Puzzle: Ensuring 12V from a 12V Deep Cycle Battery

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Old 10-17-18, 07:06 PM
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Puzzle: Ensuring 12V from a 12V Deep Cycle Battery

I'm putting LED lights and an exhaust fan, and a small inverter in a small 5x8 cargo trailer for the purpose of camping convenience.

Objective:
I'd like to tame my Deep Cycle Battery's voltage to 12V so my LED light strips don't burn up. So, I bought a 12V regulator (this) (input 12-24V, output 12V, max 20A).

Problem:
That regulator puts out 12V until I put a load on it. Then it drops to 11V. The load is only 2A. I figure I chose the wrong regulator (insufficient voltage overhead) and could use advice figuring out what sort of device to get.


Would a solar regulator charge controller work? If we like the trailer & setup, we'll probably do solar next year.


Ideal scenario:
  • INPUT; 13.5V, OUTPUT: 12V
  • INPUT: 12.3V, OUTPUT 12V
  • INPUT: 12V, OUTPUT: 12V (or close)
  • INPUT: 11.5V, OUTPUT: 11.5V (or close)

I'm OK with a little voltage drop under load, but an entire volt for a 2A load seems excessive.


Here's a 1.5 minute video where I walk through the scenario:
https://youtu.be/dOeK-RIlo5g

Any ideas would be greatly appreciated.
 
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Old 10-17-18, 07:16 PM
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That unit in your link is a 24v to 12v reducer. Not really a 12v regulator.
You don't need a regulator. Your LED's don't require precisely 12vdc.
 
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Old 10-17-18, 07:35 PM
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From what I can tell, it's a step-down regulator. Here are the specs that also agree with the sticker that 12-24V is an acceptable input range.

Specifications:
Input voltage: 24V DC
Input range: 12-40V DC
Output voltage: 12V DC
Output current: 20A (Max) / 240W

As for the LEDs running on more than 12V. I realize they don't have to be precise, but i'm pretty deep into LED stuff and have seen first hand what heat can do to the diodes on LED strips which aren't great at dissipating the amount of heat that the LEDs generate.

I can run them at a higher voltage and then use PWM to help offset that if necessary, but I'd much prefer the peace of mind of having a relatively consistent 12V power source.
 
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Old 10-18-18, 06:04 AM
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For trailer use I certainly wouldn't bother trying to regulate a battery to be even more 12v than it already is. LED's are pretty tough and most 12v ones are designed for the voltage variation that comes with automotive and trailer applications. Also the regulator is going to waste some of your precious battery charge and one look at the big cooling fins cast into it's housing I'd say it wastes a fair bit of energy as heat and probably doesn't hit it's stated 96% efficiency very often.

I also agree that what you bought is primarily designed to step down the voltage from 24v to 12 VDC. Even though the Amazon page lists it's input voltage as 12-40 it's primary job is to step down 24 volts to 12 volts. It is not designed to rigidly maintain a 12v output.
 
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Old 10-18-18, 07:38 AM
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You won't live long enough to see any difference between supplying 12V or 15V to your LED strips. The resistors molded into the strip are already calculated to supply correct drive current to the LEDs at the worst-case automotive system voltage--probably ~15 volts while charging.

Any regulator consumes (wastes) power in operation, and needs a "headroom" of about 1.2V in order to regulate. You can't get 12.0V out with 12.0V in. You would need an 11V regulator to run off a lead-acid battery and then once the battery falls to below 12V the output would be unpredictable.

Keep It Simple.
 
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Old 10-18-18, 08:56 AM
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The only (super wasteful) way I can think of doing this with commodity components would be to use an inverter up to 120VAC from the battery, then use a 12VDC power supply which you can dial in to exactly what you need. As guy said, you can't regulate voltage without headroom, and you can't get headroom without transforming up.
 
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Old 10-18-18, 03:49 PM
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You won't live long enough to see any difference between supplying 12V or 15V to your LED strips.
This is sort of beside the point, but for future internet people who come across this thread....

