And, as I said, You Real, Really, REALLY want to use higher voltages.
This is extremely obvious on dynamic stuff using DC, like servo motors,
and stepper motors and treadmill motors.
Going from 12V to 48 V is about 3x-5x better.
Going to 80 V is another 100% better.
Going to 220V is another 100% better.
The effect is exactly the same, for the same reasons, although much less
kinetic and visual, on DC PV panels.
Example.
A servo loaded at 12V, might go to 3000 rpm in 0.5 secs.
48V, 0.1 secs.
80V, 0.05 secs.
220V, 0.02 secs.
Yes, a 2.5 kW, heavy, big, servo motor will accelerate to 3000 rpm in 20 ms.
It will also deliver up to 7.5 kW of power for that time (up to 3 secs),
and thus accelerate a big heavy mass of say 20 kg to the 3000 rpm in
about the same time.
( I did not do the math for power needed for this. Depends on radius, a
lot, as kinetic energy energy = power needed depends on radial size of
object).
The difference between 220V and 12 V is enormous.
Sweet spot is 48-80 V for small systems, and 400V for big systems.
Simple comparison for thought:
At 48V, costs are low, and performance is 3x better than 12V.
The losses/results are exactly the same, and repeat, weather you charge
batteries, or use the batteries to drive loads, like motors (lights,
whatever).
In other words, the losses are doubled, once in charging and once in
using the power.
For those interested, a DC treadmill controller is about half the
performance of a servo.
Simple comparison for thought:
The more heatsinks a controller needs, the less efficient it is.
Always.
Heat = loss.
No heat = efficiency.
Modern servos, and their controllers, have almost no heatsinks (yes,
they do, but small- and a fan, mostly for peak-power cooling, at 300%
overload, for typically some ms-length peaks).
Example:
The servo motors don´t get hot.
Running at full 100% load, a modern 220V ac servo motor is not hot -
warm, but not scalding.
Because they are very, very, very efficient.
My old M head Ac 3-phase motor is very good - 1940 technology.
1/2 Hp, 18 kg mass, gets warm running 24x7, can run weeks.
This is often done, industrially.
Almost silent at 400 rpm, after 60-70 years heavy use.
My new servo brushless motor is very good - 2015 technology.
2.5 kW, = 3 hp, 10 kg mass, gets warm running 24x7, can run weeks.
This is often done, industrially.
Very low noise at 400 rpm, about equivalent.
Low noise at 3000 rpm.
Difference is about 10:1 in power, times 2:1 in mass, for almost 20x
improvement.
All above is relevant, very much, imho.
VFD drives == stepper drives == servo drives == chopper drives or MPPT
controllers.
All are about equal in design and issues, use about the same components,
and potentially have about the same efficiency.
All take in power of one type, be it DC or AC (many do both), use a
chopper to drive the voltage up at high speed (25 khz, more, whatever)
and then step it down, faster or slower.
The power electronics components are very similar, and have similar
actual physics based compromises, and market based compromises.
Surprisingly, cost is NOT a good indicator of quality, reliability or
efficiency.
All the new designs are very good, and many are made in china, really
well and really cheaply.
One final, very important, point.
Tesla, that I follow for market reasons, has about the best VFD =
inverter out on the market.
They have re-done it 12 times, in 6 years.
There is, I promise, a Very Good Reason for this.
They must have spent 10-20M $ on this, over the last years.
And they would much rather have bought the design from someone, except
really good stuff was not available, with low manufacturing cost.
Moral:
Big heavy power electronics are cheap to make, expensive to design, and
the field is still green.
(BTW.
Modern welders and plasma torches are about the same.)
On 31/08/2016 13:37, jennifer_c_richards@yahoo.co.uk [electricboats] wrote:
>
> With a large system like 2Kw you would save money by using a higher
> voltage battery system (36 or 48 volts) and using serial (with your
> 100watt panels) and perhaps in conjunction with parallel connections.
> This is quite simple as you choose the configuration according to the
> panel voltages to match the specifications of the mppt, normally
> 150vDC(avoid having a voltage to close to the maximum especially if
> visiting the tropics) input voltage (minus a safe working limit)
> determines how many panels you connect in series and the capacity of
> the MPPT determines how many parallel connections you can have in
> total per controller.
--
-hanermo (cnc designs)
Posted by: Hannu Venermo <gcode.fi@gmail.com>
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