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We are powering a circuit with a 12 Volt battery. We have a RF remote controlled Relay to turn the system on. When the system turns on the current draw is 15 Amps and then settles to 6.5 amps. The voltage drop is about 2 volts +- on start up too.(measured using a multimeter). Our problem is the RF circuit is bothered by this voltage drop and starts to act funny and not do what it is supposed to do when pressing the remote buttons. If I power the RF unit with an additional battery everything works fine. My thought is if I can put a cap on the power supply side of the RF unit it will act to smooth out the voltage issue. Can someone please let me know if I am thinking correctly and how I would figure out the correct value Capacitor. This is a small setup so I need to be able to put the cap in tight quarters. I look forward to any suggestions. Thank you in advance.

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  • \$\begingroup\$ How much current does the RF system consume? Not the load current - just what is consumed by the receiver and related electronics. \$\endgroup\$ – Dwayne Reid May 15 '16 at 23:28
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    \$\begingroup\$ If the high start-up current lasts long enough to be measured by a multimeter, it's going to take a heck of a capacitor to supply it. Are you sure your power supply isn't just underspec'ed for this load? \$\endgroup\$ – The Photon May 15 '16 at 23:54
  • \$\begingroup\$ I agree with Photon (+1). If there's a 2V volt drop @15A then there's about 0.13 ohm in the supply circuit so either the battery is underspec or you need thicker wire/better connections. \$\endgroup\$ – JIm Dearden May 16 '16 at 10:05
  • \$\begingroup\$ The current for the RF system only consumes 50 milli amps. We are using a 1300 mAh battery to power the system. Is this to low? Thicker wires is an option that I will try tomorrow. What is a boost converter and how would it work in a battery powered system. Thank you in advance! Chris \$\endgroup\$ – cerca May 18 '16 at 1:18
  • \$\begingroup\$ That battery size is extremely tiny compared to your load current of 6.5 to 15 Amps. The battery internal resistance is going to cause all sorts of problems. \$\endgroup\$ – Dwayne Reid May 18 '16 at 1:24
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Either try a big capacitor across the RF receiver being fed through a big resistor which will more or less isolate it from the sudden transients when the circuit is triggered, or (the more sophisticated, but more reliable solution), use a boost converter to feed the RF section so that the battery voltage is irrelevant, the boost converter will always supply a voltage above the battery voltage (and it'll be a fixed, regulated voltage too) so that the RF section gets a steady supply voltage under all conditions.

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