Wow, thanks to all who attended my seminar this year! I changed it up a little and made it a presentation of good-to-know FACTS about solar – every aspect of it. Ended up with about 10 minutes of open questions, and I got lucky again – I was able to answer every one with a solid response! Sorry I left my NEW box of business cards at home, but I think the 12 folks who came up to get the 12 I had were the folks most interested in future contact (I hope!). I promised I’d post the PowerPoint presentation, so here it is with the presenters notes included. MEN FAIR 2014 Presentation Nothing that will rock the world, but there might be just that one photo, or factoid that you’ve been looking for! Thanks again for all who were in the PACKED tent (even if you just wanted to get out of the rain!)

24 Volt Battery Box Vent Fan Control Circuit

Battery vent fan control switch

Schematic for 24VDC Battery box vent fan controller

One of my backup systems uses a Magnum MS-PAE 4024 inverter, which doesn’t have any built-in fan controller. Since batteries give off hydrogen during both normal and equalization charging, it’s important to vent the batteries to the outside with a brushless fan. This little circuit does the job nicely for a 24 volt battery bank. Here’s how the circuit works: Battery voltage comes in and goes directly to the LM358 op-amp and P1-R1. P1 sets the trip point where the fan will turn on. VR1 and R2-R3 provide a stable reference voltage for the op-amp. R4 adds some hysteresis so the fan doesn’t cycle on/off when near the trip point. the 4 volt zener assures that Q1 turns fully off, since the output doesn’t swing to the rails. R5-R6 assure that Q1 turns on/off completely. Q1 is good for fans that use up to 100 milliamps of current. If you have a bigger fan, use Q1 to turn on a relay… This won’t work for 12 volt or 48 volt systems, but I might design those if there’s any interest here…. Enjoy!