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Hacking a Liftmaster solar gate controller system Answered

I have a solar powered gate, using a liftmaster system. The main control box cannot have a power input above 12 dc at 30 watts. I need to be able to control the power input to about 25 watts. Due to the environment in which the system was installed, I had to use solar panels and batteries that have a higher output than 30 watts. How can I keep the volts to about 12 volt and keep the watts under 30? I tried to google adjustable amp regulators, and the answers are not clear. How can I find an adjustable amp regulator for my specific needs?

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Jack A Lopez

3 months ago

I forgot to mention, this kind of power supply you were searching for,that you call, "ajustable amp regulator," it exists, but no one calls it by that name, but rather with the words,

"constant current regulator"


Although using the word "regulator" might be redundant, because, what does a regulator do? It keeps something constant. So

"constant current"

or

"constant current supply"

might be what you're looking for.

Or it might not be.

Like I was thinking in my previous reply, your desire to reduce the current going to a load, is likely just the result of a common misconception about how electricity works.

I mean, others have posted similar questions to this forum, probably a hundred times before, and a whole bunch of those can be found just by searching for questions about how to, "reduce current" or "reduce amps"

https://www.instructables.com/community/?sort=none...

https://www.instructables.com/community/?sort=none...

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Jack A Lopez

3 months ago

Most electric powered machines are designed to work from a power supply which provides constant, or almost constant, voltage ( measured in volts).

For a power supply like this, a constant voltage supply, the amount of current (measured in amperes) that flows from this supply is determined entirely by the character of the load.

The situation is kind of analagous to horse placed next to a trough of water. How much water does the horse drink? Answer: as much as it wants to drink.

I admit this is kind of some some animistic thinking, to think of an electric machine as having a want, or desire, to draw some amount of current (e.g. 2.5 amperes) and knowing that it will predictably draw this much current when it is connected to the voltage it wants (e.g. 12 volts DC), yet this is the way it works.

Also it is not a problem when you connect a load to a power supply capable of supplying more, or even vastly more, current than the load wants; e.g. connecting a device that draws 2.5 A, to a 12 V supply capable of supplying 10 A, or 100 A, or even a 1000 A.

I mean, it is not like if you connect a horse a river, the horse gets greedy and drinks the entirety of the river's current, and consequently explodes in a shower of bloody horse parts. Rather the horse just drinks as much as it wants to, independent of the size of the river.

But I do not expect you take my word for this.

Instead, what I suggest is connecting your gate lifting gizmo to a lab bench style power supply, the kind with two knobs on it for setting limits for voltage or current, and with built in meters that display voltage (across the load) and current (flowing through the load).

Then try setting the voltage limit to { 10, 11, or 12} volts, and the current limit to maximum, so the power supply is operating in constant voltage mode. (Should I also explain what constant current mode is?) Then observe the current that flows through the load.

And, of course, multiplying those two numbers together, voltage (in volts) times current (in amperes), gives the amount of power (in watts) consumed by the load.

I mean, if you can do that exercise, with a power supply whose voltage is adjustable, and also one that displays the power going to the load, as voltage and current, then I think that might help to give you some feeling for the way electrical devices actually consume power.

The next best thing, if you cannot find an adjustable power supply, is to just put an ammeter (or multimeter configured as ammeter) in series with your existing battery (or other 12 volt DC supply), and gate lifting gizmo, and measure how much current actually flows, and see if this conforms to your expectations for how much power you want it to use.

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Downunder35m

3 months ago

If your device needs 25 or 30W then it won't use more than this.
You can connect a 500AH battery that could provide a few hundret Watt but your gate will still only use about 30W.
No need to limit this unless you already modified the system for failure.