Do resistors just turn current into heat, and therefore waste it? I am thinking of my old slot car controllers. They were barrel coiled resistors with a wiper to give you an infinitely variable? resistor. One which you would not want to touch. The relay idea seems simple. I thought I saw relays on ebay much cheaper, but they were probably much lower amperage.
-----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
> >
>
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