nigratruo
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Automatic Car Battery Cut off to prevent rundown andAAA call

Sun Aug 07, 2016 9:17 am

Hi,

I have a project in mind that would make most calls to AAA (a car help service in the US) obsolete. Most calls are for dead batteries.
For the life of me I cannot understand why not every car in the year 2016 has a cut off circuit that disconnects all consumers from the battery, hence protecting it from a rundown.

I had the idea to use a Pi for that, because there is positively absolutely no reason or use of a battery running down more once it reached around 11, 10 or 9 volts and you have around 1 car start left before it is dead, so letting it run down more will make your starter fail to crank the engine/provide enough spark voltage sufficiently to make it start.

The reason for this post is now to share this idea and get your input for it. Especially on the cut off mechanism, which I envision as a spring loaded hard disconnect, so that the Pi can trigger it with a relay, and you can just reactivate it by a push button. It should be durable enough to resist corrosion and also allow a lot of amps to run though (though with the battery is charged and also provides starting power for the starter motor), so a normal relay would not be powerful enough I figure.

The mechanism would also be very fool proof: No matter what killed the battery, was it that you left the light on, the car was standing around for a month or you sit in the car with your love interest and talk the night away while listening to music and then realize that the engine does not start anymore, it will shut off the battery at that critical junction, the point of no return.

This is not for a commercial product, this is actually due to a comment of a nephew after he noticed that batteries do run down over and over and that AAA has a whole business built on it. He asked "so why don't car companies fix this? Are they stupid?" and I replied that they probably are but that we can find a fix for ourselves. And he had done some other smaller projects with the Pi and what he did not like was that they were always theoretical, a few LEDs or a game or something else that was just done to teach him something, but nothing that gets real use in real life. Well, here is our go at that.

mattmiller
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Sun Aug 07, 2016 9:30 am

The risk assessment of disconnecting the battery while driving at night would say - don't do this :)

An alarm (powered from a separate battery of course) could be good idea

fruit-uk
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Sun Aug 07, 2016 9:45 am

There are a number of devices already available to monitor battery voltage and shut off power to low power add-ons such as dashcams.

As mattmiller stated, not a good idea for anything else!

nigratruo
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Sun Aug 07, 2016 10:00 am

Hmm, where are these devices? Have not found any, not hard disconnect ones that make sure the battery is not connected anymore to any device in the car that drains it.
By the way, you do know that disconnecting the battery while you drive does absolutely nothing, does not stop your engine or anything, because the alternator produces enough power for the whole electrical system.
But in any case, how could you ever get to a low voltage if the battery is being charged and the engine is on?
The only circumstance I could see would be if the alternator stops working, but then the battery charge light comes on and will stay on for a long time till the battery is that run down. I would create a warning buzzer that goes off a few minutes before the disconnect for any case and a override, a button you can push to disable the imminent disconnect.
But you realize that I had a specific question in my post, about the disconnect mechanism specifically.

fruit-uk
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Sun Aug 07, 2016 10:27 am

nigratruo wrote:Hmm, where are these devices?
Try searching dashcam battery saver or similar
Here's an example page https://dashcamtalk.com/battery-discharge-prevention/

mattmiller
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Sun Aug 07, 2016 11:01 am

But you realize that I had a specific question in my post, about the disconnect mechanism specifically.
Giving someone advice that could lead to their death is something a lot of us refrain from
I'm out :)

Moe
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Sun Aug 07, 2016 11:38 pm

The reason car manufacturers haven't already done this is because it's not really practical. The main problem is that battery voltage drops under load, so voltage is not a reliable measure of battery condition unless everything is switched off.

If you were to simply break the circuit when the voltage dropped below X, you would never be able to start the car because the starter motor would trip it every time.

When the engine is running you'd be measuring alternator voltage, not battery voltage, so the measurements would be meaningless. As others have hinted, cutting the battery when driving would be very unwise anyway - under conditions of very high load and low alternator output (low revs and all consumers on) the car could be reliant on the battery and your system would kill it. Also, if you have a fault with the charging circuit then sometimes you can get home on battery alone (this has happened to me twice!).

So, you'd have to link it to the ignition somehow so that your cutout was disabled when the ignition was on.

