# PWM circuit help, 24v house lighting system 450w max LED's

#### Evanguy

Joined Dec 21, 2014
81
I'm making a pwm circuit for leds at 450watts max, i have a few questions and I'm very open for suggestion
in my house i plan to make all my own power for the lights we use, I'm trying to get off the grid but i want to step into this. currently 100% if my heat and hot water are from wood that i cut off my own wood lot,

so a little about the system in planning, the house has a total of 14 rooms, and i wish to run 25watts per room, with 3 rooms getting 50 watts

i bought 450, 1w led's http://www.ebay.ca/itm/50pcs-Brand-...hash=item2c85751197:m:mA9ClcekVcDeTh--R1Ag-ww

I'm a machinist by trade, so I'm going to make aluminum fixtures to mount the leds on to hold them and to control heat also they will be slightly dishes
so the leds are directed in different directions

using 16/2 cl2 stranded wire with a 24 volt system, no more then 25w per line, longest run (1 direction) is 30 feet,
Ill be alright on the wiring of the modules and the switches and my fathers been an electrician for 40 years now so I've been around all that stuff, but I'm new to this type of electronics

i want to build a PWM controller and i wish to be able to pwm the whole system

so I'm thinking

battery bank at 24v
24v into into pwm controller
24v pwm fed into a fuse box as the "mains"
from the fuse box send out 14 lines to each room with switches and led modules in the rooms
plan to do some testing with the leds and figure how many per fixture

most times i hope to have only the lights on we need so I'm thinking probably not more then 150 watts(high end of things) at any given time but i do have 450 leds so its possible it can be that much power

I have made up three drawings mostly compiled of things on found on line, still missing a few parts, you will notice the "T" parts missing and a few resistor values missing, as I'm still undecided on them or have figured them out yet
and input on those parts would be nice, but with poking around and reading data sheets ill be able to get them

im unsure of witch circuit would be ideal for my situation, it will be on and running 24/7, i plan to build at least 2 so have backup's in case needed

#### #12

Joined Nov 30, 2010
18,217
300-350 ma, 3.2V to 3.4V
Light Emitting Diodes are not light bulbs and they are not resistors, they are diodes. As a diode, they will allow all the current you have, and they will smoke. Therefore, every LED must have current limiting. That is usually done with a resistor, and that resistor has to get rid of all the voltage in excess of the LED voltage. The point is, providing 24 volts to the LEDs means you have to use up 20.7 volts in the resistor. That is a big (86%) waste of power.

You would be much better off providing 5 volts to the LEDs and using up 1.7 volts in the current limiting resistor. About 5.6 ohms@1 watt should do the trick. That way you would waste 1/3 of your total power in the resistors.

Another way to do this is to put a bunch of LEDs in series and use one resistor for several LEDs. Six LEDs in series will use up about 19.2 volts to 20.4 volts. Use up the other part of the 24 volts with a resistor of size 15 ohms @ 3 watts. This cuts your waste heat to about 18%.

See where I'm going here?

While I'm at it, those push-pull output stages aren't necessary at the frequency you're using. You can slow the oscillator down to maybe 50 HZ and not see the blinking. At that speed, a simple resistor on the mosfet gate can drag it to the "off" condition with time to spare.

#### Evanguy

Joined Dec 21, 2014
81
well i guess i could have added more info then i did. also yes sorry i know they are not light bulbs, they are a diode that happens to also give off visible light in the process of doing their job

sorry, ill be putting these in series and parallel, i was thinking of using 7 leds per fixture and 3 fixtures per room and then feeding them 22.4v and using the appropriate resistor to limit current to amount needed.

i want to run them at 24v so i can get away with 16/2 wire as non of this will be in wall, i want to hide it under base boards and keep it discrete as possible, dropping it down through the floor at the base of the door case into my unfinished basement.

if I'm using 7 leds per fixture, 3 fixtures per room, i was going to run the 7leds in series and the 3 fixtures in parallel and feeding about 24v 1amp per room. I'm going to limit the current on the fixtures them selves or just after the switch. and this pwm is a global thing within my house so in the day all lights can be ran at 65% duty cycle or so, and any other time never more then 90% duty cycle (controlling the pwm is a later task for now its a pot)

i do see where you are going and i like it a lot, i was headed there and forgot to inform you i was on my way.

"While I'm at it, those push-pull output stages aren't necessary at the frequency you're using. You can slow the oscillator down to maybe 50 HZ and not see the blinking. At that speed, a simple resistor on the mosfet gate can drag it to the "off" condition with time to spare."

