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Re: 250watt solid-state flybacks? (fwd)



---------- Forwarded message ----------
Date: Wed, 13 Oct 1999 08:51:43 EDT
From: Bobbaust-at-aol-dot-com
To: tesla-at-pupman-dot-com
Subject: Re: 250watt solid-state flybacks? (fwd)


> Subject: Re: 250watt solid-state flybacks? (fwd)
>  
>  Hi David,
>               ditch the 2 lead acids for a start.  The power you can put 
into 
> 
>  most flybacks at 24V would be more like 50W or 100 if you were lucky.  I 
>  suspect I was the guy who said you can get 250W into a flyback.  For this 
I 
>  used a 70V supply and put about 4A in but the FETs burnt at least 30-40W 
of 
>  that so cal it 250W.   
>  The basic system is fairly simple, a square wave oscillator, a a fet 
driver 
>  chip and a large FET or bipolar.  It is easier to use fets as they draw a 
> lot 
>  less base current and make life easier for the driver.  If you use the 555 
> as 
>  your oscillator you can drive it straight into the FET as the 555 can 
>  sink/source 500ma, remember to put a snubber network in tp protect the 
555, 
>  this isn't really necessary but it easier to take little peracutions that 
>  cost almost nothing than keep blowing chips.
>  I would question whether you need that much drive power as all that the 
>  higher power seems to do is heat up the flyback and make the sparks more 
>  intense.  I have tried up to 2kW into a flyback and all it did was shoot a 
>  huge arc then blow itself to bits leaving little more than a scorched 
core.  
> 
>  For your application I would say that you want about a 100W or so.  
> Therefore 
>  I would have thought you could get away with about 40-50V drive depending 
on 
> 
>  your flyback.
>  
>  Have (Head Mounted) Fun
>  Nick Field
>  
Sounds like Nick thinks you need more voltage input than your batteries 
alone.  Some options: 
1) use 3 or 4 smaller lead acid batteries in series for 36-48 VDC as a 
source. 
2) use the 12 V battery to feed a canniballized car stereo amp, they usually 
have internal inverters that convert 12vdc to around plus & minus 20 to 30 
vdc supplies for a total of 40 to 60 vdc.  
3) use the 12v battery to feed an inexpensive auto inverter.  You can get 
these for $30 - $40 rated at 100 to 140 watts.  They have inverters and 
generate a 170-180 vdc supply.  They also have high-V high-speed switching 
transistors (probably mosfets) to produce a nice square wave for the 
"modified sine wave" output they all put out

If you get someting working let us know, this sound like something I would 
build (and wear).

Bob Baust, newbie