Model Boat Mayhem

Please login or register.

Login with username, password and session length.
Pages: 1 2 [3]   Go Down

Author Topic: a maths question  (Read 8391 times)

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,773
  • Location: Blackpool, Lancs, UK
Re: a maths question
« Reply #50 on: May 28, 2011, 05:36:23 pm »

Further to PMK, any exposed metal bits, if they are connected to any part of the supply, will be connected to battery -ve.  As an accidental grounding of a live wire is most likely to find one of these, the protection needs to be in the supply, i.e. +ve.
If the installation consists of several parts, having the -ve common and fusing the distribution makes sense.  If it just a battery, receiver, ESC and servo, it still makes sense to put the fuse where it is conventionally expected, in the +ve side.  This after 30 odd years in an industry where equipment was run on -50volts, and all the fuses were in the -ve supply, obviously apart from the +50volt supply........
Logged
"With the right tool, you can break anything" - Garfield

roycv

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,753
  • Location: S.W. Herts
Re: a maths question
« Reply #51 on: May 28, 2011, 06:08:42 pm »

Thanks PMK, thank you for your thoughts.  My shed is however nicely insulated and double glazed, it must be the house causing the problem.
Explanation is the best I have heard so will accept it.
Now what about the green stuff where the batteries go which is only ever at one end!
OK, I do take my batteries out now when not in use.

regards Roy
Logged

malcolmfrary

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 5,773
  • Location: Blackpool, Lancs, UK
Re: a maths question
« Reply #52 on: May 29, 2011, 11:00:33 am »

Quote
Now what about the green stuff where the batteries go which is only ever at one end!
Verdigris.  A copper compound, comes about where the terminals have become damp.  Being used in a damp atmosphere, they will be damp long enough for the reaction to start taking place.  The damp allows the reaction, extracting the copper, the compound spreads in the damp, the damp dries out and leaves the compound.  Since boats operate in a damp environment, its going to happen.
Logged
"With the right tool, you can break anything" - Garfield

PMK

  • Guest
Re: a maths question
« Reply #53 on: May 29, 2011, 12:05:28 pm »

In the case of SLA batteries with spade-type terminals, I usually apply a generous dollop of petroleum jelly to both connections in order to keep that unwanted verdigris at bay. A bit of heatshrink tube doesn't go amiss, either.
Getting back to the original thread (sort of), try punching the following digits in your calculator...

0.1267 + 0.6467 =

...then read the result with the calculator held upside-down.
I know, I know. But it *is* Sunday and I'm bored witless.
Logged

hopeitfloats

  • Guest
Re: a maths question
« Reply #54 on: May 29, 2011, 12:46:54 pm »

and a big HELLO to you too.  try 71077345 upside down. i'm bored too,  waiting for the MONACO GP to start followed by the INDY 500.
Logged

PMK

  • Guest
Re: a maths question
« Reply #55 on: May 29, 2011, 01:53:10 pm »

Perhaps a tad more readable with a decimal point between the "0" and the second "7".
And more...

53045
58008 (you need a bit of imagination with the number 8 on that one).
0.0761
5604
3376
57714
57716
5317.037

...... etc, blah.

Gawd, I'm *still* bored.
Logged

essex2visuvesi

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 6,134
  • Location: Finland, England, Finland!
Re: a maths question
« Reply #56 on: May 29, 2011, 06:02:01 pm »

55378008 if you calculator has enough numbers
Logged
One By One The Penguins Steal My Sanity
Proud member of the OAM  (Order of the Armchair Modeller)
Junior member of the OGG  (Order of the Grumpy Git)

RaaArtyGunner

  • Guest
Re: a maths question
« Reply #57 on: May 29, 2011, 10:21:08 pm »

55378008 if you calculator has enough numbers

Now your gretting in my area and I forgot, didn't have to turn them upside down here  %% %% {-) {-) {-)
Logged

