Hi - Newbie here. Please help us figure this out. We are desperate. Any help you provide is truly appreciated.
We recently had a Multiplus II installed at our dealership. As we were looking at the setup we found multiple problems. I.E. wrong size wires, wires not running through the shunt, wires connected incorrectly to the MultiPlus, among others. Thus, we didn’t trust them to correct the errors properly so my husband did the rewiring. I did hours and hours of research on this forum, the Victron website and the Victron FB page.
Before we made the changes to the wiring, the solar panels were charging the battery. (Picture - Before Rewiring) We did not have the trailer plugged into shore power between the time that they installed the MultiPlus and when we rewired it. After we rewired it and prior to testing the charger on the MultiPlus, I turned off the fuse to the WF-8955-AD-MBA charger so that the two chargers were not competing. After an hour to two hours of being plugged in , with the switch set to Inverter, the readings on the Shunt/MultiPlus/MPPT were the about the same same as earlier. The MultiPlus read Absorption.
The MultiPlus readings on the two screens are different even though they were taken minutes apart. (Pictures - MultiPlus The Readings on the Two Screens Do Not Match Taken Minutes Apart)
The battery wasn’t full yet the solar panels are not charging it despite being in full sun. (Pictures - Before Wiring/After Wiring)
The voltage readings on the Shunt, MPPT, MultiPlus and the multimeter do not match. They differ from .3 to .7 volts, that I have seen. I do not remember if the battery was charging at the time these pictures were taken. (Pictures - Readings Do Not Match Multimeter)
The solar panel is overcharging the battery. This was not happening prior to rewiring. These pictures were taken while the solar panels were charging the battery. (Pictures - Solar Panels Over Charging The Battery)
I hope that I have explained everything correctly and in enough detail for you to help me solve this issue. Please, we are desperate to finish this project. Thanks in advance for all of your help. If you have additional questions, please let me know. Cindy
It is a lot of text, information, and photos to get through, but you have already done a pretty good job of making the necessary improvements to the installation.
However, what I miss in the whole story are the settings made on the various Victron devices.
The basic theory for multiple chargers in a single circuit can be compared to water pressure between different pipes at a single tap. The pipe with the highest pressure will supply the tap with water, because it pushes water back from other pipes at a lower pressure.
If you want all chargers to be balanced, you must ensure that the pressure is the same everywhere. In this case, the pressure is the charging voltage.
Set the Multiplus and 2 MPPT chargers to the LFP setting and ensure that the charging and absorption voltages of all 3 have the same voltage value.
And as a final tip:
When an LFP battery is 80% or fuller, the terminal voltage will have increased, causing the charger(s) to enter absorption mode and deliver very little charging current.
The same applies to MPPT chargers; you can have as many solar panels as you like, but if the battery is (almost) full, current simply cannot flow anymore. The tank is full, so to speak.
Brief advice:
Always try to route all cabling centrally through the busbars.
Consider installing a Victron Lynx Class-T Power In plus possibly a standard Victron Lynx, if space allows.
The 10AGW wires from the MPPTs appear thinner in the photo. Wire that is too thin can cause extra resistance and consequently voltage loss. The same applies to too many transitions through fuse holders, cable lugs, and busbars.
I’m not sure what you mean because there are pictures of the settings: three pictures of different screens for the multiplus, one picture of the settings on the 75/15 MPPT and one picture of the settings on the shunt. If you’d like additional pictures or pictures of something else, please let me know.
Yes, I realize that and I tried to condense it as much as possible but I want to make sure the whole story is told and not just bits and pieces. I believe that all of these issues are related and so I made them all one post.
Yes, I knew that but somehow I have the absorption and charge settings both at 14.4. I will change this and post pictures.
Charge, absorption and float have been changed and pictures posted of the settings. As you can see, the Battery Voltage is close to the same on all 4 devices and all 4 devices match the multimeter. Thank you for pointing this out and ‘forcing’ me to verify all settings again.
I have double checked the size and it is 10AWG wiring. We wanted to use 8AWG or 6AWG wiring but my husband tells me that he could not get that size wire into the holes of the MPPT so we went with 10AWG. This is the size of the wiring nuCamp used when the trailer was built.
Do the busbars, cable lugs and fuse holders look ok or is there something that I need to change?
This, I think, is the only thing that I am still worried about. The battery is currently charging using A/C and solar and seems to be good. Do you have any idea why the voltage on the battery got this high?
