Topic: 24 hr fars fan test

[jerryg]

I have been running a test with my 4 fars using 3 with a 12 volt fan running on 7 volts to cut down on the air flow and the fourth fars running a davis fan running on 2.3 volts, which is about the voltage of the solar panel in full sunlight. I checked the input airflow with a homemade set up just for comparison not accuracy. I made a set up using a small paper plate with a hole in the middle and a toilet paper tube sealed over the hole which fit over the fan of the air flow meter. The reading of the davis fan was around 3.2 m/s and the 12 volt fans were around 3.4 m/s pretty close.  The low readings last night on the davis fan was 65.0 as well as on two of the 12 volt fans and the other 12 volt was 65.1 so real close. The daytime highs yesterday on the davis was 84.0 as well as on one of the 12 volt fans, the other two read 84.1 and 83.9 for highs so real close.  It looks like the davis fan works fine as far as air flow is concerned but the lasting ability is the question. When i was running the factory fans on my fars i had several go bad with the not running in the am after coming off battery to solar operation and having to tap the shield to get it running. I think running the fan on 2.3 volts all the time might keep it from hanging up but it probably will cut down on the usable life of the motor.  When i took one of the bad fan motors apart it had grooves wore in the commutator and the contacts were getting squeezed in the groove and stop running, thus the tap starting it again.  If you are wondering about how close the sensors are in temperature i am using the new sht31s that are very close in temp and humidity. I am going to let the davis fan run for now to see if it fails anytime soon.

[CW2274]

Thank you.
Just so folks know, I run my fan full bore @67cfm, so cutting voltage is not necessary, (at least for me) just don't seal off around the sides of the fan or you may get a back pressure issue, especially with stronger fans like mine.

[WxLover16]

For the first time I took 1 battery out yesterday evening and this morning before work (530am) I checked to see if the fan would be audible and it was (although just barely but sounded the same as with 2 batteries in) and I just checked when I got home just now and the sound isn't anymore discernible than it was with both batteries in. Just wondering, does it detect automatically a battery is out so it can give more aspiration rate in the afternoon? Also, is the difference of 1 battery versus 2 so insignificant that you can't tell a difference in the sound of the fan?

[CW2274]

For the first time I took 1 battery out yesterday evening and this morning before work (530am) I checked to see if the fan would be audible and it was (although just barely but sounded the same as with 2 batteries in) and I just checked when I got home just now and the sound isn't anymore discernible than it was with both batteries in. Just wondering, does it detect automatically a battery is out so it can give more aspiration rate in the afternoon? Also, is the difference of 1 battery versus 2 so insignificant that you can't tell a difference in the sound of the fan?

It's been a while but iirc with the ISS in the sun going full out with NO batteries in, then placing ONE in, cut the fan's power by 20%ish, guessing by sound.

[WxLover16]

For the first time I took 1 battery out yesterday evening and this morning before work (530am) I checked to see if the fan would be audible and it was (although just barely but sounded the same as with 2 batteries in) and I just checked when I got home just now and the sound isn't anymore discernible than it was with both batteries in. Just wondering, does it detect automatically a battery is out so it can give more aspiration rate in the afternoon? Also, is the difference of 1 battery versus 2 so insignificant that you can't tell a difference in the sound of the fan?

It's been a while but iirc with the ISS in the sun going full out with NO batteries in, then placing ONE in, cut the fan's power by 20%ish, guessing by sound.

I suppose taking 1 battery OUT is a middle ground situation. Not as powerful as no batteries but slightly better than with both IN. Just very hard to detect the difference. It sounds about the same, but again I suppose the difference is perhaps too insignificant to discern. How much could one battery being OUT help to improve daytime temp accuracy, maybe .5F with full sun, if that?

[CW2274]

For the first time I took 1 battery out yesterday evening and this morning before work (530am) I checked to see if the fan would be audible and it was (although just barely but sounded the same as with 2 batteries in) and I just checked when I got home just now and the sound isn't anymore discernible than it was with both batteries in. Just wondering, does it detect automatically a battery is out so it can give more aspiration rate in the afternoon? Also, is the difference of 1 battery versus 2 so insignificant that you can't tell a difference in the sound of the fan?

It's been a while but iirc with the ISS in the sun going full out with NO batteries in, then placing ONE in, cut the fan's power by 20%ish, guessing by sound.

How much could one battery being OUT help to improve daytime temp accuracy, maybe .5F with full sun, if that?

No idea, that's why I chose no batteries. I wanted it running as fast I could in the day.

