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Very similar to a question asked and answered but using solar panels.. BUT this time I'm asking, Can I use my 135Ah deep cycle battery to power a 2000W inverter and at the same time charge my battery with 50A 7 stage battery charger.

So connected in parallel. I don't expect to be drawing more than 300-400 watts 240v from the Inverter. Think of it as a home made UPS for my office

Thanks

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    \$\begingroup\$ As long as the load does not exceed the charge rrate the battery will remain fully charged and idle while the charger directly powers the inverter watts + efficiency losses. The battery just acts as a capacitor. \$\endgroup\$ – Sunnyskyguy EE75 May 23 at 4:49
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This is a normal situation in most boats (and probably RVs).

In my boat, I have a 450 Ah battery bank, a 2000 watt inveter, and a 100 Amp alternator on the engine. While underway, the alternator is charging the battery bank, while the inverter is drawing current from the battery bank to make 120 VAC to run my navigation computer (and any other 120V devices I may want to use) and also supplying power to various other 12 volt loads.

If the charger (alternator) can provide more current than the inverter and other loads require, the excess current goes to charge the battery bank.

If the loads require more current than the alternator can supply, the battery supplies the difference.

You can't really charge and discharge the battery simultaneously - although it may look like you are doing so.

As the charging source and loads vary, the battery will be charged or discharged as needed, changing modes automagically.

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    \$\begingroup\$ Thanks for the very prompt responses from both of you. Just some clarification if you can. The charger is a "smart battery charger" - 7 stages with automatic overcharge protection ( stage 7 is float) - is there any possibility that while using the inverter with say 300 Watts draw - on the 240v side, that the battery charger will sit at stage 3 (Bulk charge) and over charge the battery ? \$\endgroup\$ – Warwick May 24 at 2:17
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You can use it but it will confuse the charger in stage 4 absorption when the current does not decay due to the load and will respond with inappropriate recovery.

The charger must be able to remote detect battery current, which this does not do.

If possible Modify stage 4 with a timer instead to limit suitable time it takes to charge up the “Memory capacitance” which is the value that is often called soak charge which has a longer timer constant in seconds and minutes, vs milliseconds, . Remember a battery is just an array of capacitors in kilofarads , each with different values and different ESR and different Tau time constants.

But if leakage is excessive and detected as a battery fault in soak charge due to an external load, it cannot tell the difference.

for dumb chargers like automotive, it just keeps it at 14.2V for flooded cells so charge and discharge and battery SoC is irrelevant.

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  • \$\begingroup\$ Thank you. Answered my question nicely :) I think I will have to introduce a standard (commercially built) UPS and maybe some 12v relay to switch between the battery and the charger. I'm no electronics expert ( or even a novice) so no point in me trying to introduce some capacitor to hold things up while it switches - I trusting the UPS will do that.. \$\endgroup\$ – Warwick May 25 at 22:33

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