PINNED - Lithium battery conversion/info

[Burgerman]

Well it should not. Balance at 3.5v if you wish. But that is DIFFERENT to balance at 3.6V. So its basically doing the job over... Although at 3.5 / 3.6 they are close to the same.

The danger is that many BMS balance ALL the time at every voltage and that really upsets the pack.
On discharge, after the first 1 percent, for around the first 36 percent of the pack there is no voltage change, and it can actually climb slightly as it discharges on a cool day as it warms. So any voltage difference the BMS sees, is either because its not that accurate, or because not all cells are the same exact V anyway. It means the BMS is trying to balance a perfectly balanced pack. Most of the day. So screwing up real balance at the top.

[steves1977uk]

Since I have 45 40152 Headway cells on order to upgrade my modded Elite Whisper to LiFePO4, there's a few things I wanted to double check...

I will be using 40 cells to create a 24v 75Ah battery to replace the lead ones I have in it currently. Do the balance wires connect on the bus bars between each pos and neg? Then do they run in parallel for each 8s pack connected together?

Steve

[Burgerman]

40 Cells?

That's 5 parallel, 8 in series.

So you need 9 balance wires. That's one each end, and one in each of the 7 series "joints" you have with an 8S pack.

5 10Ah cells is 50Ah.
5 12Ah cells is 58Ah.
5 15Ah cells is 75Ah.
So you are using 15Ah cells?

What are the existing lead batteries?

[steves1977uk]

Hi BM,

I am using 15Ah cells, yes. The lead batteries are only 45Ah.

Steve

[Burgerman]

Well you would actually get a usable 50 to 60 percent of that before your mobility controller says enough. So about 25Ah. With the lithiums you get all of what it says on the tin. So range will be around 2 to 2.5 times previous range. Best take some sandwiches...

[steves1977uk]

Thanks for explaining BM

I will be using a 9-pin extension serial cable cut in half with the female end connected to the pack and the male end from the Powerlab 8 charger. Anderson connectors for the power.

Steve

[Burgerman]

The wires in those are very thin. It will work but a bit borderline. The connectors are OK but may be better to wire your own.

Or use a printer one (parallel port) and use 2 pins and 2 wires for every single connection.

[steves1977uk]

Hi BM,

Whats the name of the plug that you use for a balancing connector?

Steve

[Burgerman]

An OBDII connector.

I had an extension so used it. They have the same problem, but I cut them short and used heavier wires from a couple of inches after the connector. I used it because I had it. If I was buying a connector I would likely use and aircraft multi pin type round connector - I forget the name, or an ATX extension power connector 20 pin. That gives you 9 that you need for balance and 11 for other things, such as charger power on 8 of them, and 3 spare...

[steves1977uk]

Thanks BM, just ordered an OBD2 extension cable from ebay since it will be more sturdy than an ATX connector.

Steve

[Burgerman]

Well I am not sure they are!

But it will work. Mostly depends how thick the actual wires are.

[steves1977uk]

Would 20 AWG wire be ok for the balance cable?

Steve

[Burgerman]

Not sure about small sizes, my eyes don't work that well! The fatter and shorter the better but don't worry too much about it.

[ex-Gooserider]

Would 20 AWG wire be ok for the balance cable?

Steve

Should be, as long as the length is kept fairly short... IIRC the Hyperion only balances at about an amp, which won't give that much voltage drop if you keep the total wire length short.... I'd say less than 3-4 feet total. (Make sure to count both the length of the harness in the chair as well as the distance between the chair and charger...)

I'd rather use18 AWG, but that is arguably overkill, and it starts getting to be a challenge to find connectors that both have enough pins and use wire that size. The big advantage of the larger size is that you can get away with a longer balance lead, which might make it easier to plug the charger in...

ex-Gooserider

[Burgerman]

300mA

[maker102]

I have a pair of WKA12 100C/FR Group 24 batteries. They are separated by a hydraulic actuator, would it be best to use 72x 12Ah headway cells, or should I use another configuration. I have approximately 2" in width that I could get with a little welding. On a separate unrelated question, when you lose a quadrant of joystick use is it normally a cable problem, joystick or controller problem. Its a DX 2 Plus setup. Any Idea's? Thanks in advance for the help.

[Burgerman]

Batteries depend on space, W H L you have available. You need to aim for the highest total Ah possible in the space you have available.

I don't understand the other question!

[maker102]

If you take a circle and divide it into 4 equal sections i lost the use of one section or one quarter of the joystick. Hope this helps

[Burgerman]

I cant see how that would be possible!!!

