24 Volt Battery Box Vent Fan Control Circuit

  
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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 cir
24 Volt Battery Box Vent Fan Control Circuit - schematic

cuit 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!



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