[solved]Converting 14v to lower minimalist, efficient with common components

Hi, i have a arduino mega project on my car and i'm currently use a step down converter to power it up, but i realised that this isn't a efficient method of converting 12-14v to 5v

Then i have found 2 linear regulators with very very low quiescent current but their recomanded maximum voltage is 13.5v and absolute maximum voltage is 14.5

My car voltage is usually 13.5v-13.7v(when on) and sometimes 14v
But there is a peak voltage of more then 14.5v when i turn it on

How can i use those regulators for a long term use and in an efficiently way?

( i don't have access to buy other regulators right now but i will after a few months )

see answer last page

Define efficient. Linear regulators are not really known for their efficiency; you have to reduce by roughly 8V, probably 100 or 200mA. That is 800mW or more that is converted to heat.

sterretje:
Define efficient. Linear regulators are not really known for their efficiency; you have to reduce by roughly 8V, probably 100 or 200mA. That is 800mW or more that is converted to heat.

What i mean is i don't want quiescent current, to drain current when i only use 1mA(arduino in sleep mode) the step down converter is wasting 5mA for example

I would not use any device on a car that was rated for less than 20v to ensure there is some headroom.

If you are serious about saving small amounts of energy why not power the Arduino directly from a pack of 4 x AA NiMh cells and recharge them with a 5v regulated supply when the car engine is running. That way there is no drain on the car battery when the engine is stopped.

...R

Arduino Mega 1mA in sleep mode. Are you sure about that.
There are many parts on a Mega board that can't be put to sleep.

Some switching regulators have a very low quiescent current. 200uA for this one.

Not sure why you worry about a few mA quiescent current.
An average car battery could have a self discharge current of 20mA or more.
Leo..

14V-5V step-down converter: >90% efficiency.
14V-5V linerear converter: 36% efficiency, plus the need to deal with lot of heat.

In most definitions of "efficient" the first option wins. In your definition of "efficient" the second option wins. That's an interesting new take on "efficient".

For low quiescent current, maybe 360 nA sounds better to you? I know, not your voltage range, just to show they exist. The second link on my quick Google search got one that wastes a lot more, all of 10 uA, but it gets quite close to your input voltage requirements.

Wawa:
Arduino Mega 1mA in sleep mode. Are you sure about that.
There are many parts on a Mega board that can't be put to sleep.

Some switching regulators have a very low quiescent current. 200uA for this one.

Not sure why you worry about a few mA quiescent current.
An average car battery could have a self discharge current of 20mA or more.
Leo..

wvmarle:
14V-5V step-down converter: >90% efficiency.
14V-5V linerear converter: 36% efficiency, plus the need to deal with lot of heat.

In most definitions of "efficient" the first option wins. In your definition of "efficient" the second option wins. That's an interesting new take on "efficient".

For low quiescent current, maybe 360 nA sounds better to you? I know, not your voltage range, just to show they exist. The second link on my quick Google search got one that wastes a lot more, all of 10 uA, but it gets quite close to your input voltage requirements.

Tnx for the answers!
My step down converter have 4-5mA qu current and this is too much assuming that my car is drawing only 12mA without my project.
My project include an arduino mega, which will go to sleep after 100 sec after the car is off(i said 1mA because i suppose it won't consume more then 1mA in deep sleep )
And there is a lm358 (from a 433mhz receiver) that is always running and i don't know what is it's current.

So, i currently have 2 MCP1702 5V http://ww1.microchip.com/downloads/en/DeviceDoc/22008E.pdf
250 mA Low Quiescent Current LDO Regulator
2.0 µA Quiescent Current (typical)

but those are rated for maximum +14.5V ( exactly how my car's alternator is rated for at maximum output voltage 14.5V)

I'll order MCP1703 5V version which will have a maximum of 16V, but i can only order them after 2-3 months
meanwhile i wanted to use those that i have.

I also search for the IC that wvmarle said, and there is no shop in my county that sell this item, only on aliexpress/ebay, but there they are very expensive plus the shipping 10 USD compared to 1 usd for x2 MCP1702 or MCP1703

I'm not so in into electronics and i don't know if the regulators that i have are "efficient" in giving my the power that i want but I only want to draw 3mA( in total, i think) and those LDO Regulator seems to be Cheap, easy to use and offering low quiescent current when i need it.

May they won't be so efficient when supplying 100mA to the arduino, but in that case, the car would be ON, so the alternator

Sorry for my bad english i hope you understand. :smiley:

I hope you realise that the chip alone doesn't do much. You need capacitors and an inductor with it to make it all work (see spec sheets on how to wire it all up). I think you're much better off finding ready made buck converter modules.

Also that 16V max is rather low for a car power supply, which is notoriously noisy. You'll have power spikes galore, so get a higher rated one, and maybe look into additional protection circuitry.

wvmarle:
I hope you realise that the chip alone doesn't do much. You need capacitors and an inductor with it to make it all work (see spec sheets on how to wire it all up). I think you're much better off finding ready made buck converter modules.

