Solar Charge Controller

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UhClem
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Solar Charge Controller

Post by UhClem » Mon Mar 03, 2014 3:03 pm

In reading this article I noticed an error in the discussion about reverse power flows:

"FETs will also conduct both ways, thus creating a potential that the batteries could discharge through the solar panel. To prevent this, an algorithm is used, and when the solar voltage drops below the battery voltage the unit disconnects from the solar panel. This prevents discharge when the sun goes behind a cloud or the sun goes down."

The problem is that simply controlling the gate of the FET will not prevent the reverse power flow because there is a diode between drain and source of the power FET that will conduct even if the gate turns the device off.

To correct this problem you need another device in series. You could use a simple diode but that results in power loss. The alternative is another power FET but this time with the drain and source connections reversed. You can see that in this charge controller.
David Schultz

bparrill
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Solar Charge Controller - Load

Post by bparrill » Tue Apr 01, 2014 5:47 pm

I'm fairly new to electronics so please forgive what's probably a simple question. On this charge controller (or similar circuits), is it possible to attach a load? Would I just hook it up to a battery?

I have the need to build a remote Arduino device and would like to hook it up to a 12V lead acid battery. I have a solar panel and am debating whether to buy or build a charge controller. My problem is that besides charging the battery, the Arduino needs to be hooked up and remain on all the time.

Any tips will be greatly appreciated!

nikfj
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Re: Solar Charge Controller

Post by nikfj » Wed Apr 02, 2014 2:07 pm

My thoughts exactly and I was looking for a thread on this article. In telecom work where solar panels are a common thing, diodes are a must to stop battery drain through solar. Getting rid of any algorithms and simply putting a diode will solve the drain problem entirely. Thanks to the author thought for a decent project.
UhClem wrote:In reading this article I noticed an error in the discussion about reverse power flows:

"FETs will also conduct both ways, thus creating a potential that the batteries could discharge through the solar panel. To prevent this, an algorithm is used, and when the solar voltage drops below the battery voltage the unit disconnects from the solar panel. This prevents discharge when the sun goes behind a cloud or the sun goes down."

The problem is that simply controlling the gate of the FET will not prevent the reverse power flow because there is a diode between drain and source of the power FET that will conduct even if the gate turns the device off.

To correct this problem you need another device in series. You could use a simple diode but that results in power loss. The alternative is another power FET but this time with the drain and source connections reversed. You can see that in this charge controller.

marc4g
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Re: Solar Charge Controller

Post by marc4g » Sun Jan 25, 2015 10:58 am

This could be a nit, but the only load on the 7805 is the uP.

The 7805 VR requires a minimum load of 5ma (1K) to guarantee regulation specs.

I do not know what the load presented by the uP is, but is it 5ma?

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