reduce voltage drop between battery and controller

[Sparfuchs]

Do you think the controller is " limiting current"? Test this hypothosis.

One way is to do this. Trick the shunts in the controller into seeing ( sensing) less current than they actually are. Shunt mod the output wires.


This might damage the controller though. However, if you suspect the controller is limiting amperage, this would fool it into outputting more amps. So you could test the real amps taken and see if this is changing the number with the modification.

Not recommended and might void warranty. Only for suspect testing.

I'm not that sure anymore if this solves my problem because even if I bypass the sensors it will still notice the voltage drop and might lower the output until "it's happy" with the drop. So if it now reduces it's phase amps at big voltage drop for example by 50 amps, isn't it likely that if I'd double the two phase wires around the sensor it would lower it by 100 amps to get same result in voltage ?

 

[dominik h]

I do not think the sabvoton is able to react on voltage drops. It has only a cut off voltage point.
The sevcon and the fardriver can reduce their current to not let voltage drop below the lower limit.

My sabvoton gives full amps until it cuts off.
Two weeks ago I a had a longer highway round and drove the battery until it cuts off. The only reduction was less top speed on the last miles, there was no current reduction at all.

 

[Sparfuchs]

I do not think the sabvoton is able to react on voltage drops. It has only a cut off voltage point.
The sevcon and the fardriver can reduce their current to not let voltage drop below the lower limit.

My sabvoton gives full amps until it cuts off.
Two weeks ago I a had a longer highway round and drove the battery until it cuts off. The only reduction was less top speed on the last miles, there was no current reduction at all.

well, your battery is a 21s 97Ah battery..mine is a 19s 16AH battery. I really doubt that you've ever had even approximately voltage drop to avaluate what the sabvoton does in my case, right ?

 

[dominik h]

You could be right

I once did a ride with this battery where my battery heating was not working and the battery was very cold and nearly empty.
This was with the SVMC72260. I had a voltage drop around 10V @250A uphill. There was no reduction until the cut off point was reached.
As the controller software is the same , I think they have the same logic insde.
The Sabvoton is a very old design with only a few things to adjust. I think they missed this functionality.

 

[jigs]

Hello EV friends,
thanks to all your help in my thread "Sabvoton SVMC 72150 doesn't do full power" (link below),we/I now think that the most plausible problem is, that the Sabvoton SVMC 72150 has a "protection" that limits the current if the voltage drop gets to a (unknown) value that can't be changed. So no, not talking about "Current Limiting Voltage" or "Lack Voltage"

As I wanna get more than just 100A for a few ms I'm looking for a way to reduce the voltage drop (regardless of the voltage drop in the battery itself) between my 19s4p Samsung 21700 40T battery pack and the sabvoton at max. loads of up to 200 amps (always just for a few second bursts) and have thought of using one or more capacitors and if necessary diodes between the battery and the controller, to pretend/give the controller stable voltage... or do you have any other ideas?


More precisely: I built a battery pack from 19 serial and 4 parallel connected Samsung 40T 21700 lithium-ion cells that theoretically could handle short-term pulse currents of up to 280 amperes (70A per cell) and a continuous discharge of 100A (even 180A with temp. monitoring). What you could expect is that the voltage drops under load (specifically by about 10v at 100A discharge in my case).
But what I didn't expect is that the controller seems to have a protection that limits the maximum current at a certain voltage drop (much earlier than necessary). Since this cannot be changed in the software and it seems too complex to me to access the firmware, I had the consideration with the capacitors/diodes.

I'm not sure how it behaves with the simultaneous/alternating charging and discharging of the capacitor, but I am considering a strong diode might be required in my 8AWG wire to avoid equalizing currents (the battery can be charged with max. 24A) between the capacitor and the battery, which shouldn't increase my resistance much.

It should also be mentioned that the same wire is used for charging and discharging, which usually happens very quickly and alternately through regenerative braking.

I'm not that well versed in terms of potential, but I wonder if equalizing currents occur at all if the capacitor for charging has a lower potential to the battery, and as soon as the voltage of the bat. suddenly drops due to heavy consumption and it's potential increases, probably the lowest potential should be to the consumer/controller and not to the battery, which means that the capacitor discharge only takes place in one direction (cap. to controller) anyway?

Unfortunately, I don't have the know-how, which components are available and whether/how my idea can be implemented... or whether there is even a better solution and I would be very grateful for your ideas !

Thanks for your Help
Best regards
Sparfuchs



Sabvoton SVMC 72150 doesn't do full power: ://endless-sphere.com/forums/viewtopic.php?f=30&t=118808

Are you pertaining to the soft start of the sabvoton? Wherein from deadstop it feels weak until about 20kph?

I think its programmed that way but using timing or 2 to 3secs before giving it the full power. There is an optiom of hardstart in the android app but since i think my controller is locked so ehenever i choose hardstart it just reverts back to 3gear switch or boost.

 

[dominik h]

The sabvoton does full phase current at zero rpm. It takes less than a second to reach the full phase current. I measured this with a fluke scope meter and a rogovsky current transducer.
The Effekt of feeling weak during a start from a standstill is because of the bad efficiency from the motor in the low rpm range. Other Controllers compensate this with more phase current (boost) for a very short time, but the sabvoton does not have this function. The sabvoton does the 350pA until it overheats. In my scooter I could draw 5kwh in 30min with the SVMC72150 without any issues, that is 30min with drawing 10kW power from the battery.

 

[jigs]

The sabvoton does full phase current at zero rpm. It takes less than a second to reach the full phase current. I measured this with a fluke scope meter and a rogovsky current transducer.
The Effekt of feeling weak during a start from a standstill is because of the bad efficiency from the motor in the low rpm range. Other Controllers compensate this with more phase current (boost) for a very short time, but the sabvoton does not have this function. The sabvoton does the 350pA until it overheats. In my scooter I could draw 5kwh in 30min with the SVMC72150 without any issues, that is 30min with drawing 10kW power from the battery.

So even more so if the sabcoton controller is factory locked just like mine. I cant increase phase current.