Large Scale Central

Buck Converter Report

Electronics
#1

So I wanted to do a follow up for potential interested parties. So I ordered an RC controller from Locoremote in the UK. I will give an update on this later when I get it and can do a proper review. But for now the subject had come up on how to protect this remote and still provide enough power to run my locos at a speed I will be happy with. On another post here many people said I just won’t be happy with 12v, and I know what 14v looks like and acts like with our trains. I really wanted to get at least 14v if not 14.5v if I could do so and protect it.

The remote is rated at absolutely no more than 15v peak. Its operating voltage is 12V but after talking to Chris at loco remote he said it should work just fine at 14.5v as long as I NEVER spike it past 15v. His concern with 14.8 (14.4v) lithium ion batteries is that they charge beyond 15v initially. He was worried that I would deliver a spike of higher voltage and fry the board. So I posed the question on here and it was suggested to try a buck convertor which in layman’s terms a voltage regulator. It will give a set output regardless of the higher input. Not to be confused with a buck/boost converter which will increase a lower voltage to the same working voltage.

So I purchased These which are a buck convertor. They have an operating input voltage of 3-40v and a regulated output voltage of 1.5 to 35v @ 3A. The controller I am getting has a 2A rating so this covers it.

Now right off there is a built in inefficiency in them. No matter what the input voltage is the output voltage will be 1.5V less. So you need to make sure your battery is providing at least 1.5v more than the desired output. Since I want to run at 14.5V that means I needed at least 16V input. Now this did somewhat defeat my initial purpose of wanting to stick with 14.8v lithium Ion batteries that I already have. So I plan to switch to 18.5v batteries (5 - 3.7v cells). This should give me the 14.5V I want all the time.

So with that said I received one of these in the mail. I soldered the type of plugs I use on the input side and a pair of bare leads that will go to the motor. I hooked the input up to my bench top variable power supply and the output to my multi-meter. Right off the bat the 1.5v drop was spot on. It dropped exactly 1.5v (with some fluctuation but never more than a couple tenths of a volt). You adjust the output voltage with a little flat head slotted screw knob on top of one of the gizmos. Its the only thing you can turn so its not hard to figure out. Turning it clockwise increased voltage turning it counter clockwise decreased it. All with the input voltage remaining steady. Once I set it at 14.5v on the multi-meter with the input at around 25v I started decreasing the input voltage. It remained at 14.5v output until I reached 16v input and then at that point the output voltage decreased at 1.5v below the input voltage. Just as advertised. The final test was to shock it by rapidly turning up the voltage in my feeble attempt to create a voltage spike. I certainly could not turn my supply up fast enough to cause event he slightest bit of spike through the convertor.

So the long and short of it is that these little buck converters, at A $1.50 a piece are great for controlling voltage. Knowing I can plug in anything from a 14.8V battery to clear beyond 20+v batteries and get a constant output is pretty cool. Now I will have to buy 18.5v batteries if I want to get the 14.5v but at this point that is not a tragedy. I think I only have one 14.8V pack left after destroying one and giving one up for my nephews train. I will use the one I have left to run a critter or some smaller thing that I don’t need speed out of. I will wire a polyswitch in between the buck convertor and the controller just in case something goes bad on the converter and it wants to send a larger voltage through. I don’t even know if this is a thing but it will make me feel better having it in there.

#2

Just a heads up that the converter is not 100% efficient, so some amount of your battery power gets dissipated by the converter. Hard to tell from here how much - a few percent?

That will translate into shorter run-time between charges

#3

Okay guys, need some help here. I ran this by the guy who designed these controllers. And he is serious when it comes to protecting these controllers. First a bit of clarification which I am glad I received before cooking my new controller. Its not 14.5v that I thought he said. He said 13.5v continuous with 15v max. So I will have to turn the buck converter down to 13.5V.

