Solar setup - is my MPPT too small?

[booke23]

I bought a boat a few weeks ago and I'm trying to get my head around the solar setup. It has one 160AH LiFePO4 leisure battery and one 110AH lead acid starter battery. 

 

On the roof are two identical solar panels wired in series. Attached is a photo of the label on one of the panels, they are 190W each and they seem to work well. However I noticed that even on a very sunny day the battery monitor shows they max out charging at 15 amps, quite a bit below what I thought 380W of solar should generate. On further digging I found the panels are connected to a Victron 100/15 charge controller (photo attached). 

 

So is this setup dangerous.......ie could the panels overload the MPPT? Would it be advisable to change the MPPT for a more suitable one......a 100/30 for instance?

 

 

 

[Higgs]

How many panels do you have.  Sorry, you have two. For a single panel, the charge controller is plenty. It would cope with two panels, and would only be a bit too small for three, if it was at all possible to get the sunny conditions to reach the panels maximum output. The charge controller will increase the amp output; in hunting (tracking) for the best optimum voltage output of the panels, then reducing to increase the amps to the batteries. 15 amps seems quite respectable, for the two panels. 

 

One other thing: Your charge controller is rated at 100v. The maximum in-series voltage of three panels would exceed this limit.

 

 

 

 

Edited August 10, 2021 by Higgs

[Tony Brooks]

MPPT controllers will never exceed their maximum output, however many amps goes in so 15 amps is the maximum expected from that controller. Within reason excess input AMPs is unlikely to damage it, excess volts will.

 

In the UK a rule of thumb is to expect a maximum of about half a panel's rated output so 2 x 190 = 380  watts and at a nominal 14 volts (charging voltage) that equals about 27 amps. The MPPT controller will convert the 13.5 amps at 24 volts to the theoretical 27 amps at 14 volts (all very rough figures). 50% of 27 amps = 13.5 amps, so your 15 amps is more or less what to expect. You MIGHT get slightly more under ideal conditions in high summer with a higher capacity charger, but I doubt t would be worth the cost.

 

Please make sure the controller's maximum charging voltage is within spec for the lithium batteries. Lead acid voltages may damage them.

[doratheexplorer]

10 minutes ago, Tony Brooks said:

MPPT controllers will never exceed their maximum output, however many amps goes in so 15 amps is the maximum expected from that controller. Within reason excess input AMPs is unlikely to damage it, excess volts will.

 

In the UK a rule of thumb is to expect a maximum of about half a panel's rated output so 2 x 190 = 380  watts and at a nominal 14 volts (charging voltage) that equals about 27 amps. The MPPT controller will convert the 13.5 amps at 24 volts to the theoretical 27 amps at 14 volts (all very rough figures). 50% of 27 amps = 13.5 amps, so your 15 amps is more or less what to expect. You MIGHT get slightly more under ideal conditions in high summer with a higher capacity charger, but I doubt t would be worth the cost.

 

Please make sure the controller's maximum charging voltage is within spec for the lithium batteries. Lead acid voltages may damage them.

Very good advice.  I have 500w of panels which gives a theoretical maximum of about 35a.  So I bought a 40a MPPT controller.  But in the real world, I've only acheived over 20a in absolutely perfect conditions.  A 30a controller would have been plenty and a 20a controller would have been fine 99% of the time.

 

OP - I'd stick with what you have. 

[Higgs]

Not sure whether the charge controller can automatically detect battery type, but it is possible to select pre-sets and input user or manufacturer's parameters.  

 

 

[Tony Brooks]

4 minutes ago, Higgs said:

Not sure whether the charge controller can automatically detect battery type, but it is possible to select pre-sets and input user or manufacturer's parameters.  

 

 

 

It looks to me as if the OP's has a USB cable plugged into it so it can be set via a computer - may well be wrong.

[Higgs]

2 minutes ago, Tony Brooks said:

 

It looks to me as if the OP's has a USB cable plugged into it so it can be set via a computer - may well be wrong.

 

It is either that or temperature sensor. The unit is Bluetooth capable, through an app on the phone. 

 

 

[David Mack]

Three panels in series would exceed the maximum input voltage for that controller. But two more identical panels could be added in a 2 x 2 series-parallel configuration. You would still only get 15A out at this time of year, but in the autumn, winter and spring, when your current setup would produce 7.5A or less, that arrangement would double the output, extending the solar contribution into the autumn and spring (although in winter twice sod all is still sod all).

[booke23]

Thank you all very much for the excellent advice.

 

I have just been on a 1 week trip on the boat and at this time of year I noticed it was maxed out at 15 amps for quite a lot of the day, providing it is sunny that is! I was thinking it would produce near to 30 amps but I see now it would not....and thanks to the experience of @doratheexplorer I can see my setup would probably struggle to even get to 20 amps so upgrading the controller might not be worth the cost as @Tony Brooks suggests. 

 

The solar setup charges both the lithium battery and the lead acid battery.....I'm not exactly sure how it does this. There is a Victron VE.bus BMS along with a Cytrix-Li-Charge and Cytrix-Li-Load relay which as I understand it protects the lithium battery from over/under voltage, over/under charge and over/under temperature events. But I will try to establish the charge voltage to make sure the lithium battery isn't being damaged. 

 

@Tony Brooks The cable that looks like a USB cable I presume goes to the control panel in the electric cupboard....I don't have a photo of the actual controller but it is identical to the one below. 

 

[booke23]

54 minutes ago, David Mack said:

Three panels in series would exceed the maximum input voltage for that controller. But two more identical panels could be added in a 2 x 2 series-parallel configuration. You would still only get 15A out at this time of year, but in the autumn, winter and spring, when your current setup would produce 7.5A or less, that arrangement would double the output, extending the solar contribution into the autumn and spring (although in winter twice sod all is still sod all).

 

Very interesting, thank you David. The boat is only 40ft so I don't really have space for more panels.......well I do, but I like to have a bit of clear roof to clamber about on!

[Tony Brooks]

26 minutes ago, booke23 said:

Thank you all very much for the excellent advice.

 

I have just been on a 1 week trip on the boat and at this time of year I noticed it was maxed out at 15 amps for quite a lot of the day, providing it is sunny that is! I was thinking it would produce near to 30 amps but I see now it would not....and thanks to the experience of @doratheexplorer I can see my setup would probably struggle to even get to 20 amps so upgrading the controller might not be worth the cost as @Tony Brooks suggests. 

 

The solar setup charges both the lithium battery and the lead acid battery.....I'm not exactly sure how it does this. There is a Victron VE.bus BMS along with a Cytrix-Li-Charge and Cytrix-Li-Load relay which as I understand it protects the lithium battery from over/under voltage, over/under charge and over/under temperature events. But I will try to establish the charge voltage to make sure the lithium battery isn't being damaged. 

 

@Tony Brooks The cable that looks like a USB cable I presume goes to the control panel in the electric cupboard....I don't have a photo of the actual controller but it is identical to the one below. 

 

When the Li batteries reach a preset maximum charging voltage, the load relay will disconnect them for the Li charger and thus the LA battery and charge sources.

 

 

There are others here far better up on LI battery systems than myself but I think you will find that everything  is set to charge the engine lead acid battery, so it needs the LA voltages (say around 14.4 absorption, 13.6 float, and 15V plus if any do an equalising charge.) and the Cytrix Li charger is a battery to battery charger that is set to provide the charging voltages required by the Li bank.  If I am correct, then I am sure that you have nothing to worry about.

Edited August 10, 2021 by Tony Brooks

[booke23]

That makes sense, thank you @Tony Brooks