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[togo]

> ... Especially since 800v charging is just not something motorcycles or other smaller vehicles will be doing.  ...

Explain that, please?  Higher voltages mean thinner cables for the same amps, more kW with thinner wiring, I don't see why smaller vehicles need to be low voltage.  I mean, as the fleets grow and there are better safety stats as to the protection of the pack and the fears of electrocution diminish, I think it's quite possible we are looking and more S and less P in the battery packs.

[Doug S]

I don't see why smaller vehicles need to be low voltage.  I mean, as the fleets grow and there are better safety stats as to the protection of the pack and the fears of electrocution diminish, I think it's quite possible we are looking and more S and less P in the battery packs.

I'd have to agree. Once you get past 200 volts or so, the safety argument is pretty much moot (falling off a 50-story building is pretty much the same as falling off a 5-story building), and I expect to see electric motorcycles running higher voltages pretty soon. Some of them already are, and the ones that aren't are already starting to pay a price (incompatibility with DC fast charging being the primary penalty).

[Crissa]

Higher voltage means needing thicker insulation, more grounding, more robust structure, more education for maintenance, more specialized tools to repair, and much higher expense on the battery cells.

A Zero would need almost 8x the number of cells it does today just to reach that voltage.  That's a huge expense that won't go away with any of the new formulations on the horizon.   It's less so for a car, which already has lots of cells and are just moving them around for a lower amperage, but it's massively inconvenient for a motorcycle or other small vehicle.

The thinner cables just don't balance it out, because wattage would still require the motor to have a certain weight.   And the vast majority of cables in a bike are 5v and 12v controls anyhow.

-Crissa

I'm not saying we won't see them.  A 300v is reasonable to aim for - that sort of cables are pretty easily found as are the size of the inverters.  But the battery is still going to be much more expensive, as is the maintenance, which will eat into the possible range at a price point.  Which means cheap and easy vehicles will always want to use lesser.

And even if they use 800v, you're still going to want low kilowatt chargers for these smaller vehicles for expense or because they don't go far anyhow.  If we want e-bikes and motorcycles to catch on - not to mention Leafs and Bolts and eNiros on the used market - we need to have more than a charging network built for Taycans and Teslas.

[DonTom]

> Higher voltages mean thinner cables for the same amps, more kW with thinner wiring,

First part is false. 2nd part is true.

On a steady load, if voltage goes up, so will the current, giving you even more wattage. Means wire needs to be thicker for the extra current.

You can get more wattage with enough  more voltage even if the current is reduced,  so that is one way to make the wires thinner to get more power (wattage). IOW, design a motor at a much higher voltage and there will be less current draw for the same power.

IOW, the higher the voltage, the better but not for the reason you explained above.

-Don-  Auburn, CA

[Doug S]

Higher voltage means needing thicker insulation, more grounding, more robust structure, more education for maintenance, more specialized tools to repair, and much higher expense on the battery cells.

"...thicker insulation..." True, but copper's a lot heavier than insulation. The weight savings in thinner wire more than makes up for higher levels of insulation required.

"...more grounding..." Uh, what? Proper grounding is proper grounding. A safety ground cable has to be adequate to carry full fault currents. Again, a lower-current, higher-voltage system needs less copper.

"...more robust structure..." Again, what? You can't have stuff shorting out no matter what the operating voltage.

"...more education for maintenance..." See above. "Stay clear of the high voltage" is the same at 200 volts as it is at 1000.

"...more specialized tools..." In all cases, special care needs to be taken to disco the high voltage. Once that's done, it's business as usual. And again, 200 volts or 1000 volts, you need to be very careful around it.

"...much higher expense on the battery cells." This one's just plain wrong. The 28S 4P battery cells (or whatever it is) in my SR could just as easily be arranged as 56S 2P, or 112S 1P, giving twice or four times the battery voltage, with no penalty for weight or volume in any case, except (again) less copper required for the higher-voltage systems.Those battery packs would be able to supply 1/2 or 1/4 of the current, but power delivered would be the same, as would capacity. It's a total wash.

The real technical differences are safety (I'm minimizing it, but of course higher voltages ARE at least somewhat more dangerous) and the heavier, higher gauge wiring required by lower-voltage systems. Of somewhat lesser importance is the ability to find drive devices (IGBTs, MOSFETs, whatever the engineer chooses to use) capable of operating at the design voltage and current levels, and a very real-world consideration is compatibility with current and future charging equipment.

To me, all of this adds up to basically "we need to do what the cars do", which at the moment means 300~400 VDC or so, maybe higher in the future. That compatibility issue I mentioned last may seem insignificant, but I suspect long-term, it's the most important consideration of all.

[Crissa]

Doug, clearly you've never tried to build something using high voltage in a moving thing.  Every one of those things is more difficult every time you raise the voltage.

Insulation is a massive problem with higher voltages.  You don't just need more, you need different.  And it tends to be less flexible.  And not light.

The distance of the wires from the battery to the motor are hardly going to be more than pennies of copper.  And that length of cable needs to be able to take the spikes from regen and acceleration anyhow.  That doesn't balance out the battery pack, which also has to be many times more complex.

The price of a battery is mostly controlled by two things:  Total weight of the parts, and the number of cells.  Each cell has to be made in a processing step, and that's the majority of the time invested.  And no, you can't just move 56 cells around to make whatever voltage you want.  Even if you stack all the cells in a Zero, you're still only going to get 200v.  You'd need more than twice as many cells to get to Tesla's level, let alone Porsche's.

And as Don explained, because the wattage doesn't change, you don't gain anything in the motor size.

