1s Lipos - how to rig a balance-lead to fool charger?

[Bruce Miller 2]

Posted by Phil Green on 03/02/2017 22:44:17:

Posted by Dickw on 03/02/2017 18:24:02

I would try making up a 2s balance lead for the cell with the +ve of the cell going to middle pin of the 2s balance plug and the –ve of the cell going to the -ve pin of the balance plug. That is not trying to fool anything, but just confirming to the charger that only 1 cell is connected

The right way to do it.

And now the wrong way:

Posted by #### on 03/02/2017 20:25:36:

So what I would do is to make up a intermediate connector in the main lead with a ‘balance’ pair attached to the main neg and pos and then using a redundant 2s (three pin) balance lead but leaving off the black neg at the end. ....

Yes, I afraid I wasn’t absolutely clear on this, either. With the greatest respect to Dick, I would place the red pos balance wire from your 1 cell in the first positive end of your balance plug (whether 2, 3 or 4 cell is unimportant) and the black neg next to it. The black wire acts only as the neg for a one cell, but both neg and pos for a two cell; in this case it would usually be a different colour.

Very diplomatic Phil - and absolutely correct! However I think in the interest of 'responsible forumming' (?) we should leave a clear explanation in our trail.

A few years ago when I purchased an amazingly versatile REVOLECTRIX charger (which is never reviewed - do you not have them in the U.K?) I learned that there are TWO standards for battery cell sensing - one seems unused (but would work Peter's suggestion) and the other has become the industry standard as far as I can see and is the 'right way to do it.'

FMA WIRING - the first cell is connected to the first POSITIVE pin and the last pin detecting a NEGATIVE connection generates the cell count for the charger.

XH WIRING - (used for every battery and charger I've ever bought) the first cell is connected to the first NEGATIVE pin and the last pin detecting a POSITIVE connection generates the cell count for the charger.

The importance of this is that the first NEGATIVE pin on the charger MUST connect with the negative side of the battery and the matching first cell of the balance port wire. If you connect the main charge leads first (as you should) and then the balance plug wrongly made backwards using one suggestion earlier in this forum topic - the negative 'balance lead' meets the positive of the 'charge wire' passing current through your expensive charger - BANG - need a new battery and charger (if you're lucky!)

Grab pen & paper draw a quick circuit diagram to see what I mean - 1-cell battery's 2 wires incorrectly placed at the wrong end of a 3-cell (like FMA wiring) meeting a 'live' charger's XH wired socket... When POS meets NEG it always ends in disaster!

So I'm glad Jonathan got the correct advice and the proof is in his charging success. I thinks folks are assuming their chargers are far more intelligent than they really are. Balancing IS very important for multiple cells but a single cell by definition does not need balancing so the manual insisting on balancing is an over-assumption by readers. The charger needs to sense the right voltage in the right place to commence charge - simply a safety design for when multiple cells are in use. The successful solution is evidently proof of this.

Jonathan - I was wondering from your first post - why not just make a lead to charge TWO batteries??? (see Parallel Charging in Jan RCME) I made a lead from cheap chinese parts to charge three at a time of the tiny single cell batteries in small models and my charger just sees a 3S 300mAh. Likewise battery meters report all 3 cells separately with a button push.

Finally (sorry) somebody reported their battery meter wouldn't work with one cell which is usually correct - somewhere in the fine print mine says that minimum 2 cells needed to work but watch out as a very small 2 cell is drained quickly if you take too long! So a (very) cheap multimeter with a custom lead is quite handy to measure a single cell's voltage.

So many plugs - so many chances to 'short' circuits...!

[Jonathan M]

Posted by Bruce Miller 2 on 05/02/2017 08:42:24

[...]

So I'm glad Jonathan got the correct advice and the proof is in his charging success. I thinks folks are assuming their chargers are far more intelligent than they really are. Balancing IS very important for multiple cells but a single cell by definition does not need balancing so the manual insisting on balancing is an over-assumption by readers. The charger needs to sense the right voltage in the right place to commence charge - simply a safety design for when multiple cells are in use. The successful solution is evidently proof of this.

Jonathan - I was wondering from your first post - why not just make a lead to charge TWO batteries???...

Finally (sorry) somebody reported their battery meter wouldn't work with one cell which is usually correct... So a (very) cheap multimeter with a custom lead is quite handy to measure a single cell's voltage.

So many plugs - so many chances to 'short' circuits...!

 

Bruce - thanks for your very clear re-iteration of the electrical essentials.

Good idea about parallel charging, but I don't really need to charge more than one battery at a time, as I only use 1s in my DLGs (where capacity in mAh is more important than servo-torque in volts for any given battery weight and dimensions). My main 240v charger does 1s directly without a balancing-lead as total voltage is selectable on the unit itself, so I've already got two chargers for home use. This can also run off a 12v lead-acid, but I like to travel light when going off for a long day's thermal or slope-soaring (the pocket-charger also does Ni-Mh packs with yet another home-made adaptor!).

To measure remaining capacity of the 1s I can use my small Prolux Volts Monitor, the two pins of which just push into the Lipo's main plug (same as when checking Ni-Mh packs). This gives voltage under load (300mA) as well as resting, so a simple chart taped to the back (like on my very cheap multimeter) will reveal the remaining capacity of the Lipo.

I no longer have plug-envy...!

