Monthly Archives: May 2014

Solar IC charging a LiPo cell

Schematic used to build my circuit, provided by ST’s web-based design application. The Dout transient diode was omitted in this test.

After some frustrating nights, I finally have the SPV1040 solar charging IC working with my Iowa Thin Film Technologies photovoltaic strip. The PV puts out a nominal 3V at 25mA. Basically, the chip requires two voltage dividers for voltage and current feedback. The ratio of these dividers determines the output.

ST’s SPV1040 solar boost IC along with a 10┬ÁH power inductor and a Schottky rectifier.

While I have try and squeeze more out of it, the IC’s 100kHz PWM is able to knock this up to 5.5V at a peak of nearly 3mA. This is enough to power the TP4056, which is designed primarily for USB-powered charging. Given the relative gluttony of the charging IC, full sun is needed with the single PV strip in order to attain charging current. STM’s eval board uses a more efficient LiPo charging IC, which is something I am planning to investigate in my quest for efficiency.

Full sun charging the 3.7V LiPo cell via the TP4056 IC.

Ultimately, I’ve learned that while using alternative methods to solder an IC can be required in a pinch, it is more desirable to use known-working components and boards with the proper footprint.

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Filed under Battery power, DIY, ICs, Soldering

New steppers have arrived

Fresh from the journey from ShenZhen (via Thailand), these NEMA 17 motors have a rotation of 3.75 degrees and a phase resistance of 6.4 ohms. They are rated 5VDC at 0.5A, and are manufactured by the Minebea Motor Manufacturing Corp. The cost was under $10 each on eBay, with free (3 week) shipping.

Unfortunately the leads included have an incorrect connector, but I managed to carefully force one in order to test. As this places significant strain on the motor connector, it is not advisable to operate these motors long-term with the incorrect connector. Here are some photos.

Solid motor with incorrect connector. Notice the notches on the motor connector that do not match the supplied connector.

Significant strain is placed on the connector due to the mismatch.

While OK for testing, operating a motor with the incorrect connector will lead to premature failure.

I await a response from the eBay merchant as to how they will correct this problem. Stay tuned!

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SPV1040 and DS1337 proto boards

Instead of paying the few dollars for PCBs to accommodate these SMT devices, I gathered some materials and attempted to make my own proto boards. These were sourced originally for my cat tracker project. They have a decent square trace that accommodates 0805 SMT devices, and the FR4 isn’t difficult to cut through.

Cutting through this FR4 with a small file is easy work.

Although my soldering skills improved considerably with soldering the 30AWG winding wire to these TSOP and SOIC gull wing feet, ultimately the connection was not reliable enough, and led to some frustration in getting my SPV1040 solar IC up and running. Ultimately I located a cheap SIP proto board for the solar IC, but that is the subject of another post.

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Filed under DIY, ICs, Soldering