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Discussion in 'Electric Motorcycles' started by itnithand, Jan 4, 2019.
How about we keep CSM content in CSM?
Yeah, my fault. Doing too many things at once. Sorry.
DC is more efficient for long haul high-voltage: https://en.wikipedia.org/wiki/High-voltage_direct_current
"Depending on voltage level and construction details, HVDC transmission losses are quoted as less than 3% per 1,000 km, which are 30 to 40% less than with AC lines, at the same voltage levels. This is because direct current transfers only active power and thus causes lower losses than alternating current, which transfers both active and reactive power."
"A long-distance, point-to-point HVDC transmission scheme generally has lower overall investment cost and lower losses than an equivalent AC transmission scheme. HVDC conversion equipment at the terminal stations is costly, but the total DC transmission-line costs over long distances are lower than for an AC line of the same distance. HVDC requires less conductor per unit distance than an AC line, as there is no need to support three phases and there is no skin effect."
"A high-voltage, direct current (HVDC) electric power transmission system (also called a power superhighway or an electrical superhighway) uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current (AC) systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. For underwater power cables, HVDC avoids the heavy currents required to charge and discharge the cable capacitance each cycle. For shorter distances, the higher cost of DC conversion equipment compared to an AC system may still be justified, due to other benefits of direct current links. HVDC currently uses voltages between 100 kV and 800 kV, with an 1,100 kV link in China due to become operational in 2019."
"Practical conversion of power between AC and DC became possible with the development of power electronics devices such as mercury-arc valves and, starting in the 1970s, semiconductor devices as thyristors, integrated gate-commutated thyristors (IGCTs), MOS-controlled thyristors (MCTs) and insulated-gate bipolar transistors (IGBT)."
Interesting. I wonder why we do so much AC transmission? Maybe because the conversion electronics were too expensive, and if so, is that likely to change any time soon? Seems like converting an AC power line would be pretty expensive, so would DC only be worthwhile for new and replacement lines?
Presently they only do DC for long haul high power and there are plans for more
I don't think we are so much interested in replacing existing AC infrastructure with DC - more adding DC to the mix to connect regional grids
It's best suited for hundreds of miles and very high powers - cost of conversion is a factor that contributes to that
There's a list of them on this page: https://en.wikipedia.org/wiki/List_of_HVDC_projects#North_America
No such thing as a DC transformer.
Here are fixed ratio DC-DC voltage "transformers" which is simply a transformer wrapped by MOSFET's
It is a voltage regulator, not a transformer. High to low. I wonder what frequency it operates at?
It's not a regulator at all, there's zero regulation - the output voltage is proportional to the input voltage by the ratio of the transformer windings and you can put power in either side and take it out the other (bidirectional) just like a transformer... they're intended to feed regulators because they don't regulate... A common usage is to take 48V telecom power, using one of them to boost it up to several hundred volts (I think these are 16:1) to reduce the current and loss by the same factor, then feed that into a second one to drop it back down... they work similarly to the HVDC grid like that... The link is to the high voltage guys, they also have 4:1's and thereabouts...
It's a very simple topology... a little controller switches MOSFET's on the input and output sides of the transformer synchronously without paying attention to the input and output voltages and currents provided they are within the operating range...
I know these guys pretty well... haven't dealt hand's on so much with these mostly some other of their products....
While I wouldn't call them a "DC transformer" they are about as close as it gets and I wouldn't criticize someone that did since it's a very apt description and reasonable semantics
Further to my previous comment above, this was announced today, looks like very similar to the Honda concept that's already being trialled:
Now, if Yamaha could produce something like an electric Xmax 300 (I already have the ICE version) using this kind swappable battery tech, that would be fantastic, proper storage included and capable of some longer distances.
Before anyone starts thinking that swappable batteries are going to change everything for EMs, we need to think through the details. They work OK for limited-performance scooters. Power, speed and range expectations are fairly low. If you're going to power a scooter with a 60 mph top speed, you need a pack voltage of something like 80-100 V. The Gogoro modules are 1.3 kWh each for the original 18650 cell versions, marginally more for the latest 2170 cells. Most scooters use two modules.
Since the relative capacities of the modules are unknown (the modules will certainly age differently), it gets very tricky how you use them. If you try to parallel them, the BMS gets really complicated to prevent reversing the lower-capacity pack. Most likely they just use one at a time, which limits how much power you can produce, but it's a scooter so that's OK.
