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Comment Re:solar pannels are low voltage (Score 1) 579

I can imagine that there are way to keep it safe until it reaches the convertor (which converts it to AC and ramps up voltage to 110 or 220 depending on your region).

Yeah, they are called micro-inverters. They convert the 25-40V DC from each panel into 240V AC (or 208V if on 3-phase) in a small box at the panel. Then you run 240VAC down from the roof into your utility panel.

When grid goes away (like when a firefighter flips the main circuit breaker or pulls the meter), the only electricity you have left is 25-50VDC at each solar panel which isn't going to hurt anyone.

Comment Re:Peak demand time (Score 1) 579

FWIW, the peak demand in California typically occurs about 6PM, well after most PV installations fall off the grid (peak production from solar occurs at 12noon and solar output is largely gone after 3PM).

Peak demand varies depending on the time of year.

In the winter, peak is around 7-8pm.

In the summer, peak is around 3-4pm. Note that "solar noon" in the summer is actually around 1pm thanks to daylight savings, not 12pm.

Solar doesn't help at all with peak shaving in the winter, but it does help a lot in the summer. Peak grid demand is always in the summer due to air conditioning load.

This implies that grid tied PV solar without some sort of power storage is NOT an effective source of peak shaving.

Again, depends highly on the time of year and weather conditions. But yes, some grid storage would be very effective at eliminating more of the peak, but it wouldn't take much, just enough to shift a small portion of the generation a couple hours later.

Comment Re:How's that supposed to help? (Score 1) 148

See? By varying load and the magic of Ohm's law I can now tell voltage changes from resistance changes.

Very cool way of detecting circuit impedance. I guess the trick will be figuring out at what point do you say "hey, the resistance is changing too much, let's just slow down some amount" or "hey, the resistance is changing too much, I better shut down immediately".

This also depends on Tesla being able to accurately control exactly how much current is being pulled as well.

Comment Re:How's that supposed to help? (Score 1) 148

They already do that, by monitoring the voltage drop when the load is applied. That doesn't cover all cases though, because fires are more often caused by high resistance or intermittent junctions. If you get say a 5% voltage drop because of wire resistance it's probably no big deal because the heat dissipation is spread out over the length of the wiring. A similar drop caused by a poor junction might glow because it's concentrated in one spot. I believe that poor junctions often exhibit short term fluctuations because they're loose and intermittent, and that's the additional thing that this software mod looks for.

The real trick is distinguishing short term fluctuations that are caused by a flaky connection from some short term fluctuations caused by other big applicance turning on and off (you know, like an electric range/oven/water-heater/air-conditioner/pool-pump/etc)...

Arc-Fault-Detection may pick up some of the failure modes that lead to these issues, but when you are pulling 240V/40A to charge the car (9600W) It wouldn't take much of an issue to melt down a receptacle. And it won't pick up a high resistance connection in an outlet. A 3V drop in a small area (120W) probably more than enough to burn up a receptacle in the time it takes to charge the car but would otherwise be completely normal in most charging situations.

The proper fix here is to install a thermoswitch in the plug that triggers either a significant reduction in charge current, or shuts down charging completely.

Comment Re:Tesla can't fix the basic problem (Score 3, Informative) 148

You never see 208V measured from hot-hot in homes unless you have severe voltage sag - only 240V single phase with 120V measured from each hot to ground.

208V is commonly seen in commercial 3-phase situations, though, where you tap 2 out of 3 hots and each hot is 120V measured to ground.

Comment Re:Tesla can't fix the basic problem (Score 2) 148

Your typical house runs on 240V single phase power fed by two hots and a neutral.

Each hot is 120V, but shifted 180* out of phase, so you get 240V measured across both hots. The neutral handles any imbalance in power draw across the two hots.

Your typical household appliance runs on a single hot split phase at 120V and current is returned on the neutral line.

There's really no reason why we couldn't start using 240V directly these days and eliminate the neutral as long as all your appliances are able to run on 240V instead of 120V. Most modern electronics will run on both without issue.

Comment Re:Musk's Hubris... (Score 1) 253

While the Fire Authority's report stated the most likely cause was a "high resistance connection at the wall socket or the Universal Mobile Connector from the Tesla charging system", Tesla says its own data shows the car was charging normally, with no fluctuations in the temperature and no malfunctions capable of causing a fire.

This is key and it is important to determine exactly where this fire occurred.

The Tesla supplied UMC is designed to adapt to multiple plug types with an adapter so one can plug into a NEMA 14-50 (typical stove outlet), 5-15 (standard 120V outlet) or others.

