Balance wiring question...

[ex-Gooserider]

I'm about to install the old Headway cell packs I've built up, and had a question about the balance wiring...

They are built as 2 4S6P packs with balance wiring between each serial pair. My question is about the wiring between cells 4 and 5 (The + on one pack and - on the second)

My current lead bricks are wired up with Andersons as BM suggested in the past to allow charging from my van, and I'd like to keep that wiring setup to allow an occasional use as a 12V power source and to allow doing an emergency recharge from the van if needed....

I had planned on running an AWG 22 balance wire to each string even though they will also be connected (in 24V configuration) by the main power wiring (AWG 6) as well. I know that BM and others have said that this is the best way to wire the two packs, but if I do it this way, then it seems like BAD THINGS would happen if I then put the 12V plug in as it would mean a dead short via that 22G wire for the few seconds it would take to melt Or if I accidentally disconnected the 24V jumper and tried to drive the chair, which would mean an AWG 22 link between the two packs...

To avoid this, is there ANY reason I can't simply only connect that balance wire to ONE of the two packs and simply rely on the power wiring for the balance connection between them? If I do it that way it seems totally safe. Would it make any difference which pack I connected to?

ex-Gooserider

[shirley_hkg]

Once the 6awg main cable between cells 4&5 disconnected, the 2 halves are separated, so as the balance wires, which are open at the other end.

When the two halves are paralleled, there shouldn't be any rush current, as they are of much the same potential.

Am I correct ?

[ex-Gooserider]

Once the 6awg main cable between cells 4&5 disconnected, the 2 halves are separated, so as the balance wires, which are open at the other end.

When the two halves are paralleled, there shouldn't be any rush current, as they are of much the same potential.

Am I correct ?

Yes. the balance wires are open when not charging, BUT the balance wires between cells 4 and 5 (each pack has a wire) would go to the SAME pin on the charging plug main cable (and pretty much have to as I'm using that DB connector w/ 3 power pins and 9 signal pins that a lot of us have, so no spare signal pins) This leaves the two packs connected by just the little balance wire, when the main cable is unplugged.

So what I'm asking is whether there is any reason I have to have a balance wire on both packs, considering that I will ONLY charge with the PL-8 (or any other balancing charger) when they are connected with the AWG 6 main cable, which should be effectively a 0 Ohm connection... If I get rid of one of the two wires, then the problem goes away...

ex-Gooserider

[Burgerman]

I dod it that way on one chair. It always seems to make it appear unbalanced a little though. Why? No idea it shouldnt!

[ex-Gooserider]

Well I just did a test charge cycle w/ an improvised (thin) jumper between the packs, and had to drop the supply current down, as it was smoking at 20A worked fine at 8A... (This was temporary, NOT the way they will go into the chair!)

I noticed the IR of cell 5 was over 500mOhms, the rest were mostly single or low double digits... My guess is the added resistance of the jumper lead... I also know that you said not to worry about the IR on a pack our size, but thought it was interesting...

I am also just double checking, the 'happy zone' for a Headway is above about 3.2V cell, above 3.0 is "charge soon" and the 'panic, charge NOW' point is anything below about 3.0, correct?

I will actually need to double those numbers because of my oddball improvised voltage tester... I got a bunch of cheap pack checker boards a long time back, and found when I finally got around to testing them, that they were ALL defective and would not work on an 8S pack like they were supposed to... However I found after some experimenting that they WOULD work as 4S pack testers and that they were fine if I wired one to test the 8S pack as 4 2S packs in series - IOW nominally I should get four readings that are 2X the single cell values.... Not ideal but I don't think it is likely that I'd have a pair of cells go out of balance in opposite directions, which is what would have to happen in order for one to drop dangerously low, especially if I add in some 'fudge factor' on deciding when to charge...

My freshly charged pack is giving me 6.9+ V/cell, I am guessing the charge now point should be when the lowest cell gets to about 6.45V, and the 'panic' point should be around 6.2V - does this sound right?

I also have made a quick checker out of a 4-digit volt display mounted on an XLR plug - a bit clumsy and I need to watch out not to get to close to things, but I can leave it in place while running and watch the pack total voltage more or less all the time. I did notice though that when I plug it in while connected to the ZXD I only see 28.91V at the XLR, as opposed to the 29.20 that the ZXD display is showing... When I was building the display I was testing it w/ a bench supply, and the display tracked w/ the supply display w/in 0.01V from about 5V to 32V (the supply limit)

ex-Gooserider

[Burgerman]

I am also just double checking, the 'happy zone' for a Headway is above about 3.2V cell, above 3.0 is "charge soon" and the 'panic, charge NOW' point is anything below about 3.0, correct?