This could work with the engine off, but even then it's not simple. Choices are a) measure voltage, current, ambient temperature etc, try to predict what the expected battery performance should be and compare it with actuals; b) wait for periods of no load to do your measurements; c) rely on voltage alone and prevent the car owner from using his/her lights and/or stereo on battery power.

Finally, the practicalities. This would be a big relay - starter motors can take 200A - not impossible, but expensive. And the system would have to fail-safe so a software glitch (or dead battery that kills the Pi itself) doesn't kill the car altogether.
Submarine communication systems engineer and amateur robot enthusiast.

nigratruo
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Re:

Mon Aug 08, 2016 6:26 am

fruit-uk wrote:
nigratruo wrote:Hmm, where are these devices?
Try searching dashcam battery saver or similar
Here's an example page https://dashcamtalk.com/battery-discharge-prevention/
This does not serve this purpose at all:

quote:
----------
What is it?

Regardless of the name, this device is connected to your dash cam’s power supply and hardwired into your vehicle. The device can prevent the discharge of the vehicle battery by blocking power to the dash cam if the voltage drops below a configured value or if the configured time has elapsed.
--------------
Shuts the power off to ONLY one device. If you leave your headlights on, or any other device, the battery will still run down and you need to call car assistance to give you a jump.

All these devices are not installed directly at the battery, making sure ALL power consumers can't run down the battery.

nigratruo
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Mon Aug 08, 2016 6:53 am

Moe wrote:The reason car manufacturers haven't already done this is because it's not really practical. The main problem is that battery voltage drops under load, so voltage is not a reliable measure of battery condition unless everything is switched off.

If you were to simply break the circuit when the voltage dropped below X, you would never be able to start the car because the starter motor would trip it every time.

When the engine is running you'd be measuring alternator voltage, not battery voltage, so the measurements would be meaningless. As others have hinted, cutting the battery when driving would be very unwise anyway - under conditions of very high load and low alternator output (low revs and all consumers on) the car could be reliant on the battery and your system would kill it. Also, if you have a fault with the charging circuit then sometimes you can get home on battery alone (this has happened to me twice!).

So, you'd have to link it to the ignition somehow so that your cutout was disabled when the ignition was on.

This could work with the engine off, but even then it's not simple. Choices are a) measure voltage, current, ambient temperature etc, try to predict what the expected battery performance should be and compare it with actuals; b) wait for periods of no load to do your measurements; c) rely on voltage alone and prevent the car owner from using his/her lights and/or stereo on battery power.

Finally, the practicalities. This would be a big relay - starter motors can take 200A - not impossible, but expensive. And the system would have to fail-safe so a software glitch (or dead battery that kills the Pi itself) doesn't kill the car altogether.
You raised some good points, I thought myself that a relay will probably not work, as the starter pulls a huge amount of amps in a short amount of time (that is why we have these large batteries in the first place).

I was thinking about a screw design, that the pi could actuate a little motor that would turn a screw and disconnect it that way.
And of course it would have to be fail save.

I would probably make something that the system will not even work when the engine is running, as there can only be two situations when the engine is on:
1. Battery is being charged or alternator is providing enough juice for the whole car to run.
2. Alternator is dead, battery must be available to get to a repair shop, time is ticking down till the car will not have more energy for powering the ignition.
In both of these cases, the battery does not get discharged due to a mistake and the cut off circuit would not serve any purpose.

I would make it time delayed, so the disconnect would only kick in if battery voltage drops to less than 10 volts or so and STAYS there for a long time. Starting would not trigger it, as it would be too slow set.
An interesting fact: If you connect a battery monitor to your cigarette lighter, you will notice that battery voltage (and system voltage) does never ever drop even below 12 volts when the engine is on and the alternator is running. The reason for this is that you can't charge a car battery at 12 v or below, you need about 13 or even 14 volts and the alternator provides that, even at idle, it never drops that low. If it does, then the electrical system is damaged and the battery will start getting discharged (and the battery warning light will come on).

I have never seen a situation with my car that would ever need the battery to support the electrical system, the alternator will provide enough power (again, more than 12 v even, since it must charge the battery, even at idle (which the voltage measurement confirms). If the car uses more power, the car will automatically raise the RPMs to produce more power and this is with a 1995 Toyota, so this mechanism seems to be really robust and old.
Now the only time you could collapse the voltage enough when just running on the alternator alone is when you have a sudden spike in power consumption that coincides with extreme low rpm, like when slowing down suddenly, turning on the high beams, brake lights, seat heatings and window defroster, but this is only with a totally busted battery. If your battery is connected, it will always act as a safety buffer.

