Battery Deep discharge protection Cut Off Circuit

Dear All,

I am actually designing a 24VDC Sealed Lead Battery Cut Off Circuit for a existing trickle charger which is directly powered from the main 240VAC.

Aim is to drive to the relay :
1- when battery voltage is above 19V
2- When DC Main ( battery Charger is ON )

The circuit below uses two transistors in OR LOGIC, if anyone is high Relay will be ON ( closed ), as soon as both are input are gone relay will OFF ( Open ) .

My problem is when in real life when battery and charger are connected together circuit is neglecting Q1 output completely.

Note : This circuit works fine using one supply for both the inputs, but as soon as battery and charger is connected its start to malfunction.

Any Suggestion or help will be appreciated.

Regards

Dani

According to your circuit the relay contacts are shorting out the battery. If you drive the relay with a "battery charger on" signal, you will get a "good battery voltage" signal as well, unless you have got a really funny charger. What you have to have is a diode in series with the charger, so if the charger breaks down, the battery will not supply its "good charging volts " signal.
Frank

Hello
I fix your circuit a bit.
Check all resistor values ( R4 bigger value (2.2k))
Q1, Q2 can be smaller with Icollector ( like Bc547 Bc 639 etc.)

View attachment Battery_load_charge_01.pdf

Regards KAK

It is difficult from both your description and your (erroneous) circuit what you are trying to do.

"Battery deep discharge protection" implies protection during discharge and I can't see how that relates to a charging circuit.

Would you care to elaborate?

kak111 said:

Hello
I fix your circuit a bit.
Check all resistor values ( R4 bigger value (2.2k))
Q1, Q2 can be smaller with Icollector ( like Bc547 Bc 639 etc.)

View attachment 55307

Regards KAK

Click to expand...

Thanks alot

I will try it today
thanks

---------- Post added at 10:56 ---------- Previous post was at 10:52 ----------

Well yes there are some mistakes with the circuit.
which is rectified by KAK,
only one connector of the battery is connected to the relay.

I am just trying to cut off the battery supply when battery voltage reaches 20 v.
Because at the moment my battery charger is not having deep discharge protection, so its costing me money.

In KAK's circuit, if the charger is on, the relay will not be energised whatever the battery voltage because the collector of Q2, and therefore the base of Q3, will be at 0V.

The circuit below will energise the relay if the charger is on, or the battery voltage is greater than about 19.3