Charging a 12V 4.5aH lead acid battery

[player80]

Hi,

can anyone give me a hint how to charge a lead acid battery?

The printing on the Battery says:
NP 4.5-12 (12V/4.5Ah/20HR)
Cycle use 14.4-15.5
Standby Use: 13.5-13.8
Initial Current: less than 1.35A

I saw following article.

https://www.edaboard.com/threads/lead-acid-battery-charging-current-chart.230240/#post-982020

this says:
First phase is constant current, typically 15% of AH rating.

I picked around 200mA until it reached 12.5V (measured with the multimeter)
Now I have set it to 600mA

The voltage increases slowly but is still below 13V and it draws 0.6C so at that stage I have to wait until the current drawn decreases?

Cycle use 14.4-15.5 does that mean I can charge with 15.5V until it reaches around that?
Standby Use can anyone elaborate what exactly that means?

I have seen quite a few videos about it and read some articles but it all ends up to be a bit confusing about it. Of course I couldn't find any datasheet either...

 

[Vbase]

Cycle use is when you charge and use at the same time, like in a car. With fast charge the max voltage is 14.4-15.5V depending on temperature, 15.5V at -20 centigrade.
Standby use is maintain the battery charged with trickle current.
The easy way is to charge with 10-20% of Ah and to change to trickle current when voltage reach 14.2V.

 

[KlausST]

Hi,

there are many descriptions, totorials, even videos in the internet.
Battery manufacturers as well as semiconductor manufacturers provide application notes.

or internet sites like www.batteryuniversity.com give good informations.

or 200 hits on "lead battery charging" here in this forum.

Klaus

 

[player80]

Thank you, the information at battery university is exactly what I'm looking for.

 

[cupoftea]

The way to charge a lead acid battery (standby charging) is as follows.

1...read battery voltage...if it is below 10V, then its dead......so you either send it to recyclers, or you try to do pulse battery reformation...which doesnt garantee bringing it back to life.

1A..if batt is 10.1V or more, then charge it with a known low current (i think about 0.2C (<<)), until it gets up to 12V...then...

2....If battery voltage is 12v or more, then you embark on constant current charging.......you can usually charge lead acid at least up to 1C (**)...or 4.5A in your case. But of course it depends on the ambient temperature......because its best if you can stop the battery temperature from "running away" too high during charge.

3...When the battery voltage gets up to some 13.7V........(^^), then you switch over to constant voltage charging....that is, you simply charge it with whatever current keeps its terminal voltage at 13.7V.......

...so you will find that as you keep charging it now, the charge current will "tail off", down to like a "trickle current level".

** Check the datasheet of the cell , or a similar cell, to get the exact number for your cell
^^ Check the datasheet of the cell , or a similar cell, to get the exact number for your cell
<< Check the datasheet of the cell , or a similar cell, to get the exact number for your cell

Always remember , that with any battery , you can always discharge it at a higher rate than you can charge it.

There will be an overvoltage level, above which you shoudl stop charging it.
There will also be an overtemperature level, above which you shoudl stop charging it.


Basically, lead acid charging is briefly described as.......
1A...check its dead or not
1B...if 10-12V, then 0.2C till gets to 12V
1...constant current phase (eg 1C)
2....constant voltage
3...trickle (which i guess is a very low constant current thing)

I believe lead acids can take quite some abuse, but you shoudl always be wary of temperature build up when you overcharge resulting in high temperature, and pressure, and booooom!

We hear so many stories of how you must charge below this rate or that rate, or else disaster...and then we go into the pits at the Formula E racing tournament...and we see them heckishly overcharging the (lithium) batterys until they often are seen smoking like mad........and no, they are not following the datasheet.....they want to win the race, so they are overcharging like heck

 

[player80]

Hi,

this is exactly the kind of information that makes it confusing! And yes there are so many posts about that with "rules of thumb" but it seems like some thumbs are bigger than other ones.

First of all I charged the battery with 0.2C up to ~12.5V
Afterwards I followed up with 0.6C

The battery label says Cycle use 14.4-15.5
doesn't that mean it should be charged to somewhat in that area?

