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Are you wary of Li-Po batteries?
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 Posted: Fri Jul 24th, 2015 03:24 am
   
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Tramcar Trev
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Ok here is a schematic how to wire up these protection pcb's. Now its as clear as spring water and I should have realised from my own meanderings why the do work as well as they do. the batteries are discharged in series and are charged individually eliminating the need for balance charging and preventing over discharge....This is a 3 cell board got one on order just to see if its the same as a 4 cell board.

http://www.ebay.com.au/itm/400935943160



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 Posted: Sun Aug 30th, 2015 08:18 am
   
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Simon M
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I decided to buy one of those circuits, still waiting for it (them) to arrive. Did you have a schematic that you referred to above?



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 Posted: Mon Aug 31st, 2015 05:55 am
   
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Tramcar Trev
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Have a look at the sketch with this one, it shows how they are wired up; http://www.ebay.com.au/itm/4A-5A-PCB-BMS-Protection-Circuit-Board-for-3-Packs-18650-Li-ion-lithium-Battery-/400935943160?hash=item5d59a4fbf8



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 Posted: Mon Aug 31st, 2015 08:48 am
   
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davecttr
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I am becoming more wary of Lipo batteries. These 8 were bought about a year ago and have varied use but only occasionally discharges to the Deltang Rx 3V low voltage cutoff. Some of the ones on the right have swelled alarmingly but all still retain their 4.18V maximum charge according to my meter. Have I stored them wrongly? Is this expected behaviour? The 220mAh ones on the left are only 2 pence per battery more expensive


Last edited on Mon Aug 31st, 2015 08:50 am by davecttr



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 Posted: Tue Sep 1st, 2015 05:27 am
   
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Tramcar Trev
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davecttr wrote:
I am becoming more wary of Lipo batteries. These 8 were bought about a year ago and have varied use but only occasionally discharges to the Deltang Rx 3V low voltage cutoff. Some of the ones on the right have swelled alarmingly but all still retain their 4.18V maximum charge according to my meter. Have I stored them wrongly? Is this expected behaviour? The 220mAh ones on the left are only 2 pence per battery more expensive


Would not get to alarmed, lions of that size are not that dangerous, usually ooze brown muck all over the place but not enough lithium to start a fire unless all bundled together and deliberately ignited. Its Interesting that they have puffed up yet still work, maybe they are not vented? All the ones that I have had that have puffed up are dead and best used to throw on a camp-fire of some unsuspecting person.... They are not easy to dispose of here....



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 Posted: Sat Sep 5th, 2015 05:28 am
   
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Robert Comerford
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Herb Kephart wrote: While we are on all this battery talk--

Does anyone know of a source for IiFe single cells that are flat? I find that thickness is the thing that limits whether a cell will fit, more than any other factor. LiPo cells seem to come flat, as a matter of course, but the few LiFe cells that I can find, are round.

I also understand that LiFe cells do not require protection
circuits. Consensus?

Herb
Herb I used the 700mAH soft packs for some small model plane power packs and to power  one of my train tests. I made 3S packs by prising apart one pack and adding the single cells to another 2S pack. That might be one way of getting a single cell.

 Of course if you plan to use commercial equipment designed only for a lipo it will not charge or cut off at the correct voltages for LiFe's.

They are available on this page
http://www.hobbyking.com/hobbyking/store/__218__85__Batteries_Accessories-LiFePo4.html

LiFePO4 cells do not have the propensity to go into thermal runaway that LiCoO2 ( lipo's) do with either overcharge or overdischarge but the life will be shortened somewhat if regularly used well beyond their design boundaries. We certainly discharged these cells at rates well beyond the norm but surprisingly none ever bloated like the larger soft packs do.
regards
 Bob Comerford

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 Posted: Sat Sep 5th, 2015 08:49 am
   
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Herb Kephart
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Thanks Bob, and bookmarked.

Last time that I tried to turn a three cell LiPo into a two cell, I managed to stab the bloody thing with an xacto knife and it had a hissy fit. If I do in again, I'll know better.

(axe?) 

Herb



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 Posted: Mon Sep 7th, 2015 07:07 pm
   
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Pete Steinmetz
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Swelling batteries mean there was contamination in the manufacturing process.

All of my cells and packs that were purchased from RC sources have swollen and failed within about a year.

Companies that sell to the RC market do so because they can't sell to Dell or Apple. This is due to lack of automated equipment and inprocess quality control.



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 Posted: Mon Sep 7th, 2015 09:03 pm
   
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Rod Hutchinson
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Pete,

I have picked up on your comment and similar from other sources.

Could it be that there are possibility 3 levels of LiPo quality in descending order?

1. Hi end cameras, computers etc.
2. Bricks and mortar RC shops
3. If so, what would you view be on 3rd party providers such as those on eBay?



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 Posted: Tue Sep 8th, 2015 12:10 am
   
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Tramcar Trev
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I have no doubt that there are vastly differing qualities in these batteries even from the same brand/supplier.
I tend to make up 4 cell packs from cells I buy off Hobby King as I can simply wire up the cells to make a battery that fits where ever it can go, i.e. all the cells do not have to be joined together in a single "pack".
I also buy via ebay and this is the funny thing, the elcheapo generics I buy there seem to last just as long as the "Branded" ones I buy from HK. There is always exceptions to the rule though a bunch I recently got from eBay were all DOA but a refund/replacement was soon sent. I'm interested in knowing what storage conditions do to the life of these cells. I mean the storage they endure before being sold, it can be months....
Recently I have been using the "Protection/ charger PCBs" from eBay and now I have just discovered a really cool way of making a protective cover for battery packs, dunk the completed pack into Latex Moulding rubber; http://www.ebay.com.au/itm/Liquid-Latex-1Lt-FREE-FREIGHT-/131406209541?hash=item1e986ba205
It gives a very tough dielectric abrasion resistant coating that does not take up much space, you can always give the pack two dips to be sure to be sure...



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