^^ thanks for this, this is exactly what i was wondering, so i can use drawing 1 then, thanks, i had thought so and that was the first circuit i drew up after i looked more into pwm controllers i noticed there could be a lot more going on then my simple drawing, but i see why, its for the speeds, that are far greater then anything i need.

also "C2" is the trigger so adjusting that will change the frequency, or do you think this already low enough to work with the resistor feeding into the mosfet?

#### John P

Joined Oct 14, 2008
1,872
Actually it's very common not to run large LEDs with a resistor in series, but instead to use an electronic constant-current circuit with an inductor. That design is much more efficient, which you need to be concerned about if your input power is limited. You can buy little boards to do the job for not much cash on eBay--I've done it.
http://www.ebay.ca/itm/1-pcs-6-10x1...470280?hash=item2ed06f9948:g:U64AAOxyTMdTO6pP

However, I suggest that you didn't get the right components. Those LEDs you have will get very hot, and it'll be a hassle to build heat sinks for so many of them. I think you'd have done better to get the "star" type, where they come pre-mounted to a circuit board which has a metal core, and which can be easily screwed down to a flat surface.
http://www.ebay.ca/itm/1W-3W-High-P...hash=item21040e72f7:m:mtnGxNiwP4t_jmTWW970UGw

#12

#### #12

Joined Nov 30, 2010
18,217
JohnP has a better idea. I didn't go there because I can't design a circuit that will do what he says. Fortunately, they already exist in a retail version.

You are still missing some information. IF your seven LEDs all turn out to need 3.4 volts each, 22.4 volts won't turn them on and there is no voltage left for the resistor to work with. The constant current driver from JohnP eliminates that problem because it mostly doesn't care if you are exact about about the voltage you can provide. It will slap the LEDs with whatever voltage they need to accept 350 ma.

I did catch the part about you being able to make heat sinks. You have parts in hand? Examine them to find out if you will need an insulation layer between them and the aluminum.

C2 doesn't have anything to do with the mosfet. It's a timing capacitor. Right now, you seem to be running at 350 Hz. That will work just fine, or you could slow it all down with a bigger capacitor. Then again, the constant current drivers might be adjustable and the whole PWM thing becomes redundant. The design isn't finished. You still have more to discover.

#### ronv

Joined Nov 12, 2008
3,770
well i guess i could have added more info then i did. also yes sorry i know they are not light bulbs, they are a diode that happens to also give off visible light in the process of doing their job

sorry, ill be putting these in series and parallel, i was thinking of using 7 leds per fixture and 3 fixtures per room and then feeding them 22.4v and using the appropriate resistor to limit current to amount needed.

i want to run them at 24v so i can get away with 16/2 wire as non of this will be in wall, i want to hide it under base boards and keep it discrete as possible, dropping it down through the floor at the base of the door case into my unfinished basement.

if I'm using 7 leds per fixture, 3 fixtures per room, i was going to run the 7leds in series and the 3 fixtures in parallel and feeding about 24v 1amp per room. I'm going to limit the current on the fixtures them selves or just after the switch. and this pwm is a global thing within my house so in the day all lights can be ran at 65% duty cycle or so, and any other time never more then 90% duty cycle (controlling the pwm is a later task for now its a pot)

i do see where you are going and i like it a lot, i was headed there and forgot to inform you i was on my way.

"While I'm at it, those push-pull output stages aren't necessary at the frequency you're using. You can slow the oscillator down to maybe 50 HZ and not see the blinking. At that speed, a simple resistor on the mosfet gate can drag it to the "off" condition with time to spare."

^^ thanks for this, this is exactly what i was wondering, so i can use drawing 1 then, thanks, i had thought so and that was the first circuit i drew up after i looked more into pwm controllers i noticed there could be a lot more going on then my simple drawing, but i see why, its for the speeds, that are far greater then anything i need.

also "C2" is the trigger so adjusting that will change the frequency, or do you think this already low enough to work with the resistor feeding into the mosfet?
I think you have a basic problem with the LEDs.
They need a pretty good heatsink. There is a little pad on the bottom of them that needs to be soldered to a heatsink. This is almost impossible to do by hand without melting the plastic of the LED.

#### Sensacell

Joined Jun 19, 2012
2,723
If your whole plan is about using your limited electrical energy with high efficiency, it's essential to use a switch-mode LED driver to drive your LED's, using a resistor is terribly inefficient, especially for a single diode at 24 V.

Rolling your own LED lights is a ton of work when you consider the driver electronics and heat-sink requirements.

