Wire size for current?

[Hsnopi]

Hello Again all,
I'm the crazy guy wiring up a tank. With all of your help I got the radio working. Thanks!
Next, I need to wire the tank up with cable. I was wondering if I could use home 12/2 wire or 14/2 but I'm not sure how to calculate the rating. One alternator will put out 12v, the other will put out 24v. Not sure on the amperage but the 24v will run the radio, which pulls about one-two amps, and then the elevation gun which pulls 20. The alternator may put out up to 80 amps but only 24v. What is the math here?

The idea was to use the 12/2 yellow home wire for the 24v system and the 14/2 white wire for the 12v.
Thoughts?

Thanks!
Jeff

 

[Bluejets]

12 gauge around 20 amp and 14 gauge around 12-15 amp but depends on your route length of cable.
At low voltages the cable resistance becomes rather important.
One can find the cable.... voltage drop per amp meter.... in cable size tables (not really familiar with gauge sizes as we use mm2 in Aus.)

 

[Hsnopi]

Excellent, thanks. I think I have a lot more research to do.

 

[Tha fios agaibh]

Best to use twisted pair cable.
The advantages are the flexibility of the stranded wire and mitigation of EMI interference that can put noise on sensitive equipment.
The wire size is determined by the load, not the amount your supply is.
You can feed up to 20 amps on 14awg wire (depending on temperature).

If you want you can even make your own twisted cable by putting two individual wires into a vise at one end, and the other end of the two wires into the chuck of a drill motor. Just make the wires almost twice as long, because it will shrink that much as you twist it with the drill motor.

 

[Hsnopi]

fantastic thanks

 

[shrtrnd]

You're overhauling a tank.
Tha fios agaibh is probably right that 14 gauge will work for your elevation, but why chance it and then have to go back and rewire it again later.
A bunch of guys get funny and take rides on the barrel and your 20 amps is going way up. (The wire heats-up and the insulation breaks down)
I'm no expert on operating a tank, but I'd be leery about using 12 gauge for turret functions.
Do your calculations and determine what you need.
If this was me, I wouldn't look at anything less than 10 gauge for any tank turret function operations.
Any ex-tankers out there who know what ought to be used?

 

[Tha fios agaibh]

A good rule of thumb is to oversize wire by 125% of the motor circuit full load.
The important thing is to fuse circuit to protect the wire. So if it draws more than 20amps, it will just blow a fuse.
I was assuming his 20a number was full load current, not the normal operation draw measured with an ammeter.

 

[Hsnopi]

we don't know actually. The guy who owned/worked on the tank before did a hell of a number on it. The motors that turn the turret are unknown amperage. I need to get it taken apart and look. The elevation motor may be shot but I think it's 24v as well. Not sure. We're trying to unfreeze it right now and just get the manual elevation going for the event at the end of January.

 

[Harald Kapp]

Here's a rather complete table of wire gauges and current limits. Select from this table to minimize waste (in terms of copper weight and price). For a worst case safety margin, use the wire gauge next to the one you absolutely need acc. to the table.
Example: for 15A power transmission the table tells you to use AWG 10 wire. Use AWG 9 instead for some reserve,

For wiring in a bundle use the "max. amps for power transmission", for wiring in free air (where the wires can be better cooled) use the "max. amps for chassis wiring"

 

[Tha fios agaibh]

Here's a rather complete table of wire gauges and current limits. Select from this table to minimize waste (in terms of copper weight and price). For a worst case safety margin, use the wire gauge next to the one you absolutely need acc. to the table.
Example: for 15A power transmission the table tells you to use AWG 10 wire. Use AWG 9 instead for some reserve,

For wiring in a bundle use the "max. amps for power transmission", for wiring in free air (where the wires can be better cooled) use the "max. amps for chassis wiring"

That is for high frequency power transmission and 100% skin depth.

The National electric code say 14 awg is good up to 25amps provided all terminations are rated at 90c and ambient 30c. Usually terminals are rated at 75c so that would limit it to 20amps.

BTW, 9awg wire is not really on the market. Available sizes are #10 or #8.

 

[Hsnopi]

Fantastic, thanks.

In addition, to travel a distance, is it better to have higher amps or higher volts? My thought is amps. I ask because we have a 12v system off an alternator and I'm using a 12 to 24v up converter. So the upconverter would be better placed closer to the destination than source, yes?

 

[Tha fios agaibh]

Fantastic, thanks.

In addition, to travel a distance, is it better to have higher amps or higher volts? My thought is amps. I ask because we have a 12v system off an alternator and I'm using a 12 to 24v up converter. So the upconverter would be better placed closer to the destination than source, yes?

The higher the voltage, the lower the current necessary for the same power.
So higher voltage requires smaller wire because less amperage is used.
This is why transmission lines carry hundreds of thousands of volts.
So putting your boost circuit near the source would allow smaller wire to be used. Remember to size wire ampacity larger than the full load current to allow for start up current. So, although 14awg would work, I'd use 12awg to be on the safe side.

 

[hevans1944]

Probably too late now, but did anyone think about increasing the DC voltage from the alternator to 24 VDC? Probably not compatible with your other stuff at this point in time...

Yes, do as @Tha fios agaibh suggested and put the up-converter close to the source of power but use adequately sized wire from there to the load.

 

[Sadlercomfort]

I would love to see some pictures of this tank

 

[Tha fios agaibh]

I would love to see some pictures of this tank

Me too. Primarily the inside.
Cool stuff!

 

[Hsnopi]

Well the alternator is a 12v. Unfortunately I can't post pics of the tank until March. In fact, I was informed today I'm not supposed to discuss this in detail until March. So I have to somehow remove the specifics other than to say "tank". However, I WILL post pics once allowed. Stupid contracts.