Power Supply as Battery Charger?

It depends on the power supply.
If it's a comercial supply just use it in current mode.
If you are building the supply it should be considered to be providing current not voltage.
The battery will pull any supply down to about 12.xxx volts.
You should aim to control the current to a value which the transformer can provide (and is suitable for the battery) until the battery voltage reaches say 12.3v (the exact figure should be obtained from the batter manufacturers website) at that point you should switch to a trickle charge.
There are plenty of basic voltage regulator chips which will work in current sense mode.

As an example I have a charger for my golf trolley gel battery, it gives 3A until the voltage reaches the required level and then switchws to 0.5A which is a safe trickle charge. It just needs 1 regulator and comparator (or op amp) and a few other components.

Del

Battery chargers start at less than £20GBP.

http://www.halfords.com/ (usual disclaimer).

You say it is a 24 Vdc battery charger but are using it to charge your 12 vDC automotive battery. Does it have adjustable setting to switch it to 12 vDC or have you assembled something to achieve this?

Automobile power systems are fairly crude as far as voltage regulations goes. Automotive voltages typically vary from 10vDC ~ 16 vDC and in cold weather and or poor or low charged cold battery will drop down to even 8 vDC when starting, which is hard on the starter as it pulls significantly more current (if it is available) to start the vehicle and thus overloads and can burn out your starter. FYI: automotive starters have a VERY low duty cycle due to the very high current loads that they utilize. One is only supposed to crank the starter for 15 seconds out of every 10 minutes! Operating voltages can go as high as 18vDC in automobiles. This applies to older battery chargers as well. If the charger is at 14+ volts with no load on it then as the other posting indicates, when you put it onto the battery it is pulling the voltage down to the ~ 12 vDC because of the load on it and the chargers lack of modern power regulation. Most of the little household power adapters that power common low voltage electronics so that the manufacturer does not have to go through the hassle and added time and expense of getting it certified for high voltage safety. If you check these crude power supplies they do the same thing: the voltage is higher with no load on it and will (hopefully) pull down to the approximate required voltage. Most such low power electronic devices have voltage regulators to handle this.

As your charger is just fine at 14 volts as the battery starts to get fully charged it may rise up again closer to the 14 vDC output though it will unlikely go this high while attached to the battery. As this is what it is at under no load in is unlikely to damage either the charger nor the battery itself. As noted by the other respondent, what is of concern is the charger continuing to over charge it even when the battery has basically reached its fully charged capacity for the condition of the battery. Thus his instructions to reduce the current as overcharging it will reduce its life. If you are around when the battery is being charged and have a volt meter, check the voltage occasionally with the charger attached and charging. If the voltage is starting to rise then the battery is likely (close) to being charged. Before wet cell acid automotive batteries were sealed and one had to add water to them sometimes, one could remove the caps and if you can see hydrogen bubbles rising in each individual cell it is as charged as it is going to get. If yours has removable caps it's a good procedure to remove them while charging anyway to allow the hydrogen gas to vent more readily and reduce the danger. Sometimes one or more of the individual cells (there are usually 6 in a 12 vDC automotive battery) doesn't bubble or nowhere near as much as the others do. These cells are sulphated and have greatly reduced capacity.

yes it is adjustable and made a setting to 14V.

Ordinarily, if your power supply is robust, then your settings should work well, for the main (bulk) part of the charge. In a programmed charger, typically, the constant voltage phase of a charge, (after the constant current part) will be at 14.4 V, until the amperage drops to a low value (such as below 1 amp) (Greater than 14.4 volts at any point will cause gassing of the electrolyte, and will eventually boil the battery dry.) Then, with the battery fully charged, a maintenance charge at 13.8 V can be held indefinitely.

It is normal that your voltage will drop to 12 volts initially, because (assuming the battery is in good condition) your current will then be 5 as limited by the power supply. As the charge progresses, the voltage will slowly climb to your power supply voltage setting, and current will fall.

After the battery has been charged and taken off the charger its voltage will quickly drop to 13V (or so) and then more slowly to about 12.6 or 12.7, its normal no-load operating voltage.

