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

[Jonathan M]

I've bought a Turnigy B405 pocket charger for charging 1s 750mAh glider Lipo batteries in the field (using a redundant 3s 3300mAh pack as power-source). The problem is that, despite being marketed at able to charge 1-4s packs, the charger won't work unless a balancing lead is connected - and of course 1s packs don't have balancing leads!

But is there a way of splitting off the single cell's positive and negative supplies into a home-made 'pretend' 2s balancing plug (which would be the common and does the positive or negative go into this)? Will the charger be happy with, say, two (fictitious) cells both reading 3.8v when the total is also 3.8v (rather than 7.6v as if it was a proper 2s)?

[Gary Manuel]

Doesn't the charger have a "none balance" mode?

[Denis Watkins]

As Gary says Jonathan, scroll through the menus and there should be a default 1S charge,

Look for 3.7v setting

[Denis Watkins]

From the manual Jonathan

WARNING! It is NOT recommended to charge a LiPo battery which is not wired for
balancing. Such types of LiPo have NO means to protect the equipment or the user
from damage that could result from an overcharge condition of any cell in the pack.
NON-BALANCED packs are wired so the charger can only detect the voltage of
the entire pack (not individual cells), so there is only one charge lead. It’s highly
recommended to ONLY use such types of LiPo packs if they have a built-in charge
safety circuit which prevents any single cell in the pack from being overcharged.
Simply connect the battery’s main power lead to the charger’s banana jacks
(noting correct polarity).
The image to the right shows the
LiPo set up with the balance board

[Denis Watkins]

Guys, the charger does scroll to 1s on the left of the screen by moving the arrow to 1s

Then recommended 1C is set 3.7v

[Jonathan M]

Denis

But 1s cells are never wired for balancing.

Also, I cannot fathom - neither from the manual nor by experimenting - how to even get to an arrow on the left of the screen to show, let alone select the chosen number of cells.

The only thing I can change is the charge rate.

From the manual:

Edited By Jonathan M on 03/02/2017 15:07:07

[Jonathan M]

Also from the manual - which indicates that the arrows on the left hand side are only to show the state of each cell during and after charging:

This charger isn't fit for its stated purpose!

...which gets me back to my original question: how can I wire up a 'pretend' balancing plug to fool the charger into understanding that we've only got one cell, and will this work?

[Gary Manuel]

Try this video Jonathan.

[Denis Watkins]

OK Jonathan, connect up your supply battery, select Li Po, connect your single cell, you cannot connect a balance as there isn't one,

Then go to charge voltage and set 3.7v

[Jonathan M]

Posted by Denis Watkins on 03/02/2017 15:53:17:

OK Jonathan, connect up your supply battery, select Li Po, connect your single cell, you cannot connect a balance as there isn't one,

Then go to charge voltage and set 3.7v

Gary - that video confirms my experience: one can only alter the charge rate, and the video guy reckons, as I do, that the charger just 'senses' the voltage.

Denis - as above, I cannot set/select/choose 3.7v! It might sense that its 3.7v, but it won't work without a balancer - it just gives me an error reading (ERR 008) - which is nonsensical.

Which is why I thought about making a pretend balancer leading off the two-pole supply to fool it.

Edited By Jonathan M on 03/02/2017 16:16:41

[Denis Watkins]

Hi Jonathan, This charger will charge 5 types of cell chemistry, and 4 of those Chemistries do not use a balance lead, so the charger will charge a single cell. No one will come forward to dodge a charger into accepting wrong information simply because an overcharge could result in fire.

Choosing another Chemistry will undercharge the Lipo slightly, before the charger switches off. I do not think any of us wants to recommend kidding the charger for obvious reasons

I have no doubt that following the correct sequence that this charger would charge a 1S Lipo

There is some part of the process involves holding buttons in for a time, and in order, and at above 10v input voltage. Is the input Above 10v?

[Denis Watkins]

To add, fitting a 3 cell Lipo to the input, does not ensure 10v, this needs verifying too.

[Dickw]

Posted by Jonathan M on 03/02/2017 14:09:51:

..................................

But is there a way of splitting off the single cell's positive and negative supplies into a home-made 'pretend' 2s balancing plug (which would be the common and does the positive or negative go into this)? Will the charger be happy with, say, two (fictitious) cells both reading 3.8v when the total is also 3.8v (rather than 7.6v as if it was a proper 2s)?

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.

If that doesn’t work then it I agree it cannot charge 1s Lipo.

Dick

[Peter Beeney]

Jonathan, it very much seems to me that the charger won’t fire up until it sees a voltage on the balance port, but I’d suspect that any number from 1 to 4 will be ok. This is to absolutely ensure the charger has automatically set the right number of cells, because you are unable to do this manually.

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. In fact such a lead would be ideal as the 2 wires into the connector to save a little bit of knitting.

If you are a bit adept at tinkering with these little bits and pieces just bodge up a temporary lead to give it a quick whizz; and then when it works ok (I’m convinced!) you can make it a bit more permanent.

