BEC to turn 2s into 3s voltage?

[midwest_rippa]

Could someone with a little more electronics experience explain why it is not a good idea to use a 12v bec to up a 2s battery before the esc? Had this weird thought in the shower and asked "what if"

thanks

[Steve g]

Short answer, a Bec can't increase the voltage higher then the input voltage.

Sent from my SAMSUNG-SM-G920A using Tapatalk

[mikemcE]

Bec regulates voltage. A transformer raises or lowers.


Hang up and Drive

[midwest_rippa]

so then its possible to use a transformer to up the voltage to 3s? im not planning on doing this just trying to understand how electricity works

[mikemcE]

Originally Posted by midwest_rippa

so then its possible to use a transformer to up the voltage to 3s? im not planning on doing this just trying to understand how electricity works

I would think so, but I would just use a 3s


Hang up and Drive

[Rekreant]

Originally Posted by midwest_rippa

so then its possible to use a transformer to up the voltage to 3s? im not planning on doing this just trying to understand how electricity works

You could but the losses would be too great it’s only runs in about 35% efficiency

[Ditchrat]

Originally Posted by midwest_rippa

so then its possible to use a transformer to up the voltage to 3s? im not planning on doing this just trying to understand how electricity works

Sure people do it all the time. However the amount of space needed for the equipment and the heat lose really makes it prohibitive.


Short answer go read a book about electricity, any time put into learning about it will be worth the investment.

[Steve g]

To add to ditchrats post, you also lose amperage. A 50 percent increase in voltage results in 50 percent decrease in amps. Factor in efficiency and you'll get closer to 40 percent.

Sent from my SAMSUNG-SM-G920A using Tapatalk

[gonper]

Well there is DC/DC convertors now that are quite efficient what ever if they are step-up (output voltage higher than input) or step-down (output voltage lower than input voltage) and even jut regulators that compensate higher or lower voltages to a fixed regulated output.

But they are normally used for secondary systems, for example:
In a RC car with 3 systems:
The main current system is the motor/s power on a RC car that works lets say at 12V
And the radio system (RX, Servos, etc.) is a secondary system that works lets say at 6V
And we can have may be another secondary system (Led lights) that works lets say at 3V
As the secondary systems are the ones that uses less current they are the ones that will be recordable to instal the DC/DC convertors (That we call BECs)

The reason to do it this way is in order to save money, space, weight, and because it will have less looses (more efficient)

[Hydrocarbon92]

I don't want to sound rude, but the first few posts here offer seriously outdated info (pre-60's).

What you're probably looking for is usually called a buck-boost converter (or just boost or step-up converter). Basically a solid-state version of the old-fashioned copper/iron transformer, although the method is totally different. They're used in everything from $1 solar lights to high-end PC servers. They are usually TINY compared to transformers and offer efficiencies above 95%. Most don't supply much power, but you can get some that supply over 100 watts. The down side is they're usually much bulkier than a BEC of a similar power rating unless they use SMD inductors (wire-wrapped hoops).

I use a $1 version for the 12v LED lights in my truck and they're tiny. They supply about 12 watts (1 amp @12v) without overheating and can be adjusted well over 24v from as little as 3v.

[Ninomaniac]

By the way, transformers work only on AC, not DC.

Sounded to me like the original question was can you power the ESC with 3s voltage off a 2s pack using a converter. Theoretically yes, but you would only lose power, generate heat and it would have to be one big piece of electronics to handle the current.

[Rekreant]

Originally Posted by Hydrocarbon92

I don't want to sound rude, but the first few posts here offer seriously outdated info (pre-60's).

What you're probably looking for is usually called a buck-boost converter (or just boost or step-up converter). Basically a solid-state version of the old-fashioned copper/iron transformer, although the method is totally different. They're used in everything from $1 solar lights to high-end PC servers. They are usually TINY compared to transformers and offer efficiencies above 95%. Most don't supply much power, but you can get some that supply over 100 watts. The down side is they're usually much bulkier than a BEC of a similar power rating unless they use SMD inductors (wire-wrapped hoops).

I use a $1 version for the 12v LED lights in my truck and they're tiny. They supply about 12 watts (1 amp @12v) without overheating and can be adjusted well over 24v from as little as 3v.

Good luck finding a buck booster that can work with 2-3s lol. It may be old info, but it still applies. also talking about 95% efficiencies id like to see some links, because even computers tend to only have 85% on their power supplies, and those are pretty dang bulky.

[Ninomaniac]

There are ICs listed on Texas instruments' site that work with e.g. 3-40V input and output.

