Why is my voltage dropping

[mystic pizza]

I have a couple of panels in series that produce 70V into a charge controller dropping to charge 12V batteries.

Every few hours the voltage drops to 14V on the panels before climbing again slowly over a period of time (no shading). I have two identical arrays, and they both do exactly the same thing.

If i turn the isolation switches off and then back on, they will show 70V again.

Any ideas please?

 

[DThames]

What type of charger? It sounds like the charger is loading the cells down.

 

[mystic pizza]

What type of charger? It sounds like the charger is loading the cells down.

They are outback flexmax 30 mppt controllers

 

[MisterSandals]

They are outback flexmax 30 mppt controllers

That's a top notch SCC.

Are the batteries fully charged by chance?
Have any pics that might reveal some clues?

 

[DThames]

They are outback flexmax 30 mppt controllers

I have a couple of panels in series that produce 70V into a charge controller dropping to charge 12V batteries.

Every few hours the voltage drops to 14V on the panels before climbing again slowly over a period of time (no shading). I have two identical arrays, and they both do exactly the same thing.

If i turn the isolation switches off and then back on, they will show 70V again.

Any ideas please?

MPPTs have a normal voltage range. If the input is below that range (like early before the sun is fully on the panels) I have observed that mine will act more like a PWM charger and the PVin will be just above the battery. I wouldn't expect that in full sun unless the MPPT is dumb and has to seek the best load point with poorly designed logic.

 

[MisterSandals]

I have two identical arrays, and they both do exactly the same thing.

They aren't connected to each other are they? Distinct circuits from array to SCC to battery, right?

 

[mystic pizza]

That's a top notch SCC.

Are the batteries fully charged by chance?
Have any pics that might reveal some clues?

I think they are actually tracers, but badged as outback, so probably made by tracer, not outback.

I cant get a pic until tomorrow now as the sun has gone. PICs now added

They aren't connected to each other are they? Distinct circuits from array to SCC to battery, right?

They are two separate arrays connected to the same cells through individual charge controllers

 

[mystic pizza]

They aren't connected to each other are they? Distinct circuits from array to SCC to battery, right?

 

[mystic pizza]

The above images were taken within seconds of each other.The lower voltage shows before I turned the panels off, the second image shows the panels switched back on again

 

[mystic pizza]

MPPTs have a normal voltage range. If the input is below that range (like early before the sun is fully on the panels) I have observed that mine will act more like a PWM charger and the PVin will be just above the battery. I wouldn't expect that in full sun unless the MPPT is dumb and has to seek the best load point with poorly designed logic.

Thanks. Its happening in the middle of the day in full sun.

 

[MisterSandals]

What are your charge parameters?
Without knowing how high "success voltage" is, it almost looks like it thinks the battery is full so tapering charging.

 

[mystic pizza]

What are your charge parameters?
Without knowing how high "success voltage" is, it almost looks like it thinks the battery is full so tapering charging.

13.9 boost, 13.9 float, but surely the panel voltage would not be dropped to produce the required float?

 

[MisterSandals]

13.9 boost, 13.9 float,

Maybe this is confusing the controller? Its confusing me but that's easy.
I dunno. Maybe try a sensible float of 13.4?

What does "State Check" show when its doing the 14V thing? Just grasping for clues...

 

[mystic pizza]

Maybe this is confusing the controller? Its confusing me but that's easy.
I dunno. Maybe try a sensible float of 13.4?

What does "State Check" show when its doing the 14V thing? Just grasping for clues...

OK. Thanks. I'll give it a try to tomorrow and see what happens.

 

[Browneye]

I have a XTRA3210N and it was doing this for awhile, but hasn't now for some time.
PV input is generally about 44V, but for some reason the controller will report 14 or so volts. I have a PV disconnect - so switch it off, back on and voltage resumes to normal.

I couldn't figure out why it was doing this either, but seems to have quit - it's been normal for some time now. And I never had any overlapping charge settings, so I'm not sure that could be it.

Sorry I don't have a magic solution, other than to say I experienced the same thing.

 

[Bud Martin]

OP: Did it ever work correctly before?
"They are two separate arrays connected to the same cells through individual charge controllers"
Are you referring 'CELLS' as the batteries?
"individual charge controllers" Are you saying you have more than one controller?

 

[mystic pizza]

I have a XTRA3210N and it was doing this for awhile, but hasn't now for some time.
PV input is generally about 44V, but for some reason the controller will report 14 or so volts. I have a PV disconnect - so switch it off, back on and voltage resumes to normal.

I couldn't figure out why it was doing this either, but seems to have quit - it's been normal for some time now. And I never had any overlapping charge settings, so I'm not sure that could be it.

Sorry I don't have a magic solution, other than to say I experienced the same thing.

Many thanks

 

[mystic pizza]

OP: Did it ever work correctly before?
"They are two separate arrays connected to the same cells through individual charge controllers"
Are you referring 'CELLS' as the batteries?
"individual charge controllers" Are you saying you have more than one controller?

Yes, more than one. I recently changed the system and the controller settings to include lithium cells, and as a result have been keeping a, closer eye on the settings.

It may well have been doing it previously, but I didn't notice.

 

[mystic pizza]

An update.

I changed the setting on one of the controllers to 13.9 boost, 13.5 float,and it appears to have dropped into float properly.

The other one I have left set as it was, and it still putting in some current. Both remain at the higher panel voltage.

 

[rickst29]

I will guess that your "problem" consists of the controller switching between MPPT and PWM mode, very likely inspired by setting "Boost Voltage" and "Float Voltage" the same. Your "Boost Return" Voltage is also a significant parameter WRT the operation of the MPPT controller.

In PWM mode, the rapidly cycling "straight-through" connection pulls the measured PV voltage down, to be only slightly above the desired battery charge voltage. While the batteries become more charged, the proportion of "disconnected" time increases, and PV voltage being shown will tend to increase. It is IMO an error of design to show "PV Voltage" from the connected state value, but that seems to be what it's doing.

This was SWAG, of course. In this scenario, the fact that only 2-3 watts of power was being pulled was probably also a factor in the controller abandoning MPPT mode.