"T i m" wrote in message
news
On Thu, 21 Sep 2017 08:54:26 +0100, "Dave W"
wrote:


"Dave W" wrote in message
news

snip

Some further thoughts:

Ok. (and thanks for such Dave). ;-)

The display of Vo should stay fairly constant as the current is ramped up
and down.
If it doesn't, the assumed value for Rt can be adjusted until it does.

So Vo is our calculated cutoff voltage Dave?

Yes, the 50% discharged point.


I suspect the motor current will be very noisy, making any digital display
very
erratic and difficult to read.

All that would be 'damped' by sampling Dave.

It depends how often you sample, the duration of the sample window and how
many samples you send to each display reading.


Better to use a mechanical meter, with a big
capacitor across it to smooth out wobbles.

I already have such a solution in some monitoring kit I've made up
(moving coil meter and suitable shunt) but that's no good for any
logging of course.

Or perhaps use software to create
a
running average.

That's the idea. See, once I have it 'electronically' I can do loads
of things with it (like logging to an SD car to provide a 'Battery
Life' record.

A meter would be easy to read in bright sunlight.

I only intend using this in England Dave. ;-)

The meter could have a big mark at 12.19V, with perhaps everything below
11.5V
marked in red, as that's where your discharge graph starts to drop like a
stone.

Sure, analogue meters are great for showing stuff (and why I still use
them) and during the initial runs of anything I come up with may well
include some analogue versions of both Volts and Amps, just to provide
a 'simple' comparison. The problem is a moving coil voltmeter is a lot
more expensive than an electronic one (or even an electronic
wattmeter!) and it really only serves as an indication that there is
around 12V there (because you are only interested in the range 10 -
15). I did think of using a 10V zener and a 5V meter as at least then
you would have an expanded range. ;-)

Surely the cost of the meter is a mere drop in the river compared with the
cost of boat and battery? The meter should be driven so that when the
battery voltage is below 10V the meter is still on its zero mark, and
full scale for 15V. You are driving it from the Arduino so it can be
any old range e.g. 10mA fsd.


If you are using a simple rheostat to adjust the motor current, that's a
big
waste of energy in the form of heat.

Agreed. It's actually what Minn Kota (the people who make the
outboard) call 'Speed coils' that are just resistors in the underwater
unit somewhere and selected via a multi-way switch in the outboard and
controlled by the tiller / twistgrip.

Better to have an efficient
switched-mode
power converter to convert the battery voltage into motor voltage.

Quite, and something (else) I'm working on Dave. ;-)

Ideally this would have current feedback to compensate for the resistance
of
the motor, in effect raising the voltage as more current is taken.

Yes, that could be good.

The
control
knob could then be calibrated directly in propeller speed.

Yup. ;-)

The feedback could be further modified if you know the relationship
between
boat
speed and propeller speed, and the knob could be calibrated in boat speed.

Whilst that would vary between boats (and there are 5 we may use it
on) it might be of more use than just some arbitrary values.

You could have a float sensor to vary the calculations depending
on how low in the water the boat is, causing variations in drag.

This
would be helpful for estimating journey time.

As would the current etc.

Cheers, T i m

p.s. Part of the whole 'electric outboard' experiment is to build a
test tank (I now have kindly donated by Mr Lamb of this very group)
and again, use an Arduino micro controller and voltage, current, load
(strain) and water-speed measurement, initially make comparisons
between the efficiency of resistor V PWM speed control and later, prop
/ leg hydrodynamic improvements (or not). ;-)
--
Cheers, Dave

On 21/09/17 14:28, T i m wrote:
On Thu, 21 Sep 2017 13:22:57 +0100, The Natural Philosopher
wrote:

On 21/09/17 11:50, T i m wrote:
So, cummon, have a go at being the solution, you know you want to.;-)


Seeing as its you t i m, no, I dont want to.

Yeah, nice cop out mate! Just like the Linux questions I've challenged
you with in the past when you initially portray you know what you are
doing and pretend to offer help but when you are really tested you go
very quiet ... ;-(


Oh dear. You are in denial.

