Hey all,

I'm a biologist/maker who is trying to make a custom lighting setup for photographing small insects with a iPhone + macro lens. I am considering using this small 12V LED ring (https://www.amazon.com/dp/B078VVR7C...1YUZP0IG&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it) and 23A battery(ies) for the job and I have a few questions:

1) In creating this circuit, will I need a to add a 12V resistor to the circuit to limit the voltage coming into the lights, or does it look like that is built into this product? I see a little black rectangle placed after every three LEDs. I know that many LED strips have resistors built into them but I am uncertain about this product.

2) If I used one or two A23 12V batteries to power this ring, would that give me a reasonable amount of time to use the light? I expect that I would want the light to run for at least two hours (longer is always better). I don't have a sense of how to gauge how much time I would get from a single battery or two.

3) Besides soldering in a switch, a battery case with leads, and possibly a resistor, what other features would I need to make this circuit effective for my basic needs?

Thanks very much in advance!

 

Those already have the resistors, you just need to connect to 12V.

They do not list a current fir that ring, but I am going to guess it is 50mA x 4 or 200 mA. The A23 has 55mAh capacity, so it will last maybe 10 minutes.

Edited to add: But it probably cannot supply that current at all and will fall to less than 12V immeduately when connected.

I would recommend 8 AA cells.

 

I would recommend 8 AA cells.

Either that or a sealed lead acid battery (SLA) capable of 12 volts at 7 amp hours. Such a battery will measure 2 1/2" thick by 6" wide and 3 3/4" tall.

[edit] @BobTPH stated that this is overkill. Yes, it is. I meant to preface my comment with "If space is not an issue" meaning if you don't have any space restrictions, a larger battery would serve quite well for future growth.
[end edit]

[edit #2] Even 8 AA batteries is going to take up some space. With AA batteries, if they're standard alkaline batteries you're going to be spending money on replacement batteries depending on how frequently you use the system.
[end edit#2]

ASSUMING 200mA draw (or 200mAh) a smaller battery with a 1Ah capacity will give you approximately 5 hours of burn time. And SLA's are rechargeable with a simple 12V charger. No special charger needed.

One thing about SLA's, they don't like to be stored without being charged once every three months. Fail to charge them regardless of usage and they will go flat on you. You'll want to recharge it after every use. But if you store it for a period of time longer than 3 months then you'll want to put it on a charge.

Here's a 5 amp hour battery, smaller than the one I described for $20.99.
Here's another 5 amp hour battery but it's NOT an SLA, it's a LifePo battery and will require a special charger. This one has a builtin Battery Management System (BMS) meaning it's hard to harm the battery. It has definite advantages over an SLA, but even with a BMS you'll still need a battery charger that can charge the battery at the correct profile. Failure to properly charge the battery may result in a failed battery. This battery also has the added benefit that it can be stored for long periods of time without having to worry about keeping it charged every three months.

 

If 200 is correct, a 5Ah battery is severe overkill for a 5 hour run time. It will run for 25 hours.

To the TS: If you have one of those lights, please measure the current at 12V. Right now, we are only guessing. But I think it is safe to say that an A23 or two will not do it.

 

severe overkill

Yes, I know it is. I meant to preface my comment with "If space is not an issue". But yes, it's overkill for sure. But speaking personally, I'd rather the higher capacity battery than one that can just fit the bill. Unless space is a concern, having a larger battery means if I run into an unexpected delay or issue I still have workable lighting time to get the job done. AND I don't have to recharge the battery (Lifepo) every time I use it. It's ready for the next time I want to give it a go. Besides, who's to say that in the future the TS may want a longer work-life span for larger projects.

Here in Utah the DOT has repeatedly closed portions of the freeway just to add another lane. I've been here 17 years and almost every year they're closing part of the freeway to upgrade for the increased traffic. Years ago I made a suggestion to DOT concerning one point of congestion in my neighborhood regarding a particular intersection. They rejected my idea in favor of upgrading the intersection. Since then they've upgraded it twice, and now they're talking about adding a new on and offramp a half mile north just like I suggested years ago. As it is - people use the nearby intersection to access both the freeway to travel to Salt Lake City AND to access Hill Air Force Base. In the mornings it can take several light cycles just to get through that intersection. IF they would have moved the freeway on-ramp half a mile north years ago they would not have spent as much money on the intersection AND saved tons of money. But they like to engineer for obsolescence. It insures they have a job next year because what they're doing now will no longer be useful in the year to come.


This is the worst intersection I've ever seen. And no - let's not take this thread off topic. My point is 'Why build for obsolescence when one can build with headroom for the future?' For sure, the intersection is much better than before. But it's woefully insufficient for today's needs. And with future growth - I'm thinking of selling and moving. ANY time I have to go through that intersection I have to add a good 30 minutes just for that intersection. Yes, 30 minutes is no exaggeration.

 

Edited my post (see post #3)

[edit] @BobTPH stated that this is overkill. Yes, it is. I meant to preface my comment with "If space is not an issue" meaning if you don't have any space restrictions, a larger battery would serve quite well for future growth.
[end edit]

[edit #2] Even 8 AA batteries is going to take up some space. With AA batteries, if they're standard alkaline batteries you're going to be spending money on replacement batteries depending on how frequently you use the system.
[end edit#2]

 

Thanks for the feedback from both of you!

 

Take a look at Big Clive's solution for photographing small objects. Making the LED ring large enough will eliminate hot spots and reflections. Well worth 12 minutes to watch this video.

 

An associate of mine used to comment that if something is worth doing, it is worth overdoing.
So my question is how often would this light package be used? And for how many accumulated hours? and consider the cost of those 8 AA batteries, plus the battery pack to hold them. Now consider the service life of a smaller 12 volt gell cell rechargable many times. They will last at least 5 years if not abused , broken, or frozen. Also, if a year from now the TS decidesto use more LED strips, or higher powered ones, that 5 AH battery will serve very well.

 

Speaking of over-kill .............

A small Gell-Cell can be automatically kept fully charged by your Car
with a simple 5-Amp-Diode to drop the Voltage slightly, ( minus ~0.7-Volts ).

Then build the following simple Circuit to efficiently regulate
the Current to as many LEDs as You like.
You can put 4 or 5 LEDs in series with a switch across half of them,
or put a switch across all but 1 of the LEDs if You don't need that much light.
.
.
.
.

 

One thing about white LEDs is that the colour temperature can vary with current. So if uniform illumination brightness and colour temperature is important, you want to power those LEDs from a regulated 12 volt source. If you happen to have 18 to 20V cordless tool batteries lying around, get/make a connector for the battery (broken tools are a good source, or you can buy adapters, or 3D print them), then add a buck converter to turn 18V nominal into 12V regulated.

Alternatively... get a 5V ring light (or LED strip) and run it from a power bank. That would be a bit simpler.

 

Put similar LEDs in series strings with only one lower value resistor to limit the current for each 3 or 4 string. That is more effircient because much less voltage needs to be dropped across the resistor. With an adjustable switcher power supply you can have series strings with more LEDs and not need much resistance at all.