Future electrical systems

[Snaker]

A while back I had a conversation with an electrical engineer regarding low voltage circuits and wiring. We were dealing with the industry standard of 24v DC circuits. He was telling me that there is a push to up the typical standard to 48v DC. This would allow manufactures to use higher gauge wiring (thinner). The benifits would be cheaper, less weight, less space and is based on Ohms law (higher voltage = less current = thinner wires). I wasn't too impressed because from my perspective it means weaker wiring that breaks easier.

He also mentioned that automotive applications would follow for the same reasons and I could expect to see vehicles going to 24c DC in the future. Has anyone else heard of this or is this guy blowing smoke?

He also threw a trivia question at me. Fuses/circuit breakers are meant to protect what electrical component? Without much thinking I said the power source and he gave me the grand slam, said I was wrong, its the wiring. What answer would you all give?

 

[Wayne County Hose]

He is correct. The automotive industry has been experimenting with up to 80v systems. The higher voltage is way more efficient. Most new electric forklifts are at least 36vdc up to 72 and 80vdc but the motor controllers convert over to 3 phase AC voltage.
Fuse size is usually determined by wire size unless there is a critical component they are trying to protect. So offhand I would say listen to this guy.
For the record I have a 2 year degree in electronics and have been an electric forklift mechanic for 26 years. There are guys here with way more electronic knowledge that can elaborate further but your buddy sounds accurate to me.

 

[weedpharma]

+1 for above.

The fuse is designed to blow to stop the wiring from melting and causing a fire. Different styles of fuses blow at different multiples of the carrying current. Also depends on the current and time.

A 10A wire fuse will carry 10A forever, say 15A for minutes and 20A for seconds. A short circuit will blow immediately. (These are examples to illustrate principle, not absolute values). Typical wire fuses blow quickly at about twice their rating. Circuit breaker operate at much closer to ratings.

To protect a wire that will burn at 20A, you would use a fuse rated at no more than 10A.

Now for Basic Electronics (101).

Ohm's Law tells us that Voltage (E) = Current (I) x Resistance (R).

Power (P) = I x E So if we double the voltage, we halve the current for the same power.

If we halve the current in the wire, we reduce the the voltage drop in the wire (E = I x R). We can now reduce the size of the wire. This is why the feeder wires from power stations run at hundreds of thousands of volts. This also reduces the power loss (P = I x (I x R)) in the transmission cables as the power loss is proportional to the current squared times the resistance of the wires.

In modern cars, we now have LED lights with much less power requirements. This allows for smaller wires and less cost.

Weedpharma

 

[kjung17]

This is all good theory. It does not explain the reality of on board data systems (CAN Bus) that currently run on 2.5 vdc. I can't imagine an 80 volt battery capable of starting a 13.5 liter diesel, even with the reduced amperage required. It would weigh a ton.

 

[Snaker]

I poked around in a couple of old electronic text books. They didn't address the subject much except to say:
"The purpose of the fuse is to prevent excessive damage in case the resistance is accidentally shorted"
and
"Many circuits have a fuse in series as a protection against an overload resulting from a short circuit. The purpose is to let the fuse blow before the components are damaged."

I found an electrical handbook that described fuses/circuit breakers as being called overcurrent devices and stated:
"Any overcurrent device you use must having a rating in amperes, not greater than the ampacity of the wire which it protects".

So, I guess it is the wiring.

 

[Snaker]

This is all good theory. It does not explain the reality of on board data systems (CAN Bus) that currently run on 2.5 vdc. I can't imagine an 80 volt battery capable of starting a 13.5 liter diesel, even with the reduced amperage required. It would weigh a ton.

These issues would be of no problem with an increase of voltage. Your television has a low voltage digital circuit in it.

The upsized battery would be one of the easiest changes and most beneficial to the user. Anyone familar with the old 6 volt systems can relate to the improvement that came with the change to 12 volts. Increased voltage batteries have no requirements for extra weight or size. A similar evolution can be seen with cordless handtools. They have gone from 3.6 volts to whatever is the latest and greatest now and the size and weight has not changed significantly.

 

[weedpharma]

......... I can't imagine an 80 volt battery capable of starting a 13.5 liter diesel, even with the reduced amperage required. It would weigh a ton.

The power required to start the engine is the same whether it be from a 12 volt source or an 80 volt source. An 80v battery would only need to be similar in size to the 12v battery.

Weedpharma

 

[Snaker]

+1 for above.

The fuse is designed to blow to stop the wiring from melting and causing a fire. Different styles of fuses blow at different multiples of the carrying current. Also depends on the current and time.

