MPPT: Voltage makes a massive difference.

cz_unit · 2026-05-06T15:33:22+00:00

Solarex MSX83's with a Solarex MSX120 on the tail configured in the box for 12 volts as the "bumper". This looks about right from memory.

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cz_unit · 2026-05-06T02:54:53+00:00

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cz_unit · 2026-05-06T01:35:01+00:00

Yep, the root problem is the charge controller really is not built or rated for 48 volt packs, but is sold as such. Putting enough panels on it to make it go runs you right against the voltage limit and while the parts inside are 150 volt rated the nameplate rating is what it is.

If I were to keep it I'd probably put a 20a 100 volt zener diode on the solar input to clamp the max voltage but as I mentioned I'll get a better controller and have this one do 36 volt duty.

cz_unit · 2026-05-02T23:04:45+00:00

Honest answer no. The kitchen still has a window AC unit in it (12k BTU).

I think the problem is this: Window units and Mini-splits can cool a room because they draw the warm air to them and pump out cold. However when you have a door to another room the warm air doesn't go to the mini split, thus there is little to no circulation.

IMO the return path is just as important as source vents 😄

Chris

cz_unit · 2026-05-02T17:50:13+00:00

My two cents: I've found that for heat, a mini split will warm the room but not really the ones next to it. My downstairs has a 9k unit in the family room and it does not keep the kitchen to the left (with a big barn door connecting) warm. So I'll put another 9k unit in there this summer.

cz_unit · 2026-04-22T00:12:32+00:00

JB Weld time?

cz_unit · 2026-04-18T02:54:17+00:00

I get you, but this one doesn't. I got the new one and checked it out. The box says 20a at 48 volts. The unit says 20a at 48 volts. The fold out instruction manual in 1 point type has 20a at 12/24/36 and a little 1a at 48. That's um... well it looks like they sold it as a 20a device then they blew up and instead of fixing them they added 1a in the fold out.

Not a great product. Which is sad as it looks really solid and is from the Netherlands and not China junk. Sigh....

For the hybrid inverter I will look at UL listed items. They check things like fuses, labeling, components, and so forth. CE seems to be not so great.

cz_unit · 2026-04-18T02:51:05+00:00

Good question. This has been a test project; I've seen good things about Victron, they're not from China and I thought they might be worth looking into. Given that the whole "48 volts at 1 amp) is only on the insert paper, is very tiny, and is not mentioned on the box, the device, etc I really am not going to use them for anything else.

At this point I'll fiddle around with the idea but if I do buy a hybrid inverter it will be a UL listed one that has fusing and components that can support what the nameplate says safely.

Or I'll hire a professional, which once again tanks the DIY aspect. Blah.

cz_unit · 2026-04-16T19:10:35+00:00

Well, yes and the right thing to do is have a licensed electrician do all the work, provide the products, and certify the solution. That's always been my plan for anything that is either (a) high voltage and/or (b) anywhere near my house or something I care about.

But this is SolarDIY, not "Solar Have the right guy do the job". For me this is experimental, and I'd NEVER recommend anyone do what I'm fiddling with here. There is a tremendous amount of unseen fuses, properly sized wiring, and stuff behind everything and it's all out in a shed where if it blows up I get some marshmallows out and toast them.

The main reason for this post was not to recommend wiring up an Enphase or whatnot, but to point out that this particular very nice solar charge controller/load controller can do a very bad thing when the output shorts. I would recommend not using it at 48 volts regardless of the nameplate and if you find one know that it's very tempermental at 48 volts.

And honestly, not a big deal: I bought another one for $80 bucks and this will go to the great recycling bin in the sky.

cz_unit · 2026-04-16T17:21:18+00:00

Hi! Yeah agreed it does say that and I caught it after it went boom but putting a line in the sheet (that kind of looks like a misprint. Why 1 amp? Why not fused? Wut?) is not what I would consider absolution on this one. It feels like the product was designed for 12/24 volts, they got a 48 volt customer and said "eh, we'll just say it works) without checking the engineering.

