Monday, September 30, 2013

Regrets????


I dunno about this....I just signed up to link my Google+ account to the Voltage Multipliers Inc. blog.  I'm not exactly sure what that means....

You may notice a different profile image.  Beyond that, I'm not sure what to expect.  I WILL be monitoring it, though.

Are any of you out there Google+ users?  Are your blogs and/or websites linked to your Google+ account?  Would you mind sharing, either here, or privately? 

Oh!  And today I wrote my first mobile advertisement for high voltage power supplies.  I used our HighVoltagePowerSupply website, and Daniel Deshenes' phone number for the contact.  Please don't inundate him with phone calls just yet....give it a few days.  (Just kidding) 

Thanks for your patience.

Friday, September 27, 2013

Voltage Stress vs. Isolation Voltage


In a rectifier assembly that generates heat through forward or reverse power dissipation, isolation voltage is often overlooked.   

One strategy frequently used is to use a metal base plate under the diodes.  It’s use helps dissipate heat so the diodes stay cooler.  When components stay cooler, the general effect is greater reliability. 


High Voltage Diode Spacing
High Voltage Diode Mounted Over Metal Base Plate
 

Grounded Base Plate and Heat Dissipator


If circumstances are such that the base plate is grounded, then the voltage gradient between the internal diode leads and the external ground plate is concentrated in the encapsulation material between them. 

 If the potting material is rated at 500V/mil, it will probably and eventually fail at 500V/mil stress.  The failure will most likely result in a short between a high voltage diode lead and the grounded base plate. 


 Reducing Volts/mil Stresses

 
One way to reduce the volts/mil stress of the potting material is to increase the distance between the diode lead and the base plate.  That will increase the isolation voltage, but at the same time, the thermal conductivity will decrease because the thermal path has increased by the same amount.  Keeping the thermal path between the diode to the base plate is the key to getting the heat out of the diode.    

Isolation Voltage and Thermal Conductivity


In other words, isolation voltage and thermal conductivity are on opposite sides of the spectrum.  It's a delicate balance between heat dissipation and isolation voltage when outside operating conditions place a ground plane near a base plate, and the rectifier assembly runs hot.  

Sources of Heat


Heat can come from forward losses (Vf, If), and reverse power losses (Vrwm, Ir).  Several factors influence heat generation - operating temperature, operating frequency, signal type, forward voltage drop, to name but a few.


Designing a rectifier assembly, be it a high voltage stack, single phase or three phase bridge, or even stacked bridges, can push design limits to the max. If you have any questions about designing your rectifier assembly, give us a call.  We’d be happy to assist you in any way possible.

 

Wednesday, September 25, 2013

VMI Does It Again - For the 21st Year in a Row!


Every year for the past 21 years, VMI has participated in the annual Relay for Life benefiting the American Cancer Society.  One weekend during the month of September or October, VMI's team walks the track for a solid 24 hours.  In order to participate, the team must raise $100 per team member.  This year, VMI raised over $4,350, ranking 6th out of 70 teams.  

Kudos to the team!  Planning is year-round, and many people volunteer their time and talents to make it happen. 

VMI's 2013 Relay-for-Life Team Members


2013 TEAM VMI SUMMARY

Team Members: 24

VMI is the second longest running Team at the event.

Visalia was the first city in California to have a Relay-for-Life event. 

Total money raised was $4,355.52.  We ranked 6th out of 70 Teams this year.

Our fundraisers included candy sales, bake sales, ice cream sales, Frito boats, tacos, hot dogs, and novelty items.  
 
95% of the money raised came from our VMI employees! Wow!

Thank you to everyone at VMI for supporting this great effort of service to our community. We are also well known in the Relay For Life community. 

On Monday 09/23, the Visalia Times Delta newspaper included pictures of our team as well as a small article on a family member of one of our team members.

There will also be an article on Saturday of our team.

See y'all next year!

Monday, September 23, 2013

2014 Sales Seminar is ON!


After seven years (7) we are finally down to almost Six Months to the big event that you have all been waiting  for.  The answer to ” are we going to have a Sales Seminar?”, the answer is YES.   So SAVE THE DATE !

When: April 8-11, 2014 ( arrival on Tuesday – departures Friday)

Where: Visalia Marriott  and Convention Center
   300 South Court Street
   Visalia, CA 93291 USA 

Your Ideas - Please Share! 

Is there something you'd like to bring up?  Your ideas on topics you would like discussed are welcome.  Diodes?  Power Supplies? Lead times????  We welcome your suggestions.  Please email or call or otherwise contact us by January 2, 2014.    
 

Arrivals, Departures, and In-Between Schedules


VMI will work with each of you on arrival times April 8th and provide pick up transportation from Fresno Yosemite International Airport (FYI) Fresno CA to Visalia.  We will do the same for departures on Friday April 11th.

