Group 24 cells

[Burgerman]

230Ah? Still waiting here! About 4 weeks to go.

[jefferso]

Awesome, thanks for posting these updates jefferso!

I am in the same process, just a couple steps behind you!

You're welcome, hope they're helpful. Yours is looking good. Hope you can post photos too. So many different people's photos have been useful while working on the project.

[jefferso]

What happens if some overly helpful PA or helper plugs in my old charger to the XLR port while I'm in my old chair or in bed or something?

Will it charge the LiFePO4 pack at 12 amps, just without balancing? Or not even charge unless voltage is 28.2 or lower?

I think my Victron charger which I use for travel has a Lithium setting which has a higher voltage.

[Burgerman]

It will charge, and will send the first cell to reach 100% up to a high voltage. So dont! Hide the old lead charger. Or take the fuse out. Or tape over the XLR on the charger. Or something.

Lithium, lead, have similar CV voltage. Dont go near that new battery with a lead, or a lithium charger unless it also balances cells! Like the PL8. Or trouble!!!

[Superchunk]

230Ah? Still waiting here! About 4 weeks to go.

Nah 160Ah got a permobil.

[Burgerman]

Since you can only get about 40 to 45Ah from lead bricks that still gives you the same range as 3+ full sets of lead batts.

[shirley_hkg]

What happens if some overly helpful PA or helper plugs in my old charger to the XLR port while I'm in my old chair or in bed or something?

Will it charge the LiFePO4 pack at 12 amps, just without balancing? Or not even charge unless voltage is 28.2 or lower?

There is way to use dump charger for your pack safely , if you were away from home and you don't want to carry PL8+PSU with you.

Let me know.

[Burgerman]

He means dumb. As in no balancing or settings etc.

[Superchunk]

What happens if some overly helpful PA or helper plugs in my old charger to the XLR port while I'm in my old chair or in bed or something?

Will it charge the LiFePO4 pack at 12 amps, just without balancing? Or not even charge unless voltage is 28.2 or lower?

There is way to use dump charger for your pack safely , if you were away from home and you don't want to carry PL8+PSU with you.

Let me know.

I'm interested in this, does it involve a BMS?

[shirley_hkg]

YES.

[Superchunk]

YES.

Go on then. Shoot me your recommended bms suggestion.

[jefferso]

I am interested too.

[shirley_hkg]

It's pretty primitive, that's just a BMS with a matching male Dsub to plug into chair's connector.

Belows is 10 years old. You can now find a modern BMS with user programmable parameters.

[jefferso]

Yesterday I went about 5km and ran my ventilator most of the day on the chair. The joystick indicator stayed all green. The Permobil phone app seemed confused for the battery, showing 83% for a while, then 98% then 96% then 98% again.

But today attempting to charge, I tried to charge at 40 amps instead of 30 amps. It worked for a few minutes, then said power supply unstable. I set it back to 30 amps.

I am now getting Cell 4 going very high on charge, so it immediately goes to CV and bypasses Cell 4. I tried discharge and Cell 4 goes immediately below the low voltage and the discharge ends.

Is Cell 4 likely bad? That's the one that had a spark across it when assembling the pack.

I also had a SAFETY CODE 17: Cells No Add Up when I tried charging with 35 amps.

[Burgerman]

What you have there is a bad connection. I think. Very common.Either some connection is loose. Or you didnt solder everything and are relying on crimps...

Can be a balance connector, main battery terminal connection, charger end, battery end, the subD in the middle, or somewhere.

Clean all surfaces, use switch cleaner, and solder anything that is crimped.

The Permobil phone app seemed confused for the battery, showing 83% for a while, then 98% then 96% then 98% again.

Its IMPOSSIBLE to determine the state of charge of a lead battery to within 30% or so based on voltage.
Its also equally useless trying to do that with lithium. All it can tell you is this:

GOOD (top 5%)
NORMAL (85% of the battery where the voltage is almost constant)
Empty and you should charge! (bottom 10%, as it drops away fast at the end)

So as usual a wizz kid programmer that hasnt a clue about batteries has made an "ap"... Which is completely useless.

[jefferso]

Thanks! Definitely a loose connection. The terminal nut on cell 3 positive seems like it had only been hand tightened. A clue was the smell of melting plastic. It caused enough heat to melt some of the insulation on the interconnect cable and melted the plastic terminal cover. Got those off, got everything cleaned, wound some electrical tape over the damaged insulation on the interconnect cable. Put it back on with new spare insulation boots (fortunate they come in batches of 20 instead of just 16), checked and tightened all terminal nuts. Only had time for a five minute test charge, but all cells were very close in voltage and none of the covers or cables were warm.

I guess the lesson is if you have a helper who doesn't have experience with things like this, or isn't by nature careful and methodical, just saying "tighten them all" isn't sufficient. I guess it's best to watch and confirm for each one.

