Victron multiplus II 2x120 24v will not invert or charge,need help to troubleshoot

[Jackel440]

Good evening everyone,
I will lay out my system and then ask about my current issue
I have a 5th wheel camper that I installed a Victron Multiplus II 2x120 24/3000/70-50, Cerbo GX with touch 70,Lynx shunt and lynx distributer,
I am using 2 Redodo 12v 100ah batteries with low temp charge protection. No solar panels.
this system has been running for a bout a month in my rv and has worked flawlessly till now.
Last week we had high temps hit god old indiana and my ac in the house quit. So my wife fired up the air conditioning in the rv to help cool our golden retriever down. no problem, the air was on but she didnt know that both ac came on and would blow the breaker do to too much amp draw from the 20amp outlet on my shop. So it looked like the invertor ran the air on and off for an hour and a half before it shut down due to low voltage.
I got home and luckily the camper hadnt got too warm for Maverick. I reset the breaker and turned off the other ac unit. The Multiplus started recharging the batteries and all is well.
The nxt day or so I started getting Low voltage alarms from the Multiplus every hour or so. I found the lynx shunt was showing 26.64 volts but the Multiplus was saying it was reading 18.1v I checked the batteries with my multimeter and it was matching what the Lynx was saying.
I decided to check the firmware after trying to figure out why the voltage readings didn't match. I updated the firmware on the Multiplus and the Cerbo I think.
Now the Multiplus shows dc voltage fluctuating at 26.97 to 27.02v
it is in float mode but the battery says "idle" and is greyed out on the touch display
The Lynx shunt shunt shows 26.54v 0.0a, 0w
the Multiplus will pass power through like normal but will not charge the battery or use it to supplement or just invert without a/c input.
I have checked all connections to make sure they are tight. nothing is loose or running hot.
I'm a millwright and not an electronics guru but I do love this stuff and have been learning a lot during this installation. Things have been great till now and I just need to figure out what needs to be done to trouble shoot to find a solution to my problem.
I have sent an email to the battery manufacturer about what I need to do to check and verify the battery condition. They were awesome to respond with other questions I had during my instalation. So I hope to hear from the tomorrow.
Any ideas or suggestions are appreciated and I will try to walk through them best I can.
thanks everyone for your time

 

[justinm001]

If the MP was reading 18.1v and the lynx was 26.64v what was the load past the lynx? You need to test the voltage at the MP not under load and when under load with a multimeter.

What gauge wire?

Do you have easy start for the AC? When an AC starts it pulls a bunch of power, mine are as much as 120v 67a (8000w). At 24v this is 335a and if not thick wire it'll get low voltage

 

[Jackel440]

If the MP was reading 18.1v and the lynx was 26.64v what was the load past the lynx? You need to test the voltage at the MP not under load and when under load with a multimeter.

What gauge wire?

Do you have easy start for the AC? When an AC starts it pulls a bunch of power, mine are as much as 120v 67a (8000w). At 24v this is 335a and if not thick wire it'll get low voltage

My apologies for the late reply, work,farming and family took me away.
The 26.64v was at the batteries and at the shunt going to the MP.
The MP won't even take a load from the dc side it's only passing through. I'm still constantly getting the low voltage alarm about every hour or so.
The system is 1/0 gauge wire.
The issue is the ac was being run on shore power like I've intended and been doing. For the reason I've not yet installed the soft starts on the ac units. Unfortunately my wife turned the ac system on while I was at work and she didn't know the second ac unit would come on and over load the shore power breaker. So it was running on shore power then switched to battery. She left the dog in the camper and went to a doctor appointment.
It's was unbearably hot and I'm not sure the ac units were cycling but just running nonstop.
( I now kill the breaker to the front ac so this won't happen when running on my 20 amp shore power cord)
I've been in contact with the Redodo batteries and have been doing tests with the batteries to see what's up with them. I've removed them from the rv and charged them individually.
They charged up and after resting showed 12.94v.
They then asked me to put a load of 60watts or more on them for 3 minutes. I did that and after waiting 30 minutes they read 13.31v. Redodo thought they may have went into an overcharge protection. I sent them the results of this last test and hope to hear back tomorrow.
Now with no batteries in the battery bank in the RV. The touch 70 still shows the battery voltage of 26.6 on the screen even though nothing is there. I would've thought it would've shown nothing.
Had to take the camper to a horse show for my wife this weekend. Sucked having to hurry and get there and get plugged back in since the fridge couldn't run on the batteries even though they were in there.
I'll update this thread on what I hear back from Redodo.