What do they say ...'All mouth and no trousers ...'? (Damn, now I have
to get that image out of my head ...). ;-(

Cheers, T i m



--
Microsoft : the best reason to go to Linux that ever existed.

On Thu, 21 Sep 2017 21:23:26 +0100, "Dave W"
wrote:

snip

I suspect the motor current will be very noisy, making any digital display
very
erratic and difficult to read.

All that would be 'damped' by sampling Dave.

It depends how often you sample, the duration of the sample window and how
many samples you send to each display reading.

Correct. You could sample every .5 seconds, put the results of 20
samples into an array and then display the average value (or something
like that anyway). ;-)


snip

Sure, analogue meters are great for showing stuff (and why I still use
them) and during the initial runs of anything I come up with may well
include some analogue versions of both Volts and Amps, just to provide
a 'simple' comparison. The problem is a moving coil voltmeter is a lot
more expensive than an electronic one (or even an electronic
wattmeter!) and it really only serves as an indication that there is
around 12V there (because you are only interested in the range 10 -
15). I did think of using a 10V zener and a 5V meter as at least then
you would have an expanded range. ;-)

Surely the cost of the meter is a mere drop in the river compared with the
cost of boat and battery?

Yes, sure.

should be driven so that when the
battery voltage is below 10V the meter is still on its zero mark, and
full scale for 15V. You are driving it from the Arduino so it can be
any old range e.g. 10mA fsd.

In this case I was going to make a straight analogue meter Dave, both
amps and volts mounted in a suitable box and to be (optionally)
plugged in series with the load. If the voltage drop at max current
affects the voltage too much I'll run a separate cable back to the
battery directly.

But you are right, I could run it from the Arduino but I was hoping to
keep this bit 'KISS'. ;-)

snip

Whilst that would vary between boats (and there are 5 we may use it
on) it might be of more use than just some arbitrary values.

You could have a float sensor to vary the calculations depending
on how low in the water the boat is, causing variations in drag.

Now that would be a step too far mate (and way too complicated to
compute). ;-)

Cheers, T i m

"T i m" wrote in message
...
On Thu, 21 Sep 2017 21:23:26 +0100, "Dave W"
wrote:

snip

should be driven so that when the
battery voltage is below 10V the meter is still on its zero mark, and
full scale for 15V. You are driving it from the Arduino so it can be
any old range e.g. 10mA fsd.

In this case I was going to make a straight analogue meter Dave, both
amps and volts mounted in a suitable box and to be (optionally)
plugged in series with the load. If the voltage drop at max current
affects the voltage too much I'll run a separate cable back to the
battery directly.

I don't understand.

--
Dave

On Thu, 21 Sep 2017 23:52:05 +0100, "Dave W"
wrote:


"T i m" wrote in message
.. .
On Thu, 21 Sep 2017 21:23:26 +0100, "Dave W"
wrote:

snip

should be driven so that when the
battery voltage is below 10V the meter is still on its zero mark, and
full scale for 15V. You are driving it from the Arduino so it can be
any old range e.g. 10mA fsd.

In this case I was going to make a straight analogue meter Dave, both
amps and volts mounted in a suitable box and to be (optionally)
plugged in series with the load. If the voltage drop at max current
affects the voltage too much I'll run a separate cable back to the
battery directly.

I don't understand.

Because there are times when a straight 'old fashioned' analogue panel
meter can show (in a human sense) things better than a digital display
(and why few car speedos are digital today AFAIK) I intend, as a
parallel project, making a two panel meter box with an in-line plug a
socket to match the outboard to battery connectors so that I can just
put it in series with anything I'm playing with to give me a
quick_n_dirty display of volts and amps. ;-)

The current can be read anywhere in the system but if there is any
significant resistance in the lead between the battery and where I
have this box, I can 'remote' the voltage mater supply / sense wires
directly to the battery terminals to remove the influence of the
voltage drop over the cables that will range from 0 at no current to
maximum (that should still be pretty low in ideal circumstances) at
full current.

