Do most builders/users not use inverter precharge?

[Ampster]

My sequence for booting my SolArk is to power up the AC before the battery. I assume that the AC charges the capacitors so when I switch the DC breaker I assume the capacitors are charged so I have not experienced any issues.

 

[Rocketman]

I don’t know why more people don’t install a pre-charge - I did on my MotorHome battery. It’s probably because there is not an easy automatic “device” to do it.

For my system there was - I used a Batrium bms, it used a large contactor (relay) to make & cut power. I used a Rec Bms pre-charge to control the contactor- so it always automatically pre-charges.

I think most people don’t feel it’s a $200 issue…

 

[Skypower]

What I find amazing is how I have been unable to find any warning in my MPP LV6548 manual in regards to pre-charging.
I powered down this weekend to add another battery and the precharge button was handy. Once I enabled charge/discharge on the bms’s the LED was lit and was a nice reminder to not close the circuit just yet. The charge switch is a DPDT and the LED is fed by both inverters when the breaker is open but has two diodes to keep inverters isolated. The trick was to find an LED with a low enough current draw that it doesn’t try to charge the inverters itself.

 

[Skypower]

My sequence for booting my SolArk is to power up the AC before the battery. I assume that the AC charges the capacitors so when I switch the DC breaker I assume the capacitors are charged so I have not experienced any issues.

Great if you can do that but some want the DC first.

 

[Nobodybusiness]

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.

Normally if I have to turn my inverter off I leave a small grid connections plugged up.

Can be a little 10 gauge cord from Grid to AC input.

Just flip the AC breaker on upon startup and it appears to charge everything.

Re engage the batteries no problem.

Probably is an arc in the AC breaker but who cares about 240v20 amp breaker.
They seem pretty resilient and if not oh well.

 

[Nobodybusiness]

Great if you can do that but some want the DC first.

I’m not trying to be a smart ass here but why?
It just requires very little AC to charge the thing..

 

[Ampster]

Probably is an arc in the AC breaker but who cares

Especially since AC crosses zero sixty times per second so arcing is not the same issue as DC

 

[Nobodybusiness]

Especially since AC crosses zero sixty times per second so arcing is not the same issue as DC

Yea. Seems like a no brainer to me but maybe he doesn’t have grid. Dunno..

 

[Skypower]

I’m not trying to be a smart ass here but why?
It just requires a little AC to charge the thing..

For instance a single MPP LV6548 inverter can run “battery less”, however when using two inverters for split phase it must have a battery. Mine faults or hangs unless the DC come on first.

 

[Ampster]

Great if you can do that but some want the DC first.

I don't know what my SolArk wants but I just routinely sequence the AC and then the solar before flipping the DC breaker.

 

[Nobodybusiness]

For instance a single MPP LV6548 inverter can run “battery less”, however when using two inverters for split phase it must have a battery. Mine faults or hangs unless the DC come on first.

Good to know. Didn’t know that about those unit. We both have Sol-Arks..

 

[Skypower]

Good to know. Didn’t know that about those unit. We both have Sol-Arks..

Just an MPP quirk and a valid logical question.

 

[HarryN]

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).

That is because they are buying a victron 3000 and think that it is a 3000 watt inverter - it isn't.

I have tested it against the 2 000 watt commercial grade / US made inverter that I normally use and a honda 3000. Using a mixture of load types, they all topped out at 2400 watts. It might do 3 000 watts with a purely resistive load but that is a pretty rare load.

Comparing this to their quatro 5000 - completely different beast that really goes the mile - the numbering system is a bit - cloudy.

Inside of a vehicle where it can be very warm - both of the inverters are essentially 2000 watt inverters based on temperature de rate effects.

It makes it a complicated discussion with customers to explain it.

As a practical matter - I can run every tool and load that I own including the items that come with 20 amp cords and so can my customers.

 

[Nobodybusiness]

That is because they are buying a victron 3000 and think that it is a 3000 watt inverter - it isn't.

I have tested it against the 2 000 watt commercial grade / US made inverter that I normally use and a honda 3000. Using a mixture of load types, they all topped out at 2400 watts. It might do 3 000 watts with a purely resistive load but that is a pretty rare load.

Comparing this to their quatro 5000 - completely different beast that really goes the mile - the numbering system is a bit - cloudy.

