How would you build a 250Amp précharge circuit

HKZBob

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Nov 7, 2020
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Hello Forum, I am building a 250A précharge due to the fact I am corona bored.

The is nothing else to do.

Here my project. It is a test board, sorry but not perfect. Using hot glue to makes things stick.

To power my précharge circuit I am using a battery pack. Here my parts.

For the delay circuit I am using an AE delay ⏲️. This is connected to my 250A inert gas filled relay. Automotive Type.


The trigger switch is activate the small 12V Relay which has a cement resistor and a light bulb in series. When I pull the trigger switch the current is running though the resistor the light is on and bypasses the big contacter/Relay. I am precharging my load with 100mA.
It that is enough 😉 is driven by the delay time which can be adjusted from 2s to 30s and more.

The current consumption of the contacter is 300mA when it is acting connected.

Is will connect the contacter with the remote switch on my 2000,00000Watts inverter.

What do you think, is a precharging current of 100mA is sufficient. I have no idea about the cap sizes of my inverter.
5Tau = R x C.

Will see maybe on the scope.

Regards Bob
 

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svetz

Works in theory! Practice? That's something else
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Hi Bob!

The current isn't important (other than not frying anything), you just need to know it to calculate the time the bypass circuit needs to remain connected to complete the pre-charge before switching to full battery.

The time is an interesting calculation since current flow is dependent on voltage which changes as current flows. Which is to say even if you calculated the value theoretically the actual practical value would be different (due to temperature changes).

If I understand you correctly, you bi-passed the problem with a swag from a timer? if the light's out when the contactor flips I'd say your good (led right?).

Another way might be to use a relay. That is when the precharge circuit stops flowing there's no power to the relay which then closes the contactor, the contactor closing also locks the precharge circuit out of the loop.
 

HKZBob

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Nov 7, 2020
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52
Yes I took a low cost delay timer to retard the main contacter. Maenwhile the small contacter paraelle is précharge the circuit over an resistance.

I use what I have in my toolbox.

Greetings.
 

HaldorEE

Photon Sorcerer
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Apr 20, 2020
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Simplest solution is use a voltage comparator that switches based on the voltage on the inverter side of the resistor. Once the caps are charged up the voltage should be relatively close to the battery voltage. This is assuming the inverter is turned off when you plug in your battery pack.

If this is for an RV application, then other DC loads would confuse the issue too. For residential power, this should be a non-issue. Unless you have battery heater pads.
 

HKZBob

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Nov 7, 2020
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52
This is a éducation project to use it in front of an inverter
 
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