What should the recharge rate be when charging a battery

If you compare watts in to watts out you have to take into account that the battery charging voltage is higher than the battery discharging voltage. This varies somewhat depending on the temperature, speed of charge, and battery type. Some lead acid batteries are used in a standby condition in which they are rarely cycled, but kept constantly on charge.

These batteries can be very long lived if they are charged at a float voltage of 2. This low voltage is to prevent the battery from losing water during long float charging. Those batteries that are used in deep discharge cycling mode can be charged up to 2. Another inexpensive way to charge a sealed lead acid battery battery is called a taper charge. Either constant voltage or constant current is applied to the battery through a combination of transformer, diode, and resistance.

The unregulated chargers mentioned above are taper chargers. A better, and not very expensive, alternative is a regulated taper charger. These don't let the voltage climb higher than the trickle charge voltage, so they can be also be used to maintain a battery.

They won't damage the battery if left on charge too long even when left on the battery permanently , and they don't change their charging characteristics if the line voltage should change. Regulated taper chargers are very useful when you need a 12V or 24V battery backup. A taper charger in parallel with the battery, in parallel with the load makes an effective battery back-up. You should take care to ensure that the taper charger is designed to give continuous current equal to the load plus some left over for battery charging.

It is also important that the current limit of the taper charger is the voltage-cut-back method, and not the hiccough method or other PWM methods. An example of suitable switching type regulated taper chargers that can be used in battery back up applications is here.

There are two ways to make a regulated charger. The first is to use a transformer and a linear voltage regulation circuit. This has the disadvantages of weight and heat, but it is still inexpensive.

The second uses a modern switching power supply in a wall mount or desk mount package. These low-power high-frequency switchers are surprisingly cheap, efficient, and small. They are rapidly taking over the overnight charging requirement in consumer equipment. An example of a switching-type taper charger is here. A more sophisticated and not much more expensive charger uses an electric circuit to control the charging current.

This method is useful for recovering batteries that have suffered from extensive storage without charging, but is capable of overcharging a battery if there is not some voltage limiting function, usually from the transformer.

For this reason these chargers are limited to slow charging. To accomplish this, a constant voltage method of charging called standby or float charging is used. The recommended constant float voltage is 2. Maintaining this float voltage will allow the battery to define its own current level and remain fully charged without having to disconnect the charger from the battery. The trickle current for a fully charged battery floating at the recommended charge voltage will typically hover around the 0.

The float charger is basically a constant voltage power supply. As with cycle chargers, care must be taken not to exceed the initial charge current of 0. This method uses two constant voltage devices. In the initial charge phase the high voltage setting is used.

When charging is nearly complete and the charge voltage has risen to a specified value with the charge current decreased , the charger switches the voltage to the lower setting. This method allows rapid charging in cycle or float service without the possibility of overcharging, even after extended charging periods.

Lead acid batteries are strings of 2 volt cells connected in series, commonly 2, 3, 4 or 6 cells per battery. Strings of lead acid batteries, up to 48 volts and higher, may be charged in series safely and efficiently.

However, as the number of batteries in series increases, so does the possibility of slight differences in capacity. These differences can result from age, storage history, temperature variations or abuse. Fully charged batteries should never be mixed with discharged batteries when charging batteries in series. The discharged batteries should be charged before connection. When a single constant voltage charger is connected across an entire high voltage string, the same current flows through all cells in the string.

Depending on the characteristics of the individual batteries, some may overcharge while others remain in a slightly undercharged condition. To minimize the effects of individual battery differences, use batteries of the same age, manufacturer, amp hour, and history and, if possible, charge in strings of no greater than 24 or 48 volts.

Lead acid batteries may be used in parallel with one or more batteries of equal voltage. When connecting batteries in parallel , the current from a charger will tend to divide almost equally between the batteries.

No special matching of batteries is required. If the batteries of unequal capacity are connected in parallel, the current will tend to divide between the batteries in the ratio of capacities actually, internal resistances. When charging batteries in parallel, where different ratios of charge are to be expected, it is best to make provisions to assure that the currents will not vary too much between batteries. Power Sonic sealed lead acid batteries perform well both at low and high temperatures.

The effect of temperature on charge voltage is less critical in float applications than in cyclic use, where relatively high charge currents are applied for the purpose of short recharge times.

The charging rate, in Amps, is given in the amount of charge added the battery per unit time i. Note that the battery is only "theoretically" discharged to its maximum level as most practical batteries cannot be fully discharged without either damaging the battery or reducing its lifetime.

Each battery type has a particular set of restraints and conditions related to its charging and discharging regime, and many types of batteries require specific charging regimes or charge controllers. For example, nickel cadmium batteries should be nearly completely discharged before charging, while lead acid batteries should never be fully discharged. Furthermore, the voltage and current during the charge cycle will be different for each type of battery.

Typically, a battery charger or charge controller designed for one type of battery cannot be used with another type. Skip to main content. Leave this field blank. Search form Search. It depends on the car. You can check on the fuse for the car lighter to find the upper end for your particular vehicle. There is an unofficial standard that the power point socket should supply at least 8 amps, but many cars supply 25 to 30 amps to the socket. This will allow watts to be safely drawn.

Q: How much does a car battery weigh? How many amp-hours does a car battery contain? A: A car battery's weight depends on the size of the battery, but is typically between 30 and 50 lbs, with most running around 41 lbs 14 kg to 22 kg. The chart above lists maximum discharge rates at cold temperatures.

This would be a power of around 10, watts. Q: What about charging a sealed car battery? A: Sealed car batteries are the same chemistry as the flooded car batteries, but their construction makes them less prone to water loss because any gasses can be recombined before venting. So a sealed car battery can be charged with the same chargers as flooded batteries, except for the ancient chargers that have poor voltage control.

Q: What is the car battery charging current? A: A car battery can be charged an any rate from zero to hundreds of amps.

They are designed to discharge at high current, so they can also be charged at high current. Modern car battery chargers have high voltage precision, which makes them safe to use at just about any current that you can afford to buy.

If you are sizing a charger for float charging, anything above mA should work fine. Q: Should I disconnect a car battery before charging? A: It isn't necessary to disconnect a battery before charging. Any drain while the car is turned off will be minimal. The charger's voltage won't be high enough to do any damage to the car. It is important not to remove the car's cable from the battery terminal while the alternator is going, it could cause a voltage spike called a "load dump" surge.

Q: How long does it take to charge a 12V car battery from flat? A: Charging time depends on the battery and the charger. For a battery being charged by the car's alternator it can take an hour of driving to get it fully charged. Car batteries range from 40AH to AH, and alternators range from 45 amps to amps.

If you are using a battery charger, a 10 amp charger will take 4 to 11 hours to fully charge the battery, a 2 amp charger will take days. Of course you don't have to get the battery to full charge to get it to start the car. Q: Can I use a car battery charger as a power supply? A: Older car battery chargers can be used as power supplies, but the newer ones have a safety feature.