 

[justinm001]

You need to check the voltage at the studs of the MP. On the cerbo go to the device list and check the voltage at the MP and the shunt.

The cerbo should show the shunt voltage on the main page.

Also if web enabled check vrm under advanced and you can see a chart of voltages then compare the MP to the lynx depending on time. If the voltage is fine but then under load it goes to low voltage it's likely a cable.

 

[Ykdave]

I’d vote for bad cable/connection/fuse

If the multi plus doesn’t want to turn on because of the low voltage/no battery situation I would pull the cables off of the multiplus and start checking them for damage and checking resistance across them

 

[Jackel440]

You need to check the voltage at the studs of the MP. On the cerbo go to the device list and check the voltage at the MP and the shunt.

The cerbo should show the shunt voltage on the main page.

Also if web enabled check vrm under advanced and you can see a chart of voltages then compare the MP to the lynx depending on time. If the voltage is fine but then under load it goes to low voltage it's likely a cable.

I’d vote for bad cable/connection/fuse

If the multi plus doesn’t want to turn on because of the low voltage/no battery situation I would pull the cables off of the multiplus and start checking them for damage and checking resistance across them

I would like to say thanks to both of you for making me go back to basics. Ive been chasing my tail down several different paths to what i thought was wrong.
1st the system was overloaded and ran down to nothing.
2nd after resetting the breaker and starting the system up and recharging the batteries the low voltage alarms started coming on
3rd I was getting different voltage readings from the battery bank,shunt compared to the multiplus
So I was convinced I had a battery issue and was conversing with Redodo the battery manufacturer. They had me do several different tests to check the batteries. I was convinced they were the issue and spent the last 2 weeks trying to figure out what was going on.
Redodo was great to deal with and they helped me out. we figured out that the battery did go into low voltage protection and we had to restart it. So after doing that and the batteries worked fine doing a load test. So I put the batteries back in the rv and still have the same low voltage alarm.
So now after reading and reading the owners manuals for the invertor and cerbo and shunt. I came to the conclusion that I had to go back and recheck stuff like you guys had said. So im pretty sure I checked them before but you guys were correct and both connections at the Multiplus were loose. So I tightened them up and thinking that maybe i had found the problem.
Restarted the system and still have "low voltage alarms"
I fired up the ol'voltmeter and I had 25.5 volts at the battery and going into the shunt. I had 17.5v at the Multiplus. Now this made no sense to me. So I pulled the covers off the shunt and distributer. All those connections were tight. Fuse in distributor to the multiplus is good.
Now I find the fuse in the shunt is blown. Here is what was throwing me off. With the fuse removed and the disconnect switch on, the shunt shows 25.5v incoming voltage and then after the removed fuse it is showing 17.5 volts. So the shunt is putting lower voltage into the system. I was watching the a chart on the vrm pages and was seeing the voltages dancing from 17.5 then to 25.5 up and down.
I dont know why it is doing that and it totally threw me for a wild goose chase.
Does anyone know why the lynx shunt would be putting 17.5 volts onto the downstream side to the distributor and onto the Multiplus? Is this normal operation? There is a white wire attached to the bus bar at the fuse location and attached to the circuit board. So I assume it has something to do with the monitoring. Anyways this issue has had me going in circles and I missed the blown fuse because I was still seeing voltage readings on the multiplus and from the lynx shunt on the Cerbo GX.
I have ordered a new fuse and when it arrives Hopefully that will fix my problem and the system will be back up and running. I will report back with my results.

 

[HarryN]

Consider to run small wires to a normal fuse block instead of to a big bus bar like a lynx.

For example - this basic fuse block from bluesea or equivalent.

ST Blade Fuse Block - 12 Circuits with Negative Bus - Blue Sea Systems

Compact ATO® / ATC® fuse block consolidates branch circuits and eliminates the tangle of in-line fuses for electronics and other appliances.

www.bluesea.com

Small wires aren't really capable of dealing with the amps that are available on a heavy duty bus bar - so IMHO are not safe / protected. Also can be subject to mechanical damage.

