DIY battery backup

[19Mateo83]

Todays project is a diy LiFePo4 battery backup. I wanted to make something small that will run my 120v return pump and a wave maker for as long as possible. Never hurts to be prepared right? This will be an Amazon build, I started off with an inexpensive12v 18ah LiFePo4 battery.

since I want to run 120v ac pumps off this I needed a small inverter to get as much life out of this battery as possible. I found a 150w pure sine wave inverter that would fit the bill without too much excess power usage.

And to keep the battery charged I needed a float charger.

Now for the fun part! I needed a 120v controlled relay that will automatically switch over to the 12v dc in the event of a power failure. Well lookie there. Amazon sells one of those too.
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The plan is to keep the battery tender plugged in and connected to the battery. The output from the battery will run through the relay and then into the inverter. That will be connected to the outlet that the return pump and wave maker are plugged into. In theory the relay *should* automatically switch my power from the wall to the battery cleanly without back feed. Any electrical engineers in the crowd?

 

[19Mateo83]

The pumps I will be running on this is a sicce .5 and a hygger wave maker. The sicce consumes 8w and the hyggar consumes 14w at its max. I use it on low which is about 8w also. Combined draw of 16w.

first order of business, a draw down test of the battery with the inverter powering the 8w return pump.

No better time to test than while I’m getting the new tank filled and going. (I had it in a bucket last night as well).
Total run time on a full charge was 15 hours. With some fancy math I determined I will need two of these batteries to get the 14 hour backup time with a 16w draw. (I could probably get a crap time more if I wired the DC wave maker in directly…. But not this time.)

Stay tuned for Part 2 where we will be wiring and testing the system and the relay. (I’m still waiting on parts to arrive.)

 

[Stoneyed]

Looking good!

I did something similar with a dead UPS. Pulled out the dead batteries, and wired it to 2x deep cycle batteries. Haven't installed it yet (need to figure out where to put it), but it charges/discharges properly, and cost me nothing (already had the batteries).

 

[BZOFIQ]

The problem with a lot of these solutions is that you're upconverting 12-24V DC back up to 120V only to be converted back to 12-24V, extremely inefficient process.

With today's DC pumps/powerheads a much simple solution could be devised using a power supply and a DC UPS module DR-RDN20 from Meanwell.