Power to You Battery types
This article will touch on
- Battery basics
- Battery types
- Sulphur Build up
- Parasitic Drain
- Discharge/Charging cycle
- Smart Battery management
What is a battery?
It is a store of energy created by a chemical reaction. The lead acid battery has been around for a very long time since 1859 in fact when it was invented by Gaston Planté. For those who would like to read more please see the following link ( http://en.wikipedia.org/wiki/History_of_the_battery)
Gaston Planté invention was different in that it was the first-ever battery that could be recharged by passing a reverse current through it. The battery has been the mainstay of starting engines and powering those annoying toys at birthdays and holidays for a very long time. We are all familiar with the cry of anguish when the battery dies just as someone completes a level or in the middle of an important call.
Today you will find a many different battery types Lithium, Gel and Dry cell for example. On the whole, these are grouped either as Primary Cell ( non-rechargeable) and Secondary Cell (rechargeable). A primary cell is usually found in your TV remote with Secondary cell commonly found in your car, phone and, of course, powering your WFP system. Our focus will be the standard Leisure or Deep cycle lead acid battery commonly used in WFP systems.
It is well worth mentioning the difference between the Leisure battery and a Vehicle battery.
A car's battery is designed to provide a very large amount of current for a short period of time. This surge of current is needed to turn the engine over during starting. Once the engine starts, the alternator provides all the power that the car needs and slowly recharges the battery. So a car battery may go through its entire life without ever being drained more than 20 percent of its total capacity. Used in this way, a car battery can last a number of years. To achieve a large amount of current, a car battery uses thin plates in order to increase its surface area.
A deep cycle battery is designed to provide a steady amount of current over a long period of time. A deep cycle battery can provide a surge when needed, but nothing like the surge that a car battery can produce. A deep cycle battery is also designed to be deeply discharged over and over again (something that would ruin a car battery very quickly). To accomplish this, a deep cycle battery uses thicker plates.
A car battery typically has two ratings:
CCA (Cold Cranking Amps) - The number of amps that the battery can produce at (0 degrees C) for 30 seconds.
RC (Reserve Capacity) - The number of minutes that the battery can deliver 25 amps whilst keeping its voltage above 10.5 volts
Typically, a deep cycle battery will have two or three times the RC of a car battery, but will deliver one-half or three-quarters the CCAs. In addition, a deep cycle battery can withstand several hundred total discharge/recharge cycles while a car battery is not designed to be totally discharged.
So What causes a battery cell to Deplete?
Connecting the battery to a load, in this case, your pump. When under load the Sulphur reacts with the Lead in the cell and generates electrical current (amps). During this reaction both the positive and negative plates in the battery become coated with Lead Sulphate. As the Current (stored energy) is drawn from the battery the plates become more and more coated. As the process continues the voltage is also decreasing.
Most manufacturers would recommend a battery should not be discharged below 10.5V as the build up of Lead sulphate will at this point cover most of the cell. This lead sulphate is a soft material and can be separated back into Lead and Sulphuric acid when the battery is recharged. However excessive depletion of the battery can cause the lead sulphate to harden into crystals on the lead plates. This will mean the cell is less able to hold a charge and will not last as long. Ultimately over its life, this is also why your battery will become less able to hold a charge.
Batteries also discharge via Parasitic discharge when not under load.
All batteries, regardless of their chemistry, will self-discharge. The rate of self-discharge for lead acid batteries depends on the storage or operating temperature. At a temperature of 26 degrees C, a lead acid battery will self-discharge at a rate of approximately 4% a week. A battery with a 125-amp hour rating would self-discharge at a rate of approximately five amps per week. Keeping this in mind if a 125 AH battery is stored for four months (16 weeks) over winter without being charged, it will loose 80 amps of its 125-amp capacity. It will also have severe sulphation, which causes additional loss of capacity. Keep your batteries charged while not in use!
Maintaining the battery state requires regular charging either by use of an intelligent charger or Split relay.
The most important thing to understand about recharging lead acid batteries is that a converter/charger with a single fixed output voltage will not properly recharge or maintain your battery. Proper recharging and maintenance require an intelligent charging system that can vary the charging voltage based on the state of charge and use of your deep cycle battery.
A split charging system can be of help in replacing some of the current (amps) you use during the working day. But it must be remembered that these are not going to put back all the current you use during the working day.
Equally how much current a split relay can replace is governed by many factors. The amount of time driven speed and size of the alternator will all have a bearing.
Bear in mind
At start up the engine requires a high amount of amps to start commonly taking up to 25% - 35% of the vehicle battery capacity if we assume an 85AH battery then start up uses approx 21 amps ( this can be higher depending on temperature and weather conditions) Starting the car in low temp of below freezing will draw much higher current)
Once the engine is running the alternator is solely responsible for the electrical needs of the vehicle plus has to recharge the batteries.
On a modern vehicle this can include
- Running the engine
- Powering any engine management systems
- Wind screen wipers
- Air Con if fitted
- Heating system
Based on the above the alternator may have to produce between 40 and 75 amps.
On top of the above we are now charging a second battery from the alternator plus any device EG mobile phone MP3 player that is plugged into the Power outlet (cigarette lighter socket)
Note: In cold weather the current draw from the alternator will be much higher.
Both the Vehicle and leisure batteries are designed trickle charge, This means only low current is passed to the batteries as the recharge. It can take the Vehicle battery some time to recover amps used at engine start up.
The alternator will prioritise the vehicle battery and vehicle system over any auxiliary charging, This means only a small amount of the available current is used to charge the leisure battery at any time.
As current is draw from the battery volts also fall. The volts will remain stable for a few hours then suddenly drop of the cliff (Diagram attached) for this reason the pump will run happily for a number of hours then suddenly stop as the volts fall off rapidly.
