A friend of mine is wondering if it is possible to get rid of a 3-second power shortage when you start an old vehicle (press the starter). He is using the power from the 12V supply from the vehicle and he is thinking of attaching a huge capacitor for it, simply.

  • Is this safe?

  • Is there a way to calculate which capacitor to use?

  • Are there any other methods to achieve this?

Thanks in advance

  • \$\begingroup\$ Remember that one Farad is one amp for one second where there is a voltage drop of one volt .So you can stop the power cutout with a diode and a big cap .Find out what your current is because this determines the size and cost of your proposed capacitor . \$\endgroup\$ – Autistic Aug 26 '17 at 13:06
  • 2
    \$\begingroup\$ You should mention how much current the load that needs the constant 12 V needs. If it is only a few Ampere then consider using a DCDC buck/boost converter module. This can upconvert the lowered 12 V (which might be 8 V when starting) to a more or less constant 12 V. BTW this does not only affect older vehicles but also new ones. The current that the starter motor needs can be more than 100 A which simply makes the battery's 12 V drop a few volts due to the internal resistance of the battery. \$\endgroup\$ – Bimpelrekkie Aug 26 '17 at 13:15

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