One of the little fun things about wires is that they can break inside or crack inside of the insulation and you can't so easily tell by looking at them. The smaller the wire, the more likely this is to happen. You might think that this could be easily found by measuring resistance on a simple meter, but life isn't always so easy.

 

[justinm001]

With the lynx shunt removed you're seeing 17.5 volts at the MP? You shouldn't have any voltage if there isn't a fuse.

The batteries should plug right into the shunt and nothing else. It sounds like you have a small cable plugged into the battery positive and it's bypassing the fuse but not thick enough to get much voltage.

 

[Ykdave]

I haven’t used a lynx shunt so I’m purely speculating here but what I think you’re seeing on the downstream side 17v is a “phantom” voltage induced by the shunt monitoring circuit.

The circuit isn’t capable of handling much current so you’re seeing the low voltage with the multiplus idle, then under load the voltage just drops off and causes the multiplus to cut out

Another thought, is that 17.5v still there with the multiplus disconnected from the mains? Possibly just seeing power that’s coming from the multiplus itself

Side note, adjust your multiplus settings so you don’t overload your shore power or battery protection in the future!

 

[Jackel440]

I haven’t used a lynx shunt so I’m purely speculating here but what I think you’re seeing on the downstream side 17v is a “phantom” voltage induced by the shunt monitoring circuit.

The circuit isn’t capable of handling much current so you’re seeing the low voltage with the multiplus idle, then under load the voltage just drops off and causes the multiplus to cut out

Another thought, is that 17.5v still there with the multiplus disconnected from the mains? Possibly just seeing power that’s coming from the multiplus itself

Side note, adjust your multiplus settings so you don’t overload your shore power or battery protection in the future!

I believe your correct in that I'm seeing the downstream voltage from the monitoring circuit.
The multiplus was set to only pull 18 amps from the shore power. It was inverting to supplement the load when I believe the 2 acs came on along with the residential fridge. Again I had no idea that my wife was turning it all on while I was gone at work. If I had been home I would've killed the breaker to the second ac and it would've been fine. I still need to get the new 50 amp outlet installed on my shop.

 

[Jackel440]

With the lynx shunt removed you're seeing 17.5 volts at the MP? You shouldn't have any voltage if there isn't a fuse.

The batteries should plug right into the shunt and nothing else. It sounds like you have a small cable plugged into the battery positive and it's bypassing the fuse but not thick enough to get much voltage.

there is nothing else plugged into the shunt to supply voltage. there is a white wire from the shunt circuit board that is attached on downward side of the fuse,and a red wire before the fuse.I can only assume that this is a part of the shunts monitoring circuits, when turning on the disconect at the battery bank the shunt showed the banks correct voltage. when I turn off the disconnect it shows 0 voltage. But i would get the 17v reading at the distibuter and at the Multiplus.

 

[Jackel440]

New fuse in shunt and she is working like she should! Lots of little things were throwing me off the trail when diagnosing. Im no electrician but Im learning. I was making things way to complicated thinking it was some programing error or something of that nature. Im thankful to you guys who helped me along the way.

 

[justinm001]

there is nothing else plugged into the shunt to supply voltage. there is a white wire from the shunt circuit board that is attached on downward side of the fuse,and a red wire before the fuse.I can only assume that this is a part of the shunts monitoring circuits, when turning on the disconect at the battery bank the shunt showed the banks correct voltage. when I turn off the disconnect it shows 0 voltage. But i would get the 17v reading at the distibuter and at the Multiplus.

Im not sure what these wires are or where they should be. I have a Lynx shunt but can't remember them. Likely they're for the power to the shunt to convert it to 5v to power the lights and board.

Getting 17v at the MP when you don't have a fuse is a major concern. But it does take some time for the MP capacitors to drop power so it's normal for voltage to slowly drop to 0, especially if there's no load.

 

[Jackel440]

Im not sure what these wires are or where they should be. I have a Lynx shunt but can't remember them. Likely they're for the power to the shunt to convert it to 5v to power the lights and board.

Getting 17v at the MP when you don't have a fuse is a major concern. But it does take some time for the MP capacitors to drop power so it's normal for voltage to slowly drop to 0, especially if there's no load.

I forgot to take a picture of the wires.They do go to the board so I assume they are to either power it or for monitering. That 17v current is what is throwing me for a loop. After trying to get my system working the last couple weeks Im going to let it run for awhile. I might pull the fuse and replicate the situation and try to replicate the 17v situation in the future.