Dew heater power consumption?

[Tiki]

I appreciate that my question is a bit like asking 'how long is a piece of elastic', but roughly hower much power would it take to keep a 4" refractor objective clear under 'typical' UK conditions? I only need a ballpark figure to decide upon battery capacity.

[Jessun]

At full blast a dew strip that size draws around 0.7A, so if you have it on full blast then a typical 7Ah powertank drains in 10 hours. That's the theory, but in practice it will drain that battery quicker - you won't get every drop out of it, and it's generally cold, so the battery won't perform as in a test lab. So maybe 5 hours.

This is on full blast though, but these strips are pulse modulated, so they go on and off in pulses, and a little control box looks after that. I've been out in severely damp conditions with every surface covered in dew, still being fine using about a 50% setting to keep a SW120 lens clear. That means being back to around a whole 10 hours again fot that size battery.

But it all adds up when you start to connect mount, dew heaters etc! I bought a 7Ah powertank very early on, and it's the only buy I ever regretted in this business....

/Jesper

[Uplooker]

Curent = Voltage / Resistance

Power= Voltage x Current

Ian

[billhinge]

I use mains to connect mine and my 30A psu has voltage and current dials, according to those I once calculated 28W in another thread (with the controller and 2 strips - one for 11 SCT and finder)

[Gina]

The maximum I have for my dew heaters (for the ED80 and ST80 scopes) is 2A @ 12v ie. 24W but I've never yet required more than half power. So say an amp at 12v per scope.

[billhinge]

Sounds about right, think I used 13.8v as my voltage rather than 12v so that would explain the difference

[Tiki]

Thanks for these helpful replies. It gives me a rough idea of what i'll be needing capacity-wise.