Looking for pulse-rated zener.

[Watson A.Name - \Watt Sun, the Dark Remover\]

Jim Thompson wrote...

I never could understand why Western houses eschew basements.
A full basement is a VERY useful thing to have. Get double
or half-again the floor area of the house in one quick step.

Well, some areas of the coutnry have to have basements because of the
tornadoes. But here in So. Calif, we seldom have basements, I'm
guessing the reasons are:

Because the dwelling is on a sandy soil that has a shallow water table,
so the basement would be easily flooded.

Because most of the housing built after WW2 used a poured cement slab
for the floor.

Because in a bad earthquake, the rest of the house would fall into the
basement.

Because it's cheaper to build a second story out of wood than dig a hole
and pour concrete walls, needed for earthquake reasons. Also since it
doesn't get cold here, the insulation doesn't have to be that great, so
the second story is even cheaper.

Probably a combination of the above.

I think that this place has a cool basement.
http://www.earth-house.com/Homes_4_Sale/Atlas_E_Silo/atlas_e_silo.html

 

[Winfield Hill]

colin wrote...

The same thing would happen with the simpler RC snubber accros a single
switch as was suggested before, but put a diode in series with the inductor
so that when the current stops the diode blocks the voltage acros the
capacitor causing current in the reverse direction through the coil.

when the switch opens the current travels through the resistor and
(discharged) capacitor, initialy creating the necessary voltage across
the R, then when the curent drops the voltage acros the resistor falls
and the voltage across the capacitor has risen keeping the voltage high
enough all the time the current is flowing for a fast fall time/peak
voltage, when the switch next closes it discharges the capacitor through
the resistor as it turns on the current to the coil.

o
|
C|
C| coil
C| L
|
|
V diode
-
| R
+-----/\/\----+
| |
| D | C
||-+ ---
||<- ---
o-----||-+ |
| S |
-+-------------+-

Yes, that's good. One must be careful not to select R too small,
because then the FET's current at switch-on might be excessive.
And one musn't selecting R too high, because then it'll develop too
much voltage from the inductor's current at switch-off, forcing us
to use an artificially-high-voltage FET. Selecting R so its maximum
voltage drop equals the maximum capacitor voltage sounds promising.

Applying this to Mark Becker's 8uH 15A 1us shutoff requirement, with
C = 33nF and R = 7.5 ohms, we get a snappy 0.7us coil-current switch-
off, a maximum FET voltage of 190V, and a maximum FET current of only
19A for 0.5us at switch-on. The coil is slow to get up to its 15A
current, saving the FET any extra stress.

We need a high-current diode rated for more than 200V. I used both
halves of a MUR3040, but despite being a fast-recovery part it still
suffers from a reverse-recovery-time delay. This means the inductor
rings badly (at 4MHz, 380Vp-p in my model) unless its damped. Adding
0.01uF plus 150 ohms in parallel does the job nicely, and also reduces
the FET's Vd-max to 180V and Id-max to 18A.

One big downside to this approach to capturing the inductor's energy
is another 15W of power continuously dissipated in the series diode.

 

[colin]

colin wrote...

Two different effects... The slowing of the turnoff means the
coil can flyback and dI/dt discharge as it's doing so, without
reaching the avalanche voltage, if carefully done.


You're asking if oscillation doesn't happen in the event of a
slowed transition, as in the zener case? It certainly can with
high-voltage MOSFETs, although the dV/dt slewing output helps to
hide it, on the one hand, and perhaps to dampen it, on the other.

Yes thanks thats what i was asking, as both cases have the vds>20v @ high
curent. Trying to think of a way of avoiding it yet still using a more
deterministic way of setting the peak voltage.

Actualy i was wondering if a cascode mosfet arangement would behave any
better, again it might make it less noticable as the bottom device would
stay more in control of the current, although i would be worried about this
as long ago I had some nasty oscilations when i was trying to make a high
voltage power supply with several series mosfets (600v mosfets were very
limited at the time), but unfortunatly i never had the time (or the
experience back then) to get to the bottom of all the diferent modes of
oscilations.

Colin =^.^=

 

[Robert Baer]

Winfield Hill wrote:

[...]

One question, Mike. Did the house have a good gutter system, with
drainpipes, to keep roof drainage away from the basement walls?

Thanks,
- Win

Very astute question, Win. The drainage was very poor. The gutters were
full of leaves and warped so they wouldn't drain properly, and water
just spilled over in the middle. But you don't notice these things until
the first storm, after you have signed the lease and moved in.

The downspouts were normally connected to drainage pipes to take the
water away from the house, but these had been removed to make cutting
the grass easier. So the water stayed along the exterior walls.

The basement wasn't sealed - the concrete was bare. After the first
storm, there was several inches of water in the basement. A great deal
of wood that was stored lying flat on the floor turned out to have mold
underneath.

The landlord promised to fix everything but it never happened. Then
winter set in and it became impossible to do anything. Ottawa had an
extremely low vacancy rate at the time, and the landlords could get away
with anything. You counted yourself lucky if there was a roof over your
head. Some of the places I looked at were just incredible.

All these things were against city code. But lack of enforcement meant
doing the best to try to fix things myself. This turned out to be
impossible. An amateur with a paintbrush cannot seal a concrete
basement. It takes professionals with the proper equipment, and it
should have been done when the house was built.

I tried to leave as soon as the first symptoms started, but a vacancy
rate of 0.3% in the middle of winter meant there was nowhere else to go.

My big mistake was underestimating what mold can do to your health. The
worst symptoms didn't really show up until after I moved. By then it was
too late.

Since then I have found many basements that are sealed properly but may
have accumulated cardboard boxes full of paper or clothes. Even if the
basement doesn't leak, the cardboard accumulates moisture and provides
an excellent place for mold to grow.

So if you can smell a musty odor after returning from shopping, mold is
growing somewhere and it should be corrected.

Mike Monett

Check the rental laws.
I understand that in most states (US) that a lease of one year or
more, even tho it *states* one year (or more) in reality means
"indefinite" which translates to *any* amount of time the renter
desires. Some states may require the lease to state one year and one day
at minimum for that interpretation.
A lease less than one year runs for the specified period.
Something to consider and use.

 

[Robert Baer]

Jim Thompson wrote...


I never could understand why Western houses eschew basements.
A full basement is a VERY useful thing to have. Get double
or half-again the floor area of the house in one quick step.

Well, some areas of the coutnry have to have basements because of the
tornadoes. But here in So. Calif, we seldom have basements, I'm
guessing the reasons are:

Because the dwelling is on a sandy soil that has a shallow water table,
so the basement would be easily flooded.

Because most of the housing built after WW2 used a poured cement slab
for the floor.

Because in a bad earthquake, the rest of the house would fall into the
basement.

Because it's cheaper to build a second story out of wood than dig a hole
and pour concrete walls, needed for earthquake reasons. Also since it
doesn't get cold here, the insulation doesn't have to be that great, so
the second story is even cheaper.

Probably a combination of the above.

I think that this place has a cool basement.
http://www.earth-house.com/Homes_4_Sale/Atlas_E_Silo/atlas_e_silo.html

I guess i better use some of my "pocket lint" and get that shack...