Solar panels. In series or parallel?

[noelex]

In normally circumstances I would agree with what you said and if the different in Amps was large enough to warrant a bigger control I would had invested in one .
But yes there always a but , my panels as listed as max power 5.18A
I take that to be in 100% best possible factor test no shading .
So thats just under a amp for my control .
although when the sun is above all panels I do see 20A for some time here in the Med
Which surprise me .

.72 of a amp even if it's reach isn't going to do any different to the MPPT or I wouldn't think so .

When fitting out this boat at the time we only had room for 2x100w why I brought the 100/20 MPPT since then I had some SS off the back when I fitted and extra two panel .
When weighing up if I should invest in a second MPPT to take the min of Amps the extra panels would put out if any I decide after talking to Victron that a small amount of extra current wouldn't do any damage to the control but it would restrict me to the max Amps the MPPT would allow.
it was spend another €200 on another MPPT or stick with what I have and possibly lost .72 Of a amp on a few days in the summer .

The 20A rating of the MPPT is the maximum output, not the maximum input current. This is a very common misunderstanding.

If your 100w panels are rated at a maximum current of 5.18A, a little maths shows they must have a Vmp of 19.3v. The controller will take this 5.18A @ 19.3v and convert it to a higher current at battery voltage. At 14v the 5.18A becomes a theoretical 7.14A.

As you have four panels, when the batteries are at 14v the panels can deliver 4x7.14=28.6A. Therefore if your panels deliver their rated output, the small 20A controller is not costing you 0.72A, but a substantial 8.6A.

The panels will not deliver their rated output often or for a long time, but under more common reasonably good conditions a 20A controller will be wasting a significant amount of power.

 

[GHA]

In normally circumstances I would agree with what you said and if the different in Amps was large enough to warrant a bigger control I would had invested in one .
But yes there always a but , my panels as listed as max power 5.18A
I take that to be in 100% best possible factor test no shading .

100w panel your likely get about 6A or maybe a little more at the batteries on a good day, the mppt will only output 20A so if every panel is having a good day you'll lose about 4A . But very rare if ever as you say, I've similar with 200W going through a 75/10 which was ordering the wrong box, but works OK and both panels will never realistically be outputting max at the same time.

 

[sailaboutvic]

The 20A rating of the MPPT is the maximum output, not the maximum input current. This is a very common misunderstanding.

If your 100w panels are rated at a maximum current of 5.18A, a little maths shows they must have a Vmp of 19.3v. The controller will take this 5.18A @ 19.3v and convert it to a higher current at battery voltage. At 14v the 5.18A becomes a theoretical 7.14A.

As you have four panels, when the batteries are at 14v the panels can deliver 4x7.14=28.6A. Therefore if your panels deliver their rated output, the small 20A controller is not costing you 0.72A, but a substantial 8.6A.

The panels will not deliver their rated output often or for a long time, but under more common reasonably good conditions a 20A controller will be wasting a significant amount of power.

Sound as if my sums are out John
Although that's in perfect condition,
two panels are on each rails so even on a good day one shaded , the only time there no shading on any is for a very short period when at anchor and the sun is directly above .
Some how for that small period of time I can't justify spending €200 on another MPPT .
If I could find somewhere to put another panel then that be the time to invest in another control .
But on a mono hull its petty hard , unless I use flex panel but that mean secure them to the roof and then there be more shading to deal with .

 

[noelex]

Some how for that small period of time I can't justify spending €200 on another MPPT .

I understand.

Make sure your controller has good ventilation. The Victron controllers rely on passive cooling and run quite hot even under normal operating conditions.

Victron recommend a maximum array size of 290w for this controller (@12v) and a maximum array Asc of 20A. I suspect limitations in cooling capacity when delivering at or close to the maximum current are a factor in this decision. The larger models have significantly larger heatsinks.

 

[sailaboutvic]

@noelex
After winding me up the other day telling me how much Amps I was losing
Here your a penance you can answer me this question .
I dig around in my odd bits and found an old Chinese MPPT and rewired one panel through that .
Now the V+ from the MPPT when straight to the batteries V+
The v- when to my BMV shunt on the out put side .

So here the question ,
Why is the BMV not seeming the Amps from that panel ?
The MPPT showing 5.5A
If I put a clump meter at the batteries it's showing 5.5 A
Of I put a clump meter over both V+ leads coming from both MPPT at the batteries that's show 23A
But the BMV only showing 17.5A

 

[noelex]

@noelex
After winding me up the other day telling me how much Amps I was losing

I am pleased that by installing an extra controller, even a cheap Chinese one (I am not a great fan of those things), that you managed to extract another 3A over the maximum 20A available from the single controller. Think of the potential.

