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Building lipo packs
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 Posted: Thu May 16th, 2013 03:59 pm
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mwiz64
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Well, you've reasoned it out in your mind and at this point I'd say, knowing all that you do about the potential dangers, proceed with caution. Keep checking things until you can come to a point where you are comfortable with the knowledge that what you're doing is OK. I wouldn't recommend giving anybody advice about running lipos that way without also giving them the additional information about the dangers of lipo use and then cautioning them to do the tests and make the checks themselves.

Lastly, doesn't the Stanton system deal with all this itself?

Robin2 wrote:
If you envisage a locomotive sitting on rails which are connected to a suitable charge voltage you will understand how there is no scope for balance charging.

It would be possible to do a balanced charge when a running session is completed. Then the loco can be removed from the track and the internal wiring can be altered. It's not practical to remove the batteries for charging. Neither is there room in the loco for the usual style of charging plugs. (There wasn't even room for a switch - I had to make one).

The batteries I have are rated at 15C for discharge. The motor I have won't draw more than 4C when stalled and my "charger" won't go above 1C, and in practice will probably be at 0.5C.

Based on my experience with lead-acid batteries I am assuming the real capacity of the LiPos is also only about 50% of the sticker capacity.

I am hoping (though not yet tested) that the batteries will seldom go below 70% of full charge as each loco will spend most of its time on the charging track.

...R

Last edited on Thu May 16th, 2013 04:01 pm by mwiz64



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 Posted: Thu May 16th, 2013 04:06 pm
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mwiz64
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Woodie,

You're the guy I'm worried about the most. You've said you don't balance charge. Do you ever look at the condition of the individual cells in your packs to see how close they are? If you'd just do this once a month and bring them up to balance I'd feel better. I know you don't need my endorsement on anything you do. I just don't want to see you suffer the consequences.

W C Greene wrote: My opinion here...r/c flyers and car racers want to get back in "the action" quickly and therefore tend to push the charge which leads to...you know. I have seen it again and again...why anybody would invest a grand or more in a nice r/c plane or car and then have ONE cheap battery is beyond me. A slow, almost trickle charge is OK for Li Pos and since we are running trains here, you should have maybe more than one loco to use while one is being charged. I don't "cotton" to charging from the rails, it seems to defeat the purpose of true wirelessness and the tiny contact area between rails and wheel tread is not a good way to recharge. But again, it is my opinion here. I have been running wireless for many years now and actually do have some experience with these things. Thank goodness we have this forum to inform ourselves about this "niche". I never discuss r/c trains with the guys at the LHS, the train store guys look at me with a "whaaat?" stare and the r/c store guys believe I am running a toy train around the Christmas tree.
Once again, I am very glad to see this discussion going on, even though it is far above my head/understanding. All I can add now is "KEEP IT UP".

Woodie



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 Posted: Thu May 16th, 2013 04:17 pm
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mwiz64
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Another thought:

If you wanna avoid all this stuff consider running a motor that has a higher KV (RPM per volt rating)and then use a single cell battery. I know it's not as efficient as a higher voltage system but there are tradeoffs in everything. A little less efficiency but a simpler and safer solution seems like a good tradeoff to me but as with everything, YMMV.

I'm glad I don't model in HO. I can afford the space of a balance tap plug on my 1:35n2 size stuff.

Last edited on Thu May 16th, 2013 04:18 pm by mwiz64



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 Posted: Thu May 16th, 2013 04:49 pm
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W C Greene
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Mike-no worries here. I have Li Pos that are 10 years old and still are OK. Just patience and care are what's needed.

Woodie



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 Posted: Thu May 16th, 2013 05:08 pm
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mwiz64
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Alright, 10 year old batteries with no problems. That sounds like a good program you've got going there because I believe you run your stuff quite often.

Tell us what batteries you use, brand, capacity and cell count. Tell us exactly how you charge them and what equipment you use to accomplish that.