It is a pretty robust system, but again: The cut off circuit would only be active when the engine is off or more precise: if the key is not set to ignition.

The cut off voltage should be easy to determine, I have noticed that battery voltage will not drop fast in a healthy battery, even if it is not being charged.
But there is a point of no return, which might be different for every car. It is the point when the battery reaches a certain low voltage where it can no longer provide enough power for the starter and the ignition at the same time (it can happen that you can crank the starter still, but the ignition voltage is too low and the car does not start). Battery health is not such a big factor really, as in a weak or damaged or old battery, the voltage will just drop faster and reach the cut off voltage.
BUT and here is the kicker: Batteries often die because there is no protection circuit like the one I propose:
Normal car batteries do not tolerate deep discharging, they get irreparably damaged. Every time they run down, they take a little damage, till they are all broken. There are of course marine batteries, that allow deep discharge.

So I wonder how long my batteries will last in the future once they cannot possibly ever run down.

klricks
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Mon Aug 08, 2016 1:13 pm

Using a RPi and required monitoring circuits will cause the very thing you are trying to avoid.... a dead battery.
On most cars the only significant power draw when the engine is not running is the headlights. So if the car has a headlight timer, either OEM or aftermarket, then there is no point to adding a battery monitor circuit.
Unless specified otherwise my response is based on the latest and fully updated Raspbian Buster w/ Desktop OS.

nigratruo
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Tue Aug 09, 2016 3:43 am

The Pi will decharge the battery, but very slowly, it will likely take weeks till a battery is dead and only when not driving the car ever. But then again, what do you think they Pi will do when the battery reaches the cut off? It will turn it off and no harm done.

There are A LOT of reasons why a battery will get discharged, it is not just the headlights.
Worldwide, most of emergency calls for car assistance are always a dead battery, see here:

https://www.theaa.com/breakdown-cover/w ... kdown.html
And this has not changed in 30 years.

So the question would be: if my circuit is not needed, what all these breakdowns?

I personally want to be able to say: I never ever want to have to rely on somebody having to give me a jump start or having to call emergency services for a dead battery.

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rpdom
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Tue Aug 09, 2016 5:25 am

From the page you linked to, you can see that the majority of problems occur with old batteries in the winter. (I've experienced this myself a few times when the battery was worn out, but didn't need to call any one, just replaced the battery with a good one).

During summer you use less electrical power. Also the engine is easier to crank and quicker to fire due to the warmer weather. In winter the electrical needs can shoot up and an old battery can't cope any more.

Your idea may save a very small number of problems, but I don't think it will be enough to justify its use.
nigratruo wrote:The Pi will decharge the battery, but very slowly, it will likely take weeks till a battery is dead and only when not driving the car ever.
From that report:
Check that everything electrical is turned off when you park up – even an interior light, boot light, or radio left on overnight can kill a battery when it's cold.
A typical interior light takes about 5W. A Pi (depending on the model) may take 2-5W. Still think it will last for weeks?

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Ronaldlees
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Sat Aug 13, 2016 3:55 pm

On my old truck, the cable to the starter is separate from the other electrics, so I wouldn't have the need for a big relay. A manual switch could cut off all non-starter circuits when the truck is not in use. Then, there'd be no monitor device current to worry about. But, someone would accidently hit the "big switch" while driving on the road, and have an accident. So, no suggestion for that! Yet, I remember just that sort of thing used as a "poor man" theft protection device back in the sixties/seventies.

But, while that idea worked for my 1963 Chevy (my first car) - it wouldn't be accepted by people today because all of the futzy-stuff that modern vehicles have (car alarms, clocks, etc) would be turned off too.

But, I think some of your ideas are interesting. May have to take another look under the hood of that old truck :-)
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Moe
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Mon Aug 15, 2016 11:29 pm

The point I was trying to make is, a lead acid battery is not an exact science. As a (not very good, admittedly) analogy, it would be like trying to measure how tired a horse is. The variation in the size, strength and the age of horses would easily drown out the parameters you're trying to measure. And that's assuming you already know the exact specification of the ideal horse.

You could put a shunt resistor in the low-power (not starter motor) circuit, use it to measure current as well as voltage, and calculate battery condition on that basis - i.e. IF (battery voltage is <X volts when load is Y amps) AND (ignition is off) THEN cut battery.

