Quattro 48/8000 Startup from Battery

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kevin88252 asked Apr 21, '24

Quattro 48/8000 Startup from Battery

Hello guys

We are facing a issue that is mentioned a few times somewhere in the internet but i can't find a real solution for that.

We have 3 Quattro 8000/48 connected to 8 Pylontech US3000c batteries.

But when turning on the system from the battery (no PV, and no AC in available) the battery starts to turn on and goes straight in a alarm state and turns off again.

I've connected a fluke oscilloscope to see what the voltage and currents are doing:

First, the batteries do not turn on simultaineously but one after the other, meaning that all startup current is pulled only from the master battery.

The battery does a soft start, meaning the voltage goes up from 0 to 48v in about 3 seconds slowly.

However when i connect the inverters, the voltage raises to about 3v the current spikes to more that my meter can measure ( >250A) then the voltage goes immediately back to 0 and the battery is in alarm state.

This is a classic capacitor issue and could be solved with a resistor and a delayed contact bypassing the resistor after the bus voltage is slowly charged.

But it's this really the only solution? How is it possible that there are so many setups like this out there and no one else is struggling with that problem?

Thanks for advice

Pylontech inverter current draw Quattro-II

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Answer 1 · 2024-04-21T05:50:09Z

duivert answered · Apr 21 at 05:50 AM

Hi i think you dont have enough battery power, minimal advice from victron is 18x us2000 so in your case minimal 12x us 3000

See: https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom

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Answer 2 · 2024-04-21T05:53:06Z

nickdb answered · Apr 21 at 05:53 AM

Part of your problem is that is way less battery than those inverters should have. With a mismatched config you are more likely to run into these issues when 24kVA of inverter (not including the peaks it is capable of) needs to pre-charge off 18kW of battery. The 3000's are light in the pants from a charge/discharge performance so this is to be expected. If you have solar chargers, turn them on first before powering the battery, it is another technique to pre-charge.

Alternatively, make sure your batteries are all online, and then connect one inverter at a time, that may be less likely to cause the BMS to wobble. Each should be isolated anyway for safety.

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Answer 3 · 2024-04-21T06:06:40Z

Alexandra answered · Apr 21 at 06:06 AM

@kevin88252

A big precharge resistor will help.

But does not fix the ultimate problem of undersized bank and the inrush it needs. And then complicated by the low voltage of Pylons (which collapse under load as well making higher amp draws). If this is their first start and they are on the out of the box soc even worse.

In your settings don't allow the system to drian the battery bank down under 15/20% (so system shut down before the bank) to prevent future problems of having to precharge on a depleted bank. And dont start the system with large loads.

BYD have the best precharge and bank start up on the market.

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kevin88252 commented · Apr 21 at 07:11 AM

Is your answer in short really "you bought shitty batteries, go and buy yourself some BYD batteries!"?

The Pylontech batteries are now here so replacing them is not really a solution...

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duivert kevin88252 commented · Apr 21 at 07:23 AM

Pylontech or byd could be a discussion on itself ;)

Pylontech’s are fine, but you really need more of them…

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nickdb ♦♦ kevin88252 commented · Apr 21 at 07:28 AM

It is a comment that shows many do not consider precharging in their decisions, many batteries do not have precharge circuits at all, those that do, don’t have these issues. It is a reasonable comment since your question was broadly about how people deal with this situation. I use a variety including both pylon and BYD, appropriately sized it generally just works.

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Answer 4 · 2024-04-21T07:27:15Z

kevin88252 answered · Apr 21 at 07:27 AM

Thank you guys for your replies...

About not having enough batteries:

I am almost sure that somewhere in the victron Pylontech manual i have found that 6 batteries are sufficient and i have 8?

And i can have even 20 batteries as long as they are starting up one by one, the capacitors are always charged only from the first battery and the other batteries won't help at all...

Yes, currently we start up the system either with providing AC or PV and then turning on the batteries. That works fine but is not really a good solution as it can happen that there is no auxiliary power available...

