Incompatible 100w solar panels? 100w x 4 in series

wpns said:

Because the Zener would have to be rated at 400W? And the crowbar would have to be rated at Isc for the maximum overpanelled case. Much easier to publish specs and require that they not be exceeded.

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I was thinking of those cold winter mornings when the sun is just coming up. The panels are over voltage but producing almost no current. Once the charge controller has enough current to work with, it pulls the panel voltage down to a safe level.

Yea I think I spoke too soon. Woke up this am. Now panels are still shaded but the controller still said it was night and had 0.2V PV. Unplugged the solar and plugged it back in and now it's sitting at the open circuit voltage of 21V since I just have 1 panel connected. I don't think it'll actually end up charging once the sun is on the panels but we shall see... Im thinking I'll have to try and haggle the seller for a replacement...

Yea it doesn't work. 22v PV now. I'm seeing correct voltage but nothing will initiate charging so it's a nice paper weight now. My pwm controller is already at 1A charge and this mppt just sits at 0A

matttelz said:

Im thinking I'll have to try and haggle the seller for a replacement

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So you blew it up and now you want a replacement? It was working before you added more series panels, no?

wpns said:

So you blew it up and now you want a replacement? It was working before you added more series panels, no?

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Correct but my 4 series panels shouldn't have exceeded the 100v max... I monitored it pretty close and the max I ever saw was around 90-91v

matttelz said:

Correct but my 4 series panels shouldn't have exceeded the 100v max... I monitored it pretty close and the max I ever saw was around 90-91v

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That's an easy 108 if it normally maxes at 90-91v.

Take the Voc reading from a panel and multiple it by 4 (because you have 4 in series) and the multiply that by 1.2.

THATS your max volts possible.

I just went and looked up your panels.

24.3voc x 4 = 97.2v

97.2 x 1.2 = 116.64v

POOF

matttelz said:

shouldn't have exceeded the 100v max

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Shouldn't have, or couldn't have? @Crowz and others have pointed out you were skating pretty close to the edge.

230w with 3x100w panels is not unreasonable.

That's 76% which is perfectly reasonable in real world conditions

I suggest looking into "overpanelling" if you are looking for more power

Crowz said:

I just went and looked up your panels.

24.3voc x 4 = 97.2v

97.2 x 1.2 = 116.64v

POOF

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Oh well...I reserve the right to get smarter then....

Wish I would have known that somewhere but alas my own ignorance might have got the best of me with this device. Thanks for sharing. I haven't heard that one but I will definitely know for next time!

Sometimes I research as I go and other times I experiment...looks like this one got the best of me. That darn 4th panel got me good... I kind of figured the seller won't replace the item, especially now that it would appear to be my own fault. Kind of surprised the unit still powers on and reads voltage just fine...just doesn't charge. I'll stick with my PWM controller for now till I can save up enough to give MPPT another go... this time maybe a much larger one so I have a way wider safety margin.

matttelz said:

I'll stick with my PWM controller for now till I can save up enough to give MPPT another go... this time maybe a much larger one so I have a way wider safety margin.

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With the four panels in parallel, right?

matttelz said:

I couldn't figure out all spring why my 4 panel setup which should be getting around 380-390W would cap out more so around 240-260w.

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260w would be about 65%. Thats about what I would see with grape solar 100w - 4s with very hot panels.

sunshine_eggo said:

With the four panels in parallel, right?

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Yes.

Lol I like how this thread has progressed.
1) beginners corner
2) bypassed safety check and went straight to danger zone
3) up in smoke
4) show and tell

Haha

matttelz said:

Yes.

Lol I like how this thread has progressed.
1) beginners corner
2) bypassed safety check and went straight to danger zone
3) up in smoke
4) show and tell

Haha

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In parallel the voltage would be constant and current would add.

So well below the max voltage. Seems like you are adding volts as if they are in series.

So, confirm please the connection method.

Series
Mppt negative -> panel1-> panel2 -> panel3 -> panel4 -> mppt positive

Or Parallel
Mppt positive ->> panels positive -->> panels negative ->> mppt negative

I ended up getting a new 60A version of the charge controller. Should be here next week. Sadly no refund/return but again it was my fault so I'm not really disappointed by that.

This time around I'll definitely stick to only running 2 panels in series. Apparently this new controller supports up to 720w and a PV range of 20-80V so using some math....

24.3V x 2 = 48.6V
48.6V x 1.2 = 58.3V which should be well within the safety margin

In the meantime when I see some additional 100ah batteries go on sale I'll probably pick up a few more. My idea is to have at least 5kw of battery storage at this point. I've been able to successfully work with 2kw and my solar setup just fine for a couple of months now without getting close to needing recharging from the grid. I use my setup to power my 3 laptops, monitor and desk lights in my office.

