finding a high-quality 24VDC power supply

[jedimasterben]

that doesn't make sense to me. the purpose of the switch to constant current mode is to limit power consumption near the peak of the supply's capability, not suddenly increase power consumption.

The spec sheet says the constant current voltage range for my 24V model is 12-24V. This seems to fit with what I thought, that the constant current mode accommodates a drop in voltage, never an increase.

...no. The purpose of the switch from constant voltage to constant current is because of how LEDs work, as this is primarily a constant current LED driver but with constant voltage capabilities. LEDs want constant current, and the HLG senses this and switches to constant current mode.

You want to know how many watts each uses at full power (24v) as that will tell you how much current capacity you need.

 

[rwb500]

i see you just deleted the "voltage doesn't matter that much" sentence, but that is the key.

voltage is everything. it doesn't matter if it is in constant current or constant voltage mode as long as voltage does not exceed 24V. If it were in constant current mode and it was trying to kill my pumps, voltage would exceed 24V. Absolutely nothing bad can happen to the pumps if the supply voltage does not exceed 24V. You cannot force feed them current at 24V or less.

I don't mean to argue with you because I appreciate your help but you have told me that I have a risk of frying my pumps, and now I need to figure out if that is true or not. If you can tell me how exactly this driver would fry a 24V pump I would love to know.

 

[wgraham]

This is what I use to power my four pumps 2 WP60 and 2WP40 four over a year with no problems
http://www.ebay.com/itm/SUPERNIGHT-...334?pt=LH_DefaultDomain_0&hash=item4d14c106ee

 

[perkint]

I have to admit, I've wondered myself what happens if, for example, you connect a 0.1A 12V fan, to an LDD1000 on a 12V supply? That is the sort of scenario you are discussing (effectively, at least as i see it).

Tim

 

[wgraham]

I have to admit, I've wondered myself what happens if, for example, you connect a 0.1A 12V fan, to an LDD1000 on a 12V supply? That is the sort of scenario you are discussing (effectively, at least as i see it).

Tim

The 12V .1A fan would take only the current it need unless you hook up in series with the LDD1000, but in parallel it would work

 

[jedimasterben]

i see you just deleted the "voltage doesn't matter that much" sentence, but that is the key.

voltage is everything. it doesn't matter if it is in constant current or constant voltage mode as long as voltage does not exceed 24V. If it were in constant current mode and it was trying to kill my pumps, voltage would exceed 24V. Absolutely nothing bad can happen to the pumps if the supply voltage does not exceed 24V. You cannot force feed them current at 24V or less.

I don't mean to argue with you because I appreciate your help but you have told me that I have a risk of frying my pumps, and now I need to figure out if that is true or not. If you can tell me how exactly this driver would fry a 24V pump I would love to know.

I didn't mean to worry you too much, more than likely the power supplies supplied with the pumps are only at 50-60% load with the pump at full power, so if they add up to 10A total possible output, I would only expect 5-6A of that to be ever possible to use. Switching to constant current is what you don't want, as the pumps are only constant voltage and pull only the amount of current that they need. When I said the voltage didn't matter originally, that was in reference to whether you're considering running it at less than 24v, you plan your power usage according to the absolute maximum that the devices would pull.

I have to admit, I've wondered myself what happens if, for example, you connect a 0.1A 12V fan, to an LDD1000 on a 12V supply? That is the sort of scenario you are discussing (effectively, at least as i see it).

Tim

No, actually that would not work. LDD have only one output type, constant current, so it would be pushing the full 1A to the fan at all times, which should kill it instantly.

 

[perkint]

The 12V .1A fan would take only the current it need unless you hook up in series with the LDD1000, but in parallel it would work

I know in parallel (I do actually do that on one of my LEDs with an ELN and regulator) - i was suggesting it as the only thing connected, as a theoretical analogy to the discission about the HLG swapping to constant current mode.

No, actually that would not work. LDD have only one output type, constant current, so it would be pushing the full 1A to the fan at all times, which should kill it instantly.

I know - i assumed it would kill it, but how? It will keep ramping the voltage up trying to achieve its 1A rated current, but the fan will not draw 1A when only getting 9V (the max the LDD will be able to supply based on a 12V supply). Will it do the same as it does with LEDs which exceed its capable output (it will flash them slowly)? But as the flash would be massively over voltage and at 1A, it would just blow the fan?

Tim

 

[oreo57]

No, actually that would not work. LDD have only one output type, constant current, so it would be pushing the full 1A to the fan at all times, which should kill it instantly.

Hmmm. not quite sure about that. It would depend on the Power supply.. The LDD would attempt to increase the voltage (thus the amps) to meet the 1A requirement.
Using a 12V PS there is no more headroom.
You use a 48V ps it will boost the voltage until the fan frys though..
The LDD doesn't "push" current AFAICT...only changes the potential which draws more current..