It is well documented that these adapters can melt - it appears that in some conditions the adapter's PINs do not establish a good connection leading to overheating. Here are three examples:

http://www.teslamotorsclub.com/showthread.php/15304-Plug-Adapter-on-my-Universal-Mobile-Connector-has-melted
http://www.teslamotorsclub.com/showthread.php/18092-Schmelted-UMC-NEMA-14-50
http://www.teslamotorsclub.com/showthread.php/23212-Scary-issue-with-Nema-14-50-adapter-melting

Now that doesn't mean that's what happened here. Faulty 14-50 outlets (no fault of Tesla) have also caused similar issues. There are two examples in this thread:

http://www.teslamotorsclub.com/showthread.php/19576-Burned-220V-Adapter

If it were me, I would not be using the Tesla UMC (Universal Mobile Connector) for daily charging - these plugs/outlets are not designed for daily plugging/unplugging. I would use the Tesla HPWC (High Power Wall Connector) instead and save the UMC for actual mobile use.

I am also not crazy about the design of the adapter plugs on the UMC. Not only do the pins appear not to necessarily mate very well (compare these pins to the connector that actually plugs into the car!), but the extra length of the adapter exerts extra leverage on the outlet/adapter which makes it easier to end up with a poor connection unless you support the UMC well.

Comment Re:Damage on the wall side (Score 1) 253

NEC says that for continuous loads, you can pull up to 80% of the circuit's rating. Charging an EV qualifies as a continuous load. Below is a list of common copper wire sizes found in your typical home and it's 100% / 80% ampacity (assuming 60C rated insulation which is most common):

14AWG: 15/12A
12AWG: 20/16A
10AWG: 30/24A
8AWG: 40/32A
6AWG: 55/44A
1AWG: 110/88A

Note that for the last two, you typically would be using that wire on a 50A or 100A circuit, the max continuous loads on those would be 40A or 80A respectively.

Your typical plug for charging a Tesla Model S would be a NEMA 14-50 outlet rated at 50A. You might be able to find 75C rated outlets/wire, in which case one can use 8AWG wire for a 50A circuit instead of 6AWG.

Comment Re:a Leaf takes about 1.5kW (Score 1) 1010

12A/110V.

Not 1kW.

If you want to be pedantic, your typical outlet will supply 120V.

Not 110V.

If a 15-20A outlet can't handle 12A current - then it's defective and should be repaired. You're generally only going to trip the breaker if something else is also plugged in to the same circuit and is drawing a significant amount of current.

Definitely, more EVSEs should be installed.

Comment Re:More than theft (Score 4, Informative) 1010

Actually, a 15A breaker may or may not trip at 15.1A. There is quite a bit of fudge room in the spec. You can pull quite a bit more than 15A on a 15A breaker for a short period of time.

Google for "Circuit Breaker Characteristic Trip Curves" for what may or may not trip a breaker.

Some interesting facts:

It is possible to pull between 95-115% of the rated current of a breaker basically indefinitely without it ever tripping.
It is possible to pull 150-240% of the rated current of a breaker for 60 seconds before it trips.
It is possible to pull 300-600% of the rated current of a breaker for 10 seconds before it trips.
It is possible to pull 900-2000% of the rated current of a breaker for 1 second before it trips.

Comment Re:Look up those words before you use them (Score 1) 363

Peak production from solar occurs at 12 noon, peak demand occurs at 6PM.

If you're going to be an condescending asshole, you might as well get your facts correct. :-P

Peak production for solar in the summer generally occurs at 1 PM, not 12 PM (during non-daylight savings time the peak is at 12 PM).

Peak demand for the year is generally between 3-5 PM, not 6 PM and typically around 4:30 PM.

At 4:30 PM solar output is starting to drop, but is still producing significant power since many utility scale plants use tracking systems which allow production to remain very flat for a few hours around solar noon. Fixed pitch solar can easily be biased towards mid-late afternoon peaks by aiming farther west rather than south which most systems aim for in order to maximize energy production instead of aiming to match production to demand.

It would not take much storage for your typical home PV system to shift load to the utility peak - probably no more than 5-10 kWh of storage for your typical house.

References:
California ISO Today's Outlook
California ISO Renewables Watch
California ISO Peak Load History
Are Solar Panels Facing the Wrong Direction?

Comment Re:They should upgrade the warning ... (Score 2) 526

People say lots of things on the internet, does not mean it's true.

Inside the Tesla battery pack
The engineer who disassembed the pack (Ingineer) did not find any evidence of intumescent goo.

And if you want to see what the pack looks like after a less severe incident with a trailer hitch, look here:

As a point of interest, here's the result of a tow hook impact on a MS that resulted in significant battery damage, but no fire. The battery had to be replaced.

Easy to see that the bottom of the pack is aluminum, not steel from that picture (look at the size of the welds and how the aluminum shredded around the impact point) While steel would be stronger than aluminum, the weight of steel is just way too high to justify using it over aluminum.

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