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MPPT solar charger needs adjustments

I recently built your MPPT Solar Charger (SILICON CHIP, February 2011) and I have noticed that at the start of each day it goes straight to float charge. This is even if I have used substantial battery power the night before. In order to make it do the full charge regime I have to switch open the connection between battery and controller to fully de-energise it for 30 seconds so that it starts afresh and bulk charges when the Sun comes up.

I have also noticed that if I switch on a big load during the day, so much so that the voltage drops to below 12.45V (even down to 12.0V for a few minutes), it still will not go to a bulk charge. This is not right. I am using two 40W amorphous panels in parallel and a 12V 110Ah SLA battery.

Is there any updated software yet to fix this problem? (B. H., via email).

• We have not upgraded the software since there are no problems that we know of. Bulk charge occurs if the battery drops below 12.45V. It is how the battery voltage is monitored and the set-up adjustments that affect this reading.

Failure to start the bulk charge after a night-time period could just mean that the VR3 adjustment needs altering. This adjustment sets the voltage that is detected by microcontroller IC1 (ie, it sets a divided down value of the battery voltage).

If VR3 is set to give a higher voltage than it should, IC1 will not detect the 12.45V low battery voltage correctly and bulk charge will not begin. Alternatively, the 5V supply might not be exact as set by VR1.

Check the set-up as detailed on page 48 of the February 2011 issue for VR1 and VR3. If the adjustments are correct, try setting VR3 so that the TP1 voltage is a little lower than the calculated voltage of 0.3125 x the measured battery voltage.

In addition, the compensation adjustment at VR2 for battery temperature can affect the charging voltage.

Lightning trigger for digital cameras

I read with interest the project on the Lightning Detector in the July 2011 issue by John Clarke. I will be keen to purchase a kit and see how this works.

Has SILICON CHIP ever had a Lightning Trigger project for digital cameras? I have checked the archive list and there appears to be no project of this nature listed. I would suspect that this would make an interesting project and would be extremely popular. I have seen results from triggers that have been purchased overseas showing stunning lightning shots.

Is this a project that SILICON CHIP might consider in the future for the popular Canon, Nikon and Pentax cameras? (R. H., Woomera, SA).

• That’s an interesting question. Given that a lightning detector would have to operate the “shutter” on a digital camera, how could any digital camera be fast enough to take a picture of a lightning flash which lasts about 200 milliseconds? We understand that most lightning photos were taken by cameras with the shutter open. Having said that, it would be simple enough to add a shutter release Mosfet to the Lightning Detector.

Incidentally, there is no kit for this project but SILICON CHIP can supply the PCB for $25 plus $10 for postage and packing.

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