[Rekreant]

Originally Posted by Ninomaniac

There are ICs listed on Texas instruments' site that work with e.g. 3-40V input and output.

yes but at what amperage?

[Ninomaniac]

Relatively low currents, certainly not enough to power a decent ESC but enough for a servo. A bigger more complex circuit could probably be made for higher currents...

BTW, I am not saying that it makes sense in this case at all, just that it may be possible

[Hydrocarbon92]

The reason they aren't common is because most DC devices are designed with a higher voltage supply to begin with. 2nd is their inherent design downfall - they need fairly large inductors & capacitors.

Most elec. engineers design with a sufficient supply voltage to begin with, which is why boost converters aren't as popular as dc-dc step-down converters (BEC's). Honestly if you need several amps at 12V when running a 2S battery, you are WAY better off getting a small 3S battery and regulating it's output with a BEC. The following 750mah battery is cheaper than a Castle BEC yet can pump out 48 AMPS, although that would drain it in a minute.

https://hobbyking.com/en_us/turnigy-...hort-lead.html

Originally Posted by Rekreant

Good luck finding a buck booster that can work with 2-3s lol. It may be old info, but it still applies. also talking about 95% efficiencies id like to see some links, because even computers tend to only have 85% on their power supplies, and those are pretty dang bulky.

First off, buck-boost means input can be either below OR above output & boost means input must be below output (usually 1-3v). The "boost" circuit uses mosfets to charge inductors, then when they switch off the collapsing magnetic field turns into voltage. An automotive coil uses the same principal to turn 12v into 20k volts. The only energy lost is really just resistance of the wiring & the mosfets' on-resistance. Switch-mode BEC's efficiencies are similar, while linear BEC's are in the 20-40% range (voltage dependent).

Here's just one example, 2A hitting 94-96% in the 100mA to 1A range.

http://www.ti.com/lit/ds/symlink/tps63070.pdf

This is a complete module, although it's using a fairly old IC and is only listing "above 90%". It can do 15W, but can peak at 3A if you had sufficient cooling. Newer designs use BGA chips that have much better thermal designs.

https://www.dfrobot.com/product-444.html

The XY8018 is used in many garden solar lights. When there's no solar panel output, it starts switching power to an inductor (green, looks like 1/4w resistor), boosting the 1.5v battery voltage up to 3v.

https://ez.analog.com/community/univ...r-garden-light


Google is your friend if you fail to find this convincing.

[Rekreant]

All of those are at super low amperages, and thus entirely useless for powering an ESC....

[Steve g]

Those buck boost examples are not any where near rated for the question that wa asked. And like rekreant said, way too under powered for an esc. Fine for a set of LED lights, but that's not what the question was about. Don't get me wrong, good info, just out of spec. Bottom line is, you can't create more power/energy then what is given. P=IxE. Where P is power(watts) I is amps and E is voltage. Let's say you have a 2s battery that can push out 100 amps at 8v. So 100x8 gives us 800 watts of power. Now attach a step up transformer to push it up to 12v. Still only have 800 watts coming in, so to find the amps, we divide 800 by 12, and get 66.67 amps. So that's a decrease of 33.3 amps, before factoring in efficiency. A realistic efficiency at these power levels is 85 percent. So that drops the 66.67amps to 56.67. So technically it could work, assuming you have a large enough 2s battery with enough discharge current to supply sufficient current at 12v, but the tramsformer would be large and expensive (relatively) and pretty much pointless.

Sent from my SAMSUNG-SM-G920A using Tapatalk

[Hydrocarbon92]

Obviously they're not as my first post made it clear that much over 100W isn't common. The rest of my posts were to correct info that DC-DC boosters don't exist or were horribly inefficient.

Originally Posted by Hydrocarbon92

Most don't supply much power, but you can get some that supply over 100 watts.

As I mentioned in my second post, getting a 3S if you want 3S power would be far easier & the proper way. If the OP's question was a bit more clear or I read his mind better I'd have had a much shorter post lol. Asking for "3S power" doesn't explicitly ask for 600 watts or more.

[robert@castle]

There is this kinda sketchy device that was on sale for a while:
https://www.horizonhobby.com/turbo-kick-dynf1020

By my understanding of it, it had a boost converter in it that would boost the 2s input to 3s and charge a set of capacitors up to that voltage. When the servo line was activated, it turned on a MOSFET that connected the charged capacitors to the output to give a momentary boost of speed.

What I'm not sure about is if it uses a MOSFET to disconnect the battery while running off of the capacitors, or if it used a diode to prevent the higher voltage from flowing back to the battery. The diode would be a lot easier, but would incur a 0.7V drop, so the ESC would never see a fully charged 2s pack.