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Old 05-13-11, 06:57 AM   #1
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Default inverter fan control circuit problem

I have a fan control circuit that i built for my inverter because my inverter fan is always on and its quite noisy so this circuit allows you to adjust at what temperature the fan kicks in and the circuit is powering off the battery voltage.
The problem i have with it is that its not only sensing temperature to turn on fan but also whenever the battery is charging and the voltage is rising you can hear when the fan kicks in when the voltage reaches about 13V.
The circuit operates off 12V but as i said before its powering off the battery which whenever the battery voltage rises high past the 12V then the fan kicks in. In the night this does not happen as the battery is not charging in the nite because the charge comes from the sun. And if the temperature in the inverter rises to a certain height then the fan comes on which is correct as i set the pot on the circuit to turn on the fan when this happen. But in the day when the battery is charging and the input voltage rises past the 12V then the fan comes on even thou the inverter is still cool. If i adjust the pot on the circuit to stop this from happening it will affect the temp. sensing point for the fan. Whenever you set the pot one of the points get affected either the thermal setting for when the fan suppose to turn on or the fan comes in too early when its senses a rise on the input voltage of the circuit.

This is the site that contain the circuit. Please click the link at the left side of the page that name temperature control then you will see the page with the circuit as well as all the details about it. It is a very simple little circuit that can easily fit in any inverter regardless of how the inverter might be well compact.
The Heatsink Guide - All about PC cooling

What can i do to make the input voltage always remain at 12V regardless of what the battery voltage is? Remember that it has to be a small modification to the circuit because i dont have a lot of space to mount it in the inverter.
I was thinking about a small fixed 12V regulator addon for the circuit but i was thinking that maybe if the battery voltage drain below the 12V then that fixed 12V regulator might not operate efficiently. I was thinking about a small 12V transformerless power supply also that just took in the 110VAC of the inverter and step it down to 12VDC to power the fan circuit and with this way you know the inverter would be always delivering that 110VAC to the power supply which in turn would be powering the fan circuit with a fixed 12V at the input as the power supply voltage would not decrease or increase.
Also i was wondering if there is any area on the inverter that always produces a fixed 12V regardless of the battery voltage as i could use this section to power the circuit.

If there is another fan circuit that is very small that would not be affected from a rise/decrease in the input voltage but just senses either to kick in when a certain heat/load is detected then please share it with me.
Please tell me what are your suggestions/comments.

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Old 05-13-11, 04:59 PM   #2
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Use a lower voltage voltage regulator, for example 10V. You will have to recalibrate the potentiometer to get it to start at the right temperature.
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Old 05-13-11, 07:29 PM   #3
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You could add a temperature controlled switch in series with the fan's power line..

Attic fan thermostat 85F thermal switch solar electric - eBay (item 190527871313 end time May-28-11 21:53:37 PDT)

I've used these type switches on heat-sinks to kick on the fan when they got over 100 deg F.

You might be able to find something similar in an automotive supply store..

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