On 12/07/2020 23:35:40, John Rumm wrote:
On 12/07/2020 09:55, T i m wrote:
On Fri, 10 Jul 2020 17:23:50 +0100, John Rumm
wrote:

snip

Now in theory you could build a 9V drill that draws 40A and gives the
same performance, but in real life physics is a bitch, and 4 times the
heat losses in the drill, and much thicker windings in the motor etc,
make it a non starter before you even get to the question of the quality
of cells you will need that can supply the 40A on a regular basis.

So as a first order approximation, the bigger the voltage on the drill,
the better it will perform - other things being equal.

Drill or electric car. ;-)

One of the improvements they did the Enfield 8000's (PIEV) is raise
the battery voltage from 48 to 72 and adjust the gearing to match
(more revs, less current).

Pulling away fast in my (48V Moke version) would see around 400A and
cruising at 30 mph around 200. ;-(

I believe modern EV's have the battery voltages up much much higher so
you don't need cables as thick as my thumb everywhere. ;-)

Yup, 400V or thereabouts seems quite common.

MOSFETs are affordable for controlling voltages up to 600V. For higher
voltages you would migrate to IGBTs which have much greater losses.

I can't see EVs going much higher in voltage.

On 12/07/2020 23:53, Fredxx wrote:
On 12/07/2020 23:34:38, John Rumm wrote:
On 12/07/2020 00:32, Fredxx wrote:
On 11/07/2020 23:09:35, John Rumm wrote:

For theoretical stuff that no one makes, you could in theory have a
theoretical drill with a lower voltage that works as well as an actual
drill with higher voltage. Yes I agree, as a thought experiment its
worth 10 seconds consideration. Now lets move on.

However within the range of tools from one maker, targetting the
same market, they will typically all use battery packs that use the
same Samsung / Sony / Panasonic cells, and will design to keep peek
current at a level that will not kill battery packs after only a few
cycles.

Which is just confirming the point I am making.

What that tool designers know what they are doing?

Yes, pandering to marketing hype.

Lets try this from a different angle; what would be the point in making
say a 12V tool, that has the same power output as an 18V one? Where is
the actual advantage?

You will need more expensive cells that can cope with higher average and
peak current delivery. More copper in the wiring, and the motor
windings. More expensive semiconductors in the speed controllers. If you
are going to go for parallel arrangements of cells to get the energy
density, you then have new problems matching the cell characteristics,
and charging them without overcharging some cells. Then in use you have
more heat dissipation to worry about - so less endurance and more waste
energy.

So you end up with a more expensive tool that is heavier, where
additional battery packs are more expensive, and probably won't last as
many cycles. Basically you are on a hiding to nothing.

So does marketing come into it, yes of course you get bragging rights,
and in reality Makita's 40V tools will only offer marginal performance
gains over their equivalent 2x18V products. However I will concede that
it means they can bring 2x18V levels of performance to tools where the
form factor would not suit two battery setups. (e.g. take the combi
drill, they don't do a 2x18V combi drill (it would ruin the handling),
so the 40V tool does actually make sense if the jump in torque to 140 Nm
is necessary for your application).

Its seems perverse to dismiss higher voltages as *just* hype, however if
you may have to accept that being enlightened you are going to be stuck
with less effective tools for some jobs.



--
Cheers,

John.

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On 12/07/2020 10:05, Chris Hogg wrote:
On Sun, 12 Jul 2020 08:59:28 +0100, T i m wrote:


It was funny how often 'laymen' thought they could advise me (it's
owner, driver and maintainer) on how I could extend the range of my
electric car.

'If you had a dynamo running off one of the tyres ...' and when you
explained to them *why* that wouldn't help (and they weren't talking
of any type of regen braking), all they would do is switch to another
idea, like having a wind turbine mounted on a trailer (to charge the
batteries when moving, not parked). ;-(

ROTFL; I wonder how many greens actually believe that sort of thing?
Quite a lot, I suspect.


Well we all have wind turbines attached to our chimney stacks as once
advised by the green lobby.!

Just go on Youtube and see how many schemes there are for creating free
energy and then wonder why none of them have been adopted by the energy
industry. Perhaps it's true there is a conspiracy by the gas and oil
industries to stop innovation into alternatives

For entertainment, I watched one of these video where first a microwave
oven has to be stripped apart to get a coil. Attach a small magnet to a
bit of rubber and in turn attach this to the end of a long tube which is
positioned above the coil (the magnet being close to the coil). Connect
the coil to a digital multimeter and 'bang' the tube. Hey presto the
multimeter shows by vibrating the tube/magnet it generates some free
power. The idea is that by mounting the tube outside the wind will
vibrate it. I assume that with tens of thousands of these tubes a house
could become self sufficient in electric power.

Remember Dick Strawbridge who made the TV series about his new green
lifestyle and driving around in cars fuelled by the local chip shop oil,
harnessing the power of the stream that ran through his 100 acre
property that barely powered a 25W light bulb etc.? He seems to have
given up that utopian existence - perhaps reality struck!



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