Aren't relays basically a remote switch? On the schematic for the Javelin the batteries are close to the motor and the wiring is all heavy gauge/ I think what he is using is just regular switches. A relay is when you have a low amperage switch (such as on the dash of a car) that controls a remote relay (under the hood, closer to the end use) that is a higher amp switch that actually closes the high amp circuit. A starter solenoid is the ultimate example. Modern cars have a whole series of 12 volt relays for controlling high output devices, remote control, and delayed control. Switches sound cheap. relays may not be needed.
Carrying this intellectual exercise a bit farther... Javelin has two settings - 12 v full on and 24 v full on. We always talk about motors being rated as continuous use and utlimate use. How does this factor in? Seems like when the switch is thrown you get full power at whatever voltage is selected.
-----Original Message-----
From: hardy71uk <p0054107@brookes.
To: electricboats@
Sent: Thu, Jul 9, 2009 4:10 am
Subject: [Electric Boats] Re: Relays to replace a controller
in the 19th century they sometimes had complicated switching to give speed control for example switching 24 times 2 volt cells in various series and parallel combinations .Also series and parallel motors. Nowadays it is normally cheaper and simpler to use an electronic controller unless youve been given a pile of free relays to play with or only want a couple of gentle speeds.
Chris S
--- In electricboats@
>
> resistors = cheap, relays = expensive, controllers = more expensive...
>
> Remember that the increase in torque is nearly instantaneous - a large prop on a small boat and something might tear off - though there is probably some way to introduce a capacitor to slow the current rush down.
>
> I've considered it in the context of systems redundency - I have a brushless but could carry a brushed motor and rig such a setup in a pinch.
>
> Controllers eat about an amp, relays probably much less and so I would think the efficiency would actually be higher - except the loss of fine-grained control means you will burn amps when you don't need to (you are more likely to over-throttle than under) - that could amount to a 20% overall loss in range for example. So now you are carrying more batteries than needed - and where is the savings in that?
>
> -Keith
>
> --- In electricboats@
> >
> > What does the group think about replacing a controller with relays that reduce the voltage from 24 to 12 volts? What is the efficiency loss and what other problems would be expected? And could the same thing be done with a 48 volt system, reducing it to 36, 24 and 12? There must be some reason why older golf carts used resistors to reduce speed rather than reducing the voltage.
> > Thank you
> >
>
[Non-text portions of this message have been removed]
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch format to Traditional
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe
No comments:
Post a Comment