From: Watson 'Atto Parsec' Name
Subject: Re: Limiting total wattage for a constant-current dummy load?
X-Newsreader: MicroPlanet Gravity v2.60
Date: Mon, 11 Nov 2002 18:44:23 -0800
NNTP-Posting-Date: Mon, 11 Nov 2002 19:43:13 PST
Organization: InReach Internet
In article <email@example.com>,
jmuchow@SPAMMENOTcamlight.com talked about...
> I've got a 1.2-50V (approx.), 0 -10A constant current dummy load
> circuit (MAX480 op-amp, ICL8069 reference, and IRF540 for the load)
> working beautifully, but I have a problem I can't seem to find a
> solution for.
> I'm limited to about 50 watts for the load right now with the single
> MOSFET device and heat sink I'm using now. But, I can use the load
> with a current "setting" and load voltage that can significantly
> exceed the 50 watt limit if I'm not careful to figure out the wattage
> in advance.
> How can I allow both extremes of current/voltage (10A at up to 5V, or
> 1A(at up to 50V) to flow in this circuit but still limit the overall
> wattage dissipated? I can easily control the current to limit it to
> 10A through the IRF540, but I'm stumped as to how to use the voltage
> to determine the wattage the load would have to dissipate *before* I
> start the darn thing up.
> I'd love have an LED come on that told me "power is too high" if I
> selected a current level that would exceed 50 watts (or any arbitrary
> value) with the voltage present at the MOSFET load.
> Can anyone point me in the right direction? I couldn't find any info
> on the IR, National, Zetex, TI, Fairchild, or Linear Tech. web sites.
Have you ever thought about using several light blubs in series/ parallel
to give you a dummy load? If you burn one up, it doesn't cost you an arm
and a leg.
I just made a dummy load out of a 2SC2625 on a heatsink from a defunct PC
SMPS. I put a 2k 2W pot and 56 ohm 1W resistor in series between the base
and collector, and connected the emitter and collector across the power
supply. I can suck 10 or 15 watts before the heatsink gets noticeably warm
in a few minutes. Works pretty good. If I need more load power I have a
couple big old resistors, like 5 or 10 ohms, 50W or so, about 5 or 6 inches
long. And I have a pair of 25 ohm 50W Ohmite rheostats that I can adjust
to in-between resistance values.
But light bulbs are a cheap and effective way to get a dummy load that's
easy to tell when it's loading a power source. If you really need to load
it down, use an auto headlight.
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you put NOSPAM in the
Subject: line. alondra101 hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html