battrey chargers 1

[dw7672]

a funny situation happened to me , my battery is supposed to give me an output of 12 volt , to use it to chnarge a 12 V , lead acid battery , on no load the chnarger gives me 16 volt , my battery now is on load and it gvies me 16 volt , when I charge it to the charger it gives me 13 volt , I am not getting it at all is this logical , plz help me guys
thnaks

 

[itsmoked]

dw7672; Your question makes no sense to me.... Please read it and try again to make the question clear.

 

[dw7672]

it smoked ,
is it right that a 12 volt DC charger , gives me 16 V ( when reading it using the multimeter) , on no load , and when I put the charger on my 12 V , lead acid battery , it gives me 13 volt ( when I use the multimeter ) to read it
hope I was clear!!

 

[rbulsara]

Your post is not very clear. Please fill the answer to the following, using a good digital voltmeter (not the readings of the charger):

1. Voltage measured at battery terminals alone when no load is connected and also not connected to the charger.

2. Voltage measured at the charger alone, with no battery or load connected.

3. Voltage measured at charger terminals when battery is connceted but no load.

4. Same conditions as in 3 but measure voltage on the battery terminal

5. Voltage at the battery terminals, just after charge but before connecting the load and disconnceted from the charger.

6. voltage at the battery with only load connected but no charger.

7. Type of load, distance of battery from the charger, size of wires etc..

This will help some to understand your condition better and come with some answer..

 

[dw7672]

thnaks , the answeres are like this using a good digital voltmeter
1- 10.87 volt
2-16 volt
3-13 volt
4- 13 volt
5- 11 volt
6- 11 volt
7- the load is a microcontroller board , wire are normal thin wires ditsance is 10 cm
thnaks

 

[rbulsara]

The source voltage is constant. When charger is not charging its open circuit. (draw a charger as ideal voltage source with internal resistance in series).

When you connect the battery (draw a load across the open terminals of your diagram), and you will see that their is current thru the circuit, with some voltage drop across the internal resistance of the source and some across the load. So the voltage at the battery terminals will be less than the OC voltage. In your case it appears to be by 3V...

Hope this make some sense..When you connect the load, there is further drop..

 

[TransmitterTamer]

Be careful, because the output of most battery chargers is rectified AC, with little to no filtering. The chemical changes taking place in your battery as it charges probably are not significantly affected by ripple voltage or current, but your electronics may be affected. And please remember that the voltage peaks on the output of an unloaded charger might be quite high (30 plus volts for a 12 volt battery charger), so be careful how you connect and disconnect your equipment, battery, and charger. Your electronics might not survive the unloaded output of your battery charger.

 

[itsmoked]

dw7672 your second post was MUCH clearer. Thanks.

It is very normal for your charger to read that higher voltage when not connected and a lower voltage (but higher than 12V) when hooked to the battery.

TransmitterTamer's warnings are all true too.. Unless you have an above average Volt Meter the readings you get when the charger is unhooked are probably off by volts.

For your info 12V car batteries are really 13.6V when fully charged, so you should see this after your battery is charged up.

 

[DanEE]

I would doubt you have this type of charger, but it's worth pointing out that some automotive type chargers (high end microprocessor controlled 3 stage chargers and, with an equalization phase) for flooded wet cells can briefly take the voltage up to as high at 16.2 volts..

Since the microprocessor knows exactly what the charge VI curve looks like over time, it can take it up to this high a level to do a fairly quick and safe equalization on a seriously run down battery and typically for only a brief e.g. 15 minute period before ramping down..

Obviously these chargers were never meant to be doing this while sensitive electronics are hooked up to the battery..

The important thing is that you know what your charger max voltage is during during bulk, absorption and float in relation to the max voltage the regulators (that I'm assuming) are on your cicuit board can take.

Second, you need a charger built for driving loads in addition to the battery, otherwise (inexpensive) chargers can hang in stage 2 absorption mode and cook the battery..

It typically takes a microprocessor controlled charger to not hang in stage two and go on into stage 3 float mode.

Here is an example of a charger that would work fine in your application that I have some personal experience with..

http://www.batterystuff.com/productdisplay.html?id=374&c=82&f=Samlex_12Volt_15Amp_battery_charger

Here is a simple tutorial I put together for for my ham radio club. If you need to know more about battery chargers in general, this might helpful w/o getting too deep..

http://home.4x4wire.com/deddleman/section_battery_chargers.html

btw you values for 1, 5 & 6 sound low really low..

Either you have an inaccurate meter or the battery is in bad condition. Are you using a known accuracy digital volt meter to measure pure DC & DC plus AC rms values?

 

[boreholelogger]

You will get a higher voltage than 12VDC to charge a lead acid battery because you need the current to flow through the battery and if they are the same potential (12VDC) it will take ages for them to come to equilibrium, rather than a few hours with your charger.

 

[boreholelogger]

Sorry I meant if you had two 12V batteries side by side one flat and the other fully charged. It will take a lot longer to charge the battery as when they become close to the same energy level in each battery not much current will flow. Therefore your charger being higher than 12V (13.8VDC)will charge the battery up to 12VDC and a little over. Otherwise you would be waiting for weeks.