Float Battery Charger

Batteries must be charged at 1/10th of their Ah capacities. It mean if you can control current,ur 200Ah battery will take about 20hrs to fuuly charge

Then the charging current will be 200AH/10=20 Amp and the charger specifications indicates that it is only 10 amp continuous ?

and what about the load which is also connected in parallel with the battery ?

It will extend the charging time. The arithmetic is simple.

The AH of the battery should be great enough to do the job it needs to preform. The amount of time it takes to charge that battery will be the AH of the battery divided by the amp output of the charger.

But the amp output of the charger will feed the load also- not only to charge the battery ?

What's the load?

It is 10A Maximum.

What's the load?

It is 10A Maximum.

. . . . eeerrrh.

. . who's on first?

Zacky

If you connect a 10A (@24V) load and a discharged 24V battery across the output of a 24V 10A charger, you will overload the charger. Based on the charger's overload protection, it will either blow a fuse, trip a breaker or cycle on and off to protect itself from burning up. Best to select a charger that can supply both the battery and the worst case load.

Initially, most of the charger's current will flow through the discharged battery because it's series resistance will be less than the 2.4 ohm load. As the battery charges, the current will be divided between the battery and the load. As the battery approaches full charge (float voltage usually about 27V for lead acid) most of the current will flow through the load, but the charger will not advance into it's trickle charge mode because it will still have to supply up to 10A to the load. The time for the battery to fully recharge is not very predictable.

Better yet is to supply the load with a separate power supply and keep the battery float charged separately through an energized 1P2T relay, which when power is lost drops out to connect the battery to the load.

Hope this is useful.

2x 12V Battery could be connected in series and each battery should have 100AH capability. If more AH is connected then charging time will be longer then 10H .

Any more detail info is needed please sent me e mail at

kyilmaz@globalpowerdesign.com

Kadir Yilmaz

www.globalpowerdesign.com

\

Ok Zacky,

Let me give this a try.

If you have a 24V/10 Amp battery charger that delivers 24/10 Amps continuously then you will require a battery bank that is sized so that the 24/10 Amp power supply NEVER causes the battery bank to become overcharged. Follow? What I think Zacky is asking is what size battery bank does he need to make his 24V/10 Amp charger act like a trickel charger. Usually the questing is asked the other way around. What size charger is required to charge my battery bank of xAh.

You want the charger to supply the load (10 Amps) while the batteries are floating at full charge and provide a trickle charge during the rest of the time. If the power goes out, the batteries automatically kick in and everything is still powered up.

This example is based on a 12 volt battery system. You will have two batteries in series and a bunch in parallel (as per your question). For 6 Volts you would have 4 in series and a bunch in parallel. The batteries are 100% fully charged when each cell is at 2.45 V (14.7V for battery). This number will vary depending on the manufacturer.

The general rule for trickle charging is C/300. (This information is always provided by the manufacturer.) So you need a battery bank where the 10 Amps = C/300. If my math is correct you would need a 3000 Ah battery bank to keep you batteries at the trickle charge level.

Let's go a little further. Why not. If you are using a 12V 100 Ah batteries you would need 2 in series and 30 of these series connections in parallel.

One step further. The time to recharge the batteries depends on how low they are drained. This state of charge (SOC) should not be allowed to go below 25% or 11.9 V per battery (23.8V for 24V system)

Time to charge assuming no load and 80% SOC (65% DOD) would be:

TTC = (1-SOC/100) * Rated Capacity / Rated Output of Charger + 2 hours or

= (DOD/100) * Rated Capacity / Rated Output of Charger + 2 hours

= (1-80/100) * 100 Ah / 10 Amps + 2 hours = 4 hrs per battery or 4 * 60 = 240 hrs

If the batteries only see very occasional use, and the load is away near the 10 Amp max, then you should have no problems. The batteries can stay in trickle charge for a long time, I should qualify that by stating it depends on the battery construction, Flooded, Sealed, Gel or AGM will respond differently under the above conditions and also the spec on your charger. If the SOC goes below 95% often, this would not be the option.

In the end though I believe your batteries would probably fail prematurely because it would take too long to provide enough current to get them back up to 100% charge if they get completely drained plus you have to factor in self discharging. Also the batteries require an occasional topping up or +100% charging for maintenance that the charger cannot provide.

Disclaimers apply. Check manufactures specs. Ultimately, size the battery bank for your load and the amount of hours per day it will be used for, then purchase Deep Cycle batteries, 3 stage charger and a battery monitor.

Greenja

Hi, Greenja: I think that after all your math calculations the final TTC= 240 minutes not hours. Good try.

Jose

Ideally .this can charge a 24 v 100 AH battery bank (two 12 v batteris in series).

However, a 24 V lead acid battery bank in good condition will reach about 26.4 V at full charge. The charger maust be able to handle this.

Since it is a float charger, either source may supply the current. When the charger output is off (mains shut down), the battery bank supplies the current. Back up time will be limited to about 70% draining of the battery.

If the load is continuous without any shut down at all, there will be further scaling down of back up time. There has to be some sort of current limiting as well.

bioramani

Zacky, your question is about FLOAT CHARGER. Most of the replies are related to BOOST CHARGING & NOT FLOAT CHARGING.

Function of Float charger is to (a) Feed the connected load. & (b) Trickle/Float charge ( nomenclature may slightly differ ) the connected battery.

Battery capacity is decided based on desired backup time and then the BOOST CHARGER rating is decided, depending on type of battery, permissible charging duration etc. etc.

For 24 V 10 A Float charger, theoretically upto 1200 Ah battery can be connected, though not practicable ( thumb rule @8mA/Ah ).

To sumup, depending on your load current, remaining current is available for float/trickle charging of battery. If your load current is 8 A, then 2 A is available for float/trickle charging, sufficient for upto 250 Ah battery.

Thanks and regards

Ashok Toshniwal, Bangalore, India

That is true only for a fully charged battery. Float chargers are used in uninterrupted supplies. During power out the battery in circuit supplies the load and gets discharged. On power resumption this depletion plus the load current have to be handled by the charger.

bioramani

Bioramani, your explanation is for FLOAT CUM BOOST CHARGER & NOT for FLOAT CHARGER. In UPS this is how it is provided, in which case, "resumption of this deletion" is done at a voltage higher than the one required for FLOAT CHARGING. Inverter circuit of the UPS is therefore designed to operate from "Battery end cell voltage" to "Max. boost charging voltage". Once the battery is fully charged, the "FLOAT CUM BOOST CHARGER" voltage is automatically switched from BOOST CHARGING VOLTAGE to FLOAT CHARGING VOLTAGE, or else the battery will continue to see HIGH BOOST CHARGING VOLTAGE & WILL GET IRREVERSIBLY DAMAGED.

Thanks and regards

Ashok Toshniwal, Bangalore, India

Is the charger fitted with electronics to stop the battery getting overcharged? If not, you need to add such a control otherwise your battery (assuming its in the range of 100 - 200 AH) will overcharge, gas and get damaged....

Simple battery chargers ruin more batteries each year than many believe....

You could add some electronics to a simple charger to achieve this.

May I recommend that you control the charger to charge before the battery voltage before it gets down to 25.2 volts and to stop charging once it gets to 26.8 volts.

This will stop any damage happening to it due to undercharging (assuming its not a leisure battery) or gassing when over charging......this should give it a very long life.....