Sizing electrical wire 12V

Nick Zentena · Apr 22, 2005

I picked up a couple of fans and a battery today from the surplus store. I didn't buy any wiring because the guy told me I could use what I have [24 gauge] The two fans total 1.5 amps and I figure about 10 feet round trip. Now I just did a little searching and it seems I need thicker wire. Is that right? The leads on the fans are even thinner then the wire I have.

jimgalli · Apr 22, 2005

Are these going to be "hard wired" in as permanent fixtures like a vent fan in a bathroom? If so, yes you do. What drives the wire size in that case is the circuit breaker at the far end that turns that circuit off. If it's a 20 amp breaker you need #12 wire. If a 15 amp breaker you need #14 wire. If you're simply plugging them into an existing household outlet, any old zipcord is fine. 24 sounds a little light perhaps.

Lee L · Apr 22, 2005

jimgalli said:
Are these going to be "hard wired" in as permanent fixtures like a vent fan in a bathroom? If so, yes you do. What drives the wire size in that case is the circuit breaker at the far end that turns that circuit off. If it's a 20 amp breaker you need #12 wire. If a 15 amp breaker you need #14 wire. If you're simply plugging them into an existing household outlet, any old zipcord is fine. 24 sounds a little light perhaps.

When plugging 1.5A 12VDC fans into the wall (assuming the 120VAC North American standard), I'd suggest using the thinnest possible wire you can find. It will then act as a fuse and if it melts quickly enough, may protect the fans.

Lee

Calamity Jane · Apr 22, 2005

With low voltage direct current the concern is voltage drop.

The best and cheapest wire for 12 volts is sold at places like Canadian Tire or your local trailer parts dealer and is used for trailer wiring. It is usually available in 1, 2 3, and up to 5 conductor and can be "unzipped" into smaller groups.

Don't pay any attention to the small wire size on the fan - they didn't worry about voltage drop over a few inches.

Don't forget that lead-acid batteries product hydrogen gas if charged rapidly so make sure you have ventilation - wouldn't want ya to go BOOM!

John Cook · Apr 22, 2005

Hello Nick,

Jim is absolutely correct about the wire gauge for household amperage.

However, your 12 volt battery setup is a little different. You will have 12 volts, 1.5 amps and 18 watts. (Multiply amps times volts to get watts.)

Check out the American Wire Gauge table on this website: http://www.powerstream.com/Wire_Size.htm

It calls for a minimum wire size of 20 gauge for your amperage. Your 24 gauge wire is rated only for 0.577 amps. I would allow for a margin of error and go with the popular 16 or 14 gauge.

I was an electronics technician in the US Coast Guard. Just another example of your tax dollars at work. ;0)

Nick Zentena · Apr 22, 2005

So what guage do I need then? :confused:

Jane this place seemed cheaper then Canadian tire. Most of the stuff was even new -)

It's a sealed battery is it still going to vent? Not much of an issue I can take it outside to charge. I figure the battery will only need charging about once a year. It's a wee bit bigger then the load really needs.

Nick Zentena · Apr 22, 2005

Thanks John. I'll see if I can find something like 14 guage for a little extra safety.

titrisol · Apr 22, 2005

Nick, if you can go with gauge 16 (used in auto-wiring).

Donald Miller · Apr 22, 2005

Nick Zentena said:
I picked up a couple of fans and a battery today from the surplus store. I didn't buy any wiring because the guy told me I could use what I have [24 gauge] The two fans total 1.5 amps and I figure about 10 feet round trip. Now I just did a little searching and it seems I need thicker wire. Is that right? The leads on the fans are even thinner then the wire I have.

Considering your stated amperage and DC voltage, you'll be fine with 20 guage wire

jimgalli · Apr 22, 2005

Thanks for not being too rough on me....I missed the 12V in the title:~)

Lee L · Apr 23, 2005

jimgalli said:
Thanks for not being too rough on me....I missed the 12V in the title:~)

Jim,

Hope you took my response as intended, just a little light-hearted teasing. It was obvious to me that you'd just missed the header and mention of the battery, but I couldn't resist doing the joke, however lame. Can I claim this as a momentary lapse after showing restraint by never once having risen to Scarpitti bait?

Normally, I would have added something constructive, like an answer to the question, but I was literally logging off to head in to work at the time.

