Battery Pack Issue

[Gnomatic]

i wonder if someone can get a hold of the 48 V joystick and controller from Bounder - - that can be used on any chair then ? as long as you make the battery 48V ?

I'm pretty sure that's exactly what the guy in the modified Bounder thread did. He took vanilla 24v Bounder frame, modified it bto his liking, bought the 48v electronics from 21st Century, and then built a huge 48v lithium pack for it. I'm real curious what kind of cells he used, I don't think there's anyway you could build a pack with that large of capacity with Headways.

On a side note, I'm still not quite sure how pumping 48v into 24v motors doesn't burn them up.

[Burgerman]

If its any good, programmable enough. And $$$$$$$$$$$$$

[Burgerman]

Because power is watts. Amp limits occur only at low pulse-widths and are still limited to the same amp level as before.

[expresso]

talking with bounder - David - i got a good feeling if you had to deal with them on purchasing items from them on your own etc, - it comes down to the cost then - which i would think its very expensive - but never know - can work out a deal

when i mentioned about the programmer etc, - he was willing to sell it to me easily and at a much better cost - than whats on paper - we didnt get into how much less - but just the fact that they are not SHY to do it and understand the need for it etc, -

i am sure if you wanted to get the other items from them with your own money - the chances are good they will work with you - NO one else has a system set up for 48V out of the box - so its either this way - which you know will work - or your way BM etc, and very few of us can do what you done - a hand full your guys here can -

it might cost more than what your paying for your new Chair there getting the joystick controller etc, from Bounder - then you have to build the pack for it - i see it costing thousands !!!! without the pack - then add the pack a few more thousand -
i think i be sticking with my 24V for a long time

[Gnomatic]

i am sure if you wanted to get the other items from them with your own money - the chances are good they will work with you - NO one else has a system set up for 48V out of the box - so its either this way - which you know will work - or your way BM etc, and very few of us can do what you done - a hand full your guys here can -

Exactly really want to do 48V some day, and am happy somebody makes an off-the-shelf control system for it. The Roboteq thing is WAY over my head.

I'd still need to figure out something for my 24v power seat functions. Something like this would probably work, along with an external switchbox or joystick to control the seat. I don't really like those cheap Chinese voltage converters though. I had the 24v-->12v version of that converter on my X5. Eventually it went up in smoke, literally, and what I was powering wasn't drawing anything close to the converter's rated capacity. Still went up in smoke.

[Gnomatic]

Because power is watts. Amp limits occur only at low pulse-widths and are still limited to the same amp level as before.

Same amps true but double the energy(Watts). Wouldn't more energy pumping into them = more heat/shorter life?

[cdb0ewm]

Here's a picture. It really only uses minimum P222 parts. There is still lots to figure out/do.

[expresso]

i see

[Burgerman]

Amps are what burn out and heat up motors. You put more heat into a motor at stall than at any other time. Because its 100% wasted energy. At this point a typical powerchair motor will be Amp limited by the controller to 100, 120A maximum typically, by a reduction of pulse-width (volts). So it may be receiving say 8V equivalent. Depending on motor impedance. If you now double the battery voltage, the controller reduces the pulse width by half, again, to leave you with the exact same 100 or 120A limit. And so the motor still sees the same 8V... So at stall no change at all.

As you increase speed the motors 'generator' effect means less and less current is drawn. Once you reach full speed, free running, even at double the speed with your high voltage battery the motor draws the same low 5 or 7 Amps as it would on a 24v system at half the speed.

The only proviso is that you don't exceed the motors 'fly apart' rpm! And that would be a bit serious. So I tested an AMT motor for some hours at 60 to 72V before running it in a chair at 45V. (about 8000 rpm) without any problems and it stays cold.

And that you don't exceed the motors AVERAGE wattage rating for long periods because that would damage it through heat. So on a road, no problem. But don't try and drive up a long steep hill at 16mph... Or at say 6 to 8 mph across a mile of sand on a soft beach. Because its possible in these conditions to draw a high current (up to stall amp level), for long periods at speed, because of the added load plus volts. So you need to understand whats going on.

[Gnomatic]

Amps are what burn out and heat up motors. You put more heat into a motor at stall than at any other time. Because its 100% wasted energy. At this point a typical powerchair motor will be Amp limited by the controller to 100, 120A maximum typically, by a reduction of pulse-width (volts). So it may be receiving say 8V equivalent. Depending on motor impedance. If you now double the battery voltage, the controller reduces the pulse width by half, again, to leave you with the exact same 100 or 120A limit. And so the motor still sees the same 8V... So at stall no change at all.

