How to avoid Victron capacitors from rushing the batteries on setup? Nothing I'm trying is working...

[AlaskanNoob]

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.

And I don't think the Pylontech batteries turn on and deliver power at the same time. Even though they're networked together with a master, it switches itself on, then the next, then the next, and so I think the problem is the in rush is hitting that master battery first before it has switched the rest on. Annoying. 38KW of batteries all wired individually to the bus bar should handle these capacitors, but the way they sequentially turn on keeps that from helping. I wish Pylontech would send out a time stamp to the slave batteries so they all turned on at the same time, but maybe that kind of precision is too much for electron flow.

How do others handle these capacitors?

 

[Hedges]

It wouldn't be the capacitors that are insatiable. Are there any DC loads? Using a DMM, does voltage rise but settle with a steady drop across the precharge resistor? (or use clamp DC ammeter to check.)
Use a lower resistance value if necessary to charge faster, or to pull higher against continuous load if you can't disable load.

 

[AlaskanNoob]

It wouldn't be the capacitors that are insatiable. Are there any DC loads? Using a DMM, does voltage rise but settle with a steady drop across the precharge resistor? (or use clamp DC ammeter to check.)
Use a lower resistance value if necessary to charge faster, or to pull higher against continuous load if you can't disable load.

No DC loads at all. The only loads are the MPPT and Quattro and EG4 and Cerbo GX itself, but I turn those all off before I turn off the Pylontech batteries. So the caps should be juiced up fully when I turn the batteries off and there should be no draw on them.

I haven't set up any loads yet.

I'll try to check with the DMM. I know the light bulb that I used as the pre-charge resistor lit up bright and stayed bright for much longer with the addition of a new Quattro to the mix, but it eventually dimmed out. So I thought all was well. And was wrong. Which happens a lot.

 

[Quattrohead]

How long does your light bulb take to dim and exactly what are the specs of said light bulb? I'm thinking that it just has too high of a resistance and possibly your technique for switching over isn't ideal in some way.

 

[AlaskanNoob]

How long does your light bulb take to dim and exactly what are the specs of said light bulb? I'm thinking that it just has too high of a resistance and possibly your technique for switching over isn't ideal in some way.

With one MPPT it took about five seconds to go dim. With the MPPT and Quattro it took about thirty seconds.

From at least one person on the Victron Community page, the problem apparently is the capacitors discharge quickly after a minute or two. If that's the case, that would explain the issue. I had thought they would last for a week.

But given they were fully charged by the Pylontech and I took off all loads and did my adjustments in no more than three minutes before turning the Pylontech back on (and still getting the alarm) I tend to think they are right. Those capacitors just don't hold a charge.

 

[Hedges]

The device probably has DC/DC converter powering its electronics, a few watts standby. That discharges the capacitors.
If you measure the current it stabilizes at by end of precharge, you can determine a resistor value to pull up close to battery voltage. (DC/DC will draw varying current depending on input voltage, complicating the calculation.) A lower resistance might do what you want. Electric space heater instead of light bulb?

 

[Quattrohead]

Safety, you don't want 50 volts hanging around on terminals if you're not expecting it, so it probably has resistors to bleed off the voltage from those capacitors.

 

[400bird]

Safety, you don't want 50 volts hanging around on terminals if you're not expecting it, so it probably has resistors to bleed off the voltage from those capacitors.

Yup, agreed.
It is designed to not hold a charge on those capacitors. The OP made a bad assumption. It will need a precharge every time it is disconnected.

 

[AlaskanNoob]

Yup, agreed.
It is designed to not hold a charge on those capacitors. The OP made a bad assumption. It will need a precharge every time it is disconnected.

That makes sense. The manual talks about the capacitors keeping a charge even when it's turned off, but it makes sense that it would dissipate it for safety reasons.

 

[Brett V]

There are bleeder resistors on the capacitors. They’re a safety feature and frankly, I’d be more concerned with the design if they weren’t there.

 

[HarryN]

I start with a charger that will charge up even against a "battery" of zero volts.

Can be a solar charger or 120 vac charger / power supply. (unfortunately I don't think the V solar charger will do this )

Another option is to fire it up on a small AGM bank if you want a true "cold start" capability.

Last but not least - you can get the bus bars / caps up to around 40 - 50 volts just hard wiring some small panels with the right Voc to it.

 

[chrisski]

I used this switch

https://www.amazon.com/Blue-Sea-9001E-Battery-Switch/dp/B000K2MCR2/

Which has an always on (1+2) to prevent the discharge that you could be seeing when you disconnect the light bulb.

Actual term is “Make-before-break contact” not “always on.”

 

[AlaskanNoob]

I start with a charger that will charge up even against a "battery" of zero volts.

Can be a solar charger or 120 vac charger / power supply. (unfortunately I don't think the V solar charger will do this )

Another option is to fire it up on a small AGM bank if you want a true "cold start" capability.

Last but not least - you can get the bus bars / caps up to around 40 - 50 volts just hard wiring some small panels with the right Voc to it.

I didn't even think about this. I have an EG4 chargeverter wired up to the bus. I suppose I could keep the batteries off, fire that up through the generator first so that it charges the caps and takes the brunt of the cap inrush, and then turn the batteries on and turn the EG4 off?

