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I'm on the process of building a new version of my ebike electronic systems and I'm searching for a way to lower the voltage of the battery (13s = 54,6v fully charged) to 12v/5v for the accessories and various electronics.

I would like to keep my main microcontroller (which is a STM32 based board) powered at all time (with sleep modes) to be able to get GPS, GSM and battery monitoring running when necessary, and then switch (with mosfets/relays) the bigger loads if needed. Given that I would like to keep the thing connected all the time, because my battery box is screwed, I would like the quiescent current to be as minimal as possible, to avoid any unnecessary current consumption.

So i started to dig up in my boxes to excavate various DC to DC converter I have, and found 3 of them which I tested on my PSU at 54,6v input :

  • RCNUN E-Cart Fixed 12v, 10A : 15mA quiescent current
  • SUKUZU Fixed 12v, 10A : 8mA quiescent current
  • LM2596HV variable buck 3v-48v, 3A : 5mA quiescent current.

Given that my battery bank is around 15Ah, 5mA would not be really dramatic, you could still run the thing for more than 4 months. But I'm trying to find a more efficient way to do it. So I looked at Ti's website and found this little chip : TI LM46002

Which provides pretty impressively low quiescent current : less that 30µA.

But I was wondering if it would be the correct way to go and if you had simpler way to get a 12 or 5v out of 60v max battery bank.

I hope my question is clear and that it's not a repost, I searched on the forums, schematics and stackexchange, but I might have missed the perfect answer.

pipe
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Valentin Bonnet
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  • The battery for your eBike is only 15Ah? How long does that last when riding? – JRE Jan 05 '18 at 13:59
  • I built this first battery with 18650 scavenged from laptop batteries. It's around 17Ah, and I can do around 70km. I plan to build a new pack soon with much higher capacity and quality cells. – Valentin Bonnet Jan 05 '18 at 14:04
  • My advice is to just go with the pre made module. Building a DCDC with 60 V input is a tad dangerous, and not very easy. If you can afford 5 mA, stick with that. – Vladimir Cravero Jan 05 '18 at 14:06
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    If the system in sleep mode is using much less than 5mA, you could just add a simple, low Iq linear regulator that would provide the supply during sleep, and turn on the DC-DC only when more current is required. – dim Jan 05 '18 at 14:37
  • @VladimirCravero Dangerousness is not really an issue here, I know how to handle high voltages/currents and be careful for my life ;) I build the battery bank myself from old laptop battery cells.I think for now I'll stick with my current controller that already embeds a buck with 15mA, I'm optimizing everything and powering down all the peripherals when not needed to save power. Thanks for your input :) – Valentin Bonnet Jan 09 '18 at 13:19
  • Be aware that the quiescent current draws might be specified for no load at all, while you're looking to power some components (GPS, GSM) at all times. Be sure to study the converter specifications under light load conditions (as opposed to _no_ load). – marcelm Aug 01 '18 at 21:05
  • @JRE _"The battery for your eBike is only 15Ah?"_ - 15Ah @ 60V is about 1kWh, or 0.45 HP for 3 hours. Or some 10 times what a fit adult human can probably output. I'm no expert at eBikes, but it doesn't sound energy-starved to me... – marcelm Aug 20 '19 at 15:12

4 Answers4

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I think this chip is a very good option if you always want an supply from 13s battery.

I'm seeing that the problem is to get a power supply with 60 V input (max) and low quiescent. Lower input voltage gives more options with low quiescent current.

With this in mind, a suggestion would be to use a second low power & low voltage battery (1s o 2s) that gets charged from the 13s, and supplies the low voltage electronics, and that totally switches on/off the higher voltage power supply that charges the battery. Its a bit trickier but could also work.

GGross
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Step down converter like LM46002 is good and effective to get 12V or 5V with >80% eff. But note that with small load like your case (28mA), eff will lower.

anhvanthe
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I can personally¹ suggest the LTC3637 if you want to build a circuit yourself. The quiescent current is 12µA (so pretty low), and has some nice additional features like current limiting, if you happen to require it.

But keep in mind that both the TI and LT chips require that you design a PCB around them, you can't really solder it on a prototype board. So it may be unwise in your case, especially for an one-off thing; the pre-made modules could be the better option for you.

¹ I've built several hundred chargers on this design for an application that is not very dissimilar than yours and from what I hear they work well in practice.

anrieff
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Your TI chip is a good choice.

I've quickly looked for canned DC-DCs on mouser and didn't find any that fit your requirements. That's weird, as your voltage is within the standard range for 48V input converters. You could try to look from other suppliers.

If you can solder it, I'd recommend one of the LT/AD Silent Switcher chips like LT8461 though. The EMI-friendly design makes it much simpler to achieve a good layout.

bobflux
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