Freerails Home 
Freerails > Model Railroad Forums > R.C. The Future Now If You Desire > Revisiting 1-Cell Versus 2-Cell Li-Po Batteries

Freerails IS ACCEPTING new Members ... To join Freerails ... See how to Register as a Member in the 'Joining Freerails' Forum

 Moderated by: .  
AuthorPost
davecttr
Registered
 

Joined: Sat Nov 9th, 2013
Location: United Kingdom
Posts: 527
Status: 
Offline
Sorry about starting a new topic but multiple searches have failed to find the original one where the subject was discussed. I conducted some tests yesterday and think i now have the answer!

Briefly my problem was some of my large locomotives draw about 0.4A which is marginal for a 9V Pololu regulator fed from a single cell lipo. Using 2 cells in series vastly increases the efficiency of the Pololu which can handle up to 0.8A or more, however do you still get the same run time? For example a large loco with a 1S 220mAh battery may run for 30 minutes. Will the run time be the same for 2 batteries in series?. Generally the last discussion reckoned that the extra battery gave more efficiency but no longer run time as you were just getting double the voltage.

The tests.
TEST 1 - I fitted a loco with a 9v Pololu and a single 70mAh lipo, set the Rx LVC cutoff to 3.4V and ran a timed test hauling 8 coaches at scale 60mph.

Result - the LVC stopped the loco after 21 minutes.

TEST 2 - 2 x 70mAh batteries were used in series with the LVC cutoff set to 6.8V. Again the loco hauled 8 coaches at a scale 60mph

Result - I stopped the loco after 47 minutes as I was worried the LVC had not worked. I need not have worried.

The test 1 battery had a residual voltage of 3.68V and the test 2 batteries 3.70V and 3.72V

so it seems that adding a second battery in series not only allows the Pololu to power a demanding loco plus you get at least twice the run time.

Happy Days!

fallen
Registered
 

Joined: Wed Apr 3rd, 2013
Location: United Kingdom
Posts: 197
Status: 
Online
Very useful info Dave, thanks for taking the trouble!

The point about the voltage step-up circuits is that the more they step up the voltage the more they also step up the current. So roughly if they double the voltage to the receiver then they also double the current drawn from the battery.

So the same physical volume of battery could be either a big 1S or two cells wired as a 2S with twice the voltage but half the current capacity. Or as I think we concluded last time that two cells could be wired in series as 2S or in parallel as a 1S battery with twice the capacity, and it would make no difference to the duration, give or take the chages due to the efficiency of the convertor.

What you have done is slightly different. When you add the second cell, the voltage from the cells doubles so the convertor is not having to do so much work. It is not having to push the voltage up by so much. As a result it does not increase the current draw so much either. The current drawn from the two cells will be roughly half that drawn from the one cell. So the two cells should last roughly twice as long, which is what you have.

Good to know how it works out in practice though - many thanks for the info.

Frank

davecttr
Registered
 

Joined: Sat Nov 9th, 2013
Location: United Kingdom
Posts: 527
Status: 
Offline
Thanks for describing the physics behind all this. I admit I can't get my brain around the concepts but at least it seems to work.

I can now start converting my big locomotives to 2S operation. I expect to get an hours use out of a pair of 220mAh batteries which is ample for my 15-20 minutes average run time in an operating session.

d10ng
Registered
 

Joined: Thu Jul 19th, 2012
Location: Lichfield, United Kingdom
Posts: 55
Status: 
Offline
Dave,
Do your locos need the step up still with having 2 cells? Would 7.4v not be enough to run them at scale speeds?
I'm still trying to determine my HO diesel needs, but will go either 9v step-up with a 1s or just a 2s if I can find the right sizes.

davecttr
Registered
 

Joined: Sat Nov 9th, 2013
Location: United Kingdom
Posts: 527
Status: 
Offline
With testing I found that 7.4V was not enough to give me speeds over a scale 60mph when hauling 12 coaches. The 9V Pololu allows all my express locos to have top speeds of 60 to 70 mph.

Another advantage of using a voltage regulator is you get the same throttle response and top speed throughout the battery discharge cycle. A pair of unregulated lipos will deliver 8.4V when fully charged but this will then drop to 6V when the batteries need recharging.

I have decided all my locos will have voltage regulators fitted, most with 9V Pololus but maybe one or 2 will have the 5V version

Rod Hutchinson
Registered


Joined: Fri May 8th, 2009
Location: Mooroolbark, Australia
Posts: 527
Status: 
Offline
That's interesting Dave. I am in the throes of setting up a 2S. However my locos are geared locos so whether to add a 9v stepup is something for me to mull over.

