Victron MPPT

[Edendeb]

Hello calling all the solar experts!
We have a Victron 75/15, what is the maximum watt panel we can have?
Debbie

 

[Carpmart]

Hello calling all the solar experts!
We have a Victron 75/15, what is the maximum watt panel we can have?
Debbie

Theoretically around 200w, but you could over panel a little, with the assumption one rarely encounters optimal conditions…

 

[Guigsy]

Approximately 15 amps x 12 volts = 180 watts (actually a bit higher than that because batteries can charge at 14v).

If you put a larger panel on, it'll produce as much power as it can. Which just means on clear days in the summer, it'll produce the same output as a larger controller until the middle of the day, when it'll top out at ~180 watts. But throughout most of the year, you won't hit the limit.

 

[Jev88]

Useful to remember in many MH situations.....

Watts / Voltage = Amps

Eg.

120W / 12V = 10 Amps

Your solar panel will also have a sticker stating the potential maximum output to guide you.

 

[Edendeb]

Thank you everyone

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[Lenny HB]

 

[headlight]

View attachment 1026573

Yes the 75/15 is rated to 220 watts.
I have a 75/15 running 2 x 115 watt panels so 230 watts.
The most wattage I've ever seen, in the UK, from my 230 watts is 204 watts.

 

[Hoovie]

View attachment 1026573

Hi Lenny,
Bear in mind that that that Max Wattage rating - and all the power ratings on the Victron MPPTs - are based on a charge voltage of 14.7V.
If you have Lithium and likely charging at 14.2V max, you will have a lower maximum power output. Also when you are charging, the voltage will be lower and so the maximum possible power en-route to a charged battery will be lower than the maximum quoted.

I tend to over-spec the controller to give a better headroom. Very true that a panel rarely achieves its full output, but when it can it would be annoying to then have the controller throttling it.
I am installing a 200W Panel in a few weeks time and instead of using a 75/15 MPPT - which would be ok 'offically' - I am fitting a 100/20.

Yes the 75/15 is rated to 220 watts.
I have a 75/15 running 2 x 115 watt panels so 230 watts.
The most wattage I've ever seen, in the UK, from my 230 watts is 204 watts.

I have only ever used my Motorhome in the UK, and more specfically for the great majority in Scotland and North of England. BUT ... I have seen 100% output many times. Limited to in the summertime and the hours around high noon, but it still happens! I wonder if your maximum is a bit limited for the reasons I gave above? a 75/15 charging Lithium to 14.2V will max out at 213W - and will be lower at lower voltages (the limiting power factor is not actually the quoted power rating, it is the max output current - if you have ever seen the output current at 15A, that is the controller maxed out)

(and FWIW, I have actually seen >100% a few times with the Victron Series 4a Panels I have installed as they can output more than the quoted rating)

 

[Guigsy]

Hi Lenny,
Bear in mind that that that Max Wattage rating - and all the power ratings on the Victron MPPTs - are based on a charge voltage of 14.7V.
If you have Lithium and likely charging at 14.2V max, you will have a lower maximum power output. Also when you are charging, the voltage will be lower and so the maximum possible power en-route to a charged battery will be lower than the maximum quoted.

I tend to over-spec the controller to give a better headroom. Very true that a panel rarely achieves its full output, but when it can it would be annoying to then have the controller throttling it.
I am installing a 200W Panel in a few weeks time and instead of using a 75/15 MPPT - which would be ok 'offically' - I am fitting a 100/20.


I have only ever used my Motorhome in the UK, and more specfically for the great majority in Scotland and North of England. BUT ... I have seen 100% output many times. Limited to in the summertime and the hours around high noon, but it still happens! I wonder if your maximum is a bit limited for the reasons I gave above? a 75/15 charging Lithium to 14.2V will max out at 213W - and will be lower at lower voltages (the limiting power factor is not actually the quoted power rating, it is the max output current - if you have ever seen the output current at 15A, that is the controller maxed out)

(and FWIW, I have actually seen >100% a few times with the Victron Series 4a Panels I have installed as they can output more than the quoted rating)

I agree. But if you've spec'd your solar setup so you collect enough to keep you going in the spring and autumn, then chances are that you're going to be collecting way more Ah than you need by the height of summer. If I had to make a choice between a 200w panel with a 100/20 and a 250w panel with a 75/15, I'd take the latter. So I'd argue you've better off over spec'ing the panel than the controller.

 

[AdrianChen]

I agree. But if you've spec'd your solar setup so you collect enough to keep you going in the spring and autumn, then chances are that you're going to be collecting way more Ah than you need by the height of summer. If I had to make a choice between a 200w panel with a 100/20 and a 250w panel with a 75/15, I'd take the latter. So I'd argue you've better off over spec'ing the panel than the controller.

