ST heads for battery bank charging

[bschwartz]

Is there any reason you wouldn't just want to use a variable DC power supply instead of the harmonic windings?  It would bypass the bridge diodes and provide a nice smooth input.  On second thought, where would you get the 120v ac (or what ever your power supply needs)..... nevermind.

[NoSpark]

Marcus, do you mean rheostat or dial type variable resistor? Like this http://cgi.ebay.com/Ohmite-6-300W-Rheostat-Type-N-25-Ohm-3-46-Amps-Used_W0QQitemZ370329832500QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item563960cc34. A heavy duty one like this one would not have to be temporary and I'm considering installing one myself for on the fly fine adjustment of AC voltage and might do what you have in mind.

[sarawnw]

Hi

It is interesting that the required field winding voltage is lower than the desired output voltage from the main ST generator windings.  Using a standard B type heavy duty external voltage regulator for a car alternator should work great.  Most of the automotive solid state voltage regulators have current limit on the field driver and over voltage protection on the alternator output,  There is less chance for the ST head to burn up. I could be wrong, all comments welcome.  You couls use an A type alternator regulator, The B version is what I have on hand. 

What to do:

1) Rectify the output of the ST generator with a 10O amp or more  full wave bridge rectifier.  These devices have a large metal plate that needs to be attached something that stays cool like a heat sink or the air cooled stator housing.  The current rating was figured by taking the power rating of the ST head and dividing by 120Vrms and multiplying by a safety factor of 1.5, picking the next higher available current rating.   Don't forget the fuse or circuit breaker rated for voltage and current you plan to run.  If you have a 12KWatt ST generator, 12KW/120Vrms equals 100Amps available current to charge with.  Since it is desired for the fuse to blow before head,  Pick 60 amp fuse or circuit breaker

2)  Clean up the rectified DC with Electrolytic capacitors with a voltage rating of atleast 1.5 times your intended output voltage and as much capacitance as possible to get rid of the pulsating current.  If you plan to switch between 28 volt DC and  120 or 240 VAC using a switch,  Make sure to disconnect the rectifier and capacitor bank if the capacitor voltage rating is less than  200volts.  ( this would be fun to watch,  similar to your car bursting into flames and then having to replace it)

3)  Using the B type regulator,  Connect one side of the ST field winding to the negative side of the rectified DC output.  Connect the positive side of the rectified DC to the alternator output terminal and ignition switch terminals of the voltage regulator.  Connect the the unused ST field winding  to the field terminal of the voltage regulator.  Use of a fuse in series with the filed lead is a good measure of saftery. 

4) The harmonic windings is not used and secured appropriately

5)   Connecting a battery bank to the rectified output of the ST Generator paying attention to polarity.



Placing a switch in series with the ignition terminal can be used to disable the generator output( more or less) and reduce current draw when engine is not running. 

What did I miss or should be concerned with?  I would suggest running the ST head at rated speed to ensure cooling of both the head and rectifier module.   


Which do you think would last longer, an ST head or a high output heavy duty alternator?

Sara

[mobile_bob]

Sara:

thanks for the off the shelf and somewhat out of the box thinking

to start with

#1, #2 seem reasonable, keeping in mind though most folks want to use an st5 which is limited in current capacity.

#3 will limit the output voltage to that of the regulator, so if it is a 12volt regulator, even an st12 at 100amps is going to do well
to produce 1200-1400watts, twice that if you have a 24volt regulator to work with, but there are many looking for a 48volt solution
and i am unaware of any mass marketed off the shelf 48volt regulator suitable for charging a battery bank.

#4 seems like a good thing too.

now my other concerns, and i present them because i don't know
my st7.5 needs 62volts at 2.7amps @full loading.  i suspect the field would have to be driven hard
at 14volts to get the machine to produce useful power at 12volts nominal, and many oem regulators can
drive 5amps of more into a field.  i don't know if the field can handle that , or whether one can even get the
field to take 5amps with only 12volts presented? probably not.

as for which would last longer?  for 12volts or 24volts, all things being equal, my money would be on the high output alternator.

for 48volts?  might be a tossup

bob g

[Lloyd]

http://books.google.com/books?id=uQMKAAAAIAAJ&pg=PA128&dq=alternator&lr=&rview=1&cd=3#v=onepage&q=alternator&f=true

Vintage Electrics