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shannon-zimmerman avatar image
shannon-zimmerman asked

Victron Multiplus 3000 not turning on/causing voltage drop

Hi all. I am having trouble with my Victron Inverter/Charger in my new electrical setup. My battery bank is showing a voltage of 13.2 all along the terminals. I have 4/0 cables going from my lynx distributor to my inverter/charger along with the 400amp fuse. I have read the Victron Manual front to back. The problem is that when I power my system on (master switch), nothing happens. My DC power doesn't work, my battery monitor, solar charge controller, NOTHING powers on. The voltage drops at the battery terminals and ALL other connection points to 2.37 volts!! When I disconnect the inverter cables from the lynx, everything works and voltage is consistent with the battery 13.2V... I have DC power and my solar and everything works beautifully (which is a relief since it's a new setup). But I'm beyond frustrated with the inverter charger.. I have tested the cables and I've even made new ones and swapped them out because my first thought was faulty crimps. I've tried everything. I cannot find an answer after days of "google" research in addition to the manual. Now I'm beginning to think there's something wrong with the inverter? It's brand new and has not powered on.. the lights won't flicker or anything. I have a shore power plug wired to it with nothing plugged and a breaker box with the main breaker turned off. I have thought about trying to plug into shore power, but I'm nervous about doing that. PLEASE can someone help me figure out what's going on, it's driving me crazy.

There's a picture of my system below but note that I've added a second battery since that photo was taken thinking that my battery bank could be the issue. I'm wondering if it has something to do with the BMS, perhaps my batteries aren't charged enough to power the load? How much power does the Multiplus require to turn on? I am getting 13.2V at the terminals though indicating a 70% or so SOC.. but the batteries weren't "resting" for long when I checked that voltage with my multimeter. My SOC on my Victron shunt isn't accurate yet since I just set up my system and haven't had a full charge yet. But I would think that the Victron would still turn on?? I'm going to charge the batteries fully tomorrow to see if that works, but I doubt it at this point.

Here are some specs of my solar electrical system in my camper van:

Victron Multiplus 12V 3000 Multiplus inverter/charger

2x206AH SOK lithium batteries

2x Victron lynx distributor (bus bar system)

1 Victron Orion 30amp DC-DC charger

600 Watts of solar panels

60 MPPT Renogy Solar Charge Controller

Victron SmartShunt

tempimageshluwy.gif



Multiplus-IIMultiPlus Quattro Inverter Chargervoltage
tempimageshluwy.gif (5.8 MiB)
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10 Answers
snoobler avatar image
snoobler answered ·


IIRC, that battery is limited to 100A discharge.


The surge that occurs when the capacitors charge is probably tripping the BMS overcurrent protection (hence the absurdly low voltage), or you are shorting the battery terminals in another way.


I don't see where the inverter + connects to the Lynx.

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snoobler avatar image
snoobler answered ·

The surge is massive but brief - likely well over 200A.

Most get past this by temporarily putting a resistor in series with the circuit to limit current flow. You can also do it as a parallel bypass. After several seconds, you remove the resistor and make the connection. This needs to be done every time you break the circuit between the batteries and the inverter terminals, i.e., use the main cut-off switch.


You could simply put a resistor between these two points for several seconds before you turn it on:


1643085688743.png


A 1Ω 25W resistor would be fine. You know you've made it when you can measure battery voltage at the inverter terminals.

An incandescent or halogen light bulb works too.


1643085688743.png (2.5 MiB)
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Sean Flanagan avatar image Sean Flanagan commented ·

I am confused on the basic physics of this. If the current draw is in the hundreds of amps when the capacitors are charging and the voltage is in the 12 V range, then the power draw would be in the 1000's of watts range (P = IV). Wouldn't the resistor need to be rated for a lot more than 25 W? Is the idea that, because the current is only flowing for a few seconds, the resistor will be able to handle the large power draw that is well above it's rated power?

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snoobler avatar image snoobler Sean Flanagan commented ·
No. The resistor is ... a resistor and thus limits current according to Ohms law:


V = I * R

12V = I * 1Ω

I = 12A max.

While the initial power will be notably higher than 25W, it rapidly decreases as the voltage delta decreases. The resistor never generates enough heat to be damaged - kinda like how starting an electric motor has a surge 5X the run current, but it doesn't blow fuses or trip breakers - it's short duration.

Another option is a #2 pencil sharpened at both ends. You'll get about 6Ω of resistance, and I also mentioned light bulbs - those have the benefit

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Sean Flanagan avatar image Sean Flanagan snoobler commented ·
Thank you for explaining that ... that makes sense now.