I have lived long enough to see the effects of even 12V on a typical LED strip. They do not dissipate heat well. I have seen some change hue over time, some develop a burn mark in the middle of the LED, and often the cheap epoxy covering yellows. Often, these are warm/hot to the touch even when only powering a partial strip. I have seen all of these issues at 12V. Check out forums that are specifically dedicated to LED lighting and this is very common. LED strips are by nature terrible at dissipating heat, and heat is what degrades/kills LEDs. I'd recommend at least knowing about this if you plan on using LED strips from Amazon that are at the $25 or less price point. Keeping them dimmed a bit is a good way to extend their life and prevent issues mentioned above.

The resistors molded into the strip are already calculated to supply correct drive current to the LEDs at the worst-case automotive system voltage--probably ~15 volts while charging.
I don't believe that's the case with common LED strips anymore. Most automotive parts, definitely. At the $25 or less price point, the resistors are calculated to sell the strip. If you can decrease the well-being of the LEDs by allowing more current through them, you can increase lumens and therefore increase sales. These strips are designed for home use, where a regulated 12V is easily available via wall wart.

My extensive reply may seem overkill/harsh - no hard feelings to you. I'm pretty deep into the world of LEDs and have a particular fascination (borderline spectrum disorder) with how amazing/innovative the LED world is at a professional level (see Bridgelux) yet how even name brands are going downhill fast with their consumer offerings. The downhill-ness is mainly related to insufficient heat sinking.

If you go to the automotive market (which I think you're referring to with your 12-15V note), Philips is being very innovative with their automotive LEDs that actually fire backwards in order to bring the heatsink out front where it can dissipate the heat (see amazon item B00P2D41OQ).

Any regulator consumes (wastes) power in operation, and needs a "headroom" of about 1.2V in order to regulate.
I charged up the battery and found this to be true. At 13.2V is when it started maintaining a consistent 12V under load.

The only (super wasteful) way I can think of doing this with commodity components would be to use an inverter up to 120VAC from the battery, then use a 12VDC power supply which you can dial in to exactly what you need. As guy said, you can't regulate voltage without headroom, and you can't get headroom without transforming up.
Thanks. I think that sums up the general consensus/observation and answers my question.
 
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Old 10-18-18, 04:10 PM
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As you are finding out, batteries are not a particularly stable Voltage source. A car works its battery from 8.5 to 14.5 volts. Crank to max charge. You have an issue from 12 to 13.2 apparently using the same type of battery.
Lots of options, most you won't like.
Use 2x 12V batteries in series, and use your apparent convertor to make a stable 12V. If yours won't do that, with various loads, others will. Not hard.
Option 2. Use 2V SLA cells and wire up a 14 or 16 volt battery using 7 or 8 of them; use, again the step down regulator.
Option 3. Fix the cheesy LED issue with something better than a simple Resistive drop. Use a LM317 in either a constant I or constant V mode.
Option 4. Increase the heat sinking of your present LED stack; use oil or metal for cooling, your choice.
Option 5. Make 120V with the 12V battery, and use household LED's. This is actually my least favorite option, but still worth considering if you don't want to design anything.
 
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Old 10-18-18, 05:03 PM
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This all seems like apply NASA level rocket science to a trailer. It seems like a lot of thought and expense on saving some pretty inexpensive LED's. All the lights in my trailer are LED and I power them with everything from stacks of alkaline D cells, sealed lead acid and three cell lithium ion and have never had a problem or a single LED fail even with all those varying voltages.
 
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Old 10-19-18, 12:22 AM
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Originally Posted by telecom guy View Post
As you are finding out, batteries are not a particularly stable Voltage source. A car works its battery from 8.5 to 14.5 volts. Crank to max charge. You have an issue from 12 to 13.2 apparently using the same type of battery.
Lots of options, most you won't like.
Use 2x 12V batteries in series, and use your apparent convertor to make a stable 12V. If yours won't do that, with various loads, others will. Not hard.
Option 2. Use 2V SLA cells and wire up a 14 or 16 volt battery using 7 or 8 of them; use, again the step down regulator.
Option 3. Fix the cheesy LED issue with something better than a simple Resistive drop. Use a LM317 in either a constant I or constant V mode.
Option 4. Increase the heat sinking of your present LED stack; use oil or metal for cooling, your choice.
Option 5. Make 120V with the 12V battery, and use household LED's. This is actually my least favorite option, but still worth considering if you don't want to design anything.
I like option 1 with the 24V.

