Solar Controller Help!

[-Icarus-]

Hello! I'm having difficulty with my solar controller, and I'm not sure why. The current system I'm running is a Victron Energy 100/20 48V solar controller, run into a 48 volt LiFePo4 battery bank, and it's run off a Sunpower 320W/48V solar panel. Previously, I was running a 48 volt lead acid bank, and before that I was running a 12 volt bank, with a 100/30 controller. The solar panel and equipment runs are all 8AWG, and the battery to system runs are all 2AWG.


I'm getting heavy throttling on my solar charge input, and I'm not sure why. The highest I saw was roughly 175 watts to the bank, but it quickly dropped off to 60-70 watts (roughly 1 amp), and it's stayed there without change. The controller was behaving similarly on the previous bank; it would sit at ~100 watts when connected, no matter the sun state. I figured this was because I had a dead battery (one of the batteries in the bank dropped down to 10.0 volts unexpectedly, and never recovered). Hence, the lithium. Oh, and the same lead-acid bank previously ran on the 100/30 with no issues whatsoever. I regularly saw 320-350 watts from the panel.


The strangest thing, is that if I disconnect the battery bank, the solar controller immediately jumps charge to 90-150 watts! This is to accomodate the load (charging a computer, fans, etc). As soon as I reconnect the battery though, the charge immediately drops to 60-70 watts again, and just stays there. The temperature seems to be fine; the unit isn't hot to the touch.



I'm really stumped, and I could use some help. Thanks in advance!

[rslifkin]

If the OCV and VMP of your solar panel aren't both above 60 volts, I wouldn't expect that setup to work. The panels need to be significantly higher voltage than the battery bank you're trying to charge.

[-Icarus-]

No, the panel voltages are around 50-58 volts. That makes a lot of sense! I guess I need to cobble something together. Do you think I could put a spare 12 volt panel in series with my 48 volt panel? I have an extra 120 watt 12 volt panel that I could hook up.

[HeywoodJ]

AFAIK the Victron controllers are all 'buck' converters - they can reduce voltage but not increase it. There are 'boost' MPPT controllers on the market, and buck/boost units, but these are much less common. Still, something along those lines would be the simplest solution. Once you get to 48V systems is may narrow the field a lot.

If you want to add a panel in series to boost the voltage it would be unconventional to add a different panel, but it is possible. The critical factor is that the current output of the two panels should match, the string can only produce as much current as the lowest current panel in the string - that panel essentially regulates/prevents the other panels from contributing any current in excess of the low panel's capacity. If you had a 12V panel that had a higher current rating than your 50V panel then you could probably get away with it, you would lose a little from the 12V panel. But if your 12V panel is lower current it will restrict output from your 'main' panel and you're back where you are today. One caveat to all that, the current rating of the panels should match in all light conditions, which can be difficult if you have different cell technologies, and Sunpower is different from most.

[Rohan]

You might get better responses in the generator/battery/solar forum:

https://www.cruisersforum.com/forums/f14/

[markcouz]

Originally Posted by Rohan

You might get better responses in the generator/battery/solar forum:

https://www.cruisersforum.com/forums/f14/

Gotta say the responses received so far are spot-om, no need to duplicate the thread.

The panel voltage is too low.

[Pete7]

I am curious why you have a 48v bank on a Trident 30ft yacht? Is this for electric propulsion by chance?

If so, add an identical 320w solar panel and a new MPPT, or a pair of slightly smaller panels that fit the specs of the existing 100/20.

[-Icarus-]

Originally Posted by Pete7

I am curious why you have a 48v bank on a Trident 30ft yacht? Is this for electric propulsion by chance?

If so, add an identical 320w solar panel and a new MPPT, or a pair of slightly smaller panels that fit the specs of the existing 100/20.

I'm actually on a different boat now! I came into possession of a vessel called Semira, a Pearson Invicta 37. I've been doing a full refit, and yes, the battery bank is for an electric motor. I currently have an el-cheapo 3 horsepower motor in for prototyping purposes, but once I'm happy with the setup, I'm going to acquire a 10KW motor for auxiliary propulsion. I hate diesel maintenance.



Thanks for all the replies! Ultimately, I've decided to go with installing another 100W/12V panel in series. That should bring the voltage up considerably; I'm going to be redoing the solar installation anyway (two 400W panels in series, roughly 90V total potential), but I need to get mounting hardware fabricated, so for now I'm going with what I have.


Here's a terrible video of the motor's first test run : https://www.youtube.com/shorts/YmZJ5...?feature=share . I improperly sized the sprockets; It's got a 5:1 ratio, and it actually needs a 10 or 11:1! The motor as installed pushes the boat at roughly 1.8 knots in a flat calm, and with the proper ratio should accomplish 3.5 knots.

[AKA-None]

Did you touch across your circuit breaker there