I noticed some brand new (66 plate) single decker pure electric buses around
Waterloo today. They look very nice (apart from the huge battery pack on the
roof) and certainly have a good turn of acceleration off the line. I notice
however that their unladed weight is 12 tons which is more than a lot of
double deckers, presumably because of the battery. I wonder how efficient that
actually makes them when you calculate it all the way back to the power
station?

--
Spud

On Thu, 8 Dec 2016 14:42:44 +0000 (UTC), d wrote:

I noticed some brand new (66 plate) single decker pure electric buses around
Waterloo today. They look very nice (apart from the huge battery pack on the
roof) and certainly have a good turn of acceleration off the line. I notice
however that their unladed weight is 12 tons which is more than a lot of
double deckers, presumably because of the battery. I wonder how efficient that
actually makes them when you calculate it all the way back to the power
station?

I suspect that the box on the roof isn't the heavy battery pack. The
whole back half of the bus has a high floor, and given the absence of
a diesel engine, I think that's where the batteries live. It means
that there are only a couple of step-free seats; the others are all in
the high back end.

They presumably have regenerative braking, so the weight won't make
too much difference to the efficiency. But it explains why there won't
be any double-deck battery buses.

Of course, they're being used to eliminate local pollution in the city
centre, not to save energy. But they apparently have a much lower
running cost, no doubt partly because they need less maintenance.

They're not as quiet as I expected; obviously there's no engine noise,
but the transmission has a loud gear whine.

On Fri, 09 Dec 2016 13:57:45 +0000
Recliner wrote:
I suspect that the box on the roof isn't the heavy battery pack. The
whole back half of the bus has a high floor, and given the absence of
a diesel engine, I think that's where the batteries live. It means

Wonder what the roof thing is then. Its pretty large , way too large to be
an aircon unit. Perhaps its braking resistors for when the regen braking can't
cope?

They're not as quiet as I expected; obviously there's no engine noise,
but the transmission has a loud gear whine.

Thats probably the noise of the motors themselves I would imagine. There's
probably little if any transmission to speak of.

--
Spud

On 2016\12\09 13:57, Recliner wrote:
On Thu, 8 Dec 2016 14:42:44 +0000 (UTC), d wrote:

I noticed some brand new (66 plate) single decker pure electric buses around
Waterloo today. They look very nice (apart from the huge battery pack on the
roof) and certainly have a good turn of acceleration off the line. I notice
however that their unladed weight is 12 tons which is more than a lot of
double deckers, presumably because of the battery. I wonder how efficient that
actually makes them when you calculate it all the way back to the power
station?

I suspect that the box on the roof isn't the heavy battery pack. The
whole back half of the bus has a high floor, and given the absence of
a diesel engine, I think that's where the batteries live. It means
that there are only a couple of step-free seats; the others are all in
the high back end.

They presumably have regenerative braking, so the weight won't make
too much difference to the efficiency. But it explains why there won't
be any double-deck battery buses.

This can't be right! Pushing a bus that's twice as heavy through the
streets has to use twice the energy, and regen braking won't change that
equation.

On Fri, 9 Dec 2016 16:06:54 +0000
Basil Jet wrote:
On 2016\12\09 13:57, Recliner wrote:
They presumably have regenerative braking, so the weight won't make
too much difference to the efficiency. But it explains why there won't
be any double-deck battery buses.

This can't be right! Pushing a bus that's twice as heavy through the
streets has to use twice the energy, and regen braking won't change that
equation.

Probably depends how effective the regen braking is. I suspect in london
traffic with its slow stop start the answer is "not very" as regenerative
braking doesn't work very well at slow speeds.