The you might catch it before a damaging deep discharge - but even then you'd probably have to factor-in the capacity of the battery in question. And I don't see how this would prevent many rescue call-outs - the power needed to start an engine depends on the engine, not just the battery.
Submarine communication systems engineer and amateur robot enthusiast.

nigratruo
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Thu Aug 18, 2016 9:29 pm

rpdom wrote:From the page you linked to, you can see that the majority of problems occur with old batteries in the winter. (I've experienced this myself a few times when the battery was worn out, but didn't need to call any one, just replaced the battery with a good one).


nigratruo wrote:The Pi will decharge the battery, but very slowly, it will likely take weeks till a battery is dead and only when not driving the car ever.
From that report:
Check that everything electrical is turned off when you park up – even an interior light, boot light, or radio left on overnight can kill a battery when it's cold.
A typical interior light takes about 5W. A Pi (depending on the model) may take 2-5W. Still think it will last for weeks?
Yes, it might, if you check your facts, 2 to 5 watts is not what a Pi uses when you rig it for low power consumption, which of course I would do here. Also, the Pi is DOING NOTHING most of the time.
A normal car starter battery has quite A LOT of capacity and I have to calculate it, how long it would last. But the point is that if you let the car sit around for weeks on end, of course, the battery will discharge in any case. I have had cars sit around for 3 months and then could not start the battery anymore, because just the car turned off car electronics being connected to it managed to discharge it slowly bit by bit.
For this case, I have manual turn off switches on all my cars to make sure this does not happen, again the Pi would do a better job here, making sure no matter what happens, the battery cannot get discharged more than a certain state by the car.

nigratruo
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Thu Aug 18, 2016 9:44 pm

Moe wrote:The point I was trying to make is, a lead acid battery is not an exact science. As a (not very good, admittedly) analogy, it would be like trying to measure how tired a horse is.

You could put a shunt resistor in the low-power (not starter motor) circuit, use it to measure current as well as voltage, and calculate battery condition on that basis - i.e. IF (battery voltage is <X volts when load is Y amps) AND (ignition is off) THEN cut battery.

The you might catch it before a damaging deep discharge - but even then you'd probably have to factor-in the capacity of the battery in question. And I don't see how this would prevent many rescue call-outs - the power needed to start an engine depends on the engine, not just the battery.
You can measure how tired a horse is, by seeing how much weight it can pull how fast. And: how fast it gets tired.
Same with the battery, if you have a fixed discharge value in how many amps you are pulling, you can watch the voltage decline and the worse the battery, the faster it will go down. But again, I think that batteries would last A LOT LONGER if they don't have these damaging deep discharge cycles due to run downs. If a battery is low already, trying to start the car (and failing) will put the nail in the coffin, as the starter is an ordeal on a low and/or damaged battery.
And remember: Batteries are specifically sized for the engine and (most of all) starter that the car has.
Measuring the capacity of any battery is not trivial, and I have always thought that a Raspberry Pi battery tester might come in very handy, where you can enter the capacity and the voltage of the battery and the Pi then discharges the battery with a fixed load and monitors it to see how much capacity it really has. That is a little more complicated doing with electronics, but in software it is real easy.

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rpdom
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Thu Aug 18, 2016 9:56 pm

nigratruo wrote:
rpdom wrote:A typical interior light takes about 5W. A Pi (depending on the model) may take 2-5W. Still think it will last for weeks?
Yes, it might, if you check your facts, 2 to 5 watts is not what a Pi uses when you rig it for low power consumption, which of course I would do here. Also, the Pi is DOING NOTHING most of the time.
Can you cite a source for your claims? The power consumption figures of the various Pi models are well known. About the lowest you can get is a Zero or A+ at 1-2W when idling and virtually everything shut down.

nigratruo
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Wed Sep 07, 2016 7:43 pm

Oh, I thought I showed that link with the power consumption:

http://www.jeffgeerling.com/blogs/jeff- ... zero-power

You can also measure it yourself, with a device that shows how much power a USB device uses, very useful
https://www.amazon.com/DROK-Multimeter- ... B00S2HJAUE

