How long is the wire, and how much of a voltage drop can you tolerate? According to the table here: http://en.wikipedia.org/wiki/American_wire_gauge , 22 ga. copper wire will melt with 41A struggling to flow through it.
A rough estimate shows you are going to drop about 0.56 volts across a 22 gauge wire at that amp and voltage. That looks like one foot of wire would generate about 20 watts of heat, which doesn't sound safe to me. If I were you, I'd definitely go to thicker wire, but I don't know how much thicker would be considered safe. Much depends on your length of wire, as Phil suggested, and also the ambient temperature. In short (no pun intended), that's a lot of current you're running through that wire.
Surely this is the peak temporary current you anticipate. (Just what are you building, and how are you switching that?). Even the cables going to your car's starter motor would be undersized if they had to continuously carry that peak current (>100A in some cases).
After seeing the table to which Franklin linked, I'd say more like solid copper rod. Got any old fallen-down barns nearby? Some of them have old lightning rods laying around.
15 amp house wiring uses #14 wire and gets slightly warm with 15 amps through it for any length of time. I would suggest a minimum of awg 12 for 35amps. AWG 10 would be even better.
A few years ago, while building the LED Light Beams for a big store in New York, we used several 24v/13A power supplies for the burn in racks. We loaded each power supply with 8 beams which drew 1.1amps each, so 8.8 amps total draw. The 8 beams were connected to a breakout board which was connected to the power supply with 2 sets of 18 AWG feed wires. The length of the feed wires was 18". In that setup, after running for 24 hours, the wires would be warmer than room temperature, but not warm enough to be of any concern. For 18 AWG, you typically rate 16 amps, so for two we were at 32 AMP capacity (4 times our actual usage). For 35A, I would use 12 AWG or two feeds of 14AWG.
Another thought to keep in mind is your connectors. Our customer supplied the original setup for the first batch of complete 6.5 amp beams (consisted of 5 sections of the beams mentioned above and a shorter one. It also used a 40A power supply broke out to 5 beam units) and stated that doubling the wires into a single connector was well within the current load. However, after 11 hours worth of burn-in time it was proved otherwise. After my investigation for the safety report write up, I found out the connectors they used were rated for 10 amps max and we had 32.5 amps getting shoved down it's throat. Luckily, the trace on the board acted like a fuse and stopped the current before any major damage occurred. That setup is the picture attached and the result is the other picture. After that incident, we separated the feed lines to individual connectors and used 4 feed lines to two breakout boards for the 5 beams. The customer isn't always right and they were a little shocked at how they missed the rating.
yes, it was a very fun, interesting, and challenging project.
What are the distances? ... Even if your distance was 1 foot (2 feet round trip) from your power source to your load, with a 34.5A load and using 12 Gauge, you would need to dissipate 7.8 Watts of heat over that 1 foot distance. With a 10 Gauge that drops to 4.9 Watts. The difference in cross section circular mils between 12 Gauge (6530cm) and 10 Gauge (10380cm) is almost half, So doubling up on the 12 Gauge (13060) would be slightly better than the 10 Gauge alone.
Also, consider the voltage drop. A 5V drop in a 120V circuit may not be a huge deal. But a 5V drop in a 24V circuit is much more significant. And the voltage drop is strictly current-dependent, regardless of the driving voltage.
davidsaunders
Posts: 1,559
Comments
-Phil
BOOSTER CABLES!
Surely this is the peak temporary current you anticipate. (Just what are you building, and how are you switching that?). Even the cables going to your car's starter motor would be undersized if they had to continuously carry that peak current (>100A in some cases).
Have a gander at the motors & controllers at http://www.electricscooterparts.com and http://tncscooters.com
After seeing the table to which Franklin linked, I'd say more like solid copper rod. Got any old fallen-down barns nearby? Some of them have old lightning rods laying around.
Another thought to keep in mind is your connectors. Our customer supplied the original setup for the first batch of complete 6.5 amp beams (consisted of 5 sections of the beams mentioned above and a shorter one. It also used a 40A power supply broke out to 5 beam units) and stated that doubling the wires into a single connector was well within the current load. However, after 11 hours worth of burn-in time it was proved otherwise. After my investigation for the safety report write up, I found out the connectors they used were rated for 10 amps max and we had 32.5 amps getting shoved down it's throat. Luckily, the trace on the board acted like a fuse and stopped the current before any major damage occurred. That setup is the picture attached and the result is the other picture. After that incident, we separated the feed lines to individual connectors and used 4 feed lines to two breakout boards for the 5 beams. The customer isn't always right and they were a little shocked at how they missed the rating.
yes, it was a very fun, interesting, and challenging project.
-Phil
Incandescent light bulbs are banned for sale in Europe: http://inhabitat.com/europes-incandescent-light-bulb-ban-begins-today
I heard one entrepreneur is selling them not as light bulbs, but "heating spheres". Ingenious loophole!