[LROBBINS]

If it's an inductive joystick, it has 4 moving coils and one fixed coil inside the pot (or vice versa - my mental image without opening one up is now of one moving coil and 4 fixed - one in each quadrant). A broken wire to one of the quadrant coils (or an open coil winding) might cause this. I've had and fixed broken leads to the moving coil, but have never seen a failure of a fixed coil's wires. Tiny connecting wires, and even finer magnet wire in the coils, so repairs are a bit tricky, but when you don't have a spare readily available, it can be done.
Ciao,
Lenny

[Burgerman]

But wouldn't that give a start up error, and reverse would be 1 wheel too?

[LROBBINS]

Don't know. The coil wires are not the same as the output wires that go to the board - those are downstream of the circuit board that's in the pot. My recollection, not terribly reliable given my biological RAM, is that when we had a broken moving-coil wire (happened more than once in 25 years) it just gave constant 0 (2.5V) output, no startup or out of range error, so a broken wire on one quadrant coil may just give 0 for that quadrant (and perhaps just half throw in the opposite quadrant as they probably work as some kind of bridge).

I'll break for a few minutes and go look inside an old pot down in my shop - at least I'll see whether there's 1 moving or 4 moving coils.
Ciao,
Lenny

[LROBBINS]

The old pot from a DX-ACU has 4 fixed and 1 moving coil and a circuit board the diameter of the pot with two multi-pin ICs and many SMD discrete components. I haven't tried to identify the ICs, but my guess is that there's a two-channel frequency to voltage converter in there. The controller will not know if there's a fault in there if it doesn't send the voltage output out of range. Again, the last moving coil open did not shut down the ACU because I was able to drive the chair from Rachi's switch interface connected to the master remote (DX-SCU) while my fallible memory says that a real ACU failure, such as unplugging it, shuts down the chair.

Ciao,
Lenny

[steves1977uk]

Should be, as long as the length is kept fairly short... IIRC the Hyperion only balances at about an amp, which won't give that much voltage drop if you keep the total wire length short.... I'd say less than 3-4 feet total. (Make sure to count both the length of the harness in the chair as well as the distance between the chair and charger...)

I'd rather use18 AWG, but that is arguably overkill, and it starts getting to be a challenge to find connectors that both have enough pins and use wire that size. The big advantage of the larger size is that you can get away with a longer balance lead, which might make it easier to plug the charger in...

ex-Gooserider

Hi ex-G,

The cable length won't be any longer than 3 meters, and the balance connector plug has 9 26awg (could be 28awg) open-ended wires that have solder on them already.

So there needs to be thicker cables from the battery pack, which are soldered onto the thinner balance wires for a more stable voltage reading? Have I got that right?

Thanks BM and all others for helping me to understand this and to get it right!

Steve

[Irving]

I don't know for sure but my guess is that the Hyperion checks cell voltage when its not drawing balance current; i.e. it discharges for a while then stops, waits a while (a few tenths of a second) for things to settle, checks the voltage (at a very low current, say 10mA so voltage drop insignificant), and starts discharging again if need be (at least that's the right way to do it). The sizing of the balance wires therefore, as long as they can handle 300mA safely, I would have thought is not critical. 26awg is 0.04ohms/foot so at 10mA sense current the drop is .04*.01V = 0.4mV/foot so up to 10ft (3m) is inside the 5mV accuracy BM sees on his testing. Longer than 3m I'd go to 24awg up to 6m and 20awg for 12m but that's getting silly

On 26awg at 300mA balancing the power lost in the wire is 0.3 * 0.3 *.04W/foot = 3.6mW/foot so no problems there.

[Burgerman]

It watches and displays cell voltage all of the time. It watches TOTAL voltage as it charges for 30 secs, and decides on how many amps, and then looks at cell voltages individually for 10 secs while it stops charging. And while charging if any cell exceeds the set voltage it sinks it by up to 300ma to hold it to the correct point, and throttles the charge amps back to whatever level is needed to ensure it can do so.

It does a few other things too. Long wires just extend charge time a fair bit if the pack is very far out of balance.

[Irving]

It watches and displays cell voltage all of the time. It watches TOTAL voltage as it charges for 30 secs, and decides on how many amps, and then looks at cell voltages individually for 10 secs while it stops charging. And while charging if any cell exceeds the set voltage it sinks it by up to 300ma to hold it to the correct point, and throttles the charge amps back to whatever level is needed to ensure it can do so.

It does a few other things too. Long wires just extend charge time a fair bit if the pack is very far out of balance.

So you're saying it reads cell volts while discharging? So how does it compensate for wire variations? At 26awg & 300ma the voltage drop is .04*.3*2 = 24mV/foot, that's 75mV on a 1 metre balance lead. The tolerance on the wire resistance, joints, etc. would make it impossible to meet your 5mV accuracy across different parallel cell groups in the stack. to get that level of accuracy you'd need separate sense and balance leads to each parallel cell group. It has to check cell voltage when not discharging...