If you try to scale this up from e-scooters to EMs things get complicated. Many think a Zero SR's range is marginal, even between quick fill-ups. You'd need roughly 10 Gogoro modules to match the SR's range. Take a look at a current Zero's battery pack and any arrangement of 10 Gogoro modules next to each other. Where are you going to put 10 of those things on a Zero, in such a way that they're all easily accessible, without messing up the looks? It's an EM so you need WAY more current than a little 1.5(?) kWh module can deliver, so this is where it gets complicated - at 80-100 V that's either too little if you parallel them all or too much if you series/parallel them. Let's say you work that out with a system voltage change (likely going to series/parallel). Now you need to change them all at a fill-up (because paralleling is involved), so hopefully the swap pod has that many. If it's short a few but you need anything you can get at that point, it gets more complicated to do a 'partial fill' without risking damaging the batteries and/or the bike. (Pairs, if you are paralleling two-pod series strings? Which pods are paired together? What happens if you get it wrong? How does the BMS sense the lowest capacity string (or module within a string) if the strings are paralleled? How does the controller know how much to limit current draw and when?) Both the BMS and the rider need to understand what's happening and how to do it right.
Do you start up a whole new standard intended for EMs with a different voltage, even thought some if these problems would still remain? What does that do to your business model?
And then when solid state batteries become available and the new chemistry changes the system voltage (again), progress marches on and leaves your existing infrastructure behind. Solid state might not just require different system voltages, it might make the whole swap scheme irrelevant due to its fast-charge capability.
So far I've seen nothing mentioned about how any of these details are to be managed. (I've even seen one article say it's a good thing that you don't have to charge at home any more. Seriously? Wouldn't filling up your ICEV be much more convenient if you could do it at home?) There's lots of promo talk, but no details. Until we have those no one can know if this is a good idea or not. Better to know what you're getting enthusiastic about before you strike up the band.
I had the same thought. One of the big advantages of EV's is that you can charge at home, and start every day with a fully charged battery.
I hate stopping for fuel on my commute.
I read the gogoro link and one claim that I don't buy is "This means the cost of the battery, which can be anything up to half of the bike’s total value, could be discounted off the price of the vehicle." You need one to begin with in order to swap it!
I'm a huge fan of the idea of swap-able batteries but understand the issues well. I do think it's ideally the best way to address the long time it takes to charge. Even with a really fast charging system I don't think they'll achieve much less than 10-15min in the not-too-distant and that's too long for me.
It's how I do my e-bike - I completely understand were comparing apples and pomegranates though. But it's so nice to just grab a fresh one and drop it on the bike...
I don't see swap-able batteries getting rid of at home charging... why on earth would that be? The batteries would have essentially watt-meters built in so a user could be charge by watt-hours which makes way more sense than a fixed swap charge. Any home recharging should incur no or just a marginal maintenance fee... At least in my ideal....
What's to stop the companies providing the battery swapping stations from providing the same batteries that can be taken out and charged at home? Make a charge based on time away from an official charging station (so you don't just keep batteries for months/years) and then you have the best of both worlds. Get home late and not have time to get to a swap station, so charge at home for the next day. Also, if you have a battery that's only at 30%, why not stop at a swap station, get a fully charged battery for 70% of the full charge cost (or maybe a small surcharge to do so), so you would in effect be 'topping' up your power level? There are many combinations/charging policies possible that it's just a technicality/admin issue to be solved but the idea of having swapping stations where you can 'reload' probably faster than filling a gas tank is definitely the way forward. Even Honda and Yamaha think so but what do they know?
I still think the best and simplest way is to just use watt-hour meters in the batteries which will almost certainly exist in the batteries no matter anyway. Charging stations charge their rate for a given amount of watt-hours and at home is a much reduced rate - a charge for "maintenance and wear" without a fee for the energy.
These things did not exist when AC and DC where battling out for supremacy in the late 1800's. It works by converting DC current to AC, running it through a AC voltage transformer, and converting the AC output back to DC.
Here are some fun facts.
The small USB wall wart transformer, that you connect your phone to, works by converting AC to DC, then DC to AC at much higher frequency, then it converts the voltage using small AC voltage transformer, then the AC is converted to DC again for the output.
If you get electric shock from AC at household voltages. When the voltage switches polarity, current goes to zero, and you're "kicked away" from the power source. When you get electric shock from DC you can stick to the power source. That makes electric shocks from AC of shorter duration and therefore less dangerous than DC.
The solution to this easy. You see, we are working with electricity and 21st century technology here. Electricity works at close to light speed (roughly 95% in copper). Modern FETs (Field Effect Transistors) also work very fast.
The series connected batteries are not connected together parallel at all. You connect to them one by one on the go. You simply draw power from one string of batteries for a microsecond. The voltage in it will drop, but before it drops noticeably, you stop drawing power from it, and start drawing power from the next string of batteries. Before the voltage in that starts to noticeably drop you switch to the next one, and so on. If one series connected string of batteries starts to get weak, BMS will notice and skip it when switching between batteries. This allows you to mix and match different size batteries with different charges.
You could also use the old fashioned way. Connect them together in parallel when load is applied. The fully charged batteries will have higher voltage under load so more current will be drawn from them.
From: https://en.wikipedia.org/wiki/High-voltage_direct_current (I don't mind providing sources)
"The first long-distance transmission of electric power was demonstrated using direct current in 1882 at Miesbach-Munich Power Transmission"