Choosing a Diode for 12V Battery Charger: Tips and Recommendations

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Discussion Overview

The discussion focuses on selecting an appropriate diode for a 12V battery charger circuit to protect against potential damage from reverse voltage when the mains supply fails. Participants explore various diode options and methods for protecting the circuitry, particularly concerning heat dissipation and current ratings.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • Hylton inquires about suitable diodes for a 12V battery charger, mentioning a maximum charge current of 5A and a trickle charge of 600mA at 13.8V.
  • Hylton's friend suggested using a 1N5408 diode, but Hylton expresses uncertainty after reviewing the data sheet.
  • One participant notes that the 1N540x series is rated for 3A and suggests using a 1N4007 diode from the output of the regulator to its input to prevent the output voltage from exceeding the input voltage.
  • Another participant emphasizes the importance of heat management, calculating that a 5A current with a 1V drop results in 5 watts of heat, and recommends the FMB-G24H diode for its lower heat production and insulated case for mounting.
  • This same participant reiterates the standard protection method to avoid having a diode inline with the supply to mitigate heat issues.

Areas of Agreement / Disagreement

Participants present differing views on the appropriate diode choice and methods for protecting the circuit, indicating that no consensus has been reached regarding the best approach.

Contextual Notes

There are unresolved considerations regarding the heat dissipation implications of different diode choices and the specific current ratings required for the application.

Hylton Conacher
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Just joined and looking for information on which diode to use to protect a 12V battery charger circuitry connected to a battery. it is charging. Should the mains supply fail ie battery charger has no forward current, the battery may apply voltage and current to the circuitry damaging the LM338 voltage regulator.

Charge current is max 5A and the trickle charge at 600mA Voltage is 13.8 V

A friend suggested a 1N5408 but am not sure looking at data sheet.

Help appreciated.

Regards
Hylton
 
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Thread moved and title changed to fit the topic.
Hylton, I also removed the link to your personal e-mail. I believe it is against the rules to have personal information like this in the main forums. To easy to exploit and all, you know.
 
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Drakkith said:
Thread moved and title changed to fit the topic.
Hylton, I also removed the link to your personal e-mail. I believe it is against the rules to have personal information like this in the main forums. To easy to exploit and all, you know.

Tnx Drakkith, all understood.
 
the 1N540x series are 3 Amp rated

the usual way to protect a regulator is just to put a 1N4007 from the output of the reg chip to its input
cathode to output pin. This prevents the voltage output becoming significantly higher than the input voltage

Dave
 
Heat will eat you up in this application. 5 amp x 1 volt drop = 5 watts!
Try this: FMB-G24H
It's a bit expensive, but it will produce less heat and it's case is insulated so that you can put a dab of petrolatum (vasoline) on it and mount it on most any metal surface to shed the heat.
 
Mike_In_Plano said:
Heat will eat you up in this application. 5 amp x 1 volt drop = 5 watts!
Try this: FMB-G24H
It's a bit expensive, but it will produce less heat and it's case is insulated so that you can put a dab of petrolatum (vasoline) on it and mount it on most any metal surface to shed the heat.
which is why I suggested the standard protection method so that there isn't a diode inline with the supply :)
 

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