Large Scale Central

Battery Voltage Choices

General Discussion
#1

I have converted my engines to Airwire board and batteries. I just went ahead with the battery they recommended as it seemed straight forward. I didn’t give thought to the voltage provided and how that will limit speed and possibly pulling power of the locomotives. I am working on my last engine conversion and realized that the max voltage for the engines can be up to 22 volts. The batteries I am providing are only 14.8v. There are other higher voltage batteries available that I didn’t consider at the time.

I am curious why they only recommend 14.8 volt battery and not say 18 or higher batteries that I see available. I also wonder just how much difference in speed/pulling power I would have gotten if I had higher voltage batteries.

I understand that generally going really fast is not realistic for diesel engines and I wouldn’t necessarily run them at full speed but sometimes it might be nice to have the option to run them at a faster speed then their top speed.

Thoughts?

#2

“fast” is a non-quantifiable term. (https://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-laughing.gif)

I set my system up to be able to product prototype top speeds.

This can be difficult with some of the diesels. My “ah ha” moment was the Aristo E8’s. Now I am running DCC, so there is a 2-3 volt drop through the decoder vs. the track voltage. I had 20-21 volts on the track, and the loco would only go a scale 62 miles per hour. In this case, this is a passenger loco. By raising the track voltage to almost 24 volts I was able to get to about 92-94 smph unloaded.

So this all depends on what speeds you will run, loads and effective grades (you have a grade on a curve as I remember).

The battery folk may scream about this, but if you are talking mainline standard gauge modern diesels, 14.8 volts will not give you scale speeds that are typical. (I hope people read this last sentence carefully, we are talking mainline sg modern diesels, not a ng steam loco that rarely goes over 25 mph).

Early Airwire had some limitations in max voltage as I remember, which might be part of the poor “blanket” recommendation.

Greg

#3

In my mind; the faster you run, the faster it wears out. Our drive trains tend to be our weakest link,

Things to watch out for; going straight at curves, leaning/falling, throwing the last cars off as you tail whip them through the curves, string lining across a curve … wheel and flange wear as you increase centrifugal forces as steel/brass might only look like …

An edit: as I was writing the above, I was wondering why you didn’t pick DCC as it has those voltages a constants.

No Sir! I completely agree that a bullet needs a good load with fresh powder

#4

John, no question all that is true, but that was not the question.

I think if Nicolas measures his smph like I did, he would be surprised at top scale speed with the 14.8.

And Nicolas’ did clearly give the caveats that he would not be running the top speed all the time, but to have the ABILITY to do this. As I posted, I went through this and was surprised at my measurements and results and how much difference a few volts made.

One thing I learned is that speed vs. volts is NOT linear, often the last few volts to a motor makes more difference than the first few volts.

Greg

#5

I merely mentioned those things and conditions that speed might cause. You hadn’t posted yet (to my knowledge, so I wasn’t responding to your post until the edit).

Happy Rails

#6

Ah. Thanks for the info. I see that you can get 18.5 v 6700 mah LI batteries and even 22.2v. The USA Trains manual says the range of voltage for the SD70 is up to 22 volts.

I just briefly, tried out the SD70 I have not converted yet on the track with track power and it does move significantly faster then the same engine on battery. I tested the power pack though and it was outputting quite a bit more then 22 volts. At some point I will test out the various voltages on the track powered engine to get an idea of just how fast it goes.

On Airwire’s FAQ I found this

"All AirWire decoders can tolerate up to 28 volts. Naturally, the motor must be capable of safely handling the battery voltage used. Most motors are rated at 12 to 22 volts. However, higher voltages cause the motor to generator more electrical noise which will cause a reduction in the radio reception range. We recommend the 14.8V lithium battery pack. It is a perfect compromise between radio range and pulling power. It is also one of the more economical packs and one that we offer for sale. "

I already have the last battery for the last engine to be converted. Converting all 6 engines at this point to a higher voltage battery would be expensive, time consuming, and put extra wear on taking apart the engines. When the batteries start to fail, I’ll probably re-evaluate which batteries to replace. Ideally I want all the engines to have similar batteries so when I run them in consists they all go about the same speed.