Cheers, T i m

"T i m" wrote in message
...
On Thu, 21 Sep 2017 23:52:05 +0100, "Dave W"
wrote:


"T i m" wrote in message
. ..
On Thu, 21 Sep 2017 21:23:26 +0100, "Dave W"
wrote:

snip

should be driven so that when the
battery voltage is below 10V the meter is still on its zero mark, and
full scale for 15V. You are driving it from the Arduino so it can be
any old range e.g. 10mA fsd.

In this case I was going to make a straight analogue meter Dave, both
amps and volts mounted in a suitable box and to be (optionally)
plugged in series with the load. If the voltage drop at max current
affects the voltage too much I'll run a separate cable back to the
battery directly.

I don't understand.

Because there are times when a straight 'old fashioned' analogue panel
meter can show (in a human sense) things better than a digital display
(and why few car speedos are digital today AFAIK) I intend, as a
parallel project, making a two panel meter box with an in-line plug a
socket to match the outboard to battery connectors so that I can just
put it in series with anything I'm playing with to give me a
quick_n_dirty display of volts and amps. ;-)

The current can be read anywhere in the system but if there is any
significant resistance in the lead between the battery and where I
have this box, I can 'remote' the voltage mater supply / sense wires
directly to the battery terminals to remove the influence of the
voltage drop over the cables that will range from 0 at no current to
maximum (that should still be pretty low in ideal circumstances) at
full current.

Cheers, T i m

OK understood. You could use the voltage between the two ends of the
current-carrying wire from the battery as input to your Arduino current
sensing arrangement. The resistance of the lead is the current shunt.

Cheers, Dave

On Fri, 22 Sep 2017 11:19:03 +0100, "Dave W"
wrote:

snip

The current can be read anywhere in the system but if there is any
significant resistance in the lead between the battery and where I
have this box, I can 'remote' the voltage mater supply / sense wires
directly to the battery terminals to remove the influence of the
voltage drop over the cables that will range from 0 at no current to
maximum (that should still be pretty low in ideal circumstances) at
full current.


OK understood. You could use the voltage between the two ends of the
current-carrying wire from the battery as input to your Arduino current
sensing arrangement. The resistance of the lead is the current shunt.

Funny you should say that ... that's exactly what I did on the
electric racing bike I built, measuring the voltage drop over the
longest battery cable and after calibration, displaying it as current.
;-)

The thing with this project though is I want to try to keep it all
modular / flexible to it would be better to keep the current
measurement 'local' to any meters etc. I'm hoping to use a hall effect
module with integrated amplifier chip to make it easier to interface
with the Arduino etc.

Also, with mostly 20mm^2 copper leads (2 x 2m) from the battery to the
outboard I'm hoping that at my typical 15A draw I'll not get
sufficient voltage drop for it to be worth measuring (although I know
I will etc). ;-)

Cheers, T i m

"The Natural Philosopher" wrote in message
news
On 21/09/17 11:50, T i m wrote:
So, cummon, have a go at being the solution, you know you want to.;-)

Cheers, T i m

Seeing as its you t i m, no, I dont want to.

You'd be wasting your time.
He's like PHucker, a plaster for every corn.

"pamela" wrote in message
...
On 21:28 20 Sep 2017, T i m wrote:

On Wed, 20 Sep 2017 20:24:23 +0100, pamela
wrote:

snip bm's drivel

If you find Tim's inquiry to be too boring for you then why
don't you skip to the next thread?

Because he doesn't find it boring, he finds it exciting (because
it confuses him) and he is only too pleased that *someone* will
talk to him (and I do it as part of his virtual care in the
community) ;-)

You can't force Tim to adopt your alternative philosophy of "If
you seem to be losing power, don't you just seek the next
charging point and charge them?".

Quite ... he said he had read the entire thread but still had no
clue whatsoever about what was actually going on!

Aww, but bless him for at least having a go pamela. ;-)

Cheers, T i m

It's one thing for 'bm' to want to do a sloppy job if he was in
the same situation as you but then he went ballistic just because
you want to do it thoroughly. Why does he care so much?

You think I care? LMFAO.
I'd prolly get around 'his pretend problem' somehow.