[jefferso]

The Permobil phone app seemed confused for the battery, showing 83% for a while, then 98% then 96% then 98% again.

Its IMPOSSIBLE to determine the state of charge of a lead battery to within 30% or so based on voltage.

When I had the pack in previously the Permobil app was confused and wrong, but more consistently wrong. I suspect the wild swings were a result of the connection getting better or worse as things vibrated around. So the app and the control's indicator lights might be useless for knowing specifics but can be occasionally useful for drawing some conclusions. Like if you lose one green light early in a typical day, rather than late in the day as usual, something might be wrong and then you might do a top-up charge or be extra cautious. I've had that and then found out the chair hadn't been charged overnight and had only started in the morning before I got up and someone forgot to tell me.

I guess that app does some math for its guess of range. I wonder if it will start to estimate a longer range once I've gone a long way without charging or if all the app's assumptions are based on lead acid capacity.

[Burgerman]

When building battery packs, putting engines together, or whatever I always have a couple of tiny paint markers.

So when going around checking things like terminals, they get a tiny blob of say blue. To tell me I checked it. Then I will always go around a 2nd time (essential on engine cylinder heads, brake disks, clutches, etc) and dab some red... To tell me I checked! So I cant miss one.

When they needed loctite, I dab say, yellow so that I know not to recheck. If you look at a brand new car or bike you sometimes see that they did something similar.
That was when building drag bike engines and v8 car engines etc. Many years before wheelchairs.

So when doing batteries I now carried this over. Just with typex mark. And I still miss one. Especiall on the old headway packs. Those have say 80 cells. And a bolt each end. So 160 to do. Always 159 were tight...

I now have a tousch up paint from a car with an integral brush sat on the shelf awaiting my new cells.

[Burgerman]

I guess that app does some math for its guess of range. I wonder if it will start to estimate a longer range once I've gone a long way without charging or if all the app's assumptions are based on lead acid capacity.

Whatever it does it will never even be within 30 to 50% and so ahaving a percentage scale that reads in 1% increment is frankly rediculous.

What it basically is is a voltmeter. It adds in some data averaging. And it probably ignores the voltage under load or when above a specific level and thinks that this is due to regen. Its also attempting to equate the level of peukert losses by watching how fast the voltage is falling on average. So basically its about 3 different types of guestimation/fudge, all multiplied together in a sad attempt to guess whats left. Which isnt actually possible.

Theres only 1 battery chemistry that you can do that with and get a sensible result. Rather than a "feel-good" number that most battery meters give! And that is lithium ion. The type of cells used in laptops, phones, EVs, etc. Those little lithium ion cobalt firework ones. And the similar chemistry lithium polymer. Because on those the voltage falls in a nice even way as they are discharged. All very mapable and repeatable. On those a BMS and a battery meter are quite good at knowing state of charge or charging.

On lead, and on lifepo4 they just cant ever be.

But you wont need them to be. Even with 160Ah you will find it hard to run them low enough to ever worry. And the ADVANTAGE of this little loose terminal episode is that you learned to recognise the issueson the PL8 graph. I cold see it was a connection issue just because a voltage cannot fluctuate up and down in that way on 1 cell (or a few of its neibours) intermittently. A bad cell will be constantly the same but high or low. The advantage of charging with that charger is that unlike a drop in lead brick solution, or a typical BMS you can get early warnings or clues before you damage a cell or end up stuck miles from home.

[shirley_hkg]

High heat seemed to have caused high resistance to wires.
Better have it replaced.

[jefferso]

Did a full charge today and everything seems much better. Cell 4 showed up as lower than the others for a while, but it kept getting bypassed yesterday so maybe that's not unexpected. I guess I'll see how it does with the next full charge.

It put back 23.5 Ah, and maybe a total of 4 or 5 Ah yesterday before the melted plastic smell, which is about what I would expect for 5km and using the vent most of the day.

High heat seemed to have caused high resistance to wires.
Better have it replaced.

So the heat might have affected the interconnect cable's resistance? Not just melted the insulation? I'll check on getting a replacement.

[Burgerman]

Cell 4 was just lower.

Should be almost perfect next charge or so.

Cable resistance should be fine. As long as they are soldered. And are STILL soldered! Personally I would take a careful look. Maybe measure resistance but that needs a very very good meter. If in doubt swap it.

[jefferso]

I switched the power supply to the new ZXD and did a charge at 40 amps.
Seemed to work well and cells were much closer at the end. The ZXD is pretty quiet even at 40amps. The PL8v2 is louder.
The ZXD was showing 18.97 Ah while the charger was showing 18.504 Ah. It was using 41.24 amps to drive the charger at 40 amps.

