MP2659 - Solar + Lead-Acid

DC-DC Power Converters
1

Hi,
I am working on a 12V lead-acid battery charger powered by a 12V 10W solar panel.
I am considering the MP2659 as a battery charge controller, configured with VB set to 4.35V, CELL set to 3.
The solar panel delivers 17.4V/0.58A at maximum power point, so I would set the input regulation current to 0.58A.
I would also program the NTCDET bit to ‘1’ and tie NTC to VCC, in order to set the MP2659 in regulation mode.

What do you think about this design ? Has anyone tried to achieve the same thing ?

Best regards,
David

Edit : I had not seen the this reference design at the moment of posting, sorry for that ! Any feedback will be apreciated anyway. Has someone tried to power the system directly from the charger output rather than using a diode OR ?

1 Like
2

Please bear in mind that the maximum power of 17V and 0.6A is only reached under maximum sun. In conditions of normal sun the maximum power that you can extract from the panel will be lower. For a simple peak power circuit you should add another control loop that backs off charging current if the panel voltage falls below its Vmpp ( a parameter that is reasonably stable across a range of illumination) . Look at your solar panel data sheet VI curves you should have several and what you see is that Voc changes very little with illumination but Isc varies directly with illumination. The point at which the VI curve reaches its maximum value is also only slightly affected by illumination

1 Like
3

Thanks for your advice.
In my understanding, if I set Vdpm (input voltage regulation) slightly under 17V (maybe 15-16V), the charger should stay around the MPP under any reasonable illumination.
This way, the Ilim setting will ensure that we get maximum power when Vin > Vdpm, and Vdpm will keep us on the MPP when the illumination decreases.

I have only one IV curve on my solar panel datasheet (Serelio KS-10T). But I will experiment with the evaluation board to find if this works.

I might not add an additional control loop, because I’m trying to keep the cost as low as possible.

4

Sounds like you have it. Good luck

8

Your design sounds reasonable for a basic 12V lead-acid battery charger using the MP2659. Setting the VB to 4.35V and CELL to 3 for lead-acid battery charging is appropriate.

However, there are a few considerations:

  1. Input voltage regulation: Since the solar panel’s maximum power point voltage is 17.4V, which is higher than the battery voltage, you’ll need to ensure that the MP2659 can handle this voltage without exceeding its maximum input voltage rating. You might need to add a voltage regulator or a voltage divider to reduce the panel voltage to a safe level if the MP2659 cannot handle the full panel voltage.
  2. Input regulation current: Setting the input regulation current to 0.58A is suitable for the panel’s maximum power point current. This helps ensure that the panel operates efficiently.
  3. NTCDET bit: Setting the NTCDET bit to ‘1’ and tying NTC to VCC for temperature compensation is a good practice, especially for lead-acid batteries, as they are sensitive to temperature variations. This helps maintain the proper charging voltage based on the battery’s temperature.
  4. Verification: It’s always a good idea to simulate your design or prototype it to verify its performance before finalizing it for production. This can help you identify any potential issues and ensure that your charger works as intended.

As for whether anyone has tried a similar design, it’s possible that others have used the MP2659 or similar components for similar applications. However, it’s always a good idea to verify the suitability of your specific design for your requirements.