Large Scale Central

Electronics Question

Electronics
#1

So I have a ignorant electronics question. If I normally run Lithium Ion at like 14.4V-14.8V whatever they are I can never remember exactly but in that 14V range. I know when batteries are charged fully they have an initial voltage that exceeds their rated working voltage. It takes a bit to bleed off that higher voltage. Here is my question. If I am using electronics where the manufacturer says that ABSOLUTELY voltage can not exceed 15V, is there something that can simply put wired in between the battery and the control board that will limit the voltage to under 15V? I am assuming that my lithium ion batteries when fully charged would exceed 15V since they are already at that upper end of the voltage limit. I am a water guy and this to me would equate to a pressure regulator where by the supply pressure can vary but the output pressure does not exceed a certain pressure. Is there an “SIMPLE” electrical equivalent like some sort of resistor? I know what circuit breakers do and that doesn’t seem to be what I would need because this is not an amperage overdraw issue. I just need something to deal with initial voltage until it gets to its rated voltage. I hope this makes sense.

The other option, is I could change the battery packs and go with a lower voltage set up. A quick look on Tenergy’s page it looks like the lithium Ion options for voltage are 14.8V or 11.1V. Will 11.1V run trains in a manor that I will be happy with? I don’t run high speed super trains. I very seldom run a train anywhere near over half of its capable speed. I also do not run 30 car consists. Would 11.1V run my USA trains GP9 with say as many as 15 cars should I get the notion and give me a reasonable speed and not run the battery down super fast. I realize I can increase mAh hours at any voltage and increase running time but if I understand things, all other things being equal, that a battery with lower voltage but same mAh rating won’t last as long given the same load. Basically I won’t have the space to ad more cells to increase amp hours so I will be stuck (again assuming) with the same relative size packs with the same amp hour ratings but lower voltage output? yes-no?

I am wanting to put a new to me system in my current GP9 build and if it works well and I like it I maybe switching over to it entirely. So knowing what it will require electrically makes a difference in determining if I really want to go this route or not. The person who has turned me onto it loves it in his smaller 7/8ths stuff. It sounds like a neat system and something I would like to consider. But I have to be confident it will run larger locos.

#2

You can put “back-to-back” 3 amp diodes in series with the battery. Each pair will drop the voltage ~0.7 volt. But of course when the battery gets down to its “working voltage” this will also be reduced accordingly.

Another alternative is to use a “Buck” converter where you set the maximum voltage and the converter will not let it exceed that value.

No, 11.1 volts will not provide a satisfying speed. The 14.X volts is slow enough.

#3

Todd Brody said:

You can put “back-to-back” 3 amp diodes in series with the battery. Each pair will drop the voltage ~0.7 volt. But of course when the battery gets down to its “working voltage” this will also be reduced accordingly.

Another alternative is to use a “Buck” converter where you set the maximum voltage and the converter will not let it exceed that value.

No, 11.1 volts will not provide a satisfying speed. The 14.X volts is slow enough.

Thanks Todd. I will be curious if anyone else has a comment on the 11.1V not being “enough”, that’s my fear. And it may be the limiting factor. the diodes I don’t like because as you mention it drops whatever voltage is there so as the battery drains the problem gets worse. But this “buck converter” is what I I was hoping was a possibility. Something that could be set to a certain voltage and its output was steady as long as the input met or exceeded the setting. For this current project I will have room for electronic “stuff” in the front loco as all the batteries will be in the second loco. I will take a look at those and maybe thats the ticket.

#4

Todd Brody said:

You can put “back-to-back” 3 amp diodes in series with the battery. Each pair will drop the voltage ~0.7 volt. But of course when the battery gets down to its “working voltage” this will also be reduced accordingly.

Another alternative is to use a “Buck” converter where you set the maximum voltage and the converter will not let it exceed that value.

No, 11.1 volts will not provide a satisfying speed. The 14.X volts is slow enough.

