Testing a Car Battery Charger for 6-12V Batteries

[mrjeffy321]

I have a car battery charger (for 6 or 12 volt batteries), that I don't know for sure if it works or not.
I want to use it for a power supply in an electrolytic cell, so I decided to test it out to see if it worked. When I hook it up and plug it in, nothing happens, the needed doesn't jump on the amp meter which is built into the case, nothing happens in my cell, so I am not even sure if it is working. But then again, it could be one of those "smart" battery chargers that can tell when the battery is fully charged and automatically shuts off, and maybe it thinks my "battery" is charged. Or, perhaps the resistance in the cell is so low that it is shorting it out and it automatically turns itself off to prevent damage. The again, it could just be broken.
I don't have any car batteries to test it out on.

What characteristics does the battery charger use to determine if thr battery is completely charged or not, high resistance, low resistance, something else?

My battery charger has two settings, one to charge 6 volt batteries and one to charge 12 volt batterues, but it is suppose to put out 6 amps on both. Is this an ideal case, and in reality, I will never get that? Or can I expect to really get 6 amps out of the charger when I plug it in. I used to use computer power supplies as a power source, they claim to be x volts at y amps, but it never lives up to its promist, is this the same case?

 

[berkeman]

Set it for 12V and hook it to a car battery. Does the Amp meter swing up now? If so, it just needs to have some minimum battery voltage present before it will turn on. That's what my charger at home does.

I'd recommend using something else to power your electrolytic cell. Oh, and many computer power supplies have a minimum load requirement. If they are not ballasted up to their minimum output current, they will often have their outputs out of regulation (usually high, but they can also oscillate). If you ballast a computer power supply to its minimum output current (see the supply's specs), it should definitely stay in regulation. -Mike-

 

[mrjeffy321]

getting side tracked from the battery charger for a minute (since i don't have a car battery to test it out on now),
I am looking at a computer power supply (the old kind that has a switch/button to control the power to it), it has its outputs listed:
+5V - 23 amps
+12V - 9 amps
-5V - .5 amps
-12V - .5 amps

but I don't see a minimum load requirement specifically listed. Am I to assume (using V = RI), that I need to have a resistance of .22 ohms to get the 23 amps it claims to supply? or 1.3 ohms at 12 volts for 9 amps?
Looking at the log I kept from my last electrolytic cell run (about 700 hours of cumulative running time), generally, my calculated resistance through the circuit/cell was hovering ar just around .4 ohms, and I was using the +5V terminal from the power supply. Or is this minimum load requirement much higher than this, so by actually increasing the resistance, I would increase the current (how strange is that).

 

[berkeman]

Usually there will be a minimum load for each output, specified in the datasheet for the power supply. Try to use the model number and manufacturer of the power supply to get the datasheet or other specs from the web. Often the jellybean supplies for PCs don't have very good specs if at all on the web.

You could try this for a starting point if you can't find the specs. Try ballasting 1A on the +5V and 1A on the +12V. If that doesn't bring them into tolerance, try pushing the +12V ballast to about 5A. If that doesn't work, beats me what to try.

 

[mrjeffy321]

What do you mean by "ballasting"? I am not familiar with this term used in electronics.

I know there are two types of computer power supplies, I think they are called "AT" and "ATX" power supplies. One of them is an old design not used much, if at all in new computers and has a real switch that will actually turn the power off, as opposed to the newer power supplies that don't really turn off, but insted have a constant voltage through a button that controls the rest of the power to the power supply. I can't remember which is which.
I am/was using the older type with the switch.

I found this page,
http://web2.murraystate.edu/andy.batts/ps/PowerSupply.htm
that looks very interesting, and even talks about turning a ATX power supply into a power supply that will supply a much higher output, closer to its theoretical output. The design even takes into account the minimum load needed by the +5V output in order to opperate correctly, in this example, it uses a 10 ohm, 10 watt resistor to trick the power supply into thinking it is plugged into a mother board.
Does this look like a practical thing to do?

I couldn't find any data on my particular power supply, it is old and an obscur brand, but on some pages describing the minimum load, it says it is usually about 10%, whatever that means when referring to resistance.

 

[willib]

tell me about your electrolytic cell.. what are you using it for..??

 

[mrjeffy321]

My electrolytic cell is used to make [Sodium] Chlorate with Hydrogen gas and Chlorine gas byproducts.
The higher the current, the more electrons I am putting into the reaction in a shorter amount of time, and thus I have to run the cell less.
For example, using my old method, I ran the cell for the entire month of Feburary, the whole month, night and day (although there were some periods of time when the cell shut itself off for whatever reason), if I can get a reasonably constant, and high current, I can cut that time down to just a few days.
I though a car battery charger would be good because it is designed to output high currents for long periods of time, and since I could never get the computer power supply to work as well as I needed it to, I thought it would work out great.
But if I can get the computer power supply to work the way I need it to, even better, since I already have several spare power supplies, and they are much cheaper than battery chargers, and theorecally, they can output much higher current.

