andrew-aikman avatar image
andrew-aikman asked

MPPT 75/15 - Consumption - why is consumption high when there is no load?

Hi all,

I am new to solar and need some help. I have a simple solar set up two 300w panels, victron MPPT 7/15, victron phoenix 24v 250 inverter and two 140ah AGM batteries in series. Attached to the MPPT load I have a USB charger to power a mobile phone. I also have a blue tooth dongle attached to the inverter to link to the phone / app.

I have a breaker in between the panels and the MPPT and fuses between the MPPT and batteries and between batteries and inverter - all on the live wire.

When everything is off - no load on either the USB or inverter (inverter is switched off) the Victron app is showing consumption of 50Wh.

The system ahs been running for around 2 months. Initially consumption was no more than 40wh but in last week or so it has been over 100wh (but with load - laptop / two monitors c100w - 140w).

Questions I have are:

1. Is this normal / typical?

2. If not normal what could be causing it? Problem with MPPT / batteries / connections / panels / fuses?

Any help / advice greatly appreciated.

MPPT ControllersMPPT SmartSolarmppt charging
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3 Answers
mrseas avatar image
mrseas answered ·

Turn off “load” in the CC settings. Problem solved.

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Jan Neumann avatar image Jan Neumann commented ·

I also had a consumption of 250 mA (shown in the smart shunt and measured with clamp meter) without any real load on the system while load was turned off in the configuration. Only after cutting off the solar controller completely from battery- and solarpower for a minute and reconnecting and by that rebooting my blue smart mppt 100/20 48 the consumption was zero. I think that this is a bug in the firmware.

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Trina avatar image
Trina answered ·


How are you using two 300w panels with a 75/15? Even in a 24v setup that"s overloading it most of the time unless your panels are really old and put out at best 1/2 or even 1/3 the rated amps ever.

600w /34 stc probably and at least 8-9a ?

Convert that to 24v with losses and still WAY over that 75/15a output rating. You could blow the 2nd stage in your controller if those panels ever come close to spec on a cold day!

I'd get a 30a or 40a controller soon and swap out. Or just a second 75/15 for the other panel (if your panels don't do much amps out anymore) and completely split your array and set the MPPT's the same (you can link them to share a saved settings file I think?) as they won't fight each other at all as long as they have the same settings.

Just sayin'

Unless you made a typo or I misread something.

P S.

-0.10a draw then x20÷ hours @ 24v~27v system is how many watts? There's your phantom draw in the screenshot. Is that load running in difference from usual?

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Vance Mitchell avatar image Vance Mitchell commented ·

If I had to guess, looking at the history they are 300w eBay panels that are really only 180-200w maximum.

To the OP, I wouldn’t worry about 50wh consumption.
so long as your batteries are reaching full charge each day and going into float you should be fine.

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andrew-aikman avatar image andrew-aikman commented ·

I purchased the set up as a kit. The 300w panels are in parallel to limit the voltage. Amps is still a problem though so I have fitted a 15 amp breaker between the panels and the MPPT. The panels are Jinko Solar JKMS320M-60B-MX. Short circuit Current = 8.01A NOCT. I reckon the chances of getting this are very low.

Ive installed a smart shunt 500 today.

The consumption numbers seem to have sorted themselves out over last few day's. I havent changed anything until today. So I am not sure what is going on.

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tomwarden avatar image tomwarden commented ·

Thanks for posting this, I had the same question, but my system is running off 12 volts. Just so I am clear is the below correct?

-0.10 x 20 = -2

-2 ÷ 24(hours) = 0.083333333 watts

My daily consumption (with no load) varies between 20 and 30Wh and I am trying to figure out how to calculate to that figure.

Screen Shot.png

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Peter Silbernagl avatar image Peter Silbernagl tomwarden commented ·
HI tomwarden, You have probably worked this out by now. Here is how I would do the calculation. 10mA x 24 hours x 50V (say for a 75/15 MPPT) /1000 = 12 Wh. If you measure more than that, then the self consumption must be higher.

Am I missing something? Hope it helps, Peter

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Trina avatar image
Trina answered ·

The other thing I see is that your system might be going in and out of bulk/absorb/float too soon? That would require some playing with settings in your mppt. Are you using a battery monitor at all?

If not, seriously consider it. You can get really cheap tiny things on-line that will give you at least some good info the mppt does not if the bmv isn't in the system plan.

I'd say it's a critical tool having a good battery monitor.

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Peter Silbernagl avatar image Peter Silbernagl commented ·
Hi Trina, I have a similar problem with a set of 100/20 MPPT, where the self consumption has gone up to more than 200 Wh per day each. It used to be under 50 Wh per day each. You mention the time spent in Bulk/Absorb/Float. What would you recommend for LiFePo4 batteries in parallel? My six MPPTs spend about 33 - 40% of their time in Bulk, 3 - 5% in Absorb and the rest (about 60%) in Float.
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