Question for the Electrical Engineers!

[Peter]

I have a hydraulic power pack to wire up to a 12v vehicle system.

The motor is rated at 1.8kw, which at 12 volts needs a 150 amp supply?

The power pack runs a tipper unit, so it will be run for 30 seconds at a time, and not too often.

What cable size should I be using, the online calculators I have tried say 50mm2, which seems a little on the large side. I am wondering if a low duty cycle means I can get away with a smaller cable.

At the moment I have a 70 amp fuse and 4.5mm2 cable, which is probably a little undersized but is all I had to wire it up at the time. It blew a 60 amp fuse, so I upgraded to the 70.

Thanks

 

[NeTree]

Your wiring "should" be 1.5x the FLA of the load, but let's assume 150A. You didn't specify the distance from the battery to the load, but I'll assume about 15 feet. That would mean "0" gauge wire, or 50mm2.

The short duty cycle means you could get away with smaller wire, but remember your wire should be 1.5x the FLA rating, but not less than 1x the FLA.

Go with the 50mm2 (8mm) and rest assured. Whether or not it's specified, you should also run a ground of equal size, also from the battery. Steel is a crappy conductor.

 

[Peter]

Yes, length of run is 5 metres max.

One more dumb question, is that 50mm2 the sum of both + and - cables or do both need to be 50mm2?

That size of cable seems to be easier to buy single core battery cables rather than a twin core.

 

[NeTree]

Both need to be 50mm2.

 

[Peter]

Cool, thanks.

 

[SkwerI]

In America would that be 6 gauge wire? Or 4 gauge? Halfway decent jumper cables are usually 8 gauge unless you get the high dollar ones.

 

[NeTree]

That would be 0 gauge.

 

[SkwerI]

Around here anything requiring that much power would be driven off a PTO. I'm assuming there will be at least two or three batteries hooked up in sequence to power this thing? My bucket truck has two batteries and the cables coming off the batteries are 4 gauge.

 

[Thor's Hammer]

Thats quite a small Hydraulic pack Brian. I've seen ones twice that size running off a single 12V battery, from the factory.

 

[lumberjack]

Duty cycle matters alot in that regard, Brian.

1.8kw= ~2.4hp. Similar to a dump trailer's power pack. Some winches have a 4.5+hp motor on them, but the duty cycle isn't continuous. The problem with smaller wire is voltage drop which increases the amp draw which increases heat build up in the wire.

 

[SkwerI]

My buddy Dave has an electric over hydraulic dump in his truck and the cables are 8 gauge I believe. My dump trailer will dump 14K lbs and it only uses 8 gauge wiring as well. Just how massive is this system that requires wiring 8x as heavy? You must be dumping 50K lbs!

 

[NeTree]

Your dump trailer wiring is also VERY short.

 

[lumberjack]

On my gooseneck dump trailer I have a 4 gauge wire running from each battery to ground, each battery to the solenoid, and two wires running from the solenoid (100 amp continuous) to the motor.

Maybe next year I'll put a PTO on the truck, that would be sweeeet.

 

[Thor's Hammer]

x8 as heavy? lost me there. The pack is half the size of the one in your picture, and dumps 2200lbs. 8mm wire is not that heavy.

 

[SkwerI]

Ed, my point exactly!!! Why would such a tiny dump motor require 0 gauge wire? That's ridiculously oversized and I'm not an electrician.

The heaviest wiring I have around here is the cable I use to hook my generator up to my house fuse panel next to the electric meter when the power goes out. According to Erik this isn't a heavy enough wire for Pete's application.

 

[Thor's Hammer]

I'm not sure about the gauge sizes, but 8mm is not that big at all. About $3 a meter.

 

[NeTree]

Brian, how many watts is your genny? Also, keep in mind AC wire sizing is different from DC wire sizing.

Regarding the wire gauge, you're assuming the best-case scenario that the motor will draw less than the nameplate. Sure, 10 gauge would probably run it just fine.

From an engineering standpoint, however, I have to assume that at some point, the pump could seize (maybe it didn't get used in awhile, something mechanical breaks and jams it, etc.) causing a locked-rotor scenario on the motor. The motor will then draw many more amps than normal. I have to size the wire according to this theoretical load because safety demands the fuse blow before the wire melts.

 

[NeTree]

I'm not sure about the gauge sizes, but 8mm is not that big at all. About $3 a meter.

American Wire Gauge doesn't line up with metric, really, but 8mm is about "0" gauge wire. And I agree, it's not that big, really. I work on systems fed with multiple 4/0 for each phase, and one system fed with 1" by 5" copper bars. Now THAT'S a shitload of juice.

 

[SkwerI]

Brian, how many watts is your genny?

6000 watts I believe.

 

[NeTree]

So, your genny is 50 amps, the rating of #10 copper wire. Bearing in mind also that this isn't a permanent installation, but a temporary hookup... it's code. (Assuming you also have the appropriate transfer switch also installed.)

 

[lumberjack]

Also the genny is at 10-20x the voltage of the pump, the higher the voltage, the lower the amperage for a given kW. You can shove 200hp+ (150kw) down near a mile of 10ga wire, at 4kv AC no problem. (Underwater ROV, Schilling Robotics)

 

[NeTree]

Yup; I can feed a 2 HP 480v/3 phase motor with 18 gauge all day. In fact, I do.



Then there's stator resistance, field flux density, cosine of phi, power factor... oh yes, we could go on.

 

[Al Smith]

It's a short duty cycle so you could down size the wire .Were it I ,I'd use 4 gauge welding cable though .

Duty cycles are a little goofy when you deal with the code .Like you can way over fuse branch circiuts used on welders as one example .

The big problem with undersizing wire even on short duty cycles is not the fact you might burn it in two .It has more to do with the fact that with a large load the resistance factor goes up exponetually .It's kind of like putting 10 pounds of chit in a 5 pound bag .When you are dealing with 12 volts any resistance becomes a true head ache .

 

[NeTree]

Resistance = heat.

 

[NeTree]

It's a short duty cycle so you could down size the wire.

Is it still a short duty-cycle if the solenoid contacts arc closed?