VDC ripple improvements

[MichaelHayes]

Hi Jeroen,
There is a lot of reasoning in there… Firstly, on 3 Phase, capacitors are only useful to the extent of the unbalance of the phases. If all three were balanced, there is no 2nd harmonic ripple to deal with. As for single phase, you have to remember that capacitors “filling in the gaps” means they have to source that charge from somewhere and that is from the battery. remember that for a capacitor,

i=Cdv/dt

The C will be the sum of the internal and external capacitance. The current flowing through to the load will have monumental ripple current (200% when expressed as peak to peak ripple!) so while i am not saying you are wrong it very much depends on where you measure. If you can back up with oscillographs of the DC voltage and current both before and after the external capacitors, it will very much enhance the discussion, cheers

[smueff1970 (Thomas)]

Good moning,
yesterday i messured a few things.
victron multiplus II 48/5000 3 phase with 2 multiplus for each phase.
4 batteries with each 9,8 kw.
discharge load with ~ 25A

so you can see the ripple of 0,7V. fzsonick says the maximum is 1% => 0,5V.
if i increase the discharge current so the ripple will also increase.

charge with 25A the ripple seems ok:

Thomas

[Jeroen2 (Jeroen Kuijf)]

Good evening Thomas,

I’m in RIO on a big job, but I found some time.
Your measurement tells me directly 1 thing.
With that very low base current,
you should have less than 0.1 to 0.15v ripple.
Indeed salt batteries are very slow releasing electricity.
(Sorry I write short lines,
there is something wrong here).
On IMO vessels we do not work with salt.
Basically only lead acid.
What shows me is that it “ripples” about 3 times more than lead acid.
I would recommend on each inverter an extra capacitor to start with.
And on the battery terminal a huge super capacitor.
Let me make some calcs, and discuss with my colleagues.
I will revert to you asap about our recommendations.
This, as it quite more extreem as I’ve seen in decades.

Regards, Jeroen.

[Jeroen2 (Jeroen Kuijf)]

Good evening Thomas,

We checked, more asap can not be…
The market is limited at the moment.
You are going to cry…$$$.
To start with;
1 piece, SM0165-054-ATH Licap, 165F, 54V max.
You do not charge higher than 54V, correct?
To put over your batterij terminal.
Sorry, cheapest and most F for the $.

6 pieces, ALS70A334QS063, 0.33F, 63V,
Or better.
12 pieces, 0.27F, 63V, to cope more amps.
To put on your inverter terminals.
Why directly on the terminals.
Easy, 1 phase has load, others not.
Then it reacts directly for that phase (inverter) faster.

We say the market is limited, failure of bigger components availability at the moment.
So, we cannot make a CLC for your issue.
Of course we can, out of multiple smaller components, but to many $$.
And a huge impact on your busbar, space…

1 thing I can say that you might improve 45-50%.
This, as we do not know this chemistry of your battery completely.

My advise, show the above to the battery manufacturer.
Let’s see what they say and comment.
More input, better results.
@ Thomas, can you give a link what bat you exactly have.
So, we can analise the release of electricity better.
We know already partly from the test you did.
But, we do not know the full data, you see?

Just to understand, I’ve seen lead acid bats with 42 years of age and still working…
Yes, they lost capacity, 40-45% or so…but still!
Filtered air injection, catalyzers on top, drain to get the sludge out and filtered and recicled, you name it…
It’s all about cycles, less cycles, longer life…meaning a big battery.
Besides, bigger battery and thicker cables, less ripple, longer life.
No, over-or-under charging, less absorption, more float, longer lifetime.
Easy as it is, read the Victron book (energy unlimited) that’s a good book to start with.
We used it already in the beginning of the nineties or so, written only in Dutch at college, I remember.

Regards, Jeroen.

[Jeroen2 (Jeroen Kuijf)]

Good afternoon Thomas,

Any updates or further findings?

Regards, Jeroen.

[Jeroen2 (Jeroen Kuijf)]

Good evening,

The results are in when we started monitoring at 16 January if the batteries have indeed an higher charge and discharge efficiency due to a capacitor bank to reduce ripple.
The preliminary results showed us about 3% already in January.
Now 6 months later it’s even better.
We can say that we gained about 4% over 6 months monitoring in comparison without capacitors mounted.
We made also an AI graph in VRM to monitor this better, go to below VRM site, then click advanced, then last graph, called, “battery energy monitoring”.
We see that the charged and discharged lines came closer, meaning an efficiency improvement.
These batteries are lead acid, for Lithium we do not know yet but I’ll post it when we find out as well.

VRM Portal - Victron Energy

Regards, Jeroen.

[Jeroen2 (Jeroen Kuijf)]

Good morning,

The results are in and we made a simplified general sheet for everybody to use at will.

We do not see any difference between a lithium and a lead acid battery having to cope with a ripple, other that the lead acid is smoothening the ripple itself a little and the lithium does not, and that it is also battery capacity related, e.g. the bigger the battery the better it copes with ripple.

The ripple we created was a resistor in the positive wire to the battery from the inverter as that is the most common issue that people use too small and/or too long wiring, not tightened enough lugs, too many fuses, bad fuses and/or holders, not enough battery capacity, etc .

We were able to eliminate that ripple easily by 50% to 90%, pending the power taken or loaded.

See the chart attached with our solutions for the 3 most commonly used voltages and for the most common single inverter systems in our green solutions world.

These systems can either be used for single phase and for 3 phase, the result will be the same.

Ripple eliminator.pdf (76.7 KB)

I hope that with the help of this sheet there will be less issues; with ripple alarms, premature battery failures, premature inverter capacitors failures, flickering lights, overload alarms, etc.

Regards, Jeroen.

[alexpescaru]

Thank you for your tests and efforts.

