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Thread: Dew Heater

  1. #1
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    Default Dew Heater



    A guy in my club came up with a project for making a dew heater & a four channel power distribution box that would cost about $45. Sounded like a fun project & a chance to work with some of the folks. Then it dawned on me, I have an Evolution and do not own a DC power supply. His project runs off 12v and the best the scope puts out is a 5v for a USB device. He said with a little work it could probably be redesigned for 5v. My concern would be the drain on the battery for a small heater.

    I was wondering if anyone out there may have used the USB port on this scope, for what kind of device, and what kind of drain they saw on the battery.

    Thanks

    Tony

  2. #2
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    Default Re: Dew Heater

    I would be a bit leery of running higher powered equipment from the mount.
    If you got one of these it would power your mount and a dew heater for a couple of sessions.
    http://www.harborfreight.com/3-in-1-...ter-62306.html
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  3. #3
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    Default Re: Dew Heater

    I'll put my $.01 of advice in. Notice I didn't say $.02 as my knowledge is limited compared to other members here.

    I have two dew heaters for my imaging rig. I too was going to build a controller box as the cost for a four port is expensive. While researching I came across two issues that were brought up by seasoned imagers.

    They commented that the manufactured controllers have pulse modulation instead of constant voltage which is not supposed to work as well. Also, if running the heaters off of the same battery that is controlling the mount, it could cause concerns with power interruptions of some sort.

    Now, I don't propose to understand exactly why or if this actually IS a problem but since it stuck in my head, I figured why chance it. So I purchased a separate li-ion battery for my heaters. It is very small and inexpensive. I also purchased the Thousand Oaks Controller.

    Now MANY members have built their own controllers and haven't heard too many complaints and you are not imaging so you should be okay. Just an FYI.
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    Default Re: Dew Heater

    Hmmmm, I wouldn't, dew controllers can take a lot of power, most USB outputs are only 500ma which is nowhere near enough, check it out first, or look here on my site for an idea of a DIY 12v power hub,
    www.ollyspages.co.uk
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    Default Re: Dew Heater

    The Evolution has a pretty low rated battery so I'd say no way is it worth it. Look at the power consumption required for the dew strip required for the size of your scope (if it's any larger than 6" it will take a reasonable amount! Get a separate battery - it's better that than a session ruined because you run out of power or under-powered for the dew system to work efficiently enough given the conditions.

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    Default Re: Dew Heater

    Here is one surefire method of controlling dew, though not one that comes highly recommended!

    Dew Control.jpg
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    Default Re: Dew Heater

    Quote Originally Posted by KT4HX View Post
    Here is one surefire method of controlling dew, though not one that comes highly recommended!

    Dew Control.jpg
    That does have the advantage of keeping you nice and warm though as well on those extra chilly nights!
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    Default Re: Dew Heater

    A bit hard on the dark adaptation though!
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    Default Re: Dew Heater

    I power the mount and heaters from 120V to 12V adapters and my heaters are DIY, but all heaters are the same in that they use resistance create heat. Much of it is wasted, but the goal is enough heat transferred to the glass/boundary air to keep the glass above the dew point. Commercial heaters might use film or tape rather than nichrome wire, but the problem and the math is the same for all designs. If you measure the resistance of a length of heater wire, or of a complete heater you use Ohm's law to calculate the initial draw on the power supply. This is the maximum current the supply will have to provide. After this start up peak, the resistive element warms up and the current decreases. But you should use a supply rated at more than the peak current draw.

    When you have a controller there is some added complication based on the type of controller. There are many sites with plans and information about dew heaters.

    The point made in a previous post about USB as a power source is a good one, even though more power is available from USB 3 and C and you can buy powered hubs, they are not going to work well for heating. The current draw for the same power output would increase by 2.4X.

    PWM controllers produce noise and the inexpensive ones at least create a variable load which might I suppose cause a problem for some mounts and some power supplies. Whether or not this is a practical concern I don't know.

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    Default Re: Dew Heater

    Yea I would not try to run dew heaters off a USB buss.

    One thing to consider is that all things being equal as the voltage goes down the current goes up. so 5 watts at 12 volts is .4 amps, at 5 volts it would be 1 amp

    Ive heard that running the dew heaters off a 'seperate' power supply is a good idea and there may be 'some' merit to that I run everything off one 12V battery with no issues. Though it is a monster of a battery.

    Here is a link to some dew heaters I built not to long ago.

    DIY Dew heater bands
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