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I wish to use a 12v deep cycle battery (I used to use this for my CPAP, when camping) put it on a constant charge, preferably a cheap trickle/float charge circuit, like found at Harbor Freight.

I want this to power two devices:

  1. will run on any voltage between 7v and 12v. (an Arduino UNO)
  2. a 12v liner actuator, that has a max draw of 5A, and will run for just a few minutes, twice a day.

Keeping in mind the trickle charge, and my understanding the battery will run higher than 12v itself, I'm expecting I'll need to regulate the voltage to keep it at or just under 12v. This is not something I've ever done, and I've spent some time googling it, but there seem to be so many variables in other people's projects, I got a bit confused.

Please advise. I wish to learn.

The actuator I'm looking at is this: https://www.amazon.com/dp/B07KPPZP6X but it has no data sheet listed. The charger: https://manuals.harborfreight.com/manuals/62000-62999/62813.pdf Neither of these have been purchased, so I'm not dead-set on these models. No, not a car door lock. Application is to close a chicken coop door at night, and re-open in the morning. Want to use the battery so it still runs in case of power failure.

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  • \$\begingroup\$ Please provide links to the datasheets for the trickle charger and for the actuator. We need to see what voltage the trickle charger provides and what voltages the actuator can tolerate. \$\endgroup\$
    – Elliot Alderson
    Commented Jan 21, 2019 at 14:21
  • \$\begingroup\$ Is the linear actuator a car door lock motor? \$\endgroup\$
    – Passerby
    Commented Jan 21, 2019 at 14:23
  • \$\begingroup\$ Without knowing the characteristics of the battery, this can't be answered. 12V batteries are seldom 12V. Either they are above it, or below it, depending on charge cycle. You probably want some manner of step-up regulator to keep the voltage at a constant 12V. But if the battery can be 14V, it turns more complicated as you'd need some buck/boost or such. \$\endgroup\$
    – Lundin
    Commented Jan 21, 2019 at 15:01
  • \$\begingroup\$ Based on the scant information on the vendor site, the actuator draws 5A when running. It will be expensive to build a dc/dc converter at that current level, and your CPAP battery may not provide enough current anyway. \$\endgroup\$
    – Elliot Alderson
    Commented Jan 21, 2019 at 15:25

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I don't think you need to regulate the outputs to these devices at all. I have one of these Harbor Freight trickle chargers, is does eventually run the battery terminal voltage up to the 13.2V stated, though with a car battery it can take days to get there if the battery is not initially near full charge. It's only intended for maintaining charge, but your loads are likely low enough that the energy in/out is sufficient to maintain the state of charge.

The regulator in the Uno is a NCP1117ST50T3G per the datasheet for the Uno and will tolerate 20V. This is reflected in the tech specs tab on the Arduino website.

The exact model of the linear actuator doesn't appear on the Firgelli website, but it looks like that's just a brushed DC motor, which will be tolerant of a 10% variation of supply voltage with no issue.

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