Todd, or anyone else, with the buck converter is output constant at the set voltage provided input voltage is at or above the setting? In other words if I want 14V output and provide 16V at the battery initially but that dropping to 14V after use will the output of the buck converter always be 14V if that is where it is set? Or does it decrease at the same rate as the supply power, for example if input is 16V and output is 14V will out put drop to say 12V if the battery drops its supply to 14V? I am assuming not by what you mentioned but want to make sure. Because after looking at them this seems like a good way to go.

#5

What about a “Buck-Boost” converter. Look at me I almost look like I know something. In my reading about “buck” converters ( they are named because they “buck” the system by reducing voltage as opposed to a boost converter which “boosts” the system by increasing voltage).

A next evolution from the “buck” convertor is the “buck-boost” converter. I did answer one of my question in that a “buck” converter maintains a constant output across a range of equal or higher input voltage. So say our battery produces max 16V and we set our “buck” converter to 14V, the converter will produce a constant 14V until the battery discharges to a point where it’s output voltage drops below 14V. At that point the converter basically is no longer used and you are now relying on the battery voltage as it drains below 14v and with it goes the “oomph” you get from it until it no longer powers the loco. As your battery reaches a point of producing say 11V all you will get at the motors is 11V.

Now a “buck-boost” converter has the added ability to boost voltage from a lower voltage to the higher constant voltage. So as the battery produces more than 14V the converter is acting in “buck” mode. But when the batteries output drops below 14V it will switch to “boost” mode and increase the voltage to the constant 14V. So as the battery drops to say our 11V again it will still output 14V. Obviously there has to be a trade off and the remaining stored energy in the battery will dissipate quicker than it would unboosted which means that period of time where it is operating at below 14V will be shorter and thus reduce the overall life of the charge but you will have full performance until the charge is dissipated.

What this means is that no matter what the voltage output is (higher, equal, or below the desired voltage setting) the output from the buck-boost converter is constant through out the entire life of the charge in the battery and thus should mean that the locomotive will run from full charge to dead with the same performance. The down side is they are big. Much bigger, from what I gather, than a simple buck converter. But in my application where one locomotive will hold nothing but electronic and the other the batteries, i am thinking I should have room.

So why are we even having this discussion when there are already other alternatives without having to add all this other stuff. This system has a very small for what it does receiver board so it fits in small areas. It is run from bluetooth on an Iphone or android so no need to have separate controllers. With the particular version I am looking at it will supply a not to exceed 15V (so 14V in my case) 2 Amp supply to up to four motors. It includes sound and light triggers. I can have one receiver power two locomotives (two motors each such as the dual powered trucks of the USA GP9) from the same controller (my phone). Those are the pros.

The cons are that it will be somewhat wire intensive between the two locomotives. Each of the trucks has its own set of wires. There is also the battery wire connection. And at then a pair of wires for lights so that the head lamp of each locomotive is on depending which locomotive is running forward. The other con is the limited power input requiring a converter to keep it from hurting itself with the desire 14.8V working voltage of Lithium ion battery packs.

The only next reasonable option to me is going with the Revo Train Engineer system which I know many many people use and most of my club uses. Since it allows locomotive to be MUed it will run two locomotives simultaneously with a single controller. The down side is that each locomotive must be set up as individuals and thus won’t have a lot of battery space as each will need its own electronics. Battery power will almost have to come from a battery car and supply power to both locomotive but albeit much less wiring than above. It would have the advantage of giving each locomotive the ability to be powered on its own. Not critical to what I am doing but would make all locos much more versatile. Expense. Revo to run two locos is more expensive than the system I am looking at. Again in the long run not a deal breaker. Another minor detail is the need for a controller instead of the phone I am never without. With the RCS-Australia stuff I am already using I see no practical way to couple two locomotives for smooth operation. I am not sure you can have one controller linked to more than one receiver at a time.

Now all of this is me processing and thinking aloud. Does anyone see a flaw in my understanding or logic? I think I am at least going to play with this set up in my GP project since I want to run two locomotives together constantly as one locomotive.

#6

I’ve used buck converters a lot to drop ~22v DCC to a set DC level for trackside consumers. They’re great, especially the ones with a numeric output display. And cheap. Haven’t used a boost type, but I’ll assume you’ll lose amperage if your output is higher in voltage than the input.

I’d recommend buying a couple (one to fuse, one to use, haha!) and just play around.

