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TIPS ON BATTERY BOOST VOLTAGE

There is not really a "correct" voltage to boost charge a battery because batteries all have different characteristics which vary with time, temperature and age.

When a battery is in a 'flat' state, you have a condition that all the "plates" (which are a lead 'pasta' type of material bonded together) are melded witha level of SULPHIDE BI_Oxide, packing onto the plates of the battery.
For a battery which is requied to charge and discharge continuously, such as the recreational and solar deep cycle batteries, the "lead pasta" plates are much thicker than in a normal vehicle(automotive) battery.
Due to this "level" of SO2(which is packed onto the plates) the "charge" process is one of reversing the "packing" of these ions on these plates-thereby removing them. Due to this thickness level which covers the battery, the internal resistance is much higher.

As an example

A maximum current which you can push back into the battery for short periods would be around 70% of the battery's Ampere hour rating. If it is a 100A.h , you could push in about 70A for 10 to 20 minutes, without doing any damage to the battery. ( this period is not considered 'continuous'). However, to be able to push even 30-40A into a flat battery, you have to overcome the increased internal resistance, and this you can only do by increasing the voltage during charging - that is 'BOOST'(high voltage) charging. If you don't Boost it, you will still get chemical reaction with some charging, but at a much slower rate. For instance, you will find that a flat battery boosted at 14V, will take about 5 minutes before drawing 40A, but wen boosted to 16V will reach 40A within 30 seconds! The drawback of course, is if you boost it for too long, you could find these currents going up to 200A. This is not critical for very short periods, but leaving it on for long periods would damage the battery. car battery

The chemical reaction in a battery is fairly slow, and when Boosted, it takes a while to reach full chemical activity as the SO2 layers are removed layer by layer from the lead plates. This means that Boosting batteries for periods of about 5 minutes even up to 18V might not cause any damage at all. You will, however start causing damage if you find the battery is starting to "boil". During the boiling process the chemical reaction is so fast and active, that you find that the SO2 layers are not being removed layer by layer but are actually extracted from the lead plates in big parts - and that is what causes the damage. The big "particles" then never dissolve completely, and subsequently, drop down to the bottom of the battery where they start causing shorts between the plates. The ideal solution therefore, is to put as much back, as safely as possible, but to limit it to the stage before damage can occur.

It is also very clear that you can not in any way get the same rate of recharging with a low voltage, a high voltage is much better. As an example, the CSIR experimented with some batteries and found, for instance, that if they take a 100A.h battery and pulse it with 1000A pulses of 300 milliseconds long ( this happened at around 80V), that they could fully recharge a battery in about 3-4 minutes, whithout overheating it.. the duration between the pulses is just long enough to make sure the chemical reaction just 'settled down' before it got struck again with another 1000A pulse.

If you would look at Solar regulator specifications, you will also find that most of the very good ones in the world will have a battery Boost facility , which automatically activates when the battery was discharged below a certain point. (This battery Boost charging level is set to around 15.5V to 16V). The battery will be charged in Boost mode for up to 20 minutes. The regulator will also have a built-in function to "cook" the battery at least once every 30 days. The reason for this is that if they are often discharged they become 'lazy' and need re-activating. This 'cooking' is regulated at around 15.5V for about 2 hours. Remember, that in this case, you are working with a limited current supply represented by the Solar panels, so there is an upper limit to the current peak.

If you have cold conditions where the battery is sitting at -5C or less, the chemical reaction in a battery is even slower, which means than one can even boost the battery with up to 20V for the same period, with the same affect.. As a further example, a 100A.h battery (at -10C) to recover to a 10 A.H. stage, would take about 40 minutes with 14V; about 15 minutes with 16V and about 4 minutes with 20 V. If you have the same battery at 40C all these periods are reduced by about 6 fold, so temperature plays a major role in battery recharging capabilities. The 'rule of thumb' used in the Solar industry is about 15V per Degree C

THE VERY BEST WAY TO BOOST A BATTERY

This would be to apply a high voltage(even up to 20V) onto a hot battery but to be sure to measure the current going into the battery and, as the current increases to about 50% of battery capacity, drop the boost voltage accordingly to maintain the maximum current. You will find a NEW flat battery going down from 20V to 15.5V in two minutes, while an OLD battery will do that in about 5 minutes.This facility will be incorporated into the new SBMS and Unipower 299 unit whithout incurring excessive electronic engineering.

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