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Topic: Is there a safe reliable relay to use with Arduino (Read 339 times) previous topic - next topic

DangerToMyself

I've been reading up a bit on relays as I intend on using a few in a project I am working on. The basics of the project is turning on/off a 100w LED light at specific times. The light will consist of a single 100W COB (Chip On Board) LED that needs 34VDC~3A(max) to operate.

Is there an affordable/safe/reliable means to control larger loads? Well, I know there has to be. I guess I should be asking "What is an affordable/safe/reliable means to control larger loads?" I really don't like the thought of using the cheap Chinese relay board I bought (got it for testing code more than anything). And don't want to burn down my house either. :o

I've spent a bit of time searching the web this morning for a UL listed relay and not had much luck. It would appear they don't really test individual components all that much. I did find the PowerSwitch tail but it seems a bit pricey when I know there are waaayyy more cost effective options out there.

What should I be looking at? Point me in a direction folks.

Thanks!

jackrae

Why not use a mosfet with low side switching

DangerToMyself

Why not use a mosfet with low side switching
That was a thought I had at the outset of this project. I don't recall why I turned away from that path. But somehow, I got the idea that a relay was the way to go and didn't look back.

I have several of the FQP30N06L mosfets and heat sinks (link to PDF data sheet). I'm not seeing why they wouldn't work. Or am I missing something?

avr_fred

You're on the right path with a mosfet switch- since you're switching DC at 30 something volts. The parts you mentioned are fine for the application, logic rated and 35 milliohms on resistance. That's  about 0.3w dissipation at 3 amps so a small heat sink should be fine as well. You should have a fuse (poly or thermal) inline with the LED since 100W is enough to heat things to dangerous levels, given the right circumstances.

Your original post prompts me to say that you can kill yourself or burn the house down just as easily with a UL listed relay as a $1 bargain relay. When it comes to load switching, it's more about specifying the most appropriate device, with the required ratings, proper protective devices and installed in a proper enclosure with the correct wire size and insulation. Easy, right?

The power switch tail meets a market demand for makers that want to build and sell things that control AC mains without having to go through the incredibly costly product testing required to market a consumer product. That's how it survives at what seems to be rather high prices for what it does. One competitor and *poof* their margins would disappear.

DangerToMyself

You're on the right path with a mosfet switch- since you're switching DC at 30 something volts. The parts you mentioned are fine for the application, logic rated and 35 milliohms on resistance. That's  about 0.3w dissipation at 3 amps so a small heat sink should be fine as well. You should have a fuse (poly or thermal) inline with the LED since 100W is enough to heat things to dangerous levels, given the right circumstances.

Your original post prompts me to say that you can kill yourself or burn the house down just as easily with a UL listed relay as a $1 bargain relay. When it comes to load switching, it's more about specifying the most appropriate device, with the required ratings, proper protective devices and installed in a proper enclosure with the correct wire size and insulation. Easy, right?

The power switch tail meets a market demand for makers that want to build and sell things that control AC mains without having to go through the incredibly costly product testing required to market a consumer product. That's how it survives at what seems to be rather high prices for what it does. One competitor and *poof* their margins would disappear.

I very much appreciate your comments. I will most certainly have a fuse installed. I was looking into that aspect earlier today. Who knew there was so much to learn and so many options with a fuse? Can be a bit mind boggling. Well, I guess you folks knew that. Thanks again!

Wawa

A 100watt 34VDC~3A ~34volt 3Amp COB LED needs a constant current driver/supply.
Not a relay or mosfet or constant voltage supply.
Google something like "Meanwell dimable 100watt LED driver".
Leo..

DangerToMyself

A 100watt 34VDC~3A ~34volt 3Amp COB LED needs a constant current driver/supply.
Not a relay or mosfet or constant voltage supply.
Google something like "Meanwell dimable 100watt LED driver".
Leo..
You are correct. However, I have no intention of "powering" an LED, or anything else, with a mosfet. I, as was said in the original post, merely want to be able to turn off/on the power using an Arduino. And I don't think I want to connect a 100w LED driver directly to an Arduino.

rdashorizon

#7
Jul 20, 2017, 12:48 pm Last Edit: Jul 20, 2017, 01:08 pm by rdashorizon
I've done exactly what you're attempting before, controlling a COB LED (Bridgelux Vero series), with an Arduino.

The easiest way to do simple on/off switching with these lights is to use a driver than can dim to 0, Meanwell LDH series for example. All MW drivers with the 3-in-1 dimming function interface easily to Arduino and using the TimerOne library to generate a 10KHz PWM means you get smooth, efficient dimming functionality if you require it. Using a 10k pulldown on the dimming line ensures the COB gets turned off if anything goes wrong on the control-side.

 I've run sets of lights controlled this way with timing provided by a DS3231 safely for ~14 months.

Wawa

and using the TimerOne library to generate a 10KHz PWM means you get smooth, efficient dimming functionality if you require it.
That does not make sense. 10kHz is way to high to be able to dim low enough, even for 8-bit PWM.
LDHxxxx dimmers work on about 500kHz, and you need at least one ot two periods of that to make the dimmer work.
Do the maths.
Leo..


rdashorizon

That does not make sense. 10kHz is way to high to be able to dim low enough, even for 8-bit PWM.
LDHxxxx dimmers work on about 500kHz, and you need at least one ot two periods of that to make the dimmer work.
Do the maths.
Leo..


Excuse me? Have you actually looked at the datasheets for any of the LDH series? Acceptable frequencies for PWM are stated in the range of 1KHz-10KHz with specified curves for both ends.



In this case taken directly from the LDH-45 series datasheet.

Wawa

Note the flat blue line between 0 and 10%.

You can have 10kHz PWM.
You can have 12-bit or even 16-bit PWM.
But you can't dim down to a low PWM value with a high PWM frequency and a high resolution.
Leo..

DangerToMyself

rdashorizon ... Thanks for the input. I looked into the MW LDH series. If I'm not mistaken (and I could be), none of those output enough current for a 100W LED. Which requires around 3 amps max (as I'm sure you know). The largest output is around 1000mA.

I also looked into other Meanwell "3-in-1" drivers. There are a few that would do the job. However, as I need 3 total, those are way out of my price range at this time. Maybe in the not so distant future I'll upgrade to MWs. But for now, I'll have to go a more cost effective route for the current budget.

Wawa

Search for "250w boost LED driver" on ebay.
Leo..

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