Prototype waterproof versions of Linear and Switching Voltage Regulators (BEC)
2. Linear Voltage Regulator 5v 1a
3. Digital Voltage Regulator 5v 3a
5. Battery Voltage
6. Linear Voltage Regulators. Dropout voltage, Heat, Efficiency
7. Digital Voltage Regulators. Voltage, Current, Heat, Efficiency
8. Voltage Regulator test bed.
9. Adjustable 3A Voltage Regulator.
10. Current load tester
Voltage Regulators are electronic devices that change their input voltage into some other fixed output voltage. When placed in line with a battery it gives a steady output as the battery voltage reduces.
The most common form of voltage regulation is the 5v BEC output from an ESC Speed Controller. The voltage is feed back to power the receiver via the ESC signal cable. The receiver then powers other equipment.
The standard output voltage is 5v as many products using Integrated Circuits require a 5v supply. A PICAXE microprocessor runs on 1.8 to 5.5v.
BEC supply from Mtronix Viper range is 1.2a max (or 1.5a on the back page) but no voltage.
It is commomly assumed that the BEC output is fixed at 5v but this is wrong as it varies with the current load. These devices should be called “Voltage Limiters” as they limit the voltage to a maximum value which is not 5v.
There are two types of voltage regulators Linear BEC or Digital UBEC (Ultimate BEC) alternatively called SBEC (Switching BEC).
Output Voltages are usually specified in 5 or 6v nom. I bulit my own adjustable regulator to make these tests. Fixed voltages can be made for any value.
This voltage regulator is of the Linear type so the difference between the input and output wattages is given off as heat. 5v and 1a nominal output with current and tempreature overload protection.
Max input 20v. Only values upto 12v have been tested as this is the limit of my testing equipment.
Encapsulating the components in a case to waterproof them restricts the rate of heat disipation so high currents and voltages are limited.
The maximum values were obtained after running the regulator for 30 minutes to allow the tempreature to stabilise. Higher values are possible for short times, the system will shut down partially or completely if the heat and current rise over its limit.
Max Current for Input Voltages:
0.3a/12v, 0.4a/10v, 0.6a/9v, 0.75a/8v, 0.8a/7.8v, 0.9a/7v, 0.9a/6v.
4.9v maximun output. If input drops below 6v then the in/output difference (voltage drop) is from 0.6v at 0.9a to 0.9v at 0.5a
Input voltage can go down as low as 4v but it advisable to go no lower than the nominal output. 8.2v LiPo are resrticted to 0.7a max.
Efficiency = Output/Input watts = 80% at 5v 0.8a to 50% at 9v 0.5a
Max heat disipation: (Wattsin - Wattsout)
2.6w before casing softens.
2.6 to 3.2 watts casing softens and swells up.
3.2w regulator is shut down by its internal tempreature overload.
Full test results.
Explination of Linear Voltage Regulators including graph of voltage drop over time.
This voltage regulator is BUCK configered to reduce the voltage.
It does show up a surprising result in that thw input current is always smaller than the output current. Over double at 12v.
Specification: Input 20 — 5v, Output 5v 3a.
5.05v output, 12v input, 2.5a, Voltage drop = 1.3v
4.44v output, 5v input, 0.3a, Voltage drop = 0.6v. It is advisable that the input voltage should go no lower than the nominal output.
Efficiency = Output/Input watts = 95% at 5v 0.3a to 85% at 12v 2.5a
Maximum current is 2.5a above which the current overload protection cuts in shutting it down completely or partially. It is not due to over heating and the case did not distort.
Full test results.
Explination of Digital Voltage Regulators including graph of voltage drop over time.
|5v 0.9a Linear BEC||5v 2.5a Digital BEC|
5v 0.9a Lbec £6.45 UK & W Europe P&P £3.50
5v 2.5a Ubec £6.45 UK & W Europe P&P £3.50
|Linear BEC |
4.9v 0.9a max output
5.1v 2.5a max output
Cased in UK
|All products are tested and must not be used outside their specification|
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The commonly accepted that 75% of the battery’s rated capacity is the minimum voltage that can be used, below which the battery will be damaged.
The graphs below are from actual tests. Batteries used: Old 7.2v NiCd 2.4Ahr and new 6.0v NiMh 3.3Ahr.