Now here is where I am confused. He is highly recommending and pretty much will only guarantee the product if it is connected to 10 X AA NiMH or 3 cell Li Po (li Ion) battery packs. Lets forget the NiMH for . . .well forever. I will scrap using the controller before I fight trying to hide 10 AA batteries in my Forney and honestly I don’t care for battery cars. I will go back to what I was doing before I switch to a big brick of NiMH. But lets discuss 3 cell Lithium batteries. At 3.7v per cell this is 11.1v. Now from what I have experienced and tested they do over charge. My Tenergy charger is putting like 16.2v or something in that ball park into my 4 cell Lithium Ion (14.8v) packs. I fully charged one and stuck it on my multi meter and it was giving 16v and change.

From what I gathered from an inference that he made (not an out right statement) is that this over charge is what I should be working with. i got the impression that he was saying the over charge lasts quite some time before the battery comes down to its working voltage rating. So his argument is that the 11.1v Lithium ion 3 cell pack will run at closer to 13v (and therefore close to the max input of 13.5V) for a considerable time. If this is the case then what is the 11.1v rating?

Now with all things considered he does not at all like the idea of using a buck converter. I have asked why and he never really has answered that question and I am waiting for a response now that I have asked him directly why he does not like the idea of having a buck converter knocking down a higher voltage to 13.5v (or 13, or 12, or 11 for that matter).

Please don’t read into this that he is not being helpful. Quite the opposite. He has been prompt and has tried to thoroughly explain his thinking. Problem is he is an electrical designer and I am a moron. I am sure much of what he is thinking/saying he is considering as information that should be intuitive. He doesn’t realize that I only got them fancy indoor 'lectric lights last week. He just hasn’t dumbed it down enough yet for me.

So help me try and understand this. What does the voltage rating on batteries mean if 1) they charge to much higher and 2) remain at a higher voltage for its working life. Is that a “minimum” working voltage?

Next why his reluctance to use a buck converter? Am I missing something about them where they could fail and dump more voltage to the controller than what I have it set for? I would think, with out any idea of what I am talking about, that they would fail and burn up and stop producing power altogether.

#4

Jim,

The buck converter I got does list this in percentage but I don’t remember what it is. But after running up and down the voltage dial on the input side it remained pretty constant at a 1.5v loss. So there is most certainly a loss. And it is one of the reasons I am wanting to use something like an 18v battery to combat the loss.

#5

It isn’t about voltage loss, it is current loss. Think of the battery as having a fixed capacity of water like a tank. The buck converter will use a bit of the water as it drains out to perform its function. And you can think of the water pressure to be similar to the voltage. Since there’s only so much water in the tank, the buck converter uses a few percent to perform its magic.

Now, as I understand it, buck converters are what is called a “switched” power supply, That means that it switches the power on/off really rapidly as part of the conversion process. The converter will have a filter to try to smooth that out a bit on the output but it may have much more “ripple” to the voltage than the battery.

My electronics fu is decades old so it may be that somebody else here is more up to date.

Does any of that make things more understandable?

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#6

That’s just the way batteries are rated. If you measure a fresh 1.5V AA lithium it will read about 1.8V
1.5V is what is refered to as the “nominal voltage”. Think of the nominal voltage as the “mid-life” value.
The battery itself will not remain at the high voltage for its working life. This is why we use buck regulators.

Consider your 14.8V battery. It’s high charge is 16.2V. For arguments sake let’s say it’s “minimum safe charge” is 13.4V. The “minimum safe charge” is the value below which you can’t discharge the battery without harming it physically (shortened life, shortened life cycle …) A “good” buck has a settable minimum at which point it will shut down the circuit to protect the battery. So you can run the battery from 13.4V thru 16.2V. You have measured a drop of 1.5V so you can safely get 11.9V thru 14.7V from the pack. In other words, running 16.2 thru 13.4V minus the 1.5V drop is a usable range of 14.7V thru 11.9V.

If you want to get 14.5V out to the choo-choo you need a battery with a minimum safe voltage of 16V.
Its full charge value need only be less than the rating of the buck input.

