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alaskannoob avatar image
alaskannoob asked

How to avoid Victron capacitors from rushing batteries when setting up????

I thought I had got everything set up to avoid the Victron MPPT RS capacitors and the Victron Quattro capacitors from demanding a massive in rush from my "battery bank." I bought a light bulb to use as a resistor and used a separate 48V battery bank to pre-charge my capacitors in the MPPT RS before I turned on my 38KW of 8 Pylontech US5000 batteries. That worked, no alarm from the Pylontech when they were switched on.

But once I wired up the Quattro, it took forever for the light bulb to dim as the current filled up both the Quattro and MPPT capacitors and although the bulb did go dim, when I switched on my Pylontech batteries I got an alarm on the first of eight batteries. That alarm quickly went out and everything was fine.

Then, I did some wiring so I turned off the Cerbo GX (I put a toggle switch on the wire to flip it on and off to keep it from robbing the capacitors on the system) and I turned off the MPPT and the Quattro. Did my wiring and figured I didn't need to pre-charge the caps since they should be full after running for several days in a row. But nope, flipped on my Pylontech and got an alarm again.

How are we supposed to deal with all this Victron equipment connected to a bus bar with caps that apparently are insatiable and don't stay charged? I hate seeing the alarm on my expensive batteries every time I need to make a change.

How do others handle this?

in rush current
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3 Answers
Kevin Windrem avatar image
Kevin Windrem answered ·

It doesn't take long for the capacitors to discharge -- maybe a couple of minutes.

There are several commercially available soft start units specifically to handle precharg inverters, etc when switching on the battery bank. The Lynx BMS is one but expensive if that's all you need from it. REC makes one also.

If you can deal with manual soft start, then a resistor (or your lightbulb) ACROSS the contractor or manual DC switch works fine. You'll need a manual switch to bridge the resistor across the contractor since you don't want it on all the time. Doing it this way insures that the caps don't drain after disconnecting the alternate charging source.


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alaskannoob avatar image alaskannoob commented ·

Well, that explains my issue then. I thought those capacitors held a charge for at least a week or so, enough to keep from me having this issue at least.

That's why I spliced my Cerbo GX power cable with an off/switch to keep it from robbing the caps (and to avoid stressing the plastic connection by pulling the power cable out of the unit and pushing it back in all the time). I guess that wasn't needed.

I'll look into these other options to see if they can apply. Since I have 8 lithium batteries connected to my bus via 8 individual positive cables and six positive cables from the bus to 2 x MPPT RS and a Quattro, I'm going to guess there will be no cost effective solution here.

Sure would have been nice had Victron built this into their capacitors since multiple capacitors damaging the batteries sure seems like something worth avoiding.

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kevgermany avatar image kevgermany ♦♦ alaskannoob commented ·
Most good kit has a resistor across the capacitor to drain it... for safety.
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Al avatar image Al alaskannoob commented ·

Do you have a 3 way battery isolator?


You could just do the lower diagram here: (I have no affiliation, but it's a simple diagram)

https://climbingvan.co.uk/van-conversion/electrics/how-to-pre-charge-an-inverter-easily/

1696881049620.png

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1696881049620.png (71.2 KiB)
alaskannoob avatar image alaskannoob Al commented ·

I don't have a three way switch, but that looks like something worth investigating, thank you!

I suppose I'd have to get three of the three way switches (two for the two MPPTs and one for the Quattro).

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jetlag avatar image
jetlag answered ·

Did I get it right, that you "just" want to avoid a gigh inrush current when connecting/switching on the Battery to the Victron System?

Then buy a simple push button switch (not a switch with fixed on/off positions) and put a ~20Ohm 10W Resistor in Series. This you then just put inparallel to you main battery switch.

You push and hold the button for e.g. 5s and then turn on the main battery switch. All capacitors will be pre-charged and no inrush current will flow. And in case the main battery switch is disconnected, the "pre-charge" circuit is also off and no draining from battery will happen.

Such a pre-charge circuit will cost <10$ and you don't need a 3-way battery switch.

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alaskannoob avatar image alaskannoob commented ·

Yes, just trying to keep the caps from both MPPT and the Quattro from slamming my batteries on startup. Your solution sounds like a good one. I'll put some thought to it. How would it be wired? I don't have a main battery switch.


In my case I have 8 positive cables going from 8 batteries to the bus bar, 2 positive cables going from the bus bar to the Quattro, and 4 positive cables going from the bus bar to 2 x MPPT RS.

Would this require 3 buttons or is there a way to do it with only one?

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nickdb avatar image
nickdb answered ·

The easiest way, by day, is to power your MPPT(s) and let it sort the caps before powering the batteries, then the inverter.

This is the most common, and easiest way of doing it. Works fine and doesn't break anything.

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Al avatar image Al commented ·
Don't the MPPT docs say to power them up from battery before connecting solar?
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alaskannoob avatar image alaskannoob Al commented ·
Yes, at least for the MPPT RS anyway.
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nickdb avatar image nickdb ♦♦ Al commented ·
If it is a brand new install and nothing has ever been powered, that is simply to help them auto select the correct battery voltage. That is also easily done via VC, and doesn't apply to existing systems.
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Fideri avatar image Fideri nickdb ♦♦ commented ·
@nickdb so if I am doing rewiring of an existing system, that won't work? I will not change anything else on the the 48V system.
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alaskannoob avatar image alaskannoob commented ·
That makes sense. I don't know if it would work in my setup or not (it might) because my MPPT delivers what the batteries request through the Cerbo via DVCC. I would think the MPPT wouldn't provide power unless the batteries were on and asking for it.
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