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

  • From: Roger <roger.g3tdm@xxxxxxxxxx>
  • To: modeleng@xxxxxxxxxxxxx
  • Date: Wed, 30 Mar 2005 18:03:20 +0100

Hi,

    Let me add my two penny-worth to this discussion.

    Firstly - regenerative braking and diodes.   Surely the alternator 
already has diodes in it which will allow current to flow in one 
direction only - the direction of charging.   If the battery voltage 
really gets up to the values quoted then I would be more worried about 
the batteries giving up,  rather than the alternator.   Also to reach 
those figures the current being pushed into the batteries from the 
motors (acting as a dynamo) must be quite horrific.   Also a lot of 
hydrogen must be produced!

    Regarding how to limit the charging current,  when the motor is 
drawing 96 amps.   I would suggest either adjusting the gearing between 
the engine and the alternator or the speed of the engine,  so that when 
the motors are drawing this maximum current - the charging system is 
only putting the sort of current into the batteries that the engine is 
happy with.   The regulator will be giving maximum voltage to the field 
windings,  but the alternator output current is limited by the speed of 
the alternator.   This is similar to turning on rear screen heater,  
headlamps and other heavy current consuming things in the car,  when the 
engine is just idling - the alternator cannot keep up with the demand,  
and so the battery is called upon to supply some current,  as soon as 
the load reduces (as in the loco case),  or the engine speeds up (as in 
the car case),  the battery is re-charged.

    I'll retire back to lurking mode and see how the discussion proceeds!


       Cheers,


          Roger Mason,  in St. Agnes
where it has been a rather dim,  gloomy,  day.

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