--
Spud

On Fri, 9 Dec 2016 16:06:54 +0000, Basil Jet
wrote:

On 2016\12\09 13:57, Recliner wrote:
On Thu, 8 Dec 2016 14:42:44 +0000 (UTC), d wrote:

I noticed some brand new (66 plate) single decker pure electric buses around
Waterloo today. They look very nice (apart from the huge battery pack on the
roof) and certainly have a good turn of acceleration off the line. I notice
however that their unladed weight is 12 tons which is more than a lot of
double deckers, presumably because of the battery. I wonder how efficient that
actually makes them when you calculate it all the way back to the power
station?

I suspect that the box on the roof isn't the heavy battery pack. The
whole back half of the bus has a high floor, and given the absence of
a diesel engine, I think that's where the batteries live. It means
that there are only a couple of step-free seats; the others are all in
the high back end.

They presumably have regenerative braking, so the weight won't make
too much difference to the efficiency. But it explains why there won't
be any double-deck battery buses.

This can't be right! Pushing a bus that's twice as heavy through the
streets has to use twice the energy, and regen braking won't change that
equation.

The energy cost is mainly to accelerate the bus, and much of that is
recovered with regen brakes. The rolling resistance is not only
relatively small, but these inner city buses don't spend much time
coasting along.

On Fri, 9 Dec 2016 14:30:45 +0000 (UTC), d wrote:

On Fri, 09 Dec 2016 13:57:45 +0000
Recliner wrote:
I suspect that the box on the roof isn't the heavy battery pack. The
whole back half of the bus has a high floor, and given the absence of
a diesel engine, I think that's where the batteries live. It means

Wonder what the roof thing is then. Its pretty large , way too large to be
an aircon unit. Perhaps its braking resistors for when the regen braking can't
cope?

Yes quite likely. Could also be the aircon or cooling radiators for
the batteries, which are likely to get quite hot. There might be more
of a clue if you can see one from above; for example, you can see the
hydrogen cylinders in the open-top box on the roof of the
hydrogen-powered buses.


They're not as quiet as I expected; obviously there's no engine noise,
but the transmission has a loud gear whine.

Thats probably the noise of the motors themselves I would imagine. There's
probably little if any transmission to speak of.

There's a reduction gearbox, which probably makes more noise than the
motor(s). There may also be some sort of prop shaft and differential.

On Fri, 09 Dec 2016 16:20:53 +0000
Recliner wrote:
On Fri, 9 Dec 2016 14:30:45 +0000 (UTC), d wrote:
Wonder what the roof thing is then. Its pretty large , way too large to be
an aircon unit. Perhaps its braking resistors for when the regen braking
can't
cope?

Yes quite likely. Could also be the aircon or cooling radiators for
the batteries, which are likely to get quite hot. There might be more
of a clue if you can see one from above; for example, you can see the
hydrogen cylinders in the open-top box on the roof of the
hydrogen-powered buses.

Seemed to be completely enclosed IIRC.

Thats probably the noise of the motors themselves I would imagine. There's
probably little if any transmission to speak of.

There's a reduction gearbox, which probably makes more noise than the
motor(s). There may also be some sort of prop shaft and differential.

If the motors and traction controllers are similar to that on trains they could
be pretty noisy. Doubt there's a prop shaft - transverse mounting makes the
most sense to me with the diff built in.

--
Spud

The Red Arrow BYD / Alexander-Dennis Enviro200EV buses have iron-phosphate batteries at the rear and in the roof pod, which also incorporates the aircon unit. The driveline comprises two 90kW wheel-hub motors and water cooling system plus regenerative braking system.

There are also five BYD double-deck battery buses in (intermittent) use on route 98.

DRH

DRH wrote:
The Red Arrow BYD / Alexander-Dennis Enviro200EV buses have
iron-phosphate batteries at the rear and in the roof pod, which also
incorporates the aircon unit. The driveline comprises two 90kW wheel-hub
motors and water cooling system plus regenerative braking system.

There are also five BYD double-deck battery buses in (intermittent) use on route 98.

Thanks, that's interesting. Were the additional batteries in the roof pod
added to increase the range? They sound like an afterthought.