I was really surprised when I measure the consumption of a Pi that I was just using, that was not even rigged for lower power usage. Recommendations are usually including spikes:
your power supply has to be able to handle them, otherwise your Pi will crash when it spikes and does not get as much power as it needs, so you need a buffer cushion to handle that. We all had RPIs crash because the power supply we had was not sufficient. But that is not relevant for long term power consumption.
I wish car batteries were built by real engineers, not these quasi half baked car mechanic types that don't now what Amp hours mean, most car batteries are not labeled correctly how much capacity they have, so I have to try it out to see how much capacity mine has. The above site does not even talk about under clocking the CPU, what that would do in terms of power consumption, I would assume that you cannot really get much lower than that, as it might be rock bottom.
There might also be a worth effort to let it do micro sleeping, where it will spend 5 seconds every 10 seconds being totally sleeping, where the CPU will not execute anything and the wireless will get switched off completely.

The real life measurements show the difference between theory (how much people think it actually uses) and real life (where you go check what everybody assumes as truth). I have found that in many aspects of computer science that people often just take for truth what they read, without checking it themselves ;-)

boyoh
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Wed Sep 07, 2016 11:16 pm

Problem solved , Keep a well charged spare battery in your boot.
Iff you suspect a low battery change it.
BoyOh ( Selby, North Yorkshire.UK)
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Moe
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Wed Sep 07, 2016 11:24 pm

You can measure how tired a horse is, by seeing how much weight it can pull how fast. And: how fast it gets tired.
Same with the battery, if you have a fixed discharge value in how many amps you are pulling, you can watch the voltage decline and the worse the battery, the faster it will go down.
How do you fix the discharge current? Current depends on both resistance and voltage. You need to measure both, calculate the average power over a fixed period of time, then convert back to Amp-hours. In any case, you don't want to measure overall capacity, you want to know its state of charge at a particular point in time - without discharging the battery in the process.
I wish car batteries were built by real engineers, not these quasi half baked car mechanic types that don't now what Amp hours mean, most car batteries are not labeled correctly how much capacity they have
The problem is not the engineers; it's the technology. Your are expecting a chemical device to behave consistently and linearly regardless of age, temperature and state of charge. The real world doesn't work like that.
Submarine communication systems engineer and amateur robot enthusiast.

nigratruo
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Thu Sep 08, 2016 1:56 am

What I was driving at is this: I don't even know the capacity of my current car battery. Every normal battery has the capacity printed on it, in ampere hours. Mine shows cold crank amps, but NO indication how much capacity it has when new.

nigratruo
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Thu Sep 08, 2016 1:58 am

Keeping an extra battery in the trunk is very wasteful and not what this forum is about. I'm trying to build an intelligent solution with the Pi. Do you know how much a lead acid battery weighs? Really bad for fuel consumption.

mosespi
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Thu Sep 08, 2016 8:52 am

Here is my take on this and others may have mentioned some of it as well.

There is no fool proof way of correlating a certain voltage in most batteries to a start or no start point. Age of the battery, temperature, engine temperature (hot or cold start).. it all plays a part too, making it even more complicated. But measuring a car battery at 10, 11, 12 or whatever volts and deciding if it will start a car or not is incorrect.

If I was tasked with this sort of feature.. to get your one last start cut off point.. I would start with finding a way of estimating the condition of the battery under a starting load. You may have seen car mechanics hook up a load tester to a car battery and read the meter, this is what you need to 'program'. You can do this by monitoring the voltage under your known starter load (which should stay *fairly* consistent).. you will likely need a few dozen readings per second during the cranking/starting procedure to get a good idea of what is going on. Then you can figure out at what point you want to call your battery good, marginal, bad, etc.. This will give you a a basic battery condition to display to the driver and also an important factor to mix into your battery voltage vs capacity equation. I'm sure I'm missing some points, but I think you would need this much at least to get you started (haha).

You then can factor in other more minor readings if needed, temperature, time since last charge/start (resting voltage is different in the first few hours), amp draw, apply a safety margin, etc.

My current car has relays on the headlights, interior lights, and I think accessory power inside the cabin. If I leave any of them on for a long duration (in certain cases of course), it cuts their power. You notice this after you have left the lights on, as the car takes a start cycle to reset everything back to normal. I've seen several cars come with these standard now.. some call it rundown protection. For not much expense they cover problematic lights/accessories people likely forget about the most. They probably work on simple timer and maybe ignition/key state.

