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Pre-energizing Inverters before LiFePO4 connect?

MisterSandals

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I've read the posts about folks using an inline resister to pre-energize an inverter before connecting directly to an LiFePO4 bank. (problem was capacitors blew because they received power too quickly). And yes I plan on having a breaker in there so not exactly directly.

Is this still necessary with Daly BMS's controlling a 200amp relay on the load from the LiFePO4 bank, and the current passing thru it?
Are my inverters small enough to NOT require it?

Here is the system I am implementing (top diagram):

And if I need to pre-energize, any idea how to automatically and momentarily pre-energize the inverters? Seems missing from this diagram... I intend to have only 1 inverter attached at any time in case that matters.

Thanks for any info or ideas!
The more I read, the more questions i have... isn't it supposed to be the opposite?

My system:
200AH 12v LiFePO4
Daly 45amp Separate Port BMS
Inverter #1: Giandel 12v 1200watt Pure Sine Wave
Inverter #2: Xantrex Pro Watt 12v 600watt Pure Sine Wave
Inverter #3: Samlex 12v 400watt Pure Sine Wave
 

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Am I correct that once the inverter is on, it stays on? So only om the initial connection would you be concerted about the surge?
 
My intention is to leave it connected with power thru the relay. But if the BMS cuts off the relay for any condition (say low voltage or low temp), and that condition is overcome (batteries charge or temp rises well above 0C) then the BMS will close the relay and power the inverter.

So no, it will not ALWAYS stay on?

It would be a shame to kill an inverter every time the BMS cycles.
 
You won't kill the inverter every time. The issue with repeated long term cycling of the high current DC input is the capacitors will degrade. They are usually low quality and often can't handle that sort of cycling.

The question you need to consider is just how many times do you plan on running your battery down far enough that the BMS will have to step in and disconnect the battery.

If that's once a week (that's quite a lot really) it's not going to be a problem. Odds on something else in the inverter will die from other causes before the input capacitors degrade to the point where they are no longer able to hold the input voltage up during spikes in inverter power output.

An automatic precharge circuit need not be complex. A 10 second timer off ebay, a suitably rated relay and a 50 ohm 5 watt resistor is all that's needed (a little DIY since this is a DIY forum, but soldering resistors and transistors is not required).
 
You won't kill the inverter every time.
I don't ever intend to run the batteries below 20% or get into a freeze situation.
It sure would be nice to handle the situation since i am in the design phase.

I did not know it was a degrading capacitor situation. The videos I saw seemed to imply it was a danger all the time, especially for "large" inverters.
 
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