My other two geared locos have 1S with a 9v step up.

johnhu
Registered
 

Joined: Thu Feb 21st, 2013
Location:  
Posts: 39
Status: 
Offline
Talk about timing. :-)

I had been having an issue with some of my larger locomotives (On3 MMI loco's) that were originally configured with 3 800mAH batteries wired in parallel (so a 1S pack) supplying power to a 12v step-up which feeds a CVP airwire (convrtr) receiver.

Every so often when running, they would just come to a sudden stop for a fraction of a second, and then start running again.

Looking at the airwire receiver - which has a power LED lit when it has power - I could see that this power led blinked off when the loco stopped, so obviously the issue was power related. I checked the batteries (all ok), and also replaced the step-up with another just in case, and still it happened.

I then plugged in a spare 3s battery pack to see what might be going on, and the issue stopped happening. So I came to the conclusion that there was an issue with the step-up and the current being drawn by the larger motors in these models.

I have since reconfigured the batteries from 3 in parallel, to a 3S pack (with a wired in balance connector), and all has been fine.

In smaller locomotives (with smaller more efficient motors), the step-up converters have worked ok, but the ones I were using did not handle the larger constant current loads. Of course I could have purchased a different step-up that has a larger current capacity to solve this issue also.

As Dave noticed though, due to the in-efficiencies of the step-ups, I've noticed that I now get a longer run time from the 3 batteries wired as a 3S pack, than I did when the same batteries were wired as a large 1S pack with the step-up.

So for now on the larger loco's, I'll stick with them wired as a 3S pack.

John

Rod Hutchinson
Registered


Joined: Fri May 8th, 2009
Location: Mooroolbark, Australia
Posts: 527
Status: 
Offline
The stepup experiences presented are providing clarity in their performance.

The issue of current draw for different size motors seems to have an impact on the ability of the stepup to perform.

Changing motors to low current draw but highly geared, such as the locos by Bernard Snoodyk, is an option but complex mechanically.

Last edited on Mon Apr 4th, 2016 06:14 am by Rod Hutchinson

Bob R
Registered


Joined: Thu Nov 20th, 2014
Location: Springfield , Nebraska USA
Posts: 632
Status: 
Offline
Johnhu

I have had similar experience with the step up regulators when used in higher amp draw engines. The Pololu regulators are current protected. When too much current is drawn they shut down for a moment and then reset automatically. Keep in mind that the more the voltage is stepped up the more the current draw. I use 1S lipos in my small engines with minimal amp draw but use 2S in larger engines.

Bob R

mwiz64
Registered


Joined: Mon Mar 26th, 2012
Location: Fenton, Michigan USA
Posts: 1330
Status: 
Offline
If you raise the voltage, you lower the current draw for a given work load...at the motor but sometimes a different winding on the motor is necessary to take advantage of the higher voltage, do to the KV of the motor. Of course, the opposite is also true. If you run a lower voltage, the current draw will be higher for a given work load..... and your battery will run dead quicker. Voltage boosters, as you've seen, use up energy. There ain't no such thing as a free lunch. Run the voltage you need from the battery and skip the booster, if you can.... even if it means running two really small cells. Or at least be open to giving that a try. You might just be surprised at the duration of the charge. Higher voltage is more efficient.

mwiz64
Registered


Joined: Mon Mar 26th, 2012
Location: Fenton, Michigan USA
Posts: 1330
Status: 
Offline
If you raise the voltage, you lower the current draw for a given work load...at the motor but sometimes a different winding on the motor is necessary to take advantage of the higher voltage, do to the KV of the motor. Of course, the opposite is also true. If you run a lower voltage, the current draw will be higher for a given work load..... and your battery will run dead quicker. Voltage boosters, as you've seen, use up energy. There ain't no such thing as a free lunch. Run the voltage you need from the battery and skip the booster, if you can.... even if it means running two really small cells. Or at least be open to giving that a try. You might just be surprised at the duration of the charge. Higher voltage is more efficient.

W C Greene
Moderator


Joined: Fri May 4th, 2007
Location: Royse City, Texas USA
Posts: 8253
Status: 
Offline
Yes, I agree with Mike on this. But then, I always find room for the batteries, it's called "creative cramming".

