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

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.
    image
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  • 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.
    image
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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.
    image

  • 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)
    image

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)

12S- (50.4V input capable)

-16S- (67.2V input capable)

-20S- (84.0V input capable)


REFERENCES

Size Scale:


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

Please add/edit/modify as you find useful

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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 :smiley:

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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).

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Awesome stuff, Thanks!
This was a well needed Thread :call_me_hand: :100:

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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.

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

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exactly :grin:

this.

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.

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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.

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A much needed thread :pray::raised_hands: thank you @sleepless

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?

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

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Thank you for putting all this together for the community!

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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

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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

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

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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

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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

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

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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

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