That said it is silly to use an LDD for this purpose no matter how you look at it..

http://www.instructables.com/id/Power-PC-Fan-using-LED-Driver/

It's not necessary to drive a fan or a motor with a constant current. They don't draw more power than whats necessary to turn them under load. Excessive voltage will be the one to watch.

 

[perkint]

That said it is silly to use an LDD for this purpose no matter how you look at it

I know! I'm guessing you were already writing when i posted my last reply - this wasn't meant as a suggestion, more a theoretical set up, similar to the discussion about the HLG going into constant current on the pumps. Just wondered what would actually happen!

Tim

 

[oreo57]

I know! I'm guessing you were already writing when i posted my last reply - this wasn't meant as a suggestion, more a theoretical set up, similar to the discussion about the HLG going into constant current on the pumps. Just wondered what would actually happen!

Tim

https://reefledlights.com/trouble-shooting/

for fun...

 

[perkint]

I agree with one of his first comments - my soldering is still not good, but it's a damn site better than it was before i started playing with LEDs!!! Not that that would have been difficult - before then, i think I'd soldered less than once every 5 years since i left school, meaning about about 4 times since then!!!

Still curious about the fan - would it just spin up to 9V and then the LDD would not be able to supply more voltage, so it'd just work (and be a silly way of doing things!!!)?

Tim

 

[jedimasterben]

The LDD would still be putting out 1A, it is a constant current circuit.

 

[rwb500]

it seems that some people don't understand that "constant current" only means that the driver will adjust its voltage, within its design limits, to try to supply a specified current. The driver cannot control anything besides the voltage at its terminals. "constant current" is simply a method of adjusting that voltage.

For example, a constant-current driver with 1A set current, 12V maximum voltage, would never put 1A across a 12V 0.1A fan, because to put one amp across that fan (assuming constant resistive load) would require 120VDC.

 

[Gorgok]

Similarly, putting the same .1A 12V fan connected to my trucks batteries (2x 1000A cranking capacity rating) will not do it any harm. Put a wrench across the terminals though...

 

[karimwassef]

So let's introduce two ideas: voltage drop and resistance.

A 12V 0.1A fan has a resistance of 120 Ohms ( 12V / 0.1A ). To drive 1A through it would require a 120V supply ( 120 Ohm x 1 A ). Since the supply can't do that, it won't run in constant current mode. But if you use a 12V supply, it'll deliver 0.1A. If you replace the fan with a higher resistance (higher power) fan that needs 1A, then the supply will deliver 12V at 1A. The voltage is fixed, but the current changes based on the load (the fan).

LEDs have voltage drops but will accept a range of currents. They're not dominated by a resistance. So 12 LEDs at 4V drop in series need a 48V supply. If they're able to carry 1A, then the supply will deliver 1A at 48V. If you have 10 LEDs, the supply will deliver 1A at 40V. The current is constant, the voltage changes based on the load (the LEDs).

 

[rwb500]

gorgok, that is similar but the battery is an example of a constant voltage supply so not quite the same teaching point.

LEDs have voltage drops but will accept a range of currents. They're not dominated by a resistance. So 12 LEDs at 4V drop in series need a 48V supply. If they're able to carry 1A, then the supply will deliver 1A at 48V. If you have 10 LEDs, the supply will deliver 1A at 40V. The current is constant, the voltage changes based on the load (the LEDs).

I don't really like this explanation, as it makes a number of oversimplifications. LED's will not accept a range of currents any more than any typical device. They have a specific current that will flow at any given voltage. "If they're able to carry 1A" really means nothing. The driver will supply whatever it is designed to, as long as it has the power to do so. "the current is constant, the voltage changes based on the load" is the exact oversimplification that causes a lot of people problems. This makes it seem like the current dictates the voltage. A better way to explain it is to say that "the voltage is adjusted to maintain the desired current."

I got the power supply I need and confirmed that it will never fry my pumps, so I think I am done here. It seems like some of you (jedimasterben) should read up on DC circuitry before continuing to give advice.

 

[karimwassef]

All power supplies have limits: e.g.
Max voltage for a constant current.
Max current for a constant voltage.
And max power. It's good to clarify that.

Loads also have limits:
Max current for a fixed voltage drop LED.

I use 2A LEDs at 0.7A to extend their life, so an LED has a fixed voltage drop but will accommodate a range of current levels up to the max rating.

Thanks for making the sharing even better

 

[d0ughb0y]

this is like using premium gasoline on a crappy car<name a="" crappy="" car="">.

any led or computer power supply should suffice to meet the objective of using 1 power supply instead of 10.</name>