12 volt extension lead?

[michaelmorris]

Mrs M and I have recently blown all our savings on a motorhome. We plan to have loads of long weekends away, many of which will be in rural sites with lovely dark skies.

I’ll be packing my Astrotrac and DSLR and hoping to get some nice widefield shots with camera lenses.  My present Astrotrac set up relies on a large and heavy lead acid battery pack for powering the camera, Astrotrac and dew heater.  The battery pack is very heavy and bulky and I’d rather not lug this around in the motorhome. 

The motorhome has an external 12 volt output so it should be easy to power the rig from the motorhome’s 65Ah leisure battery.  The problem is that I anticipate that on many campsites I may need to site the Astrotrac many metres away from the motorhome to get a good view of the sky.    An easy solution to this would be to have a very long (10s metres) 12v extension lead.  Am I likely to get a significant loss in voltage along such a long lead carrying 12 volt DC current?

PS I know that an obvious solution is the buy a Lithium battery pack (such as a Tracer), but having blown all our money on the motorhome, there is preciously little money left in the kitty at the moment.

[christhebrit]

^{I do believe so.}

^{I did stuff with electrics a while ago, but one thing I do remember.}

^{DC cables are usually thicker than AC in order to provide less resistance. (different currents act differntly)}

^{you can give it a go by adapting some loudspeaker cables before buying more cables if you have some.}

^Chris

[Astroboffin]

Hi,

Not sure if this will help, but I run 12v from a bench supply, which puts out 13.8v, and my astro kit is 10m away, and the voltage at the pier is 13.3, so a loss of 0.5v, the cable I use is a normal household mains Twin and earth cable, buried in a conduit.

So if you want to run say 30m in theory you should be ok, although I would guess that the longer the cable run the faster it will drop voltage, but at 30m if it drops 1.5v then that will still give you 12.3v from a bench supply.

it may be different from a leisure battery, as they may not give 13.8v to start with though.

Hope that makes sense

AB

[Astroboffin]

You may find this useful too, as I did

http://www.calculator.net/voltage-drop-calculator.html

Regards

AB

[astrofox]

Get some wire rated at 5 amp to make up your extention. Generally my kit takes 2 amps max. But I dont festoon it with dew heaters all over the place.

[rob0971]

Over 10m you will get a fair drop in voltage unless you use a very large cable. A lot of astro gear gets a bit funny if the voltage drops below 12v. Use the voltage drop calc as suggested above.