Tag: Batteries

AGM Batteries: A Dependable Classic

AGM batteries have long been a reliable choice for various applications, from uninterruptible power supplies (UPS) to marine and recreational vehicles. They utilize a glass mat separator, which is saturated with electrolyte to ensure minimal maintenance requirements and a spill-proof design. AGM batteries are known for their:

• Deep Cycling Abilities: AGM batteries can withstand deep discharge cycles without significant performance degradation, making them suitable for applications requiring frequent charging and discharging.

• Vibration Resistance: Their construction offers enhanced durability against vibrations, making them ideal for mobile applications like RVs and boats.
• Maintenance-Free Operation: Sealed design eliminates the need to add water or electrolyte, reducing maintenance efforts.

Lead-Carbon Batteries: Merging Tradition with Innovation

Lead-Carbon batteries combine the strengths of traditional lead-acid batteries with advanced carbon technology. This hybrid approach brings several advantages, making them a preferred choice for applications such as renewable energy storage and telecom backup systems. Key features of Lead-Carbon batteries include:

• Enhanced Cycle Life: Incorporating carbon technology extends battery life and improves cycle performance compared to standard lead-acid batteries.
• Fast Charging: Lead-Carbon batteries can accept higher charging currents, reducing the time required for recharging.
• Partial State of Charge Tolerance: Lead-Carbon batteries can operate efficiently even at partial states of charge, minimizing the risk of sulfation.

LiFePO4 Batteries: Pioneering Energy Density and Longevity

Lithium Iron Phosphate (LiFePO4) batteries have taken the energy storage market by storm, offering high energy density, exceptional cycle life, and lightweight construction. These batteries have become the go-to choice for electric vehicles, renewable energy systems, and portable electronics. Key advantages of LiFePO4 batteries include:

• High Energy Density: LiFePO4 batteries offer a high energy-to-weight ratio, allowing for more compact and lightweight designs.
• Extended Cycle Life: With thousands of charge-discharge cycles, LiFePO4 batteries outlast many other battery types, contributing to lower long-term costs.
• Safety: LiFePO4 chemistry is inherently stable, reducing the risk of thermal runaway and fire incidents associated with some other lithium-ion chemistries.

Tailoring Your Choice to Your Needs

Selecting the appropriate battery technology involves understanding the unique benefits and limitations of AGM, Lead-Carbon, and LiFePO4 batteries. AGM batteries offer reliability and deep cycling for applications requiring constant charge-discharge cycles. Lead-Carbon batteries blend tradition with innovation, excelling in renewable energy storage and backup power scenarios. LiFePO4 batteries lead in energy density and longevity, making them ideal for electric vehicles and energy-intensive applications. By assessing your specific requirements against these technologies’ strengths and weaknesses, you can make an informed decision that aligns with your goals for efficiency, reliability, and sustainability.

DC ripple occurs when the Voltage of a DC system oscillates, usually only on a scale of milivolts. It can happen for a number of reasons.

• Volt droop – As you discharge a battery, the Voltage drops. Volt droop refers to the phenomenon by which the voltage drops disproportionately low under a heavier load. Say if you discharge a 12V battery from 13V down to 12V. If the load was heavy for the battery’s size and you turn it off once the battery reaches 12V, you will see the voltage come back up – maybe to 12.1, maybe to 12.5 – depending on how heavy the load is. This is not DC ripple on it’s own, but DC ripple occurs due to Voltage droop when loads are uneven – and most loads are. A 240V battery inverter will pull more power at certain points in the wave, which causes the battery Voltage to oscillate at a rate of 50Hz – too quickly to show up on a multimeter, but can be observed on an oscilloscope.
• Charging methods – Most methods of charging a battery do not provide a truly constant voltage to the battery. On the extreme end you have switch mode power supplies and PWM solar controllers which let through high Voltage pulses. Even high quality charging equipment tends to allow small ripples and smart chargers use high Voltage pulses to sense battery Voltage (still go for a 3 – stage charger if you can – the benefits far outweigh the small disadvantage).
• Rapid charge – discharge cycles. So you’re charging your batteries from solar at the same time as you’re using them. Output power isn’t constant, neither is input power, and the load includes an inverter. You have DC ripple due to the inverter power, an uneven draw, and uneven input power all at once.

So why does this matter?