#7

Going back to your water analogy, you are well on your way to understanding basic electronics…

Voltage can be thought of as pressure.

Amperage or Current can be thought of as volume (GpM etc.)

Resistance is similar to Friction Loss affecting both Voltage and Amperage.

I will second that the 3S 11.1V LiIon packs are not enough voltage except in a very slow speed switching operation. I run 14.8V packs in mostly steam and small diesels that generally run at less than 20 scale MPH.

One thing to keep in mind with any converter, buck or boost: There are losses in the circuit. For a buck converter to output 15V it probably needs near 17V at the input. As mentioned above, the boost converter’s losses are in current.

I really think you will be OK with the 4S LiOn packs without any limiting.

#8

All of the Bucks I have used have a 3v drop from input to output. But there are probably more efficient ones out there. I buy the cheap ones as they are fine for my applications.

I use LM78xx voltage regulators to protect my smoke stacks in my engines. Where the xx is the max voltage you want. So, if you want to limit the voltage to 15v, you would use an LM7815. It can get pretty hot, so should be sinked. I screw mine to the engine’s lead weight and use thermal paste.

#9

Well I was unaware until now of a voltage drop across the converter which does make sense. And if it is as much as 3V then there would be little to no reason to use one with 14.8V Li Ion batteries as opposed to unregulated 11.1V Li Ion packs, essentially the same thing. The ONLY reason to stick with 14.8V Li Ion is because I have them. If I have to buy higher voltage Li Ion to get a good working voltage across a converter then I might as well switch chemistry and get closer to an unregulated pack at or near 14V.

The manufacturer has been really good at helping me work through this. He recommends NiMH AA size rechargables. he says 10 at 1.2V would have a peak voltage of around 14.5V. Now I am wondering really how true that would be 10 cells at 1.2 V is only a working voltage of 12V. But 11 would be 13.2V and as long as it stayed below 15V fully charged might work. This is just numbers I am using from him. I of course have not verified any of this. I am going to take one of my Li Ion packs and charge fully and test its initial peak voltage.

If we switch this conversation to a different battery chemistry, what really are my options. Keep in mind that the way this project is designed I have the entire shell of a USA GP9 to hide batteries in. But I also don’t want it to weigh 10#s. Ideas and thoughts?

#10

Voltage drop yes for buck converters, but you were also asking about buck-boost converters, so that’s a different story.

Cheap pair: https://www.amazon.com/dp/B07NTXSJHB

Nicer one: https://www.amazon.com/dp/B07VNDGFT6

Dang it, now you got me wanting to buy one to play with…

#11

Cliff Jennings said:

Voltage drop yes for buck converters, but you were also asking about buck-boost converters, so that’s a different story.

Cheap pair: https://www.amazon.com/dp/B07NTXSJHB

Nicer one: https://www.amazon.com/dp/B07VNDGFT6

Dang it, now you got me wanting to buy one to play with…

One of the things the guy mentioned with a buck boost converter is the Amp rating. Since the controller I am looking at is 15V with 4-2Amp out puts the converter would need to be a 10Amp converter.

Like you I do want to buy one and play with it. It is intriguing. Are you saying that a Buck-Boost converter will not experience the voltage drop? If I use 14.8V Li Ion I can get 14V from it?

#12

Well…

You can use a “boost” to change <14 volts to 18 volts for a continual 18 volt source then use a “buck” to reduce the 18 down to a continual 14 volts.

#13

Mean while in Idaho close to Devon’s house

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#14

I use these in my deadrail cars:

They have an important feature:

Under-voltage protection shuts off the device when the battery is depleted to prevent damage to lithium and lead-acid batteries

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#15

That looks like just the ticket. I need to at least get my hands on one of these and play with them. but I am liking the idea.

#16

Devon,

It comes without instructions, after several emails with the seller (was very responsive
to the issue) I came up with an instruction sheet. The “version [12]” parts are summaries
of my email exchange.

“Included instruction sheet” is a copy of what does come with it, not very useful by itself.

“KeepPower batteries” section has the data I used to calculate the cutoff voltage.