Woodie

davecttr
Registered
 

Joined: Sat Nov 9th, 2013
Location: United Kingdom
Posts: 527
Status: 
Offline
As I am running 00 scale finding space for the batteries is the main challenge so a single cell solution is attractive. For most of the locos a single cell with a 9V regulator works just fine and I can get up to 1hr of use before battery replacement (I recharge my batteries outside the loco). For some of the locos drawing 0.4A or more I use 2 cells in series with the 9v Pololu booster, again 1 hour run time is possible. Two cells giving 7.4V does not give a high enough top speed and 3 batteries occupy to much space. For some pairs of locos a regulator is needed anyway if you want to consist them. I also don't like the top speed reducing as the battery discharges.

mwiz64
Registered


Joined: Mon Mar 26th, 2012
Location: Fenton, Michigan USA
Posts: 1330
Status: 
Offline
The other solution is to get the MFG's to offer motors wound to turn faster so the lower voltage gives the performance you need. It's a simple thing for them to do. Just put in thicker wire and fewer winds.... or look for suitable motors that are already made with "hotter" windings. One could also change the gearing... I'm not saying these things are easy to do, just that they are possible solutions to running lower voltage.

And Dave, I'm not saying what you're doing is wrong. I'm pointing these things out for other people, that might be reading this thread, to consider. My models are larger so I can find space for more cells in the battery.

Last edited on Tue Apr 5th, 2016 06:30 pm by mwiz64

W C Greene
Moderator


Joined: Fri May 4th, 2007
Location: Royse City, Texas USA
Posts: 8253
Status: 
Offline
Yes, I have the space...1:35n2...so I use what will fit. Normally I use 2C 1200MAH or so Li Pos. On a point to point layout with plenty of switching, a lower "top end" is just fine. Someday, battery technology will catch up with OO9 and even N scale but in the mean time....

Woodie

mwiz64
Registered


Joined: Mon Mar 26th, 2012
Location: Fenton, Michigan USA
Posts: 1330
Status: 
Offline
One of the things that helps you and I out, Woodie is that we model subjects that run pretty slowly in the first place

davecttr
Registered
 

Joined: Sat Nov 9th, 2013
Location: United Kingdom
Posts: 527
Status: 
Offline
Here in the UK 00 scale means basically locos produced by Hornby and Bachmann with some other smaller manufacturers. They are all designed to run on 12VDC and the DCC 16V? ends up about equivalent. So no chance of them substituting lower voltage motors. A direct plug in replacement can motor would be ideal, 6V might work well.

fallen
Registered
 

Joined: Wed Apr 3rd, 2013
Location: United Kingdom
Posts: 197
Status: 
Online
As Rod says, changing the motor and gearing can be a bit of a challenge, but if the problem is that the motor is old, either old and worn or just an old design, then changing just the motor, not the gearing, can work OK and may be less of a problem.

I have done this on a couple of n gauge chassis for 009 locos and it has worked well.

Frank

mwiz64
Registered


Joined: Mon Mar 26th, 2012
Location: Fenton, Michigan USA
Posts: 1330
Status: 
Offline
NWSL sells several replacement motors and publishes their RPMs at 12v. They also sell replacement gearing sets.

All you have to do to check the speed of your motor is take it out, put a makeshift, paper or stick propellor on it, run 12v thru it and tach it with a model airplane tachometer you buy at the local hobby shop. I know, that's not super easy but if you're going to re-motor anyway, why not figure out what you have in the first place?

mwiz64
Registered


Joined: Mon Mar 26th, 2012
Location: Fenton, Michigan USA
Posts: 1330
Status: 
Offline
BTW, adding one more tooth on a pinion can be easy enough and make a big difference.

Budd
Registered


Joined: Tue Jan 12th, 2010
Location: Adelaide, Australia
Posts: 105
Status: 
Offline
I'm just trying this 1C + step up configuration in an Athearn Mikado and mine was cutting out as well, the Polulu was getting quite warm, so if I use a 2C pack with the step up will it function better, the speed is a bit slow with just 7.2V. I'm using a 9V step up.
I don't know what that engine pulls (in mA's), I set it up tomorrow and see if I can get a reading.

Wayne from Oz.

davecttr
Registered
 

Joined: Sat Nov 9th, 2013
Location: United Kingdom
Posts: 527
Status: 
Offline
The Pololu regulator has a temperature cut off and I think a high current one. These operating might trigger a low voltage cutoff (LVC) in the Deltang RX. I experience these occasionally and have not been able to determine the cause.

A 9V Pololu with a 1S lipo can't handle locos pulling about 0.4A or greater. Some of my locos draw about 0.5A so using a 2S battery means the Pololu can handle up to 0.9A. There are efficiency graphs on the Pololu page.

I determine the amps draw of my locos by running the loco under load and measuring how long the battery lasts. For example the little 70mAh batteries I use for testing will give 1 Amp for 4.2 minutes. If a loco under test hauling 12 coaches at a scale 60mph stops after 10.5 mins the current draw is about 0.4A. This is marginal so I would probably use a 2S battery.

when using 2S batteries I manually set the LVC to 6.8V. this is to ensure a safety margin as my made up 2S batteries are not matched pairs.