I would consider using an integrated DC-DC constant-current regulator "puck" as per the attached file.
You would be able to run several LED's from one puck, in a series connection - with high efficiency.

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#### Evanguy

Joined Dec 21, 2014
81
John P, Yes i see exactly what your saying, i probably should have looked into this more, but i did have to start some where lol
also about the leds, i seen the star ones, but didnt get them because ill make my own heat sinks that work for all the leds in each fixture
also on the water jet at work, i could get quite a few of those heat sinks cut out, and then i can change the thickness if my heat sinks dont work as planed, Thanks for the links its opened up a few more options

#12, i see what you mean about the voltage being at 22.4 and no voltage left for the resistors to work, i havent even considered that at all, i love learning, thanks. and no i dont have parts in hand yet they are in the mail as of 2 days ago. but ill look into them and see, if they dont need the layer i was planning on using thermal paste to attach them to the heat sink, but also little wire holders to hold the led down,

and the only reason i was talking about the cap and the mosfet was because you said i cant go to high of frequency with the simple resistor into the mosfet and the cap sets the frequency i figured so i asked if its going to set the frequency to under the amount i should stay under without a push pull setup. you answered that, Thanks.

Ronv, i believe it will be a lot of work, i hope to get one fixture a day done once i get all the parts here, and instead of soldering them i was going to use a wire clamp to hold them down and also thermal paste under them, much like a cpu is held down in a PC

Sensacell, now we are getting somewhere, thanks and i did plan on running them in series, 24v into 1 led isnt the plan, i believe the work load will be huge, i would like to get this finished within a few months kinda of thing.
and in that link you sent me there are ones that will work with 1000ma, so i could use one per room after the light switch powering all the leds per room. also i see pwm input i could run another single wire for that control..

thanks guys your helping a lot and making me learn, i like.

#### Evanguy

Joined Dec 21, 2014
81
Ok, so ive changed around what i plan to do. i now plan on using local(on each led fixture) STCS1 chip circuits for constant 1300ma.

Now ill be using 16/3 wire so i can send pwm along with the power for each circuits pwm input.

Ill have a new circuit drawing up tonight i hope. it also coveres the whole system.
Battery->Fuse->switch->scts1->leds

24-12v buck converter->555pwm circuit->scts1 chip

I also feel i should put a 100uh inductor in series with the leds but im unsure of where and if it will effect pwm

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#### #12

Joined Nov 30, 2010
18,217
A 555 PWM circuit doesn't care if you have enough microhenries. That's a triac you're thinking of.

#### tcmtech

Joined Nov 4, 2013
2,867
I don't get the whole endeavor and concept here.

