Re: [electricboats] Complex design issues

Check you math. All panels in series as in 6S for 16V/7A panels is 96/7, not 96/14.

On 2024-12-08 9:55 am, Dale Shomette via groups.io wrote:

So Jeff, you have two sets of three panels, each three panels in series and each three panels with their own controllers. You believe they are 16volt/7amp panels, correct? So in series, the maximum voltage from your three panels would be 48 volts and seven amps.

Together, the six panels (as individual sets of three) would theoretically pull out 96 volts and 14 amps. Are your Victron controllers charging your batteries individually? Why do you need two Victron 150/35's when one would handle both sets of three panels? Why not put each two of the six panels in series with each other, then put the six in parallel. Wouldn't that give you a maximum of 48 volts and an increase to up to 21amps to your battery bank? Of course, I have no idea how big your battery bank is and 48 volts might not do it for you. I will need a minimum of 54 volts for each of my four battery banks but will be charging them individually. I think your Victron 150/35 would be perfect to do that but was thinking that at full charge of a bank, I would just switch over from that bank to the other and only need the one controller. Is that reasoning sound from your perspective? By the way, what is your average collective sunlight day where you are? 

Thanks Again,

Dale

On Thu, Dec 5, 2024 at 10:32 PM jeffsschwartz via groups.io <jeffsschwartz=hotmail.com@groups.io> wrote:

Hi Dale,

It's been a few years since I picked them up but I believe they're 16V/7A.  I have 6 of them so I wire 3 in series and then the output from the 3 into the MPPT controller, then repeat for the second controller.  When I look at the output from the panels on the Victron app on my cell, I'm seeing around 54V go into the batteries per controller.  I've never seen the total current from both controllers go about 3A even on the sunniest of days.

 

On a mid summer, no cloud day, I'll get a total charge of around 2 KW between the two controllers.  That may partially be due to panel placement, my boat's on a 3 point mooring facing south so the angles are not optimal.

 

Regards,

Jeff.

Re: [electricboats] Complex design issues

So Jeff, you have two sets of three panels, each three panels in series and each three panels with their own controllers. You believe they are 16volt/7amp panels, correct? So in series, the maximum voltage from your three panels would be 48 volts and seven amps.

Together, the six panels (as individual sets of three) would theoretically pull out 96 volts and 14 amps. Are your Victron controllers charging your batteries individually? Why do you need two Victron 150/35's when one would handle both sets of three panels? Why not put each two of the six panels in series with each other, then put the six in parallel. Wouldn't that give you a maximum of 48 volts and an increase to up to 21amps to your battery bank? Of course, I have no idea how big your battery bank is and 48 volts might not do it for you. I will need a minimum of 54 volts for each of my four battery banks but will be charging them individually. I think your Victron 150/35 would be perfect to do that but was thinking that at full charge of a bank, I would just switch over from that bank to the other and only need the one controller. Is that reasoning sound from your perspective? By the way, what is your average collective sunlight day where you are? 

Thanks Again,

Dale

On Thu, Dec 5, 2024 at 10:32 PM jeffsschwartz via groups.io <jeffsschwartz=hotmail.com@groups.io> wrote:

Hi Dale,

It's been a few years since I picked them up but I believe they're 16V/7A.  I have 6 of them so I wire 3 in series and then the output from the 3 into the MPPT controller, then repeat for the second controller.  When I look at the output from the panels on the Victron app on my cell, I'm seeing around 54V go into the batteries per controller.  I've never seen the total current from both controllers go about 3A even on the sunniest of days.

 

On a mid summer, no cloud day, I'll get a total charge of around 2 KW between the two controllers.  That may partially be due to panel placement, my boat's on a 3 point mooring facing south so the angles are not optimal.

 

Regards,

Jeff.

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Re: [electricboats] Complex design issues

Hi Dale,

It's been a few years since I picked them up but I believe they're 16V/7A.  I have 6 of them so I wire 3 in series and then the output from the 3 into the MPPT controller, then repeat for the second controller.  When I look at the output from the panels on the Victron app on my cell, I'm seeing around 54V go into the batteries per controller.  I've never seen the total current from both controllers go about 3A even on the sunniest of days.

 

On a mid summer, no cloud day, I'll get a total charge of around 2 KW between the two controllers.  That may partially be due to panel placement, my boat's on a 3 point mooring facing south so the angles are not optimal.

 

Regards,

Jeff.

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Re: [electricboats] Complex design issues

Jeff, what's the volt and amperage rating on your panels? Why use three controllers, one for each panel?

On Thu, Dec 5, 2024 at 3:15 PM Dale Shomette via groups.io <dashoway=gmail.com@groups.io> wrote:

Thanks Jeff. I'm taking a look at Victron now.

On Mon, Dec 2, 2024 at 10:46 PM jeffsschwartz via groups.io <jeffsschwartz=hotmail.com@groups.io> wrote:

I'm using Victron MPT 150/35 charge controllers on each of my 3 panels that are in series and it has no issue evening out the voltage.  It has a rotary switch that lets you set the charge profile depending on the battery chemistry.  I don't think it converts excess voltage to current (probably just regulates it down to the correct level) but it has never damaged the batteries during charging.

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Re: [electricboats] Complex design issues

Thanks Jeff. I'm taking a look at Victron now.