 

[berkeman]

The term "ballast" in the context where I used it just means to add some load to the supply's output. Kind of like adding ballast to a boat or submarine, I guess.

The link you showed with the computer power supply tips looks pretty good. What voltage and current are optimum for your electrolytic cell application?

 

[mrjeffy321]

For my cell, 5 volts would be fine, and for current, the higher the better (with in reason), I would be over joyed is I could get a steady current of say 10 amps (my previous trials were averaging about 1.5).

I did a little experimenting with an ATX power supply the other day.
I went out and got some 10 ohm, 10 watt resistors as described in the link and prepared to play around with the power supply.
After figuring out that the gray wire (I have no idea what its propper name is, it is not labeled) had to be grounded to get it to turn on, I then began to test each wire for its voltage. the +5 V and + 12 V [really outputs about 10.5] are my best bet obviously.
I first tried using the +5 V with the 10 ohm resistor in series with an amp meter, and amazingly [math works], I got a current of .51 amps! Now this is really low for my uses, but it does prove that it is working correctly
(5.1 volts = 10 ohms * .51 amps)
then I tried the +12 volt using the 10 ohm resistor, and nothing on the +5 V, I got about .9 to 1.0 amps here, getting closer to a usable current.
then I prepared a test cell (put some salt water in a jar and assembeled it like my real cell would be), without any resistors wired into the circuit, except the cell, I was getting a much higher current (up to about 5 amps using the +12 V wire). 5 amps is great, I'd like more if I could get it, but I guess is really depends on the resistance in the circuit and how low I can get it to increase the current.

A couple times though, something strange is occurring.
I try to test the current through the cell, I turn the power supply on, the fan starts to spin for a second, but then immedeatly cuts off. It is like the power supply is turning itself off because it is over loaded, but how can it? I could do something two times, using the same set up and get two different reactions from the power supply.

It appears that the power supply has a built in minimum load becase it appear to work fine without an additional resistance built into any of the wires (except for the freak occurences described above).

Can you think of any other way to increase the current through the cell?
the distance between the electrodes make a big difference, also the concentration of electrolyte effects the internal resistance, but those I can only control to a small extent. Is there any thing circuit wise I can do? I thought about taking another +12 V wire and connecting it to the ground through a resistor, this creating two, parallel, circuits that the +12 V must supply, increasing the overall current out of the power supply, but no so much though the cell.

 

[Brad_R]

Hi, hope its okay to add something?

If youre doing something that releases Hydrogen gas, then before trying to get more current? Do you have a setup that is safe enough in case something catches fire, or worse? same for chlorine gas?

Ive found that the ATX supplies put out 12v with no load applied but the 5v don't as described. There is a way to get more current, the car battery charger should put out more current than the pc power supply at 12v, but when you move current you produce heat.

So as long as the cell is encased in something with a ventillation hose and safety setups expecting that it could catch fire? then more current is easy.

 

[mrjeffy321]

My set up will indeed release Hydrogen and Chlorine gas, but not to worry, the gasses will be a safe distance away from the power supply and will quickly dissapate into the surrounding environment (Even if I tried purposely to light them, all I would get is a slightly brighter flame and perhaps a popping sound).
Actually, one time I was standing near by watching the cell opperate, using a AT power supple, and I started to see smoke come out of the power supply, then the smoke got really black, I quickly unplugged it and took it outside and blew out the fire. To find out the cause, I opened up the power supply and found a very small burnt black spot burried on the underside of the circuit board in the corner, otherwise no damage, and the power supple still works (but I don't trust it any more).

Idealy, I would love to collect the gasses (both H2 and Cl2), in separate containers, to be saved for later use, but it is too hard to make a cell that will allow for both making chlorate as quickly as possible, and collecting the gasses, so sadly, I must let them just float off to freedom.

I have now switched over to this new thread,
https://www.physicsforums.com/showthread.php?t=79892
since I am focusing on using computer power supplies, insted of the car battery charger which was the original aim of this thread.

 

[willib]

i understand your problem now..your cell resistance is too high..
to get more current to flow through your cell you have to find a way to reduce the resistance..

 

[willib]

maybe if you put the plates closer together that might work..

 

[KingNothing]

To see if a charger works, just touch the two ends together...if it's working, it will spark.