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Building lipo packs
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 Posted: Thu May 16th, 2013 08:45 pm
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DavidT
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Bill,
They are called 'step up' regulators or convertors. Here's a link to several http://www.pololu.com/catalog/category/132.

To ignore conversion losses, I suggest you assume the lipo is 3v. To produce 9v from 3v requires extracting 3x the energy so the run time will be reduced by that proportion. The 12v version needs 4x energy. So the lower the step up the better.

The disadvantage with these is I don't think they have low voltage protection. My receivers can provide that but it adds complexity.
dt.

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 Posted: Thu May 16th, 2013 08:57 pm
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Robin2
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@Bill, when you start considering different voltages you need to think in watts and watt hours. Volts x Amps = watts. So 3V x 4A = 12 watts which is the same 12v x 1 Amp.

My 80mAh Lipo cell theoretically contains 3.7V x 0.08Ah = 0.296 W-hours. If the voltage was boosted to 12v it would still only contain 0.296 W-hours.

If the 12v motor used 0.1A = 1.2W it would run for 0.296 / 1.2 hours or 14.8 minutes. Also, if the motor was drawing 0.1A at 12v it would be drawing 0.1 x 12 / 3.7 = 0.32 amps from the battery.

@Mike, what is the Stanton system?

...R

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 Posted: Thu May 16th, 2013 10:32 pm
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mwiz64
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Go to NWSL and look at the Stanton SCab RC system. Here is a link.

http://www.nwsl.com/S-CAB_Radio_DCC_Control.html

BTW, he contributes here regularly and you can ask him all sorts of questions about it.



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 Posted: Thu May 16th, 2013 11:42 pm
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1whudson
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Thanks for that information David. By the way, I am having a terrible time finding connectors for the two power wires on the Rx60-2. I need to connect them to a 3 pin lipo. What 3 pin connector do I need and do I just forget the balancing pin/pad when attaching it? Is anyone else having this problem when trying to locate the correct male/female connectors? Standardization is obviously NOT an industry standard!

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 Posted: Thu May 16th, 2013 11:44 pm
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johnhu
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1whudson wrote:
Herb

I have heard of these things that can increase voltages as you just mentioned. What is the proper name for such a thing? Is it a device or chip or what? AND if you step a 3.7v lipo to 12v how much quicker does it discharge to the point of needing to be recharged? I mean if its original voltage of 3.7 would normally go for say 4 hours how many hours would it last stepped up to 12v? If I would only lose half of its normal usage and we were talking about hours instead of minutes then I want one! Again, what is it, what is it called and how much additional space is required?

Bill


I know them as "step up voltage regulators", but I'm not sure if that's the correct name or not.

I've been using regulators from Pololu that David mentioned successfully with his Rx60 receivers.

Personally I only use the 5v step up regulator, because I find that the 5v maximum gives me a perfectly good top speed in the On30 locos I'm powering (Davenport). How many of us ever actually run a loco at full speed (12v)? I'm sure we'd be lucky to go above half speed most of the time.

I tried the On30 Davenport on a straight 1S lipo (3.7v), but it wasn't quite enough, hence the use of a voltage regulator. Now I have the volts needed, but without the need to balance charge. I could have gone for a 2S battery (and skipped the balance charge as per what Woodie does), but I could fit a bigger capacity 1S battery into the loco. (ie: a 180mah 2S fits in the hood, or a 260mah 1S battery). The voltage regulator fits down the side of the cab under the window (hidden), a tiny slide switch (on/off) down the other side, and the receiver in the cab roof. The charging cable (micro-jst plug) tucks up inside the cab also and is barely visible. It just gets uncoiled out the cab doorway to charge.

Oh yes, the Deltang receivers allow me to hookup the 1S battery so that it can monitor the battery and cutout when the volts get too low (3v) so as not to over discharge the boosted battery.

As for running time, I've noticed no obvious difference or drop in running time (using a 260mah Turnigy nanotech 1S lipo) but I usually only operate for an hour or two, and recharge after that before the lipo has run down. I've not runout of juice during the operating session to make it an issue. Plus I'm only stepping the voltage up from 3.7v to 5v. Going from 3.7v to 12v I'd think would have more of an input, but I can't say what. The Pololu website has efficiency graphs, etc - but I'll leave that up to the electronics engineers to decode.

I'd try finding out what voltage you actually need first, and not assume that you must have the full 12v the motor is capable of. You might find that 5v or 9v is as much as you would ever use anyhow.

I hope the info helps............

John

Last edited on Thu May 16th, 2013 11:47 pm by johnhu

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 Posted: Fri May 17th, 2013 12:07 am
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1whudson
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Thank you Johnhu. I have already settled on th 2S lipo without the stepup solution. I find the 7.4v is just right with its 200mAh. I have yet to solve to my satisfaction the on/off switch situation yet. What switch did you use and is it hidden? Is the switch located between the battery and the receiver? Did you only interupt at the positive pole or both poles? Finally, what do you know about the reed switch? Didn't know you were getting in so deep did you?