A small observation…

All these tests are for low frequency inverters, like Multiplus. In this case, the DC source and capacitors are directly involved in the conversion process and they are the single ones that work hard for the conversion.

But in the case of high frequency inverters, like Multi RS range, there is a “two stage” conversion.
One that lifts the battery voltage to about 400VDC and one from 400VDC to 230VAC.
Both stages have their capacitors, but now is the tricky thing…

The first 48VDC → 400VDC conversion is at about 60-100kHz and the second conversion is trying to generate the 230VAC 50/60 Hz voltage from the 400VDC.

You can access the first stage capacitors and improve them, but because they are working at tens/hundreds of kHz, then the ripple issue must somehow be looked from a different perspective…

Not to mention that the second stage high voltage capacitors are somehow difficult to access.

See below what I mean…

[Jeroen2 (Jeroen Kuijf)]

Good morning.

I see and know, but we were just looking for a solution for the ones with indeed a ripple on the battery side, many topics the last years.

Installed with Multis standard and compact, quattro, even Mastervolt and Outback amongst others.

In all cases the ripple reduced drastically as described above.

Of course to save money, things must be calculated, so we overdimentioned the examples slightly to get the correct effect, but the questions were also to have something standard to install, that’s what we finally made and can be used for each individual case as a start point solving most cases directly.

Normally we only work with 24V installations but recently we could do some tests on 12V and 48V ones as well.

Random top quality available parts are used, the big capacitors can, of course, be replaced with many small ones parallel to increase ripple current capabilities and other space layouts.

We thought it’s much easier like this, (KISS, keep it simple stupid), less parts, less trouble, one drawing, plug and play, short instruction so that even non specialists can understand how to reduce a ripple by themselves, answering all their questions at once.

Regards, Jeroen.

[Jeroen2 (Jeroen Kuijf)]

Good morning,

Today we were able to witness weak AC input and the ripple related to it of a 3 phase system while charging the batteries.

As can be seen the lowest input voltage creates more ripple while charging.

I just thought to show it, as here it is very clear to see how important the power supply is to our homes.

With regards, Jeroen.

[Jeroen2 (Jeroen Kuijf)]

Good afternoon,

We will purchase an ATO Isolated DC Voltage Sensor for Ripple Voltage, version ATO-WBV332U05-S.

Its a handy device with lots of ranges and seems to be quite accurate.

We will test it and let you know the results.

Regards, Jeroen.

[mattie170 (Matt)]

Hi Jeroen,

I’ve got dc ripple warnings coming now and then on my system, always when a large load comes in, sometimes vrm catches the ripple but more than likely not, just a warning and if the load is big enough then I’ll get a inverter overload at the same time as the system is derating I presume. I’m thinking about looking at adding some capacitors to the system to help smooth this out but need some feedback for what would be needed for each inverter. System spec’s below: The system is running in peak shaving so the dc side can go from doing nothing to 50kw’s instantly and back off again.

18 off 15kva multiplus 2
32 off 32kwh batteries
Connected via the below, cable length is for each positive and negative
Inverters to Busbar (per inverter) = 2 x 120mm2 , Length = 3.2m
Busbar is 200mm x 40mm aluminium, average length between inverter and batteries is 8.8m. If the positive is longer the negative is shorter by the same amount and vice versa. All cables are equal lengths and all inverters have the same distance in total to each battery, everything is equal.
Battery to Busbar = 95mm2, length 2.7m
600amp bussman fuse for each inverter, No dc isolator at the moment as I had issues with them.

At 12:06 it showed a warning and overload on l1 and l2 but even if you zoom in you don’t see a spike, there is a picture below of the inverter layout.

Be interesting to get other peoples feedback, I feel the dc ripple is worse on the 3 phase system. I run a single 15k quattro at home which I run up to full load with various heaters and other house hold loads including multiple water pumps, on almost equal total length cables as above but smaller cross section overall and I don’t get warnings.

Cheers

Matt

[Jeroen2 (Jeroen Kuijf)]

Good afternoon Matt,

For this we need a little more time to give you an utmost answer.

We will give you an answer asap as we must discuss this with various collegues which are in different time zones all the time.

What we can tell straight away right now from your info is that there “must be” (is) a big resistance in your setup, mainly…cable lengths and fuses (read the specs of these)…

Based on the above info we will now start the process of calculating your DC-side resistance issues.

With the very best regards, and thank you Matt for reaching out to us, it will be solved soon (expect early next week the response), Jeroen.

P.s. We will keep this one “open” for the public as this one is utmost rare for such a “bigger” installation, thank you.

[mattie170 (Matt)]

OK great, thank you.

Yeah I’m sure it is to do with the cable length but to keep all cables equal length and the room size I was working with, the length couldn’t be avoided unfortunately. Even if we made the busbar larger I don’t think it would get it down enough. That’s not an option anyway.

Bit of google ai results on the bussmann fuses showing the resistance and volt drop below:

[Jeroen2 (Jeroen Kuijf)]

Good morning Matt,

What is the voltage drop from the battery to the inverters when having a big load?

You write that your cables are 8.8 meter, am I correct that from each inverter first a cable goes to the fuse and then to the batteries.

That would then be more than this 8.8 meter?

Well, for this inverter and cable length 150mm2 should have been used or twin 70mm2.

I presume that you will not be willing to change the cables, so the only advise we can give to start with is to put at least one capacitor per inverter directly on the battery terminals inside the inverter, our choice would be ALS70A274NT063, as it can handle a healthy ripple current of 34A at 100Hz.

Or, the ALS70A334QS063, as that one can do 41A.

Bigger capacities are hard to get for the moment for 63-100V ones, test first with these and if needed then add a second one to each inverter.

With the very best regards, Jeroen.