idcspnt vs udcspnt  [SOLVED]

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Gregski
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idcspnt vs udcspnt

Post by Gregski »

coming at this from a newb perspective, so I am not questioning this I am just asking (if that makes any sense) FYI this is dealing with a Tesla Model S Gen 2 charger

I guess I should first ask for a definition of "setpoint" as to me that means a fixed value, if you will. So my first question would be if we have a DC amps "setpoint" and a DC volts "setpoint" which one wins?

Or is the idcspnt actually a bit of a misnomer and it's more of an idclim (yes I know there is another idclim already) so perhaps an idcmax would be a better name for it, if for no other reason to avoid some confusion

here they are as defined by our Wiki:
  • idcspnt
    DC charge current limit. An additional limit to charge power. It is also mapped to the CAN bus so if you have a BMS that calculates a maximum charge current you can forward this to the charger.
  • udcspnt
    This modifies the constant voltage setpoint of the chargers. This value is transmitted directly to the modules without further processing. It lets you add a constant voltage phase to your charge process. When reaching this voltage the chargers will control the current to maintain this voltage.
So it sounds to me as if the udcspnt overrules the idcspnt, but can it force the idcspnt to exceed it's defined limit in order to meet the predefined udcspnt? Otherwise what's the point, ha ha

And what's the point of setting a DC voltage setpoint anyway, wouldn't we want to get to our full charge as quickly as we can? Again just asking as a newb to the game.
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Re: idcspnt vs udcspnt  [SOLVED]

Post by johu »

setpoint aka control target aka the quantity you want to achieve. If you set your oven to 200°C then this is your temperature setpoint. The oven will heat until it reaches it and thereafter try to maintain it.

None of both can be exceeded. If you set your idcspnt to 45A but the resulting voltage is above udcspnt, the chargers will cut back until they reach udcspnt. If you set 10A idcspnt and udcspnt is NOT reached then idcspnt will still not be exceeded. It's just like a lab power supply.

Personally I see no point in a static constant voltage phase but rather in a BMS commanded one. I.e. the BMS controls idcspnt so that no single cell exceeds its limit. People who don't use a BMS tend to use udcspnt or udclim instead.
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Re: idcspnt vs udcspnt

Post by Gregski »

johu wrote: Wed Jan 12, 2022 5:56 pm setpoint aka control target aka the quantity you want to achieve. If you set your oven to 200°C then this is your temperature setpoint. The oven will heat until it reaches it and thereafter try to maintain it.

None of both can be exceeded. If you set your idcspnt to 45A but the resulting voltage is above udcspnt, the chargers will cut back until they reach udcspnt. If you set 10A idcspnt and udcspnt is NOT reached then idcspnt will still not be exceeded. It's just like a lab power supply.

Personally I see no point in a static constant voltage phase but rather in a BMS commanded one. I.e. the BMS controls idcspnt so that no single cell exceeds its limit. People who don't use a BMS tend to use udcspnt or udclim instead.
Thank you I appreciate that, and not being rude but when you say "None of both can be exceeded." I think you mean Neither of the two can be exceeded, correct?
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Re: idcspnt vs udcspnt

Post by johu »

yes, neither ;)
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Re: idcspnt vs udcspnt

Post by Gregski »

great I'll be sure to add this to my book

for dummies.jpg
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