Yeah, so I'm using the XL4015 with a 100w solar panel. I have the XL4015 set to 7.35vdc to charge a SLA 6v lantern battery.

The diode is working, but the current is limited to 200mA, instead of the full 300+ mA it would get if there was no 1N5822 diode in series, to prevent the darkness at night from drawing power from the battery... If it was a windmill or wind turbine, then the battery wouldn't power the motor at night, ....

So why the heck is it not as efficient when the diode (1N5822) is in place?
meter reads 0.209v Vf for the diode(s). That's good.

So it's charging.. obviously... that's good too. But not as much current as I'd like..
k, so I did a LM358n with an LDR and a n.FET and the stupid XL4015 draws 10mA from the battery... and when there's light, something goes wrong.
Anyways.. that's why I'm doing the diode thing. Simple components, to do a simple job. No need for ICs or Microcontrollers to cut power (OPEN CIRCUIT) when the sun goes down.. just a freaking diode with the right current rating, and a nice diode (Vf), ...

The XL4015 is set to 7.35v @ 2A max, and yes, there's power. Adjusted the XL4015 to charge the battery @ 7.35v @ 2A max, and it's only getting 0.3A (w/o diode), and 0.2A w/diode)... So idk what the heck is going on here... I watched the videos on YouTube and they say they start conducting once the voltage is good past the diodes Vf.. ok... so that's 0.209v for these puppies..

Main Question ::: Idk why the current is reduced is my question..
BONUS Question ::: Why was the XL4015 sinking current when the OpAmp wasn't outputting to the gate of the mosfet...?

Negative of the battery was on source.
Negative OUTPUT of the XL4015 was going to Drain.
The OpAmp was getting power from the 6v battery. Neg to Neg, Pos to Pos. (6.35v)
Positive of battery goes to Positive Output of the XL4015.
Solar Panels are connected to INPUT of XL4015. (It's Night time).
Output 1 of OpAmp is going to Gate of n-FET.
Potentiometer is set to 5v going to POSITIVE (non-inverting) input of OpAmp.
10k from positive in series with LDR to ground. LDR resitance goes high, so does the voltage.
More resistance towards ground, means more voltage output (voltage divider).
That Voltage from the LDR and 10k resistor voltage divider, will go to (inverting input) of the OpAmp.
Voltage goes high, it turns OFF. Sends no voltage to the gate of the n-FET.

So the negative gets cut.. the battery will not get current flow from Drain to Source.
Funny thing with mosfets is that they can be used with AC too from what I heard.. So the polarity doesn't matter.
Btw, the gate and source has... had a 33k pull down resistor, to prevent the mosfet from floating..
I tested the gate and the output of the OpAmp, and the voltage was ZERO.

So... that's weird..
Tnx in adv., for any help on this..

 

You may think that the written word is pure gold. However, a schematic diagram of what you are doing would be ever so helpful in identifying the problem. A load, like a battery, does not take a fixed current and it is a mistake to expect it to do so. A load will take an amount of current based on the voltage and its internal resistance, which you have neither mentioned, nor quantified.

 

Really have no clear idea what you are doing from your rambling description.
As PB, stated, post a schematic (the language of electronics) of what you have.

But why not just increase the output voltage of the XL4015 to compensate for the diode forward voltage drop?

 

The XL4015 is not an MPPT controller. If the panel is not producing the required current, the XL4015 is going to try to regulate its output voltage, and in doing so will collapse the supply voltage from the panel, moving the cell voltage to somewhere it is not very efficient.

Also, your charging current will reduce if you reduce the voltage by 0.2V.
If you want to block reverse current flow AND charge at 7.35V, put the diode inside the feedback loop, and make the feedback resistors as high as the datasheet allows, as they will take some current at night.

 

You may think that the written word is pure gold. However, a schematic diagram of what you are doing would be ever so helpful in identifying the problem. A load, like a battery, does not take a fixed current and it is a mistake to expect it to do so. A load will take an amount of current based on the voltage and its internal resistance, which you have neither mentioned, nor quantified.

I understand the charge curve of SLA Li-ion, Lifepo4, etc.

The charge current will go down, ... as the battery becomes charged to the desired voltage.
This is easy stuff... We know this very well now.
Having a meter shows that right now, the battery is at 7.20v, and the XL4015 is putting out (after the diode), 7.29v.
and it's charging right now at 0.290A, good sun right now. The battery started at 6.34v earlier this morning.

So, the battery is almost charged to the voltage that was set by the XL4015 which is 7.29v, so that's good.
I don't really think I need to complain anymore, because the circuit seems to be working.. If I try it with my 3s4p Lion pack and if it's still getting low current and I know my battery pack is lets say 10.5v then I know we got a problem.. If I set the XL4015 to 3A, and it's only giving me 0.3A at midday solar... the diodes are funky or I just really suck at electronics, let alone power electronics.

 

I understand the charge curve of SLA Li-ion, Lifepo4, etc.

The charge current will go down, ... as the battery becomes charged to the desired voltage.
This is easy stuff... We know this very well now.
Having a meter shows that right now, the battery is at 7.20v, and the XL4015 is putting out (after the diode), 7.29v.
and it's charging right now at 0.290A, good sun right now. The battery started at 6.34v earlier this morning.

So, the battery is almost charged to the voltage that was set by the XL4015 which is 7.29v, so that's good.
I don't really think I need to complain anymore, because the circuit seems to be working.. If I try it with my 3s4p Lion pack and if it's still getting low current and I know my battery pack is lets say 10.5v then I know we got a problem.. If I set the XL4015 to 3A, and it's only giving me 0.3A at midday solar... the diodes are funky or I just really suck at electronics, let alone power electronics.

I asked nicely for a schematic, and I got another paragraph. Do you want help, or not?

 

You may think that the written word is pure gold. However, a schematic diagram of what you are doing would be ever so helpful in identifying the problem. A load, like a battery, does not take a fixed current and it is a mistake to expect it to do so. A load will take an amount of current based on the voltage and its internal resistance, which you have neither mentioned, nor quantified.

 

I asked nicely for a schematic, and I got another paragraph. Do you want help, or not?

 

So it does work, ... maybe it was a bad OpAmp chip... Because it does work, .. the battery is the source of voltage for the OpAmp..