It is only natural to want to improve or hot rod your system. Know the limits, though.
Despite all the political controversy, Facebook remains a useful tool, especially the “groups” if you are into a special interest. I don’t have a FB account, but I hijacked my wife’s account to join a group of folks who also have the mobile solar generators, like the one I bought. (See TurboBeast story).
There is a wealth of information to be shared on such a complex combination of mechanics and electronics. Some people are very knowledgeable and some are total newbies. There’s lots of sharing and lots of creativity.
Let’s examine the system. There are 10 solar modules, 60 cell units from 230 to 270 watts, depending on build date. They are arranged in two strings of 5, meeting in a MidNite Solar (MS) combiner box and brought under control by a MS250 charge controller. The MS250 charges 4000 lbs. of forklift batteries, which may be flat plate or the newer tubular plate flooded lead acid batteries. The batteries supply a pair of Sunny Island 6048 inverters, which combine to output 12kw of 110/220 power. The Sunny also controls my autostart diesel generator, so I’ll have to try really hard to run down those batteries.
The 12kw output will easily supply most houses, I think. I’ve seen houses run on less. The weakness in using these rigs to run a house, though, is that they have only 2500 watts of solar and around 1000 ah of battery. 2000+ ah is working great for me. I have found the hard way that the recently revised recommendations for battery sizing are much more practical than the older assumptions. And more expensive, of course.
The 2500 watt solar limitation is pretty much a physical limitation. There are just so many panels you can mount on a 17′ trailer bed. Yet, since these were built, panel output has increased.
Courtney, for example, after consulting with me, replaced his panels with 60 cell 320 watt panels. That’s a 700 watt boost and he stayed safe.
The MidNite Solar charge controllers rate things a little differently than some others. Many show the output CURRENT in their names, like an Outback FlexMax 60 is rated for 60 amps or a FM-80 is rated for 80 amps. If you want to power the world, I think there is even a FM-300! But the MS250 is talking about volts, when it puts a number in the name. Whereas the FM is rated around 150v, if I remember right, the MS is rated at 250v. The difference affects how many modules and what kind of modules you can put in a series string.
With a 150 v limit, you’ll find that 3 typical 60 or 72 cell panels in series is a good way to go. They each have a peak output of around 36 or 46 volts, but always consult the data sheet or the label on the back of the module. On the Sunelect.com website you’ll usually find a datasheet download available. Yes, consult the sheet. I have bought some modules from Roberto that had 90 volt output. I just run those in parallel on a 150v charge controller.
With the MS250 controller, you can easily run a string of 5 60 cell modules, as long as you stay with in the power rating of the controller and the 320 watt modules do this. Then one of the guys, Mike, comes up with this: “I bought one with the panels swapped out for 72 cell, 370 watt panels. Nothing has burned up yet, but it has problems. The Midnite is in “hypervoc” mode most of the time, and screams like a banshee. I wouldn’t recommend it.” Mike lives life on the edge.
The problem is that he has exceeded both the voltage and current ratings of his MS250 charge controller. That it is still running is a testament to robust design, but I suspect that controller will live hard, die young and leave a charred corpse. Which reminds me, do you have a fire extinguisher around your system? Mike admits that his charge controller is literally hollering about its working conditions. The proper way of doing this upgrade would be to add an additional charge controller. He’s about to buy a new one, anyway! Or two, if he wants to put it right.
Dale had another solution: Leave off two of the panels, which would defeat the upgrade, “Or, wire the two left off panels in series, straight to the battery? What could go wrong overcharge the battery if there’s not much load on the system, but otherwise maybe ok. One 72 cell panel wouldn’t be high enough voltage to charge the battery”
OMG, NO-OOOO! It might actually work, but if you left it unattended for a while you could boil out the batteies, which I think run around $5-6000 EACH. You’d also miss out on that MPPT goodness that a quality charge controller can provide.
I guess what this comes down to is think creatively, share ideas with others, ReadTFManual, and keep a fire extinguisher handy.
–Neal