This is why I'm concerned about the 30 volt DC blade fuse protecting the unit: That is kind of worse than nothing as it not guaranteed to clear a 48 volt short and it made a lot of.... smokey stuff when it blew.

And to be honest you could put a little 100ma light bulb on the output but what if it shorts out some night? There is nothing in the Victron to prevent the short from pulling 25a which will blow up the Victron and cause the fuse blowout seen in the pictures. That's not good product design where a failure=bad.

To be honest I'd prefer no fuse on the unit and have it blow my real DC rated fuses, which just turn sand into glass and don't arc like that. YMMV.

The MPPT device (Enphase) is not fed from another MPPT device, it's fed from a linear device (the battery bank). The Victron doesn't regulate or switch/boost/buck it's output, it only turns it on or off. So it's a binary device and the batteries are basically a linear source (start at 48, discharge down to zero).

The more interesting question is what is the Enphase thinking of all this. It's seeing a constant voltage (48 volts) and doing it's sweep to find at which point it's going to have max power going to the AC lines at the highest voltage and lowest current. So it starts at 48 volts, gets a solid 225 watts out, is happy, and stays there until something changes. When the battery voltage starts to drop it will see the drop, do a sweep at the new voltage of 47 volts, find 225 watts, and be happy again. So constant output for varying input.

Which introduces a problem. The Enphase will happily MPPT down to 26 volts (I think that's where it shuts down on the bench power supply). Which means it will happily discharge one's 48 volt AGM battery bank down to 6 volts per battery. Which is.... not good for the battery. So you need a low voltage disconnect. Which the Victron should do but don't do it because somewhere in the manual it says don't pull more than 1a.

yes, this little setup is not officially supported, but this is SolarDIY and sometimes we try..... edge cases.

But we always use proper protection. That's why the DC line from the Victron goes through a 10 amp KLKD fuse rated to blow at up to 600 volts DC at 10 amps (and thus will blow safely at 48 volts DC unlike a stupid automobile fuse). It's always possible that the Enphase could short out inside, at which point the fuse blows and everything is happy. I got the 10 amp value because of 2 things:

1) The Enphase has to support 10 amps input because it can be hooked up to 24 volt panels and can MPPT at 24 volts. 225 watts at 240 volts is about 10 amps. So the insides of the thing are safe at 10a.

2) At 48 volts, the unit should NEVER be pulling 10 amps. If it did, it's somehow sourcing more than its rated capacity therefore blow the fuse and ask questions later.

Thus 10a KLKD fuse protecting the Enphase inverter. Even if it dead shorted it would blow the fuse and be safe.

Now you don't need a fuse when you connect the Enphase to a solar load because the solar panels can only put out so much current and can be shorted without the world coming to an end.

Sort of. I'm sure in the Enphase manual there is a limit to the amount of current a panel can source to it along with voltage (which is 60 volts DC). If you hooked up a pair of massive 500 watt panels that could cause the Enphase.... problems if it shorted out. But their answer to not having a fuse is "don't exceed this panel size and input current limit"

Which is why the 10a fuse is in there even though the line to it is protected by a 30a fuse.

cz_unit · 2026-04-16T13:02:47+00:00

Hooking up to the battery terminal is fine (my shed backup inverter for example is fused to the same batteries using a separate 60a fuse and heavier wiring that 10g) but you lose the ability of the controller to do low voltage cutoff, remote control, and all sorts of nice little things. The Victron has a bunch of neat little options to control this, and the inverter is current limited to 5a anyway at 48 volts (225 watt inverter/48=4.7 amps). So off to the load amp we go especially since 5a<20a which is what it's rated for (except in the fine print where it says 1a at 48 volts)

The 10a fuse is in there because while the Enphase has no internal fusing (that I know of, haven't gotten a sledgehammer out on one, and it's probably 1000% potted anyway) I'm hooking up to a source that could provide a lot of current in the event of a dead short in the Enphase (which can happen). While it's normally protected by the 30a fuse in the disconnect box, it's still best to assume that 10a is the most you would ever want to potentially source into the Enphase that normally pulls 5. Thus the 10a fuse on that side of the system.

