Trouble powering multiple par LED lights via battery - Page 1
Forum section: electronics / beginners

author: jasonemry
author_rank: Newbie
timestamp: April 09, 2025, 06:18:55 am
content: I have 8 110v par LED lights I am trying to convert to battery-powered. I took out the AC transformer and added a buck converter for the fan, but when I connect more than one light to a DC power source, each light draws less power. Ideally I would have four lights per battery pack. What am I missing to achieve the desired power output to each light? Thanks kindly in advance for any help.

author: Jinxinyang Technology
author_rank: Newbie
timestamp: April 09, 2025, 08:26:06 am
content: This phenomenon is usually caused by insufficient power supply capacity or improper line design.

author: KimLum
author_rank: Contributor
timestamp: April 09, 2025, 12:08:42 pm
content: Not much info to go on.. I understand that you "step up" the voltage from the batteries to 110V, but whenever you do that you also "step down" the amperage. If your battery outputs 10A @ 12V and you step up the voltage to to 110V, the available amperage will drop to 10 / (110 / 12) ~= 1.1A minus what's lost in the conversion.

author: jwet
author_rank: Frequent Contributor
timestamp: April 09, 2025, 05:01:04 pm
content: There is nothing to go on here. What size is the battery (amp-Hours), watt wattage are the LED's. What kind of battery. What is the buck converter? Etc. Its likely that the buck converter wont make the 2.4 amps required or the battery is overloaded. Get an inexpensive multimeter and take some measurements.I'll pick some numbers to show you how the problem works. Your situation might be different- make substituions. LED PAR lamps are often 7W each, at 12v, this is 7/12A or 600 mA. A 12v battery about the size of a brick is 15 A-Hrs capacity meaning the product of output current and time in hours is 15. These ratings are usually accurate at about a 10 hour rate meaning that you can supply 1.5 amp for 10 hours. With 4 lamps, you are drawing about 2.4 amps, a bit above the C/10 rate so you'd expect less than the full capacity, perhaps 80%. So 15/2.4 is 6.2 hours and you could get around 80% or 5 hours.If you are using something like a 3 series 18650 battery with a capacity of 3 A-Hrs, you are severely loading the battery and would get less than an hour. You might want to look at packs designed for high rate discharge. The cells have a prefix of INR.I didn't go into the buck converter because I don't know where it fits?Take care.

author: jasonemry
author_rank: Newbie
timestamp: April 10, 2025, 03:24:23 am
content: Thank you kindly for your reply. The issue I'm having persists even when I connect to my lab power supply which has ample power, using 5.5x2.1mm DC connectors and splitters to power them. The 8S BMS I'm (ideally) using to power 4 units is rated for 10A. The AC transformers I took out are 100W and put out about 30v each.So, ideally, I'm attempting to make a 30v battery, and using a step-down for the 12v fan, and there is also a 5v wireless DMX module with its own step-down after that. I've used the lights in sync before with their original AC transformers in them and the DMX modules installed, so I am just trying to replace the power supply with DC now.I didn't get into great detail about the batteries before because the issue persists when connected to my lab supply, but I did forget to even mention that hah. And to clarify there will be no AC power anywhere in my circuit. Just ~100W 30v > 12v > 5v ... x 4 units

author: jasonemry
author_rank: Newbie
timestamp: April 10, 2025, 03:34:37 am
content: I realize I may be coming up a little short in my wattage with 10A, but I will get a higher rated BMS if/when I get this solved with even just two lights.