Thanks for all the advice. You answered my question: no. No simple way of capping this at 12V. At this point, things are fine at 11V. I'll continue to monitor things, and if the LEDs start to drop out once the battery voltage goes lower, I'll hook them up to the battery and make sure to dim them via PWM.

Originally Posted by Pilot Dane View Post
This all seems like apply NASA level rocket science
Compliment appreciated.
 
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Old 10-19-18, 07:31 AM
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I'm definitely not as deep into the LED world as you are. My wife would consider me a "flashlight fanatic", but I wouldn't :-)

I've been suspicious that no-name manufacturers are over-driving their LED products in order to boast of extreme performance. Apparently you've verified that to be true.

All considered I think I would choose to fabricate a simple regulator using an LM317 or LM338 and calculate fixed resistors for a steady 10-11V output, or use a potentiometer for a useful dimmer. Probably somebody has already invented that, packaged it nicely, and can be bought from China for $8.99 delivered.
 
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Old 10-19-18, 11:47 PM
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use a potentiometer for a useful dimmer.
Yes.... they've been available for years. It's called a PWM (pulse width modulated) controller. It doesn't actually resistively reduce voltage. It pulses the power on and off very fast. The faster the pulse..... the brighter the light.

Although they technically reduce voltage..... they don't self regulate.
They are sold everywhere..... even on amazon.
PWM controllers
 
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Old 10-20-18, 02:10 PM
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Rule of thumb from many years ago is that you want the input voltage to a regulator to be at least 3 volts higher than your desired output voltage.
IE: If you want 12V out, you should put 15V in. This is for a National Semiconductor 7812.
 
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Old 10-20-18, 03:37 PM
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All advice given is good. The failure to listen to that advice has been unfortunate and the "all future readers" are advised to follow the replies given.

Bud
 
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Old 10-22-18, 10:24 AM
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Originally Posted by Bud9051 View Post
All advice given is good. The failure to listen to that advice has been unfortunate and the "all future readers" are advised to follow the replies given.

Bud
Really?

There's a lot of good advice in this thread for sure. Which advice am I failing to listen to that you think is unfortunate?

If it's about whether or not 12V LED strips can tolerate 14V, I'll make my stance clear for future readers:
  • If the LED strip is designed for automotive use, then it's very likely to be just fine with 14V.
  • If the LED strip is *not* designed for automotive use, then it's very likely to have problems if supplied with 14V.

In summary, check out your LED strip to see if it was designed to handle the additional voltage. Mine is not.
 

Last edited by keith204; 10-22-18 at 10:49 AM.
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Old 10-22-18, 10:41 AM
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Originally Posted by ThisOldMan View Post
Rule of thumb from many years ago is that you want the input voltage to a regulator to be at least 3 volts higher than your desired output voltage.
IE: If you want 12V out, you should put 15V in. This is for a National Semiconductor 7812.
This probably highlights my reason for this post. The rule of thumb makes sense as a rule of thumb, but a rule of thumb doesn't take into account various types of regulators (switching, linear, linear low-drop-out) and others I may not be familiar with.

Being aware of LDO regulators for smaller things had me wondering if there was something similar for the situation at hand. The answer seems to be no.
 
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Old 10-22-18, 10:48 AM
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Thanks for the replies. I'm going with a selector switch:
  • Left: Battery power
  • Center: Off
  • Right: Regulated

That way, when the charger is hooked up and the supply is 14.4V, I can switch to a safer voltage. When the battery supply gets down to 12 or 12.5V, I'll switch to direct battery power.
 
 

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