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Car battery as powersupply

Started by Stefan, Apr 04 2013 09:51 AM

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10 replies to this topic

#1 Stefan

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Posted 04 April 2013 - 09:51 AM

Hi,

I did a lot of Netduino projects so far, but never one like I have in mind now.

I want to connect a Netduino Mini in my motorcycle for data logging and GPS tracking. Now, my motorcycle has a 12V "car battery" which can provide quite some amps.

Now I know the mini can get quite hot when powered with 12V. Also, I know car batteries aren't very stable; when I start the motor, there are large fluctiations in the power supply.

So I would like to feed my Mini just a stable 5V.

I -think- I know how to do this, but I am not sure. So before I blow something up, I would love to get some advise.

Parts of which I am thinking:

- 1x 1A fuse - to prevent that my Netduino circuitry is pulling too much amperes, for example if something is shorted

- 2x 1A diode - to be sure power flows in the correct direction

- 1x 5V voltage regulator (LM7805?) - To downscale ~12V to 5V

- 1x 100�F transistor on the 12V side - To stabalize the voltage levels

- 1x 1�F transistor on the 5V side - To stabalize the voltage levels

My application won't use many amperes while idle. I'm only a bit afraid a voltage regulator like the LM7805 will turn a lot of power into heat, thus wasting my battery.

So, any thoughts? Dos and donts?

_{"Fact that I'm a moderator doesn't make me an expert in things." Stefan, the eternal newb!}
My .NETMF projects: .NETMF Toolbox / Gadgeteer Light / Some PCB designs

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#2 NooM

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Posted 04 April 2013 - 09:58 AM

as always, i suggest a switching regulator, add a large enuff kondensator at the input side, done. it works from 6v to ~24v and outputs stable 5v

http://www.ebay.com/...=item3a74b337d4

My PlayGround and some Code

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#3 Stefan

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Posted 04 April 2013 - 10:28 AM

Thanks, if I use the LM2596, like you point out, what will be the benefit from that? 'm a newb in this area, so please help out

Already found a schematic for that specific component at http://amanda.member...LM2596S_50.html

(I want to make my own PCB, instead of linking multiple modules here)

_{"Fact that I'm a moderator doesn't make me an expert in things." Stefan, the eternal newb!}
My .NETMF projects: .NETMF Toolbox / Gadgeteer Light / Some PCB designs

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#4 NooM

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Posted 04 April 2013 - 10:46 AM

its a switching regulator, not linear. so it can supply up to 2 amps w/o getting hot.

i also experienced good stability and no noise when using it. so it might be good for your motorcylce thingy

when you start it.

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#5 Maurice

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Posted 05 April 2013 - 02:01 AM

An alternative buck converter that works quite well and is small... http://www.adafruit.com/products/1065

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#6 Stefan

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Posted 05 April 2013 - 04:34 PM

An alternative buck converter that works quite well and is small... http://www.adafruit.com/products/1065

Looks interesting, but expensive. I heard DC-DC converters are way more efficient though, so maybe I should go for this....

_{"Fact that I'm a moderator doesn't make me an expert in things." Stefan, the eternal newb!}
My .NETMF projects: .NETMF Toolbox / Gadgeteer Light / Some PCB designs

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#7 Jack Chidley

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Posted 06 April 2013 - 08:44 AM

I don't think that efficiency is going to be a big deal - the power requirements of the electronics will probably be insignificant when compared to the bike - if you're worried, just make sure that the electronics are only turned on when the bike is turned on.

I'd say that the first option, "LM2596 Power Supply", is going to be adequate. Probably needs fuse protection on the input side (1A ceramic fuse) and some smoothing on the output.

I really like the Traco Power regulator. My first choice in batteries is NiMH AA rechargeable - 5 of these in a holder would give you a very long lived power supply, 4 would probably not be enough (4 * 1.2V = 4.8, pretty close to the 4.6 minimum).

If weight is not an issue, then SLA (Sealed Lead Acid) are impossible to beat for the money. You can get them in a 6V package. Couple that with the LM2596 and you have a dirt cheap power supply. It's inefficient, bulky and heavy but for many applications that isn't going to be a problem.

Has anyone found a good boost regulator? I have picked up one from JeeLabs...

Edited by Jack Chidley, 06 April 2013 - 04:48 PM.

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#8 NooM

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Posted 06 April 2013 - 08:56 AM

lm2577 as boost up. ebay also has modules where you can limit the current supplied

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#9 Stefan

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Posted 06 April 2013 - 11:14 AM

I don't think that efficiency is going to be a bid deal - the power requirements of the electronics will probably be insignificant when compared to the bike - if you're worried, just make sure that the electronics are only turned on when the bike is turned on.

I'd say that the first option, "LM2596 Power Supply", is going to be adequate. Probably needs fuse protection on the input side (1A ceramic fuse) and some smoothing on the output.

I really like the Traco Power regulator. My first choice in batteries is NiMH AA rechargeable - 5 of these in a holder would give you a very long lived power supply, 4 would probably not be enough (4 * 1.2V = 4.8, pretty close to the 4.6 minimum).

Well, I want to use the motorcycle battery, so it automaticly charges. I think that's the best approach, since it's always available. One of the things I want the mini to do is act like a tiny alarm. So it requires constant power. Loss in transforming the 12V to 5V should be brought to a minimum, otherwise it would drain my battery constantly.

_{"Fact that I'm a moderator doesn't make me an expert in things." Stefan, the eternal newb!}
My .NETMF projects: .NETMF Toolbox / Gadgeteer Light / Some PCB designs

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#10 Jack Chidley

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Posted 06 April 2013 - 04:44 PM

SLA vary in power from about 1.3 Ah to about 8Ah (6V typically for bikes and 12V for cars). What's the power draw of a mini?

How long between recharges before the power draw of the mini becomes a problem? Even constant drain might not be a problem if needs are low - I think that the mini's needs are in the order of mA. Even a tiny AA battery manages 2.4Ah (high quality eneloop) at 1.2V - that'll be about 800mAh at 3.6V.

Of course, I may have completely misunderstood how this works... I am not an expert.

Jack