Tuesday April 8th, 2014  Welcome Reception at the Visalia Marriott

Wednesday  April 9th, 2014
  • Breakfast Buffet
  • VMI Plant Tour (Bus transportation provided)
  • Morning meetings
  • Lunch
  • Afternoon meetings until 5:00 PM
  • Dinner (approx. 6:30 PM
Thursday April 10th, 2014
  • Breakfast Buffet
  • Morning meetings
  • Lunch
  • Afternoon meetings 1:00PM to 5:00PM with break at 3:00PM
  • Thursday April 10th 2014 Closing Dinner and Rep Awards & Recognitions
Friday April 11th, 2014
  • Departures
Please let us know if you have any questions .  More details to follow as we get closer to the Main Event.

We are looking forward to seeing everyone again in VISALIA!

 
Kind Regards,

VMI and CalRamic

 

Wednesday, September 18, 2013

Custom High Voltage Three Phase Bridges

AMRAAM Missile
Photo Credit 
If you're of a certain age, you may remember when high voltage three-phase-bridges (3PB) were all the rage.  Usually they were of significant wattage to power ground-based radar or missile guidance systems.  I didn't know much about the actual applications beyond the electrical requirements of some of the bridge rectifiers, but I was keenly aware of the pain level of building them.  From a manufacturing point-of-view, one particular group was a nightmare to build.  From what I hear, the transformer makers had it easy.  It was the rectifier manufacturers whom the system designers threw under the proverbial bridge (no pun intended).
Schematic of High Voltage Three-Phase Bridge
The challenge was balancing the age-old size and performance dichotomy.  They are two qualities that are directly proportional.  The more space you have, the higher the reliability, presumably so you can spread things out.  As size goes down, so does performance.  Price, on the other hand, is a mixed bag.  As size goes down, price goes up.  As performance goes up, price goes up.  Price, performance, or size.  Pick any two.  (I don't make the rules, I just observe them).

VMI is in the business of designing custom 3P bridges.  Most of our designs fall in the high-voltage-high-current category.  Typical ratings are 3kV, 100mA, or say, 10kV, 10mA.

Key Characteristics of High Voltage, High Current Three Phase Bridges


It's tough to know which characteristic is most important because they are all intertwined.  In terms of performance, how you get the heat out has the most immediate impact on performance.

Heat

Nothing eats up a component faster than heat.  Heat can come from many different sources in a bridge - too fast of an operating frequency, too much forward current, insufficient cooling or thermal transfer.

There are several ways to deal with heat.  The three most common ones are -

          1.  Additional internal heat sinking
          2.  External heat-sinking systems
          3.  Component de-rating

Internal heat-sinking means you add a thermally conductive object, such as a copper heat sink, to the package.  A copper plate soldered to the leads of a diode increases the thermal path area through less thermally conductive materials, such as epoxies, and is often referred to as a 'heat-spreader'.

External heat-sinking systems include mounting the assembly on a water-cooled base plate, running it in oil, or convection cooling.


3P High Voltage Bridge with Metal Housing, Solder Turrets, and Mounting Holes
Component de-rating works by specifying devices that can easily handle the required operating conditions without breaking a sweat.  An example is using a diode that's rated for 500mA when the actual system requirement is only 50mA.  A de-rated component is usually larger, so space might be a limiting factor.  A 500mA diode will have a larger body diameter than a 250mA diode.      

Mounting    

Common mounting strategies include embedding inserts - mechanical, threaded, sleeves - into the body of the assembly.  The inserts provide a way to attach the assembly to a base plate or frame.  The connection is usually made from the bottom.

Threaded through holes are also common.  This method is also used to attach to base plates or printed circuit boards.



Packaging

A metal housing has the added advantage of providing a larger thermal path vs. that of an epoxy shell.  The disadvantage is that it's conductive, and in high voltage applications, care must be taken to ensure terminals do not arc to the metal casing.

A metal housing often includes mounting holes, making the assembly process a bit easier or more secure.  

Terminals

Quik-connect terminals like the one's shown below are popular, and are popular.   They are easy to connect, and do not require soldering.  You can solder to them, if you like.  Other options are flying leads, pin-mount, solder terminals, or high voltage connectors.  There are many to choose from, you just have to make sure the wire ratings will handle the output voltages, and the wire should be compatible with any encapsulation materials you may be using.
     


Quik-connect uninsulated tabs

Electrical Specifications

Typical 3P bridge specifications call out the Vrwm rating per leg, and average Io for the whole bridge.  The theory is that each leg of the bridge will see 100% of the current for 1/3 of the time.

Other parameters that may be included are isolation voltage (terminal to ground, terminal-to-terminal), thermal impedance, reverse recovery time.

In addition, operating frequency and temperatures are factors in selecting the right diode for the job. 

If you need assistance in picking the right diode for your discrete bridge, or need design assistance, give us a call.  It's our business.