Switching current limiter for safe charging of large capacitors, and short circuit protection

[P E Schoen]

This might do the job at 50kHz or so:
http://www.ebay.com/itm/Replacement...123?pt=LH_DefaultDomain_0&hash=item35bce6f06b
$13, free shipping.

I have a pair of EE cores, part number D66 343-C-027, and there are N27
markings on it. I also have some bobbins that might be for an even larger
core, but with a square center. These cores have a cylindrical center 0.642"
and the overall dimensions of each half are 0.642" thick x 2.75" wide by
1.357" high.

I'm not very good at magnetics, so I would need to know how much power these
cores can handle at various frequencies, and the volts per turn at
frequencies such as 25kHz, 50kHz, and 100kHz.

The biggest core I found is:
http://www.ebay.com/itm/E100-EE100-...799?pt=LH_DefaultDomain_0&hash=item3a71ebd00f
but it's $36 + $20 shipping.

Most of the ones on eBay are EE42 and EE55.

Here is a pretty big toroid core:
http://www.ebay.com/itm/Blue-Ferrit...761?pt=LH_DefaultDomain_0&hash=item3cc0254521

Thanks,

Paul

 

[Joerg]

"Joerg" wrote in message


I happen to have about 12 or so powerstat cores that were damaged in an
early design of ETI's breaker test set. They are Staco 2510 and were
supposed to be rated at 9.5 amps and 280V, or almost 3kVA at 60 Hz. But
the unique brush design (a thin flat carbon piece rather than the usual
wedge) overheated, cracked, and then the brush assembly landed on the
windings and caused major damage. I was going to use them in
series/parallel to make a breaker test set rated at 4000 amps and 12V.

But those cores are about 25-30 lb each. However, by running them at 2
kHz I think it would be possible to get at least 10kVA.

You had an unusual source to get those but the DIYer who wants to build
this project may not.

I tried using some small ones first. They were only 175 and 300W, so
they would power the VFD and spin the motor under no load, but died
under power. My second movie about my project shows this. I was going to
get a 2000 or 3000 watt unit, but they are mostly 12 VDC. And they are
not isolated. There is a 150 VDC internal bus, which is probably 300 VDC
for the 220V models. So I could probably pick up the voltage there. But
they are about $1/watt. And I already had the toroid, and the heat
sinks, and the big capacitors, and the heat sinks.

$1 a watt? No way. I have a pretty good 300W inverter and those can be
had for around $30. You do not need an expensive modified sine version
and you may not even want that because they modulate the 150V rail.

Not sure how good these are:

http://www.harborfreight.com/2000-watt-continuous-4000-watt-peak-power-inverter-95596.html

24V versions cost more but not a whole lot because that's the voltage
for trucks and buses in Europe.

I've dealt with them before. I'll see what those look like. But I found
some on eBay that are supposed to be good for 3000 to 7000 watts:
http://www.ebay.com/itm/E80-Large-T...330?pt=LH_DefaultDomain_0&hash=item27c830594a

If you want to make this into a DYI instruction or fun project for
others EBay may not be the ticket. Once the auction has ended and all
ferrites are gone -> game over for everyone else. You need something
from a catalog that can be bought for years.

These inverters also contain information: How small a toroid they got
away with and at which frequency. You'll have to multiply that by a
healthy factor because DYIer won't have inductor winding machines and
can't get custom wire or copper stock for the primary.

They are generally rated at 2VA to 50VA, but those are very conservative
ratings for 1% or better metering. They will probably handle about 5x
that at 60Hz, and I think they will also work on 2kHz to get a much
higher V/turn. I have a box of them so maybe I'll try it. If the
secondary winding can put out 300V at 5A, that's 1500 VA. And the hole
in the donut is big enough for a total of 16 turns of #10 enamel wire,
good enough for 60 amps at 24V at 50% duty cycle.

Watch the core temperature when you do stuff like this. It can appear to
rise slowly but inside it's an angryf volcano.

That is the same principle as an autotransformer. I'm working on a
design for someone who wants to boost 48V to 96V, at 200A or more, and
for a 2/1 boost it makes the booster half the size. But for a 24V to
300V, the savings are less than 10%.

10% is 10%

It's also about efficiency because the first 12V (or in your case maybe
24V) are always 100% efficient.