And keep posting the 240 G-Clarons. One of these times you'll hit me when I have the funds available.

Lee

John Cook · Apr 23, 2005

Hey Jim,

Anyone who backs over small trees in his Bubba truck can't be all bad. Got to cut you some slack, as you're one of us!

Donald Qualls · Apr 26, 2005

No, your sealed, aka gel-cell battery won't vent, unless you seriously overcharge it and pop the safety pressure release. That, and their low cost compared to NiCd or NiMH, are why they're used for things like emergency lighting and similar indoor applications.

If the electronics tech says you can use 20 gauge for a single fan, and 16 or 14 for the combined load, then any larger wire size (smaller number) will also work. As suggested, if you're going to be drawing 3 amps through the main wire (1.5 A times two fans, wired in parallel), you should certainly have something heavier than the 24 ga. that the fans use for their final pigtails. You should also include a fuse in series with the combined load, preferably about a half amp higher rating than what the fans will draw (so in this case, about 3.5 amp) -- that way, if something shorts, it'll blow the fuse instead of burning the insulation off the wires (a car battery can melt 4 gauge jumper cables, and even a gel-cell is capable of delivering more than enough current to melt pretty heavy copper wire, though your solder joints, if used, will melt first -- but the insulation will burn before solder melts, and it's pretty stinky stuff).

Nick Zentena · Apr 26, 2005

Actually the combined is 1.5 amps. Each is 0.74 but close enough to 1.5 amps. I picked up 20 feet of 14 gauge wire for less then $2.50. The smaller wire wouldn't have saved enough to matter. Right now I've got everything but the bulbs and the wood. When I went to order the bulbs they were having one WEIRD phone glitch.

I was thinking about a fuse but wasn't sure how important it was. I added a switch so I can leave the fans on intially to let the bulbs warm up.

Now to just twiddle my thumbs while I wait for bulbs.

Jon Shiu · Apr 26, 2005

Nick Zentena said:
So what guage do I need then? :confused:

Jane this place seemed cheaper then Canadian tire. Most of the stuff was even new -)

It's a sealed battery is it still going to vent? Not much of an issue I can take it outside to charge. I figure the battery will only need charging about once a year. It's a wee bit bigger then the load really needs.

Hi, joking aside, a battery needs to be kept near full charge, but not overcharged, to prolong it's life. Also it would self-discharge just sitting there.

Jon

Donald Qualls · Apr 28, 2005

Jon is correct -- the proper way to maintain a gel cell is to keep it on a low-current trickle charge continuously. I'd have to look it up to confirm, but what I recall is 1/100 of the battery's amp-hour rating is a good value for the trickle, so if you have a battery rated at (say) 20 amp-hour, trickling it at 0.2 amp would be just right for continuous maintenance. Better still is a charger with a sensor that will start and stop based on the battery's terminal voltage, but this is serious overkill for surplus gel cells -- the charger would cost you about $80, and you can replace the battery every 2-3 years for $20 a pop, most likely (if you're buying surplus, that is). Even a 0.1 amp trickle would probably be adequate in the low draw usage you envision; trickle charging in this range and not running the fans long enough to discharge the battery below, say, 80%, you should get a life of four or five years from a gel cell.

Nick Zentena · Apr 28, 2005

Dead Link Removed

That's the battery I got. Cost a little more then $10 US. I think I paid $14 Canadian. It's rated for main power which I think means it can handle charge/discharge.

Calamity Jane · Apr 28, 2005

I hate to contridict but a gel-cell, any lead-acid battery, should (ideally) be charged with a current-limited, voltage-regulated charger. A constant curret "trickle charger" is more suited to Ni-Cad batteries.

If the voltage is not limited, the battery will bubble and loose liquid over time. Voltage on a 12 volt group is normally limited to 12.8 to 13.4 volts. The (charge) current is normally limited to 1/10 to 1/3 of the rated capacity.

I have a number of gel-cell batteries that are pushing 30 years old and still truckin

BTW: I am a designer with a major electrical utility. Batteries and d.c. wiring are somewhat familiar to me ;-)

Nick Zentena · Apr 28, 2005

Canadian tire was nice enough to put a charger on sale this week. It's nicer then my old one so I picked it up. It includes a 2amp mode for small batteries and settings for sealed batteries.

Sizing electrical wire 12V

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