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发表于 2009-9-15 08:56:47
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Battery Temperature Charge Voltage per cell Charge Voltage for a 12 Volt battery Gassing Voltage per cell Gassing Voltage for a 12V battery
-20 °C * 2.67 to 2.76 16.02 to 16.56 2.97 17.82
-10 °C * 2.61 to 2.70 15.66 to 16.2 2.65 15.9
0 ° C * 2.55 to 2.65 15.3 to 15.9 2.54 15.24
10 °C 2.49 to 2.59 14.94 to 15.54 2.47 14.82
20 °C 2.43 to 2.53 14.58 to 15.18 2.415 14.49
25 °C 2.40 to 2.50 14.40 to 15.00 2.39 14.34
30 °C 2.37 to 2.47 14.22 to 14.82 2.365 14.19
40 °C 2.31 to 2.41 13.86 to 14.46 2.33 13.98
50 °C 2.25 to 2.35 13.5 to 14.10 2.30 13.8
Voltage table for standby use charging:
Battery Temperature Charge Voltage per cell Charge Volage for 12V Battery Gassing voltage
-30 °C * 2.7 16.2
-20 °C * 2.34 to 2.38 14.04 to 14.28 2.97
-10 °C * 2.32 to 2.37 13.92 to 14.22 2.65
0 °C 2.30 to 2.35 13.8 to 14.1 2.54
10 °C 2.28 to 2.33 13.68 to 13.98 2.47
20 °C 2.26 to 2.31 13.56 to 13.86 2.415
25 °C 2.25 to 2.30 13.5 to 13.8 2.39
30 °C 2.24 to 2.29 13.44 to 13.74 2.365
40 °C 2.22 to 2.27 13.32 to 13.62 2.33
50 °C 2.20 to 2.25 13.2 to 13.5 2.30
* Note that a fully discharged battery freezes solid at about 0°C, a fully
charged battery freezes about -40°C.
Overnight Charging
Unregulated Transformer-Based Chargers
These are the absolute cheapest chargers around. They consist of a wall mount transformer and a diode. The transformer is designed to deliver 13 to 14 volts over a reasonable current range. The biggest problem with this approach is that when the current tapers off, the voltage raises to 15, 16, 17, even 18 volts. At these high voltages electrolysis of the water in the battery starts in. These must not be left to trickle or float charge a battery, they must be disconnected when the battery is fully charged. This is not a problem with flooded batteries as long as you check the water periodically and refresh it. Sealed lead acid batteries can recycle the generated gasses as long as they are being overcharged at less than C/3. However, leaving the battery to be overcharged even at C/10 will corrode the plates if left on for weeks at a time.
The transformer is so designed as to limit the current while the battery is in absorption mode. As the battery voltage rises the current decreases to top off the battery. Because the transformer is used to control the current and voltage these chargers are typically heavy and get hot.
Note to our OEM customers: even though we support our OEM customers with unregulated transformer chargers to help them stay cost competitive, many of our new customers come to PowerStream because someone else sold them an unregulated charger without explaining the tradeoffs, and the end-user complaints forced them to look for a better charger. Most of the time the complaints come from commercial customers rather than consumer customers. We prefer to offer the inexpensive regulated chargers that use switchmode power conversion.
Taper chargers
Another cheap 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, 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 simple 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 suprisingly 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.
Constant current chargers
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. This charger will switch to a constant-current mode when desulfating is necessary, and to a multistage precision charger at other times.
Constant Voltage Chargers (Taper plus current limit)
A circuit that is set for the maximum allowable charge voltage, but has a current limit to control the initial absorption current can produce a very nice charger. This type of charger can both charge at a reasonable rate and maintain the battery at full charge without damage. Not all constant voltage chargers are made equal, however, because the maximum voltage is a function of temperature. A temperature compensated charger is a little more expensive, and should be used where the temperature varies significantly from room temperature. The large chargers at An example of a switching type taper charger is here are constant voltage chargers.
Fast Chargers
Fast chargers are higher power units, designed to charge in less than 4 hours. These chargers require active charge termination and often have advanced features such as battery test, bad battery recovery, and automatic maintanence.
Typical Charging curves for PowerStream quick chargers.
This charger starts at 8 amps and maintains a near-constant current until nearly full.
This is the fundamental algorithm of the PowerStream quick chargers for lead acid batteries. The curve shown is for a 24 volt (12 cell) battery charger, but the curve is similar at other voltages. The timing depends on the size of the battery you are using. At point #1 the battery is tested. If the battery is bad a rejuvenation algorithm is started. If the battery is good the charger goes into constant current mode until the voltage reaches 2.3 volts/cell. Then at point #2 the charger goes into constant voltage mode until the current drops to about 10% of the initial value, indicating a nominally full charge. Then at point #3 the charger goes into float charging mode at about 2.3 volts /cell to complete the fill and to maintain the battery. At this voltage the battery is safe from overcharge.
Examples of fast chargers are shown at http://www.powerstream.com/scooter.htm
The exact details of current and time depend on the charger size and the battery size.
Maintenance, keeper or 'tender' Chargers
Any multistage charger that has a "float" mode can be used to maintain batteries during the 'off-season.' Particularly useful are the small, inexpensive switchmode chargers that consume very little excess power, or the small low-power chargers that can automatically desulfate lead acid batteries.
Custom design and manufacture of state-of-the-art battery chargers, UPS, and power supplies for OEMs in a hurry! |
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