Firstly, at high enough voltages, DC ripple carries similar risks to AC current. This isn’t worth worrying about with a simple 12 or 24 Volt system, but at higher Voltages it is something that professionals need to be aware of. Battery life – DC ripple basically charges and discharges your battery very fast. Whilst only at the scale of mili – or – micro – volts, these mini – cycles do add up and long term shorten the usable life of your battery. How much will depend on the type of battery and the severity of the DC ripple. Batteries with a higher internal resistance experience a greater degree of DC ripple – So lead batteries typically fare worse than lithium batteries of the same size. On the flip side, the high voltage spikes put out by PWM controllers and other cheap chargers are especially damaging to lithium batteries.

What can be done to minimize DC ripple?

• Quality charging – Avoid PWM’s if possible and go for an MPPT, use quality 240V chargers as well if possible.
• Ensure your battery bank is properly sized. Lead batteries shouldn’t be discharged faster than 0.2C, or 20% of the batteries Amp – hour capacity, i.e. if you have a 100Ah battery, you shouldn’t pull more than 20Amps from it. Lithium and lead – Carbon batteries can be discharged faster, so go for these if running heavy loads.
• You knew I was going to talk about supercapacitors. These have a much lower internal resistance than either lead or lithium batteries, and have millions of charge – discharge cycles in stead of mere thousands. With a supercapacitor in parallel with a battery bank, all of those micro – cycles go through the supercapacitor first, buffering or eliminating the DC ripple effect. This is not necessarily a cost effective solution for a small AGM battery, but on larger banks it’s a no–brainer.

Lead

Lead batteries fall into several different categories;

Flooded

Flooded lead batteries are commonly used for cranking (the battery under your bonnet is almost certainly a flooded lead – acid). They contain a liquid Sulfuric Acid electrolyte. Every time the battery is charged or discharged, some of this electrolyte degrades to form hydrogen sulfide gas, which is flammable. Flooded lead batteries can produce enough hydrogen sulfide to build up and explode, so large installations require a specialised ventillation system. Flooded lead batteries can also be spilled; The electrolyte can produce dangerous / flammable fumes depending on what it comes into contact with.

AGM / Gel

AGM and Gel batteries are different but in terms of safety they fall into the same category – Non spillable, valve regulated lead acid.AGM’s immobilise the sulfuric acid electrolyte in a special absorbent glass mat, which reduces the hydrogen sulfide produced. Gel batteries, similarly, contain a sulfuric acid electrolyte that is mixed with a gelling agent. Both of these batteries are recommended to ‘not be charged in a gas tight container’ but are safe to have in an enclosed space such as a vehicle or a building. Lead – Carbon batteries generally are also either AGM or Gel batteries in terms of electrolyte, but because of their better charge / discharge efficiency and their slightly lower operating Voltage, Hydrogen Sulfide production is even lower.

Lithiuim

There are two broad categories of lithium batteries. Lithium – Ion is the general term used for lithium – Cobalt, lithium – manganese and a few other varieties. LFP, LiFePO4, lithium – Iron (not ion), or LiFePO is the term used for Lithium Ferrous Phosphate batteries.

Lithium ion batteries have advantages in weight and charge / discharge ratings but if mismanaged present a serious fire hazard as they contain a flammable electrolyte that bacomes explosive on contact with water.

LFP batteries are comparitively very safe. They handle the heat better and last longer, but are slightly heavier. Whilst the electrolyte is technically still flammable under extreme conditions, fires starting from LFP batteries are exceedingly rare and typically only occur when a high voltage bank gets short circuited, or when battery cells are mechanically damaged and then get wet. Prismatic LFP cells are some of the safest batteries available.

Fusing

Regardless of chemistry, batteries store a lot of energy and an electrical fault caused by a short circuit or an undersized conductor can start a fire simply because of the heat produced by the current. It is essential to ensure that all cables and links are correctly sized. Anything directly connected to a battery should be fused. Single – pole fuses and isolators, by convention, go on the positive terminal of your battery, and with good reason – In a vehicle, the starter battery is earthed to the chassis, i.e. the entire body of the car is negative. This means that if your positive cable comes into contact with the body of the vehicle at any point, it can create a short circuit (in layperson’s terms, this will cause electrical current to be drawn from the battery extremely fast, producing heat, which could case a fire). Fusing any cable going to the positive terminal of a battery, as close to that terminal as possible, is therefore an essential safety measure.

In higher Voltage / stationary systems, a ‘double – pole’ fuse or magnetic circuit breaker is used and generally double – sheath cable or conduit is used between the battery and the breaker. There are strict standards on the protection equipment that can be used and installation layout for larger systems.