What is a Tubular Gel Battery? — Microtex Energy
There are distinct advantages to lead-acid battery technology when compared to other electrochemical systems such as li-ion. Affordability, reliability, recyclability and safety are key issues in choosing the right battery for a particular application and lead-acid batteries will score highly in these categories. There is, however, a drawback when using conventional flooded lead-acid batteries for deep cycle applications. This is the maintenance required in topping up the batteries due to water loss by gassing. In many applications, like in Traction battery usage, there is a need to completely recharge a battery in a limited time frame. This normally will require higher voltages which in turn leads to the breakdown and loss of water from the electrolyte through gassing. These lead-acid batteries will require topping up with water, creating inconvenience and costs and in large installations which often requires expensive extraction equipment.
There are also other disadvantages, particularly with transport, storage and disposal. The liquid acid in the lead-acid battery is classed as a hazardous material which is harmful to humans and equipment. Whilst this is not considered a problem within the industry, which operates using safe and proven procedures, it is much better to immobilise the acid to prevent spillages. One fortunate consequence of acid immobilisation is that it creates the ability to recombine the hydrogen and oxygen gases which are produced from the breakdown of water inside the battery when on charge.
There are two principal methods for acid immobilisation:
- use of absorptive glass mat which holds the acid in place and
- the other, adding a fine silica powder to make a gel.
Both methods, although very different, achieve the goal of immobilisation. They also provide the added benefit of recombining the gases released on charge to reform water, thereby removing the need for the water-addition maintenance procedures mentioned earlier for flooded lead-acid batteries.
Out of these two methods, the use of silica-gelled electrolyte is universally recognised as the best solution for deep discharge battery designs. There are two main reasons for this: the first is that the use of gelled electrolyte allows a tubular positive plate to be used, which is recognised as providing the best deep cycle properties for lead-acid batteries. The second reason is that the stratification of acid associated with deep discharges and limited-voltage recharging without gassing is avoided. These are significant advantages if you have deep cycle requirements. The use of tubular plate batteries provides the most robust lead-acid battery design with the highest deep cycle capability of all lead-acid designs. The resistance to stratification is of great benefit in many applications which operate at partial state of charge, such as standby power, UPS and clean environment markets.
So why is lack of topping up such an advantage? You have to consider the problems of maintaining lead-acid batteries in remote locations with difficult access. The cost of maintaining these batteries with regular monthly or quarterly visits can be very high. For a business, this can make an installation uneconomical. The other side of this expensive coin is the maintenance, particularly in commercial environments where equipment reliability is key to providing a reliable and regular service. If batteries powering essential equipment fail due to lack of maintenance, the ramifications for credibility and reputation can be considerable. For the private user, it can be equally frustrating. For example, having to access installed batteries and obtain distilled water sometimes is not so easy, not to mention keeping a log and records for possible warranty claims. And of course, there is the situation where we are simply extremely busy and accessing and maintaining batteries can be a really time draining exercise.
There are also those clean environments where charging batteries can produce damaging or even explosive fumes, particularly in confined spaces. This is particularly relevant in computer backup and medical applications where batteries are kept in cabinets or inside complex and sensitive equipment. To remove fumes from charging batteries it is sometimes necessary to install expensive extraction equipment to remove explosive hydrogen gas and corrosive acid fumes from confined spaces in cabinets or equipment. There are also clean environment applications as in hospitals and food storage. In these environments smells and corrosive gases could contaminate food or damage human health. Looking again to the consumer applications, the last thing they need is a battery in their home, garage or solar power bank, which is producing explosive gases or corrosive fumes on when on charge.
So just how do this combination of tubular plate and GEL electrolyte work? To understand we have to look at several elements which contribute to the battery’s properties, these are:
An electrolyte which is immobilised as a GEL to ensure non-spillage and also to enable the hydrogen and oxygen released on charging (which is held inside the battery under pressure) to be recombined to form water. The benefit of immobilisation extends further, it prevents the creation of strata of acid with different densities within the cells. In flooded and sometimes AGM designs, dense acid produced at the plates during charge can drop to the bottom of the cell leaving the weaker acid at the top. Batteries in this condition suffer early failure from sulphation, capacity loss and grid corrosion. Microtex have a gel making plant imported from Germany and use high-grade German silica to give uncompromising life and performance to their Tgel batteries.
A tubular design of the battery plate. This is essentially a pressure cast lead alloy spine instead of a grid, which is covered by a fabric gauntlet then filled with the active material (PAM)
This can be either a dry lead oxide powder or a wet lead oxide slurry. A tubular design of plate has a couple of advantages: the first is that it has a higher surface area in contact with acid to give better material utilisation (as much as 60%).
The second reason is that tubular batteries and cells have the highest cycle life of the entire lead acid battery range. Under standard deep cycle test conditions (80% depth of discharge), some tubular designs can achieve over 2,000 cycles before the capacity drops to 80% of its original value.
The corrosion-resistant alloy used in the positive spine ensures the longest achievable life of any VRLA product on the market. Microtex makes their own lead alloys to ensure the highest quality and best specification for their batteries. Using an optimised lead — calcium alloy with high tin content ensures that premature failure due to positive grid growth and spine corrosion is effectively prevented. This is not the cheapest material and self-manufactured is not the most convenient way of obtaining the components for batteries, but it does give the best form of control to meet the demanding quality standards for which Microtex are renowned.
Tailor-made lead calcium tin alloys used in the positive tubular and flat negative plates almost eliminate the hydrogen and oxygen gases produced on charge. Because the volumes of gas produced are not excessive (as with conventional flooded designs) they can be recombined to form water within the operating pressure of the battery. Because the Microtex alloys produce so little gas, premature failure due to water loss is prevented.