I installed a Victron Quattro 5K inverter with four SOK 12V206Ah LiFePO4 batteries and was having this same issue as other people who posted about the voltage drop due to the BMS shutting down. I followed your sage advice and set up a temporary bypass through a 1.2 ohm 25 W resistor controlled by a breaker. I turned on the bypass circuit for 5 seconds and then off again. Then turned on the main inverter disconnect / breaker and it worked like a charm! Thank you so much :)

All of this was housed in a Midnite Solar MNDC enclosure, fyi. To make sure that the leads on the the resistor didn't inadvertently make contact with anything in the enclosure, and also to keep the leads from bending and potentially breaking, I put the resistor in a short length of PVC pipe (I drilled a bunch of holes in the side of the PVC pipe to make sure the resistor could stay cool). I taped the ends of the pipe to the lead wires with electrical tape to keep it secure.

The only improvement I would make to the set up is to have the bypass circuit on a momentary push button or a momentary toggle switch instead of a breaker. This would avoid the possibility that the homeowner would leave the bypass switch on by mistake.

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shannon-zimmerman avatar image
shannon-zimmerman answered ·

Update: (also posted on DIYsolar)
I went to the local auto electric store and picked up a little resistor. A 10ohm 25W guy. Held it in parallel for a few seconds and....
IT LIVES!!! Thank you everyone for your help, you have saved my system and my sanity

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snoobler avatar image snoobler commented ·
You might want to permanently wire that in with a momentary push-button switch to pre-charge prior to main connect. You will need it EVERY time the battery is disconnected from the inverter, including if the battery BMS ever hits low voltage disconnect.


If it's a quick disconnect without a power draw, then the capacitors might hold most of their charge, and you won't need it.

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shannon-zimmerman avatar image
shannon-zimmerman answered ·

Hmm.. okay I think you're onto something with that because I agree that it does seem like the BMS is doing something. But I now have two of those batteries, meaning 200 amp discharge maybe?

Regardless, I was trying to find that info.. how much do the capacitors need to power up the inverter? I can't find this issue replicated in any other forum and I can't be the first person to ever use these batteries (or similar) with this inverter.

I have looked at it hundreds of times searching for a potential short or something. I am trying to rule out user error before I start blaming the inverter itself hoping its an easy fix that I overlooked. But it just doesn't make sense that everything else works flawlessly. The problem seems to lie between the inverter and the battery and there are few connections there that I could possibly have messed up and I have quadruple checked.

But tomorrow I will isolate the inverter further, starting with removing all other loads, moving on to the AC lines (which is unfortunate as it was a PIA to get the 10awg cables into those little slots lol) and see if the inverter turns on when it's the only load the battery has to power. Not that my lights and diesel heater even draw anything.

The inverter is disconnected in the photo because I can only get power to my DC appliances when it's disconnected.

Thank you, you're input is appreciated!

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shannon-zimmerman avatar image
shannon-zimmerman answered ·

This is extremely helpful thank you. I will try to find a resistor tomorrow and it will be the first thing I try now before disconnecting all the other stuff. I didn't know that this was a necessary step... seems important.

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snoobler avatar image
snoobler answered ·

Saw you over on DIY solar. :)

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shannon-zimmerman avatar image
shannon-zimmerman answered ·

Yes! Haha I have never posted to a forum.. ever... and here I am so desperate I posted to three XD. But seriously glad I did. It seems that others are in agreement with what you said. Really appreciate the picture pointing out where I can hold the resistor.

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blutow avatar image
blutow answered ·

If you don't have a resistor handy, I'm 95% sure you can pre-charge the invertor with the inverter. Just plug it in and turn it on. The charger in the inverter will put out DC amps and that will charge the capacitors. Once the invertor comes up, you switch on the batteries without the surge. Again, I'm almost positive this will work because I used this approach before installing a pre-charge circuit. You may need some small DC loads present for the charger to start working, but I don't think so.

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snoobler avatar image snoobler commented ·
Good to know!
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hugues avatar image
hugues answered ·

I have the same problem with my Multiplus II,

I managed to get the inverter started with shore power, then switch to charge mode, then connect my battery. But it's not a good fix if I'm in a place without shore power.

I will try the temporary resistor.

Would like to know if the OP (shannon-zimmerman) has found a fix.

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pwfarnell avatar image pwfarnell commented ·
If you read all the replies you will see one written by the OP that they bought a resistor and it worked. You need to get a precharge resistor for your inverter.
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snoobler avatar image
snoobler answered ·

Thought I'd add to this... if you have an operational MPPT + PV or a DC-DC charger in the circuit, that's usually enough to pre-charge the caps and wake the BMS up if it tripped short circuit protection.

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