As you increase speed the motors 'generator' effect means less and less current is drawn. Once you reach full speed, free running, even at double the speed with your high voltage battery the motor draws the same low 5 or 7 Amps as it would on a 24v system at half the speed.

The only proviso is that you don't exceed the motors 'fly apart' rpm! And that would be a bit serious. So I tested an AMT motor for some hours at 60 to 72V before running it in a chair at 45V. (about 8000 rpm) without any problems and it stays cold.

And that you don't exceed the motors AVERAGE wattage rating for long periods because that would damage it through heat. So on a road, no problem. But don't try and drive up a long steep hill at 16mph... Or at say 6 to 8 mph across a mile of sand on a soft beach. Because its possible in these conditions to draw a high current (up to stall amp level), for long periods at speed, because of the added load plus volts. So you need to understand whats going on.

Thank you for breaking that down I have a better grasp of it now.

So basically, as long as you're not offroading uphill at full speed, you're not hurting the motors. That's not even a realistic scenario in real-world usage anyway.

[Burgerman]

Speed on a flat road wont hurt it. Stalled motors, no different than before. Heavy loading at speed, will hurt it if you do it for long!

[Gnomatic]

So if you're on a road and there's a long, uphill climb, would you just be careful and and not have the joystick jammed all the forward during the ascent?

[Burgerman]

I would ignore it if it was a slight hill, and if it was just a few tens of meters. If it was longer or steeper I would likely do 6 to 8 mph depending. Just think how fast it would have gone at 24v to be super safe.

[cdb0ewm]

Been working on the steps you outlined. It is working as your described but doing one cell at a time is taking a lot of time. Any suggestions on a 'cheap' Hyperion charger so I can do these single cells using two chargers. I see some used chargers on Ebay but don't want to get something that won't work.

Thanks for your ongoing help

[Burgerman]

You cant use a different charger because you are looking for small mA and mAh changes. They would vary between chargers. But also I cant actually see what it is you are doing! Why is it taking so long?

[cdb0ewm]

Each cell is taking about 2+ hours to charge plus 1 hour post charging then about 1 hour to discharge then the time to recharge x 78

[Burgerman]

Well you could have been charging at a higher rate, but you cannot change settings now or you will need to start again.

Are they all giving similar Ah?

[cdb0ewm]

so far yes

[Gnomatic]

Each cell is taking about 2+ hours to charge plus 1 hour post charging then about 1 hour to discharge then the time to recharge x 78

About how many have you gotten through so far?

[cdb0ewm]

all 78 for the initial charge and 10 for the dischargeand recharge

[cdb0ewm]

OK...
I finally finished charging/discharging/recharging the good cells as you explained above. I just received my replacement cells to replace the bad ones. I don't want to screw this up again. How should I charge/discharge/recharge the new cells and any thoughts on how to best mix the new cells with the good old ones.
Thanks

[Burgerman]

Mix new old 50/50 on each parallel group.

At least make them the same as each other.

Then assemble with fully charged cells. WITH TOTAL CARE and no loose bolts, heat shrink in the way, and test every bolt several times... Solder cables properly.

[cdb0ewm]

SHOULD I JUST CHARGE THE NEW ONES AND SOAK FOR 1 HOUR

[Burgerman]

Just charge them all the same. When assembled it will still need charge/balance and then discharging by say 30Ah or so then recharge to test.

[cdb0ewm]

OK... got the pack all assembled. I still trying to check every step so I don't have another screw up. Before I connect the balancing wires I want to make sure it's right.

[Burgerman]

correct

[cdb0ewm]

Thank you. One other question. Given that each pack contains 6 cells, does it matter what cell the balancing wire is connected to in each pack as long as it conforms to the diagram above?

[Burgerman]

No, all cells are connected together with heavy bus bars and they behave as 1 big cell.

[cdb0ewm]

I understand but given there are 13 'packs' each consisting of 6 cells does it matter if I put the balancing cable on cell 1 or cell 3 or cell 5, etc of each individual pack

[Burgerman]

Dont understand your terminology.

No, all cells in your "packs" are already connected together with heavy bus bars and they behave as 1 big cell.

Pack = a bunch of cells in parallel/series as required for a device. A battery.
Cell = 1 cell.
Parallel group of cells of which there can be 4, 8, or in my case 13, for approx 43V in use.

You connect each parallel group. Since all are in parallel it makes no difference which one you connect. Obviously they need to be in the right order.

So, start at the neg, at 0V, and each group gets a wire. 3.2v, 6.4v, 9.6v, 12.8v, etc etc... So you need 9 wires for 8 groups of cells. 14 wires for 13 parallel groups of cells.