[jerryg]

You have to keep in mind that the circuit for charging the batteries and running the fan is pretty simple. During the day the fan is running off of the solar panel and the batteries are not in use but are being charged through a current limiting resistor circuit along with a series diode that is reversed biased when the solar panel is putting out voltage so acts like an off/on switch. When the voltage from the solar panel drops below the battery voltage the diode turns on and the fan is then running off of the batteries. The solar panel can output only so much current and when charging the batteries in the am there is less voltage available to run the fan but as the batteries charge up and use less current the fan gets more voltage and runs faster. The fan circuit from the solar panel has a low value series resistor in series with the lead , which is to isolated the solar panel from the charging batteries, and limits the max voltage to the fan do to voltage drop across that resistor. I measured the voltage on the fan in full sun after the batteries had most of the day to charge and it showed 1.9 volts. The fan never gets the full output of the solar panel. Having two batteries is to double the power available to insure the fan can run all night.  This is important as the day's get shorter which means less time to put a good charge on the batteries. 

[CW2274]

Outstanding explanation! 

[WxLover16]

Outstanding explanation! 

I agree! Apparently Jerryg REALLY knows his stuff wrt the electronics on the VP2. That was very awesome to read! Do you think that being in the south (both of us), that we should still get enough sunlight in the winter (with shorter days) to charge a battery enough to last the whole night?

[CW2274]

Outstanding explanation! 

Do you think that being in the south (both of us), that we should still get enough sunlight in the winter (with shorter days) to charge a battery enough to last the whole night?

Can't speak for you, however I damn sure know I do. 

[jerryg]

Down here in southeast texas we get too much lol. I use ac power for my stations now, just like having consistent power to the fan. Getting a good charge on the batteries is important, that is why you need to be sure that your batteries are in good shape. Batteries in good shape will charge better and hold that charge longer than those that have been charged and discharged a lot. Nicads have a certain number of charge/discharge cycles before they get to a point where they are charging up full less and less till they just don't last long and die at night when they are being used. If i lived further north and had the real short daylight hours and wanted to get as much run time at night i would put in fresh batteries  when the daylight started getting shorter and save the removed batteries to use when the days got longer.

[CW2274]

I use ac power for my stations now, just like having consistent power to the fan.

Amen.

[WxLover16]

Outstanding explanation! 

Do you think that being in the south (both of us), that we should still get enough sunlight in the winter (with shorter days) to charge a battery enough to last the whole night?

Can't speak for you, however I damn sure know I do. 

CW2274, please check your PM's. Thanks

[ct]

I think running the fan on 2.3 volts all the time might keep it from hanging up but it probably will cut down on the usable life of the motor.

For the past 4 months I've been running a Jameco motor in my VP1 FARS at 3.0v (1900 RPM) during the day and 2.2v (1400 RPM)  during the night.  No problems so far.  The fan is powered by a LIPO battery which get solar charged during the day and has enough capacity for approximately 3 nights of power.  Battery reaches full charge by about 1PM in winter.  A hall effect sensor is used to monitor the fan speed and reports through my sensor gateway, so I will know if the fan has failed.

[jerryg]

That's good to know i am using the same motor in my davis set up, gives me hope it won't crater too soon.

[WxLover16]

I think running the fan on 2.3 volts all the time might keep it from hanging up but it probably will cut down on the usable life of the motor.

For the past 4 months I've been running a Jameco motor in my VP1 FARS at 3.0v (1900 RPM) during the day and 2.2v (1400 RPM)  during the night.  No problems so far.  The fan is powered by a LIPO battery which get solar charged during the day and has enough capacity for approximately 3 nights of power.  Battery reaches full charge by about 1PM in winter.  A hall effect sensor is used to monitor the fan speed and reports through my sensor gateway, so I will know if the fan has failed.

Another VP1 still running! How long have you had yours for?

[ct]

Another VP1 still running! How long have you had yours for?

12.5 years, still with original sensors.  I've added a SHT31 on a small breakout board into the FARS to compare it with the original analog temperature sensor and the readings are virtually identical.

[CW2274]

I think running the fan on 2.3 volts all the time might keep it from hanging up but it probably will cut down on the usable life of the motor.

A hall effect sensor is used to monitor the fan speed and reports through my sensor gateway, so I will know if the fan has failed.

Ha, if you remember, I tried to get you to explain to me how this set-up works, but I ended up  , so that's when I decided on the a/c route. My solution is much easier, at least for me, but yours is more fun.

[CW2274]

Another VP1 still running! How long have you had yours for?

12.5 years, still with original sensors.  I've added a SHT31 on a small breakout board into the FARS to compare it with the original analog temperature sensor and the readings are virtually identical.

Wow, after all theses years, that's remarkable. Just don't expect the ole' boy to keep up with the 31 in extremes. 

[WxLover16]

Another VP1 still running! How long have you had yours for?

12.5 years, still with original sensors.  I've added a SHT31 on a small breakout board into the FARS to compare it with the original analog temperature sensor and the readings are virtually identical.

That is hard to believe and amazing! You must have got a very accurate (not to mention long lasting) original sensor.

[jerryg]

I was thinking the same thing, every humidity sensor i have read about has a certain percentage of drift per year.