There is another type of regulator called “buck/boost” that can provide an output higher (within reason) than the input. I use these in my G scale locos:
https://www.amazon.com/JacobsParts-Synchronous-Converter-Step-Down-Efficiency/dp/B078KQ63HZ/r

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#7

Devon,
What you are experiencing/hearing is entirely native to Lithium batteries. NiMH types will charge at 1.2V all day, and never deliver more than 1.2V. Not so the Lithium types. They charge up to their maximum and then discharge, slowly reducing voltage as they loose power. Totally unlike any battery you’ve ever used.

So a 14.4V pack is charged up to 16.2V and then slowly discharges to 12.2V where the protection circuit turns it off.

Take a look at this table, for protection of a single 18650 LiIon cell:
Protection Circuit Module Specifications For 3.7V Li-ion/Li-Po Battery Pack

Over-charge protection voltage 4.25V±25mV
Over-discharge protection voltage 2.80V±50mV
Over-current detection current 5A±1A

What this tells you is that the single LiIon cell charges up to 4.25V and then, as you use it, slowly discharges down to 2.8V. The battery/cell is rated at 3.7V as that is the sorta mid-point [as the discharge isn’t linear.] The 4-cell pack charges to 4x4.25V (17V) and turns off at 4x2.8V (12.2V).

Note it does turn off instantly, unlike a Nicad or NiMH, assuming it is protected, which all Li batteries should be.

No it doesn’t. It starts at the full charge voltage and the voltage reduces as you use the battery. Not quite linear, but close.

He probably has no practical experience with them and is reluctant to ‘approve’ it. If he does, and it fails and trashes his product, guess who you are gonna call? And there’s another upset client (you) who tells everyone on LSC about his product problems. Much better to be cautious and stick with what you know.

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#8

First,

Jim thank you for putting it in water terms. That made sense. The current loss is water loss due to pipe friction. That is something I understand.

Steve,
Great explanation. And added to what Chris at Loco Remote just responded answered all of my questions/misunderstandings. He basically said the same thing you did.

Add to this Chris explained that as a manufacturer and the one backing the product he knows what batteries do and he knows what his product does. He also explained that voltage isn’t his only concern but load in conjunction with voltage compounds the problem. As the one guaranteeing his product against failure he knows that he can safely and reliably use 3 cell lithium batteries under all conditions and have it run the controller reliably. He also explained that my 3 cell pack is going to give me 13v for over half its charge life.

He went on a bit further (and listened to me) when i said I never run more than 5 or 6 cars at not much more than half throttle. I don’t ever run trains faster than half throttle other than maybe for a brief moment. He assures me that I will get all the speed and performance I want with a 3 cell Lithium battery. He is so confident about this that he has offered me a full refund if I use it with 3 cell lithium batteries and am unhappy. Thats putting your money where your mouth is.

On a final note he did answer me about the buck converter. Its not his. He didn’t make it, he can’t guarantee it. Since he has no control over that component he can not guarantee his product. That’s fair. most user modifications void warranties. Chevy won’t let me put a blown 502 in my HHR and guarantee the transmission. So I understand that.

What I will do is get me a 3 cell pack and run his controller and see what I think.

#9

Devon - after all this, you do realize that they overcharge to the limit set by the protection circuit. The battery itself would probably go higher if you allowed it (don’t quote me on that - I think it would overheat and explode.)

You are certainly on the right track with thinking that, if it fails, it stops and won’t hurt the device plugged in to it.

I have a buck convertor on one of my locos which has an older ESC (electronic speed control) which really doesn’t like much anything above 14V. I set the convertor to 13V and I have a “14.4V” battery, so that as the battery discharges from 16V to 12V the voltage to my loco is almost constant.

I would recommend you set the convertor to the low end of the range that the battery provides. In your case, set it for 13V output and plug in the “14.4V” and the Locoremote. As the LiIon battery discharges you will have constant voltage to your loco.
Send Chris a note saying it’s entirely your choice to run his product that way. :grin:

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#10

Pete,

we crossed posted but just about everything you said he said in his last email. Again great customer service to take the time to 'xplain it to this numbskull.