A 10A wire fuse will carry 10A forever, say 15A for minutes and 20A for seconds. A short circuit will blow immediately. (These are examples to illustrate principle, not absolute values). Typical wire fuses blow quickly at about twice their rating. Circuit breaker operate at much closer to ratings.

To protect a wire that will burn at 20A, you would use a fuse rated at no more than 10A.

Now for Basic Electronics (101).

Ohm's Law tells us that Voltage (E) = Current (I) x Resistance (R).

Power (P) = I x E So if we double the voltage, we halve the current for the same power.

If we halve the current in the wire, we reduce the the voltage drop in the wire (E = I x R). We can now reduce the size of the wire. This is why the feeder wires from power stations run at hundreds of thousands of volts. This also reduces the power loss (P = I x (I x R)) in the transmission cables as the power loss is proportional to the current squared times the resistance of the wires.

In modern cars, we now have LED lights with much less power requirements. This allows for smaller wires and less cost.

Weedpharma

Back in the day I did some very limited circuit design. I had to calculate the expected current and used tables to select fuse and wire size. I never matched fuse to wire directly. After the circuit was built, it would be measured to confirm. I guess maybe it all just came out in the wash, so to speak, kind of like the "chicken or the egg" theory.

 

[Soundguy]

i agree.. fuses protect wiring primarilly.

as for the voltage jump.. it was the driving pushing 12v when stuff was 6v.

6v cables are huge. 1/0 cable.. whereas you can get by with wimpy 4ga cables in some applications on 12v.. etc.

I don't doubt we may see higher system voltages soom.

Many tractors and heavy equipment already run 24v systems. 24-26v charging systems are not uncommon...

look at some electric h=vehicles. higher volts equal small cables, and same watts for less amps..

soundguy

 

[grsthegreat]

i can see them changing automotive to 24 volt. some heavy equipment and semis already run at 24 volt. It would halve the wire diameter. That wouldn't make the wires any less safe or durable as there usually bundled in automotive and equipment anyways.

I'm an electrical contractor. We use 277 volt in lighting circuits in commercial/industrial applications . I can add more lights on a single circuit. if both are using a 20 amp breaker than both need #12 wire. However if i want to wire them so the same number of fixtures are on either circuits, then technically i would have to wire the 120 volt with #12 and the 277 volt with like a #20 :laughing: :laughing: :laughing: . Of course we never would do this... we would simply add more lights to the 277 volt circuit and cut down on the total number of circuits needed.

ex: 120 volt x 20 amp circuit = 2400 watts available (though we only actually use 80% of this for a continuous load) . whereas a 277 volt system at 20 amps = 5,540 watts available.

 

[Snaker]

i can see them changing automotive to 24 volt. some heavy equipment and semis already run at 24 volt. It would halve the wire diameter. That wouldn't make the wires any less safe or durable as there usually bundled in automotive and equipment anyways.

I'm an electrical contractor. We use 277 volt in lighting circuits in commercial/industrial applications . I can add more lights on a single circuit. if both are using a 20 amp breaker than both need #12 wire. However if i want to wire them so the same number of fixtures are on either circuits, then technically i would have to wire the 120 volt with #12 and the 277 volt with like a #20 :laughing: :laughing: :laughing: . Of course we never would do this... we would simply add more lights to the 277 volt circuit and cut down on the total number of circuits needed.

ex: 120 volt x 20 amp circuit = 2400 watts available (though we only actually use 80% of this for a continuous load) . whereas a 277 volt system at 20 amps = 5,540 watts available.

That 277 volt is some weird stuff. I had occasions of repairing equipment that electricians would hook the legs up backwards. The equipment would require a dedicated 120 circuit. We would mark the input terminals, post labels, leave notes but we still had the mystery blasted components.

 

[grsthegreat]

That 277 volt is some weird stuff. I had occasions of repairing equipment that electricians would hook the legs up backwards. The equipment would require a dedicated 120 circuit. We would mark the input terminals, post labels, leave notes but we still had the mystery blasted components.

ya, your referring to the wild leg 277 panels..where the middle leg is 277. alot of unknowing people place 120 single pole breakers there, and wonder why the equipment explodes hehe

 

[jtheise4]

This is all good theory. It does not explain the reality of on board data systems (CAN Bus) that currently run on 2.5 vdc. I can't imagine an 80 volt battery capable of starting a 13.5 liter diesel, even with the reduced amperage required. It would weigh a ton.