[Burgerman]

It does that too. And the charger pulses ON and OFF. Mostly on, off for a couple off seconds, the whole time. It gets accurate voltage readings during the breaks.
It can balance at 2 or 3ma too.

When DISCHARGING the pack it only displays cell volts. Discharges via the two thick wires.

When discharging a CELL while charging the pack heavily, it takes its accurate readings while on the rest periods. But It also watches them as it is charging at 20 amps too, allows them to go up a little higher than 3.600 initially during the longer charge pulses, by up to approx. 0.01 volts. Or it throttles back. Remember that this only happens (and slows charging) at the very end of charge.

Depending on how low volts drop when off charge. It bases this on the cell voltage change on and off load as it charges. It measures resistance. Because even with short cables the reading off load is the correct one. While charging resistance in cables/cells etc. As the charge rate drops, towards the end of the charge, (when one or more cells are requiring 300ma pull down) it becomes less tolerant to over voltage as there is less affect from the battery voltage rising due to int resistance. When it gets down to low currents its very critical. It wont allow anything above its chosen voltage. Once its down to charging at say .3 amp then its all much the same on or off charge. Unless the long cables show a lower voltage due to the 300ma pull down and the cable resistance.

Remember that hobby balance leads are about 6 inches long. Hyperion advise you not to use long ones. Because while its pulling down a cell, it may THINK the cell is lower than it really is. But will get accurate readings every 30 secs anyway.

[maker102]

Thanks all, sorry for getting off track for a few posts. Every time I come here I am blown away by the knowledge available here. Anyway I can't solder anymore and my electronics guy has finger rot so I am going to send it in for repairs. Thanks again to all that helped.

[ex-Gooserider]

Should be, as long as the length is kept fairly short... IIRC the Hyperion only balances at about an amp, which won't give that much voltage drop if you keep the total wire length short.... I'd say less than 3-4 feet total. (Make sure to count both the length of the harness in the chair as well as the distance between the chair and charger...)

I'd rather use18 AWG, but that is arguably overkill, and it starts getting to be a challenge to find connectors that both have enough pins and use wire that size. The big advantage of the larger size is that you can get away with a longer balance lead, which might make it easier to plug the charger in...

ex-Gooserider

Hi ex-G,

The cable length won't be any longer than 3 meters, and the balance connector plug has 9 26awg (could be 28awg) open-ended wires that have solder on them already.

So there needs to be thicker cables from the battery pack, which are soldered onto the thinner balance wires for a more stable voltage reading? Have I got that right?

Thanks BM and all others for helping me to understand this and to get it right!

Steve

I was originally thinking along the lines that Irving was, that the wire size wasn't that critical since there isn't actually that much current flow, but BM argues that because of the way the Hyperion measures voltages, it actually does. From your question, it sounded like you weren't clear, so I was adding my interpretation of what BM has said elsewhere, as I've noticed that helps at times...

3M is about 10', which is actually on the long side - I want to keep my setup to no more than 4-6', or under 2M... As has been mentioned, the packs that the Hyperion is officially designed to charge have balance lead lengths on the order of a few inches, I think the packs actually snap directly onto the balance leads that come with the Hyperion. Because the lengths are short, they can get away with really light wires and connectors and leave us to deal with trying to make longer leads...

I haven't started on a pack yet, but when I do, I will probably spend a lot of time "shopping" in the supplier catalogs for appropriate connectors, and might even modify the Hyperion to use heavier ones - I haven't really examined it to see if this is practical or not, but remember, "Contains no user-serviceable parts" is a dare..... (I am wanting to replace the banana plug power connectors w/ Andersons as I don't think bananas are a good choice for a number of reasons)

I do NOT like the hack of soldering heavier wires onto lighter ones, unless there is no other reasonable alternative. The solder joints themselves add resistance (solder is less conductive than copper) and it adds another point of failure.

I will be looking for something that can use at least AWG 20 wire, preferably AWG18. I would consider an option that uses multiple strands of lighter gage wire, but not real enthusiastically. I would also do my best to make all the wires the exact same length, and connector construction, etc...

Insertion force is an issue to consider, but I would also want to take a hard look at the specs for "Cycle life" or how many connect / disconnect cycles the connector is rated for. Remember that at least the chair end of the balance connector is going to get plugged in and out a LOT of times, and it is important to pick something that wears well, as worn connectors give high resistance before failing completely, which is another failure point... My concern about BM's choice of the OBD connector, or the ATX cable that he's mentioned, is that I don't think those are designed for a real high cycle count (most computer connectors aren't)

I would then worry some about contact protection against shorts / accidental contacts, and size, cost, etc...

ex-Gooserider