Also that 16V max is rather low for a car power supply, which is notoriously noisy. You'll have power spikes galore, so get a higher rated one, and maybe look into additional protection circuitry.

I know that your ic is a little bit complicated to build(at least more the the linear reg)

You really need to understand that the car's alternator isn't giving more then 14.5(at least mine)
For example when i'm driving... The voltage is maximum 13.6v

How can you be sure that EVERYTHING ELSE that's on that same circuit won't produce spikes? Such as electric motors and relays (they're notorious for producing voltage spikes, even with flyback diodes, which may or may not be installed).

prologikus:
For example when i'm driving... The voltage is maximum 13.6v

You need to have someone else drive the car while you check that with an oscilloscope.

...R

Car power is very dirty.
I wouldn't use anything that can't withstand at least 40volt in a 12volt system.
Low idle current linear regulators are not suitable because of this.
Find a switching regulator with low idle current.
The one I linked to (post#4) still needs extra input decoupling.
Leo..

Wawa:
Car power is very dirty.
I wouldn't use anything that can't withstand at least 40volt in a 12volt system.
Low idle current linear regulators are not suitable because of this.
Find a switching regulator with low idle current.
The one I linked to (post#4) still needs extra input decoupling.
Leo..

Sometimes you don't have the access to all you want,
For example i had no access to a passive keyless entry IC, so i build myself what i could using only an arduino and a 433mhz kit module, very poor in term of size but it works great

I have no access to a great switching regulator module or even ic's so i need to use cheap things, common ic's and that i can found in my country.

Maybe i could find a switching regulator with low q current but why would i use it instead of my poor regulators?? How they are better in my project, because i see them as being perfect for me. ( referring to MCP1703)

And why should i use a 40v rated regulator if the car doesn't give me that much... Imagine what it would do to the battery if this big voltage is coming to it.
Maybe as you and wvmarle said there can rarely be some short voltage spikes, but those are very easily to filter as much as i know.

prologikus:
Imagine what it would do to the battery if this big voltage is coming to it.

Your battery would probably just say "yummy!" and start sucking it all up, while at the same time your regulators are being fried. Also I doubt it's that easy to simply filter these spikes. It's not like it's just atmospheric disruption that you take care of with a small decoupling cap.

prologikus:
And why should i use a 40v rated regulator if the car doesn't give me that much... Imagine what it would do to the battery if this big voltage is coming to it.

You don't seem to have got your head around the fact that these high voltage spikes may only last for a microsecond. The battery would not notice. But that is long enough for an Arduino to do 16 steps so it (and similar equipment) would certainly notice.

Think how your body would not take much notice of the force needed to squash a fly.

...R

Hi,
What is your project, application, that needs to be so frugal with current?
If we know you complete application we may be able to give you answers more to your liking.

Thanks... Tom... :slight_smile:

I discovered that on my car's OBD2 port have a power lane of 9-11V, then i saw a schematic of my car's alternator and it actually have a voltage regulator, this might be the one from the obd2 port.
If this is true then i can use my regulator on this lane and to be on a different lane from the one that my lights, relays works.

TomGeorge:
Hi,
What is your project, application, that needs to be so frugal with current?

I just want to power an arduino mega, 1602 lcd and a lm358.
Both on 5v, and they consume about 200mA maximum. But i might need some peak current so this is why i'll want to use x2 250mA reg

prologikus:
then i saw a schematic of my car's alternator and it actually have a voltage regulator, this might be the one from the obd2 port.
If this is true then i can use my regulator on this lane and to be on a different lane from the one that my lights, relays works.

Every car alternator has a voltage regulator. What we have been saying about voltage spikes that can cause damage has taken that into account.

I don't know about OBD2 and it is possible that it has an output power line that is shielded from the voltage spikes on the regular 12v electrical system. However you would need to find the specifications to determine how many amps are available on that output.

...R

Robin2:
Every car alternator has a voltage regulator. What we have been saying about voltage spikes that can cause damage has taken that into account.

I don't know about OBD2 and it is possible that it has an output power line that is shielded from the voltage spikes on the regular 12v electrical system. However you would need to find the specifications to determine how many amps are available on that output.

...R

Right, i've been thinking the same. But i also have no idea how to find those specifications.
Maybe there is a reg in the ECU of the car, i'll try to find out more, then i can use it

prologikus:
Right, i've been thinking the same. But i also have no idea how to find those specifications.

What does Google have to say about OBD2?

IIRC there are a number of other Forum Threads about OBD2

Maybe there is a reg in the ECU of the car, i'll try to find out more, then i can use it

That is not the correct mindset, IMHO. What you need to find are the specifications.

Alternatively, choose parts that can withstand the errant voltages on the normal 12v system - as, for example, I suggested in Reply #3

...R