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duivert commented · Apr 21 at 09:05 AM

yes the manual says 6 us2000's on 1 quattro 8k minimum, you have 3 quattro's

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kevgermany ♦♦ commented · Apr 21 at 08:38 AM

You have some very experienced installers helping you in this thread. It's not crap batteries. It's a design issue. It can be mitigated, but doesn't get away from an undersized battery bank.

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nickdb ♦♦ commented · Apr 21 at 08:43 AM

It is unsupported to use AC to precharge as it stresses the input relays.

The sizing chart is in the battery setup doc, it is definitely not 6 - it is related to the potential of the inverter to pull power.

It is a recommendation, and you can get away with less on a grid-tied system, the requirements are stricter for off-grid as the inverter cannot lean on the grid.

What is forgotten is that it is a compromise if you don't match the DCL limits of the pack to the inverters, if grid is lost, you are off-grid and you could have stability issues under load or brownout conditions. Also corner cases like you are experiencing.

Bottom line those inverters can pull up to 600A or more (excluding transients) and you have 296A of battery (feel free to check the limits sent to the GX - 37A per battery).

That isn't a good ratio.

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Answer 5 · 2024-04-21T07:38:39Z

Alex Pescaru answered · Apr 21 at 07:38 AM

Hi @kevin88252

Can you start up the inverters one by one? It may solve your problem...

Alex

PS:

This is the joy of having low frequency inverters with big transformers inside... Inrush current.

Not the case of high frequency inverters like Multi RS. Some HF inverters even having DC-bus soft-start, but that is another discussion in itself.

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Answer 6 · 2024-04-21T09:40:57Z

jkkm answered · Apr 21 at 09:40 AM

You could try either of these methods. I use the 48v light bulb method with a single Quattro 48/8000 with 3 x US 3000C and 3 x US3000 to get around this exact problem

https://youtu.be/DOrJ5AH9yjM?si=h_yTjlX8l6rmVTu1

https://youtu.be/T1T1PwaTXKk?si=Ll50_wSHPOnoc5u6

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Answer 7 · 2024-04-21T11:28:57Z

kevin88252 answered · Apr 21 at 11:28 AM

Okay, thank you guys for your answers. I made a mistake overseeing that it is 6 batteries per inverter, not 6 in total.

The problem with starting one by one is i need to break the DC line and a contact that can handle that big inrush current (switching DC is always a pain, isn't it?)

I will give the system a try next week to see how it behaves under load.

The idea is to use it off grid with some PV (<1kw) and a generator. I can always start the generator if SOC is lower than 30% or load gets above 18kw...

Most of the time the load will be less than 5kw anyway.

Thanks again for explaining.

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Answer 8 · 2024-05-03T14:47:37Z

jeroen-kuijf answered · 11 hours ago

Good afternoon,

Well, the DC busbar inside the inverter has capacitor arrays, straight between the plus and minus.

When you switch off the inverter, after some time these are empty, e.g. rest voltage 4-5 volt only.

That's the inrush current you witness, with or without the inverter being switched on, nothing else.

This, LICAP SM0165-054-ATH (among other similar ones) should solve your startup problem as it can boost 2500 amp.

It also acts as just 1 extra battery and delivers between 80 and 131 amp way faster than the lithium ones at normal use.

It will therefore "protect" your lithium against these spikes and in/outrush amps as well.

Keep the cabling as short as possible to the DC busbars when mounting.

Use a 100-200W resistor to charge it, then connect to the busbars, otherwise "boom", 9000 amps.

It stores about 60Wh, yes, not much, but it will overcome a power-out, for the inverter off for about 4-5 hours, and for the inverter on at zero load for about 1-1.5 hours.

I have same and similar ones on many 24/48VDC systems, and these work just fine, a little less DC ripple and way less voltage loss/drop at high load starts, and so less overload warnings and blackouts.

At least it's cheaper than to buy 6 extra pylons for now, AND when you buy later more pylons, which you have to do, you have the LICAP as the "protector" for your system.

With regards, Jeroen.

Check me out at; https://vrm.victronenergy.com/installation/48664

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