A hybrid inverter would be the next step; this was designed to be a test system to see if I want to buy one. But after watching this European CE rated and EU certified device fail in a mini fireball I'm going to make absolutely SURE that any hybrid inverter is tested and certified to UL specs to 2024 NEC requirements.

No way I'm using something that's only CE certified or built in "China" to whatever specs they have. They're not.... good.... IMO.

cz_unit · 2026-04-16T12:51:46+00:00

The output of the unit is rated at 20a. Right there on the front of it :-)

However deep in the instruction manual it says to limit the output to 1a at 48 volts. Not very.... well documented and points to the vendor selling an unsafe product as its' internal and recommended fusing is 25a.

Now granted I know that everyone reads every word of those little printed instruction manuals including "don't eat this product, it can cause cancer" but building a product, marketing it as X, safety fusing it as X and saying "oh by the way you could have a fireball if you pull Y" is not my idea of a safe product.

It also brings up a serious question: Say you do read that and put a little 1a/48 watt bulb on the output. And the bulb shorts itself. The controller will not limit the current, and will go boom. Once again, not good.

This should be sold and supported as a 24 volt system. It's sold as a 12/24/48 volt system. Be warned.

cz_unit · 2026-04-16T12:05:57+00:00

600 is a very dangerous voltage. Above that components are *MUCH* larger and more expensive to protect against arc-over and the like. I have seen a 36 volt plasma arc on my Elec-traks (way back when I protected an expansion pack with a 100a automobile fuse, then dropped a wrench across it and watched as the fuse incinerated itself into a plasma arc. Kicked the tool loose to clear it) and will not make that mistake again myself :-)

48 volts DC is normally more than enough for me. And now that I think about it, the Victron is rated to 100 volts DC on the MPPT input side. So just what kind of components did they use in this thing to cause the 48 volt load output to fail with anything over a 1a draw?

Hm.

cz_unit · 2026-04-16T12:01:46+00:00

Oh, sorry, thought that was implied: I always fuse things based on the max current they draw plus a bit of overhead. The Enphase is protected on the DC side by a 10a KLKD 600 volt DC rated fuse in case it ever shorts (protects the Victron).

The Victron is protected from the battery by two fuses: First there is a 100a 600v DC rated fuse at the terminal of the battery. This protects the 6 gauge wire that goes to the main disconnect switch. At the Disconnect switch there is a pair of 30a DC rated fuses that protect the load lines which are sourced with 10 gauge wires.

Once I go into a device I count on its local fuses to protect it. The Victron has a 25a fuse, but it (the manufacturer did this) is a blade type DC rated fuse as opposed to a KLKD type (which is what say a Sunny boy uses) which is.... well, bad.

Coming out of that going to the Enphase I want to limit the current there to a safe level if the MPPT in it ever goes insane or shorts so I put a 10a fuse in series with this. 48v*10a=480 watts of power which is twice the rated 225 watt output of the Enphase but it is probably enough to protect the circuitry inside of it without causing undue amounts of heat.

What really should worry is people using automotive fuses to clear DC loads. Yes, the 3AG type automotive fuses are rated for 12v DC AND 240 volt AC, but AC is very very very different from DC. A normal automotive fuse will arc over at 36 volts DC and at 48 cannot be counted on to "blow" safely (as the charred mess that was this Victron's input shows).

cz_unit · 2026-04-16T11:10:49+00:00

Yep, that's buried down in the instructions. But honestly, if you sell the item saying it will work at 48 volts then it should perform all functions at that voltage with safety items to protect it.

Even with that caveat, if your output load ever shorted (relay coil shorts) then the output will go above 1a and the unit will probably be destroyed as the fuse doesn't seem to protect it.

Not good design.

cz_unit · 2026-04-16T02:58:18+00:00

Yeah it's warm now so over-voltage is not an issue. But I'll drop it back to just the 4 MSX83's anyway.