This is the simplest form of regulator whose resistance is altered as the current varies to give a constant output voltage. Usually called a BEC (Battery Elimination Circuit).
This graph is typical and not based on the linear regulator for sale above.
The Dropout Voltage is the minimum difference between the Input and Output voltages specified for each voltage regulator.
LVR1 is a Low Dropout voltage regulator requiring a voltage difference of 0.6v and can handle a 1A load.
The Input voltage must be higher than the Output by the 0.6v Dropout Voltage. When the Input voltage drops to 0.6v above the output, the output follows the input by the dropout voltage. It does not suddenly turn off as mentioned in articles.
The graph below show how the current load reduces the input voltage which alters the point where the output voltage is steady.
The voltage difference between the input and output is dissipated as heat, so BEC’s should not be used with high voltage Lipo batteries or with currents above 1A. They should be positioned in free air to help cooling.
Power Loss Watts:
Lipo (8.4 – 5.0) x 1A = 3.5w x 100mA = 0.35w
NiMh (7.8 – 5.0) x 1A = 2.8w x 100mA = 0.28w
NiMh (6.5 – 5.0) x 1A = 1.5w x 100mA = 0.15w
SLA (6.3 – 5.0) x 1A = 1.3w x 100mA = 0.13w
Efficiency % = Output wattage divided by Input wattage x 100. (Watts = Amps x Volts).
Voltage has little effect on efficiency but it increases as current increases.
The manufacturers call this type of voltage regulator Ultimate BEC (UBEC) or Switching BEC (SBEC).
There are many configurations, the main two being Buck — Reduces DC voltages or Boost — Increases DC voltages.
The input voltage is switched on and off to give a constant output voltage. Similar to using PWM in the H-Bridge to control the servo motor speed, resulting in high efficiency with little heat produced.
One problem is the rapid switching causes magnetic interference which can upset R/C transmissions so some UBECs have a Ferrit Rings on the cable.
Some UBECs have an input rating as low as 5v, the same as the fixed output. My test did not show this to be true. Maximum input can be as high as 40v
There are comments that UBECs do not like to be used with low currents but how low is not stated. Using a small resistor in my load box, I can now test with currents as low as 100ma. 5.9v is the point after which the output voltage follows the input with a voltage drop of 0.7v. Below inputs of 4.5v the output dropped rapidly until it cuts off at 4v. So inputs should not be used below the nominal output.
UBECs also have a dropout voltage, the UBEC tested here has a 0.9/1v dropout. These graphs are not for the Digital regulator being sold.
Switching Voltage Regulators have a higher efficiency than Linear versions which reduces heat output.
Efficiency decreases as voltage and current increase.
The 12v 5a Bench Supply Unit (bottom left) set at 12v is feed to the 3a adjustable Voltage regulator (bottom centre left) used to set the input voltage.
The swithch block (centre) is connected to V & A meters (top left) to check the input value. This feeds the voltage regulator under test.(bottom centre right)
The light box is used to set the current. V & A values are read off the Meter Unit. (top right)
A thermocouple wire is placed on the centr of the test VR. (yelllow meter bottom right) It is not shown in its correct position so you can see where the heat is distorting the casing; The black ring.
Upto 60°C there are no marks. 60 to 80 shows a slight ring where the casing is swelling due to softening. Over 80 the case bubbles up slightly.
The 12v 5a Bench Supply Unit supplies a range of fixed voltage 12, 9, 7.5, 6 and 5Vdc. This 3A adjustable voltage regulators allows intermediate voltages to be obtained. The voltage drop ranges from 1.7v at 3A to 1.0v at 0.5A.
The Adjustabe Voltage Regulator is of the Linear type so the difference between the input and output wattages is given off as heat. The largest possible heat sink for the case is fitted but high currents and voltage differences cause the regulator to shut down. It has thermal overload protection.
|Max Outputs for 12v supply||Max Outputs for 9v supply|
The Voltage Regulators are tested with varying currents loads using my Load Box. 21w,5w lamps and a 57R resistor are switched individually giving current loads from 90mA to over 4A at about 0.2A intervals.
Rapid Electronics multi-meters are used as they are considerably cheaper than panel meters and can be reused elsewhere.