MPPT cutoff voltage?

[PScott]

I recently purchased one of these 3000W hybrid inverters and was surprised it passes solar voltage to the battery terminals when powered down. Wtf? The end result was it over charged my battery cause I didn't have a BMS. Sure It cuts off in an over voltage situation when charging from AC and solar but it surprised me that it passed current through when powered down. Is this normal ?

GS Hybrid charger solar inverter 1000W-3000W_Shenzhen ZLPOWER Electronics Co., Ltd. UPS & Inverter

Shenzhen ZLPOWER Electronics Co., Ltd. UPS & Inverter

www.zlpower.com

 

[gnubie]

First time I've heard of a SCC or AIO doing that, definitely not the norm.

 

[John Frum]

First time I've heard of a SCC or AIO doing that, definitely not the norm.

I think the mpp aio's do that also.

 

[gnubie]

Wow. That's surprising. That'd definitely be enough to reconsider recommending them to people. I can understand there would be times where you want to trickle recover a completely flat battery, ie so low that you can't actually power on the inverter, but if what PScott is describing is how MPPs react then that's not so good.

 

[NoSmokeYet]

The display shows that power is still going to the batteries when the unit is turned off. I don't use AC power, solar only to charge and I use deep-cycle batteries so it's all good.

 

[Fred S]

The actual array voltage is passed through to the battery, and so this voltage is only regulated when the unit is on? What would be the purpose of that?

 

[nosys70]

on these MPPT there is no switch to power them down (and after all, to power down what ?, if you expect the processing unit to do some job, it looks pretty obvious that is should not be switched off ).
the only ON/OFF switch is usually the one for the inverter.
you still can unplug the main, but for the panel, there is nothing.
Well, i would say such device is build to grab any power source and recharge the battery, so it is normal behavior.
if you want to cut solar power, you need to add a switch at PV input.
and for the general behavior, you must set the parameters (source priority, voltage level for max charge or trickle).
and when delaing with batteries that size, a BMS is recommended.
I think you expect something (battery management) that is not offered by the device.

 

[gnubie]

I think the point of concern is that the unit was putting current to the battery in an uncontrolled way. Sure, a BMS would have protected the battery but suppose the battery by nature didn't require a BMS, ie lead acid. There's nothing wrong with being able to charge the battery when in soft off, it's desirable to be able to do it to cope with the situation where the battery is dead or gone into low voltage cut off. However when doing this it should still respect the charging configuration rather than just pulling the battery up to full array voltage, which is what seems to have happened here.

 

[nosys70]

there must be a problem here, because as soon any power is available (main, panel or battery) the MPPT should switch on and start to manage power inputs and outputs.
usually an MPPT system is deigned to work with a minimal power source.
A good MPPT should even have a battery backup.

 

[gnubie]

You have experience with the particular unit mentioned in the starting post?

 

[nosys70]

no , i do not get this model, i got two 2400W (the white ones ) as advertised on Will's pages.
But it is pretty obvious that a MPPT charger that is supposed to regulate the battery charging (usually with at least 2 parameters MAx voltage and trickle) should do it in any situation, else i do not really see the point of purchasing such device.

 

[Barry N]

it thinks its normal....i have also a hybrid another brand but it also charge the batterys when its powerd down.
When you set your upper and lower limit for the scc there wil be no problem its only feature to always keep your batterys full when you not use them

 

[nosys70]

yes, but what is not normal is there is state in the controller that just release power form Panel to battery without control.
if max voltage and trickle voltage is set properly you should be able to left the battery connected , getting charged (but not overcharged).
the behavior described (if correct ) is abnormal.
BUT... i got a 8 cells 24v pack i charged without BMS, and i ended up with 2 cells showing 3.7V while the others showing 3.4.
So you can imagine the battery can be damaged even if there is no abnormal behavior from the MPPT.
i drained down the cells and installed a BMS, then charged again. This time all cells were charged with same voltage.
So basically , even with a working MPPT , you can get a "flawed" battery that requires a BMS.
I would say that even with a perfect battery, you take risks to use it without BMS.

 

[Barry N]

it's normal, the charger can not see the voltage of different cells only the whole pack voltage and charge it to your set voltage.
So if there is a imbalance i your packs it wil charge to your set voltage but one cell could be higher then other cells but the overall voltage can be 24 volt.
ALWAYS USE A BMS... problem solved….

 

[JoeHam]

Really need @PScott to clarify.

Is it working as a normal MPPT when powered off? That is, does it regulate the voltage?

If so, then it appears that the power switch is for the inverter function only and it works like a normal MPPT SCC regardless of the inverter state.

IF that is the case I would say it’s normal.

IF it is passing unregulated voltage when the switch is off I would say that is definitely abnormal.

It’s hard to discern from the OP which we are talking about.

 

[Barry N]

MMPT has nothing to do with charging.
on/off switch is only to turn on and off your inverter,the charger charge to your set voltage!! (even when the inverter is off) your problem is that you are not using a BMS that protect your cell of over charging and you not burning your house down

 

[Ampster]

MMPT has nothing to do with charging

I am not sure what MMPT is?
MPPT (Maximum Power Point Tracking) is an algorithm used to get the optimum energy out of panel whether to charge batteries or power an inverter to service loads. The other term used in this thread is the inverter brand which is MPP. The white boxes that @PScott described may be charge controllers but I don't know. What PScott has not told us what is the data about the overcharging event?
Cell voltage of each cell?
High Voltage Disconnect setting on his charge controllers?
A clear understanding about the MPP and the white boxes.

 

[Barry N]

I am not sure what MMPT is?
MPPT (Maximum Power Point Tracking) is an algorithm used to get the optimum energy out of panel whether to charge batteries or power an inverter to service loads. The other term used in this thread is the inverter brand which is MPP. The white boxes that @PScott described may be charge controllers but I don't know. What PScott has not told us what is the data about the overcharging event?
Cell voltage of each cell?
High Voltage Disconnect setting on his charge controllers?
A clear understanding about the MPP and the white boxes.

@Ampster it whas a typo

I have a mpp solar hybrid v2 when the inverter is off it charges always the batterys and cut off at my set voltage

 

[JoeHam]

MMPT has nothing to do with charging.

I should have said MPPT SCC which has everything to do with charging as it is the only way all of my batteries get charged.

It helps me to understand problems with the all in one units if I know whether the OP has a problem with the MPPT SCC part, or the inverter part or the AC charger part.

I think this issue is with the MPPT SCC part but it’s not clear to me. Hope that helps clarify.

 

[Ampster]

@Ampster it whas a typo

I have a mpp solar hybrid v2 when the inverter is off it charges always the batterys and cut off at my set voltage

Yes, that is how it should work. We haven't heard from @PScott to clarify. I did reread the thread and the white box comment was irrelevant.