You might not want to use a power supply frequently for this purpose, because you are asking a relatively expensive piece of equipment to do a job that can be done by a cheaper charger (and perhaps slightly better by a modern cheap charger, most of which are now controlled to charge at the optimum voltage and currents, in stages.) On the other hand, an older cheap charger may treat your battery poorly, quite possibly getting it up over 14.4 V.... So, for occasional use, your power supply will do fine.

If the battery voltage is low when you connect the charger, of course the charge voltage will drop, this is due to the current draw. As the battery reaches full charge the current will drop and the voltage will rise, they call this trickelle charging. I would not advise to charge the battery at 24 v but if you can get 14v out of the 24v supply it may be ok, but then again if it develops a fault it may fry your battery, best to stick to tried and proven methods for charging batteries to ensure that they have a good and long life.

Cheers

Joe

Now iam very concerned, iam deviating from the actual work and not able to reach to a conclusion. I think the better option would be to buy a battery charger.

Cheers

Satya

Everything is just fine and working ok a long as the power supply isn't getting to hot, which is doubtful. Just feel it with your hand after it has been charging the battery for a little while: 15 ~ 30 minutes. Don't let it overcharge. If you haven't figured out any other way to determine if the battery is charged from these postings, then check the voltage and once it rises and then levels off it is as charged as it is going to get. If your battery is in decent condition it will likely be fully charged in ½ ~ 1 day.

What you hand should do the job just fine, but there are much better, more effective and sophisticated battery chargers on the market now a days to be sure.

Depending on your finances:

If low, use what you have a watch out for and check the two things I posted above. It is very unlikely that you will have any problems with what you have now and it will do the job just fine for you. The voltage drop when you hook it up to charge it is normal and nothing to worry about. It won't damage the battery if you leave it on a little to long, but you wouldn't want to just leave it on for a week or more.

You say it is a 24 Vdc battery charger but are using it to charge your 12 vDC automotive battery. Does it have adjustable setting to switch it to 12 vDC or have you assembled something to achieve this?

You seem to have misread what he wrote. He has a power supply, capable of supplying 24 volts. It is not an ordinary battery charger. Like most commercial power supplies, his has a voltage control and a current control. That's why he wrote that he set the voltage at 14 and the current at 5. With those settings, one would expect the charge to start at 5 amps and that the initial voltage would be only somewhat higher than the dead battery voltage, just as he has observed. The current limit on the power supply keeps the current from exceeding the set value. That means that the voltage must initially be low. After a long enough charge, the voltage limit will come into play, and amperage will have dropped back.

I think no problem. Once the battery gets some charge the voltage will slowly raise. Your power supply behaving like CC in the beginning of charging once current goes bellow 5Amps the voltage will buildup.

Dear Friend,

Well the voltage has dropped to 12.1 volts means the 24 v D C supply ,you have , does not have sufficient VA /watt ratings.

While doing this experiment pl put an ammeter in the charging circuit to know the effect of your connections on batteris.

As the time passes you will see voltage of 12.1 will increase.

Pl inform.

Well I did not understand when u said the power supply did not have sufficient VA/Watt ratings. I found that as the battery is charging the battery voltage is increasing also the power supply voltage is increasing, the current shown by the power supply is fixed at 5 amps and is not changing (the maximum current limit i can put is 10amps but as a precaution i have limited it to 5amps).

As a conclusion both the battery voltage and the power supply voltages are increasing simultaneously.

Please let me know if i explained clearly.

Regards,

Satya

Hi,

I don't TOTALY agree with what Saraswat Bhaurao`s posting says in these circumstances, though what he said is accurate and valid.

Your setup is working just fine and there is nothing to worry about with either the battery or the charger so long as the battery doesn't try to draw more current that the power supply can supply, which is highly likely when the battery is significantly discharged. But this is `normal` conditions for older batter chargers.

If the power supply is not getting very hot then there is no problem with it.

Just watch out for your battery being overcharged. Info has been posted here for ways to determine that. If your battery won`t take a charge then it is most likely that the plates are to sulphated and won`t take a charge anymore which is what 90% of such batteries `die from`.

`Clean Flow` aftermarket automotive products used to sell a small bottle of blue liquid that dissolved the suplhate off of the plates. Sometimes it worked and the battery would last for years more Other times it didn`t. They stopped selling it a couple of years after these automotive lead acid batteries no longer had removable caps to access each cell. It is an available chemical though but I`m sorry I don`t remember it`s name.