Yep.

My freshly charged pack is giving me 6.9+ V/cell, I am guessing the charge now point should be when the lowest cell gets to about 6.45V, and the 'panic' point should be around 6.2V - does this sound right?

Err... What?

I also have made a quick checker out of a 4-digit volt display mounted on an XLR plug - a bit clumsy and I need to watch out not to get to close to things, but I can leave it in place while running and watch the pack total voltage more or less all the time. I did notice though that when I plug it in while connected to the ZXD I only see 28.91V at the XLR, as opposed to the 29.20 that the ZXD display is showing... When I was building the display I was testing it w/ a bench supply, and the display tracked w/ the supply display w/in 0.01V from about 5V to 32V (the supply limit)

Well mine are both (I have 2) exactly the same as my slightly expensive recently calibrated Fluke.
So its very likely that watever you are measuring with is the thing thats not correct.

Look at these!
https://www.wheelchairdriver.com/board/ ... start=2010

[shirley_hkg]

Is there any current flowing ?

[ex-Gooserider]

My freshly charged pack is giving me 6.9+ V/cell, I am guessing the charge now point should be when the lowest cell gets to about 6.45V, and the 'panic' point should be around 6.2V - does this sound right?

Err... What?

See my note above about the way I had to wire my checker - I'm measuring TWO cells in series and reading it like a 4S pack, so each should be reading 2X the voltage of a single cell...

I also have made a quick checker out of a 4-digit volt display mounted on an XLR plug - a bit clumsy and I need to watch out not to get to close to things, but I can leave it in place while running and watch the pack total voltage more or less all the time. I did notice though that when I plug it in while connected to the ZXD I only see 28.91V at the XLR, as opposed to the 29.20 that the ZXD display is showing... When I was building the display I was testing it w/ a bench supply, and the display tracked w/ the supply display w/in 0.01V from about 5V to 32V (the supply limit)

Well mine are both (I have 2) exactly the same as my slightly expensive recently calibrated Fluke.
So its very likely that watever you are measuring with is the thing thats not correct.

Look at these!
https://www.wheelchairdriver.com/board/ ... start=2010

The voltage I got at the ZXD terminals agreed w/ my meter - there was some charge current flowing to the chair, so possibly it was the voltage loss in all the wiring... I also noticed the voltage on the XLR reader did go up as the battery charged more, and the ZXD current dropped... I'm not terribly worried about it at any rate... I seem to remembering that Will was saying he found the most important aspect of the XLR display was to see how much the voltage dropped when driving the chair, and how fast it recovered...

We have now gotten the packs installed in the chair, though that turned out to be a far greater ordeal than we expected... A friend 3D printed some nice ABS battery boxes, and we had to solve some minor fitting issues, and I'm not sure just how we screwed it up, but we managed to smoke the main battery harness AND the power module, and ended up having to troubleshoot and replace all that.

And then couldn't get the chair top cover on because the boxes were a bit to high for the cover to go down where it should so for now we left it off. I'm sort of OK with that, except it means I don't have any fenders and my clothes will get soaked any time I have to use the chair in the rain...

Finally to top it off, when putting the seat back on, the much welded seat frame broke... The seat is now being held on with a cargo strap, and the leg rigging on that side is being held on with some stainless steel zip-ties.... Not good, but at least it will get me home (I hope)

ex-Gooserider

[Burgerman]

Sounds lke an engineering masterpiece.

[ex-Gooserider]

Sounds lke an engineering masterpiece.

What do you expect from Pride? Free Junky parts?

ex-Gooserider

[ex-Gooserider]

Seat frame is now more or less fixed again... Got a friend to help me get it apart and MIG'd a piece of angle across the top, then put it together, and it is now at least as good as it was, probably better.

He also took a bunch of measurements that may enable us to fab a new frame from scratch...

ex-Gooserider

[ex-Gooserider]

I'm now experiencing a strange intermittent error... Incredibly frustrating as I have replaced the JS pod, power module and Redel cable w/ other parts that I had previously tested as good, and still having the same symptoms...

So far has only happened when starting or stopping, or doing tight quarters back and forth, not while rolling at any significant speed. The chair will abruptly stop... Sometimes the LED's don't indicate any error, sometimes I get 7 flashing, which is supposed to be "Possible Joystick Problem - Check that joystick properly centers. If problem persists, change controller"

I ONCE got an 8 flash "Possible Controller Problem - Ensure batteries are charged and check all connections and wires - If problem persists, change controller"

If I power cycle, or unplug and replug the Redel cable (sometimes takes several tries) the chair will start working again...

