how to charge 40 AH battery.

[asimraufawan]

Hi All,

I m using 10 batteries of 12 v in series to make 120 V DC for a converter input
each battery is rated 40 A/h.

I want to charge all the 10 battries conected in series.

Is it possible & how.

Thanks

 

[IanP]

Batteries can be charged at different rates depending on the requirement ..

Typical rates are:
- Slow Charge = Overnight or 14-16 hours charging at 0.1C rate
- Quick Charge = 3 to 6 Hours charging at 0.3C rate
- Fast Charge = Less than 1 hour charging at 1.0C rate

Because of the “high” voltage (10 x 14.7V = 147V fully charged) options 2 & 3 may be difficult to realize, so, option 1 - @ 0.1C, you have to build a 147V@ 4A battery charger ..
Probably the simplest solution would be a 600VA step-down (or auto-)transformer with the secondary winding producing somewhere around 150Vac, followed by a rectifier and a power resistor ..

IanP

 

[asimraufawan]

I have 2.2 KVA stepdown transformer ,what if i charge the batteries with it
& how much time will it take to charge.

Thanks

 

[IanP]

2.2kVA transformer at 150V can give you roughly 14.7A, that's like quick charging, I'd say - 3-4 hours ..

IanP

 

[asimraufawan]

the attached is the circuit diagram kindly tell me is it right or any suggestion for safety.

Thanks

 

[fg]

An important thing to consider when charging batteries is the battery chemistry (NiCd, NiMH, Li-ion, lead acid, etc.).

Discharged lead-acid batteries cannot be charged full within a few hours. Lead-acid batteries require 10 hours or more to charge full if they are discharged.

Additionally, lead acid batteries should always be stored full charged, lest sulfation of the plates occur.

Li-ion batteries on the other hand, should not be stored full charged. The battery chemistry matters very much indeed and must be considered when batteries are charged, discharged, and stored.

The below quote is valid only for certain types of batteries:

Batteries can be charged at different rates depending on the requirement ..

Typical rates are:
- Slow Charge = Overnight or 14-16 hours charging at 0.1C rate
- Quick Charge = 3 to 6 Hours charging at 0.3C rate
- Fast Charge = Less than 1 hour charging at 1.0C rate

The above is correct for NiMH batteries (at least many modern types). When using "Quick Charge" or "Fast Charge," overcharging may occur and some circuitry is required to terminate the charge if e.g. the temperature of the batteries rises too much. Overcharging can also occur when "Slow Charge" is used.

NiMH batteries are often charged at a constant current. Overcharging is possible even at the 0.1C rate. Some NiMH chargers use a timer to terminate charging.

However, the constant-current charge method does not suit lead-acid batteries well as a primary charge method. (Some lead acid battery chargers, however, do first apply a constant current, then a constant voltage charge.) Lead acid batteries are usually charged at a constant voltage with current limiting. Lead acid batteries can be left on a "float charge" for a long time without causing harm to the batteries. The float charge voltage might be something like 2.25 volts/cell (13.50 volts for a 12 volt battery).

Using only "float charge" (which means a relatively low charge voltage), a discharged lead acid battery will take some 48 hours to reach a full charged state. As mentioned above, some lead acid battery chargers first apply a constant-current charge (to reduce the charge time) and switch to a constant-voltage charge mode after the battery voltage has reached a specified value.

For NiMH batteries, there are different methods to detect a full charged condition.

One method is based on temperature monitoring: when a battery has reached a full charge state, it begins to generate heat. The charger is then supposed to detect this shift in temperature and terminate the charge or at least reduce the charging current.

Another method used for NiMH batteries relies upon detecting a drop in battery voltage during a constant-current charge. This method seems quite unreliable to me, being that the said voltage drop is very small for NiMH batteries (for NiCd batteries on the other hand, it is somewhat more pronounced). In my opinion, this method should not be used at all for NiMH batteries due to its unreliability.

It looks like NiMH batteries do not lend themselves well for "float charging". I think that when charging NiMH batteries, one should primarily use a constant-current charge and terminate the charge (or reduce the charge current significantly) after a "full charged" voltage has been reached (some 1.42 volts/cell).

If someone knows more about the problem, please let us know.

@asimraufawan: The circuit you showed needs some form of current limiting, whatever type the batteries are.

I again stress that the charge method and charge time depend heavily on battery chemistry (NiCd, NiMH, Li-ion, lead acid, etc.).

Regards.

 

[asimraufawan]

i m using the lead acid batteries

 

[IanP]

As I mentioned before the rectifier has to be followed by a “power” resistor that is absolute must in such simple chargers ..
Its value and power rating depends on the current, but I’d say that the resistance could be around 4.7ohm and power rating roughly 150W .. see attached picture ..

IanP

 

[fg]

i m using the lead acid batteries

That makes things a great deal simpler than with many other types of batteries. I recommend using a constant-voltage charge at the float charge voltage and with current limiting, as IanP suggested.

The float charge voltage is somewhat critical:

Float voltage refers to the (somewhat) constant voltage that is applied continuously to a voltaic cell to maintain the cell in a fully charged condition. The appropriate Float voltage varies significantly with the chemistry and construction of the battery, and ambient temperature. With the appropriate voltage for the battery type and with proper temperature compensation, a float charger may be kept connected indefinitely without damaging the battery.

With a 6-cell (nominal 12V) lead-acid battery the correct float voltage is in the range 13.5 - 13.8 V at +25 °C and changes by about 0.1 V for a 5 °C change in ambient temperature. Not compensating for this will shorten battery life either by over- or under-charging.

(https://en.wikipedia.org/wiki/Float_voltage)

According to the above, a thermal compensation should also be used.

Regards.