Re: off topic. electronics project

On Fri, 29 Mar 2013 10:56:19 greig corlett wrote:
> a bit off topic but im sure there is some electronics enthusiasts on here.
> 
> I am in the process of building a micro hydro generator from an old smart
> drive washing machine.  i have rewired the stator to give an output voltage
> between 60 and 120v depending on speed and mostly load.  I need to build a
> regulator which will charge a 48v battery bank and be capable of around
> 5-7A or about 250w.
> 
> I was hoping to be able to use a 3 terminal regulator like the lm317 with
> current boost transistors but since this regulator has a max voltage of 37v
> would not be suitable.
> 
> Is the another similar regulator which is capable of the voltages and can i
> use boost transistors in the same way with the higher voltage/ power
> required.
> 
> Thanks guys for your help it will be very much appreciated.

it's probably a better topic for the makerspace list .... but here goes ....

so your goal is not a 'boost' but how to drop the voltage without using some 
giant resistor that will dissipate heat and waste energy (ideally you put in 
120v at 7A in and get 48v at maybe 16Aish out) - I assume you've taken the 
output from your generator, rectified it with a bunch of diodes and dropped it 
into some large caps (say 1000uF) so you're starting with a DC voltage between 
60 and 120v

If you use a traditional voltage regulator like a lm317/etc (with or without 
transistors) it will drop the voltage by getting hot - it acts like that big 
resistor - to drop from 120v to 48v at 7A by getting hot you have to be able 
to dissipate (120-48)*7=500W - about half a bar on an electric heater - it 
will glow!

Instead you want some sort of switching regulator - the sort of thing that's 
normally used to generate something 48v from AC - it's going to involve a 
controller IC (a quick search on Mouser shows a possible chip as an example 
FSFR2100 - just one of many many chips - I'm not recommending it here, just 
using it as an example) a scary inductor or transformer and a diode and/or 
transistor or two, some caps and possibly an optocoupler 

These things tend to run at 100kHz-1MHz (for efficiency) you'll need to put it 
in a good metal case so it doesn't radiate all over the AM band and take great 
care about how you lay out the PCB

	Paul

PS: be careful about the word 'boost' in this context - it has a technical 
term when describing switching power supplies that's not exactly the same as 
how you used it above

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