The batteries will be off at first, so I can have the EG4 put out 52V and 100A initially which should be more than enough power to get the caps squared away. Then I can dial the EG4 back to 52V and 10A just to make sure the caps aren't depleting. Since the batteries will be off, they won't be taking any of that juice into them so I shouldn't have to worry about over voltage or anything.

Then I'll flip them on and I shouldn't get any alarms. Then turn the EG4 off. Assuming the EG4 doesn't have an issue with the cap inrush, this would be a great solution already built in that I didn't even think of. Or maybe I'm just going to be transferring the issue to the EG4 instead. I guess I'll find out.

If it does have an issue, I can use one of those push button switches and a resistor for my EG4 connection to the bus bar since that's just one cable to worry about instead of 8 from the batteries.

 

[HarryN]

I didn't even think about this.

Desperate people come up with interesting solutions.

 

[42OhmsPA]

Here's the resistor I've used with 2 different 48v AIOs (thanks to whoever recommended them on here).
I simply put a small pig tail on one end and jump the switch/ breaker until the AIO boots then flip the switch on.

YiePhiot 2PCS 50W 25 Ohm Resistor Aluminum Case Wirewound Chassis Mounted Compatible with Ring Doorbell, Nest Hello Doorbell, SkyBell Doorbell Etc https://a.co/d/hWtTG31

 

[AlaskanNoob]

If I use the EG4 to do this, is it possible I'd be supplying too much power from the EG4 to the caps? Or do the caps simply take what they want. I've heard that loads draw, sources don't push. So if I set the EG4 to provide 48V and 100A, the caps should simply take what they want rather than having too much power pushed to them, right?

 

[Hedges]

Do you mean EG4 chargeverter? 100A limit should be fine for caps. The idea is to avoid 10,000A surge from lithium batteries.

But I think that equipment is way overkill for precharge. Anything current limited would do. The only trick is how to avoid overheating the precharge equipment. And that is only a problem if inverter draws significant load, like it powers up and feeds loads. Otherwise, resistor value and wattage takes care of handling a brief pulse.

Do the precharge, and check with voltmeter to see how much voltage drop remains across the precharge resistor. If any significant amount, get a lower resistance resistor. And maintain precharge application until switch has been closed.

 

[AlaskanNoob]

Do you mean EG4 chargeverter? 100A limit should be fine for caps. The idea is to avoid 10,000A surge from lithium batteries.

But I think that equipment is way overkill for precharge. Anything current limited would do. The only trick is how to avoid overheating the precharge equipment. And that is only a problem if inverter draws significant load, like it powers up and feeds loads. Otherwise, resistor value and wattage takes care of handling a brief pulse.

Do the precharge, and check with voltmeter to see how much voltage drop remains across the precharge resistor. If any significant amount, get a lower resistance resistor. And maintain precharge application until switch has been closed.

Yeah chargeverter. That would be great if it's overkill for pre-charge because I suppose that means it will work. I already have it wired up to my bus, so if it will work then I don't have to do anything. And as a lazy guy, that's what I prefer. I just don't want to end up sending too much power from the EG4 to a bus bar that only has a Quattro and MPPT caps on it to take the power. I think even if I set 48V and 100A on the chargeverter, it will only provide whatever power the caps demand. I'm assuming the caps can't therefore get "too much" power from the chargeverter but of course I have no idea. Batteries obviously get over voltage and such so...I dunno. And, also, I'm hoping I'm not just moving the inrush demand problem from the batteries to the EG4. Hopefully it can handle the cap demand without an issue.

 

[AlaskanNoob]

The one concern I had with my new chargeverter plan was that when I turn the batteries on with the chargeverter going, they might over voltage. My plan was to charge the caps with the chargeverter then dial down the voltage on the EG4 to 48V. My thought was that when I turned on the batteries, that lower voltage should keep full batteries being turned on from overcharging.

Turns out, I think, this will work. I say that because I just learned that the Victron MPPT does basically the same thing. If it loses connection to the battery BMS (which will happen if you turn off the Cerbo GX) it doesn't know what charge the batteries want. So it will actually reduce its voltage to 48V so that it continues to charge a low battery (and I assume not overcharge a full battery). According to Victron:

Err 67 - BMS Connection lost​

This error shows when the charger is configured to be controlled by a BMS, but does not receive any BMS control messages. In that situation, the charger stops charging by reducing its output voltage to the battery base voltage (12V/24V/36V/48V). This is a safety mechanism, the reason to still enable the output is to allow a system to self-recover from a battery low situation.

So my plan will be to have batteries and equipment off. Fire up the chargeverter to supply 48V and 100A. Flip the breaker to supply that power to the bus which should charge the caps of the MPPT(s) and Quattro. Hopefully there isn't an inrush problem with the chargeverter. Then after a bit I'll turn on the batteries. Once they're on, flip off the chargeverter.

 

[42OhmsPA]

Seems complicated but it should work.
A resistor to jump the breaker/disconnect would probably be much easier, have any #2 pencils or old light bulbs laying around?