OK, that was a wind up .

Why the shunt was not apparently reading the correct current is difficult to say without seeing the wiring.

The only possibility I can think of is that the Chinese regulator input was connected to the wrong (battery side) of the shunt. That is not a wind up. I have made far more mistakes on boat electrics over the years.

If this was the problem, the battery monitor would not see the output of the Chinese controller, which if I understand correctly is exactly the issue.

If that is not the answer I will have to think of another penance. Would re-reading all the YBW anchor threads for the last year suffice? I cannot think of worse punishment .

 

[sailaboutvic]

I am pleased that by installing an extra controller, even a cheap Chinese one (I am not a great fan of those things), that you managed to extract another 3A over the maximum 20A available from the single controller. Think of the potential.

OK, that was a wind up .

Why the shunt was not apparently reading the correct current is difficult to say without seeing the wiring.

The only possibility I can think of is that the Chinese regulator input was connected to the wrong (battery side) of the shunt. That is not a wind up. I have made far more mistakes on boat electrics over the years.

If this was the problem, the battery monitor would not see the output of the Chinese controller, which if I understand correctly is exactly the issue.

If that is not the answer I will have to think of another penance. Would re-reading all the YBW anchor threads for the last year suffice? I cannot think of worse punishment .

Nan connected to the correct side of the shunt the side every thing else comes off , and everything's else register .
So you better start looking haha .
My partner said she fed up keep making the bed ( batteries under our bunk ) and any more ideas from you and you can very well come and make it haha .
The Chinese MPPT is a real MPPT I had it open and it seen to have the right works inside , it use to run my old batteries until I invested in the Trojan and replace it with Victron BMV and MPPT .
Really not joking the money I spend on the Trojan and Victron stuff I would had been much better off keep buying cheap HD batteries and throwing them away every 4 years .

 

[noelex]

Nan connected to the correct side of the shunt the side every thing else comes off , and everything's else register .
So you better start looking haha .

Oh no .

My partner said she fed up keep making the bed ( batteries under our bunk ) and any more ideas from you and you can very well come and make it haha .

I think your partner has a good point, but “Bedroom” problems are perhaps beyond the scope of the forum

The Chinese MPPT is a real MPPT I had it open and it seen to have the right works inside

For anyone thinking of buying a controller it is important to understand that MPPT is not one technology. To produce a good MPPT controller that tracks the solar panel voltage accurately and maintains the panel at its MPP, particularly on boat with the rapidly changing conditions and shadows is tough ask. Even when this done the battery charging algorithm needs to be adjustable and sophisticated if it is charge the battery as rapidly and accurately as possible.

That is not to say that less expensive controllers are always a wrong choice, but just because they are MPPT, even when genuinely MPPT, does not mean you should anticipate similar performance to more sophisticated circuitry in more expensive controllers.

Nevertheless, I think wiring up this Chinese controller is good idea. It will at least roughly show the additional amount of power that is available from the system and you will therefore you will be in a better position to decide if a more permanent upgrade is worthwhile.

To solve your misreading battery monitor I am sure someone else will have the answer, if not drawing a circuit diagram is often helpful.

 

[rogerthebodger]

Of I put a clump meter over both V+ leads coming from both MPPT at the batteries that's show 23A

I would do the same on the V- leads from the MPPT's on both sides of the shunt they should be the same 23A on both sides of the shunt. If not the shunt or the BMV is not displaying correctly.

 

[sailaboutvic]

John there not much of a circuit diagram There only two wires , one goes to the batteries the other to the shunt .
Maybe I didn't Didn't do it justice when I called it a cheap Chinese MPPT , brought it some five years ago I think around £80 and it simply to set up but much cheaper then Victron stuff .
It was sold under MPPT solar charger controller.
There was some test done on my model and all came up with good results.
Ok going back to my problem , no not the bed .
After sitting out of the sun for a while and a couple of cool beer , it came to me .
I wasn't taking in consideration any load coming out of the batteries so taken the freezer was running and another load that explains it .
So other half happy I not pulling the bed to bits again and I'm happy as on my four beer .
Any more ideas mate , kept to your self I done enough work the last month , batteries , saildrive now rewiring this

 

[noelex]

I am glad you solved the problem without any bed lifting. Our batteries and main shunt are also under the bed so I can sympathise.

Yes, the battery monitor will only read the net current, you need to turn all the loads off to read the solar panel input.

If it is a reasonable quality product I would consider leaving the second controller wired in place permanently. I think you may be surprised by the extra power available, but at least you will know one way or the other.