I know you might be wondering how charging can float right? Here is the answer to your question. When we talk about a floating charge, this is the kind of charge that is applied to the battery so that its capacity is maintained at full charge or close to the full charge.
Float charging comes in handy when a battery is going to be stored for long periods. Floating chargers provide a floating charge.
Floating chargers are special in a way that they keep the battery topped up close to the battery’s full capacity. The floating chargers give 0.2 volts to 0.6 volts of power beyond the full capacity of the battery.
These chargers are in most cases used on power backup batteries which are on standby. The main function of the trickle chargers is to ensure that the battery is maintained at full power or close to full power so that if the battery is needed, they are readily available for use.
Is a Trickle Charger the same as a Float Charger?
Even though these two chargers work under the same principle of ensuring the battery is provided with a reduced charge voltage over longer periods, the two chargers are different.
When you compare the two chargers you will find out that a floating charge has a system capable of switching the charger on and off. If the charger detects the battery is charged to capacity, it automatically switches off and it will switch on to have the battery topped up when the voltage drops.
Whereas the floating charger is more automatic, the trickle charger on the other hand is more manual. It has to be switched off manually when the battery is charged to capacity. It also gives current at a lower and continuous rate.
Quite a number of float chargers can adjust the amount of voltage as the temperature inside the battery changes meaning they are already compensated for temperature.
Trickle chargers on the other hand can cause thermal runaway if temperatures rise inside the battery. Unlike their counterparts, they are not compensated for temperature.
Can a charger fail during a Float Charge?
Yes, it is true that for some reason, a charger might fail during float charging. The float chargers are made to provide the battery with a low voltage current over a long period so that the battery is maintained at full capacity or close to full capacity. If the battery charger fails for whatever reason, the implication is that more charge will be allowed into the battery.
This means the battery is likely to overcharge. The rate at which water breaks down into hydrogen and oxygen gases will drastically increase when the battery is overcharged.
As the gases keep on being produced the electrolyte will eventually dry out. When the electrolyte dries out what follows suit is that the internal heat will rise resulting in thermal runaway.
At this point, when the battery tolerance is exceeded, the battery will start to melt as a result of too much heat.
There is also a case where the charger may fail in a way that does not provide the battery with the required charge to have the required charge levels maintained. If this is the scenario, the battery will run out of power through self-discharge.
When the charge is too low in the battery, sulfation may occur and that will lower the capacity of the battery. When a battery stays discharged for longer periods, there are chances that the battery might be damaged completely to warrant a replacement.
Can I Put More Than One Battery on Float Charge?
The answer is Yes. When you look at a car battery, it has 6 cells each giving 2 Volts when connected in series thus giving a total of 12 Volts of the battery.
The same technique applies and even with a float charger, a string of batteries can be connected safely in series to have the charge maintained at full or close to the full capacity.
An equal amount of current flows through all batteries in the string when a float charger is connected. Taking into consideration the condition of the batteries, the required results may be obtained.
Take note that only batteries with the same charge levels should be connected. You need to have any undercharged batteries charged until the charge level gets to the required capacity before having it connected to the string.
If it is within your capacity, it is advisable to limit the battery strings to a maximum of 48 batteries. Again, when connecting the batteries its advisable to use batteries of the same age and amp hour rating.
A parallel connection can also be made to the battery charger for float charge. However, in a parallel connection, the current from the charger will be divided almost equally in the batteries that form the parallel connection.
While in series connection the battery capacity and age were a factor, in a parallel connection the current is divided among the batteries depending on the capacities and internal resistance.
Relationship Between Temperature and Floating Charge
Float charge efficiency is reduced at extremely low temperatures. A more rapid increase in temperature above 400C (1040F) increases the charge efficiency as well and in that state, there are dangers of thermal runaway if temperature compensation is not done in a timely and specific manner.
If the operating temperatures are beyond the range of 50C to 350C (410F to 950F), then temperature compensation by the floating charger will be required.
For best results, Given the temperature, the below compensation chart gives the float charge per cell
| Temperature | Float Voltage per cell. |
| -400C (-400F) | 2.38 – 2.43 |
| -200C (-40F) | 2.34 – 2.39 |
| -100C (140F) | 2.32 – 2.37 |
| 00C (320F) | 2.30 – 2.35 |
| 100C (500F) | 2.28 – 2.33 |
| 200C (680F) | 2.26 – 2.31 |
| 250C(770F) | 2.25 – 2.30 |
| 300C (860F) | 2.24 – 2.29 |
| 400C (1040F) | 2.22 – 2.27 |
| 500C (1220F) | 2.20 – 2.25 |
What is the Float Charging Efficiency Of A Battery?
The floating charge efficiency depends on the state of charge of the battery, charging rates, and also temperature.
The charging efficiency is usually expressed as the ratio of the Ah delivered to the battery during charge to the Ah discharged after full charge.
As the cell decays, there is self-discharge. The floating charge should be above 2 Volts per cell if the battery will be stored for more than 1 year. Before connecting the charger, have the open-circuit voltage confirmed.
For best results, always match the battery to the charger like for instance, use a 24V-rated charger for a 24V battery.
Can I Apply a Float Charge to the Lithium Battery?
A floating charge can be applied to a lithium battery even though the charging profile of the lithium battery slightly differs from that of a lead-acid battery. In the case of a lithium battery, the battery charges very slowly and will take longer to charge to capacity.
Lithium battery will still retain more than 70% of its rated power even after 24 Months. This has been shown by experiments done.
Even an AGM battery can be float-charged to keep it charged to capacity. During the reconditioning of an AGM battery, a floating charge is also applied.
Conclusion
In effort to ensure that the battery maintains its full charge and does not suffer sulfation, applying a floating charge to a battery in storage is very important.
Any loss due to cell decay shall be compensated for. The floating charger which compensates for temperature as well is required as a tool for maintenance.