#7

I probably should have been a bit more clear, the older generation decoders, no longer produced, had some issues.

One thing was that they were sold as 10 amp decoders, but they were not. If you read the site and specs carefully, you would see that they were 120 watt decoders.

Indeed, at 12 volts, that is 10 amps, but no one was using 12 volts, and some people did indeed push the limit of the 120 watt rating, in the early days people were running multiple locos from one decoder, often diesels and of course we are back to even 14.8 volts on a diesel is usually not enough, not to mention 12 volts.

The newer gen AW stuff is more tolerant in any case.

Have you set off a marked distance so you can time the loco and see what the actual scale miles per hour are? It’s usually surprising.

Don’t the AW decoders have speed matching CV’s? you should be able to match dissimilar locos.

Greg

#8

I haven’t yet. Its raining now so I’ll have to wait until a dry day. I have a good stretch of straight track made of 5 foot track segments so I should be able to easily measure speeds.

They do have abilities to change speeds mappings of the engines. I haven’t played too much with it yet. I suppose once I take some measurements I can modify the engines to match up.

Regardless I already own 14.8 v battery for the last engine to be converted. I dunno what the shelf life is of batteries that are not used. I could stash that one and save it and buy a higher voltage battery but then I have a spare battery sitting on the shelf and one engine that moves significantly faster then the others.

I will say that or the brief period I was able to try the engine out with track power, it was going fast enough around my 10 foot diameter curves that I was afraid it was going to not stay on the track. It was not pulling anything at the time though so I am sure that would slow it down some.

#9

Well, my 2 cents, for what its worth. Would you really ever want to run at a true scale top speed? Most of our layouts are small in comparison to what the 1:1 guys actually run on, and our curves are tighter. Just because an F unit can run at around 74 MPH (with freight gearing), it looks better to my eye running at 35 to 45 SMPH. I know that the new diesel locomotives can run fast, but when I pace the trains around here in my van, I see them going 30- 45 MPH.

#10

My understanding is that batteries in storage will eventually self discharge. Eventually. So if you are going to have one “as a spare” you might want to look into what needs to be done to keep it healthy.

#11

When I pace trains around here they are going 70-80 mph. Passenger faster.

Also, AGAIN, Nicolas stated:

“I understand that generally going really fast is not realistic for diesel engines and I wouldn’t necessarily run them at full speed but sometimes it might be nice to have the option to run them at a faster speed then their top speed.”

(the top speed limited by 14.8 volt batteries)

Guys, when we want to be helpful, shouldn’t we read the question carefully and do the OP the courtesy of answering his question, even though we may do things differently ourselves?

I don’t run battery, but I’m not lecturing Nicolas on why he should have gone track power, likewise I’m not “helping” him by telling him to “don’t do that”… (although personally in this case I completely agree with him, especially since he has steep grades)

Greg

#12

The recommendation for the 14.8 v battery is as Airwire states, transmitter range. Don’t ask me, ask them.

I have both 14.8 v and 18.6 v batteries, and I really cant tell much difference in max speed. There is a bit of difference in what load the 18.6 v battery will start up a hill, probably due to Watts.

Caveat: There are those who think that I am not to be trusted with a light switch.

#13

Nick I will try to answer your question I am Battery not DCC This is airwires answer to 14.8 volts
"14.8 Volts - This voltage is the best option for long range radio operation. Higher voltage causes much more interference to be generated by locomotive motors which can impair distant radio operation. Higher battery voltages are not recommended since they will wear out locomotive wheel treads and axle bearings much faster." That is a quote from AirWire

My self I have used 14.8 Volt battery’s for over 10 years now on grades over 4 percent and that is with 48 cars. I also have run over 2 hrs. with smoke at train shows pulling over 34 well cars with weight in them. I do know a battery person who has gone to 18 volts but that was he could power other Locs. But with higher voltage comes a large size and the question of how to get it in.