Rod Hutchinson
Registered


Joined: Fri May 8th, 2009
Location: Mooroolbark, Australia
Posts: 527
Status: 
Offline
Wayne,

I am converting my 1S + Pololu to 2S + Pololu. I am doing it because I physically can and because of the electronic theory that has been presented recently.

mwiz64
Registered


Joined: Mon Mar 26th, 2012
Location: Fenton, Michigan USA
Posts: 1330
Status: 
Offline
If you could get 3s to fit you could eliminate the Pololu and your charge would last even longer..... Or you could use smaller cells and maybe have the same duration with but with less heat and complexity. Just sayin....

Rod Hutchinson
Registered


Joined: Fri May 8th, 2009
Location: Mooroolbark, Australia
Posts: 527
Status: 
Offline
Thanks for that.

Yes, plenty of choices.

davecttr
Registered
 

Joined: Sat Nov 9th, 2013
Location: United Kingdom
Posts: 527
Status: 
Offline
mwiz64 wrote:
If you could get 3s to fit you could eliminate the Pololu and your charge would last even longer..... Or you could use smaller cells and maybe have the same duration with but with less heat and complexity. Just sayin....

Yes, it is all down to how much space you have. I am lucky in that all my passenger locos can achieve at least a scale 60mph with a 9V Pololu. The smaller freight types have a single battery because of space problems and the larger freight locos run on a simple 2S battery without Pololu. The nominal 7.4V is enough to give over a scale 25mph and most freights in my modelling period were restricted to about 25mph top speed!.

I have one mixed traffic loco that generates a lot of LVC cutoffs and I am going to try that one with a 3S battery and disabled LVC.

Budd
Registered


Joined: Tue Jan 12th, 2010
Location: Adelaide, Australia
Posts: 105
Status: 
Offline
davecttr wrote:
mwiz64 wrote:
If you could get 3s to fit you could eliminate the Pololu and your charge would last even longer..... Or you could use smaller cells and maybe have the same duration with but with less heat and complexity. Just sayin....

Yes, it is all down to how much space you have. I am lucky in that all my passenger locos can achieve at least a scale 60mph with a 9V Pololu. The smaller freight types have a single battery because of space problems and the larger freight locos run on a simple 2S battery without Pololu. The nominal 7.4V is enough to give over a scale 25mph and most freights in my modelling period were restricted to about 25mph top speed!.

I have one mixed traffic loco that generates a lot of LVC cutoffs and I am going to try that one with a 3S battery and disabled LVC.


I am getting a bit of track here but I have had the discussion at a couple of DC and DCC railways where I operate (with my BPRC engine) about how big a BPRC railway can become before it is too big to manage, my comment was that you may become limited by the amount of battery charging you would have to manage (assuming you don't have some form of auto track charging).
Out of interest Dave, how many engines do you have?

Wayne from Oz.

Budd
Registered


Joined: Tue Jan 12th, 2010
Location: Adelaide, Australia
Posts: 105
Status: 
Offline
mwiz64 wrote:
If you could get 3s to fit you could eliminate the Pololu and your charge would last even longer..... Or you could use smaller cells and maybe have the same duration with but with less heat and complexity. Just sayin....

So you are saying that a 600mA 3C pack will last longer than a 600mA 2C pack + Polulu?

Wayne from Oz

davecttr
Registered
 

Joined: Sat Nov 9th, 2013
Location: United Kingdom
Posts: 527
Status: 
Offline
Out of interest Dave, how many engines do you have?

Wayne from Oz.


I have 20 converted and another 10 to do. An operating session on my layout will use about 15 locos with over 20 batteries. My locos do not have an on-off switch and I use freshly charged ones at each session. I use an E-flite 4 battery charger and am going to buy 2 USB chargers. With these I can charge 24 batteries in under 4 hours. This is easy to do in an evening. I also have three Tx-22, One handles the main line passenger locos, the second freight locos including a consist and the third branch line and mixed locos. I have not populated this one yet.

fallen
Registered
 

Joined: Wed Apr 3rd, 2013
Location: United Kingdom
Posts: 197
Status: 
Online
Budd wrote:


So you are saying that a 600mA 3C pack will last longer than a 600mA 2C pack + Polulu?

Wayne from Oz


That's right Wayne, If the Polulu steps the voltage up it must also draw more current than is being supplied to the loco, by at least the same factor as the voltage is increased. If the Polulu draws more current, the 600mAhr cells in the 2S battey will run down faster than those in the 3S battey which just supplies the loco current direct.