What did you end up getting?

Word to the wise -

Adding batteries in parallel -

Fully charge all batteries before connecting
use a bus bar of sufficent size for the current all batteries can put out (i.e. 4 x 200amp batteries = 800a bus bar, you can fudge here a bit IF it is mounted in metal or on a non-flamable surface)
If your cables from battery to bus bar are longer than 12" put a fuse on both ends - MRBF on the battery posts and either MRBF or class T at the bus bar end.
Make sure to use a class T between the bus bar and the inverter.

The reason for the extra precautions is with 3 or more batteries in parallel a short either from a defect inside a single battery or from shorting at the battery post of one of them. All the current from the other batteries will be dumped through the bad batteries wire to the short.
i.e. 4 x 200ah batteries = 800amps total. Assume one has an internal short. Now the current from the other 3 (600amps) will be pulled into the short. Even 2/0 cable will get hot enough to melt the insulation off in a single second.

Now, when I am building a setup like that I prefer to use cables capable of my battery current - then the fuse is sized 125% of that.

So 200amp battery = #2 welding wire (204amps) and a 250amp fuse at both ends of the wire. The alternative is to use 2/0 and fuse at the bus bar end. This depends on the internal BMS to cut current if there is a short on it... BMS fuse shorted if they blow... But you can decide if you want to take that risk.,

for 100amp batteries in parallel I would use #2 windy nation welding wire and 125amp fuses on each.

It never hurts to use larger wire than needed.

robbob2112 said:

What did you end up getting?

Word to the wise -

Adding batteries in parallel -

Fully charge all batteries before connecting
use a bus bar of sufficent size for the current all batteries can put out (i.e. 4 x 200amp batteries = 800a bus bar, you can fudge here a bit IF it is mounted in metal or on a non-flamable surface)
If your cables from battery to bus bar are longer than 12" put a fuse on both ends - MRBF on the battery posts and either MRBF or class T at the bus bar end.
Make sure to use a class T between the bus bar and the inverter.

The reason for the extra precautions is with 3 or more batteries in parallel a short either from a defect inside a single battery or from shorting at the battery post of one of them. All the current from the other batteries will be dumped through the bad batteries wire to the short.
i.e. 4 x 200ah batteries = 800amps total. Assume one has an internal short. Now the current from the other 3 (600amps) will be pulled into the short. Even 2/0 cable will get hot enough to melt the insulation off in a single second.

Now, when I am building a setup like that I prefer to use cables capable of my battery current - then the fuse is sized 125% of that.

So 200amp battery = #2 welding wire (204amps) and a 250amp fuse at both ends of the wire. The alternative is to use 2/0 and fuse at the bus bar end. This depends on the internal BMS to cut current if there is a short on it... BMS fuse shorted if they blow... But you can decide if you want to take that risk.,

for 100amp batteries in parallel I would use #2 windy nation welding wire and 125amp fuses on each.

It never hurts to use larger wire than needed.

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Yea, I currently have 10" 2awg wires between both batteries in parallel, as I add more I think I'm going to need a bus bar setup. Should I fuse each battery for safety? I currently don't have any fuses since I only have 2 batteries but I know that will change in the future...

I'd ideally like to go to a 24V system but I might have to wait for that.

I was able to get a good "deal" on the Pow-M60-Pro controller. I've seen some controversy regarding the quality of the controller but apparently I didn't learn from my first experience with the 40A so I'm willing to test out the 60A version...lol

I'm not too concerned about pulling heavy loads with my setup. If anything, I'll likely max out around 500W max with what I currently have hooked up to my inverter. The inverter alone is only 1200w so even if I get into a situation where I need it to run a fridge/freezer as backup power in-case of a power outage from the grid, I still won't be pulling a ton of power.

Quite honestly, long-term in this home might be up in question which is why I'm less likely to invest more and more into a full blown solar setup. The home is soo incredibly inefficient since it was built in 1948 that I don't expect even the best system to be able to power this home entirely off grid... In the summer, I'm using around 50-70KW daily...

If I had to guess, I'll probably pick up 2 or 3 more batteries, build some type of cart/wheeled storage container for everything and call it a day...

Oh and with the size of each full size container for the 100AH batteries, at some point when I get 4 or 5 batteries, I'd like to disassemble each one and consolidate just the cells and BMS into a smaller form factor...so that would also likely change the wiring setup. The full size battery cases for these 100AH batteries are a complete waste of space ATM...