Put in 25 Ah from running the vent on my chair all day, moving around in the house and doing seating adjustments and standing.
It had put in most of the charge within 45 minutes. Amazing to charge at 40A and put in a day's worth of use in under an hour. Of course it will take longer when I go out, and travel some distance but impressive compared to all night charge for an average day and even then probably not charging long enough to be really good for the MK gel batteries.

[shirley_hkg]

Put in 25 Ah from running the vent on my chair all day, moving around in the house and doing seating adjustments and standing.

Not difficult to imagine how you were restricted in a pair of MK Gel.

[jefferso]

What happens if some overly helpful PA or helper plugs in my old charger to the XLR port while I'm in my old chair or in bed or something?

I taped it over and then ordered a "Neutrik Dummy Plug For XLR" from ebay. I thought it would be stiff plastic but it's kind of flexible rubber. It seems to work anyway.

https://www.ebay.co.uk/itm/155081501653

[Burgerman]

Seating takes almost nothing. The vent takes more than the chair indoors I would expect. But rolling a good distance wont use as much extra as you think. Indoors takes almost as much.

No charger is 100% efficient. Maybe 80 to 90? So you always put more watts in than you send to the battery. So the power supply and PL8 figures are correct.

So how many days of indoor use with a vent attached will you get?
160Ah??? Div by 25ah daily = almost a week. So you can get a safe 5 days and have a day and a half safe reserve.

Keep a record for a few weeks so that you know a true daily indoor average.
Then do the same on a long run outdoors. And keep a record of distance and ah each day/date.

Afer a while you will know how far, how often, and how many days to go between charges mentally without a battery monitor. Also watch for a light to go out, note that too, with Ah returned. To get a mental idea.

A few weeks of that and you will have a good mental image of whats possible and how discharged it is.

[jefferso]

It's pretty primitive, that's just a BMS with a matching male Dsub to plug into chair's connector.

Belows is 10 years old. You can now find a modern BMS with user programmable parameters.

I am interested in this as an option for travel to use with my Victron Blue Smart IP22 Charger. It does 12 amps and has bluetooth which is handy for seeing how much it has charged and it's only 1.3 kg (2.9 lbs) and is relatively compact 235 x 108 x 65 mm (9.3 x 4.3 x 2.6 inch).

Also for travel I was thinking of taking a PL8 and finding a cheap lightweight power supply. Maybe something like this 24V 10A 240W Power Supply Adapter:

https://www.amazon.co.uk/Adapter-100-24 ... 0CD7KJ8HJ/

or this AC 110-220V to DC 24V 10A 240W Voltage Transformer Switch Power Supply Converter:

https://www.ebay.co.uk/itm/126257933744

or something similar, e.g. a 12v 33a version for £12.99

Hardly ideal for quick charging, but could add back a reasonable amount overnight.

[Burgerman]

10A 24V less losses at charger and voltage increase to 28.8V charge means that even maxed out you will see 6 to 7A charge. Thats OK but if you are putting back 160Ah that would take almost 27 hours! Which is why we use powerful hobby chargers. I apreciate that you likely wot b fully discharging them but its not ideal... But even a 50% charge is still 15 hours.

At 40A that takes 4 hours for 160Ah. And a bit to balance.

Why are hobby chargers so much more powerful than standard full sized types of car or wheelchair chargers?

Because while we may only fly with batteries the size of a pack of cigarettes, and maybe 4Ah, (4000mAh) they are 90 to 150C rated. So a tiny battery may need to be capable of way more than 100 plus Amps in a helicopter "punch out" or a fast plane for e.g. This is what lipo excell at. Well that and exploding!
That 150C rating means a tiny 2x3x1 inch 4Ah battery can do a crazy 600Amps! It will literally out perform a car battery when starting a car. And crank it for longer. And it means that a 10C (or more) charge rate is normal - very low in fact.

We charge a 4Ah battery at 40A only because we not have more! 60A charge would be fine if we could. So full charge from zero, takes literally 1/10th of 1 hour. Or 6 minutes and under 1 min to balance.

Its fortunate that they are so powerful. Works out great for us and charging LiFePO4 packs of 100 to 400Ah...

[Burgerman]

According to this, you basically put everything back in under 35 minutes. Just left about 1% to add and balance. So more amazing than you said!

So in cases lilke that, probably better to reduce charger to 20A. Less stress on everything. You should use 30A if you need to. And 40A if its heavily dischared. Then less heat, less chance of melted cables or other issues. The advantage of an adjustable charer.

You can increase termination current a little. By around 25%. So if its set to say 200mA for e.g set to 250. Keep doing that until it ends after around 15 to 20 mins after it is at CV balanced. Its pretty good already. Manual fine tune! Its not critical. But why not.

[jefferso]

It's pretty primitive, that's just a BMS with a matching male Dsub to plug into chair's connector.

Does it get power from the XLR plug? or do you have to provide external power for it?