Yes I know it's old and obsolete Pilot+ gear, but definitely a frustrating problem because I've changed ALL the electronics....

ex-Gooserider

[ex-Gooserider]

Also, I've got the Pilot+ cable and software but I'm not sure just what the optimal settings are for it, and I suspect my replacement controller is not set ideally...

I remember that BM once had a writeup on the best settings for a Pilot+, but I haven't been able to find it... Can you give me a pointer, or repost?

Particularly what is a good starting point for the compensation on 2-pole motors?

Thanks,

ex-Gooserider

[Burgerman]

Just read the R-Net one, pinned at the top. Same thing, same settings, just different controller.

[ex-Gooserider]

Just read the R-Net one, pinned at the top. Same thing, same settings, just different controller.

OK, thanks... Will do that as I'm sure I can slightly improve the current setup...

ex-Gooserider

[slomobile]

This situation worries me. Read this thread for a similar case, particularly look at the replies.
https://www.diyelectriccar.com/threads/ ... st-1130347

and https://www.evcreate.com/ev-battery-ser ... d-modules/

[foghornleghorn]

This situation worries me. Read this thread for a similar case, particularly look at the replies.
https://www.diyelectriccar.com/threads/ ... st-1130347

and https://www.evcreate.com/ev-battery-ser ... d-modules/

I thought you had 16 cells. Why are you reading stuff about wiring huge numbers of cells and worrying?

[Burgerman]

Same principles apply regardless of cell count.

But heres the thing they are all not getting And why I dont bother reading ev forums...

When you make a pack with 2, or more in parallel then you do so with identical healthy cells. Theres thousands of industrial packs that use thousands of cells. If a single cell fails on a LiFePO4 pack hen its electrically connected cell for cell to each of its parallel neibours. So a shorted or failing cell will drag down all the other cells that are in cell position 3 or whatever. And so it would be obvious. And with LFP cells thers no fire or anything so I wouldnt worry.

If I was using firework type lithium ion, and had a bunch in parallel, I would just do as tesla do. And connect each cell via a bit of thin "fuse" wire to the rest. Then any failed cell will just disconnect itself... And you wouldnt ever know.

[slomobile]

This situation worries me. Read this thread for a similar case, particularly look at the replies.
https://www.diyelectriccar.com/threads/ ... st-1130347

and https://www.evcreate.com/ev-battery-ser ... d-modules/

I thought you had 16 cells. Why are you reading stuff about wiring huge numbers of cells and worrying?

Because I'm also trying to figure out if converting the van to electric is possible. I know its not feasible, but fun to think about. And the problem described happens when just a single cell in a group goes bad. It applies to my 16 cells because of the weird 4 BMS way I was thinking about but didn't do. But I just realized it does not apply to ex-Gooserider because he does not actually have any parallel connections between packs, just serial. Misread his original post and thought the 2 packs were going in parallel. Eliminating the black balance wire on the upper pack ought to work fine for him. But I'm almost done writing a post on that other forum about wheelchairs, add on packs, and charging from vehicles, inspired by this thread. So I'll see if I can edit out my oops and still post something useful.

[ex-Gooserider]

The other big difference is that I am NOT using a BMS, so no chance of having one doing the surprise shut-off routine...

Incidentally, and I'll probably jinx myself by posting this, but whatever was causing that intermittent error seems to have fixed itself, no instances of it happening in the past week or so...

I need to grab the graph off my isolated Windows box but I have charged it once after 6 days, put back 35Ah, so a HUGE increase in range... However I noticed a bit of a strange pattern during the charge... The cells were just about perfectly balanced when I started, and tracked together for a while, and then I got a big separation where some of the cells seemed to slow down their charging for a while while the others had voltages that went up faster, and then BEFORE they started balancing, the two groups merged back together... Any reason to worry about this?

ex-Gooserider

[Burgerman]

Usually some variable resistance some place in the system. Remember we are looking at microscopic voltage differences here.

[foghornleghorn]

I noticed a bit of a strange pattern during the charge... The cells were just about perfectly balanced when I started, and tracked together for a while, and then I got a big separation where some of the cells seemed to slow down their charging for a while while the others had voltages that went up faster

Check your nuts

Cells running up faster usually indicates a loose connection somewhere.

[Burgerman]

That.

And when voltage is below 3.4V they all track together even if they are a few Ah out of balance. As they get more full, % wise the voltage suddenly spikes at 3.35x volts and does it fast.

This is the same reason you should never use any full time balance systems, balancers that balance below 3.45V during charge etc.

