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This is good, but - What happens when the BMS disconnects inverter from say an overcurrent or battery cell undervoltge event? When the BMS reconnects the inverter to battery there will be a large inrush current. Maybe large enough to clear the 125A Class T fuse. No? That is why I am interested in automatic. I have spoken to Inverter vendor and he is supposed to be sending me the input capacitance.Have you seen this:
Inverter Disconnect Switch with Precharge
To get the paper, click on the orange button at the top of this page. This circuit is designed as a disconnect switch that allows the user to pre-charge the inverter capacitors before turning the switch completely on. 26 June 2020 update: At...
I'm a bit confused by what you have described. There is a situation when powering up the inverter, but you want it to be automatic. Does the inverter power up automatically?
It's not that I don't want to use it - I actually have no reason not to. I am just interested to know what alternatives exist.
How would this work without a contactor? $70 for the REC precharge and $177 for a contactor seems mighty steep when you could do the same thing with $10 worth of parts off amazon.
It is very possible that a (clever) BMS can charge a capacitor bank. I recently did a very large circuit breaker for a client. The spec was to charge a large 1000v capacitor bank when closing the breaker. Breaker was near 100 SiC fets in parallel.
What do you have for $10? I'm all ears.How would this work without a contactor? $70 for the REC precharge and $177 for a contractor seems mighty steep when you could do the same thing with $10 worth of parts off amazon.
The problem would be blown Class T fuses. I've been trying to get Signature Solar to give me the input bus capacitance so I can figure out if the problem is real or if I am over engineering it.
Resistor $6
No. It is the BMS that powers up automatically.
You aren't paying attention. This has to be automatic. I can do it automatic for $22.
Ok, share your parts list.
I understand the conceptual problem, and I used to worry about it a lot. Even though there are reports of blowing a fuse when hooking up an inverter, I have not found it to be a problem when the BMS turns on/off in the real world. I suspect there are a couple things that mitigate the problem:
ok. give me 20 minutes to design it.
If it is built into the BMS it is even easier than that. Just dedicate a FET or two to a pre-charge circuit and put it in series with a resistor that limits the current. Turn the pre-charge on first and once the voltage gets high enough turn on the main bank of FETs. The capacitors do not have to be fully charged. Even charging them to half the battery voltage will probably reduce the surge to a low enough level to eliminate all possible problems. (For safety, you would want to limit the time the pre-charge is allowed to be on and if it is exceeded, shut everything down with an error. This would prevent the resistor from getting too hot. Alternatively, use a high wattage resistor and heat sink so even if there is a dead short on the output, the resistor does not overheat)
