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1111  Forum 2005-2010 (read only) / Troubleshooting / Re: 6v 12amp power supply on: August 23, 2010, 11:31:20 am
Mike
OK, have read th article and it contains a lot of good information but the argument of problems when discharging parallel batteries by one taking excess load and the other "charging" is flawed.   Both batteries are intimately connected and their terminal voltages are therefore effectively identical.  Internal resistance is what governs current apportionment.

Given care and common sense (the inevitable caveat) it is possible and in many cases, well used practice, to operate wet acid cells in parallel.

As I said, on this topic we shall just have to agree to disagree

jack
1112  Forum 2005-2010 (read only) / Troubleshooting / Re: 6v 12amp power supply on: August 23, 2010, 08:21:19 am
Mike
Let's agree to disagree on that one
There may be problems with the initial connection if the batteries are seriously out of balance with respect to state of charge, but this can easily be overcome to achieve the interconnection, after which they will act as one (not necassarily the sum of the individual AH ratings)
Jack
1113  Forum 2005-2010 (read only) / Troubleshooting / Re: 6v 12amp power supply on: August 21, 2010, 05:59:26 am
6 volts 12 amps = 72 watts  6 motors x 72 watts = 432 watts

Best bet is to buy a 12 volt 1000watt motor speed controller similar to those sold by 4QD in UK.  Set to operate at 50%  and wire all 6 motors in parallel.

Then get yourself a couple of leisure batteries rated at 100AH each and wire them in parallel and a decent 12 volt battery charger that can feed them with a current of around 20 amps.

The batteries will supply a clean and steady supply to the motor controller and the battery charger will feed the batteries for both the duration of the show and the remaining hours to get them back to fully charged.

jack
1114  Forum 2005-2010 (read only) / Troubleshooting / Re: High voltage on: August 17, 2010, 07:43:40 am
Flyback transformer - YES - but you will need the relevant oscillator circuit.   Even then, getting 50kV is beyond the standard TV types

Microwave oven transformer - NO NO NO

The latter is designed to deliver in the order of 1kW of power and strapping yourself across it is a "do-it-once" operation.  They don't give 50kV and strapping several in series MIGHT get you there but , say 10 in series, will give you around 10kW of ziggies !!!!

50kV at 1kW equates to around 20mA which is sufficient to do you no good at all.  Yes I know the incoming mains RCDs are rated at 30mA to save lifes but they achieve that by disconnecting when you attach yourself between the live and ground/neutral.  Using a microwave transformer effectively isolates you from the mains primary circuit so the secondary current that might flow through you will not trip the RCD.

If you really want to go down this route buy yourself a Tazer - probably illegal and modify it.
1115  Forum 2005-2010 (read only) / Troubleshooting / Re: High voltage on: August 17, 2010, 03:45:42 am
You're not thinking of building a homemade Tazer by any chance

As previous have said, if you don't know what you're doing at these voltage levels then you might just be in for a Darwinian award.

 It's the current that kills, not the voltage, so you will might survive at the expected very low currents that will be available if you go for a simple oscillator system, rather than a Tesla device.

WE used to have a TV technician who" tested" the HT oscillator output by "drawing" the spark with his finger.

The hand-in-the-pocket statement is not as daft as it seems.  I even have a certificate from my apprenticeship days in 1962 qualifying me to work on HV and certifying that I am capable of working with one hand in pocket.
1116  Forum 2005-2010 (read only) / Troubleshooting / Re: Electrical Question ... 220v power on 110v on: July 29, 2010, 07:20:22 am
If your units were linear type transformers rated to operate at 230 volts then in all probability they are for 50Hz (that being the frequency on this side of the pond).  50Hz transformers need more iron in their core than 60Hz ones so will operate off 60Hz systems OK (too much iron is no problem).  However with a 170 to 250 rating they are almost certainly switch-mode supplies and the first thing that happens within one of those is the AC is rectified to DC so frequency of supply is irrelevant.  
jack
1117  Forum 2005-2010 (read only) / Troubleshooting / Re: Electrical Question ... 220v power on 110v on: July 28, 2010, 04:50:30 pm
With such a wide input voltage it's obvioulsy a switch0mode power supply and is failing to run on your 110 supply.   What you could try is fitting a 110 - 230 booster transformer to the inpout side so's the transformer units are seeing 230 volts.  These should be readily available from the likes of Radio Shack or Tandy

