I need to vary DC voltage from about 10v to just under 20v. (like a dimmer/potentiometer) -- but programmatically via an arduino.
What are the best way(s) to do this? (It'll be in a high vibration environment, if that matters).
I have stable voltages at 13.8 ("12v"), 5, and 3.3 As well as the 19.8v that I need to bring lower...
I need to cycle it about 2-4 times / second, so if using just a circuit (ala 555) is best, I can just turn on/off the cycling of power ie: let it be the 10v, 20v, or cycling up and down.
I cannot just shoot between 10 & 20 -- have to ramp up & down...
Do you have a schematic of the part you have to apply this varying voltage to.
At some stage you have to interface to that, whatever D/A you are going to use.
Impedance/drive current are as important as varying voltage.
Leo..
The 'interface' for it is non existent -- it's just "on or off" thru a buck/boost converter that goes from 13.8 to 10.5 or 19.8 (based on which line was brought to 13.8 -- there are two hot-lines and one ground. One line puts out 10, another puts out 20).
I need to inject myself not in those power lines, but after the converter so I can ramp up and down the power rather than jerking the voltage. From what I can tell, the amperage does change much (about 2 amps @ 10v, and 2.4amps at 20)
No schematic; I didn't build it; just need to alter how it works...
Grumpy_Mike:
You need to say what sort of current you are expecting to draw from this voltage before we can suggest a proper design.
I realize I didn't post it initially, but I did say 2 amps and 10 to 20v dc.... Not sure what else I can measure here that would help clarify the situation -- so if you could be more specific, I would be happy to gather that information.
jAssing:
I realize I didn't post it initially, but I did say 2 amps and 10 to 20v dc.... Not sure what else I can measure here that would help clarify the situation -- so if you could be more specific, I would be happy to gather that information.
You didn't mention any about the current in your initial post.
This is a high power application - you need to explain what you are driving before
any sensible decision can be made.
jAssing:
From what I can tell, the amperage does change much (about 2 amps @ 10v, and 2.4amps at 20)
For a given load the current will vary quite a lot as the voltage goes from 10V to 20V. Ohm's law says it will double in the load. I think we need to see the reasoning behind that statement.
That amount of current is a whole different issue. You will need a few volts more input than the maximum 20V output, say something like 24V. That is a serious amount of power.
Grumpy_Mike:
For a given load the current will vary quite a lot as the voltage goes from 10V to 20V. Ohm's law says it will double in the load. I think we need to see the reasoning behind that statement.
That amount of current is a whole different issue. You will need a few volts more input than the maximum 20V output, say something like 24V. That is a serious amount of power.
thanks, Mike... I was trying to help someone out -- I'll give up and tell them hire a professional...
I think getting 24v, in and of itself, wouldn't be that hard, but "serious amount of power" -- I don't want to hurt myself if a mistake is made.
MarkT:
You didn't mention any about the current in your initial post.
Yup I admitted that -- posted it before you comment tho... No need to reply if you really don't want to help... blindly pointing out others flaws helps no one...
you need to explain what you are driving before
any sensible decision can be made.
Pretty cheap. If you look around you can find other variations as well. 2 amps at 20 volts is pretty low power requirements, you should be able to find an off the shelf PWM controlled option.
It may require you learning how to adjust the PWM frequency on the Arduino, but will be quite a bit cheaper than hiring someone
I have to ask a question then put in my $.02 worth...
The question: What is the purpose of cycling a fan/LED light from dim/slow to bright/fast at a 2-4 Hz rate? This really makes no sence that I can think of...
Now for how I would do it. First, like Mike said start with a 24 volt 5 amp (enough to do what you need) supply. Simply use PWM and a suitable mosfet to drive the load. You most likely will not even need filtering if the load is really just a LED light and a DC fan. If filtering is needed just add a small series resistor (.1-.2 ohms at 2 watt) and a fairly large Capacitor to filter the PWM into smoother DC output.
Program your Arduino to do the cycle like the fade example in the IDE at a slow rate... You will need to figure out the min and max PWM output to approximate 10 - 20 volts.
