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Overcurrent and precharge circuits

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knr

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How Over current protection circuits and precharge circuits will work? please explain a circuit for 100A current with 48V rated voltage using mosfets.
 

Hi,

A bit more information, please.
Description, timings, picture...

What do you want to precharge?
What's the expected overcurrent behaviour?

Klaus
 

Hi,

A bit more information, please.
Description, timings, picture...

What do you want to precharge?
What's the expected overcurrent behaviour?

Klaus

i need precharge/predischarge circuit to limit the inrush current that occurs when the board is powered on initially. 100A is the max rate current for OC protection
 

For this current level..............The simplest and cheapest precharge circuit is a power resistor in series, which after a set time, is fully bypassed with a relay contact or power semiconductor (SCR or Mosfet).
 

..yes also, you can also use a little power module which provides a small isolated output, which can be used to switch on a fet to short out the inrush resistor.
you may also turn on at mains zero cross to reduce the amount of inrush
 

What's the device I/V characteristic (e.g. capacitive), what's the energy consumed during precharge (e.g. 0.5CV²)?
 

Can you suggest a circuit that you are explaining?
thanks
 

Hi,

Without giving more (requested) details... it will be hard to help.
(sorry, that we can´t read your mind)

Klaus
 

Hi,

Without giving more (requested) details... it will be hard to help.
(sorry, that we can´t read your mind)

Klaus


I don't have any critical specifications for timings. Let us take 1us for now.
I need precharge and overcurrent protection circuits to protect my load.
For initial power on time, I have to use precharge circuit to limit the inrush current and after that we have to bypass the precharge circuit and use the overcurrent protection circuit.
Please suggest your circuit.
Thanks
 

Hi,

a usual fuse is an "overcurrent protection" device. If you don´t have any specifications, then why don´t you use it?

I wonder why you don´t have informatons about
* whether it´s for AC or DC
* overcurrent behaviour (how do you want it to behave on overcurrent condition?)
* informations what/how your "precharge" circuit should work.

New information is that you want "to protect your load". But you don´t give load (limiting) specifications. How should we handle this new information?


Klaus
 

current limit : 100A
Precharge time: 1usec
Protection type : fuse type
Source : DC voltage 48V
Load : capacitive
Inrush current : 240A

My precharge circuit should be on for 1usec initially when the board is powered on, after that precharge circuit has to be bypassed, allowing the OC protection circuit further.
 

Hi,

you say "I don't have any critical specifications for timings", but then you say 1us.
--> This is much too fast for a fuse to blow. Thus I´d say this is critical.

I don´t think this 1us makes sense. Or I don´t understand...

*****
You say "Load: capacitive". But no value. It may be 100pF stray inductance, it may be 100.000uF of low ESR electrolytics, it may be a battery....

From the values: 240A, 1us, 48V... it could be a 5uF capacitor. Is this the case? You want to charge a 5uF capacitor within 1us from 0 V to 48V?

Klaus
 

How is the board powered on? Usually nobody cares for 240A inrush current of µs duration in a 100A circuit, a fuse surely doesn't notice it. People are relying on "natural" limitation of current spikes by source inductance and resistance. Could be a problem for 10 ms duration and more (e.g. the inrush current caused by many mF input capacitance switched to a 48V rail).
 

Hi,

I don't want to seem rude but it's more usual to provide a circuit or an idea you are working on and can show some minimal effort put into the task rather than asking for a ready-made solution as though a forum is a burger bar - that's what people pay engineering firms to do...

Maybe you'll get lucky and someone will have an old design that approximately or entirely meets your specifications but I wouldn't hold my breath about that.
 

Hi,

you say "I don't have any critical specifications for timings", but then you say 1us.
--> This is much too fast for a fuse to blow. Thus I´d say this is critical.

I don´t think this 1us makes sense. Or I don´t understand...

*****
You say "Load: capacitive". But no value. It may be 100pF stray inductance, it may be 100.000uF of low ESR electrolytics, it may be a battery....

From the values: 240A, 1us, 48V... it could be a 5uF capacitor. Is this the case? You want to charge a 5uF capacitor within 1us from 0 V to 48V?

Klaus


Load can be a motor/charger with high current.
I was not given any precharge time, i am new to these precharge/OC protection circuits. So can you please take an example of a standard circuit for Over current protection and precharge so that i can derive what is my requirements are to be..
 

Example of method to limit inrush current, then turn on a relay (per post #4).

At powerup the load receives reduced inrush current through a low-ohm resistor.
The capacitor charges for about 1 milli-Sec, then NPN turns on the relay. Relay must be rated to deliver full power to load.

cap NPN delay 1 mSec then relay On w inrush  limiting resis.png
 

Example of method to limit inrush current, then turn on a relay (per post #4).

At powerup the load receives reduced inrush current through a low-ohm resistor.
The capacitor charges for about 1 milli-Sec, then NPN turns on the relay. Relay must be rated to deliver full power to load.

View attachment 149109


Sorry, i didn't understand what you are explaining. I want to have over current protection by sensing the current using a resistor and by using the voltage drop across the Rsense, we can do over current protection of the circuit. But i want to have the precharge circuit also, so i am getting confused in including both OC and precharge circuit.

As per my understanding, precharge circuit will be active for some initial time(some milli secs) after that it is bypassed and OC circuit will get ON.. and I clearly don't know the precharge time because i am not yet sure about load( what value of capacitance is mostly widely used in electricals like motors and chargers). As per now, you please consider the standard loads and times for precharge circuit.
 

1.
Simple current regulation. Fixed bias current is applied to transistor. Load is placed in collector leg.

2.
Simple voltage regulation. Zener diode
applies fixed bias voltage to transistor. Load is placed in emitter leg.

current regul fixed bias NPN V regul zener NPN 48V 100A.png

These simulations have the power supply ranging from 50-70 V. The load does not go above about 100 A.

These methods are resistive. Components must endure high power levels. This makes the protection circuitry itself prone to breakdown.
 

Hi,

These simulations have the power supply ranging from 50-70 V. The load does not go above about 100 A.
This is 5kW of heat. (I can heat my whole house in winter with 5kW.)

For sure here it is only for a short period of time. But in case of an error you won´t have enough time to react and switch it manually OFF. Expect an explosion.

Klaus
 
Precharge circuit design considerations

Hi,

how precharge circuits are used in industrial for high voltage applications? please explain how to design precharge circuits, what are the parameters to be taken into consideration for designing precharge circuit??

thanks
 

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