I'm working on the power supply for an automobile student team. We have an alternator that will be delivering 20 A and around 14 V max and would like to regulate that to 12 volts.

Would arranging four lm388's in parallel like this (https://www.eleccircuit.com/high-power-supply-regulater-0-30v-20a-by-lm338/) be a good option?

Thanks!

 

Why do you want to reduce the alternator output to 12V? It is a misnomer that vehicle electrics are 12V; with the engine running the output of the alternator (and the supply to all vehicle components including the battery) will be a nominal 14V.

 

What will this 12 volt regulated buss power? If several separate modules need 12 volts regulated it might be better and more efficient to use local voltage regulation at each modules using the alternator voltage as the distribution buss. Something you also need to plan for is a load dump.
https://m.littelfuse.com/~/media/el...utomotive_tvs_diodes_application_note.pdf.pdf

 

Hello,

First of all, I think you mean the LM338 in stead of the LM388.
The LM338 needs a certain voltage to be able to regulate.
The mentioned 14 Volts will be a to low input voltage.



Bertus

 

You do know what a load dump is I hope. If not -- start here

https://en.wikipedia.org/wiki/Load_dump

 

You do know what a load dump is I hope.

Is that when you empty your pants after your project catches fire?

 

Linear regulators and high current have some drawbacks, that's why switchmode power supplies now rule the world.
If you don't need to charge a lead-acid battery from the alternator, why not just adjust the alternator's regulator to 12V? Even if the alternator has an internal regulator module, it shouldn't be difficult to replace it with an external regulator (perhaps using the Motorola MC33092).
Regarding the electrical environment of a conventional automotive electrical system, check out the chapter on "Voltage Regulators In Automotive Applications" in the old National Semiconductor "Voltage Regulator Handbook" (google for pdfs).
If you need to maintain a steady 12V even through engine starting (which could drop battery voltage to near 8V), maybe some kind of step-up/down switching converter will take care of that.
And finally, do you REALLY need 12V exactly? If that's just gonna be converted down to 3.3 or 5V to run some digital electrickery, just use a suitable switching supply which will be more efficient and tolerate the wide voltage input range. (MC34166, 8-36V in, 5V/3A out, since I happen to have one sitting in front of me).

 

Is that when you empty your pants after your project catches fire?

That would be an alternate, but unintended definition. Perhaps if your automobile was rear ended at moderate speed it would produce that effect.

 

What will this 12 volt regulated buss power? If several separate modules need 12 volts regulated it might be better and more efficient to use local voltage regulation at each modules using the alternator voltage as the distribution buss. Something you also need to plan for is a load dump.
https://m.littelfuse.com/~/media/el...utomotive_tvs_diodes_application_note.pdf.pdf

Thanks for the reply. So if I were to regulate the modules individually, the highest amp module takes 6.53 amps. Would 5 lm317s in parallel make sense?

 

Linear regulators and high current have some drawbacks, that's why switchmode power supplies now rule the world.
If you don't need to charge a lead-acid battery from the alternator, why not just adjust the alternator's regulator to 12V? Even if the alternator has an internal regulator module, it shouldn't be difficult to replace it with an external regulator (perhaps using the Motorola MC33092).
Regarding the electrical environment of a conventional automotive electrical system, check out the chapter on "Voltage Regulators In Automotive Applications" in the old National Semiconductor "Voltage Regulator Handbook" (google for pdfs).
If you need to maintain a steady 12V even through engine starting (which could drop battery voltage to near 8V), maybe some kind of step-up/down switching converter will take care of that.
And finally, do you REALLY need 12V exactly? If that's just gonna be converted down to 3.3 or 5V to run some digital electrickery, just use a suitable switching supply which will be more efficient and tolerate the wide voltage input range. (MC34166, 8-36V in, 5V/3A out, since I happen to have one sitting in front of me).

Thanks! We will be charging a 12 v battery as well. We are trying to maintain a constant 12 v for the individual modules.

 

Why not just modify or simply change the field regulation to set it where you want, single LM311 with mosfet to feed the field.
Max.

 

Thanks! We will be charging a 12 v battery as well. We are trying to maintain a constant 12 v for the individual modules.

What type of 12 volt battery? If it's a lead-acid type you will need that 14 volts to keep it recharged. We really need some sort of diagram to see what you want to do, do where and at what voltage.