Bill

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 Posted: Fri May 17th, 2013 12:20 am
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wv railbaron
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Bill, I've been following you topic and have some insight from my own experience. I am trying to understand the purpose of the 11.1v need for your locos. amd the third wire on your batteries is a ground for brushless motors i think. I have a few of those and just cut off the ground wire and hooked losi 2 wire connectors to the battery. I have made battery packs connecting 2 3,7 voit batteries and have no problems with having to balance them. I believe you have been frightened by the person who told you about the exaggerated danger of lipos.If you buy good charger it will not let you overcharge or cross polarity. It will shut off or not even charge if connections are incorrect.
Steve Sherrill

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 Posted: Fri May 17th, 2013 02:52 am
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mwiz64
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If you want a good quality lipo charger that doesn't include balancing you can use the Astroflight 109. I use to use a pair before lipos came with balance taps. It automatically detects the cell count. Watch for it and make sure it detects right before you walk away from it.

It's so easy to use its unbelievable. You connect the pack, watch for the proper cell count. dial in your 1c charge or whatever charge rate you want with the only control on the charger a rotary switch and let it do its thing.

You don't ever want to balance your batteries.... Well, you've been told and you are men. Do what you think is best.

Here is a link to the 109. http://www.astroflight.com/109d.html
Here is the charger I use. http://www.revolectrix.com/pl8_description_tab.htm

Last edited on Fri May 17th, 2013 02:53 am by mwiz64



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 Posted: Fri May 17th, 2013 05:05 am
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Craig W
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Like Woodie, I too have used Lipo batteries for well over a decade and I have “damaged” more than a few in that time. Most damage occurred from high impact speeds with hard objects, such as the ground. Some were damaged by incredibly high loads on the cells, mostly because I fly my airplanes like a madman, or “over-prop” them. I’ve also ruined a large number of cells using a very fancy Hyperion charger, which for some bizarre reason did something to the cells to drastically shorten their life, which is probably good for battery sales.

Then there are trains. I think that most of us dealing in the O> smaller scales, will be unlikely, as David pointed out, to abuse our battery cells to the point where they are highly stressed and most certainly, there are a few other, limited options such as A-123 or NiMh cells, in which you have to try to destroy them.

I really don’t know why cell balancing or charging is much of an issue. There are plenty of wiring “how-to’s” on the web, which can guide you through the steps required for hooking up a balance plug to the cells. Were only talking about 3 or 4 wires on 2 and 3 cell packs. Like Woody stated, I have not had a single issue regarding cell balance, although I do check them from time to time.

Building a scale servicing/ fueling station for your layout and hooking a battery charger to the rails in that location, has worked well for my modeling needs and brings a fun and realistic aspect to operations. I use a bridge rectifier in the locomotive to keep polarity in the correct direction. None of this is rocket science, but soldering small components can be at the very least a little tricky. David T sells some pretty nifty magnetic electrical connectors, which could be used for cell balancing connectors on the locomotive. I could envision using these in my servicing station, somehow hiding or positioning them in a way, as to facilitate an under track connection.

If I’m honest about using a single cell in terms of simplicity and safety, then I must yield to Mike’s position regarding safety. I’m forced to agree with him, even though I know the ultimate power system should employ multiple cells for max efficiency. I’ve proven this to myself again and again; even when moving to cells that are half the capacity, I’ve always managed longer run-times, better starting torque and speed stability, with higher voltage packs/ motors.

I’ve also stated before; there are applications where this might not be feasible.





“I am trying to understand the purpose of the 11.1v need for your locos?”



If I might take a stab at this; re-motoring some locomotives can be extremely challenging, impractical or just plain too costly to be worthwhile, so if your locomotive came with a 12v motor, which is highly confined within the chassis, swapping the motor for something else could be a real challenge. For a few brave souls, with access to limited resources, it more or less becomes a personnel endeavor I guess. My latest conversion foray involves a Proto 2000 SW-9. Take a look at the picture and you will see all of the stuff that I’m cramming into this locomotive and you can probably appreciate the challenges it presents.

[code][/code]

Last edited on Mon Jun 3rd, 2013 12:50 am by Craig W



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 Posted: Fri May 17th, 2013 06:27 am
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1whudson
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Well, somewhere along the line I probably mentioned my desire for a 11.1v pack because my engine had a 12v motor. However, with more education and learning here on this forum so much more than I knew before joining, I have decided on the 2S 7.4v lipo. The third wire I am referring to on the multiple cell lipo is somehow used by the charger when balancing the lipo battery. I don't think ground has anything to do with it. BUT, I have been wrong so many times before, I hesitate to even make this conjecture... Perhaps those with more knowledge about the lipo battery can tell us more.

Bill

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