Power Converters Wiki (i.e. Buck Converter, Linear Regulator, UBEC/SBEC, etc)

sleepless · April 13, 2021, 5:50am

To avoid losing the answers from this frequently asked question in other threads, it seems useful to create a wiki listing commonly used power converters.

Someone, at some point, will have no idea what a power converter is or why you’d need one. I’m no expert, but here’s some background info copy & pasted from elsewhere:

WHAT:

DC-DC Converter - an electromechanical device that converts a source of direct current (DC) from one voltage level to another. Everything in this post is a DC-DC converter.

Linear Regulator (or LDO) - type of DC-DC converter where a linear component (such as a resistive load) is used to regulate the output. A linear regulator essentially turns excess voltage into heat. Inefficient but simple.

Switching Regulator - the other type of DC-DC converter that uses a switching element to transform the incoming power supply into a pulsed voltage, which is then smoothed using capacitors, inductors, and other elements. A switching regulator essentially turns the input voltage on & off at high speed to provide a lower output voltage, at high power conversion efficiency but also high noise.

Buck Converter (aka Step-Down Converter) - a switching regulator which steps down voltage (while drawing less average current) from its input (supply) to its output (load).

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Boost Converter (aka Step-Up Converter) - a switching regulator that steps up voltage (while stepping down current) from its input (supply) to its output (load).

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BEC/SBEC/UBEC (Battery Eliminator Circuit / Switching BEC / Universal BEC) - a power converter by another name, term coined in the rc/drone world. A linear BEC is a linear regulator (see above). A switching BEC is a switching regulator (see above). UBEC == SBEC.

Nominal Battery Voltage - The average voltage a cell outputs when charged. “A cell’s nominal voltage essentially defines its chemistry, the type of cell it is. For most non-LiPo li-ion cells (yes, LiPo is Li-Ion) the nominal voltage is 3.6V. This is around where the cell would spend most of its time if discharged slowly. LiPo is often spec’d at 3.7V.” (thanks @Battery_Mooch)
If you have a 10S li-ion battery pack, with 10 cells in series, your nominal voltage is 10x3.6 = 36V (typically).

Max Battery Voltage (aka Charge Voltage) - For a single li-ion cell, the standard is 4.2V. If you have a 10S battery pack, with 10 cells in series, your max voltage is 10x4.2 = 42V (typically)

Min Battery Voltage (aka Cut-Off Voltage) - the lowest safe voltage level for your battery pack before damage begins (this is not a battery wiki, consult your battery builder and/or experts on min voltage for your pack). For a single li-ion cell, the standard is 3.0V. If you have a 10S battery pack, with 10 cells in series, your min voltage is 10x3.0 = 30V (typically)

WHY:

Your 10S li-ion battery provides 36.0V DC nominal voltage (or 43.2V for 12S, 50.4V for 14S, etc etc) and you’d like to run some 12V DC headlights or LEDs for night riding.

A DC-DC power converter will take that 36V input and provide 12V output (or 5V, or 3V, etc etc)

HOW:

Here are some previously linked power converters. Typically, as excess heat can be a problem inside a closed enclosure, buck converters are the ideal choice. Anything with a higher max input voltage can be use on a lower voltage battery system (usually).

8S- (33.6V input capable)

10S- (42.0V input capable)

Turnigy HV SBEC 5A Switch Regulator (8-42V input), $9.84, 5/6V 5A max output
Turnigy 5A (8-40v) SBEC for Lipo, $7.40, 5/6V 5A max output

12S- (50.4V input capable)

