I'm working on a DIY solar inverter.

The goal is to make the battery connected to it rechargable by both energy from solar panels and AC mains (if there is power supply.)

My battery is 24V DC, AC main is at 220/240 V AC and I'm using an LM 317T for voltage regulation.

I'm stuck thinking about the right transformer for power rectification from AC source, since the voltage applied to the LM 317T input pin must be greater than the voltage leaving it.

Could you please suggest the right transformer?

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    \$\begingroup\$ What has your research endeavours led you to so far? BTW there's not enough info in your question to answer this so have a real good think about what you want and define things like space available, current into the battery, heatsinking on LM317, rectifier capacitor etc.. In other words, all the normal stuff. \$\endgroup\$ – Andy aka Oct 1 at 11:58
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    \$\begingroup\$ It's a full engineering task to design a circuit which can charge a battery from a power supply and from a solar cell system and properly at the same time monitors the need of charging, decides how much is needed from the mains operated power supply and fulfills all common security details which should be taken into the account with batteries. If you expect only a type number for a transformer you probably don't have a slightest idea what the task demands. We cannot help because we do not know anything of your current system. BTW We can help with well specified details but do not do all work! \$\endgroup\$ – user287001 Oct 1 at 12:23
  • \$\begingroup\$ You are looking for a transformer. But you seem to want it to go from AC to DC, so you don't want a transformer you want a rectifier. Also, a LM317T is a voltage regulator, not a charger controller, and it's an LDO so extremely inefficient (especially at large voltage differences). I think you need to do some more research to understand what you're trying to do. \$\endgroup\$ – Puffafish Oct 1 at 12:54
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    \$\begingroup\$ This is like saying, "I'm working on a DIY EV+diesel hybrid plug-in car. I'm stuck on the wheels. I have a 17-tooth gear, part number LM317T, and wonder what's the right ball bearing and races system for me?" I'm kind of stuck on how to reply to such a question. \$\endgroup\$ – jonk Oct 1 at 12:55
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    \$\begingroup\$ LM317 is kind of the Donald Trump of energy efficiency; you might consider a buck converter to make better use of your solar power. \$\endgroup\$ – Brian Drummond Oct 1 at 13:00

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