Hydrogen and oxygen gas are produced at the negative and positive electrodes respectively when water is broken down during charging. The simplified reactions involving the negative oxygen and positive hydrogen ions produced when water is electrolysed are:
Water decomposition on charge: H2O = 2H+ + O-
Gas evolution reaction on the positive plate: 2O- — 2e = O2 Gas
Gas evolution reaction on negative plate: 2H+ + 2e = H2 Gas
From these simplified equations, it can be seen that the charged oxygen and hydrogen ions produced by the breakdown of water are in solution as ionic species. They are then attracted to the oppositely charged electrodes where (due to the electrochemistry of the charging process) hydrogen is reduced by gaining an electron and oxygen is oxidised by losing an electron. Because the gases are then trapped, water is lost from the electrolyte. However, the Tgel design efficiently contains these gases within the voids created in the immobilised electrolyte which now become small gas pockets. These pockets effectively store the gases which become reservoirs for subsequent recombination to form water.
Tubular Gel Batteries demand High-quality materials of construction: In particular, the multitube gauntlet used in the plate and the PVC battery separators are manufactured by Microtex to the most demanding specifications found in the lead-acid battery industry. This ensures a high burst pressure in the gauntlet to resist cyclic volume changes of the active material. This volume change can lead to paste shedding and loss of capacity if lower grade materials with a lower burst strength are used.
Likewise, Microtex’s Time Tested PVC separator has optimum porosity, low shrinkage and high stability in sulphuric acid. This ensures that the battery will meet its design criteria and guaranteed life, even under very arduous conditions.
No compromise on the material specifications for bought-in components such as the pressure relief valve used to control the cell internal pressure. Unless the pressure relief valves have precisely the same opening pressures there could be water loss from some cells due to gases escaping. This causes imbalances between the individual cells of a battery which leads to early failure. Use of the highest quality components ensures that there is minimal cell to cell variation during a battery’s operation. Likewise, the connectors and containers use the best materials for the job and are supplied by certified manufacturers to Microtex’s demanding specifications. The Microtex designs, constructional materials and specifications for bought-in components are the result of decades of experience and closely working with and supporting their suppliers and customers. It is this dedicated and no-compromise approach to customer satisfaction that helps to set Microtex apart from their competitors.
Good balance of active materials within the battery. The performance and life of any lead-acid battery of any design is critically dependent on the amount of the three active materials: positive active material (PAM), negative active material (NAM) and the acid. In a fully charged lead-acid battery, the PAM is lead dioxide and the NAM is spongy pure lead. These react together with the sulphuric acid electrolyte to form lead sulphate and water in the following reaction:
- PbO2 + Pb + 2H2SO4 = 2PbSO4 + 2H2O
- (PAM) (NAM) (ACID) (Discharged plates) (Water)
This is known as the double sulphate theory and it predicts the minimum amount of active materials required to provide the rated capacity of the battery. However, this is the real, not the theoretical world. In practice, the physical characteristics, quality of the materials and the quality of the manufacturing processes will also influence how much material is required and how long the battery will last in service. The PAM has a lower efficiency than the NAM and up to 20%, more may be needed to provide the same capacity as the negative material. Added to this is the utilisation of the material, the higher the utilisation the lower the life expectancy. To complicate matters the optimised balance changes when considering recombination batteries. Microtex, in association with international German and British experts, has optimised the materials and the manufacturing process to produce the best possible balance between the plate materials and acid content in its tubular gel battery.
Other important aspects of a battery’s usefulness are its range and sizes. There are numerous applications mostly with different capacities, voltages and performance requirements. In addition to this, there are the containers or spaces where the batteries have to be fitted and in these instances, the skill of the person installing them is also an important consideration. In this respect Microtex has covered all the bases, the Tgel extensive range of monobloc and 2V cells comes in a variety of sizes and capacities to meet practically every requirement.
fully insulated and designed to carry the high loads necessary for occasional or frequent high-rate discharges. Their extensive range of 2v TGEL VRLA battery provides applications like telecom, solar, standby, switchgear and controls, power generating stations and substations, nuclear and thermal power stations, electricity transmission substations with reliable and durable backup power and energy storage. Made to order or standard size batteries in insulated steel containers are no problem for the Microtex technical and manufacturing teams. High-level technical assistance is available at no extra cost to help customers in designing the optimum and most cost-effective installation for their requirements. This includes designing and fitting zone 4 seismic racks and enclosures on customers’ premises.
The whole battery design can either use a standard sized container or be a bespoke size to meet a particular size and installation demand. Microtex will ensure that the customer receives the best advice for their requirement and budget. Again, working with the customer to give them the solutions they want, not the solutions a ‘supplier’ has; is the trademark of Microtex.
To this end, the importance of the right financial, as well as technical and engineering solution is recognised and placed at the centre of Microtex service.
Although the advantages of the GEL battery are substantial, their use is often restricted due to the higher cost when compared with standard flooded lead-acid batteries. If the value for money is the main consideration, often described as Total Cost of Ownership (TCO) is more important than initial capital outlay, then the Tgel range is almost certainly the best option. The lack of maintenance cost and the charging efficiency can certainly save money, particularly when considering remote applications such as telecoms towers and diesel/solar hybrid generators. If we then factor in the higher cycle life, which means you get more watt-hours through the battery when compared with lower cycle-life designs, the TCO is often lower for a Tgel compared to a flooded option. In this way, any differences in capital outlay are more than compensated for by the net savings in both the operating and overall capital costs.
It is fair to say that the performance and life expectancy of the Tgel battery is probably the envy of the rest of the lead-acid battery industry.
Originally published at https://www.microtexindia.com on October 13, 2019.