Any well-reviewed LM2596HV / LM2596HVS buck on aliexpress, etc (like this one: Adjustable LM2596HV AC/DC to DC Buck Step Down Converter Module
Amazon Prime - SMAKN DC 4.5-60V to 1.25-30V Lm2596hv Power Supply Buck Voltage Switching Regulator Module Step Down, $9.60, 30V 3A max output
YEP 20A HV (2~12S) SBEC w/Selectable Voltage Output, $15.91, 5-9V 20A max output
YPG 20A HV SBEC, $18.85, 5-9V 20A max output
Pololu 12V, 4.5A Step-Down Voltage Regulator D36V50F12, $21.95, 12V 6.5A max output
Pololu 5V, 5.5A Step-Down Voltage Regulator D36V50F5, $19.95, 5V 8A max output
Pololu D36V50Fx Step-Down Voltage Regulators, 3.3-12V 9A max output
GYVRM DC-DC Buck Converter Step-Down Power Supply Regulator, $12, 12v 6A max output
ChinaAutomated DC-DC Step Down Buck Converter WD5020 7~50V 20A, $18, 36V 20A max output
TDK-Lambda I6A4W020A033V-000-R, $33, 15V 20A max output
Acxico 1Pcs LM2596HV DC-DC 5-55V to 1.25-26V Adjustable Buck Power Module Step Down Voltage Switching Regulator Module, $7, 26V 3A max output
LM2596HVS LED Drive Constant Current Charging 60V 3A Step-Down Power Supply Module with Charging Indication Board Voltage Buck Converter Transformer, ?, 55V 3A max output
XP Power LDU5660S500-WD, $12.50, 56V 0.5A max output
DC/DC LM2596 HV S 60V 3A Buck Constant Current/Voltage CC CV Step-Down Module, $2, 3A max output
uxcell Power Converter Regulator DC 48V/60V to DC 5V 10A 50W Waterproof Voltage Convert Transformer, $17.49, huge, 5V 10A max output
szwengao Step Down Power Converter, huge, 12v 40A max output
RIDEN DPS5005 50V 5A Buck Adjustable Power Supply Module, $46, 50V 5A max output, color LCD w/ buttons in case

-16S- (67.2V input capable)

XWST fixed Buck Converter, $10, 3.3-9V 5A output
Fulree potted/waterproof Buck, $16, 12/24V 5V max output
YST-051 10A 120W Converter Adapter Transformer For E-bike Electric, $2, 100W 10A max outut
Ultraok Waterproof IP67 DC15-72V To DC12V 5A 60W Converter, $6, 12V 5A max output

-20S- (84.0V input capable)

e_goto 120V to 5V/12V 3A DC Step Down Module Power Supply Non-isolated Buck Converter, $2, 5/12V 3A max output
Great IT DC Step Down Module Power Supply Buck Converter Non-isolated Stabilizer, $2, 5/12V 3A max output

REFERENCES

https://forum.esk8.news/t/let-there-be-esk8-lights/
https://forum.esk8.news/t/looking-for-12s-to-5v-buck-converter-200-ma-output/
old forum esk8 lights thread
Spotting a fake high voltage buck - Fake LM2596HV Voltage Regulator Buck Converter Modules bought on eBay - YouTube
MIT Guide to Understanding Battery Specs - https://web.mit.edu/evt/summary_battery_specifications.pdf

Size Scale:

Baseplate for scale - Pololu D36V28F5 5V 3.2A - Fulree waterproof 5V3A

Please add/edit/modify as you find useful

PixelatedPolyeurthan · April 13, 2021, 11:51am

I think a great question for noobs… And me lol… is what is “nominal capacity”
When we talk about a 12s ESC we sometimes say they are for 50.4v batteries.
Slightly off topic, I know, sorry. It’s something I find to be not very explained here

sleepless · April 13, 2021, 3:57pm

Not off-topic at all! Great question - added some info above.

When looking at a power converter, you have to find one rated to be able to handle the maximum possible voltage of your battery. At full charge, your max voltage will be (typically) 4.2V x (# of series cells). The nominal voltage is just the average voltage of your pack over its cycle going from 4.2V/ea cell down to 3.0V/ea cell. Your pack’s voltage output is constantly decreasing during use.

50.4V is the max charge voltage of a 12S battery pack (4.2 x 12 = 50.4). It will only decrease from there, but all your electronic components need to be able to safely handle that maximum voltage.

The nominal capacity is then the Amp-hours available when the battery is discharged at a certain discharge current (C-rating) from 100% charged (4.2V/ea cell) to the cut-off voltage (3.0V/ea cell).