author: jwet
author_rank: Frequent Contributor
timestamp: April 10, 2025, 06:38:42 am
content: I'm trying to keep up with you here- still don't understand the problem. I'll describe what I think I know and you let me know of problems.So it sounds like the PAR lamps are 30V devices that run on 100W? This would say each lamp draws about 3.3A, so 4 would draw 13.2A. Just from the transformers, I guess you need something like 400W nominally. You have an 8S stack which should be about 32v when fresh and can provide 10A. This is about 320W. So you're 20% low on power at the jump. I don't know what life you want to get out of this but you're kind of overloaded already. I assume the 12v and the 5v for DMX is minor compared to these big lamp loads. You can add up their watts and see where you are. Its not difficult to get buck converters to have 90'ish percent efficiency.When you say an 8S stack, are your talking about 8x 18650 Cells?. They have a capacity of about 3AHr and it would be difficult to ask them to provide 10A for any length of time.The currents you're talking about- 10A are heavy- you can't run this kind of current through 5mm/2.1 type Coax power connectors- these are rated for 2A max- and perhaps a bit higher for special ones. It may be that you're getting losses in your wiring. Can you measure voltage drops when you're hooked up to the bench supply and your batteries.Good Luck.

author: jasonemry
author_rank: Newbie
timestamp: April 10, 2025, 07:57:09 am
content: I'm not as focused on the battery configuration since it happens even when connected to grounded power. For reference I am using 8 18650 cells but the lights are used for very intermittent accents so they will not be drawing full power very often.Attaching images of my lab power supply with a single light connected at full power and then another with two. Because I have used the same DC connectors in similar configurations, they are not too high on my list of bottlenecks.In the end I guess I figure if these cell type batteries can power circular saws for extended periods they'd be able to handle some blinking lights for a half hour.

author: xvr
author_rank: Frequent Contributor
timestamp: April 10, 2025, 10:29:34 am
content: How you find out that 2 lamps draw less power? Current indicator on PSU could be wrong if your lamp inject some frequency in consumed power (as it could be if it have input DC/DC and its input filtered not quite enough). Measure consumed current with TrueRMS DMM.

author: jasonemry
author_rank: Newbie
timestamp: April 10, 2025, 03:12:44 pm
content: As the photos above show, when I plug in two lamps, the amperage draw is less-than-doubled, as well as each lamp visibly dimming accordingly.

author: themadhippy
author_rank: Super Contributor
timestamp: April 10, 2025, 03:36:28 pm
content: Is that with or without a dmx cable linking the 2 lamps?

author: jasonemry
author_rank: Newbie
timestamp: April 10, 2025, 05:37:00 pm
content: All of the lights are equipped with wireless DMX modules so they are only connected by their power cords.

author: KimLum
author_rank: Contributor
timestamp: April 11, 2025, 09:30:29 am
content: Are the lamps connected in series or in parallel?

author: CaptDon
author_rank: Super Contributor
timestamp: April 11, 2025, 12:30:46 pm
content: Those lamps must have a high pulse current draw messing with your power supply and each other. Try putting a 1000uf @ 50VDC or even a 2200uf @ 50VDC capacitor on each lamp device and see if they begin to behave normally. You are showing only a single input voltage. Is the DMX receiver built in to the lamp?

author: jasonemry
author_rank: Newbie
timestamp: April 11, 2025, 02:55:47 pm
content: They are connected in parallel, and I am inputting 30v to each light which are equipped with step-down converters for their fans and DMX modules.From what I've seen, pulsing current may be the issue. I'll give the capacitors a try, thank you.

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: April 11, 2025, 03:38:21 pm
content: Schematics are the language of electrical and electronic circuits.It is not clear from your description whether you are employing a step-up converter from 30 to 110 volt.Or are you powering the lamps directly from 30 volts?

author: jasonemry
author_rank: Newbie
timestamp: April 12, 2025, 06:46:32 pm
content: I tried adding 50v 1000uf and 50v 2200uf capacitors to the circuit, but they did not provide adequate power, and only the red chips would light up. So I took the capacitors off of the original transformer board and tried them in both series and parallel. They also did not work.I'm attaching a photograph of the transformers that came with the units. The small capacitor on the DC side is 25v for the fan. The two medium-sized ones are 35v 470uf.Looking at this photo, is it obvious what I need in terms of battery power filtering to deliver the proper amperage?Again, there will be no alternating current in my circuit. I am REPLACING this AC transformer with an 8 cell 30v battery pack.