the deck motos, etc.?

>>> Robert Adsett <subscriptions aeolusdevelopment com> 5/5/2006 7:25:49 
>>> PM >>>
At 06:54 AM 5/4/2006 -0700, Eric Adams wrote:

>I have been wondering about the 48 volt Elec-trak as well. Higher voltage 
>would
>be a little more efficient, and 48 volt components are a little more 
>available
>via the forklift markets.
>
>There has been talk of overspeeding the mower motors by raising the 
>voltage,
>but I can't help but wonder about that. I would assume that the system was
>designed to safe with a fully charged 36 volts pack, which is ...what?... 
>42ish
>volts? And we are all painfully aware how much the voltage sags under 
>load on
>flooded batteries. So, would a 48 volt pack sag down to a safe voltage 
>for the
>mowers?

A couple of points to keep in mind.
         First a fully charged 48V battery will be up to 55V.  I've had 
field report of hot batteries (just off charge) with voltages up to 60V
         Second the speed of the PM motors on the deck will be 
approximately proportional to the applied voltage. The energy contained in 
the blades will be proportional to the square of the speed.  This means 
the 
energy in the blades will be more than 70% higher.
         Third, the wind resistance and mechanical resistance will keep 
the 
blade from reaching that speed but at the expense of increasing the 
current 
(higher torque to overcome the resistance and compensate for IR drops) so 
the motors will run hotter.

None of this means it can't work but it's not necessarily a minor change.


Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,   be 
they legal, genetic, or physical.  If you don't believe me, try to chew a 
radio signal. "  -- Kelvin Throop, III
http://www.aeolusdevelopment.com/ 


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