Heat Sinks for WB was RE: WBO2 testing

[Stephen Andersen]

It is starting to appear that I have significantly 
underestimated the amount of heat sink required for 
the WBo2.  I bought some small heat sinks from RS today
that are finned anodized aluminum guys about 1.5" x .75"
x .75" or so.  I guess one of these isn't enough huh?

If that is the case, I am going to have to completely 
rethink the packaging of the WBo2 and LCD/RS232 display 
boards.  I definitely have not allowed for enough room in the
box with larger heat sink(s).

Any guidance from those that have completed their WB's and 
have them functioning?

Can someone point me to a properly sized Digikey heat sink?

How do you attach the heat sink to the power transistor (I think
that is what it is, right?) and the big resistor?

Thanks,
Steve


> -----Original Message-----
> From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org]On
> Behalf Of bcroe at juno.com
> Sent: Tuesday, December 18, 2001 1:35 AM
> To: diy_efi at diy-efi.org
> Subject: WBO2 testing
> 
> 
> Measure the voltage across the lamp, and across the
> 1 ohm resistor.  If the lamp has less than 10 volts (and
> the LED is out), you are probably running in the curent
> limiting warmup mode.   The resistor will measure 
> about 1.25 volt in that case.  
> 
> You probably are using too large a lamp.  With a small
> voltage drop across the lamp and maximum current, you
> have a large voltage drop (at max current) across the 
> LT1086.  This heating it up, apparently to the point of
> thermal shutdown which dims the light.
> 
> I would find a smaller bulb, which should run at 10 V
> with reduced voltage across the 1 ohm (crossover to
> voltage regulation).  A 2" by 3" heatsink is not very 
> generous for this application, unless it has a lot of fins.
> 
> Bruce Roe 
> 
> On Mon, 17 Dec 2001 01:04:09 -0500 Glen Beard <gbeard1 at nycap.rr.com>
> writes:
> > OK, I've gotten everything soldered up, and I am testing the
> > heater circuit using a tail lamp.  The lamp turns on nice
> > and bright building its current to 1.003 Amps.  Is the LED
> > supposed to turn on after a while?  Is the LT1086 (VR)
> > supposed to get sizzling hot even with a 2x3" Al heat sink? 
> > With the smaller heat sink I had on it, the bulb would light
> > up and then start to dim again.  If I blew across it and it
> > got brighter.
> 
> > Glen Beard 
> 
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