DC-DC Buck converter issues (42V-> 5V)

Hello there!

I am trying to set up an open-source smart (extra) battery for e-scooters. One that would enable many safety features such as turn lights, battery status, LEDs under the board that react to whether you are braking or speeding or turning and so on and so forth.

However, to do so I need the means to transform 32-42V to 5V DC for the MCs.

So far I have tried using a LM2596HV buck converter module. However, as soon as you start drawing from it, it heats up tremendously.

Not knowing exactly how things work with such converters, it would simply suggest that it takes the voltage you need at the amperage you need and then simply sheds the difference as heat.

Wasting some power is not an issue here, but I would need a way to convert voltages safely without the module becoming so hot that it could damage the battery it is located near to.

Does anyone have a lead to provide? I see tons of e-bike batteries with built-in phone chargers that run similar voltages.

Many thanks in advance guys, as always :slight_smile:

pixelsafoison:
Hello there!

I am trying to set up an open-source smart (extra) battery for e-scooters. One that would enable many safety features such as turn lights, battery status, LEDs under the board that react to whether you are braking or speeding or turning and so on and so forth.

However, to do so I need the means to transform 32-42V to 5V DC for the MCs.

So far I have tried using a LM2596HV buck converter module. However, as soon as you start drawing from it, it heats up tremendously.

Not knowing exactly how things work with such converters, it would simply suggest that it takes the voltage you need at the amperage you need and then simply sheds the difference as heat.

Wasting some power is not an issue here, but I would need a way to convert voltages safely without the module becoming so hot that it could damage the battery it is located near to.

Does anyone have a lead to provide? I see tons of e-bike batteries with built-in phone chargers that run similar voltages.

Many thanks in advance guys, as always :slight_smile:

What you are describing are linear regulators. Those disspate the voltage diference between input and output in form of heat (in your case they would dissipate (42V-5V)*your amperage in heat).

Buck converter however, don't do that and so they can achieve 90%+ eficiency.

Just find a better buck converter.
However, When you say hot is hot that you can't touch or just warm?

Buck converters do run hot when you are drawing a lot of current. In most electronic systems a heat sink is used.

However some of those cheap ebay modules are very badly designed and oscillate when large currents are drawn.

Could you provide a link on converter module you are using and your schematic? How much current do you need at 5V?

Buck converters are basically power converters, and with that voltage drop you can expect ~80% efficiency.
That means that 20% of the power you're moving ends up in the buck converter as heat.
If you now power usage of the 5volt load, then you can estimate temp rise of the buck converter.
Leo..

So far I have tried using a LM2596HV buck converter module.

What you are describing are linear regulators.

Really?

How MUCH current are you drawing (and expect to draw) from the LM2596HV?

Watcher:
Really?

I didn't have a look at the datasheet, but what he was describing was a linear regulator.

And looking at the datasheet it is indeed a buck converter

How much current are you trying to draw from it?

Is the voltage actually 42v? Or is it 42v nominal, and more than that at full charge, such that it's out of spec for the converter?

Is the converter an assembled module, or did you try to build it yourself? As noted, a lot of the modules on ebay are marginal - but they should work. That is not the best DC-DC converter chip on the market, though, so at best, it might not be sufficient.

If you tried to build a switching DC-DC converter yourself and know as little as you claim about them, the chance of it working is virtually nil, as they're highly layout sensitive (ie, no breadboard, prototypes w/out a custom PCB are a crap shoot even if built with extreme care and attention to detail)

but what he was describing was a linear regulator.

Yes I would agree with that.
He said:-

Not knowing exactly how things work with such converters, it would simply suggest that it takes the voltage you need at the amperage you need and then simply sheds the difference as heat.

Which to my mind is a description of how a linear regulator works. True the words are not 100% correct but then we are dealing with a beginner and have to read what he is trying to say.

A proper description would be:-
You take the current you want, and multiply it by the difference between the input and output voltage and that is the power the regulator burns in the form of heat.

Sorry for the late reply.

I, unfortunately, do not know if it's a linear one, all I know is that it was described as a buck converter on the aliexpress page (to be perfectly honest I did not think that it would be a complex matter - ignorance is bliss)

I'm going to do some research on them but whenever it comes to voltages I'm a 100% true noob. Which is why I fuse everything, as with both battery packs combined I can draw around 1.5KW before the BMSs give me the middle finger.

I was drawing roughly 7.5W from the converter module, and the produced heat was in the "too hot to touch" range and if left alone would've probably fried itself (provided that there's no protection on the board).

Battery voltage was at 42V.

Could anyone provide a lead on how to drop 34-42V to 5V DC while allowing to draw roughly 15W? (which I'll need to power the signalling lights)

Sorry for being clueless ^^"

One of the products we build for use in large truck trailers used a buck/boost converter to supply 12 volts with inputs from 40 volts to 10 volts. Many amps for motors, etc. The entire unit is in a cast aluminum heat sink which will be mounted to the trailer frame for heat sinking.

The unit the OP shows does not even have a heat sink. At least in the pictures I saw.

Paul

pixelsafoison:
all I know is that it was described as a buck converter on the aliexpress page (to be perfectly honest I did not think that it would be a complex matter - ignorance is bliss)

So, which one? Is it a secret? Trade secret? You want to protect the privacy of the seller? We only want to look at the published specification.

It may simply be a faulty one. Or an overly optimistic specification. Buy a different one. Like you said, it is not complex.