22 August, 2015

Fuel economy in a car: Charging the battery the Arduino way - Part One

In this post we will see what details we consider to adapt a vehicle to save fuel by switching off the alternator when we are not interested to charge the battery (and take advantage of braking, engine braking, etc. to do so), taking advantage of lessons learned in the previous post . This It is especially useful in a diesel , where power consumption is much lower than in a gasoline car.

Currently any measure is little to lower the consumption of a car, and although we are in a period of decline in fuel prices, this is transitory, because as with any commodity product high demand prices will soon go back up (or keep at the highest possible price that permits its competitors).
We can change the wheels to a eco profile ones, change the oil by other more energy efficient (as we discussed), etc. And one of the points of great savings capacity (between 1 and 5% savings) is in producing electricity, generating electricity with oil is very expensive. Some people even partially hybridized vehicle for changing the alternator motor / generator and replacing the battery with a LifePo4 (Forum GoldenMotor).
You have to evaluate the suitability of this modification, as the lead-calcium batteries do not allow more than 20% discharge without damage, so there is little room to use them with a programmed charging. Ideally mount a LiFePo4 battery, but can cost more than 200 €, only useful and profitable to people that uses them a lot in short travels in the city (taxi drivers and transport vehicles).
The most innovative engines are now including programmed battery charging, so that is only activated when the low voltage level is reached, although I do not know what kind of battery this cars uses and what the procedure in detail.

Curiously, in the following video you can see how the workload on the alternator note clearly appreciate the drop in rpm (and automatic adjustment by the control unit) of this PSA 1.6 HDI diesel engine:

While it is true that we are removing the power generation resistance, mechanical resistance of the alternator (no electricity productions so no resistance to rotation)  will always exist, although very low as you can see.

The idea of the project is to monitor tha battery from the dashboard (with a small display connected to an Arduino); charging condition of the battery, when is activated / deactivated, and activate the load when load drops below 12,8V, disabling it when the voltage returns to 14V, but the details are yet to be defined.

In the case of the Citroen Xsara Picasso 2009 have the battery under the driver's seat
In each vehicle model we will have to change different changes, in this case we easily accessible battery positive (not negative, we have to get it from some grounding of the car nearby).
While the task may seem simple, it is not; for a truly intelligent control need data braking (could suffice to read voltage from the cable brake light), we need to know the engine rpm or speed, and this raises the difficulty to another level; it would be best to connect the  Arduino directly to the ECU , perhaps ODB2. The truth is that I'm very in this topic (that these people dominate).
But I want it to be an accessible modification, and using a simple accelerometer sensor for Arduino ( like this ), we know when we are accelerating, and when slowing down, turning the alternator on only when it decreases. Intelligent alternator provides the following advantages:
  • Fuel savings obviously, between 1% and 5% on short trips.
  • Lengthen the life of the rectifier / regulator in the alternator (plus bearings, etc) not being always active, always in charge of delivering 14.5V DC (amperage depends on the regime of turns).
  • Monitoring the status of the battery; if we place an amperage sensor we can tell the owner if it is time to replace the battery with low capacity with a LED or the like when it is necessary.
  • Light economy and engine brake ; to reserve space for recharging under braking and downhills (we will use the Z axis to see if we go down or go up), both engine braking as the service brakes themselves will have less wear, increasing its lifetime.
  • By monitoring burden of the lead-acid battery we can even use a battery made ​​for the occasion with LiFePO4 A123 cells with a transmission charge / discharge (BMS), more durable and useful. ITV would you spend?
  • And if all goes well, even in the future it could replace the alternator generator / electric motor to help the main explossion engine, a partial hibridization would require a large capacity battery, as mentioned above.
I had my doubts that the car could function properly without giving the alternator load (the onboard computer and control unit could jump with messages, especially if the low voltage 11,5V charging), so first of all I had to get enough data to work on.
The idea is to use a relay 120A DC (later I discovered I need a 350 Amps relay 'cause the same positive cable is used to turn on the engine, with 270 Amps peak), and an Arduino board as a control, according to the battery charge, and use of the brakes, turn the load when it suits us (down hills, or when empty 20% Battery). (The battery of my vehicle already has six years, so it will be quite degraded after 124 000 kms, will have to check its current capacity before putting it into practice).
So maybe the best thing is to place three electronic relays activated 120A peak each in parallel, to distribute the load and lengthen his life, though rarely reach that power (when activated heating resistors morning guess ( here there are Picasso previous schemes, which are similar to mine).

For testing the operation of the car with the alternator disconnected (just give a message switchboard dead battery, check operation, etc) I've located the cable coming from the alternator to the positive terminal of the battery; a fat that must withstand the peak 12V 120A, l or have separated with the dremel of going to the fuse box and relays that control the electrical power of the engine.

Once you cut solder terminal on right ring for your amperage and diameter:

That tin solder and a soldering iron over 100W or with a small burner / blowpipe, like the one I have in my hands:

This way I can put it back in place to continue to use the car while I plan and evaluate the change.

After trying on the one hand I could see that the control unit uses a wire-sensor fine leaving the alternator to check the voltage, so that does not fail whatsoever , even with the battery less than 12V, at least until the Battery charge is very low I guess, and if an error in the jump onboard computer, I hope.
On the other hand, I discovered that both the alternator and the starter using the same cable , so if disconnected, everything works but does not start (does the "clack" of the relay, but nothing else), which would I leave it on until the engine starts.

On the other hand, I checked with the current clamp that at the start consuming maximum 250/280 amperes in the two seconds it takes the snatch; if we built a battery LiFePo4 we need a BMS that can give instant 300A and manage upload / download up to 60A continuous:
BMS LifePo4 3S in Aliexpress

In the second part I hope to set that up, happy bricos and see you soon !!

Updated 06/09/15

Apparently while there is "legend" that if you disconnect the battery from the alternator while the car is running, you could fry the alternator, but nothing is further from reality , as this same happens when the battery is full; electricity demand no more than the car (in a diesel is rather limited, as it requires no sparks to explode the fuel), and not "burn" the regulator is as if the circuit was open, with alternator running on empty, nothing is damaged, simply rotate the alternator freer without electricity.
Another thing would be to disconnect the battery and leave it to the alternator which only keep the unit and the rest on; then yes some danger because the battery acts of "stabilizing" voltage, because if the alternator regulator is not properly, could give peaks spoil all the electronics, but it is not the case that arises here.

The only doubts I have left is how far the ITV passed the electrical changes that do not involve safety modifications (change the battery with a lithium yes I would, but not if it is done well and with the safest technology, LifePo4). Do any readers versed in the topic you want to enlighten us? :)

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