And I didn't say we won't see big bikes with high voltage motors.  Just that it's not relevant to cheap and small.  If Porsche's standard takes off, what bikes would be made to it?  Nothing I could afford, and I'm pretty well off.  Let alone smaller e-bikes and devices.

None of this changes how electricity gets to homes and parking places, either.  As I pointed out before:  The majority of the cost in providing power to vehicles is wiring up parking.

-Crissa

[DonTom]

Higher voltage means needing thicker insulation, more grounding,

AFAIK, EVs cannot use a battery ground by law. The reason is safety.

In a serious accident they could have to pry a person  out of a  car using metal tools. Say it's a 400 volt EV  with the negative side grounded. They accidentally cut into the positive of the battery cable in the very smashed up car. Now if they touch the frame what happens? They get fried. Say it shorts to the frame, what happens? I would not want to be close to that! High voltage at a very high current, well that  will melt things fast, could even cause the batteries to explode.

Now if the HV is not using any  grounds, what happens when they touch that same positive to the frame of the car? Absolutely nothing at all. No completed circuit. Much safer to not use a ground in an EV. It's much safer to use either a floating ground or separate wires for the negative side.

BTW, ever check the headlight voltage on your Zero? It's that, zero volts to ground or the frame with the lamp nice and bright. It also doesn't use a ground. It has its own negative wire. I have no idea why they don't use a ground for even the low voltage in motorcycles, but it probably has something to do with legal stuff, IOW, no grounds and no exceptions, not even on a motorcycle, not even when the voltage is low.

-Don-  Auburn, CA

[Crissa]

Higher voltage means needing thicker insulation, more grounding,

AFAIK, EVs cannot use a battery ground by law. The reason is safety.

Yes, it's not so simple when you have to run multiple isolated grounds.  But it's something you have to do when your power source is capable of burning through things in that instant of ground before the fuse pops.

-Crissa

[togo]

> > Higher voltages mean thinner cables for the same amps, more kW with thinner wiring

> First part is false. 2nd part is true.

Yeah I meant thinner cables per kW.  Conductor thickness, anyway, since it's sized by current/amps (lookup mm2 or gauge in a table).  Insulation will be thicker, of course.

[princec]

Is it only me that's terrified of high voltage DC? And even more terrified of it getting wet? And wondering why manus. keep insisting on putting the charging ports facing straight up where the rain comes down to collect on it?

Cas

[DonTom]

Is it only me that's terrified of high voltage DC? And even more terrified of it getting wet? And wondering why manus. keep insisting on putting the charging ports facing straight up where the rain comes down to collect on it?

Cas

It's probably more of a problem with people like me. I am not all that  afraid of HV, regardless of DC or AC. And that means I have been zapped a few times! I have worked around HV a lot during high power tube transmitter repair.

BTW,  AC is more dangerous than DC, but either can kill.

-Don-  Auburn, CA

[Doug S]

Is it only me that's terrified of high voltage DC? And even more terrified of it getting wet? And wondering why manus. keep insisting on putting the charging ports facing straight up where the rain comes down to collect on it?

Being an EE by trade, I have a very healthy respect for high voltages and the damage they can do. But honestly, if proper design and maintenance precautions are taken, it really shouldn't be an issue on a daily basis. Even heavy rain shouldn't cause problems.

An emergency situation is a different matter. I do worry about the safety of emergency personnel trying to help people as quickly as they possibly can, and spraying water all over a broken and violated vehicle. But I'd still far rather have an emergency in/on an EV than sitting on top of a 10,000 psi hydrogen tank like in one of those Toyota Mirais.

[princec]

Great article Don, thanks for that! I had always thought DC was more dangerous (on account of it arcing and causing heart to stop dead) but it seems I am mistaken. Doesn't make me feel a lot safer mind 

>  if proper design and maintenance precautions are taken

That's the bit that bothers me ... there are quite a lot of small niggly flaws in the current crop of leccy bikes that makes me worry about the overall reliability (and hence safety) of their designs. Like, if a Zero is designed badly enough that rather a lot of people are reporting they conk out in the rain because of water ingress... that doesn't fill me with confidence at all. Who's to say that water won't be getting into a bit with 400 amps going through it? And the issues with the belt drive for example belies a certain sort of laissez-faire towards engineering for real-life that worries me.

Cas

[Crissa]

A few conked out because installation flaws in the connection bus.  That's hardly evidence of laissez-faire engineering.  New things are always going to have some difficulty installing, even if they're easier.  And again, most bikes have never replaced a belt... We're going to hear about the minority here.

Definitely they need to up their processes to get into the zero maintenance thing, but missed grease, bent pins, and overtightened belts are pretty simple oversights.

-Crissa

[DonTom]

Who's to say that water won't be getting into a bit with 400 amps going through it? And the issues with the belt drive for example belies a certain sort of laissez-faire towards engineering for real-life that worries me.

Cas

Well, it would be quite difficult (in fact, not even possible) to draw "400 amps" through water as well as your body being in series with it. Water has too much resistance to draw 400 amps, and so does your body.

400 volts with water could be a problem if that is what you meant.  However, I still would NOT worry about that in  an EV or sitting on an electric motorcycle. It would be quite difficult for your body to be able to complete a circuit even if the entire thing was in a swimming pool under water with you on it.  It Just ain't going to happen.  There are much better paths than your body to short things out when the entire bike is wet. I cannot think of any reasonable way to get shocked by simply sitting on an electric motorcycle regardless of how wet it gets. Working on it is a much different story.

I would ride an electric motorcycle  in the rain as much as I would any other motorcycle.

-Don-  Auburn, CA