The other 2 common reasons for such batteries to die are that the sulphate sediment builds up at the bottom of the battery until it comes into contact with and shorts out the plates. Batteries that have more `reserve cranking current - power` have plates that are larger in size and don`t have as much space between the bottom of the battery and the plates and thus don`t have as much room for sulphate sediment.

I have successfully dumped and flushed a battery out several times using water. Preferably after dissolving the sulphate on the plates, and then renew the acid electrolyte. Though the industry cautioned that in most cases the old thinned plates wouldn`t survived the new concentrated electrolyte. I used a hygrometer and thinned it with water to the appropriate strenght before I put the new electrolyte into the battery and got good results most of the time.

Again with virtually all such batteries being permanently sealed now, the electrolyte which all automotive garages used to carry is no longer available through them.

The 3rd most common reason for a battery to die is because the plates have become thinned to the point that they no longer held there structural integrity and would warp and make contact with the other plates and short the battery out. This can sometimes happen with an older batter in a minor accident though it is not visually apparent as the battery case has no external damage or holes in it.

When jumping starting a vehicle with a dead battery, if not done properly there are 2 SIGNIFICANT problems and DANGERS!

1 - The electronics in modern vehicles can be destroyed including the main `black box` computer that can be as much as $5,000!

2 -MANY people have been blinded or killed!.

If anyone is unsure about this, please ask and I will post it again.

Happy, safe motoring to one and all.

Thanks for that info.

There are battery speicalty shops that still have the chemical. They woldn`t sell me any but offered to renew my battery for $50 - $75, which peeved me.

Well the voltage has dropped to 12.1 volts means the 24 v D C supply ,you have , does not have sufficient VA /watt ratings.

That is unlikely, if his power supply is of reasonably good quality. If he sets the current to 5A, the voltage output cannot be over roughly 12 V at start of charge (assuming the battery is well-discharged) because getting the amperage above 5A would require higher voltage... so the current limiting function of the power supply sets the limit early in the charge. As the battery voltage eventually reaches 14 V, (after a few hours on charge) then the voltage regulation will limit the charge (and the charge will have transitioned from constant current to constant voltage).

But 5 A is a reasonable charge rate for a 60 hr battery, and doesn't represent a limitation of the power supply, but instead its controlled (settable) current limiting. In other words, this could be a 24V x 50 A supply (1200 VA) and it would still produce a battery voltage of 12.1 early in the charge, if its output is set at 5A. To get a pretty dead 60 AH battery to lets say 13.8V early in the charge could require 20 or 30 amps. Late in the charge, the current will be much lower.

The main problem with a constant amperage power supply for charging a battery is that you can over charge if you do not monitor the state of charge. The battery could overheat, and you could have an explosion, if you are not careful...

Dear, its ok, if possible adjust voltage 14.5 volts and current at 4 ampair. because in this case battery works like a load and drops the voltage, connect it and wait for some time. power supply will charge the battery up to app. 13 volts and then disconnect the charger. because i think your supply have no cut off circuit.

Regards.

Some charactristics /Specs of your Supply:

1.) Power; Current Ratings

2.) CVCC / CVCL /CVCFB

3.) Controls: Voltage; Current

4.) Protections see 2. above + thermal ...

Normally any PowerSupply can be used as a Battery Charger but some points are to be considered thouthfully before using it as a charger.

more to say after your reply.

Depending upon the type (and size!) of the battery, you may want to watch out for the following:-

1) Battery voltage (when charging) above 13.2 volts) battery will gas - this is to be avoided...a short charge to 14 volts is ok to get battery charged above 70%capacity is OK, but not for long periods.

2) Assuming the battery is a standard type for cars - battery voltages below 12.6 will start to "sulfate" the battery, this is NOT to be recommended....

3) Best type for non car usage are leisure batteries - they can handle deep discharging far better than a car battery. Deep discharging a car battery can "kill" the battery the first time it happens...sadly...

4) Only charge at the recommended rates from the manufacturer....or less.

May I recommend that you search on "lead acid battery" on the web and read everything you can find!!