I have a small backup battery (7Ah SLA for now, but probably a 130Ah flooded cell outside later) for my two in-house transceivers and two things that could potentially charge this battery: a 30A 13.8V linear power supply and a small 0.5A Battery Tender trickle charger. Right now, I have my HF radio plugged into the 30A PSU and my VHF radio plugged into the Battery Tender and the battery with a simple Y cable I made. This seems to work, but it has the downside that any use of the radio (7-15A draw) drains the battery fairly quickly as the draw is an order of magnitude higher than the charge rate.

I'd like to wire all of these devices into a common circuit.

Three and a half related questions:

  • Recognizing that the Battery Tender is likely to see the power supply's output as a fully charged battery and shut off whenever the power supply is running, is there any obvious problem with having two sources of approximately the same voltage on the same circuit?
  • Since this would be in parallel, the battery would still end up providing some (half?) of the current to drive the radios when they're used, right?
  • As far as I know, car batteries are charged by simply throwing 13.8V at them from the alternator with no attempt made to reduce available current once the battery is charged. Can I just charge the battery with the power supply by simply having them in the same circuit? If the power supply is on but not powered, is it possible that it might accidentally provide 120V back into my wall socket?
  • \$\begingroup\$ I tried to diagram this with various online diagramming tools, but I'm too much of a noob at diagramming. \$\endgroup\$ – William - Rem Apr 28 '17 at 22:20
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    \$\begingroup\$ Why dont you via a fuse and shottky diode charge your SLA battery of your 13.8VDC PSU . \$\endgroup\$ – Autistic Apr 28 '17 at 22:29
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    \$\begingroup\$ The power supply will not produce 120 VAC when AC power is not available (unless it is an inverter/charger combination unit). I would prefer a proper battery charger, rather than a power supply, to charge the battery. If you have a 130 Ah battery, I wouldn't bother with the battery tender. \$\endgroup\$ – Peter Bennett Apr 28 '17 at 23:04
  • \$\begingroup\$ @Autistic - What would the fuse and diode accomplish? \$\endgroup\$ – William - Rem Apr 29 '17 at 15:38
  • \$\begingroup\$ @ William Rem .The fuse is important .If the battery got a shorted cell which can happen the charging currents could be huge so the fuse would blow .What if the PSU got a short in its output then the battery is capable of big fault current so the diode stops runback .What if the diode failed short circuit then the fuse protects . \$\endgroup\$ – Autistic Apr 29 '17 at 21:38

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