DC UPS and charger circuit

Hi

I want to design a simple DC UPS circuit that will also charge a 12V SLA battery. The attached drawing shows the circuit that I require help with.

The load resistor RL represents the device load (draws 6 amps max typically only 2 amps).

My understanding of the circuit is that when the 14.2V power supply (actually an AC/DC power source) is present the voltage to the load will be approximately 13.8V to account for the voltage drop of the diode. With 14.2V present the battery will be charged to a max of 13.8V.

When the AC goes off the battery will switch in and supply VB minus the drop of the diode to the load.

I am not positive on the function of RB but I thought it would control the max current the battery receives while charging. The current charging the battery will decrease as its voltage approaches 13.8V and I believe this is a function of (VB-13.8)/RB where VB is the voltage of the battery while charging.

I built the circuit with RB=1 ohm and measured the voltage across battery terminals and current to battery while charging. The current measured much higher (2 to 3 times) than I anticipated per my assumption above.

Does anyone have a simple explanation or a simple circuit that will do the same.

Shmedly said:

Hi
I built the circuit with RB=1 ohm and measured the voltage across battery terminals and current to battery while charging. The current measured much higher (2 to 3 times) than I anticipated per my assumption above.

Does anyone have a simple explanation or a simple circuit that will do the same.

Click to expand...

hi,
Couple of questions, whats is charge condition/state of the SLA and what is the current value you measured thru the 1R?

Just nit-picking, but the circuit as drawn wont work.
Either the diodes or the PSU/Battery are the wrong way around.
In a battery symbol the long stroke is the positive.

Back to your problem, what are you using for a power supply, and what sort of meter did you use to measure the battery charge current?

JimB

The SLA battery is new and we have looked at 2 identical batteries also. They all have the same response with the circuit. They are all 10AH batteries.


The battery +/- terminals in the circuit may be reversed also.

I am using a MeanWell AC/DC 15C power supply and set the output to 14.2 V.

I am using a AMPROBE 37XR-A to measure current. I am not using the inductive clamp type but the ones that require you to break circuit and insert lines from meter.

With a battery voltage of 13.2V the current draw of the battery was 2.2 amps

Shmedly said:

With a battery voltage of 13.2V the current draw of the battery was 2.2 amps

Click to expand...

hi,

With a charger voltage of 14.2V and a series 1hm: resistor [you say] and Icharge of 2.2A amps wouldn't give you a battery voltage of 13.2V???

Vdp = 2.2A * 1 = 2.2Vdp,,, 14.2 - 2.2 [not icluding the Vfwd for the diode ] =12V.

Check the volts/amps and the 1R

Are you getting these measurememts with R Load connected, if Yes, which way is the current flowing???

Yes there is a load connected which draws 1.5 Amp.

The current to the battery flows in the opposite direction when it is being charged.

It's always something - I found I had a bad diode. Replaced and now things make sense. Thanks for the input for it made me go back and question things.

hi friends
please send me the good ups battery charger circuit.

regards
karthick

Shmedly said:

Hi


Does anyone have a simple explanation or a simple circuit that will do the same.

Click to expand...

I would use the attached circuit. With a 10A battery limit the current to about 2A. Set the power supply so when charging with out a load the charging voltage is 13.5 to 13.8. When the power is off the battery will automatically supply power. The diode prevents the battery damaging the power supply or the battery being discharged by the power supply when the power is off.

Need 110 volt Dc Battey charger with capacity 10 amps

Hi,
Can u please send me the circuit diagram and PCB layout for DC battery charger for following specification

Input: 220 volt Ac
Output: 110 V Dc

Capacity: 10 Amphere

faithfully,
Kader Sha

Hi,
Can u please send me the circuit diagram and PCB layout for DC battery Boost charger for following specification
Fully automatic
automatic manuval output voltage regulator
charging one to six cell from 240+/-6%,50Hz
dp power supply 0-12V
output voltage rated for0.2AH of cell(five hour rating of the cell

alby paul