Saturday, Jan 03, 2009 at 11:56
How effective is advanced battery charging on a battery and can it damage the battery?
I am asked all the time; do I really need advanced charging on my batteries? What effect does a split charge diode have on charging? What percentage of improvement will our products make on a system? Will the extra fast charging boil my battery? Will it excessively gas the battery? What effect in real terms can I expect? Most of the questions stem from old wives? tales, rampant in this market. The idea behind this article, is to lay to rest all the old wives tales and offer the facts. Remember, the below results are extreme and meant to show just how hard you can charge an open lead acid battery with no adverse effects.
Part 1: The effect of voltage on battery charging
There is no magic with advanced charging systems. In effect all they do is increase the differential voltage between where the battery is and the charge voltage; in other words, the higher the voltage that is applied to a battery, the faster it will charge. However, the down side is, that if you do not control that higher voltage after the charge is completed, you will overcharge and damage your batteries. This simple experiment will show you the direct relationship between actual voltage applied to a battery and the current (amps) being absorbed by it. This will give you an insight into how your system can be improved and where the problem may lie.
This information is 100% accurate and can be reproduced on any
test bench at any time, it is not a sales gimmick from Sterling; but a help sheet to show the general public in simple graphic terms what effect the higher voltage attained by advanced charging has on batteries.
The
test is very simple and not open to misinterpretation. We will use a simple lead acid, so called 'leisure battery', of about 100 amp hrs; a low cost, nothing fancy battery. All we have done is to discharge the battery to about 50% of its capacity, then connect it to a 180 amp regulated power supply. We will simply pick key voltages and log the current the battery can absorb at different voltages as it charges.
For example, the red line shows that when the battery was 50% full at 13.2 volts the charge current was 35 amps and at 14.8 volts the charge current was 160 amps. An improvement off about 457%. However the black line on the graph which was taken when the battery was about 70 ? 75% full, shows that at 13.2 volts the current was about 1 amp (showing that at 13.2 volts the battery was full, in its opinion); whereas at 14.8 volts we were still putting in about 60 amps; a charge improvement of 6000%. (Rather an improvement to say the least).
Why the specific voltages?
The voltages chosen are real voltages which one would expect to see in real life.
13.2 Volts
This voltage appears in 2 main circumstances.
• If you use a split charge diode then one would expect this sort of voltage at the battery.
• Most alternators now have a built in temperature compensator on their regulator. When the engine room heats up (especially on a vehicle) then the assumption made by the alternator manufacturers is that the battery should be full. So as the warm air in the engine room is pulled past the regulator the voltage from the alternator is reduced; the end result is, that we have seen standard vehicle alternators start off at 14.8 volts and drop to 13.2 volts in vehicles (with the bonnet down) after about 20 minutes. This is o.k. for the starter battery but will ensure your secondary batteries never charges correctly (as per the graph).
14 Volts
This is where most alternators start from; and is a standard expected alternator voltage from a alternator.
14.4 Volts
This is the voltage used to charge sealed lead acid batteries to prevent gassing.
14.8 Volts
This is the voltage one can push up to in open lead acid batteries without any damage to ancillary equipment, which will be connected to the battery at the same time. Apart from the obvious increase in charge rate this prevents sulphation of the batteries.
Having established the dramatic charge improvement which a battery can achieve with the increase in voltage, the many sceptics amongst us will now say,
well OK, the battery will charge faster, but you will gas the battery profusely. You will over heat it and boil it; and all that extra current going into it will not being stored; but simply gassed off. Meaning in essence, that the apparent fast charge is a waste of time and that all you have done is wreck the battery. All appear valid points and are prolific rumours. Now let?s see if they are true or simply old wives? tales.
Part 2: Will this fast charge rate cause problems?
With
test 2, we take 4 x 100 amp identical lead acid batteries as per the above
test. We connect all 4 together and discharge them to the same level. Then we charge one at a time (using a 200 amp regulated power supply) and over a 1.5 hour period and see how much charge in the form of amps are absorbed into the battery. Then using an amp hour counter we can measure the actual amp hours which have passed into the battery. After the battery has completed its charge cycle at the allocated voltage, we see if the amps are actually in the battery as storage amps. We do this by discharging the battery through an inverter with a 400 watt light bulb load; timing how long each battery can run the load after it has completed its charge cycle. If the amp hour counter shows more amps going into the battery and the load runs for a longer period of time; then the amps must have been stored in the battery. We also measure the battery temperature before and after the charge run to see if the battery is in danger (50C is when a battery starts to have problems) of overheating and boiling.
Answers to the questions based on actual facts
1. Will the fast charge rate also put more into my batteries? One can clearly see that on the 13.3 volt charge only 21 amp hours were put into the battery as opposed to 60 amp hours with the 14.8 charge. An improvement of about 300%.
2. Did this 300% improvement actually go into the battery or was it simply lost in heat and gas etc? The inverter discharge
test clearly shows that the 13.2 volt battery ran the inverter for 48 minutes, whereas the 14.8 volt
test ran the inverter for 114 minutes, a clear 230% improvement. So yes, the extra amps were being stored in the battery and were accessed by the inverter and used.
3. Will the high charge rate boil my batteries? One can see the rise in the battery temperature at 14.8 volts was from 18C to 32C, which is still
well below the manufacturers recommended temperature limit of 50C. Also bear in mind that this
test was charging a 100 amp hour battery at 150 amps, in real life with 4 x 100 amp hour batteries you would need a 500 amp alternator or battery charger to be able to reproduce this
test run.
4. Is it possible to put a lot of power into a battery in 1 hr? The graph clearly shows that the bulk of the power absorbed by the charger was in the first hour. So obviously the battery was comfortable with this as the temperature rise was
well within the battery's limits.
5. Does a 100 amp hour battery give 100 amps of useful power? Simply not true; even with the best charger, at least 40% or 40 amp hours tends to be no use in a battery.
6. Are there any other benefits from this fast charging? Yes, you also de sulphate the batteries, dramatically increasing the life of them. You will also reduce the running hours of your engine and fuel costs, associated with the charging of the batteries. In fact there are no down sides to this process.
Conclusion
It?s quite clear that all the fears are old wives? tales. Now all you have to do to harness this information is to add a computer program to store the charging curves, allowing the software to control the charge of your batteries and then, hey presto, welcome to the world of advanced digital charging from Sterling power products.
The graphs associated with the above can be viewed at
www.sterling-power.com
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