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Short question topic

A place to ask general spud cannon related questions.
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Re: Short question topic

Unread postAuthor: jrrdw » Mon Aug 25, 2014 5:16 pm

I was meaning the output directly off the driver.

If I'm understanding the specs on the driver, if you have a load on circuit (high voltage generator) it stays in CC until you remove the load then the driver goes into CV which in basic terms a state of readiness. Therefore working as advertised.

May not be what you were wanting but working as advertised...Correct?

You need a Arduino and program it to do what you want....Just a thought. :D
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Re: Short question topic

Unread postAuthor: Technician1002 » Tue Aug 26, 2014 7:24 pm

Quick reply on the LED driver and Constant Current regulation.

LED's draw more current as they get hot and operate at a lower voltage. Setting an LED driver with no current regulation will place an LED in thermal runaway. It gets warm, lowers voltage, draws more current, gets hotter, draws more current, gets even hotter. until something goes and lets the magic smoke out.

Solution for driving something that needs constant Voltage.. Draw less current so it is in Voltage Regulation mode. CC is a result of drawing the current the driver is set to. On some this is not adjustable. CC is a symptiom of trying to draw 700mA from a driver that is set to 350, 500, or 700mA.

Solutions include using a higher current LED driver, using a constant voltage DC supply with enough current capacity, or using more than one LED driver in parallel for a total available current above your maximum current demand.

Adjusting the output voltage while in CC mode does nothing unless you adjust below the current limited voltage.
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Re: Short question topic

Unread postAuthor: MrCrowley » Tue Aug 26, 2014 8:42 pm

I tried adjusting the CC pot. and that seemed to help. I got it to go up to 2A (it says 2.6A is the max but that isn't controllable via the pot., I think) and voltage increase to about 2V or so as well. Spark is jumping bigger gaps with a much higher frequency (even compared to the old circuit where I had a 9V plus 3 AAAs, and a 12V to 3V 700mA step-down converter).

I realised that the 12V remote controller (operates on 12V-24V) only puts out about 8V and the LED driver supposedly requires 12V-24V. I would add more battery power so the output of the remote controller is up to 12V but I assume it won't do much since I've maxed out the current of the LED driver at 2A. Would you agree?
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Re: Short question topic

Unread postAuthor: Technician1002 » Tue Aug 26, 2014 11:30 pm

In a nutshell, an LED driver is often designed to drive a series string of LED's. High power white LED's often run at about 3.6 volts so 3 in series is 10.8 Volts. If you drive only one at 3.6 volts, you can use the lower end of the supply voltage. If you try to drive 4 or 5 you need the higher supply voltage.

The driver keeps the current high for high brightness and regulated to prevent overcurrent and overheating. Voltage varies with temperature. Some drivers to protect the LEDs will reduce current as the temperature increases to increase the life of the LEDs. It should be in the specification for your specific LED driver.

Ideally, you should set the open circuit (no load voltage mode) voltage to the maximum the load can safely handle. For example if it ran off 4 NIMH batteries, aobut 5 volts is max. A single LiPo, 3.6 volts, etc. Then crank the current to the max as protection from overload if you are NOT driving an LED. LED mode will need the max current in the CC mode set to the operating current specified by the LED manufacture and let the voltage ride depending on temperature.
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Re: Short question topic

Unread postAuthor: jrrdw » Wed Aug 27, 2014 6:36 am

Technician1002 wrote:In a nutshell, an LED driver is often designed to drive a series string of LED's. High power white LED's often run at about 3.6 volts so 3 in series is 10.8 Volts. If you drive only one at 3.6 volts, you can use the lower end of the supply voltage. If you try to drive 4 or 5 you need the higher supply voltage.

The driver keeps the current high for high brightness and regulated to prevent overcurrent and overheating. Voltage varies with temperature. Some drivers to protect the LEDs will reduce current as the temperature increases to increase the life of the LEDs. It should be in the specification for your specific LED driver.

Ideally, you should set the open circuit (no load voltage mode) voltage to the maximum the load can safely handle. For example if it ran off 4 NIMH batteries, aobut 5 volts is max. A single LiPo, 3.6 volts, etc. Then crank the current to the max as protection from overload if you are NOT driving an LED. LED mode will need the max current in the CC mode set to the operating current specified by the LED manufacture and let the voltage ride depending on temperature.


That being said...If MrCrowley's curcuit was to remain at a start up tempature. Do you think running every adjustment at the maximum the over all output would remain relieably steady?

