Do most builders/users not use inverter precharge?

[BobCollins]

Outside of this forum's geeks, I don't see anyone talking of precharging their inverter input. Even here, the discussion rarely extends beyond using a resistor before attaching the last power lead to the inverter. This, of course, ignores the times they disconnect and reattach the battery-to-inverter circuit in some other way, with a circuit breaker, disconnect switch, etc.

Here, the most convenient answer is that they never disconnect the battery. Happy for you, but I doubt this is the general case.

What I suspect is that the general case is many (most) users either ignore or don't see the spark when connecting the battery, and that the switch, etc. is suffering the arc and degrading.

This would beg the question: how quickly will living with this ignored arc cause a failure? Of course, significance of the abuse depends on the size of the inverter and the construction of the switch.

BTW, I do understand there are automatic precharge circuits, but they appear to be pretty rare. A few BMSs (such as Victron's) include an automatic precharge circuit, but they are hardly the general case. Beyond these, everything else I see is DIY construction. Most interestingly, I have yet to see a builtin precharge circuit in the front end of an inverter, which would be an obvious location.

If avoiding the arc is so important, why isn't there a commercial solution? I have explored the problem space, and a stand-alone design is quite feasible. My suspicion is that living with the arc is such a minor issue for most users that there is no market for a solution.

I am interested in thoughts, particularly if I have missed, or misunderstood, some pertinent aspects of the problem.

Thank you.

***********EDIT************

I didn't note above that my project is a vehicle mounted system, not a large, 48 V system. I didn't realize that this was (or might be) a factor.
Answers below tell me that a (the?) primary reason to precharge is to avoid having the BMS react to the high inrush current from charging the capacitors and shutting the circuit off. This makes sense to me.

What I still don't understand is why it appears that many 12 V systems do not appear to have any provision for precharging. Is there a inverter size under-which precharge is not necessary? I asked on the Victron forum if my planed Phoenix 1200 W inverter needed a precharge, and I was assured that it did.

So, my question still stands.

 

[Lt.Dan]

I think many batteries today are coming with precharge resistors with logic for them in the BMS. Even my DIY Seplos BMS has it.

 

[sunshine_eggo]

I don't think you're looking very hard. You're on Community. Go search pre-charge there.

The EG4, SOK and other server rack batteries typically have a pre-charge built-in as part of their startup instructions.

It's not about the arc. It's about the BMS shutting down due to the triggering of short circuit protection.

 

[Q-Dog]

I have disconnected my batteries twice since I commissioned my inverter 2.5 years ago, and that was for a couple of hours to add more stuff. Otherwise I never shut it off.

 

[rhino]

This would beg the question: how quickly will living with this ignored arc cause a failure? Of course, significance of the abuse depends on the size of the inverter and the construction of the switch.

I've blown a T fuse because I didn't pre-charge a Victron 48V inverter. If I recall this is not as big of an issue with 12V and 24V systems.

 

[Lt.Dan]

I've blown a T fuse because I didn't pre-charge a Victron 48V inverter. If I recall this is not as big of an issue with 12V and 24V systems.

That must've been fun lol.

 

[timselectric]

Most interestingly, I have yet to see a builtin precharge circuit in the front end of an inverter, which would be an obvious location.

It's not a problem for the inverter. So, no need for them to provide it.

My suspicion is that living with the arc is such a minor issue for most users that there is no market for a solution.

For most systems it's a one time event at first commissioning. As long as the battery can handle it, it's over in a second.
It's mostly been an issue lately with BMS's. They see the inrush as a dead short or overload and shut off.

 

[BobCollins]

I don't think you're looking very hard. You're on Community. Go search pre-charge there.

The EG4, SOK and other server rack batteries typically have a pre-charge built-in as part of their startup instructions.

It's not about the arc. It's about the BMS shutting down due to the triggering of short circuit protection.

You are absolutely right, from what I can tell, most server rack batteries do have precharge circuits. However, my application is vehicle-based, and neither the form-factor or the voltage of server-rack batteries make sense for me. I should have remembered this common server-rack feature. However, I don't see this feature in drop-in batteries or other batteries targeting the vehicle or marine market.

Question though: do the server-rack precharge systems function after the battery is "on" and a user switches a down-stream breaker/switch before the/an inverter?

I didn't realize the the BMS high current reaction was the primary issue. That would explain other things.

