12V battery charger

It would be extremely easy to design one...

Most of the more expensive chargers do switch to trickle charge after a full charge though...

For a sealed lead acid battery you will need a constant current charge up to the charge voltage and then a constant voltage charge until the current drops below a threshold and then the voltage should be dropped to a trickle charge voltage - Simple!

John.

www.Interstatebattery.com , auto-zone, pep boys, sears there is one somewhere for you

Xantrex.com

Promariner.com

Charlesindustries.com

Guest.com

Guest wrote: Xantrex.com; Promariner.com; and also Charlesindustries.com.

Could you please elaborate on which specific models by those manufactures actually turn OFF the charge upon completion. To the best of my knowledge these product all have 3 stage charging and continue charging at float voltage levels but do not terminate completely. My experience being that this is mostly a European product feature.

Victron is one of the best from what I have seen of the available products.

http://www.macmc.com/chargers.htm

Since you did not give an application Mac makes chargers in a wide variety.

Hope this helps

Take a look at this: http://sunlogic.manufacturer.globalsources.com/si/6008814249895/pdtl/AC-AC/1001356154/Battery-Charger.htm

I have a Schumacher model 1052A-PE rated 2/10/50A but I couldn't find it on the web.

Try Deep Sea Electronics, we have used their products for many years in mobile gen.sets and have found them most reliable.

Battery chargers are at:

http://www.deepseaplc.com/product/catalog/cid/14

You did not indicate the type of battery, which is important when selecting a charger. Schumacher makes a complete line of chargers for almost any need short of a full-size station battery.

For engine starting batteries, I would recommend the agricultural/fleet series. For electric equipment using deep-cycle batteries, the marine series works well. Any of the fully automatic units are "connect & forget"; once the charge is complete, they will keep the battery topped off without overcharging.

Again, something I learned from my father:

For an occasional battery charge, not for a daily use, he devised the following:

1.) Battery charger, positive side connected to positive terminal of battery;

2.) Battery, negative terminal connected to one side of a 12Volt Light bulb socket, about the size for a turn signal or brake light;

3.) Other side of light bulb socket connected to negative side of battery charger;

4.) Insert light bulb in socket;

5.) Turn on charger;

6.) Go home.

After several hours, the battery becomes fully charged. Then the full 12, 13, 14, or 15 volts begins to flow through the battery and through the light bulb. As the amps begin to increase, the bulb overheats and burns out!

I am submitting this on this forum in the hopes that someone with a more complete knowledge of electical engineering will look at it and assess whether it would work, and whether it is safe.

tomfranpat

Sounds like some of the reallyold battery chargers we used in the battery rooms where we had many batteries to charge at the same time. However one detail sounds backwards. As the battery reaches full charge the current will drop and the light wil go out. It does not blow.

However that kind of charging method has been outdated for a few decades. Constavolt was a popular brand of good quality chargers that first appeared in the late sixties. It relied on ferro resonant tank circuits on a specially wound transformer to regulate the voltage. In the late 1980's a new design came out called 3 stage. This kind was described in an earlier post. Starts as co nstant current then goes to constant voltage and then drops to float voltage when full charge is reached. The newer models then times out after a while and shuts down totally for a few weeks then wakes up and repeats the cycle if the battery has not been in use.

You wrote:-

After several hours, the battery becomes fully charged. Then the full 12, 13, 14, or 15 volts begins to flow through the battery and through the light bulb. As the amps begin to increase, the bulb overheats and burns out!

The amps will be decreasing as the battery charges, the bulb will get a higher voltage, whether or not this will be enough to burn out the bulb, I cannot say.

It seems like the waste of a bulb if it works to me.....

The resistance of the bulb will severely cut down the charging current to about the current that that particular bulb would have used....when warm say (at first), depending upon its wattage, which you neglected to mention!

This sounds a little upside down and backwards. The bulb does not blow or even go out. Its brightness dims as the battery reaches full charge.

This is a take off from the early to mid 1900's, before "dry charged" automotive batteries became popular. Battery manufacturers supplied common automotive batteries "wet", that is filled and charged. The service station or automotive jobber stocking batteries had to keep them on a trickle charge to preserve their charge and life. A battery display stand, built somewhat like a staircase, held a number of batteries. All battery grounds were connected in parallel to the negative lead of a single charger. Each positive battery terminal was individually connected through a series connected small light bulb. This allowed one battery charger to maintain a trickle charge on many batteries. The light bulbs were usually mounted behind blue jewel lenses in a decorative pattern on the display stand. When a battery was needed it was plucked from the display, all charged and ready to go. Many mechanics used the light bulb in series idea to rig a charger to maintain or trickle charge their own batteries.

Why does it dim? The voltage across the battery rises as the battery gets charged and as the load (amps) get less......surely it gets more voltage across it (the lamp), not less?

When a battery is discharged, it takes a higher charge current and drops the charger voltage, as the charge increases, the voltage across the battery also increases.....a cheap charger may go to 15 volts or more unloaded, so it will do its best to bring the battery up to this voltage as well.....gassing oxygen & hydrogen once the battery exceeds 13.2 volts (highly dangerous!) and eventually the battery might be at 15 volts or more.....(it drops once the charging is removed), which is why only a charger that is intelligent is a good charger!!!