jack
1118  Forum 2005-2010 (read only) / Troubleshooting / Re: change PWM frequency in Arduino Mega on: June 01, 2010, 04:49:40 pm
I think you might be slightly incorrect there.  once the instruction has been created and sent to the output port, the processor is free to perform other tasks.  jack
1119  Forum 2005-2010 (read only) / Troubleshooting / Re: change PWM frequency in Arduino Mega on: June 01, 2010, 03:14:22 pm
But that's exactly what PWM is.  

The output is repeated at a regular frequency, in your case 50Hz, which is 20ms total duration, with the output being switched ON or OFF to produce a duty cycle duration as a percentage of the base PWM frequency.

If you want minimum output (1%) you turn on the output for 0.2ms anf off for 19.8ms. If you want 50% output you turn on the output for exactly half the period (10ms) and off for 10ms. and if you want 99% you turn on the output for 19.8ms and off for 0.2ms.

Because the output is digital , either ON or OFF, the "efficiency" is considered 100% at all values

jack
1120  Forum 2005-2010 (read only) / Troubleshooting / Re: change PWM frequency in Arduino Mega on: June 01, 2010, 01:14:56 pm
Why not create your own PWM by using a digital output port and switching it at 50 Hz with on/off-duty being controlled by your own software

jack
1121  Forum 2005-2010 (read only) / Troubleshooting / Re: What is a T092 transistor? on: June 17, 2010, 04:18:08 pm
TO92 is simply a definition of the shape of the transistor case.
The data sheet you have specified is for a transistor of TO92 shape

The base emitter breakdown voltage is the voltage that causes the junction to "breakdown" maybe irrevocably.

Generally transistors should be considered as current amplifiers, a small amount of base-emitter current being multiplied by the transistor gain to produce a much higher collector-emitter current.

When the transistor is conducting you might expect to get a base-emitter operating voltage of around 0.7 volts, but remember it is the current that does the work so you need to set a suitable base resistor to limit this current.  Say you have a transistor of gain 50 and you want to switch collector load of around 100ma then you need a base current of at least 2 ma so a 5 volt signal might need a limitting resistor of around 2.2kohms.   Generally in such a case I'd suggest a value of around 1000 ohms to ensure the transistor is fully turned on.

jack
1122  Forum 2005-2010 (read only) / Interfacing / Re: Reversing polarity on 2 wires on: January 22, 2011, 04:44:17 am
Or you could use a pair of SPDT relays if you want to avoid using power transistors.  
jack
1123  Forum 2005-2010 (read only) / Interfacing / Re: How to solder components on protoboard on: January 15, 2011, 08:19:59 am
The pin connector is in correctly.  The IC socket and the green screw terminal units need fitting to the other side of the board.   That way all pins requiring interconnecting are on the same side (the solder pad side) of the board.   To interlink pins you should use insulation covered wires on the solder side unless your links are not crossing any other connections.  On the component side you can use bare wire providing none are crossing, but it looks neater if you again use insulated wire.

Remember to try and wind the interconnecting wire around the component pins before soldering to create a mechanical joint.  Laying wires against components before soldering does work but it isn't considered good practice.
1124  Forum 2005-2010 (read only) / Interfacing / Re: Arduino for 24V environment on: January 12, 2011, 07:14:30 am
But it ain't

And a 250ohm relay coil on 5 volts draws 20ma which is within the spec of a single I/O channel.  The writer's text seemed mainly to be concerned with inputs.

jack
1125  Forum 2005-2010 (read only) / Interfacing / Re: Arduino for 24V environment on: January 12, 2011, 04:21:55 am
I believe you can feed your 24 volt logic levels (or any higher DC voltage for that matter) directly into the arduino provided you use input resistors to limit input current to less than 1ma.   So as a provisional value I'd suggest, for 24 volts inputs, using 33k minimum.

As to outputs, you can use 5 volt relays (250ohm coils minimum) as an interface to your external circuits.

jack
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