Wire gauge in J-box and post large enough?

[Martin Amada]

Here's a question for the electrically minded.

I've been doing some rewiring of my J-box. I added a panel mounted fuse, an on/off switch and a voltage level meter. Then I started wondering about the gauge of the wire I am using.

When I bought the (electronic keyboard) connectors and the conductors that attach the J-box to the sled and run up the post, the electrical technician who sold them to me said they would carry 12 volts that distance, even though the wire is only about 24 gauge in my estimation. The wiring I am using in the J-box is about the same or perhaps a little larger, maybe 22.

I know there are formulas for this and that much depends on how many amps are being pulled. Do I have any reason to be concerned now that  I'm using a motorcycle battery for power? The number of amps pulled are a function of the device being powered, and not the power supply, right?

I should mention I have no plans to use anything on my sled requiring more than 12 volts.

Martin

[Charles King]

Unfortunately I'm not a electronic know-how. Hopefully someone else will answer.

[David L. Holmes]

Your worry is Amps, not so much voltage.  Add up the current draw of everything you intend to run with your battery (lights, LCD monitor, camera, wireless system, etc) then look up the max current that your gauge wire can handle here: http://www.gadgetjq.com/wiring_size_guide.htm

You should also install a fuse as close to your battery as possible that is rated to 50% of your max current draw.  A dead short in your system will cause a battery to run at maximum current, and a motorcycle battery can put out HUNDREDS of amps!

Hope this helps, good luck and stay safe!

[Martin Amada]

Thanks David.

How can I find out what my devices are drawing? What is my monitor likely to draw for example? For the most part I won't be using anything but that and perhaps the follow focus, which consists of an R/C servo and receiver, and for which I would add a voltage reduction circuit at the top of the sled. (And maybe a wireless transmitter.)

[David L. Holmes]

If you have the specs that came with the manual for your LCD monitor  you can get a ball park estimate of what you will be running.  For the home-built stuff, you have to measure the current draw yourself.  Cant get to technical here about how to wire a meter in series with your battery, just search online for help, or get someone you know to help you.

From the looks of everything you have, 22 or 24 gauge wire wont be heavy duty enough.  You could still use the wire you have, just double up on the leads, that would help in allowing a higher current draw.  When in doubt, go bigger 

Dave

[Tom Frisch]

You need an Ammeter to check the amperage in a circuit.
This web page explains and has a drawing:
http://www.allaboutcircuits.com/vol_6/chpt_2/5.html

You can get a digital multimeter that measures current for $30 at radioshack.
http://www.radioshack.com/product/index.jsp?productId=2103176&cp=&fbc=1&kw=multimeter&y=7&x=12&pg=1&f=PAD/Product+Type/Digital&searchSort=TRUE&s=A-StorePrice-RSK&fbn=Type/Digital&retainProdsInSession=1&parentPage=search

Also, make sure the fuse in your ammeter is big enough to not blow
when you hook it up to your equipment.

[Michael Suchar]

Martin, you may want to consider a re-setable (push button type) breaker instead of a fuse that would have to be replace everytime it blows. Re-setable breakers are inexpensive and easy to find. I paln on using one in my J/D boxes.

[Martin Amada]

Michael, that's a good idea. The only problem is I have already had the holes drilled in the box for the new parts, so I don't have a lot of leeway to make changes at this point.

I've decided that next week I will hand the whole thing over to the guy who usually does my electrical work. He'll know the right right gauge wire to use and he also makes better solders joints than I can. Maybe he'll have a resettable fuse that is the right diameter!

Thanks for the tips everyone. I should have some pics by around this time next week.

Martin