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Current draw on dew strips

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#1 Jack160219

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Posted 20 September 2020 - 08:24 AM

Hi,

  I got tired of my power tank running low when running 2 dew-not strips on my SCT, so I bought a ac -dc 12 volt transformer rated at10 amps. 
on my first night, I noted that my thousand oaks controller was blinking as soon as I plugged it in, indicating a drop to lower voltages,and no heating occurred. Anyone know why this occurred? The transformer was plugged into a 15 amp circuit. How many amps do the strips draw on full dial on the controller?  Thanks ahead. Jack



#2 Napp

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Posted 20 September 2020 - 08:29 AM

Check the voltage from the converter under load.  The Thousand Oaks controller is designed to turn off below a defined supplied voltage to protect discharging a battery too much.  The controller documentation should describe this. I suspect your converter is not supplying voltage above that cutoff.



#3 michael8554

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Posted 20 September 2020 - 09:20 AM

The 8" SCT Dew-Not is rated at 1.2 Amperes.

So two like that should be no problem for your 10 Ampere power supply.

So sounds like Napp's suspicion is correct, that the power supply is wimping out.



#4 Napp

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Posted 20 September 2020 - 09:29 AM

I looked up the Thousand Oaks controller.  Here’s the interesting part”

 

“BATTERY SAVER: Have peace of mind when using your vehicle battery, knowing that you will always have plenty of charge left to start the engine. Unit automatically turns off if voltage drops below 11.1v. At 11.25v green LED begins flashing indicating unit will turn off in approximately 30-60 minutes. With our advanced energy saving circuitry, most users can get a complete observing session without needing to start engine to recharge battery. The battery saver function can be turned off when using a dedicated battery. (Factory default =on)”

 

So it looks like you can turn off the battery saver function.  There should not be a problem running the controller and heaters off the converter.  Try it.


Edited by Napp, 20 September 2020 - 09:30 AM.


#5 scopewizard

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Posted 20 September 2020 - 09:54 AM

Many of these power supplies are rated at 12.2 vdc with no load. They (brick types) often have a 5% drop under load which can equate to 11.7 vdc. I use a 15 amps power supply set to 12.50 vdc which under 4 amps load drops 0.05 vdc.

 

All of these power supplies should not be operated for long periods above 50% of the rated amperage. If you buy one, make sure you can adjust the voltage by 10% with a rating close to 3x the continuous load.



#6 John Fitzgerald

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Posted 20 September 2020 - 10:11 AM

https://www.amazon.c...t/dp/B083LJNJNH

 

This will monitor your voltage and current draw.  I have one inline between the battery and load.  I fused it on the battery side.



#7 Jack160219

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Posted 20 September 2020 - 10:25 AM

I should have added that the blinking started even after using 2 dew strips, total draw of no more than 3 amps per the dew-not website. My ac-dc transformer is rated at 10 amps. So I can’t believe just this load dropped the voltage to below 11.5 V. Or is it? 



#8 Napp

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Posted 20 September 2020 - 10:30 AM

What is the stated spec for voltage?  Especially if this is a cheap converter I’m not surprised at all by the voltage drop.



#9 Jack160219

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Posted 20 September 2020 - 10:42 AM

I think with these issues ,I might go with a moderate deep cycle battery rated at 65A/hr. Hopefully this should do it just for dew strips. The transformer didn’t give the internal resistance number as a spec so I can’t calculate the V drop.  It would be easier though to have a good ac/dc transformer, has anyone bought a transformer that doesn’t show this drop?  The one I bought was on amazon, which I returned.




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