Inside of a vehicle where it can be very warm - both of the inverters are essentially 2000 watt inverters based on temperature de rate effects.

It makes it a complicated discussion with customers to explain it.

As a practical matter - I can run every tool and load that I own including the items that come with 20 amp cords and so can my customers.

Which of the Victron units are derated based upon temperature and how much is the derate?

 

[HarryN]

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?

More often than you think. I have built up a customer van with dual 2 000 watt inverters. V 3000 size are common.

My oldest son built a food trailer with dual 5000s

 

[HarryN]

Which of the Victron units are derated based upon temperature and how much is the derate?

AFAIK all of them, but it has been a while since I read their manual since I switched to a domestic brand.

I am not aware of any inverter that does not de-rate with ambient temp. (added - but obviously have not looked at every single inverter either )

 

[Nobodybusiness]

AFAIK all of them, but it has been a while since I read their manual since I switched to a domestic brand.

I am not aware of any inverter that does not de-rate with ambient temp.

Interesting.

 

[HarryN]

I’m not trying to be a smart ass here but why?
It just requires very little AC to charge the thing..

So the challenge is that in a van it is often like being in the middle of no where in a cold start condition. We have to work with what we have, which is hopefully some charge in the batteries and sometimes the sun shining to work with. That is pretty much it.

Temperature wise it might be (- 10 F) and people are trying to get DC to the fuel heater to run the igniter system, or 100 F and we need some DC to run the DC compressor refrigerator or a fan.

What often happens is that the BMS on some or all of the batteries trip charging up the caps in the inverter.

They can be re-set, but a lot of people don't include the necessary circuits so they end up with blown T fuses in the middle of no where, no power, and not necessarily easy access to the needed tools.

 

[sunshine_eggo]

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.

"drop-in" batteries tend to be cheap and they lack an on/off switch.

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?

Here you go:

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

Yep. It's why inverters don't have a pre-charge feature. They were designed to be hooked to sources (lead acid batteries) that could deliver a very brief surge with higher internal resistance that also served to limit the surge.

Essentially, we have decades of products designed a specific way. Now we have a market flooded with power sources with a built-in limitation that can't meet the demand. Should the inverter manufacturers tailor their design to the limitations of cheap products, or should the new products meet the need of the existing industry?

"Drop-in" is misleading. Lead-acid can deliver ridiculous surge currents at the expense of voltage. LFP has a piece of circuitry that prevents the battery from meeting the need of pre-charging the capacitors of an inverter.

I see this as a battery problem, not an inverter problem.

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.

Good news. You get to be the Guinea pig. Pretty simple... install without a pre-charge circuit. Keep a #2 pencil with both ends of the "lead" exposed (about a 6Ω resistor) handy for a quick fix.

Let's say the 12V battery has a resistance of 2mΩ (pretty typical for a decent 12V 100Ah LFP):

12V / 0.002Ω = 6000A

Doubt your BMS is rated for 6000A, and it's probably going to see that as a short circuit and trigger protection.

Alternative: Victron MPPT can operate w/o battery, run directly off PV and will provide voltage/current to the battery terminals. THIS can actually pre-charge your capacitors. The MPPT is current limited and will only output what it can. If you have PV and sunshine, you don't need a precharge with a Victron MPPT... unless it's at night.

 

[meetyg]

As Will has shown before in his videos, You can still get a nice spark even from 12v systems.
That spark tells me that there is alot of inrush current going on. So I would prefer to prevent this, even if there are no visible sparks when using switches/breakers. I'm not so sure it's healthy for the capacitors either.

In my portable solar generator, I chose to put a time delay relay that bypasses the breaker before inverter. Basically, when it had 12v it will turn on for about 10s and precharge (via resistor) the inverter. After that I can just turn on the breaker. No dramas. One downside to this, is that the time delay will not cycle on again, untill power is gone and then back up again. In case I want to precharge again, I need to disconnect the 12v power either via the breaker on the battery or the BMS discharge function.

On my stationary build, I decided just to use a manual breaker with resistor. I could have gone the automatic way, but I think that opposite to my mobile solution, once my system is up, I will rarely disconnect the batteries.

But I agree that not many are aware of this issue. I have seen some "professional" installs done, and none of them took care of pre-charge.