12V Portable Ovens

frozenpod
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Re: 12V Portable Ovens

Postby frozenpod » Wed Sep 06, 2017 10:01 am

Pretty easy to run 2 x 2.5mm^2 wires to power it.

Ducky the marine travel buddy is 120W 10A I would upgraded wiring due to the cable run and voltage drop.



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XalFish
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Re: 12V Portable Ovens

Postby XalFish » Wed Sep 06, 2017 11:37 am

Mattblack wrote:Just for future reference, what would be the max wattage before the wiring and socket starts warming up...100W?


Depends entirely on what is in there already. It's pretty common to find 120W sockets (12 volts 10 amps), but some of the cheaper ones are not really up to the job. It also depends on the wiring.

At the risk of getting slightly technical, the wire heats up because it dissipates power. The power it dissipates is equal to I*I*R, where I is the current and R is the resistance of the wire. So at 10 amps, it's 10 x 10 x R = 100 x R. Thinner wire has a higher resistance per meter, so it dissipates more power and hence gets hotter. On the other hand, thicker wire has less resistance per meter, so it dissipates less power, and stays cooler.

This little equation (power = Ix I x R) tells us something else, too. Since it goes up with current squared, every time you double the current you get 4 times the power dissipation.

The other problem is voltage drop. Any time current flows in a resistance, there is voltage drop.

Let's say you are drawing 10 amps, and using 2.5mm^2 cable. It has a resistance of say 10 ohms per km. You have 5m of red wire and 5m of black wire to your socket, so 10m all up. The total resistance of your wire is 10 (ohms per km) * 0.001 (km per m) *10 (meters) = 0.1 ohms.

By Ohm's law, V = IR, so the voltage drop is V = 10 x 0.1 = 1 volt. That means that from your 12V battery, your socket is only providing 11V.

If you pull 20 amps, it becomes V = 20 * 0.1 = 2 volts, so now you only have 10V!

And then it gets worse. The crimp terminals, the wire connection to the socket, the fuse, the fuse holder, the socket itself, the plug on the equipment- these all add MORE resistance, and even more voltage drop!

Different equipment has different sensitivity to voltage drop, but eventually, stuff stops working. And because we're dissipating the power in the wire and the socket and plug instead of in the equipment, it all heats up.

All of this is related, and you can avoid all the problems by
- Running good quality, thick cable.
- Using the right crimps, etc
- Picking the appropriate socket. If you want to run 10A, don't buy a 10A socket, buy a 15A socket. That head room helps it run cool. There is less resistance, so less voltage drop and lost power.

Good fishing :)

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ducky
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Re: 12V Portable Ovens

Postby ducky » Wed Sep 06, 2017 12:37 pm

frozenpod wrote:Pretty easy to run 2 x 2.5mm^2 wires to power it.

Ducky the marine travel buddy is 120W 10A I would upgraded wiring due to the cable run and voltage drop.


Yeah marine buddy is 10A but thats a fair bit bigger than the unit it's being compared to. The travel buddy is 6A

Having said that all the above is true. Good work Xalfish
Fishing Victoria Species Comp: 317cm's

Redfin 50cm, Yellowbelly 44cm
Snapper 90cm, Rainbow Trout 37cm, Estuary Perch 31cm, Murray cod 65cm

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Mattblack
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Re: 12V Portable Ovens

Postby Mattblack » Wed Sep 06, 2017 12:49 pm

XalFish wrote:
Mattblack wrote:Just for future reference, what would be the max wattage before the wiring and socket starts warming up...100W?


Depends entirely on what is in there already. It's pretty common to find 120W sockets (12 volts 10 amps), but some of the cheaper ones are not really up to the job. It also depends on the wiring.

At the risk of getting slightly technical, the wire heats up because it dissipates power. The power it dissipates is equal to I*I*R, where I is the current and R is the resistance of the wire. So at 10 amps, it's 10 x 10 x R = 100 x R. Thinner wire has a higher resistance per meter, so it dissipates more power and hence gets hotter. On the other hand, thicker wire has less resistance per meter, so it dissipates less power, and stays cooler.

This little equation (power = Ix I x R) tells us something else, too. Since it goes up with current squared, every time you double the current you get 4 times the power dissipation.

The other problem is voltage drop. Any time current flows in a resistance, there is voltage drop.

Let's say you are drawing 10 amps, and using 2.5mm^2 cable. It has a resistance of say 10 ohms per km. You have 5m of red wire and 5m of black wire to your socket, so 10m all up. The total resistance of your wire is 10 (ohms per km) * 0.001 (km per m) *10 (meters) = 0.1 ohms.

By Ohm's law, V = IR, so the voltage drop is V = 10 x 0.1 = 1 volt. That means that from your 12V battery, your socket is only providing 11V.

If you pull 20 amps, it becomes V = 20 * 0.1 = 2 volts, so now you only have 10V!

And then it gets worse. The crimp terminals, the wire connection to the socket, the fuse, the fuse holder, the socket itself, the plug on the equipment- these all add MORE resistance, and even more voltage drop!

Different equipment has different sensitivity to voltage drop, but eventually, stuff stops working. And because we're dissipating the power in the wire and the socket and plug instead of in the equipment, it all heats up.

All of this is related, and you can avoid all the problems by
- Running good quality, thick cable.
- Using the right crimps, etc
- Picking the appropriate socket. If you want to run 10A, don't buy a 10A socket, buy a 15A socket. That head room helps it run cool. There is less resistance, so less voltage drop and lost power.

Good fishing :)

Man, I didn't realise how dumb I was until I started reading that....I actually installed the socket myself for one of the ski-tube pumps...Now I'm going to have the fire extinguisher on the ready whenever I use it!

blacklab99
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Re: 12V Portable Ovens

Postby blacklab99 » Wed Sep 06, 2017 2:19 pm

Matt, its not about saying how dumb you were !!!
Its knowing ones limitations and admitting that I should ask the question.
Seen some horrible wiring jobs by guys that shouldn't have attempted doing so, even seen a so called expert wire up a friends new hose pump on his boat, only to see it go up in smoke and was lucky he stopped and saw it and had an extinguisher on board,,,, I wont name the company, but they still operate in Melbourne servicing motors and wiring up extras on boats !!! they even refused to take responsibility.
Me, well, I'm good at a lot of things, but, I don't muck around with anything electrical, specially when it comes to a boat where you can be in a power of sh*t km's from sure. I think people think its only batteries, its not mains, surely nothing bad can happen.
So, I know my limitations, I don't want to half arse study upon it for a week then plow into re wiring my boat, and hope I got it right. I'll be getting it done profesionally for piece of mind. Just know my limitations..............

XalFish
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Re: 12V Portable Ovens

Postby XalFish » Wed Sep 06, 2017 2:26 pm

Nothing dumb about not knowing something. The only dumb thing is not to ask :)



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rb85
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Re: 12V Portable Ovens

Postby rb85 » Tue Sep 12, 2017 8:37 pm

Something like this would be recommended to carry if you cook too many pies and cant get the boat going.

http://www.auspowerbanks.com.au/product ... gJFxvD_BwE

rb85
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Re: 12V Portable Ovens

Postby rb85 » Tue Sep 12, 2017 8:39 pm


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Mattblack
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Re: 12V Portable Ovens

Postby Mattblack » Wed Sep 13, 2017 7:48 am

rb85 wrote:Something like this would be recommended to carry if you cook too many pies and cant get the boat going.

http://www.auspowerbanks.com.au/product ... gJFxvD_BwE


I have this exact one...and coincidently came to my wife's rescue 2 weeks ago to jump start her 2lt diesel :thumbsup:


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