Finding a suitable relay should be easy, although at a few hundred amps it does start to get expensive. I don't know if I would want a whole car power 'relay', I'm not sure if it buys much protection vs expense and trouble it may cause. You also have to remember there are many other battery failures that you cannot predict with electronics and sensors.. battery plates failing, shorting, cases breaking/loss of fluid, interconnects breaking and so on.. to say nothing of the hundreds of other parts that can strand a car.

The car companies and their engineers are not stupid. Each and every 'feature' of a car costs money, maybe it is too expensive, too complicated or just not valued by the car buying public to implement right now. Maybe one day all the sensors and circuitry needed will be baked into the car already, then they can easily implement this feature, or it will just get really cheap to implement.

Sounds simple at first, but not the easiest task I would say. I'm sure I've missed some points too.

You are correct, most car starting batteries don't list the amp hour rating. I believe since you are not supposed to cycle them very deeply, the total capacity might not be all that important. There is usually a reserve capacity listed, sometimes abbreviate as RC, it is the useful capacity of a battery in MINUTES at a 25 amp draw. You can figure your amp hour capacity from that if you like.

Regards,
-Moses
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boyoh
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Thu Sep 08, 2016 9:00 am

nigratruo wrote:Keeping an extra battery in the trunk is very wasteful and not what this forum is about. I'm trying to build an intelligent solution with the Pi. Do you know how much a lead acid battery weighs? Really bad for fuel consumption.
I must admit I don't have a car , I can't drive, I'm looking at this problem in a logic way
It is night time, you are are on a long 300mile journey, 150 miles into your journey, your
Battery monitoring system indicates a battery low problem, What do you do.
You can't turn your light off ,it is night time. So your home made monitoring system
Is telling you something, you can't do anything about, If you stop your car, you will
Compound the problem , It won't restart, So take the jump leads out . And have
A spare battery, If you are bothered about the weight, leave the snow shovel and the
Bag of gravel out , Now the battery looks very cheap.
BoyOh ( Selby, North Yorkshire.UK)
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boyoh
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Re: Automatic Car Battery Cut off to prevent rundown andAAA

Thu Sep 08, 2016 11:25 am

I must admit I don't have a car , I can't drive, I'm looking at this problem in a logic way
It is night time, you are are on a long 300mile journey, 150 miles into your journey, your
Battery monitoring system indicates a battery low problem, What do you do.
You can't turn your light off ,it is night time. So your home made monitoring system
Is telling you something, you can't do anything about, If you stop your car, you will
Compound the problem , It won't restart, So take the jump leads out . And have
A spare battery, If you are bothered about the weight, leave the snow shovel and the
Bag of gravel out , Now the battery looks very cheap.
nigratruo wrote:Hi,

I have a project in mind that would make most calls to AAA (a car help service in the US) obsolete. Most calls are for dead batteries.
For the life of me I cannot understand why not every car in the year 2016 has a cut off circuit that disconnects all consumers from the battery, hence protecting it from a rundown.

I had the idea to use a Pi for that, because there is positively absolutely no reason or use of a battery running down more once it reached around 11, 10 or 9 volts and you have around 1 car start left before it is dead, so letting it run down more will make your starter fail to crank the engine/provide enough spark voltage sufficiently to make it start.

The reason for this post is now to share this idea and get your input for it. Especially on the cut off mechanism, which I envision as a spring loaded hard disconnect, so that the Pi can trigger it with a relay, and you can just reactivate it by a push button. It should be durable enough to resist corrosion and also allow a lot of amps to run though (though with the battery is charged and also provides starting power for the starter motor), so a normal relay would not be powerful enough I figure.

The mechanism would also be very fool proof: No matter what killed the battery, was it that you left the light on, the car was standing around for a month or you sit in the car with your love interest and talk the night away while listening to music and then realize that the engine does not start anymore, it will shut off the battery at that critical junction, the point of no return.

This is not for a commercial product, this is actually due to a comment of a nephew after he noticed that batteries do run down over and over and that AAA has a whole business built on it. He asked "so why don't car companies fix this? Are they stupid?" and I replied that they probably are but that we can find a fix for ourselves. And he had done some other smaller projects with the Pi and what he did not like was that they were always theoretical, a few LEDs or a game or something else that was just done to teach him something, but nothing that gets real use in real life. Well, here is our go at that.
BoyOh ( Selby, North Yorkshire.UK)
Some Times Right Some Times Wrong

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