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My old EA2 runs well but in later years there have been problems with restarting after standing. The main problems have been fixed but sometimes it happens.
The car is not used often but the battery seems to hold a good charge. But if the battery is connected to a charger for an hour or so before driving, there are no problems.
Why should that happen?
Made me think of having a second small battery which supplies the computer and sensors. It would also be charged with the alternator, but isolated from the main battery with a diode.
Would have some advantages, such as protection from surges, be independent of the main battery disconnection and boosting and low battery volts.
It is a fact that batteries left in cars that are left idle for periods of time will go flat. Usually this happens over a period of weeks or even months. It happenss in cars of all types, even older non-ECU equippped cars. With ECU equipped cars the process is accelerated somewhat due to the fact the the ECU consumes electrical energy in minute amounts to keep the ECU "live". We are probbaly only talking microamps, but it is a drain on the electrical system none the less.
It is possible that over long periods of time the ECU itself may die, losing its stored data on the last set of engine performance parameters. So when you repower the car the ECU could fire up with factory default (new car) data. The result is that the car could run ragged unitl the ECU retrains itself.
The best thing to do with a car that is not driven for a while is to connect a trickle charger to keep the battery topped up. You can even conenct a 7 day power point timer so that the charger comes on line for (say) 8 hours once a week. That should do it.
Having a timer on a trickle charger is an idea which I must use.
Tried a very low charge of only about 0.25 amps, but that is enough to evaporate the water from the battery.
Did a quick check and the battery volts is 12.4, but after an hour on low charge is 14.7V. The charger is homemade using a 20V supply, so the battery could charge to something higher than the alternator output.
The computer should hold some settings for a long time after the battery has been disconnected. Maybe there is a storage capacitor in the computer which needs to be replaced.
Maybe the charger boosts that capacitor storage.
A charge current of 250mA shouldn’t cause too much grief, unless its continuous. With a normal battery charger the current should limit to this value (about) with a battery voltage of about 14.4 volts. 14.7v is about as high as you would want to go without the battery beginning to gas excessively, (ie liberate explosive hydrogen gas) and overheat. If it does this it will lose electrolyte. I’d be a bit wary of non-commercial chargers as they may not have the correct self-regulating features.
One other thing you can do is purchase a battery hydrometer to test the acid level, providing you can get the caps off. It will tell you quite quickly what the real state of charge of the battery is, and will show up any dead or weak cells. Don’t splash acid on your clothes, they will dissolve! A well charged battery will read 1.210 to 1.240 specific gravity. A weak battery will read anything from 1.140 to about 1.200 for each of the 6 cells at normal temperature (about 20deg C). Correction has to be applied if the temperature is different, as the SG will change.
An ECU may well hold up for a long time, but some can be “killed off” if they are disconnected for 24 hours. But it does vary between different units, and no-one seems to have the real skinny on how long they take to die, especially when you want them to. It may use a capacitor, or a small on board battery. But the thing is that if the car battery is up to scratch, the ECU should be too.
If the computer has a capacitor and it charges to the max voltage through a diode, it would be protected from lower battery voltages. A higher voltage would make it last longer.
Needs information about the computer.
Yes a blocking diode would prevent the capacitor discharging back through the battery if it were to fall below the voltage of the capacitor. The capacitor will charge only to the maximum voltage presented to it by the power source, in your case the battery/charger – no more.
After that, it’s all downhill as the capacitor’s voltage holds up the ECU memory and very slowly drops over time. That could be months. Let’s say the ECU logic runs at 5v. That means the capacitor at 12v would have to discharge to a level at or below 5v for the memory to possibly become corrupted. That could be a long time!
I am only guessing. Whatever holds a particular voltage can be discharged within 24 hours? or faster if the foot brake is held down? Are we talking about new components or those 15 - 20 years old.
For some unknown reason charging before driving helps.
Have been learning a little more about lead acid batteries.
I was using a home made charger made from a transformer from a discarded fluorescent lamp, a full wave rectifier and a resistor. These batteries will try to charge to the peak voltage of the rectifier. But the extra voltage is just something like a surface charge with no power.
Added a transistor (large power one), from a junked TV as a voltage regulator, and a variable resistor to adjust the voltage. All on a timber base with nail heads as terminals.
It works well and using a timer is a good idea and it would seem that there is no point charging above 13V.
Still do not know why my car runs better if the battery has been topped up.
Hi there. A lead acid CELL (not battery) when fully charged has a terminal voltage of about 2.3v. With this, the specific gravity of the acid should be around 1.230 to 1.240. The charging curent should have dropped to almost nothing. At this stage, the cell will be mildly gassing, where the cell will be libertaing hydogen gas in very small bubbles. If you tap the side you will sometimes see the bubbles rising to the surface of the acid. Don't look using a naked flame - could be kaboom and acid everywhere! The battery charger should be a constant voltage type which will self regulate when the battery voltage approaches to max figure (as above).
Translated to the car battery, 6 cells x 2.3v = 13.8 volts. This is the nominal voltage of a car system. Alternatiors crib a bit, usually mainatining the float voltage at about 14.3 volts. This does dip a bit when under bonnet temperatures rise as the regualtor has thermal compensation to prevent overcharging.
If you charge a battery to 13v as you suggest, it will not end up being fully charged. The correct figure for a car battery will be more around 14v. A hydrometer test is always the best way to see the state of charge, and it would show that the battery wouldn't be fully charged.
Also, if you add water to the battery you dilute the acid a bit and effectively derate the capacity of the battery, if only temporarily until the battery recharges a bit. It shouldn't be an improvement.
You can buy a "battery fighter", it is a charger that will keep the battery at 14.4 volts, so wont overchrage it. For a car not used a lot, it will start easily and the battery wont need to be replaced all the time.
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