This is a very basic explanation but it is how I would start. You probably will need a heatsink for the FET also.
jAssing:
Yup I admitted that -- posted it before you comment tho... No need to reply if you really don't want to help... blindly pointing out others flaws helps no one...
It is a fan & led light source.
The whole point of these forums is to point out flaws, surely? Making sure everyone is
on the same wavelength is useful I think, posting at cross-purposes isn't generally
useful.
Is the fan a brushless fan with its own control electronics? Is it designed to be PWM'd
or does it need analog voltage control? If the latter a programmable buck-converter is
the most efficient option for dropping the 24V supply down to what is needed at any given
instance.
LEDs generally don't take to variable voltage supply BTW - is this a single LED + resistor
or something like that?
In general provide all the information up-front and you'll get meaningful advice.
The whole point of these forums is to point out flaws, surely?
AMEN !
I need to inject myself not in those power lines, but after the converter so I can ramp up and down the power rather than jerking the voltage. From what I can tell, the amperage does change much (about 2 amps @ 10v, and 2.4amps at 20)
Is the fan a brushless fan with its own control electronics? Is it designed to be PWM'd
or does it need analog voltage control? If the latter a programmable buck-converter is
the most efficient option for dropping the 24V supply down to what is needed at any given
instance.
I think it is fair to point out that all of the questions asked by the responders illuminate the fact that
further information is necessary to determine which method will work.
The wording in this statement:
I need to inject myself not in those power lines, but after the converter so I can ramp up and down the power rather than jerking the voltage
clearly indicates you have little electronics background. It would have been more expedient to start out by stating that and saying you want to control a fan and led instead of saying you want to control a voltage.
but "serious amount of power" -- I don't want to hurt myself if a mistake is made.
I wouldn't exactly call that a "serious amount of power" (less than a 100W light bulb and less than 35Vdc.
If you connect any semiconductor devices wrong you can turn a tiny 2N2222 plastic transistor into an almost lethal projectile when it blows up so there is some degree of risk involved if you are not experienced with electronics.
This is all contingent upon getting some kind of information about the fan (& led). If you have no documentation you need to at least post a close up photo of the hardware with special attention to any labeling (if any). If there is more to it than just a fan and a led then we need to know what.
The amazon link provides an interesting alternative. The uSupply looks interesting too.
MarkT:
Is the fan a brushless fan with its own control electronics? Is it designed to be PWM'd
MarkT:
The whole point of these forums is to point out flaws, surely? Making sure everyone is
on the same wavelength is useful I think, posting at cross-purposes isn't generally
useful.
Is the fan a brushless fan with its own control electronics? Is it designed to be PWM'd
or does it need analog voltage control? If the latter a programmable buck-converter is
the most efficient option for dropping the 24V supply down to what is needed at any given
instance.
LEDs generally don't take to variable voltage supply BTW - is this a single LED + resistor
or something like that?
In general provide all the information up-front and you'll get meaningful advice.
No, it does not appear to be designed for that -- moreover, the led overheats if we 'toggle' the power (the fan doesn't supply enough cooling 'on high' -- since it's operating at 'low' power, then switches to high -- the led heats up but the fan doesn't 'instantly spin faster) -- The idea is to "put the thing on high" (and leave the fan on high) and ramp up/down the led.
or does it need analog voltage control? If the latter a programmable buck-converter is
the most efficient option for dropping the 24V supply down to what is needed at any given
instance.
it seems to respond to the lower & high voltage only, an 'inbetween' power leaves it 'on low' -- there appears to be a good deal of electronics 'built into' the fan and led beyond just the simple "power in".
LEDs generally don't take to variable voltage supply BTW - is this a single LED + resistor
or something like that?
No, it seems there's more going on that simple led+resistor. I think it's one LED, but it's behind a lens that distorts the view into it -- and it doesn't seem to be easy to disassemble...
In general provide all the information up-front and you'll get meaningful advice.
I didn't think it was relevant -- next time I'll overload the info..
Regarding 'flaws' -- it wasn't the question of 'how much power', it's the timing -- I had provided the information before he pointed out that I didn't specify it in the 1st post; so does that mean he wanted some other information? anyway, I'm past that. I will try to post more info next time.