On Mon, Dec 2, 2024 at 10:46 PM jeffsschwartz via groups.io <jeffsschwartz=hotmail.com@groups.io> wrote:

I'm using Victron MPT 150/35 charge controllers on each of my 3 panels that are in series and it has no issue evening out the voltage.  It has a rotary switch that lets you set the charge profile depending on the battery chemistry.  I don't think it converts excess voltage to current (probably just regulates it down to the correct level) but it has never damaged the batteries during charging.

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Re: [electricboats] Complex design issues

On solar cells in series vs parallel: If all things were equal, series strings would not be preferred, specifically because of the direct effect that shading a single cell in the string has to the output.  It's a huge price to pay---just a splat of seagull poop on one cell that drops its output to 40% will drop the entire string's maximum current output to 40% as I see it.

So, ideally, solar panels would parallel ALL of the cells to eliminate this huge penalty.  The reason panels are not made this way is because of the very low voltage (around 0.58v Voc) put out by a cell.  Boost converters just can't boost this low voltage up to 12v efficiently, so cells are put in series on panels.  And so some of the earliest panels put out maybe Voc~18v and today's panels, with 32-96 cells have Voc from 20v to around 60v.

Now, to reduce the shading penalty, solar panel manufacturers often (always?) include some number of Germanium bypass diodes such that that panel's output will drop in voltage but can still deliver an optimal high current.  It's been suggested to use panels with at least 3 such diodes.

But let's say you have panels on port and panels to the starboard.  It might make best sense to put the port panels in series, same with the starboard ones and then either parallel up the 2 strings and connect to the MPPT controller or send each string's output separately to a converter.

 

It helps to think about lithium battery configurations for EVs these days.  It used to be (when most EVs on the road were DIY---i.e. pre-2000) that no one recommending paralleling battery cells or batteries due to risks involved.  You'd see some folks paralleling up strings and others paralleling up 12v batteries, usually without incident.  Even with lithium based EV packs, we saw in 2010-11 cars being produced with 2 parallel strings of 96 cells.  And EACH of those cells in each string needed a cell voltage manager.  Tesla went a different direction.  They realized that if they massively paralleled the cells as much as possible, then they could avoid multiple series strings, multiple BMS, etc.  Sure, there's risk that a single or leaky shorted cell will cause major issues, but they took that risk.

Back to solar cells---paralleling cells does not bring any real risk.  Each cell itself is actually made up of a lot of silicon in parallel.  For a boat, with possibility of mast, humans and other objects obscuring part or all of several cells, it seems that the best solution would be massive parallelization of cells.  And yet, at some point you need that pack voltage and so ultimately cells need to be put in series.

 

-mt

Re: [electricboats] Complex design issues

I don't understand where your coming up with 22 to 33.3 Amps (OK I think I do, but I also think you are doing it wrong).

 

It's all about the Watts. Watts is power, Watt/hrs are storage (simplified I know).

 

Look at it this way, you have 8ea 100 Watt panels, so a max total possible input of 800 Watts.

If you divide 800W by 48V, you get 16.66 Amps, and 800/72 = 11.11 Amps. But whatever Voltage your panels are putting out, the max Wattage is still 800.

So for me, I look at Watts needed for a given speed and then Watt/hrs left in my pack, to determine how far I can go.

 

Another thing to think about is power loss to conversion/heat. In your example using the theoretical max of your solar panels of 800W, your going to loose a little at the controller (The Victron 100/20/48V claims 98% conversion efficiency) so 800x0.98=784. So now your only getting 784W to the battery (assuming no voltage drop from the wires, and there are ALWAYS voltage drop from wires). There is also some loss at the battery itself.

 

I can tell you from experience that putting 100W into a battery for an hour does not net you a 100W/hr charge. I have Watt/hr meters at my batteries that count up from zero when using, and back down when charging. When fully charged the count will always be negative (until I zero them). As far as I can tell, my battery loss is around at least 0.5% (small but still relevant). So now you are down to about 780W.

 

If you add in the fact that you will also never see the full 100W / panel (unless you are in laboratory conditions) you should always factor in some loss before hand, then later measure when your system is operating.

 

You should also be careful when having 2 different batteries that you use independently. You would need to turn the discharged (used) battery off before turning on the charged (un-used) battery. If you connect two batteries with different voltages together, you will probably see some smoke, and need some new wires (unless you have the fuses and circuit breakers needed). This is just a guess of course, because I have never, ever, ever, ever, ever, done such a thing (did I protest too much?).

 

And you would also need to separate the charging system from each battery.

 

I have my battery banks hooked up to bus bars and use them all at the same time. The solar and shore power chargers AND ALL loads are also connected to these bus bars. The solar charge converters are always on so when the sun is shining all the solar power is being used first. If the batteries are full and the load is small, the solar controllers limit the output to just enough to run the load. If the load increases then the controllers increases the output to match until the load becomes more than the solar is providing (or a cloud passes over) then the load starts drawing from the battery, but only for the excess load above what the controllers are providing.

Then if the load decreases back below the controllers output the excess power from the controllers charge the battery.

 

So in your case I would recommend using both batteries until 2/3 discharged, then fire up the generator and charge them back up (boating best practices: 1/3 on the way out, 1/3 for on the way back in and 1/3 in reserve for emergencies).

 

But as always, it's your boat, do it however makes you happy.

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