Trooper63

  • Guest
Re: a maths question
« Reply #58 on: May 30, 2011, 05:40:41 am »

LOL, Changes in Latitudes, Changes in Attitudes!
Logged

sweeper

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 199
  • When all else fails, read the instructions
  • Location: On the edge of reason, in the state of Confusion
Re: a maths question
« Reply #59 on: May 31, 2011, 03:04:00 pm »

PMK,
Why must you start me off thinking? Re your replies 46/49.
Fuses in the +ve side, logical to most people if you consider the definition of a fuse ie to isolate a circuit or device from the source of potential in the event of a fault. In most peoples minds a +ve voltage is a potential while a 0v is not.
I'll refrain from the power field solutions of old (fuses in both poles) and the problems that came from this such as the -ve fuse blowing while the +ve still maintained full voltage on the circuit. Painful - from bitter experience. You may still find examples of this practice in areas that were once supplied from tramways system and later converted to AC. It's nasty but will likely be around until long after I've been "connected to earth".

It links with your discussion of current flow and electron flow. Have you ever used the widely used analogy of water flow in current flow?
People (ie the human mind) can accept the idea of water flowing from a raised bucket (representing a potential) to a bucket at ground level, but try to convince them that really the flow is from the ground up to the bucket and they'll get the sleeveless jacket out for you.
In days of old (before electronics came into the open) it made little difference to anyone. But as a student in the early 60's it screwed our minds up when we started on valve theory.

There's still your theory of the ammeter to be considered.... Those Green Shield stamps look appealing, I'm looking at very obscure ideas for that one.
More when my cell resumes normal life.
Keep the faith Mate, Rock ON.
Regards
Logged

Lt. Raen

  • Guest
Re: a maths question
« Reply #60 on: June 14, 2011, 06:32:05 am »

PMK, thats quite an interesting question you have raised on current.

I believe the reason for a more accurate reading at the negative terminal over the positive
terminal would be to do with the fact that electrons move from negative to positive as you
have stated.

Now considering this and disregarding the common convention of current flow the current
measured at the negative terminal is the whole current released from the power source.
When the current is measured at the positive, the electrons have had to pass through the
circuit and the load in that circuit. therefore, the current may be slightly altered due to losses
as the electrons have passed through the load. I am not 100% sure what these losses are
but I would imagine heat would be a contributing factor, after all any resistance will produce
some heat.

Just my 2 cents worth  %)

Tim
Logged

tigertiger

  • Global Moderator
  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 7,306
  • Location: Kunming, city of eternal springtime, SW China.
Re: a maths question
« Reply #61 on: June 14, 2011, 11:14:35 am »

PMK, thats quite an interesting question you have raised on current.

I believe the reason for a more accurate reading at the negative terminal over the positive
terminal would be to do with the fact that electrons move from negative to positive as you
have stated.

Now considering this and disregarding the common convention of current flow the current
measured at the negative terminal is the whole current released from the power source.
When the current is measured at the positive, the electrons have had to pass through the
circuit and the load in that circuit. therefore, the current may be slightly altered due to losses
as the electrons have passed through the load. I am not 100% sure what these losses are
but I would imagine heat would be a contributing factor, after all any resistance will produce
some heat.

Just my 2 cents worth  %)

Tim

Could be on to something with leakage. Maybe some conversion to heat and electromagnetic waves has an effect on losses.
Dunno
Logged
The only stupid question is the one I didn't ask

roycv

  • Full Mayhemer
  • *****
  • Offline Offline
  • Posts: 2,753
  • Location: S.W. Herts
Re: a maths question
« Reply #62 on: June 17, 2011, 04:55:00 pm »

hi PMK, I think this is my 500th posting, so it is nice to use it to say thanks PMK and to all those others that have been kind enough to respond to my queries.

There is always something new to learn, my problem is that I may have hit full storage and for every new thing learnt something else gets forgotten, but I can't remember what!

regards Roy
Logged
Pages: 1 2 [3]   Go Up