SLA battery performance

[mickelsen]

sla discharge curve

I have a circuit that will be powered by a 12v SLA battery. One of the chips in the circuit requires a regulated 12v supply. I know that the battery puts out about 14v when fully charged. I intend to use a LDO regulator for the 12v which will continue to operate as long as the input voltage is above 12.5v. What I would like to know is: how long can I reasonably expect the battery to continue to put out a voltage above 12.5v? What does the discharge curve of voltage over time look like for a SLA battery? Would it be smarter to use some kind of DC-to-DC converter to supply the 12v? If so, are there any inexpensive ones available?
Thanks in advance.

 

[Jack// ani]

sla battery discharge curve

yes...a dc-dc convertor will make a smarter choice.

discharge curve of SLA is almost flat upto to 80% (of its capacity)....so it all depends how large current you drain through it, if its too small then your battery may last many days, before the voltage drops below 12.5v

good luck

 

[mickelsen]

sla battery charge curve voltage

The board I'm designing is a motor controller and the chip that requires 12v is an HIP4081A H-bridge driver. Its data sheet says that is draws a maximum of 15.5ma. The rest of the control logic runs off of 5v. I found a dc-dc converter chip, the MAX662A, which takes 5v and produces 12v at 30ma. Can anyone tell me if they think that this chip is adequate to power the HIP4081A reliably?
Thanks again.

 

[PaulHolland]

sla battery discharge

Hi, Do you need to switch fast ??.. What kind of motor and what do you want to do ??.. Do not see a need to have a fixed 12.5V on this chip. !.

Paul.

 

[xxargs]

12v battery drain curve

yes...a dc-dc convertor will make a smarter choice.

discharge curve of SLA is almost flat upto to 80% (of its capacity)....so it all depends how large current you drain through it, if its too small then your battery may last many days, before the voltage drops below 12.5v

good luck

SLA -batterys in unloaded state (24 h) approx 13.0 Volt in full charge state, 12.6 Volt in half state charged and around 12.2 Volt in emty state.

even small discharge as 10 mA can decrace above measured value 10 -100 mV.

SLA-batterys must be charged > 12.6 Volt charge state as above before long time storing (> 48 h) or batterys will going slowing sulphate.

for make steady 12.5 Volt powering with battery, you must use DC-DC converter.

 

[PaulHolland]

12v or 7a sla battery data

SLA: Full changed cells are 2.3 V, fully discarged cells are 1.8 V around 2 - 2.1 Volts are normal operation range this is about 80% of the charge. Your 12V SLA has 6 cells so MAX = 6 * 2.3 = 13.8 Volts MIN = 6 * 1.8 = 10.5 Volts. Normal 12 - 12.6 Volts.

Paul.

 

[mickelsen]

hip4081a

The motor I'm using is an automobile radiator fan motor and I'm using it as the drive motor for a model submarine. All the examples that I've seen using the HIP4081A use a separate 12v supply for the chip, and I, likewise, don't want the chip running off the same 12v supply that is powering the motor directly since I think that the motor may cause spikes and noise on the power lines. Do you think that a MAX662A would be sufficient to drive the HIP4081A? That would isolate it from the noisy voltage that is running the motor.
Is my thinking flawed in some way? I'm certainly no expert in this type of design.
Thanks.

 

[PaulHolland]

sla battery flat

Hi, Why using an difficult component as it can be so simple, the following circuit can drive the motor left, right and stop !. all you need I would say and no difficult components. Its being used in a real product to control a motor !!.. The bridge can run from a different source as the motor voltage. There is only ONE WARNING. never run both controls high !!..

Paul.

 

[mickelsen]

vrla battery discharge curve

I want to vary the speed of the motor in both forward and reverse. I plan to control the speed with a PWM signal from a PIC microcontroller. That is the reason for using the HIP4081A. It is to simplify the interface between the PIC and the H-bridge. That is what the HIP4081A is designed for, and it is fairly easy to use provided I can get the supply voltage right.

 

[polymath]

top rated sla batteries

Hi mickelsen

Some links to manuals for VRLA Batteries.
They may help in the selection of a suitable battery. They have charge and discharge curves.
They show the output voltage and cell capacity is significantly dependant upon discharge current and temperature:

**broken link removed**
http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_VRLA_Overview.pdf
http://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_VRLA_ChargingMethods.pdf
**broken link removed**

hope these help ... Polymath