I've been buying Zilotek LED lights for $3.48 a pair that are one of the best 60 watt bulb equivalent LED light I have seen yet. They put out 800 lumens at 8 watts input which to be honest there isn't a DIY person here that will touch that price and create a equivilant end product. If it was me and I wanted to cut my electrical usage down I would not be messing around with a whole house custom lighting system with wires running wire where just for lighting I would be putting all my available AE generated power into a basic grid tie system (Store bought unit or pirate GTI build) and be using it to shave the overall utility power consumption down. Thread Starter #### Evanguy Joined Dec 21, 2014 81 I see what you are saying. and it makes sence to me and others. but i would like to get off the grid totally over time. also this would be a fun project, not worries about saving money or time and more wanting to build a system that works for me. the entire house needs new wiring. its 60 years old and here is a crazy mess of wires from people adding and changing things i have a 100amp main and there is 30 breakers all being used. the system is a mess Since i bought the house i totaly redid all the plumbing and now im pickjng away at the electrical. There are mice and squirrls in the attic with all my current wiring and its a little scary. so i want to do the lighting at 24v and rewire all the plugs for 120v bit send them intonthe basement instead of attic. and over time wire the plugs to inverters and aslo run them off my own power. This is nothjng to do with cost. i dont care if it costs me twics as much really. and even if i cant make my power for cheaper then i can buy it, atleast it helps in my quest for self sistainibilty i also grow/hunt about 80% of our total food. #### tcmtech Joined Nov 4, 2013 2,867 I can follow the want to be more self sufficient. Years ago I built my own boiler systems in order to cut my winter heating costs down to near nothing. I've also played with wind power off and on for years as well. It started out all fun but believe me manual operation of a half assed designs got old fast so it eventually got redesigned into all integrated systems that work with my existing electrical power and heating systems so that there was no where near the manual work and time involved in using any of it. Believe me if you really intend to go self sufficient put the time and money into integrating it into your modern already in use systems so that it works with the common off the shelf plug and play AC powered components you already have and use. You will appreciate the upfront work and planning of doing so later! Believe me since everything we use is designed to work around our common 120/240 VAC 60 hz power designing a totally independant electrical system for a limited application is a waste of time and money. Been there done that and it got old. If you have AE based electrical power generation you are better off tieing it into your existing AC systems over setting it up as a independent sub systems. Especially if you are intending to use it in more than just one specific dedicated location. #### mcgyvr Joined Oct 15, 2009 5,394 I was going to recommend the LDD's.. Glad someone already did they are excellent for "high power LEDs" vs resistors and ensure a fixed current even with varying forward voltages... and they are cheap enough to not have to roll your own. Put all the LDDs in your "control room" and run the outputs to each LED fixture.. Then you can supply multiple LDDs with the same 5V PWM signal and have the option of splitting it at anytime by simply adding more 5V PWM "controllers". Today you might want all lights dimmed the same.. Tomorrow you may want to set the "mood" in certain rooms vs others.. Having multiple 5V PWM "controllers" would allow that.. And then get crazy and have the ability to dim from your smartphone. Thread Starter #### Evanguy Joined Dec 21, 2014 81 Mcgyvr, Thanks. i now do plan on running the led drivers in the "control room". good idea. and I've seen the LLD-H but I'm going to need 1300ma for 24w, the 1000ma one could work if i rearranged my led strings but i would lose a few led's. so i plan on using stcs1 drivers, they also cost very little. Here is the system im planning, realistically it will be 360w total 15x24W ,max (if all rooms on at once and pwm at off) only the switch, inductor and leds will be located outside of the control room im going to build 15 stcs1 drivers, 1 pwm driver (for now, may also add an arduino in the mix), 15 led fixtures, at this stage it may be driven with a 120vac-24vdc transformer (just spent any extra money i had on our new to us, wood fire oven and stove and chimney for it, to get rid of the electric ones) or i may build it and wait until i cant get a used bank of batteries out of a forklift type rig before setting it up. its going to be a while building all the circuits ill bet, also my drawing is missing 1 led in series with the 4 strings Edit, i feel i should add some back info on this because i get what Tcmtech is saying. but im also different then most people, we use durning the winter months about 800kwh, summer is alot less. we are changing out the stove and oven for wood powered. we dont have a microwave, or a tv, my wife has hand mixers for cooking, we dry our clothes on the close line (inside winter, outside summer) we do use a washing machine though, all the heat and hot water we make via wood burning (outside boiler for summer) right now the only things that are pluged in/running all the time are; oven/stove(soon gone), clothes washer, fridge/freezer combo , well pump , 2x cell phone chargers , small radio and this computer im on(10"netbook), modem and a lamp in my bedroom. ohh also all the lights in the house, 14 rooms. we live the simplest lives we can lol, we have animals and a small farm on the go, also a large wood lot, one the house is paid off (10 more years) i plan to retire (42yrs) and just try and "live off the land" as they say, sell firewood(225$ a cord here) and snowblow (with tractor) drive ways for any income needed, also sell farmed stuff, money isnt a concern in my life

i already run my shop off a generator (welder(s), mill, lathe, lights the whole shop needs to be "started up"

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#### mcgyvr

Joined Oct 15, 2009
5,394
I will NEVER recommend LEDs in parallel without current limiting on each series string..
They WON'T share equally..

#### Evanguy

Joined Dec 21, 2014
81
ohhh, i see what your getting at, you mean one string may not play nice in the sharing game. so along with the constant current driver i should also have a resistor in series with each string of leds to set current equally between the three string?

#### mcgyvr

Joined Oct 15, 2009
5,394
ohhh, i see what your getting at, you mean one string may not play nice in the sharing game. so along with the constant current driver i should also have a resistor in series with each string of leds to set current equally between the three string?
Personally I would use a higher voltage to avoid parallel strings altogether..
Or "current mirrors" can be incorporated..
Or more "drivers"
Or different LEDs..

#### Evanguy

Joined Dec 21, 2014
81
Ive looked up current mirrors, they look good and ill poke around with them a bit more. but i see what your saying about more "drivers" and using 1 string per driver. if i did that and stepped the voltage to 36v i could run ten leds per driver.

Thanks for the help so far. i have more to look into and think about.

Also the leds i bought they are 1w ~100lm
the three watt ones were only ~220 lm.

#### Evanguy

Joined Dec 21, 2014
81
Well as you can see im trying and failing lol. if you were building a " driver and led modual" for around 18-24w how would you do it 24-36v idealy. 1w leds