Armed with that information the guys that started this thread might find a solution that meets their needs.

Last edited on Thu May 16th, 2013 05:09 pm by mwiz64



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 Posted: Thu May 16th, 2013 05:35 pm
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W C Greene
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Mike-I have the most rudimentary of chargers. I use an old Great Planes charger which uses a 12 volt power supply. When I bought it years ago, it was $29.95. The batteries are a combination of E Flight, Thunder Power, and a couple of others which I can't remember, all except one are 2 cell, one is 3 cell. I don't run the locos until they run down, I may slap a charge on a loco I want before operation and since it has no memory, the battery takes whatever charge it needs. I also have these tiny Miniatronics 2 pin micro plugs on the batteries and charger. In my 2 Porters and Model T railcar, I have TEAM LOSI 2 cell 180MAH Li Pos and they are charged with a LOSI charger that came with one of the batteries. Simple stuff that has served me quite well. Well, you did ask!

Woodie



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 Posted: Thu May 16th, 2013 06:13 pm
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Robin2
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Hi Woodie, good to hear about railway battery experience as I, also, don't think the flying / cars experience is comparable. As well as wanting to get back in the air asap flyers and drivers usually want absolute max power.

On the other hand I remain very conscious of the need to ensure balance between LiPo cells.

My reason for charging from the track is simply to top up the charge on a very small battery while the loco is standing in the fiddle yard. With 3 locos (for example) each one is likely to be on-charge for 2/3rds of the time.

...R

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 Posted: Thu May 16th, 2013 06:49 pm
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DavidT
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Lipo voltages rise when charged and drop under use. They are damaged if they stray outside their intended voltage range. If cells get out of balance then the highest gets overcharged and the lowest can get over-discharged. This usually just shortens their life, reduces top end motor speed and shortens run times. Charging at less than 1C and topping them up before they become flat is helpful.

Lipos only need balancing if they are out of balance. So if you measure them occassionally you can decide what to do. I agree with Mike that it is good practice to balance regularly. But in practice I accept higher risks with my small 2 and 3 cell packs and balance those very rarely. As a result they have a shorter life than they could have. However, I balance my 7 and 14 cell packs on every charge because they are much more expensive.

Lipos can fail without obvious cause but we can't do much about this. However, chargers often have a 'number of cells' setting. If you charge a 2 cell pack with a 3 cell setting the charger may try to raise the voltage too high. If the voltage rises significantly above it's intended range it becomes very hot. Naturally this can lead to disaster. I make sure every pack has the number of cells written on it because after a few months you tend to forget.

Lipos of one sort or another are used in almost every camera, phone and laptop. They use a charger that starts and ends with a trickle charge because the voltage extremes are the sensitive areas as mentioned above. They also have a temperature sensor in the pack which is a valuable protection feature.

Most modern cheap RC toys use lipos. Many use a single lipo. They are likely to use the same charger chip as used in cameras and phones because they are so good and so cheap. I've never seen temperature monitoring implemented regardless of the number of cells.

I don't leave lipos switched on in a device when not in use. I only charge when I am in the house. These are my main protection rules. I assemble packs from loose cells. But I make sure the make, size and voltages are identical.
Regards, David.

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 Posted: Thu May 16th, 2013 07:14 pm
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Herb Kephart
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Mike wrote

"Lastly, doesn't the Stanton system deal with all this itself?"

Neil is working on a system that can charge from the track, and the track voltage can be AC or DC--up to 25V(I think).
It uses a single cell with over charge and under voltage protection. The 3.7 cell voltage is stepped up electronically to 12V. I ran one of the prototype units--CRAMMED onto an On2½ Plymouth critter for--as I recall-- something like 45 minutes, solely on the battery. Last that I heard from Neil, he wasn't ready to market this system however.

Herb



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 Posted: Thu May 16th, 2013 08:10 pm
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1whudson
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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

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