You should fuse each battery period. Minimum would be a MRBF on each positive post. Never count on a BMS to act as a fuse in a situation like a dropped wrench.

The cheaper batteries like the 100ah versions are almost all welded post so you can't disassemble to a cell level. You can loose the case if you are very careful about where they are installed. so nothing can get at them like mice or other pests. Personally if I were concered about space and weight I would use the mini verion of the 100ah battery. I have one of these at 19lbs and it is about 1/2 the size of a car battery.

For stringing in parallel read the MFG documentation - they generally allow 4 in series and 4 in parallel. They all recommend only using a single brand/age battery which is CYA I think. It is generally recommended to stick with pouch or prismatics verse mixing them.

For your use 24 is overkill and doesn't buy you much except the ability poke more power in from a single MPPT. But you can add another MPPT when you need more recharge than you have.

What is your overall plan?

For me -
12v is fine for UPS or single purpose battery (I run my cpap off the mini and my server off a 200ah version)
24v is good for RV/trailer/etc if it doesn't have a high 12v load like an AC already in service
48v is the end goal for a house or if you are thinking of upgrading - the different parts are cheaper and the wires are 1/4th the size.

I am planning solar for the house at some point, so any component I buy like the MPPT must support the now (12v) and the future (48v). I recently bought a victron 250/100 mppt because it supports both. It is way overkill for my "now" and I will need a second one or more for the future.

I just got the 60A version delivered this afternoon. Was able to take a quick peek at the internals... Pretty solid IMO... I was only able to peak out around 310W with my 4 panels connected all in parallel, Haven't rewired them for 2 in series yet. Not great production but its probably partly due to running only 1S and also the angle of my panels right now...

From what I can tell it looks like its the newer version of the PCB so that's promising.

matttelz said:

I just got the 60A version delivered this afternoon. Was able to take a quick peek at the internals... Pretty solid IMO... I was only able to peak out around 310W with my 4 panels connected all in parallel, Haven't rewired them for 2 in series yet. Not great production but its probably partly due to running only 1S and also the angle of my panels right now...

From what I can tell it looks like its the newer version of the PCB so that's promising.


View attachment 224337
View attachment 224338

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The front of the board looks good...

The back of the board where they globbed on the solder is like amature hour.

The two up top look OK but the ones that look like they tried to add material to the run in the form of solder looks like they had a cold or undersized iron.

There's a GND Tx Rx and VCC communication solder points on the board...not sure if I were to just wire up a USB cable to it that I'd be able to do anything unless I had some sort of drivers for it but I found that interesting on the board.

matttelz said:

There's a GND Tx Rx and VCC communication solder points on the board...not sure if I were to just wire up a USB cable to it that I'd be able to do anything unless I had some sort of drivers for it but I found that interesting on the board.

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Probably a place for a little JTAG tester to come and connect and test functionality, program firmware or get a readout of some values.

You can solder in some pins/wires and hook it up to an adapter and see what you get. Just realize it should all be basics 1vpp logic levels and if you make a mistake you can brick the board.

Maybe start with an O'scope and see if there is anything there before futzing with wiring it up.

So it hasn't been super sunny this week here but I've had some time during the afternoon with little clouds. I've been seeing 320-355w on the charge controller but not really anything above that. I'm running 2S2P on my panels and the controller is showing roughly 34-36V in MPPT mode. A good bit of the day is spent around the 220-290w range with the 4 panels so its not bad but not stellar.

I'm less concerned about adding more solar to my setup ATM than adding more battery storage capacity. 2kw is pretty low and its surprising how quick I can burn through that... it'd make more sense to pick up 2 or 3 more batteries to get 4-5kw and have a decent backup system for short term. Earlier this week since we've been so hot, we had a day where the home energy usage almost hit 80kw for a single day... pretty crazy and no amount of battery/solar would replace that so I'm just trying to keep this setup in perspective of my total home usage.

Ideally I'd jump to 24-48V with like 20Kw of storage but then at that point I'm encountering issues with tying that system in my with my existing electrical and permits/code etc... I think I'll stick with the smaller DIY setup for now...

Edit: well sort of scratch that. Eco-worthy is apart of the 20% off ebay sale for July 4th. Picked up 2 more 100w panels and some additional wire I need. Looks like I'll finally be able to build the mount I've wanted for the solar panels all tied together and upped my system from 400w to 600w.
I also have an idea of running a 5k btu air conditioner off the giandel 1200w power inverter during the day in the summer but I'm not sure it can handle the load. Apparently they run around 400-500w continuous and I'm not sure on the inrush current... I figured if I run it upstairs which gets so hot during the day for 4ish hours that would be covered by battery+solar...