RadioBanter - View Single Post

February 22nd 04, 07:41 AM

wrote:

This is not directly HAM releated,
but Ham radio is used in the project.

I'm building a Solar powered RC plane.

In that plane I have 6 different solar cell planes.
For each plane I'm building a maximum power point tracker.
The heavest component of the MPP is the inductor.

I need the lighetest most efficient inductor possible.

Specifications

30uH min, 50uH prefered.
6 amps DC current max.
7 amps peak current max.
50 to 150Khz switching freq.

(The current ripple has to be low in releation to the DC current to
keep the solar cell in the "Sweet" spot.

Inductor can not be bigger than 100mm in diameter and 25 mm thick.

I'm thinking I want a Aluminium wire air core toriod, but I'm not
sure.

The weight trade off:

At the point of marginal flight. (About 3 amps in the inductor)
Weight is at an absolute premium. I can trade one watt of inductor
loss (at 3 amps) for 190 gm of mass.

Assuming 12 Ga wire in a cylindrical core 4" in diameter:
12 Ga two layers of 10 turns each gives about 45uH.
251 inches of wire for a wt of: 57gm
and a DC loss of: 1/2 W at 3 A and 2 W at 6 A

I'm a bit lost here .... any suggestions on how to proceede?
Should I consider using a toroid core?
Adds weight, and switching losses, but reduces the total feet of wire
and thus the weight.

It would be a lot easier of solar cells were not low voltage high
current devices... alas they are.

Paul (Kl7JG/6)

A powdered iron toroid inductor may be close to optimum from a weight
standpoint. Check out these part numbers from Digikey:
125 uHy @ 7.77 ADC, .032 ohms, 46 mm dia, 19 mm high, M5716 (the data
sheet may have the weight)
34 uh @ 6.4 ADC, .026 ohms, 22 mm dia, 14 mm high, M9797
63 uHy @ 7 ADC, .037 ohms, 29 mm dia, 17 mm high, M9823

--
John Popelish