Hmm, think Id raid the wifes purse for the £15

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[Hoovie]

Hmm, think Id raid the wifes purse for the £15

exactly. the price difference between 75/15 and 100/20 is virtually nothing.

 

[Guigsy]

exactly. the price difference between 75/15 and 100/20 is virtually nothing.

Also only about £20 difference between a 200w and 250w solar panel. If you have a budget...

 

[Hoovie]

Also only about £20 difference between a 200w and 250w solar panel. If you have a budget...

Let it go!

(if you really want to know, the controller is to go with a 200W Lightweight portable solar panel kit, where the physical size is a criteria for storage).

 

[Hoovie]

Also only about £20 difference between a 200w and 250w solar panel. If you have a budget...

just to answer this point, it would be daft to get a 75/15 controller and then with the £20 you may save, buy a 250W panel instead of a 200W. That is just stupid to be blunt as you are knowingly going to lose out. Getting a 250W Panel AND a 100/20 by spending a tad more is much more sensible if your budget and space allows.
The reason getting 200W of PV and a 100/20? Read my message above and previously.

now mentioned space .... I fitted 90W panels on my motorhome. Could have bought bigger ones no problem. So why didn't I? Because they wouldn't fit! 3 of the 90W panels filled in the gap between two skylights and side to side perfectly. No other size panels would have had the same match (you know, sometimes people DO research what they are doing and do what they do for a reason )

 

[Guigsy]

just to answer this point, it would be daft to get a 75/15 controller and then with the £20 you may save, buy a 250W panel instead of a 200W. That is just stupid to be blunt as you are knowingly going to lose out. Getting a 250W Panel AND a 100/20 by spending a tad more is much more sensible if your budget and space allows.
The reason getting 200W of PV and a 100/20? Read my message above and previously.

I agree. The limit isn't often budget, it's roof space. I'm just pointing out that over-panelling your controller isn't a bad thing. Sure, you might throw away a few Ah at 11am. But you'd be throwing them away at 12pm anyway because your battery will be charged regardless. Maxing for summer time yield shouldn't be your aim. You want to squeeze as much as you can from cloudy days in the off-season.

If I had a 250w panel with a 75/15 controller, it'd probably be a waste of money to upgrade the controller. Because by the end of the day, my battery would be in the same state.

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[Hoovie]

I agree. The limit isn't often budget, it's roof space. I'm just pointing out that over-panelling your controller isn't a bad thing. Sure, you might throw away a few Ah at 11am. But you'd be throwing them away at 12pm anyway because your battery will be charged regardless. Maxing for summer time yield shouldn't be your aim. You want to squeeze as much as you can from cloudy days in the off-season.

If I had a 250w panel with a 75/15 controller, it'd probably be a waste of money to upgrade the controller. Because by the end of the day, my battery would be in the same state.

I'll take as much solar I can get! After I added more solar to my roof to get 450W, I swapped out my 100/30 for a 100/50.
the 100/30 has a quoted maximum of 440W (not really true for reasons I gave earlier) so not really worth it? except why not maximise the opportunity!
Would the battery be full by lunchtime? I doubt it - 450W takes a while to fill 620Ah of batteries even when working all morning
Have I wasted money changing? Not really as I bought a 100/50 BlueSolar for less than I sold the SmartSolar 100/30 for (don't need the bluetooth).

 

[headlight]

just to answer this point, it would be daft to get a 75/15 controller and then with the £20 you may save, buy a 250W panel instead of a 200W. That is just stupid to be blunt as you are knowingly going to lose out. Getting a 250W Panel AND a 100/20 by spending a tad more is much more sensible if your budget and space allows.
The reason getting 200W of PV and a 100/20? Read my message above and previously.

now mentioned space .... I fitted 90W panels on my motorhome. Could have bought bigger ones no problem. So why didn't I? Because they wouldn't fit! 3 of the 90W panels filled in the gap between two skylights and side to side perfectly. No other size panels would have had the same match (you know, sometimes people DO research what they are doing and do what they do for a reason )

Just to clarify, in my case the reason for using a 75/15 MPPT with 230 watts of solar is that my set up was originally a single 115 watt panel with the 75/15.
I then added a second 115 watt panel, taking my solar up to 230 watts.
After speaking to a very well respected installer it was decided that it wasn't worth replacing my 75/15 with a 100/20.
If I had installed the 2 x 115 watt panels at the same time I would have fitted a 100/20 MPPT.

 

[Hoovie]

Just to clarify, in my case the reason for using a 75/15 MPPT with 230 watts of solar is that my set up was originally a single 115 watt panel with the 75/15.
I then added a second 115 watt panel, taking my solar up to 230 watts.
After speaking to a very well respected installer it was decided that it wasn't worth replacing my 75/15 with a 100/20.
If I had installed the 2 x 115 watt panels at the same time I would have fitted a 100/20 MPPT.

