Thank you very much for your help.
Bellow i will try to answer your questions the best i can.
"Now when i am running the bigger battery, the voltage drop is max 2v (from 58.8v to 56.8 - 57v), and this causes a problem : when the battery is fully charged (until it reaches 55v discharge) at every start (when i leave a stop light) the whole scooter is budging (it starts, the it stops very very briefly, and the its at full acceleration again) - this is when i press the acceleration all the way. I want to mention that you have to kick push it to engage the acceleration. After it warms up, it does the same thing, but not that bad (50%).
This does not happen if you push the acceleration lighter and after it moves a few meters you push it all the way."
Here i want to mention that the scooter is in the kick push mode, this is what i meant. It also has a non kick push mode, but i consider that this is a risk factor, cause one can push on the acceleration accidentaly.
"This almost always indicates that there is too much voltage sag (drop) at the controller itself, and that it is cutting off power to protect the battery (the controllers have an internal LVC different from and higher than that in the batteries' BMS). This, in turn, is almost always caused by a poor connection between battery and controller.
Where is the sag being measured to get your numbers? If this is measured by the controller and displayed on the controller's LCD, then this is not likely the problem. If this is measured on a wattmeter or similar device right out of the battery, or on a phone displayed from BT info the BMS is sending out, then it doesn't tell you what voltage the controller sees."
The battery was made by a friend of mine. Bellow i will put some pictures with the battery. He gave me the battery without putting jacks on it. I used XT60 connectors for the battery to controller and MT60 connector for controller to motors.
The voltage drop i measure it by reading the voltmeter (attached picture) that is connected directly to the controller (through the wires that go to the main display( attached picture) that also has the trigger acceleration.
"Also, when it cuts out, does the controller's display (if any) stay active, or does it blank? "
Its improper to say it cuts out, but i cannot find another word for it. Its kind of a small jerk that i can feel. The display stays on when this is happening.
"If you had previously had a lot of voltage sag and now had virtually none, I would suspect the controllers were cutting out from too high a power level (thermal cutout perhaps from monitoring sensors in the motor windings, for example), but since your old sag was very similar to the new sag, this is not that likley an issue--you would have had these kinds of cutouts on the highest loads like going up slopes and whatnot, as well."
The problem is that my old sag (with the old battery) was double than the new sag (with the bigger battery). Can the difference of only 2 volts cause such an increase in temperature...? I think the motors can handle more, and i belive the motors do not have any monitoring sensors (attached you can find pictures of the open motor)
"But...since it stops happening when the pack voltage drops below a certain point, this could still be the problem.
Since it is *less* of a problem after warm up, it still points more towards a connection issue than anything else, as most connections issues happen less often or affect things less the warmer it is, and are worse the colder things are.
So my first recommendation is still to check the battery-to-controller connection."
All the soldering of the XT and MT connectors was done by me and they are super solid, no cold seams.
"My second recommendation is to see if the controller has any programmability, or settings that can be at least viewed if not changed within it's own display if it has one, to see if any of those settings relate to maximum allowed power or current. (I wouldn't change them yet, just check for them)."
Bellow are the settings that i can change on the controller and what i have now :
P0=10 (wheel diameter)
P1=43 (voltage cut off)
P2=17 (magnetic poles in hub motor) - by changing these you see different speeds on the speedometer - it was 16 but it was off by 5 km/h and now at 17 its off only by 1 km/h (the problems is at 16 and 17, the jerking)
P3=1 (speed sensor function)
P4=0 (its for km/h) if i put 1 its for m/h
P5=1 (for kick start) if i put 0 its for non kick start
P6=0 (cruise mode off) if i put 1 its on for the cruise mode
P7=1 (power start) and 0 for normal start (its too sluggish at normal start)
P8=100 (motor power) i can change it from 0 to 100
P9=0 (electronic brake off, at 1 is medium and at 2 is high)
The scooter is dual motor. From the test i made, this problem is only if i use 2 motors, if i ride on single motor, this jerk is not present.I did not test yet with dual motor connected and to go down on P8 and play also with P7 (i will try this later and will come back with the results)
"My third recommendation is to verify the voltage sag on the new pack at the controller itself, with a multimeter, and then do the same test at the battery itself, to see if the sag is greater near the controller, to verify that it is not cutting out because of a connection issue."
This is kind of impossible
) i have to connect he voltmeter and the same time to ride the scooter
)
Also attached are some pictures of the bms.
Now i ask you this : is there any possibility that the controllers demands more than 60A from the bms (2x30A) even if the controllers are rated at 2x25A, and the bms cuts the power? But in this case the display should go black right? and the scooter should stop.....?
LATER EDIT :
I just came back from some tests. We have the following :
1. DUAL MOTOR, P7=1 (power start), P8=100 (motor power) > PROBLEM
2. DUAL MOTOR, P7=0 (normal start), P8=100 (motor power) > NO PROBLEM
3. SINGLE MOTOR, P7=1 (power start), P8=100 (motor power) > NO PROBLEM
4. DUAL MOTOR, P7=1 (power start), P8=90 (motor power) > PROBLEM
5. DUAL MOTOR, P7=1 (power start), P8=80 (motor power) > PROBLEM (with a 90 kg rider no problem, with me at 120 kg is a problem)
Also, the problem (the jerk) comes after you travel 3-4 meters, a fraction of a second is the jerk, then its all back to normal.
So, in my oppinion the problem lies in the controllers....what can i do with the controllers to resolve the problem?