 

[timselectric]

Question though: do the server-rack precharge systems function after the battery is "on" and a user switches a down-stream breaker/switch before the/an inverter?

No
It's activated at each startup.

 

[BobCollins]

It's not a problem for the inverter. So, no need for them to provide it.

For most systems it's a one time event at first commissioning. As long as the battery can handle it, it's over in a second.
It's mostly been an issue lately with BMS's. They see the inrush as a dead short or overload and shut off.

The capacitors in the inverter are the cause of the problem. That would be a perfect place to mitigate the problem.

 

[Lt.Dan]

You are absolutely right, from what I can tell, most server rack batteries do have precharge circuits. However, my application is vehicle-based, and neither the form-factor or the voltage of server-rack batteries make sense for me. I should have remembered this common server-rack feature. However, I don't see this feature in drop-in batteries or other batteries targeting the vehicle or marine market.

Question though: do the server-rack precharge systems function after the battery is "on" and a user switches a down-stream breaker/switch before the/an inverter?

I didn't realize the the BMS high current reaction was the primary issue. That would explain other things.

It's not targeted towards mobile/vehicle based systems, because the precharge resistor is typically not needed on smaller systems. The size of the system is debated widely, but IMO it's anything under 3000w. How often is a vehicle going to have an inverter over 3000w?

 

[BobCollins]

It's not targeted towards mobile/vehicle based systems, because the precharge resistor is typically not needed on smaller systems. The size of the system is debated widely, but IMO it's anything under 3000w. How often is a vehicle going to have an inverter over 3000w?

I like this answer because it simplifies my system.

However, I asked on the Victron forum if my planed Phoenix 1200 W inverter needed a precharge, and I was assured that it did. So, conflicting advice.

BTW, I have read discussions where people are building vehicle systems with 3000 W inverters, likely to a) run everything on AC, and/or b) an AC powered air conditioner.

 

[timselectric]

The capacitors in the inverter are the cause of the problem. That would be a perfect place to mitigate the problem.

But it's not a problem for the inverter. So it's not their problem to mitigate.

 

[BobCollins]

I think many batteries today are coming with precharge resistors with logic for them in the BMS. Even my DIY Seplos BMS has it.

I will look into what BMSs have precharge circuity. The only battery I see on SOK's site that does is their server-rack battery. From my reading, their precharge circuit is a slightly automated push button to temporarily insert a resistor.

 

[BobCollins]

But it's not a problem for the inverter. So it's not their problem to mitigate.

I don't agree, but it does have practical implications. Having the precharge function in, or right in front of the inverter, would allow the the system switches and breakers to function independently of each other and the inverter.

 

[timselectric]

That's like expecting the chilli dog maker to be responsible for keeping all bathrooms stocked with toilet paper.

 

[Tomthumb62]

How often is a vehicle going to have an inverter over 3000w?

I'm actually quite surprised how many vehicle/rv/van/mobile systems I see posted here that have 3000W inverters on a 12v system. They've swallowed the myth of "buy more inverter than you think you need" (as I did too but only a 2000W inverter).

 

[Hedges]

If you had fully charged capacitors on input of an inverter, say with inverter in standby not discharging rapidly, would you disconnect from battery and short out the capacitors?
Similar stress on them when low impedance lithium battery tries to instantly charge them.

I once told a coworker he could just short out a capacitor. He said it blew up.

 

[Tomthumb62]

However, I asked on the Victron forum if my planed Phoenix 1200 W inverter needed a precharge, and I was assured that it did. So, conflicting advice.

I just installed a Victron Phoenix 12/1200 and I don't think I did the pre-charge resistor thing properly, because each time I still got quite a big spark. The spark was actually as big if not bigger than when I hooked up our previous 2000W 12v Renogy inverter without a pre-charge resistor. All I can say is I'm not sure I did the pre-charge thing correctly on the Victron and if I didn't, it's functioning just fine. I was tired both times I did it and I think I may have simply touched both ends of the circuit to the screw threads of the 60w lightbulb. Second time I thought I was paying more attention to get the screw threads on one end and the bottom tip on the other, but like I said I was pretty tired and might have fudged it. I might end up getting an actual resistor just so I don't make that mistake again (we don't have any pencils around here anymore lol).

 

[rhino]

The light bulb seems superior to a resistor since you can tell when it is finished. There was a post about using a 48V bulb here: https://diysolarforum.com/threads/j...-with-a-25w-30ohm-resistor….64658/post-808847