My goal is to create a fail safe circuit (or rather...more of a battery protection circuit) for my 14.6v lifepo4 batteries that are charged by 33v PV panels in the event of a failure of the BMS to stop excess charging. My plan is to configure an LM324 as a voltage comparator with one input a 5v reference and the other a voltage divider. My issue is how to properly utilize the output of the LM324 to turn on an SCR.
Additional circuit info: Once the SCR is triggered, the PV panel will be shorted to stop any excess charging. For additional safety, I've opted to isolate the higher PV panel voltage from the battery voltage by a small relay.
I'm confused about the gate voltage and current requirements necessary to turn on the SCR. I've selected an MC106-6G SCR to trigger a small relay. My interpretation of the datasheet is a gate trigger voltage between 0.2 and 1 volt and a gate trigger current greater than 200uA. From searching other posts and reading about SCR gate triggering (I'm a novice trying to learn), it seems as though the current is the most important criteria for triggering.
Datasheet for the 4A SCR: ( taydaelectronics.com/datasheets/files/A-1497.PDF )
I've created the circuit with the help of an online simulator. If I put a current limiting resistor on the output of the LM324 (which should be 20mA or so), the output voltage is around 14v (much higher than the 0.2 - 1v called for on the datasheet). If a voltage divider is utilized, the current flow is below the triggering current threshold of 200uA. Can someone help with the triggering solution?
A screenshot of the circuit simulator is posted. FYI...The simulator doesn't offer a PV panel, so I've substituted a 33v battery and a 10.5A relay to simulate the solar panel when it is shorted out. The SCRs shorting the panel are BT151-500R rated at 12A each.
Datasheet for the 12A SCR: ( taydaelectronics.com/datasheets/files/A-1485.PDF )
Thank you in advance for any advice or help!
Prior to LM324 trigger:
.
LM324 triggered:
.
Post triggered LM324 (lower battery voltage) prior to reset:
Additional circuit info: Once the SCR is triggered, the PV panel will be shorted to stop any excess charging. For additional safety, I've opted to isolate the higher PV panel voltage from the battery voltage by a small relay.
I'm confused about the gate voltage and current requirements necessary to turn on the SCR. I've selected an MC106-6G SCR to trigger a small relay. My interpretation of the datasheet is a gate trigger voltage between 0.2 and 1 volt and a gate trigger current greater than 200uA. From searching other posts and reading about SCR gate triggering (I'm a novice trying to learn), it seems as though the current is the most important criteria for triggering.
Datasheet for the 4A SCR: ( taydaelectronics.com/datasheets/files/A-1497.PDF )
I've created the circuit with the help of an online simulator. If I put a current limiting resistor on the output of the LM324 (which should be 20mA or so), the output voltage is around 14v (much higher than the 0.2 - 1v called for on the datasheet). If a voltage divider is utilized, the current flow is below the triggering current threshold of 200uA. Can someone help with the triggering solution?
A screenshot of the circuit simulator is posted. FYI...The simulator doesn't offer a PV panel, so I've substituted a 33v battery and a 10.5A relay to simulate the solar panel when it is shorted out. The SCRs shorting the panel are BT151-500R rated at 12A each.
Datasheet for the 12A SCR: ( taydaelectronics.com/datasheets/files/A-1485.PDF )
Thank you in advance for any advice or help!
Prior to LM324 trigger:
.
LM324 triggered:
.
Post triggered LM324 (lower battery voltage) prior to reset:
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