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991  Using Arduino / Project Guidance / Re: P_ower supply question on: July 11, 2011, 01:26:40 pm
You might want to ensure that ALL relevant connections are made as close to, and preferably onto the actual motor cycle battery terminals.  The electrical noise introduced from the ignition coil will be buzzing merrily throughout the cable loom so you need to get as close to the battery as possible, where the effect is minimised.  I'd also suggest mounting everything within a diecast metal enclosure which is itself "earthed" to the bike frame.  This will act as a shield to prevent RF affecting the circuit.  Run all power and signal leads within screened cable, with the screening connected to the bike frame.  The use of ridiculously sized capacitors is totally unnecessary providing you take sensible screening precautions.
992  Using Arduino / Motors, Mechanics, and Power / Re: Other ways of controlling water flow on: July 11, 2011, 08:12:45 am
Plaster of Paris ?

Go to your local chemist or pharmacy - they should be able to either supply or source it for you - typically used to set broken limbs.

993  Using Arduino / Motors, Mechanics, and Power / Re: Other ways of controlling water flow on: July 10, 2011, 03:24:25 am
Why not simply visit your local junk yard and strip some valves out of scrap washing machines, dishwashers etc

They will typically be mains AC operated so you'll also need a bunch of interfacing devices, whether they be relays, SSRs or triacs.
994  Using Arduino / Motors, Mechanics, and Power / Re: Capability of Lead Acid Battery on: July 06, 2011, 12:51:45 pm
"burglar alarm" type batteries are generally SLA type (Sealed Lead Acid) so by definition are filled with an electrolyte (jelly ?) during manufacture, which bears no relationship to when the retail outlet actually sells them.

Wet lead acid are of course a totally different matter, but they are not the topic of discussion.
995  Using Arduino / Motors, Mechanics, and Power / Re: Capability of Lead Acid Battery on: July 06, 2011, 03:16:45 am
You should be very concerned about how old the battery was when you bought it.  Somewhere on the case will be stamped a date code, probably 4 numbers (month -year).  If it's more than 2 years old then I'd return it for a refund irrespective of whether it's charged or not.  Normal consumers stores are not set up to periodically refresh lead acid batteries so it's probably never been charged since the manufacture gave it an initial charge.

If you really want to test its capacity then you can do a rough and ready test by placing a resistor across it and monitoring/logging the voltage every so often until you start to see a rapid drop off (at around 11 volts)   You need of course to ensure the battery is fully charged before you start the discharge test.  On the basis of 7AH nominal capacity and using C20 as a conservative guess then you need a resistor that will consume 7/20 amps.   R=V/I  so R= 12*20/7  =  approx 34ohms.  33 ohms is a preferred value so you need one of these rated at 7 watts minimum.

Simply strap this resistor across the battery and be prepared to monitor the voltage at 1/2 hour intervals for the next 20 hours !!    True, the current will drop as the voltage decreases but it is a method of approximation only.  You can then produce a nice graph of volts versus time at your nominal 0.35 amps and from that estimate total ampere-hours.

An automatic datalogger and a constant current device helps greatly but, as above, it can be done manually, albeit it takes a bit of time and effort.
996  Using Arduino / General Electronics / Re: Need some help!! on: July 05, 2011, 08:52:13 am
led plus resistor across 5 volt supply must glow unless :-

a) no 5 volts
b) resistor defective
c) led defective
d) led connected wrong way round
e) you just dreamt it
f) you just went blind
997  Using Arduino / General Electronics / Re: Controlling 12V @ 12A with an arduino. on: July 03, 2011, 01:20:07 pm
If you care to read my earlier posting you will see I was complimenting the relay design as being short-circuit proof.  In fact I even went to the bother of giving you a mention in relation to the original emitter follower circuit.   My concern was regarding a home-made FET system to perform change-over switching by an individual not yet experienced in the problems of FET circuit design.
998  Using Arduino / Motors, Mechanics, and Power / Re: what is this part called?(shematic from playground) on: July 03, 2011, 03:59:31 am
and that's why they are often referred to as "flywheel" diodes
999  Using Arduino / General Electronics / Re: Controlling 12V @ 12A with an arduino. on: July 03, 2011, 03:53:58 am
You have a problem here.  Your original design has a reversing facility and a simple low side N channel will not provide that. You are looking to switch both + and - lines and there is now a real danger of a DIY type FET build shortening out your power supply.   If you want to go FET and you are not knowledgeable in such matters you might be better simply buying an H bridge which will provide both forward and reverse and will not short circuit the power supply.
1000  Using Arduino / Project Guidance / Re: Arduino Relays for Failsafes on: July 02, 2011, 09:15:51 am
Just out of interest, how do you propose to handle the eventuality of your failure detector system failing.  Laugh if you want but these sort of problems are typical of what Emergency Shutdown Systems designers have to handle.   The simplest way of doing it is by having multiple processors running the application in parallel then voting on a 2-out-of-3 basis.   As far as your application is concerned, whatever it may be, a simple watch-dog output is all you need - that's what it's designed for.
1001  Using Arduino / Project Guidance / Re: Arduino Relays for Failsafes on: July 02, 2011, 03:40:49 am
Yeh, that would stop the watch-dog
1002  Using Arduino / General Electronics / Re: Controlling 12V @ 12A with an arduino. on: July 02, 2011, 02:48:08 am
Using the emitter follower configuration, your relays will never see more than the voltage at the transistor bases.  As Lefty says, the relays need to be in the feed from the +12 to the collectors and you also need snubbing diodes across their coils to prevent damage to the transistors.  At 12 amps your relay contacts are going to experience a bit of arcing so ensure they are conservatively rated (say 20 to 30A rating).   I like the way you have configured your reverse switching, since accidentally switching on both inputs simply stops the motor.  Many such circuit endeavours actually short circuit the supply in the event of switching both together.
1003  Using Arduino / General Electronics / Re: battery back-up circuit ICL7673 on: June 30, 2011, 07:17:32 am
Why not simply use a couple of diodes acting as an OR gate.  Whichever system (primary supply or back-up battery) is the higher voltage will feed your load with the diodes preventing back-flow into the lower system voltage.

1004  Using Arduino / General Electronics / Re: Parallel Voltage Regulators on: June 30, 2011, 03:09:17 am
1) You cannot simply parallel regulators

2) If you cannot buy a heat sink then make one by bolting the regulator to a LARGE lump of aluminium

3) If your 5 volt load is reasonably constant, you can dump some of the excess 7 volts across a power resistor before the regulator.  Say the load is 1 amp, then dump 4 of the 7 volts across a 3.9ohm, 10watt resistor.

4) Install a small PC fan to keep the regulator cool

5) You can boost regulator output by using its output to drive a power transistor, but this is somewhat overcomplicating the issue
1005  Using Arduino / General Electronics / Re: Resistor placement. on: June 26, 2011, 05:50:57 am
If you want to minimise component count, place your three LEDs in series and use one resistor to feed the chain.  Because LEDs are "current" driven devices such an arrangement is sound providing the rated currents of the LEDs are identical.  You might see minor voltage variations across each LED but that's of no concern in such a circuit.
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