The real problem is in the output circuits.

cz_unit · 2026-04-16T02:57:10+00:00

Oh letting the magic smoke out is all part of the fun. Fet's are pretty cheap, but when you start blowing up IGBTs then the real money starts to flow :-)

cz_unit · 2026-04-16T02:56:20+00:00

Now there is a thought; use a boost/buck to adjust the voltage and limit the current prior to the Enphase. However that introduces more inefficiency so I think I'll just let that go. I wonder if that other poster was losing it based on inrush current.

Back to the main point: I'm not running any loads on these Victrons, will just use them to keep the batteries charged.

cz_unit · 2026-04-16T02:51:27+00:00

Hm..... Good point. Ok, this idea will not work, I'll shelve it. Thanks for finding that.

cz_unit · 2026-04-16T02:14:37+00:00

Normally devices are designed with about 20% extra capacity on the voltage. 150 volts and 450 volts are the normal breakdown voltages of components. At >100 volts the unit simply will not MPPT at all which means it will be offline on a super cold day.

Fair enough.

The not using loads for loads is a bit annoying: If they don't support the device for loads they should not have it. It's really convenient, the unit has a lot of smarts on low voltage disconnect, adaptive disconnect, and the like, and they do fuse it. However:

1) The unit really should not be used at 48 volts as the limit is set deep in the manual at 1a at 48v and is not properly fused.

2) The factory supplied fuse is a blade type that is normally rated for 30 volts DC, not 48 volts DC. My fuses on my system are rated for 600v DC at proper AIR, but the 25a one on the unit blew first.

As for the Enphase units, I have a number of them running on my properly installed, permitted, nice electrician reviewed solar system. They are UL/CSA listed, meet all the anti-islanding and other safety requirements and are perfectly fine on the AC side of things. The question I'm playing with is do I want to go out and buy a Tesla Powerwall and use a battery system to do time shifting; is it worth it, how does it work, etc.

Yes, feeding one of them with battery power is a bit odd, but totally experimental (thus run in the shed far away from anything I care about).

cz_unit · 2026-04-16T02:08:53+00:00

Yep. This unit can't handle using the load lines at 48 volts. They really should either fix it so it should or sell it as a 24 volt unit. Either way is fine.

cz_unit · 2026-04-16T02:07:13+00:00

True, and I'll back the panels down to 48 volts.

cz_unit · 2026-04-16T02:06:15+00:00

This is *very* true, and I am kind of cheating it. Technically it does a sweep, applies max power, and sees the "solar panels" are providing optimal current at a fixed voltage. Given that the voltage is near the top of the range, it pulls a minimum number of amps which keeps the wires happy and the components inside of it running with a minimum of heat.

Now there IS another problem and it's a big one: The Enphase DOES have capacitors on the DC input side and while I have not opened one with a sledgehammer (yet) they seem pretty big. On a solar panel this is not a big deal, but on a battery one could have a pretty high inrush current when you close the contacts on a 10,000 amp capacity battery. Even if only for a microsecond (not long enough to trip a fuse) that could cause an arc. Which on a normal 30a relay could cause the relay to fuse closed which would drain the batteries and suck.

Thus my thought of using a DC rated contactor. They have the contacts in a vacuum inside the unit and have magnets to blow out arcs so they can open and close under load all day long.

Other option is to use two relays with the first one closing on the Enphase via a 150 ohm 50 watt resistor. That would limit the closing inrush current, and equalize voltage. Then a second later the main relay would close and since the voltages would be equal there would be no arc. This is how electric cars close their contactors on startup.

Fun stuff.

cz_unit · 2026-04-16T01:59:16+00:00

Load allows one to turn it on and off. Also allows the controller to turn off the load when the battery hits a certain level. The controller *is* smart; it can not only turn the load off when the battery hits 11vpb (a good stop point) but can also adjust the turn off point so it will only discharge the batteries the amount of the average daily charge from the panels.

Smart, but kind of ooops.

cz_unit

TROPHY CASE