Edited By Jonathan M on 05/02/2017 09:57:26

[Bruce Miller 2]

Isn't it great these forum-thingys to see other's practical solutions to our 'common' problems. "Necessity is the mother of all invention" etc. We all see things from our own experience. I know nothing about those 'DLG' you mention I was only seeing from my perspective where three batteries is nice for a little indoor heli session. Thanks for your original post - interesting topic. Nice safety message to put about. Cheers.

[Gary Manuel]

Posted by Jonathan M on 04/02/2017 20:50:48:

The interesting thing is that, although the charger works perfectly with this modification, my battery-checker doesn't fire up at all with just two leads into a balancing plug. It works fine with 2 or more cell Lipos, as can be seen in the fourth photo below.

Thanks to all for the advice.

Jon

Jon.

The reason your battery checker doesn't fire up is that it needs more voltage than your 1 cell provides.

[Phil Green]

Posted by Bruce Miller 2 on 05/02/2017 08:42:24:
Very diplomatic Phil - and absolutely correct!

Bruce, my concern is that bad lipo advice could burn someones house down.

Regarding FMA, the OP clearly stated his charger is a Turnigy B405 which is wired conventionally.

Cheers
Phil

[Bruce Miller 2]

Yep Phil - quite right. FMA wiring is MOST unusual. Apart from the Revolectrix manual I have not come across it. As I posted, everything I have ever bought (or seen of others) is wired XH which really has become our industry standard. I also was a little alarmed that an early post was giving wrong advice and I wanted to amplify your simple message that the negative wire is the constant and must be respected. In years to come somebody may well read our posts and not realise the importance of your message. That's it from me on the topic "I know no more, yet now know more."

Edited By Bruce Miller 2 on 05/02/2017 11:46:37

[Jonathan M]

Posted by Jonathan M on 04/02/2017 20:55:17:

Posted by Chuck Plains on 04/02/2017 12:34:39:

Here's a great how to video from the world famous NightFlyyer on Youtube. This fine gentleman has been constantly active in the RC flight field for a thousand years. But recently lost everything due to a fire.

https://www.youtube.com/watch?v=XWli7_f_wYc

Hope that helps.

No it wouldn't help with my particular quest, so I didn't trouble myself to watch yet another video.

Forgive me if that sounded tetchy. I'm aware that my original posting terminology, i.e. 'fool the charger', made it sound like I didn't understand basic Lipo safety - which I'd never compromise, nor would I want to confuse anyone into making a dangerous mistake. I was just trying to get to the bottom of how to get the charger to read the single cell pack's voltage via its balancing port and therefore deliver a single cell charge - and the otherwise very valid warnings about never charging multiple cells without a balancer etc were just confusing the issue for me.

Clearly, in the case of two or more cells in a pack (in series), if a balancer isn't being used and one cell is faulty, then the charger would 'fool' itself into charging the whole pack beyond the limit of 4.2v per cell, with serious risk of fire or explosion.

I also plan to convert some unused 2s 300mAhpacks to 1s 600mAh by re-soldering the tabs in parallel. This will half the voltage back to 3.7v nominal but provide twice the capacity. Needless to say, cells in parallel will self-balance. If anyone is interested in how to do it:

https://www.youtube.com/watch?v=LnowTrXmGL0

Edited By Jonathan M on 05/02/2017 12:49:42

Edited By Jonathan M on 05/02/2017 12:50:42

[Peter Beeney]

Yes indeed, Bruce, I do have to hold my hands again up to this one. Certainly had I picked up a lipo pack and taken just a glance it would have straighten out my thinking; …and I had one just a few metres away… In this case I’d merely transposed the cell one slot along the 2S balance plug, so the charger would have probably read the balance lead as a 2 cell pack with one cell missing and would not have started charging anyway. I put it down to an advanced OAP condition with a memory state that needs a spot of re-formatting…

A very long time ago, back in a distant working life, I spent a great deal of time swanning around with a small bunch of other reprobates. I very quickly learnt that if you made the correct comment about a particular perplexing situation no one said anything very much at all; but if you got it a bit wrong the sky would instantly fall in… so it was a case of doing the proof reading first and making sure the homework was always up to speed. Unfortunately in this balance plug case I forgot about my own memo! But others have also made small mistakes, too, on one space mission to Mars I believe, one half of the team used the yard as a yardstick whilst the other half used the metre as a yardstick for their landing instructions! Later on one very confused capsule! And wasn’t the Hubble Space Telescope also launched with a bit of a fuzzy lens which later had to be rectified…

There have been common positive connection systems in use, cars in a bygone age had 6 volt batteries with a positive earth/chassis connection. I can remember seeing those. Also some industrial systems using large storage batteries used a common/earth positive connection, the battery voltage thus always being considered negative with respect to earth. This meant some care had to be taken when connecting equipment designed for the standard industrial common neg connection, but with practise you do get use to sorting it out. Particularly so when using mains driven test or other ancillary kit, if not double insulated it would have a green/yellow safety earth which is commonly joined up with just about everything else. This could lead to some very odd looking conditions, we always got out of it by disconnecting the earth wire and anything else that prevented the circuits from being fully isolated from each other; something I guess would not fit very well, if at all, with today’s H&S lot, but this was a fair time ago.

I think I really must try and get out a bit more to the patch for some model flying and spend less poking about at these computer keys; then that would leave me less scope for thinking errors and more time for proof reading. But it’s jolly nice to know that someone out there is always getting it right, all of the time…

PB

Edited By Peter Beeney on 05/02/2017 15:45:57