He explained the battery charge discharge thing about the way you did. And that is entirely different than what I thought but it also makes sense. I had a very big misconception that Lithium batteries were similar to NiCad in just the way you explained. Int hat they gave a constant voltage until they were dead. One thing that affirmed this misconception was exactly what you and Steve pointed out. I was completely clueless that there was built in protection on those boards that “switched” the battery off at a certain voltage. But to quote a line from one of my favorite movies “ah light shines on marble head” so the reason lithium batteries run so great and a long time and then just quit dead as a door nail (in a long tunnel) is not because they discharge equally and evenly until dead, its because of this built in circuit protection turning the battery off. Talk about an “ah ha” moment. That makes all the sense in the world. And you hit the nail on the head. He knows his product and doesn’t know the buck converter and he can’t warranty something that has been used in a manor that he has no control over. Makes perfect logical sense. And sense he has been upfront and honest from the beginning I have no greater expectation for his product than what he has claimed. Pretty smart from a business stand point for all the reasons you mention.

He and you guys have convinced me to try a 3 cell pack and see what it does. He is willing to give me my money back if it doesn’t do what I think it should do. That’s backing your product. Good guy. I have nothing at all bad to say about him at this point.

#11

A follow-up - there is no guarantee that either the battery pack or the buck has a low voltage shutdown circuit. They may or may not - Read the manuals closely -

If the shutdown circuit is in the buck, make sure you understand the battery spec and can set the buck shutdown voltage appropriately.

#12

Steve you lost me here. Maybe its the cheap buck converters i bought but I see no where to set anything like at. The only adjustment on the ones I bought is the screw that adjusts output voltage. And sense I really have zero idea what it is we are talking about I see nothing else on it to “set” other than that. Is this just because I bought the cheap dollar store buck converters as opposed to some better ones with more functionality? While I have abandon the need for a buck converter in this argument, i am intrigued by them and want to play with them. If for no other reason than to learn something new. I will certainly find a use for the ones I bought somewhere and understanding them better will help me decide how and where to use them. I could also see playing with a buck/boost just to watch it work.

#13

I took at quick look at the specs on the amazon page you linked to in the first post - I see no minimum voltage circuit either. So the question is whether you battery pack provides one.

I could also see playing with a buck/boost just to watch it work.

Check out the one in my previous post, it works well!

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#14

Steve,

Thanks for all your help. Not only has it been educational on Batteries and Buck converters but I just placed an order for a battery pack and noticed a lot of information I otherwise would have never paid attentions to. Like both you and Pete mentioned there is a lot of info on these. The one I ordered does indeed come with circuit protection for over charge and over drain. It clearly stated what these parameters were. So I have confidence that I am buying a battery that I understand and has the necessary built in protection. Considering how my others work I assume they are protected as well. can’t swear by it but I know they work well and they shut off like a switch when they hit a certain point. As for charging I have always used my Tenergy smart charger which I think has all that protection built into it as well. But its nice to have a bit of knowledge like i have now so I can buy with some confidence.

It will be fun to play with this new controller. Now the battery I bought is a 3 cell so I won’t be adding the buck converter. i don’t want to risk burning up my controller. But I look forward to playing with them more.

#15

The controller manufacturer is probably right to be suspicious of the cheap buck converters. I use some that look identical to those you linked on Amazon to set a fixed “dim” voltage on the low voltage LED down lights in my train room. When set to “dim” which is feeding the buck output to the LEDs , occasionally they will flash bright. That would be the high voltage spike your controller can’t handle.

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#16

John,

I think that’s exactly why. He has no control over the quality of the device. And as Pete points out its HIS reputation on the line not the manufacturer of the cheap buck converter

#17

What you can do is use a “boost converter” to boost a lesser voltage to a higher voltage, then use a “buck converter” to reduce it to the desired voltage. Then you avoid the problem of possible “overvoltage”

I had come up with the concept and one member on MyLargeScale is doing it based on my design to provide the proper voltage for his Sierra Sound card but using supercaps rather than a battery and there is a whole thread on it. This would let him use the sound card to just a few volts instead of the ~13 volts it was taking to keep the cap alive.

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