Re: [PSUBS-MAILIST] Interesting item on eBay web siteitem#275822570:X-9 "Y...

["Captain Nemo" <vulcania@interpac.net>]

----- Original Message -----
From: <Subscuba@aol.com>
To: <personal_submersibles@psubs.org>
Sent: Wednesday, March 08, 2000 1:14 AM
Subject: Re: [PSUBS-MAILIST] Interesting item on eBay web
siteitem#275822570:X-9 "Y...


"> Pat,
>
> Your thinking would probably be better if you considered the motor
> controllers as a switch that turns off and on at a high rate, most operate
at
> 20KHz."

Aha!  You mean it operates on a frequency cycle instead of via resistance.
OK....I'll be honest, I'm a better welder than I am an electronics tech.

"If the length of time the switch is on you have more power."

You're saying if its on longer, power is greater, right?

"If the switch is on for about 10 microseconds with an off time of 40
microseconds
> then the duty cycle is 0.2. If your battery voltage is 36 volts the motor
> gets about 0.2X36=7.2 volts. If the on time is about 40 microseconds and
an
> off time of 10 microseconds then the motor gets about 40/50X36=28.8 volts.
> Thus the average motor voltage is the duty cycle, defined as on time
divided
> by the period or the reciprocal of frequency, times the battery voltage.
> Since the power switch doesn't dissipated much power in the on or off
state
> the controller doesn't dissipate much power unlike a potentiometer."

Believe it or not, I actually followed what you just said!

>
"> The neat thing is two fold, you get speed control and through current
sensing
> you get current limit. This prevents stator demagnitization or wiping out
> your permanent magnetics used as the stator. The circuitry is actually
quite
> simple but somewhat difficult to construct due to the need to control
> parasitic inductances."

That's a new term for me.  What are parasitic inductances?  It sounds like
some unwanted transference of current in the system; if so, then what,
where, and to what effect?

 "You can buy the controllers or make your own as I did
> but the technology is not straight forward and you can throw away a lot of
> money doing it yourself."

I'm interested!

 :"As you are the Great Captain of the Nautilus:"

Oh stop it!   ;-)

"I would be glad to help with some parts and design skills."

Sounds like a plan!

 "It would be interesting
> from my viewpoint. I tried to put as many batteries in my Sub without
regard
> to motor voltage since I designed the controller myself. I can use 12 volt
> motors from the 36 volt batteries if I wanted to. The controller from Minn
> Kota was $169 and I built it for about $10 to $12 dollars since I have
access
> to sample power switches."

Let's do it.  Where do we start?
>
>
"PS Fuzzy logic wouldn't help."

I agree.  But then,  I seldom drink, and never to excess.  ;-)

This is all good, Ken; and thanks for the input.  But tell me: do you think
if I wire three 12 volt batteries in series to my 24 volt MK 4HP using the
stock controller, it will fry or not?

Always having fun!

Pat