Turnigy 5A 26V SBEC (SBEC-26V)

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The SBEC-26V is a switched mode regulated supply intended for powering electronic and servo loads at up to 5A.

Fig 1:

Fig 1 from Hobbyking shows the SBEC-26V. Not shown is a ferrite toroidal core supplied to assist in RFI suppression.

Manufacturer's information

The product description is:

Turnigy 5A SBEC is an advanced switching DC-DC regulator which will supply a constant 5A. It works with 2 - 7 Cell Lipoly pack and supplies a constant 5 or 6v to your receiver and is interference-free.

The manufacturer's specifications are given as:

Type: Switching
Input protection: Reverse polarity protection
Output (Constant): 5v/5A or 6v/5A
Input: 8v-26v (2-7cell lipo)
Weight: 18g
Unit comes with full instructions.

Testing

The SBEC-26V was powered by a 12.0V regulated supply, and a variable electronic load connected to observe the output voltage regulation. Ambient temperature was 20° and the DUT was naturally cooled (ie no forced air flow).

Fig 2:

Fig 2 shows the output regulation measurements. Though the SBEC is rated for 5A, it was not possible to obtain more than 3.7A without the SBEC shutting down within tens of ms.

The SBEC would not sustain more than 2.5A continuously, just 50% of its maximum rating. Under these conditions:

input current was 1.56A @ 12.0V (18.6W);
output current was 2.5A @ 4.45V (11.13W);
overall efficiency was 59%;
temperature rose to 130°, a dangerously high temperature; and
thermal shutdown worked in protecting the SBEC from damage, though the temperature limit was very high and might result in damage to other equipment or injury to persons.

Input voltage and current were also recorded, allowing calculation of efficiency and dissipation.

Fig 3:

Fig 3 shows the conversion efficiency. Efficiency decreases with increased output current, which will produce a compounding effect on dissipation.

Fig 4:

Fig 4 shows the SBEC dissipation.

At 2.5A load current, temperature rise of the chip case was 110°for 6.7W dissipation which suggests a thermal resistance case to air of 110/6.7=16.4°/W which allows prediction of temperature rise at other currents.

At 1A continuous current, the chip case temperature was 55° which reconciles well with prediction. At 1A continuous current on a 35° day, expected case temperature would be 70° which is hot enough to burn skin with prolonged contact.

Conclusions

The SBEC works, its continuous current rating is way less than specifications though achievable current may be higher with forced air cooling which may be provided in some applications.

The safe limit without forced air cooling is probably around 1A continuous, just 20% of its maximum rating.

If the SBEC was to supply critical components of a model system, consideration should be given to its tendency to shut down on current well below the specified maximum current.

Products

The article should not be seen as a recommendation or endorsement of any products.

The products shown in this article are from Hobbyking who manufacture products under a range of brand names, possibly creating an illusion of competition. Their products tend to be low in cost and low in quality, products are not good value when you have to throw a proportion of them in the rubbish because the cost of returning them exceeds the value of the replacement which is only available after excessive delay, many follow ups and haggling. If you see the claim [o]ther stores will force you to ship the product back to China in full retail packaging every time! Hobbyking's warranty service is professional, fair and fast, don't believe it, it doesn't work that way in my experience... I get better service from most eBay sellers!

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