PixelatedPolyeurthan · April 13, 2021, 6:40pm

Awesome stuff, Thanks!
This was a well needed Thread

Battery_Mooch · April 13, 2021, 8:16pm

The nominal capacity is what’s delivered at a particular discharge current level from 4.2V (first being charged at a particular current level to a particular termination current cutoff) down to 2.5V for most of the Li-Ion cells we use. A couple of cells are rated 2.0V or 2.75V but not the popular esk8 ones.

The standard for the discharge current level for capacity testing is 0.2C. That would be 600mA for a 3000mAh cell.

Battery_Mooch · April 13, 2021, 8:18pm

There is nominal voltage and nominal capacity. You mentioned 50.4V. Were you wondering about mAh specs or voltage specs?

PixelatedPolyeurthan · April 13, 2021, 8:24pm

exactly

this.

Battery_Mooch · April 13, 2021, 8:27pm

A cell’s nominal voltage essentially defines its chemistry, the type of cell it is. For most non-LiPo li-ion cells (yes, LiPo is Li-Ion) the nominal voltage is 3.6V. This is around where the cell would spend most of its time if discharged slowly.

Other examples…LiFePO4 has a nominal voltage of 3.2V or 3.3V, depending on the cell. LiPo is often spec’d at 3.7V.

The charging voltage for Li-ion is different. That is 4.2V and is what creates the 50.4V spec for a 12S battery pack.

Battery_Mooch · April 13, 2021, 8:31pm

Your link to Adafruit is for LiPo cells, which typically have the higher nominal voltage rating of 3.7V. The round cells we use typically have a nominal voltage rating of 3.6V.

moddedlife · April 13, 2021, 9:06pm

A much needed thread thank you @sleepless

moddedlife · April 13, 2021, 9:31pm

How come the 10a is $2 (actually the same price with shipping) and the 5a is $10? Shouldn’t it be more expensive? I want to order the 10a one but is it legit?

This one is $30. How do they differ?

sleepless · April 14, 2021, 1:48am

Thank you @Battery_Mooch for all the corrections and clarifications. I defer to you.

I’ll update the language in the first post to reflect this.

Also, let me reiterate - this is not intended to provide battery advice, and anyone with questions regarding charging voltages or cutoff voltages (or anything affecting the safe operation of your build) should consult with trusted experts

Battery_Mooch · April 14, 2021, 2:48am

Thank you for putting all this together for the community!

PixelatedPolyeurthan · April 14, 2021, 7:28am

daygreen are pretty reliable, i think @ShutterShock uses one on the front of his board?
they are waterproof… pretty much bulletproof too. Also can handle many Amps.
Downside is that they are BIG

ShutterShock · April 14, 2021, 7:32am

Hmmm no I don’t actually. I used a very small one, I can find the link if someone wants it. I do remember someone on here has used one of those though

My board has a two-part system. One is 50.4v → 12v, and then the one on the front is an LED driver 12v to 3.3v or whatever forward voltage it was that I picked for my diodes

PixelatedPolyeurthan · April 14, 2021, 8:24am

Hmm then who was it?
In any case it was battered up and still working.
Sorry Ryan

ShutterShock · April 14, 2021, 3:01pm

Lol honestly I don’t know I just remember seeing a picture once. Maybe in the “Let there be lights” thread. And no problem, tag me for whatever haha

sleepless · April 14, 2021, 4:45pm

Different vendors, different sizes, different construction. This prices on these are so cheap, it may be entirely up to volume pricing discounts.

Without having any experience with that one in particular, the main thing seems to be the massive heat seat it’s encased in. That would be necessary if you were actually going to draw anywhere near the 50A in the title. You might research ebike builds to get a better understand of these

sleepless · April 14, 2021, 4:46pm

If you’d recommend it, please post the link so we can add it for reference

ShutterShock · April 14, 2021, 6:39pm

Well the first one broke due to vibration but the second one I coated important areas in hot glue and it’s been working for a couple hundred miles

Used to be on Amazon

Is on Ali