Not much of a plan to try and kid the balance port that it has 2 fictitious cells connected, I’d say that it’s very highly unlikely to accept this anyway but if it did it might give your cell a bit of a headache, to say the very least…

The balance port is the only way the charger knows what is connected to it…

Good luck!

PB

[Jonathan M]

Posted by Denis Watkins on 03/02/2017 16:37:03:

To add, fitting a 3 cell Lipo to the input, does not ensure 10v, this needs verifying too.

Yes, safe enough on this issue. I've got a couple of Purple Power 3s 3300mAh units going begging (since I flogged the foamie I bought them for) which velcro to the back of the charger. At 100% charge of 4.2v/cell these provide 12.6v, and about 11.25v at 40% charge.

Assuming the charger only draws a nominal amount to function, a fully-charged 3300mAh should provide about 2000mAh of fuel, or at least 3-4 full charges from 35% capacity of a 1s 750mAh.

[Jonathan M]

Thanks Dick, Peter - exactly how many cells is precisely what the charger needs to be told, just didn't know which way to hot-wire a spare balancing-lead plug. And yes it makes complete sense to just tell the charger that its got one cell to charge - rather than two!

An intermediate connector is the way to go, no point in messing about with any given 1s battery.

When I started I knew very little about different battery types, chargers, soldering-irons or heat-shrink... now I have huge fun tinkering!

Will report back...

Jon

Edited By Jonathan M on 03/02/2017 19:49:11

[Peter Beeney]

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. You need to tell the charger it’s only a single cell; and any other connection position will simply tell it little porkies…

But in the unlikely event that you do get wrong it will just say mute anyway. It has to be connected correctly to start up. Which of course does complicate the issue if you are trying to make the charger start if a battery only gets slightly out of it’s normal operating limits…

PB

[Phil Green]

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 Peter Beeney 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.

[Peter Beeney]

Yes indeed, humble apologies here to Dick, he’s absolutely right, of course. I didn’t verify this to start with and I’d assumed that the battery started from the positive end when in effect it starts from the negative end. I should have looked before I spoke, it would have only taken a moment, my memory is definitely now showing it’s age...

Sorry again, I’ll just keep quiet on such matters…

PB

[Martin Harris - Moderator]

Just a thought - have you tried connecting the battery without the balance board being connected to the charger? It might be that the charger won't require a balance connection if the board isn't connected - one of my chargers uses a similar plug in board and displays a "balancer advised" message if it doesn't find one connected...

[Jonathan M]

Posted by Martin Harris on 03/02/2017 23:24:22:

Just a thought - have you tried connecting the battery without the balance board being connected to the charger?

No difference - this charger, like my 240v one, doesn't know if the BB plastic plug is/n't mechanically connected, it just needs the right electrical traffic.

I've teased apart a duff 2s, which of course is wired in series, and its balancing plug is:

1st pin black wire -> Cell 1 NEG

2nd pin blue wire -> Cell 1 POS & Cell 2 NEG

3rd pin red wire -> Cell 2 POS

I'll use this very plug with its first two pins/wires (in bold above) to make up my intermediate connector - thanks for that idea Peter!

[John Privett]

Jonathan - are you sure it won't start the charge without a balance lead connected? Maybe it needs a second button push to "confirm" that you want to charge?

Obviously the concept of balance-charging a single cell LiPo is nonsense. The manual only recommends not charging non-balanced batteries, it even goes on to explain how to do it;

WARNING! It is NOT recommended to charge a LiPo battery which is not wired for balancing. Such types of LiPo have NO means to protect the equipment or the user from damage that could result from an overcharge condition of any cell in the pack. NON-BALANCED packs are wired so the charger can only detect the voltage of the entire pack (not individual cells), so there is only one charge lead. It’s highly recommended to ONLY use such types of LiPo packs if they have a built-in charge safety circuit which prevents any single cell in the pack from being overcharged. Simply connect the battery’s main power lead to the charger’s banana jacks (noting correct polarity).

So, from a quick browse of the manual it should be possible without having to resort to silly tricks to fool the charger into balance charging!

 

[EDIT] There's also a link to an "alternative" manual on the Hobbyking page - this appears to be the same device with a different badge (Venom) The contents of the manual appear very similar though!

Edited By John Privett on 04/02/2017 11:51:24

[Chuck Plains]

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.

[Jonathan M]

John - Thanks for the help and encouragement. However I'm absolutely, totally, completely, 100% certain that there are no other buttons or combinations of buttons whatsoever that I can push. I've read and re-read and re-read several times more both the Turnigy and Venom manuals (the only difference between the two is very minor), and it is clear that there is NO WAY to manually inform the charger of how many Lipo cells are present. The ONLY way to do this is to connect a balancing-plug.

I've now achieved this by splicing a spare plug (with just two wires as per the advice above) into the main supply line. The charger now recognises my battery as 1s and charging is entirely safe and successful. My method was to cut, solder and independently seal with heat-shrink each wire in the supply line, add a plastic barrier just in case, then heat-shrink both together. The wiring is entirely safe. The photos below show this in action: the first shows the wiring setup, the second one illustrates the use of a safe-bag... which should ALWAYS BE USED... just in case, etc, etc.

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

[Jonathan M]

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.