Thanks again for your help and I hope to hear from you soon. Cindy
Two points from my side:
The shunt is connected directly via the fuse on the battery and therefore always measures the voltage quite accurately. red circle
The two MPPTs run via very thin wires to the busbar and then through this ‘relatively’ poor circuit breaker… red circle
However, the shunt is now the ‘boss’ in the Smart network and could ensure that the voltage at the MPPTs is increased, as too much voltage is being lost on the way from the MPPTs to the battery. Why not measure the voltage from the battery’s positive terminal towards the MPPTs… to see if there are any voltage drops here.
I don’t know how to do this. I use a multimeter to measure the voltage on the battery. Can you explain how to I would do what you propose?
Yes, I agree that should be accurate. I had messed up the absorption and charge settings on the two MPPTs and the Multiplus. I corrected these and now the voltage reading matches on all 4 devices and the multimeter.
We can replace the circuit breaker. This is the on that was installed by nuCamp during manufacturing so we assumed (you know what they say) it was correct. Can you recommend a brand and how many amps it should be, please?
The wire on the MPPTs is 10AWG. Victron recommends using 6AWG or 8AWG but my husband could not get that size wire to fit in the hole. I didn’t not do the wiring. This is what I was told.
Thanks for your reply. I hope to hear back from you soon. Cindy
To measure the voltage drop, simply leave the multimeter’s black probe on the positive terminal and measure with the red probe towards the MPPTs …
40A fuse output, input, 2. +distributor and then 3. the + outputs of the MPPTs … BUT only once the system is getting sunlight again tomorrow … It’s pointless when the system is idle
You should only ever be measuring a very small voltage. If the voltage increases the closer you get to the MPPT, this indicates a high contact resistance.
The multimeter isn’t a professional-grade device, of course… but it should be sufficient for this purpose… In the pictures, the voltage does, after all, roughly match that of the system.
These fuses, like your 40A isolator switch, are known for failing and having high contact resistance …
So how much solar power is connected to the MPPTs?
Thanks you. I will do that tomorrow. What do you mean by ‘very small voltage’? The multimeter is a cheap one but it does do the job.
I think that the solar panel on the roof is 190 watts. The documentation from nuCamp is not very good on this subject. This is connected to the 75/15 MPPT. The solar port is connected to the 100/30 MPPT and usually runs 2 - 100 watt Jackery Panels - for now.
Ideally, you shouldn’t have any voltage drop at all, so the display should always read 0V … which is why it’s difficult to specify a value … as close to 0 as possible … the higher the current from the MPPTs, the greater the voltage drop across faulty contacts and fuses … if they’re faulty.
It would also be important to know whether you’ve set up a smart network via Bluetooth or whether the 2 MPPTs are running on their own without a controller…
Thanks very much for replying. I WISH that I was somewhere in the PNW! lol I’m in the Milwaukee, Wisconsin area. The good news is that it seems to be working. I had the charge and absorption settings the same. I knew that the absorption setting should be .2 below the charge setting but somehow my brain didn’t tell my fingers. I think that issue attributed to 90% of the problems. It is so satisfying to look at the Victron app and see all of the battery voltage rates the same and that they match the multimeter.
I do have a question for you. When should I recalibrate the shunt and set the SOC to 100%? The battery voltage got up to 14v today. Charge is set to 4.2v. Do I wait until it gets to 4.2v or do it sooner?
I appreciate that you are following up from my first post. This is a great group to be a part of. Cindy
I assume you mean that your charged voltage is 14.2 not 4.2.
Looking at your screenshots above your absorption should be at 14.2 and the charged voltage at 14.0. I assume this is what you changed.
If your settings are correct you should never need to manually calibrate. When the battery reaches the “charged voltage” setting the shunt will set to 100%. This is one reason why it is important to regularly charge your batteries to 100%.
Good to know. I have read many different opinions on calibrating so I wasn’t sure. Thanks for clarifying. I am going to test the voltage from the battery to the MPPTs to make sure it’s not leaking voltage. We had to use 10AWG and one of the comments above mentioned that we should check that. Thanks again for your advice and expertise. Cindy
I think so. It’s a cloudy day today so I can’t do it. Is 10AWG sufficient for a 100/30 MPPT? It’s 10AWG to the bus bar (about a foot) and 8AWG out of the bus bar.
Some information about the smart networking. VE.Smart Networking
the system rises the voltage of the MPPT to compensate the loss over cable lugs or other resistors (poor crimping)
