You can, by more than that. Depends on the duration of the overload. Take a look at page 2:
-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Our only saving grace. Still no magic for energy storage... capacitors and inductors :-(
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
firmware
A typical scan would take minutes, not seconds. 850W is a small room heater, no matter how you calculate it.
firmware
Then it's liquid cooling, or some gigantic air flow. OTOH some of those ceramic space heaters are remarkably small and many have a 1500W setting. The smallest one I ever saw had the size of about two beer cans.
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"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
I'm amazed how much effort goes into taking relatively crappy inductors (e.g., spirals on silicon ICs) and turning them into something decent via application of any number of negative resistance schemes. (Although this is for filtering, not really energy storage as such, of course.) The usual problem I've seen in such schemes is that typically the input powers are well below
0dBm (223mV RMS), when 0dBm itself is usually just adequate and 10dBm would be much better.---Joel
The power is, worst-case, steady-state.
I've ordered some vitreous-enameled wirewounds from Digikey (at 3PM!) and might have them tomorrow. We have about 700 LFPM air flow. So, when they come in, we'll blow that much air on them, thermocouple/FLIR instrument them, and crank up the Variac.
We found some nice, cheap porcelain-on-steel thickfilms, 750 watts each in a few square inches. Two would be nice, but we can't get enough heatsink in the available space... hs tamp calculates to about
500C!John
I've not used spirals for any thing other than in VCO's... at around
5GHz....Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine Sometimes I even put it in the food
The original design used a switcher, but it had a tendency to blow up. The virtue of using a real resistor is that we can bring the thing up and do a lot of self-tests with no direct silicon path from V+ to ground or V-. When there's this much power involved, you don't want to just pray and hit the circuit breaker. The boost supply is used at powerup for the preliminary fet tests, as a safe, current-limited test supply voltage. Later on it's used to precharge the filter caps before we kick in the big power supply, and it's finally used as the boost voltage for kicking L di/dt into gradient coils.
I've always wondered what it's like to power up the prototype of, say, a megawatt AM transmitter.
John
firmware
With wirewound sans enamel and all that stuff you can drive things pretty hot. I don't know how hot but, for example, on a cold winter evening our wood stove has the baffle plate glowing dark red for hours. Asked the stove guys and they said it's ok. It hasn't aged a bit in many years.
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"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...
I would think that the phase noise of such a VCO wouldn't be that great, but such an oscillator is probably just the heart of a PLL so the PLL greatly reduces the phase noise within its loop bandwidth... which is probably good enough?
I believe you've said you've designed complete PLL-based synthesizers at times? You probably have some fancy PSpice macros/sub-circuits to generate/measure phase noise?
---Joel
They use a realllllyyy big VARIAC where someone has precisely determined how much power is lost in the big brush that's shorting multiple turns. :-)
This article discusses the anisotropic nature of the brush that you mentioned:
I designed a satellite spinner/launcher back in the early 90's. We had a mock-up of the launch rocket hung from a crane... big as a luxury car and spinning at 8 RPM.
I hung out behind a building pillar when it was first spun up ;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
Obama\'s resume would fit in a Chinese fortune cookie
I've always calculated those numbers by hand. I don't know if a macro would do much for me there.
...Jim Thompson
-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Obama\'s stimulus package has more pork in it than a pig farm
I think we're talk VARS here, not W.
Driving a coil with a linear amplifier produces ~ the same losses in the driver as if it were running into a short circuit. The power losses have got to go somewhere.
For power ratings, review the input line hardware, fuses and thermal limiters present.
RL
The 850W into a 20 ohms resistor indicated that he is driving at 42 amps average. It's still a lot of current for the traditional MRI excitation/relaxation sequences. My guess is that they are trying directional excitations, rather than relaxations. If that's the case, they have to realize the increased power requirements and to drop the size and cost restraints.
firmware
Oval wirewounds stack up on standard bolt/spacer hardware to allow air flow. You'd want ten or more in parallel to get your 20 ohm target.
FSOT55-100 FSOT55-250
Huntington parts are off the shelf at digikey. No ceramic glaze to crack.
These are used in passive loads and exhibit long service life under the usual abuse. Fan advised.
RL
The imaging gradient coils run a good fraction of an ohm. They are typically water cooled.
John
The early ones were tube designs, and used a pair of custom output tubes. Modern solid state Am broadcast transmitters are modular designs where they use whatever number of identical RF output stages they need to achieve the rated power. They are built & tested at the module level. Harris Broadcast builds high power solid state transmitters. They have pulled all the white papers off their website that described the designs. Now its another crappy website with loud music. :(
Their first generation design used banks of matched TO-3 transistors in each tray. The transmitter ran directly off either three phase 208, or the standard 240 volt single phase service. No power transformer, just a big modulated switch mode power supply to generate the AM signal. I've seen piles of trays damaged by direct lightning hits here in Central Florida from a 5 KW transmitter for a station near Leesburg.
The transmitter detects failed modules and switches them out of the system, then notifies the engineer of the problem by email.
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On a sunny day (Mon, 02 Mar 2009 15:45:25 -0800) it happened John Larkin wrote in :
Red hot wire = fire hazard = explosion danger?
and the inductive component?
RL
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