Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - Paul and Sabrina's Cheap 3 Phase Inverter (AC Controller) with Field Oriented Control

e*clipse · 11-24-2015, 05:02 PM

OK YEA! I may have some good news.

I've been working through a torroid core inductor design. It can get pretty involved, but the first stab at it with some big fudge factors thrown in is really encouraging.

There is really good info on inductor design here:
Powder Core Documents | mag-inc.com

The first thing you need to do is calculate the L*I^2 value; it's in millijoules.

So, using the worst case of 0.273mH from and 200A prior examples:

LI^2 = 0.273E-3 * 200^2 = 10.92milliJoules

Now, for a first stab you look it up on one of a zillion charts in the core catalog. That's the first reference in the link. These charts give rough suggestions for appropriate cores based on the L*I^2 value.

For my first stab at it, I looked up kool Mu cores and standard powder (MPP) cores.
On pg 77, there's a kool mu core #77095 that could work. It's OD is 48mm and it weighs 86 grams. Yes, grams.
Working out more details, you calculate how many winding wraps it will require. There is a number called the "inductance factor" Al, used in these torroids. In this case, it's 57nH/T^2. Divide 0.273mH/(57nH/T^2) and find the number of turns: 69.

Now, you can't just use the 69 turns number, because it's based on no load. In a number of examples (remember the zillion charts) they came up with about a 70% difference. I'm sorry about the fudge factor thing, but this is REALLY just a rough stab at it. Adjusting for the difference, I came up with 98 turns.

Using two #6 AWG wires with a current loading of 800A/cm^2 allows 200A. Again, I don't know if this is good, but it will handle the current and will fit in this size of torroid.

If you don't trust these numbers, and I really wouldn't blame you - LOL! The biggest torroid they sell has an OD of 166mm (6.5") and weighs about 2.2 kg.

So let's say half the inductor weight is core and the other half windings. That would be about 4.4kg in an absolutely worst case scenario.

Long story short - even with big fudge factors and using a huge torroid, it would be possible to cut the inductor weight to between 5 and 10lbs.

- E*clipse

11-24-2015, 05:02 PM	#2372 (permalink)
e*clipse Permanent Apprentice Join Date: Jul 2010 Location: norcal oosae Posts: 523 Thanks: 351 Thanked 314 Times in 215 Posts	OK YEA! I may have some good news. I've been working through a torroid core inductor design. It can get pretty involved, but the first stab at it with some big fudge factors thrown in is really encouraging. There is really good info on inductor design here: Powder Core Documents \| mag-inc.com The first thing you need to do is calculate the LI^2 value; it's in millijoules. So, using the worst case of 0.273mH from and 200A prior examples: LI^2 = 0.273E-3 200^2 = 10.92milliJoules Now, for a first stab you look it up on one of a zillion charts in the core catalog. That's the first reference in the link. These charts give rough suggestions for appropriate cores based on the LI^2 value. For my first stab at it, I looked up kool Mu cores and standard powder (MPP) cores. On pg 77, there's a kool mu core #77095 that could work. It's OD is 48mm and it weighs 86 grams. Yes, grams. Working out more details, you calculate how many winding wraps it will require. There is a number called the "inductance factor" Al, used in these torroids. In this case, it's 57nH/T^2. Divide 0.273mH/(57nH/T^2) and find the number of turns: 69. Now, you can't just use the 69 turns number, because it's based on no load. In a number of examples (remember the zillion charts) they came up with about a 70% difference. I'm sorry about the fudge factor thing, but this is REALLY just a rough stab at it. Adjusting for the difference, I came up with 98 turns. Using two #6 AWG wires with a current loading of 800A/cm^2 allows 200A. Again, I don't know if this is good, but it will handle the current and will fit in this size of torroid. If you don't trust these numbers, and I really wouldn't blame you - LOL! The biggest torroid they sell has an OD of 166mm (6.5") and weighs about 2.2 kg. So let's say half the inductor weight is core and the other half windings. That would be about 4.4kg in an absolutely worst case scenario. Long story short - even with big fudge factors and using a huge torroid, it would be possible to cut the inductor weight to between 5 and 10lbs. - Eclipse