The battery is now in stage 2 charging at 14.5V (the current is getting less).
up to that voltage it should run in constant current mode, once the current drawn reaches around 3% of the charge the battery should be charged in stage 3
" full charge is reached when the current decreases to 3–5 percent of the Ah rating"

BU-403: Charging Lead Acid

BU meta description needed...

batteryuniversity.com

The charge drawn before I disconnected the first battery was 0.25C (for some time), Battery number two is slowing down at 0.345C now (both at 14.5V).


So I don't see that it should be 13.7 -- the printing moreover says 13.7 is within the standby range not within the use range.
The proposed 13.7 would cause a premature depletion of the battery no?

Certainly I'd like to see the datasheet but the battery from the store seems like a reseller
labelled unit (... technology ltd) which has no website and no datasheet on the internet.

 

[cupoftea]

I would say make 15.5V the abs max, and never go above that.

14.4-15.5V is , as you say , for cycle use.....ie when its also supplyign the load......the problem here is, when if the load is sometimes on sometimes off.....what do you do then......well...this is where battery temperature monitoring comes in...glue a thermocoupel or NTC to the battery, and monitor the temperature as you charge........stop charging above a certain temperature.

So this could be you algorithm......charge it with whatever current you want, up to whatever voltage you want....but stay below 15.5V and below say 50degC battery case temperature.......but check that temperature, in case it explodes....or just put it in a solid but ventilated case when you charge it

 

[player80]

Well the way I do it I install it into a kid car when full and take it out when empty, but I think about adding an LED because last time the battery voltage went below 6V when applying some load (without load it recovered to 11.90V)
I think even though this is a trivial application it's a good topic for me to learn more about batteries.

 

[BradtheRad]

battery voltage went below 6V when applying some load (without load it recovered to 11.90V)

It's normal for lead-acid battery voltage to 'bounce back' after you remove load. The drop in voltage is not necessarily harmful for short periods although you'd get greater power and speed if you were to upgrade to a stronger battery.

Here's a simple battery monitor adjusted so that 10V is the transition point between the green or red led's, as this screenshot portrays.

 

[tonigau]

The proposed 13.7 would cause a premature depletion of the battery no?

The CV setpoint determines the time it takes to recharge in this stage. 13.5V = long time, 14.5V = less time.
If you have your charger max volt (CV) set to 13.7V, it will still full charge but will take much longer.
This is why 13.5V~13.8V is chosen for the standby use so the battery is not adversely affected (as much) by permanent applied charge voltage.
CV charging a gel battery at 14.8V will likely vent gas before it can recombine to h2o & may degrade positive plates.

Standby use is where the battery always has applied voltage like fire alarm panel, security alarm or UPS.
I have replaced hundreds of 12v batteries in these applications, the constant applied 13.8V eventually kills the battery.
In contrast, there are smart standby supplies that charge the battery periodically then let it rest most of the time, these have very long battery life.

Charging at ~14.5V or more is faster charging, but will pay the price of less battery life especially GEL VRLA type.
Calcium type is the exception, they require higher charge volts.

So its all about replacing the Amp hours that were removed & a bit more for charge efficiency.
--> Faster charging will reduce life if it is significant relative to battery size.

I charge as follows: (for the 12V 4.5Ah VRLA gel battery)
Using the bench supply, set Current to 500mA, set Volt to 14.1V, connect battery & wait till the current drops to a low value**. That's it !
If you have only shallow discharged then this time will be short (don't leave too long at 14.1V)

Watching the supply meters can see Volt display increasing to 14.1V, then see current reducing.
To verify your charging you can record Amp-Hours, this is easy for CV mode as the current is constant. [Amps x Time], for CV mode the current is reducing so not so easy unless you log current & RMS the data.
** < 100mA, I often reset the CV to 13.5V for a while after, helps to balance cells.
PS: --> Make a special cable for charging with a fuse & put a big reverse diode on the power supply. (yes I learned the hard way)

I use small 12V gel batteries around my workshop that spend most time at rest (some are over 14 yrs old & still usable).


Typical Lead Battery Charging profile

 

[player80]

Thanks for the hint with the reverse diode, I'll add that. I'm also using a benchtop powersupply for charging.