[SOLVED] Why 12Volt 75Ah Lead Accumulator Battery Giving 25.6 ac voltage

[Pushpkant]

I have a 12 volt lead acid battery giving 12.5 dc volt measured by multimeter, but when I measure the ac voltage it is showing 25.6 volt.

Is the battery is damaged or it's normal behavior of lead acid battery?

Is this the reason why my DC-DC converter doesn't give constant output voltage of 10V?

 

[Audioguru]

A battery gives a DC voltage, not an AC voltage. Maybe your multimeter is broken.
A 12V lead-acid battery that measures 12.5V with no load is almost dead. It should measure 13.2V to 13.8V when fully charged.
We know nothing about your DC-DC converter since you did not post its schematic and parts list here.

 

[KlausST]

Hi,

it makes no sense to measure a dc battery voltage with an AC range.
The result is meaningless. (as long as it is no "true RMS" voltmeter; this should show 12.5V in DC as well as in AC range)

Klaus

 

[Pushpkant]

Thanks AudioGuru and Klaus....

I have an SMPS of 24Volts/2Amp my multimeter gives zero reading on the AC range on it, while it is giving 25.8V when I connected this on the battery.

By your posts it is clear that a battery normally doesn't give any AC rms voltage, but I can't figure out why it is giving the result like this?

One more thing in the ac range measurement when the polarity is reversed it gives zero on the battery, But when I connect to the SMPS it is giving zero on reverse as well as on forward polarity.

I am using an M830BZ MASTECH multimeter.

 

[chuckey]

An analogue multimeter does read DC on its AC ranges, it just has a bridge rectifier in the way and the calibrations are changed to change a mean to a RMS indication.
Frank

 

[KlausST]

Hi,

Maybe your DVM uses halfbridge rectifying, then it shows different voltage even in AC when wires are interchanged.

Klaus

 

[Pushpkant]

Hi all,

Now it is clear from theory of lead acid battery that it can't give any ac voltage at all, in any circumstances when open circuit. Hence it is clear that my multimeter has to do with this problem.

So, this topic is useless to talk, perhaps I must buy a new multimeter with true rms value.

But still I don't get the voltage behavior of the battery.
can anyone tell me about the charging and discharging, voltage and current behavior of the battery respectively.

I have been tried to make a dc-dc converter with battery charging facility but the output is not constant as well as the charging is also very unpredictable in nature.

Thanks

 

[ads-ee]

Unless you really know what you are doing. I would be very very careful with building your own lead acid battery charger. If you do it wrong you can end up with a battery that can generate Hydrogen and end up in a potentially ugly accident.

https://www.youtube.com/watch?v=d_TnsHu2u4c

Imagine having your face over that battery...

 

[colin55]

"A 12V lead-acid battery that measures 12.5V with no load is almost dead."

This is totally FALSE. A 12v lead acid battery should read 12.6v after it has been charged.

During the charging process it will generate a "floating charge" or "floating voltage" up to 15v due to the resistance of the bubbles of gas and also the type of material used in the plates. This voltage is the reason why they call some batteries "maintenance free" or "sealed" because they do not produce gas bubbles until a high voltage is developed across each cell. If you keep the charging voltage below this voltage, the battery will not produce gas and can be sealed.
You cannot measure the battery voltage immediately after charging due to the "floating voltage" it will show on a voltmeter. You need to wait 10 minutes and then apply a load for a short time to settle the activity within the cells.

 

[Pushpkant]

thanks ads-ee, I will be care while charging the battery.