If the battery is at around 95% charge, or less, then the highest cell voltage you see may be "balanced" as far as capacity is concerned. This voltage may be a few mV higher, due to a real voltage difference due to cell matching issues, due to temperature differences, or because the balancer you have in a BMS or charger, or all day active balancer may not be accurate enough. Can also be because the CRIMPED balance, or terminal connector metals are a different metal or oxidised over time which is then a tiny battery... Creating a voltage across the joint. Enough to throw off balance... So you end up with the balancer trying all day long to balance an already balanced pack. And since the voltage DOESENT equal STATE OF CHARGE below 3.4V then it can unbalance the pack by many Ah over time.

[ex-Gooserider]

Well things seem to be working well so far, no more problems w/ the chair controller cutting out on me. I've charged the chair TWICE since installing the pack, and probably will again in the next day or two - it is really a huge change going from the end of life lead bricks that I needed to charge multiple times a day (basically plugging into the ZXD any time I was in my space for more than a few minutes) to going 10+ days between charges Getting rid of range anxiety is a real thing!

I think I do need to make some changes in my PL8 program as it does not seem to be ending the charge when full, instead keeps going for a long time at around 0.7A and all cells at the same voltage w/o ever getting to the 0.3 or so specified in the program... This may be due to the power draw of the Pilot System even when off?

If I'm understanding what I've read in the other threads I need to:

Lower the charge voltage to 3.55V (if it isn't there already)

Make sure balance is set to start at 3.50V

Increase the end current to something that will shut down 15-30 minutes after all the cells have reached the balance voltage.

Possibly turn on the Fuel display (mostly for amusement)

Other changes?

Thanks
ex-Gooserider

[Burgerman]

That sounds about right. Some cells that are less than new will take at least 30 mins to drop lower but if they are all balanced and at the specified voltage then no point waiting. Theres nothing up there capacity wise...
When you set a lower than the recommended 3.65V it takes a little longer to balance and to get from 99.9 to 99.9999% if you care! But the cells care.

So dont worry if it takes a while.

[ex-Gooserider]

Did another charge today (9/10) put in about 75Ah. The previous charge was on 8/29 for 63.5Ah, so this cycle was about 12 days, so around 6.25Ah / day of typical use...

Does this sound reasonable?

Pack is nominally 90Ah (6P-8S of Headway 15Ah cells) so it looks like this is about the right length of time between charges, more or less...

FWIW the little XLR plugin voltmeter I made was showing around 26.02V when sitting, and would drop to around 25.5 running mostly straight, and dip down to high 24V on launch or turns at speed, etc. When I stopped it would fairly quickly but not instantly go back to 25,9 but then take several minutes to climb back up to over 26.0. I remember that Will said he thought that the speed at which the voltage recovered was a good indicator of the approximate state of charge, and this seems about right...

ex-Gooserider

[Burgerman]

At 244Ah measured on the Docan 230Ah cells, and divided by 6.25Ah per day used, thats 40 days... So you could charge every 35 days and still have 5 days use in reserve!

You dont use it much do you?

[ex-Gooserider]

I agree the Docan's would be better, but I'm using what I have...

I use the chair a LOT - I'm in it probably at least 10-12 hours a day, but most of my time is either sitting in front of the PC or doing short back and forth running around the Asylum and doing stuff in the shops. Remember that it is a weedy 2-brush motor Pride chair even if it has been hopped up w/ an 80A Pilot+ system and programmed to more or less your suggested tuning.... Doesn't matter how much you soup up a turd, it's still a turd...

ex-Gooserider

[Burgerman]

Probably not very heavy, quite low geared and slow.
I wonder how many miles 244Ah at 26V would take that... You wold probably make the next state.

[Williamclark77]

I remember that Will said he thought that the speed at which the voltage recovered was a good indicator of the approximate state of charge, and this seems about right..

Yep. I've been using homebuilt lithium packs since 2012 or 2014. Long time. I had gotten to where I could see the current voltage, drop, and recovery after a quick throttle jab and guess the returned ah to within 3 to 5ah ON MY CHAIRS. You will quickly figure it out after a few charges for yours. Swapping volt meters will throw you off if they have different refresh rates. Same with sketchy cell or wiring connections.

Don't over think it. It's not that complicated. It will spoil you.

Now, combine higher voltage efficiency with brushless efficiency and really see range anxiety go away. I didn't even put a voltmeter in the joystick housing on this last chair I built. Less wires and one less switch. KISS. I check the battery from my phone every few days and typically charge it every Sunday night. 105ah pack. Typically returns around 40ah. And that's only if I run a lot. I do typically charge it the night after I mow my yard or something similar.

You could absolutely duplicate it.