Micro fans and heatsinks anyone???
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Re: Short question topic

Unread postAuthor: Technician1002 » Wed Aug 27, 2014 10:33 am

Set the voltage to to below the absolute maximum your device will accept without damage. This is for protection. Too much voltage lets the magic smoke out. Set the current to just above the maximum start up current of your device so if your device is overloaded or shorts out, the current is limited to a safe value. Due to the complaint the regulator is in current regulation, I presume the regulator is rated for less current than your load. Can you find out how much current your load would normally draw if connected to high current batteries such as NIMH or LiPO at it's rated voltage.
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Re: Short question topic

Unread postAuthor: MrCrowley » Wed Aug 27, 2014 4:00 pm

Technician1002 wrote:Can you find out how much current your load would normally draw if connected to high current batteries such as NIMH or LiPO at it's rated voltage.
That's a good idea, I'll see if I can pick up some batteries to test it with today. Do you think 2800mAh is enough, such as these wired in series?
http://www.surplustronics.co.nz/product ... h-battery-

I was playing around with the circuit a bit more last night. I did as you said and adjusted voltage (to 3.5V) while there was no load attached, attached a load and adjusted the current. It seems when you turn the CC dial clockwise (i.e. higher current) it gets to a point, about 1.75A or so, where the CC light turns off and the current drops down to about 1.5A and is no longer adjustable until you turn it anticlockwise again. I left it on the maximum I could get, ~1.75A, with the CC indicator light still on.

http://www.surplustronics.co.nz/product ... adjustable
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Re: Short question topic

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Re: Short question topic

Unread postAuthor: Technician1002 » Fri Aug 29, 2014 5:48 pm

Set it back to keep the voltage constant. Many supplies like the one you are feeding will draw higher current at low voltage in an attempt to keep the output power up. The reason the current dropped (and was not adjustable) is because the LED driver was supplying all the current needed at the full regulated voltage (CV mode). When the current is dropped below the amount needed, the other circuit tried to draw more current and the voltage dropped as a result (in CC mode). To get reasonable performance you again turned up the current (at lower voltage) until the current needs are met and the voltage later began to rise. When the power needs of the circuit are met, the mode switched back to CV.

Remember in power in DC, Watts = V times A. 1A at 3 volts is 3 Watts. So is 2A at 1.5V. If what you are feeding is designed to operate at 3Volts, It is best to run it at 3 Volts. CV is like a circuit breaker and should not be in CC mode except when driving an LED or other load needing constant current regulation instead of a fixed voltage.
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Re: Short question topic

Unread postAuthor: Juggernaut12121 » Sun Nov 09, 2014 10:57 am

Quick and stupid question, I'm planning on making a piston valved hybris with custom made aluminum cylinders (two to hold the o-rings and one to back up the sealing face). I can't figure out quite how thick to make them. So far I've thought of making them 1/2" thick each (2" diameter), but I think it might be overkill. I'm not too sure which aluminum I'll ise either. Any insight?
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Re: Short question topic

Unread postAuthor: Talk » Sun Apr 12, 2015 4:50 am

Is an all metal tyre schrader valve different that bicycle schrader valve? because i tried to refill my bicycle schrader valve once from a near by gas station and it didnt work :?:
qev2.JPG
if I have set up like this(for single shot), do I fill air chamber from P or A(schrader in air chamber)?
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Re: Short question topic

Unread postAuthor: wyz2285 » Sun Apr 12, 2015 9:07 am

If the QEV is store bought unmodded, fill from P.
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Re: Short question topic

Unread postAuthor: Brian the brain » Tue Apr 14, 2015 2:30 pm

If you modify it, you can fill from A.
You will need to poke a tiny hole in the piston...NOT in the center part!
When I say tiny ...I mean..poke a hot paperclip through the outer rim, or drill a 1mm hole...that small.

stay clear of the center ( seals the out port) but also from the outside as it might cause a tear under stress.

A weak spring behind the piston will help it close.

Do not attempt unless you fully understand.
Piercing the center will make it useless.
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Re: Short question topic

Unread postAuthor: Doodmens » Tue May 19, 2015 9:44 am

So I am going ahead and ask a question...

Is there need for a formula to calculate basically everything to do with a pneumatic air gun (and, on request, a combustion gun)?

Or is there already such a thing out there... Haven't seen one yet though.

Why would I ask that?
Well, I have done a school project recently where I built an air gun with a partner and tried to calculate the muzzle velocity and optimise it. So we came up with some formulas and some experiments and this seems the place to share those.

The formula we have now is for a simple ball valve pneumatic gun, and it takes in respect the pressure, volume of the air tank, mass and effective surface of the bullet, barrel length and size, and the friction of the bullet. It's not a 100% accurate, due to some approximations, but pretty close.

We are working on a more complex formula for calculating a lot of things about semi-auto rifles using QEV's.
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Re: Short question topic

Unread postAuthor: Tep » Wed May 20, 2015 3:24 am

GGDT (gas gun design tool) has you covered there Doodmens...

http://www.thehalls-in-bfe.com/GGDT/

That program has pretty much everything in it. That said the actual workings of the program are a bit of a mystery so if you have an advanced maths / physics interest (if that's what you mean by school) then you may be able to further the understanding a bit?
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Re: Short question topic

Unread postAuthor: Doodmens » Wed May 20, 2015 10:58 am

Ah cool, didn't know about that! My formula is a lot simpler and based off of the standard end-of-highschool physics/maths knowledge. This guy has also got the thermo- and flowdynamics in, which is really cool! I'll humbly retreat to my cave now :D
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