I also hope Jon the God Father of Battery posts his findings

Richard

#14

Thanks for all the help. My layout is a fair size with some good sized stretches of straight runs. The tightest curve I have is 9.5 diameter and that is only for a 1/4 of the circle. The rest of my layout is at 10 foot diameter curves. All switches are #6 switches as well. While these curves are not as gradual as I would like it was what worked in the space I have.

I’ll be doing some measurements once is stops raining with my battery/track power engine and update with the results based on voltage and no car load.

#15

Also for anyone wondering here http://rldhobbies.com/hje-6s2p.aspx is a 22.2 volt battery, and here http://rldhobbies.com/hje-5s2p.aspx is an 18.5 volt battery. From the specs it looks like the higher voltage batteries are a little longer but otherwise very similar. SD70’s and GP8-38’s which is all I have in my fleet all have room to spare for a larger battery then what I put in so space would not be an issue.

#16

Higher voltages may well affect the range of an AIRWIRE Rx because it is using the 900 Mhz band. No such problem exists with 2.4 Ghz.

I regularly supply pcb protected Li-Ion 5s packs for larger Aristo and USAT 6 x axle locos. No range problems at all.

#17

Airwire states the higher voltage causes more motor noise and it affects range. Honestly a pretty poor state of affairs. I wonder if people have tried shielding the receiver part of the circuit board.

Also, how about 0.01 noise caps on the brushes?

Surely there is a solution to this receiver problem.

Greg

#18

I am by no means a battery expert, but for reference I run a Bachmann K27 with an Ariwire G2 board and 18.0 volt 5600 mha battery with no ill effects of the motor. That said, my installation utilizes all the OEM Bachmann electronics and is installed entirely in the tender. This additional shielding of the OEM electronics plus the additional distance from the drive motor may be the ticket. I have no issues controlling the ESC from over 100 feet away.

#19

I have about 30 locos. 14.8v has worked fine for me. Just a matter of preference. Personally, I don’t like the Lionel racing around the track look. Too each his own.

#20

From an electronics perspective, there’s no reason why you can’t use a higher-voltage battery. The latest Airwire stuff will run just fine on 22 volts. (Stated maximum input voltage is 24v.) However, don’t forget to take battery life into consideration. If the battery pack is internal to the locomotive (cannot be swapped out), you need it to last the duration of a typical operating session so you’re not changing out a dead locomotive halfway through the session. I would not sacrifice longevity for speed “just in case.” Yeah, the extra voltage is nice to have if you want to run flat out at a club display or something like that, but if your space is limited and going to a higher-voltage pack means using a pack with lower capacity, you run the risk of not having enough life in the battery to get you through a session. Better in that instance to run slower but longer.

What’s the more likely scenario for needing a little extra “just in case?” Is it more voltage to run faster, or more capacity to run longer? The 22.2 volt pack from RLD listed above has 12 cells. It’s rated at 6700mAh. That’s two 22.2v, 3300mAh packs in parallel. At that capacity, that’ll get you anywhere from 5 to 10 hours run time. Now, take those same 12 cells, but configure them for 14.8 volts, giving you three packs in parallel for a capacity of 10Ah. You’ve now got a battery that will run your loco 9 - 15 hours or more on a charge. It won’t run quite as fast, but if you don’t need the speed, you won’t miss it. And you’ll be charging your battery less.

I use that pack as an example, but it’s important to note that most installations aren’t blessed with the space for such a large pack. Even in a big diesel with a long hood, by the time you put this pack, the electronics, a speaker, and (if you want) a smoke unit, you’re looking at a very tight fit. In most installations, the choice between voltage and longevity is a choice between 2 - 4 hours running at higher speeds or 4 - 8 hours at lower speeds. (The lower-voltage batteries are often cheaper, too.)

Later,

K