[modeleng] Re: Topsy - to charge and how to charge, that is the question!

  • From: Peter Sheppard <peter.sheppard@xxxxxxxxxx>
  • To: "'modeleng@xxxxxxxxxxxxx'" <modeleng@xxxxxxxxxxxxx>
  • Date: Wed, 30 Mar 2005 11:48:28 +0100

John,

Thanks for that.

I note the use of the diode, but shouldn't it be the +ive terminal to the 
battery ? (the pointy end!)

With regard to the petrol/electric bit, my main concern is that when the motor 
is pulling serious current (it limits at 96A on 24v dc) then the alternator 
will try and fill that gap (or at least it will try until it current limits).

I only have a 3/4 hp petrol engine driving the alternator, so I have visions 
that it may stall.  The only thing I suppose is to try it.  I have no idea what 
the maximum charge current of a 24v alternator is - any suggestions?

Cheers

Peter





<snip>
> To prevent any external voltage source damaging the alternator such as
> regenerative braking you need a heavy current diode in the main alternator
> output connected so that its normal output current is conducted but any
> reverse current is inhibited. Just connect the diode +ve terminal to the
> alternator and the negative terminal to the load.
<snip>
> This would be a standard sort of setup and will solve any problems of
> overcharging and reverse current through the alternator. The charge will
> also automatically increase to take up the load of the motor.
>
> John Rippengal.
>
> From: "Peter Sheppard" <peter.sheppard@xxxxxxxxxx>
>
>
> > All,
> >
> > Next phase.
> >
> > Last night I finally got the electrics in state that I could try it.
> >
> > Apart from the petrol engine not running properly (it ticks over OK but
> > seems
> > to suffer from fuel starvation at higher revs - it runs for a while then
> > dies!)
> >
> > With the alternator field "off" the voltage was around 26.2 volts (one
> > battery
> > was in use on an electric locomotive over the weekend, so the volts may be
> > down
> > slightly).  With the engine running and the field on (apart from slowing
> > the
> > petrol engine quite markedly - and this was with no load on the battery!)
> > the
> > battery volts rose to around 28v.
> >
> > So, it looks like the alternator works.
> >
> > So my question remains, what is better, weaken the field (which is
> > intrusive to
> > the alternator) and leave the engine running all the time, or leave the
> > field
> > as is and switch the charge to a dummy load whenever power is taken by the
> > motor?  I am still concerned by regenerative braking taking the volts up
> > to 36
> > and damaging the alternator.
> >
> > I suspect it will depend on how much time the locomotive is running (i.e.
> > hauling, not charging), versus sitting there idling (and thus charging).
> >
> > Cheers
> >
> > Peter
>
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