Frank

mwiz64
Registered


Joined: Mon Mar 26th, 2012
Location: Fenton, Michigan USA
Posts: 1330
Status: 
Offline
 
Of course the 3-cell battery will last longer than the 2-cell with a voltage booster.


Just look at the thing physically.

One fuel tank is 1/3 larger than the other.


The voltage booster isn't magic...  ;)


Budd
Registered


Joined: Tue Jan 12th, 2010
Location: Adelaide, Australia
Posts: 105
Status: 
Offline

I must have had a blonde moment when I posted that original question.  :us:


Wayne from Oz


mwiz64
Registered


Joined: Mon Mar 26th, 2012
Location: Fenton, Michigan USA
Posts: 1330
Status: 
Offline
 
Wayne,

Once long ago, I asked the same question,

and got a similar answer to the one I gave you.


Michael M
Registered


Joined: Thu Jan 26th, 2017
Location: San Bernardino, California USA
Posts: 1674
Status: 
Offline
Before I blow myself up...

It's probably here somewhere, but I can't find it.

In very simple words how can I wire two single cell 3.7 volt LiPo batteries in series to get 7.4 volts?

Due to space constraints I can't use a 7.4 volt LiPo.

Rod Hutchinson
Registered


Joined: Fri May 8th, 2009
Location: Mooroolbark, Australia
Posts: 527
Status: 
Offline
Michael M wrote:
Before I blow myself up...

It's probably here somewhere, but I can't find it. 


In very simple words how can I wire two single cell 3.7 volt Li-Po batteries in series to get 7.4 volts?  

Due to space constraints I can't use a 7.4 volt Li-Po.


The Centre Black Cable Is For Charging Only. 

 The +- For Running.





Helmut
Registered


Joined: Sun Feb 17th, 2013
Location: Friedberg, Germany
Posts: 1183
Status: 
Offline
 
And don't forget that when you want to charge that,

use a balancing charger by all means !

(it needs the Black 'middle-cable' for this)


Bob R
Registered


Joined: Thu Nov 20th, 2014
Location: Springfield , Nebraska USA
Posts: 632
Status: 
Offline
Michael M wrote:
Before I blow myself up...

It's probably here somewhere, but I can't find it.

In very simple words how can I wire two single cell 3.7 volt Li-Po batteries in series to get 7.4 volts?

Due to space constraints I can't use a 7.4 volt Li-Po.


Not sure I understand....

If you have room for two single cell batteries, why not room for a two cell battery?

I mostly use two cell batteries. 
I make up my own, as the two cell packs at hobby store never seem to be what I need.

You can almost always find Li-Pos that fit your space availability. 

In many applications I mount the two cells seperately,
and wire them together to fit in available space. 

I personally do not wire for balance charging, because of the size of connectors. 

I do use battery protection circuits though,
as they afford protection against an individual cell being discharged to low. 

In the many years I have been using Li-Pos I have not had any problems. 


Picture shows a two cell battery with protection circuit I soldered up. 
For size reference the cells are 402035's  which is 4mm thick, 20 x 35mm each
(about 1/8" thick, 3/4"x 1 1/4")





Michael M
Registered


Joined: Thu Jan 26th, 2017
Location: San Bernardino, California USA
Posts: 1674
Status: 
Offline

Bob,

Thanks for the info.


The batteries are going in the cab of the loco,

with one on each side of the cab. 


Using single cell Li-Pos,

I can tuck each one into the corner, and out of sight.


But I want to wire them together to give me 7.4 volts,

and to be able to charge both together.


Bob R
Registered


Joined: Thu Nov 20th, 2014
Location: Springfield , Nebraska USA
Posts: 632
Status: 
Offline
 
Nothing to it. 

This picture is not the best, but you can see a battery on each side of the tank engine.

Both are connected to the battery protection circuit (optional) in the lower left. 

Next to it, the 2 pin charge jack (white connector). 

The other white connector, outside the engine, is the plug to the motor.





Michael M
Registered


Joined: Thu Jan 26th, 2017
Location: San Bernardino, California USA
Posts: 1674
Status: 
Offline
 
My 3.7 volt Li-Pos finally showed up. 

So now all I have to do is wire them in series and get them installed. 

They should fit inside the cab sidewalls with no problem.


Michael M
Registered


Joined: Thu Jan 26th, 2017
Location: San Bernardino, California USA
Posts: 1674
Status: 
Offline
 
Finally got around to wiring the Li-Po batteries. 

They work and charge fine. 

Just need to finish installing them and I'm good.



UltraBB 1.172 Copyright © 2007-2016 Data 1 Systems