And a perfectly valid thing you have done. I would have recommended you do the same.

The Victron Controllers have a hard limit on the voltage input of the panels - so you would never want to connect panels in series that would take you above 75V on a 75/15, but they don't care how much current is coming in from the panels - anything that would take the output current of 15A just gets capped. You could connect 1000W of solar to a 75/15 and it would work perfectly and no damage would occur - you just would not get more than 15A out the controller.
(PS. other controllers are not always so forgiving).

To give another example, I will be fitting a 100/50 Controller next month to support a 320W Solar Array. The 100/30 would be a perfect fit capacity wise, but there is enough room on the roof for another 300-400W of solar in the future which might happen. Spending a bit extra on the larger capacity controller at a fairly minimal extra cost to provide future proofing can make a lot of sense, especially when the step-cost is so close. (A few years ago the difference in price between each size of Victron MPPT was much greater and at that time, you would likely NOT do this approach unless you were sure you would add more solar. The current prices mean that for a new installation, it doesn't make sense not to.)

 

[AdrianChen]

I agree. The limit isn't often budget, it's roof space. I'm just pointing out that over-panelling your controller isn't a bad thing. Sure, you might throw away a few Ah at 11am. But you'd be throwing them away at 12pm anyway because your battery will be charged regardless. Maxing for summer time yield shouldn't be your aim. You want to squeeze as much as you can from cloudy days in the off-season.

If I had a 250w panel with a 75/15 controller, it'd probably be a waste of money to upgrade the controller. Because by the end of the day, my battery would be in the same state.

Personally I selected the smallest controller for my two types of panels that the Victron model said would avoid any clipping at both high and low temps. The panels were what could be fitted in the available space. Hoped to get the max output I could.....

But I screwed up and told the installer to put in a 15 instead of a 20 which will clip at low temps according to the model (my OCD is egging me on to change it and flog the 15)

Looking at the outputs for the two sets of panels and their respective controllers over the winter shows the fully specified one has proportionately done better than the underspecified one. especially on the poor days when there is mist/rain/fog etc, and these are days when the batteries would happily take more.

Someone told me the processor (for MPPT) might be faster in the bigger controllers so doing better in poor conditions - seemed unlikely to me, it could be the result of shadows from the aircon / aerials / fridge chimney bird droppings etc - but there is a difference.

So in my case I guess other factors are probably making more difference than the 15 vs 20 amp choice.

Ultimately the OCD will win, and I'll sell the 15 and replace with a 20!

 

[mikash]

And a perfectly valid thing you have done. I would have recommended you do the same.

The Victron Controllers have a hard limit on the voltage input of the panels - so you would never want to connect panels in series that would take you above 75V on a 75/15, but they don't care how much current is coming in from the panels - anything that would take the output current of 15A just gets capped. You could connect 1000W of solar to a 75/15 and it would work perfectly and no damage would occur - you just would not get more than 15A out the controller.
(PS. other controllers are not always so forgiving).

That's incorrect. The controllers do have a maximum current on the panel/input side that should not be exceeded. The output side however will throttle amps down to the maximum output without issue.
So two 200W panels with 20V output voltage and 10A output current would work with the 75/15 in series (40V/10A) and would nicely throttle down to 15A output for a 12V system , but would cause overcurrent shutdowns to avoid damaging the controller when wired in parallel (20V/20A) instead of throttling down since the 75/15 is specced for 15A max PV short circuit current.

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[Hoovie]

That's incorrect. The controllers do have a maximum current on the panel/input side that should not be exceeded. The output side however will throttle amps down to the maximum output without issue.
So two 200W panels with 20V output voltage and 10A output current would work with the 75/15 in series (40V/10A) and would nicely throttle down to 15A output for a 12V system , but would cause overcurrent shutdowns to avoid damaging the controller when wired in parallel (20V/20A) instead of throttling down since the 75/15 is specced for 15A max PV short circuit current.

I am sure that that is not the case in operation, but fair enough. have to agree to differ.

 

[mikash]

I am sure that that is not the case in operation, but fair enough. have to agree to differ.

Matching solar modules to MPPT charge controllers - Victron Energy

Life used to be so simple; in a 12V battery system you took a ‘12V’ solar module, watched carefully that the maximum PV current would not exceed the charge controller maximum current and the system would work. Unfortunately due to the fact, that with PWM controllers the PV module is not feeding...

www.victronenergy.com

There are two limits, when determining the maximum array size that can be connected to an MPPT:

1. The Maximum PV open circuit voltage (Voc at STC)
2. The Maximum PV short circuit current (Isc at STC)
   Both values are specified in the datasheets of all our MPPT Solar Charge Controllers. Those two ratings of the PV array must not exceed these MPPT limits.

You don't have to take my word for it, that's straight from the horse's mouth.