Finally, “Summary” is my instruction sheet. Note that I calculate the cutoff @ 2.7v (ie NOT
the 2.5v Keeppower lists) to be a little kinder to the cells. Also note that I didn’t bother to
use a dummy load when adjusting amps with my Fluke meter, it IS the dummy load.
Just be sure to use a meter rated well above the current you want to set, and that it is fused!
Use an external fuse if in doubt…

==================================================================================================
version 1:

There is no under-current. The three potentiometers are as follows:

1. Under-voltage (minimum input)
2. Max voltage (output)
3. Max current (output)

In order to set the minimum voltage you would need to provide a voltage source that is the
desired minimum. Adjust the POT so that the fault light turns on, then adjust it until the
fault light starts to turn off.

To set the maximum voltage monitor the no-load output voltage with a multimeter and adjust
the POT as desired.

To adjust the maximum current you need to power a dummy load. Turn the voltage up all the
way and turn the current down all the way. Connect a resistive load and monitor the current
with a multimeter, adjust the current limit up until the desired current has been reached.
The dummy load doesn't need to handle much power because the current limit can be set with
a low voltage. A long wire could be used.

> How would you adjust the under current, hook up a variable DC supply set to the minimum,
> then twiddle the UC pot till output stops?
> How about the max current limit?  Would I need a 5 amp sink of some sort to accomplish this?


==================================================================================================
version 2:

The board is regulating the output power using two variables, the voltage and the current.

In order to set the output current you need to make sure that the voltage limit is not getting
in the way,  that the output is not being constrained by the voltage limit.  Otherwise the
current limit is not having an effect.

In practice it is only necessary to set the output voltage high enough that the current can
reach the desired setting.  The voltage only needs to be turned up while setting the current
limit. With a load the voltage will be constrained by the current limit.  That's what is
needed in order to set it.

> Sorry, I meant under-voltage.
> Confused by:
> "Turn the voltage up all the way" and "the current limit can be set with a low voltage",
> they seem at odds...
> If I turn the voltage all the way up (ie 30 volts) and try to set 7 amps, thats 210 watts,
> or am I missing something?


==================================================================================================
Included instruction sheet:

DCMOD-C Fault Light

The fault light indicates that the input voltage is lower than the current under-voltage setting.
The under-voltage protection is designed to prevent batteries from over-discharge.
Most customers will need to adjust the UV potentiometer on first use.  With the input voltage
connected, turn the UV pot counter-clockwise until the fault light turns off.  It may take up
to 30 rotations.


---
KeepPower batteries:

IMR26650 Li-ion Rechargeable Battery UH2652:
4.2 volts full charged voltage and 2.5 volts discharge cut off voltage

IMR 26650 6000mAh Li-ion Battery UH2660:
4.2 volts full charged voltage and 2.5 volts discharge cut off voltage


==================================================================================================
Summary:

The three potentiometers are as follows:

1. Under-voltage (minimum input)
2. Max voltage (output)
3. Max current (output)

The board is regulating the output power using two variables, the voltage and the current.

In order to set the output current you need to make sure that the voltage limit is not getting
in the way, that the output is not being constrained by the voltage limit.  Otherwise the
current limit is not having an effect.

In practice it is only necessary to set the output voltage high enough that the current can
reach the desired setting.  The voltage only needs to be turned up while setting the current
limit. With a load the voltage will be constrained by the current limit.  That's what is
needed in order to set it.

---
To adjust the maximum current (5amp) you need to power a dummy load. Turn the voltage up (cw)
all the way and turn the current down (ccw) all the way. Connect a resistive load and monitor
the current with a multimeter, adjust the current limit up until the desired current has been
reached.  The dummy load doesn't need to handle much power because the current limit can be set
with a low voltage. A long wire could be used.

To set the maximum voltage monitor the no-load output voltage with a multimeter and adjust
the POT as desired.

In order to set the minimum voltage (16.2v) you would need to provide a voltage source that is
the desired minimum. Adjust the POT (cw) so that the fault light turns on, then adjust it (ccw)
until the fault light starts to turn off.

=====
Vout:	16
Vmin:	16.2v	(6 x 2.7v)
Cmax:	5amp
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