The battery itself has very little internal resistance, one can see that if a wrench is accidentally used across the terminals, so when the battery is fully charged, all the voltage will be across the lamp......it will be at its brightest!!!

I have not got the time, or a battery to use to check this out at the moment, but I will do once my kitchen and hallway are finished!!

I feel that the lamp will get brighter as the charge progresses......

Andy, since you volunteered to do the experiment, and so others reading this can get a better handle on it, just remember that the light bulb is in series with the positive lead (not parallel). The bulbs used in the mid nineties were of the 20 watt varieties and 6 volts was the standard at the time, however, 12 volts is not a problem. Also remember that internal battery resistance cannot be measured, it must be calculated, ohms law again. Anyhow, I'm sure you can handle it. Oh, don't forget the calculations for resistors in a series (resistor1 is the lamp, resistor 2 is the battery). It would be interesting if you installed an ammeter in series with the light bulb, a voltmeter across the battery terminals and a voltmeter across the charger leads before the light bulb. Tell me if the light bulb brightens or dims as the battery voltage rises due to charging. Hint: if the voltage fed to the bulb is 14.2 and the battery voltage is at 13.2, which is where the other bulb lead in connected, what is the voltage drop across the bulb? Sorry to get a little lengthy and hope I didn't confuse anyone. Be happy to answer more questions though.

I hear you, but I need to experiment to fully follow that one, when the weather is warmer.

Then how did the original poster get the idea that the bulb would burn out?

Hi FKIA,

How are ya? I shouldn't jump into the mix but you are confusing me a bit.

'The bulbs used in the mid nineties were of the 20 watt varieties and 6 volts was the standard at the time'

20 watt I'm with ya but 6 volts? mid nineties?? I'm sure you meant mid fifties, eh?

Yes, I meant mid-fifties and prior. I guess when you get old three things start to go. The mind is first, and I can't seem to remember the other two. Thanks for picking that one out.

Look at these links for some circuits:-

http://www.aaroncake.net/circuits/charger2.asp

http://www.discovercircuits.com/B/batt-chrg.htm

A normal charge light (as in a car dash) goes out as the charger volts rises above the battery volts, i.e. showing there is no battery discharge.

Normally one charges about 0.5 to 1.5 Volts above battery voltage depending on battery type. Again lead acid batteries are fairly robust and take a voltage range. Hence they are charged with what are referred to as 'constant current'; although the current does decrease as they reach full capacity. As the volts rise the current decreases.

Many batteries (lead acid) are self current limiting when charging, starting with a large charge current tapering off as they become charged due to the rise in internal resistance.

Modern more sensitive batteries (Ni-Cd, NiMh, Li-ion, etc.) are charged with 'constant volts'; the voltage (dependant on the battery type) is maintained and the current tapers off as the battery voltage rises to meet the charger voltage. The charger is specific to the battery type and often current limiting. The battery temperature is critical and monitored in expensive battery chargers as in a UPS [Uninterruptible Power Supply]

The huge current when shorting is the discharge - due to low external resistance.

The DSE site I left a link to sell both types of charger in switch mode & transformer / rectifier form.

As previously stated some chargers have 3 stages, more complex units are taper chargers.

A lead acid cell is 1.8V to 2.2 fully charged [2.2 x 6 = 13.2V] so the charger sits ~14V to trickle charge the battery at a few mA when charged.

Johnbob, you might want to recheck that data on charge methods. You said; "As previously stated some chargers have 3 stages, more complex units are taper chargers"

I do believe its the other way round. A fixed voltage charger will result in a taper charge. As the lead acid battery voltage rises, the amount of charge current tapes off. The more complex micro processor controlled chargers are the ones with 3 stage charging. First stage is bulk at a constant currnet, once the batery terminal voltage reaches a value corresponding to 3/4 of full, the micro processor locks the output voltage at the maximum value for that kind of battery. This is called the absorption stage. when full batery voltage is reached, the smart chargers readjust the target voltage to a value designated float voltage. This voltage varies dependent on ambient temperature.

By contrast, NiCad batteries are supposed to be charged with a constant current always. Many of the portabel tool battery packs had a thermal sensor inside. AS the batery heated up from the constant current, it reached a temp that tripped the sensor cuting of charge curent.

Krishna,

Go to the web site for Schumacher Electric. In the past I have purchased several of their 12 volt chargers which just shut off at the end of charging. Before writing this post I looked up their web site and it looks like their current units drop to trickle charge, but you should contact them

here in the US. i have two great battery chargers. made by black and decker. they are smart chargers. have a microprocessor inside. not only shuts off at full charge, but shows charging amps, full charge, and fault conditions. also does equalization and reconditioning. i think this means that after the battery is at full charge, you put it on recondition, and it pulses power to the plates, making the sulfides fall off.

It converts them back into plate material. If they just fell off (as actually happens without such a device, they build up on the floor of the battery and eventually are high enough to short out the plates.....

There is a more detailed description here.