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So I'm trying to figure out how to safely power a small 12V deep cycle battery with a home built wind generator. It's a 36VDC motor that outputs around 5V with low wind, and 12V with lots of wind (1A - 3A). I would like it to power a small speaker, mp3 player and arduino, so low power consumption. (measured total = 400 mA)

I've looked into MPPT controllers etc, but those seem to be targeted for large 300W+ systems, and are pretty expensive.

My first idea was the following, see schematic

A buck-boost DC converted doubles the voltage, it goes to a LT1038 voltage regulator, that outputs 14.2 volt to the battery. The battery is specced to charge between 14.1v and 14.7v

Is this safe to do?

Is it dangerous to keep the voltage at charge voltage? Or should it be set at float charge voltage of 13.2V?

If you have other suggestions or schematics I would really appreciate it!

I'm also looking at chips like the BQ24450, but it's a steep learning curve.

Many thanks!!

Schematic

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First of all you did not say how small is your battery.

Charging a Sealed Lead Acid to 14.0-14.8V is OK for cycle use - like charging it overnight, then disconnect the charger and slowly discharge through the day. If this setup is going to be permanently wired with the charger, a better option is to keep the voltage near the float levels - 13.2-13.8V.

Using a linear regulator is far from perfect. The main drawbacks are:

  • it will overheat at strong winds
  • you will loose valuable energy in heat dissipation, instead of storing it to the battery

I recommend you to find some CC/CV boost module (there are plenty ready assembled modules on the market for a couple of $) whos output current can be limited to a value safe enough for the battery - like 0.1C or 0.2C max. C stands for battery capacity. (0.2C for 7Ah means 1.4A current.). Set the maximum output voltage to a value in between 13.2-13.8V or 14.0-14.8V depending on your battery specifications and usage mode.

Edit: Some example of CC/CV boost module: enter image description here

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  • \$\begingroup\$ Thanks! I had a look around the shop and found a couple of these guys laying around: amazon.com/Voltage-Regulator-Converter-DC4-5-30V-Isolation/dp/… This is what you mean right? So I could hook the generator up to this, set it to 13.2-13.8V, and hook it up to the battery? The battery is not that small, it's a 32Ah 12v Deep cycle battery \$\endgroup\$ – Matt Nov 3 '17 at 13:52
  • \$\begingroup\$ Product name does not match the product itself. I know these very well, 'cause I use them too :) This is a CV buck non-isolated converter. You need CC/CV boost converter or buck-boost like this: amazon.com/dp/B0757NRLD7/ref=sspa_dk_detail_1?psc=1 Look for a module with at least 2 potentiometers. \$\endgroup\$ – Todor Simeonov Nov 3 '17 at 14:27

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