Also be aware a battery can loose up to 5% of its capacity a week just sitting on a shelf or almost 6 amps a week with a 110 AH battery. For this reason alone if the battery is not being used over the weekend or longer period it should be attached to an intelligent charger.
Always fit the correct rated fuse as per the manufacturers guidelines for the device being fitted.
During a recharge cycle dependant on how low the starting state a battery will draw high current and volts initially with the amount of current and volts diminishing as the battery tops up, This means it can take longer to go from say 12.5V to 13V than it takes to get from 10V to 11V (Ohms law)
How much current is replaced in the Leisure battery This is difficult to answer. For example the pump could draw per hour around 3 to 5 amp an hour (double this for a two pump system). Now if we work on the basis that for up to 30 minutes the alternator will prioritise the vehicle battery and engine systems then current to the leisure battery may only be 2 - 3 amps an hour so much less then is being used.
NOTE: a system with no electronic pump controller could draw up to 8 amps an hour:
In honesty the above figure may be higher or lower, without testing the amps going to the leisure battery I can not be precise. Clearly though less is being put back in than is being used.
Note: In some cases fitting an auxiliary electrical system to your vehicle may invalidate the vehicle warranty. If unsure check with the Vehicle dealer for advice.
Some controllers offer features which can help manage the battery, display voltage and shut down the pump in the event of the battery voltage falling to low. The battery voltage is available at the touch of a button on the V11 range, which quickly displays the measured battery voltage. However, the controller is continuously checking the available voltage. A Charging controller monitors the state of both leisure and vehicle batteries. The controller will shut down the system when the battery is too low, below 10.5 volts on the V11, preventing irreversible battery damage. But will also start the charging process when it detects additional voltage is available ie. From the alternator because the engine is running.
This gives confidence at the end of the day that you have enough battery power to finish that job without having to swap or recharge the battery.
Low Battery Cut Off Override
Our V11 digital controls feature this as standard. Simply choose to override the low battery cut off and you can continue to work even if the battery voltage drops below 10.5V. This can be by the simple click of a button. The controller will still display accurate voltage and give a low battery warning.
Note: There is no such thing as a free lunch! Running your battery below 10.5 volts could cause permanent damage to the battery cells.
So this is an emergency option when you simply have to get that important job finished and want to avoid re-visiting your customer the next day to finish the job.
Extended Battery Life
Our engineers have worked to make the V11 Pro digital controller, even more, energy efficient, allowing you to work longer on the same charge. Less energy use means:
- • longer battery life
- • less recharging
- • efficient energy transfer battery to pump
- • less wasted energy
What difference can a control make to battery life?
The diagram above is for illustration purposes. It shows how a leisure battery could discharge over a working period. Note that voltage and amps are steady for up to two hours. We see a fall off in the 2 - 3 hours range and after 3 hours the voltage falls off is dramatic.
So how does this relate to a typical WFP battery powered system as used in a van?
1. Operating at maximum a 100psi 5.2 LPM pump is capable of drawing around 9 amps an hour.
Most Leisure battery manufacturers recommend that you should not use more than 50% of a batteries capacity on a regular basis. Continually draining a battery below 50% of its capacity then recharging will affect the cells ability to hold a charge. ( As outlined above sulphate crystallization is speeded up).
As the cells degrade the less time it will take to use 50% of the capacity. By capacity, I refer to the current draw from the battery (amps) as the pump draws current the amps held in the battery fall as do the volts. The lower the volts the greater the drain of amps from the battery.
2. What does this mean in real terms? The following figures are based on running a single pump with no form of controller.
A 75 amp hour battery, running a single pump at full power could be at 50% of capacity in 4.5 hours. Or a 120 AH battery in 7 hours (Red and Green).
3. Using a pump control can reduce the current draw from the battery, extending the working time per charge. For example if we reduce the current draw to 4 amps ( the average draw with a controller flow rate between 60 – 70) then a 75 AH battery could take up to 9 hours to be discharged by 50% - A 120 AH battery could take up to 15 hours to be reduced to 50% capacity (Blue and Yellow).
Note: If two pumps are used the current drawn is doubled e.g. up to 18 amps an hour if running without controllers or 8 amps with controllers.
Some leisure batteries can be drained to 80% of capacity occasionally. However continued use in this way will shorten the life of the battery, so always follow the manufacturers guidelines. Use of a pump controller could extend the use per charge of your WFP system when compared to a system with no controller. All our controls are fitted with a volt meter and battery management.
Note: The diagram above is, for example, purposes, actual discharge rates will vary system to system and are dependent on battery condition, water flow rates and other factors. While a controller will allow you to work longer per charge, the amount of time will vary.
In summary, then it is better to have a leisure battery (deep cycle) powering your WFP system as they are better suited to long continuous periods of discharge at a constant current draw. A vehicle battery is not designed to produce current over a prolonged period of time but for very short high energy bursts. Running a pump for several hours will reduce the life of your vehicle battery and may mean you end up with a flat battery and then waiting for the breakdown guys.
In addition, a deep cycle battery is capable of discharging and recharging many times over.
Keeping a battery maintained will help extend its life, remember to regularly charge it even after a period of inactivity (it can lose up to 4% per week of capacity while not under load). Use an intelligent charger which can vary the charge as a battery voltage recovers.
Use the correctly rated fuse to protect the wiring, pump and (if you have one) controller from sudden current surges.
I hope this article has shed some light on batteries. I have tried to keep it straight forward as the amount of information available is massive.A little regular maintenance can extend the life of your battery and give you trouble free days of work.
In the end, the choice of battery and how you choose to work is a personal decision. I hope this article will provoke questions about how a system can work as efficiently as possible.