Underperforming Renogy MPPT controller?

[Smoza]

Hey all,

Bit of a newbie here, but Renogy won't reply to my support request.

I have 400w of panels, wired in series and parallel, ie 2 X 200w sets. On a winter day here they put out about 32v @ 6a total to my Renogy 20a rover controller.

This outputs to a lithtech 100ah Lifepo4 battery.

According to the Bluetooth BMS on board the battery, with no other loads connected, it generally only receives about 6-7a at approx 13v.

By my calculations, that would suggest I'm only getting roughly half the output from the panels to my battery.

Shouldn't the controller step up the amps much higher to use as much power as possible from the panels?

Cheers.

 

[snoobler]

Welcome to the forum.

32V * 6A = 192W

13V * 6.5A = 84.5W

I assume these readings were taken at completely different times.

I also assume your panels are perfectly perpendicular to the sun with no shading and clear skies. If not, you will lose a lot of your solar potential.

400W/12V = 33.3A - your MPPT is undersized. It has the potential to send only 20A when your array can supply as much as 33A.

So, the maximum you can get from your 400W array is about, 20A * 14.6V = 292W.

If the battery is in absorption or float mode, it doesn't matter how much solar is available. It will only send what the battery can accept.

A good way to test the output of an MPPT is to draw loads greater than the array power, 292W in your case. That way the MPPT is forced to provide the maximum power available.

 

[Smoza]

Welcome to the forum.

32V * 6A = 192W

13V * 6.5A = 84.5W

I assume these readings were taken at completely different times.

I also assume your panels are perfectly perpendicular to the sun with no shading and clear skies. If not, you will lose a lot of your solar potential.

400W/12V = 33.3A - your MPPT is undersized. It has the potential to send only 20A when your array can supply as much as 33A.

So, the maximum you can get from your 400W array is about, 20A * 14.6V = 292W.

If the battery is in absorption or float mode, it doesn't matter how much solar is available. It will only send what the battery can accept.

A good way to test the output of an MPPT is to draw loads greater than the array power, 292W in your case. That way the MPPT is forced to provide the maximum power available.

Hey thanks for the reply.

These panels are on my van, so I don't expect full power due to the angle.

And yeah I realise the mppt is undersized, especially if I were to get anywhere near full power.

The readings are from the controller itself, which I have tested against my multimeter in the past and found to be pretty darn close, and the output to the battery is from the BMS, which I assume to be at least in the ballpark.

It doesn't seem to matter what the SOC is for the battery, it'll happily pull >30a from my alternator so I think it would be pulling more from the controller.

I could attach a decent load next sunny day and see what happens?

But from my calculations I've never seen the controller at more than about 60% efficiency so I'm considering going back to a cheap pwm controller on one 200w array and the mppt on the other array.

 

[snoobler]

Depending on your latitude, 6-7A from winter sun on a flat panel may be the best you can get.

If the battery is not in absorption mode, then it can probably handle however much current the controller can deliver. If you're only getting 6-7A solar, yet you can get 30A alternator at that moment, the battery isn't the limiting factor.

How have you calculated efficiency?

 

[Smoza]

Depending on your latitude, 6-7A from winter sun on a flat panel may be the best you can get.

If the battery is not in absorption mode, then it can probably handle however much current the controller can deliver. If you're only getting 6-7A solar, yet you can get 30A alternator at that moment, the battery isn't the limiting factor.

How have you calculated efficiency?

32V * 6A = 192W

13V * 6.5A = 84.5W

This would indicate about 44% efficiency yeah?

Measurements taken at exactly the same time.

Which seems very odd to me, so not sure what is going on

 

[Smoza]

Oh and I'm near Vancouver, so my expectations on winter sun are fairly low!

 

[snoobler]

Yeah. 1.09-2h/day? You have very little sun available.

I would question your efficiency calculations and the controller output. That implies about 100W is getting consumed by the controller. I just can't believe that. Does it get scorching hot? If not, something is amiss. If you have a clamp ammeter or other device that can verify amps into the battery (BMS?), I would double-check the Renogy numbers.

There was a recent post by a user who was experiencing extreme temperatures with Renogy MPPT. It's possible there's some sort of defect, but his was getting molten hot.

 

[Smoza]

View attachment 35501

Yeah. 1.09-2h/day? You have very little sun available.

I would question your efficiency calculations and the controller output. That implies about 100W is getting consumed by the controller. I just can't believe that. Does it get scorching hot? If not, something is amiss. If you have a clamp ammeter or other device that can verify amps into the battery (BMS?), I would double-check the Renogy numbers.

There was a recent post by a user who was experiencing extreme temperatures with Renogy MPPT. It's possible there's some sort of defect, but his was getting molten hot.

Ok yeah, I'll have to verify both what the array is putting out and what the battery is receiving.

Cheers for your help, will report back.

 

[Jetdust]

How do you like the battery? I picked one up for a homemade solar generator..