The CAN bus is independent of the overall system voltage. CAN is a communication protocol from electronic module to module. Each of these modules have their own voltage regulators inside, so they're essentially blind to the battery voltage. Modern electronics all run at 5V or less and need regulation. Connect 12V directly to a CAN transciever and you'll let the smoke out just as fast as if you directly connect 80V.

 

[Wayne County Hose]

The CAN bus is independent of the overall system voltage. CAN is a communication protocol from electronic module to module. Each of these modules have their own voltage regulators inside, so they're essentially blind to the battery voltage. Modern electronics all run at 5V or less and need regulation. Connect 12V directly to a CAN transciever and you'll let the smoke out just as fast as if you directly connect 80V.

Ha-haaaa! Yep, we all know that the factory puts smoke in every electrical component. It's this smoke which makes it work. When you let the smoke out it no longer works. It's true.
I also work with CAN-BUS systems. +5v isolated. In my field it's used with anything from 24v batteries to 80v systems. Lights, fans, almost anything other than motors and their respective controllers run off a dc-dc converter.
Cadillac had prototypes with 72v batteries the same size as a standard automotive battery. Most electric cars now are running over 300v to the drive motors. Get used to it boys, high voltage is coming.

 

[Pooh_Bear]

A $500 dollar TV tube will blow first to protect a 50cent fuse.

The reason I heard for increasing the voltage in cars is the alternators can only get so big. The big SUVs and luxury cars with all the fancy gadgets and options that take a lot of power would benefit from the increased voltage.

Also saw a news blurb years ago about replacing the battery with a giant capacitor. The battery is normally only used for starting the vehicle's engine and after that the alternator is used to supply power to all the systems. And it would recharge the capacitor. Never heard any more about the idea.

Pooh Bear

 

[BrierPatch]

A while back I had a conversation with an electrical engineer regarding low voltage circuits and wiring. We were dealing with the industry standard of 24v DC circuits. He was telling me that there is a push to up the typical standard to 48v DC. This would allow manufactures to use higher gauge wiring (thinner). The benifits would be cheaper, less weight, less space and is based on Ohms law (higher voltage = less current = thinner wires). I wasn't too impressed because from my perspective it means weaker wiring that breaks easier.

He also mentioned that automotive applications would follow for the same reasons and I could expect to see vehicles going to 24c DC in the future. Has anyone else heard of this or is this guy blowing smoke?

He also threw a trivia question at me. Fuses/circuit breakers are meant to protect what electrical component? Without much thinking I said the power source and he gave me the grand slam, said I was wrong, its the wiring. What answer would you all give?

I am guessing that this guy was more of an industrial engineer. I agree that higher voltage means smaller current for the same amount of power, I think we can all do the math, but you have to draw a line some where. If it was just about wire size and power it would be a no brainer, but there are other factors involved such as safety, component design, insulation and so on. Why stop at 48vdc why not go with 110vac which is already common and plenty of equipment already exists? Why not 480, 4160. I guess what I am getting at, is there is a point of diminishing returns and other factors involved.

His answer and your answer are both correct for fuses/circuit breakers. So his statement that your answer is wrong is wrong . It is very common to state that they are there to protect the wiring in a power distribution scenario, however that is only one aspect and I would say is a little inexperienced or over generalizing to say that is all they are for. Fuses and circuit breakers are used to protect equipment and components as well.

As far as the car thing, I believe there are alot more factors involved with deciding where to draw the line for voltages. I could see going to 24vdc not being much of a problem, but when you start getting higher voltages you have to better inusulate everything, especialy what the driver and passengers come in contact with. Don't forget our cars get exposed to road salt and water which make an excellent conductor. The higher the voltage the easier it is to short/break down the insulation/start conducting. People leave their windows accidentally rolled down, we don't need someone being electricuted trying to roll up their electric window. This is an exageration, but you get the point. So at what point is the trade off of how much of the car operates at a higher voltage and how much has to operate at a reduced voltage. What are the effeceincy losses, what are the compenent costs, conversion factors, what are the gains, I guess I am glad this is not my field.:confused2:

Who knows what the future will be?

 

[grsthegreat]

I know that the Prius engine is working with a 201 volt battery package. Its 3 phase and uses a inverter to change the 201 volt dc battery voltage into 500 volt dc to run engine.

its coming

 

[Soundguy]

i hope it's a demand system, as dc to dc inversion, even with today;s technology is awefully inefficient.

soundguy

 

[kjung17]

Engines burn fuel. Motors run on electricity. ;-)

 

[BethesdaEC]

Engines burn fuel. Motors run on electricity. ;-)

Then why is Detroit called Motor City?

Some boats have outboard motors.

I somewhat subscribe to what you say but there is not a hard convention.