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

  • From: "Phill Smith" <steam@xxxxxxxxxxxxxx>
  • To: <modeleng@xxxxxxxxxxxxx>
  • Date: Thu, 31 Mar 2005 23:07:22 +0800

If you want, I have the circuit/wiring diagram somewhere for the 24V voltage
regulator that I built for my tractor's generator. It will work OK for what
you want, as it is adjustable in it's output voltage, and will work happily
on an alternator.

Cheers,

Phill.

----- Original Message ----- 
From: "John Rippengal" <j.rippengal@xxxxxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
Sent: Wednesday, March 30, 2005 5:55 PM
Subject: [modeleng] Re: Topsy - to charge and how to charge, that is the
question!


> You should have a voltage regulator which controls the field current so
that
> when the battery reaches its proper charged output voltage the alternator
is
> reduced to just a trickle charge. Some alternators have an internal
> regulator but if not it is easy to fit an external regulator. For 28volts
I
> suppose  you will neeed to source the regulator from an aircraft supplier.
> 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. It must be mounted on a
> good heat sink. Make sure that the voltage regulator input terminal is
> connected after the diode as you will lose about 0.7volts through the
diode.
> Not sure of the load but it is easy and cheap to buy diodes that will
carry
> say 70 amps.
> 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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