ANT BMS : parameter to change the precharge apply time ?

BartDP

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May 11, 2021
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Hello All,

I have 2 converters connected (in parallel) to my BMS and so to my battery.
When connecting only one I don't have the 'precharge failure', but when using both I have.
Changing the precharge current parameter in the BMS ( configurable between 10A and 60A) doesn't seems to help, even if setting this to 60A

Seems my chargers don't take more then 0,5A in precharge mode ( this 0,5A is read from the BMS display), may be due to the construction of the inverters ( no direct connection to the capacitances, kind of MPPT system )
I'm not sure if this 0,5A is the real amperage they take or the average of a high frequency switched 60 amps ...

I can read on the display from the chargers that they just don't reach the total battery voltage ( about 15 volts missing from the 65 V to apply )
So apply just a bit longer the precharge current would solve the problem.
But I can't find a parameter to change the pre charge current apply time.
Does someone know if this apply time can be changed ? And if so how ?

Alternative would be to ask this at ANT themselves, but I can never where find a support contact ....

Thanks for any reaction !
 

alfu

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Jul 15, 2021
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Which model Ant and which Bluetooth app are you using? I have found MaYi-BMS can't set anything with my Ant 24AHA-TB, but MyBMS ("bms" onscreen) will set parameters but is buggy.
Both will set a precharge A but not time.
Vorteks BMS will not connect at all.
 
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RCinFLA

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Jun 21, 2020
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Most BMS have multiple parallel series cutout MOSFET's to get the required series resistance low enough for total rated pass current.

It is a no-brainer for BMS to sequentually fire up the parallel MOSFET's over 10's of usecs of turn on time to reduce turn-on surge current through BMS during activation.

Other, not quite as well controlled, is ramping MOSFET gate drive voltage to gradually drop their Rds_ON. Most BMS don't have strong gate drivers to series MOSFET's so there will be some ramping on all BMS's with series MOSFET's.

Your issue might not necessarily be just the amount of current but how long it last with double the caps to charge. Limiting precharge to 0.5 amps seems really strange. Probably just a sampling/averaging dilution of measurement.

Try setting a lower prechg current. If your inverter/charger has a setting for 'activate upon power up' try setting it to stay off when power applied.
 
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BartDP

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May 11, 2021
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I'
Which model Ant and which Bluetooth app are you using? I have found MaYi-BMS can't set anything with my Ant 24AHA-TB, but MyBMS ("bms" onscreen) will set parameters but is buggy.
Both will set a precharge A but not time.
Vorteks BMS will not connect at all.
I'm using a 32S 100A Ant BMS with the 'MY-BMS' (blue Ant logo) on a Android Samsung Edge 6
Having no problems with the app, only some popup/messages are not translated and still in Chinese.
Bought it at AliExpress IC GOGOGO Store.
Seems they have recently changed the label on the new BMS-ses ( Circular QR code label on the BMS to get the app )
And they are also showing screenshot from the new app ( different from the version I'm using )
 

alfu

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Jul 15, 2021
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It is a no-brainer for BMS to sequentually fire up the parallel MOSFET's over 10's of usecs of turn on time to reduce turn-on surge current through BMS during activation.
That could be possible. The Drains of all pass transistors are commoned, as are the Sources of each bank, respectively, but the Gates are all driven individually.
 

BartDP

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May 11, 2021
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It is a no-brainer for BMS to sequentually fire up the parallel MOSFET's over 10's of usecs of turn on time to reduce turn-on surge current through BMS during activation.
Like to find a way to extend the period they do this ...
 

BartDP

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May 11, 2021
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Try setting a lower prechg current. If your inverter/charger has a setting for 'activate upon power up' try setting it to stay off when power applied.
GTIL's seems not to have this parameter, but I will try next time to connect the BMS if both invertors are OFF
 

alfu

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Jul 15, 2021
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Like to find a way to extend the period they do this ...
These mosfets do the incredible things they do because they are full on, like switches and don't dissipate energy. Running partially on can fail them due to heat because they are a resistor then, not a switch.

The controller likely ramps up drive with PWM. Could see that with a scope. I DO know that when it enables charging, the current ramps up ~3s.
 
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