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Why do I get a voltage drop from my solar panels....? Answered

I am building my own solar panels and installing them as I go. So far I have mounted three 70 watt panels. I have a twenty amp controller and a 1500 watt pure sine wave inverter. With the array switched on and connected to the batteries (8 x12 volt 134AH) via the controller everything seems fine with a steady 13 -14 volt charge coming through. But when I connect the inverter the PV volts drop to around six and seven volts....The batteries are wired in parrale but not directly to each other. Instead I connected them to a buss bar hoping for equel drain and charge... I then connected the wires from controller and inverter to the bars... I thought this may have been the problem so swapped them all around having the controller wires to the battteries, then the inverter directly to the batteries... It made no difference and the voltages remained the same....I am hoping now that the reason maybe that I do not have enough panels to power the system and as I add more panels the voltage will rise...... l Any thoughts on this will be very welcome.....?


As a follow up for anyone interested I was using a 20 watt charge controller... I have since changed this to a 60 watt charger... The system now seems to be operating properly with no voltage drop....?

Voltage drop outs can occur on a solar Pv system when the Incoming grid voltage exceeds 253v, Solar inverters have to shut down if this happens causing your system to stop generating, I had this problem and solved it with an Eco Box here is a link to the site www.thevascogroup.co.uk I have my system externally monitored and after installing this box my system is now producing about 14% more.

i have a solar panel of 12V and i want to connect with 12 volt battery through charge controller than pv show different values like 12.6 , 11.1 , 10.5 , 9.6 ... so i am fully confused, please tell me about thats logic or problem?

i've a solar panel of 38volt and i want to connect with 12volt battery through charge controller, then pv shows 12 volt on pv side and battery side, so i am fully confused, please tell me about thats logic?

This is very normal, it's known as voltage drop. It's caused by the charge controller drawing current from the panels. Essentially, the charge controller is putting the 'missing' volts to work, and so they become unavailable to measurement.

A bit late, but not all chargers support charging and loading the batteries at the same time. They have a micro-controller that monitors the battery's voltage while it charges. Adding a load to the battery then would cause a voltage drop, which the charge regulator might interpret as a fault, and a safety mode kicks in which is meant to prevent a dead battery from being charged.

In your case though, you were experiencing a voltage drop on the panel side, which indicates that your regulator drew more current when the inverter was turned on. In this case, your regulator saw the voltage drop caused by the inverter's load and interpreted it as a need to charge the battery bank. Essentially it tried to charge your full batteries, but actually delivered it's current to your inverter. Not great for the charge regulator.

I have the same problem but I wnat to know what should be don in winters? does anyone have idea about the range of voltage dip in case of snow?

Hi It seems to me that you pv's to battery ratio is wrong. You have 1056 amp hour batts and 3 x70 watt panels . Your panels will be charging at a rate of approx 11.6 amps. That means that it will take 100 hours at full sunshine to charge you battery bank.You will see 13/14 volts coming from panels but amps are low. When you turn on your invertor even with no a/c load, it sucks the amps and then your batteries show nearly true voltage. disconect your panels from batts and run a volt meter over the idle batteries, see what true voltage they have. Good luck Cheers


7 years ago

Yeah, when the voltage drops then typically you're drawing too much current. Most solar panels will have both a "no load" voltage rating, and a voltage rating for a certain load current.

Is your system doing this without a load attached to the inverter?

Thanks for the promt replies... Everything works fine until I plug the inverter in... and the strange thing is the inverter can be switched OFF and the voltage still drops....

I was hoping that the inverter was drawing some power before the batteries causing the drop... but if it's not even switched on..???...

Yes the inverter works fine.....

My idea is to convert the garage and workshop over to solar power then as I add to it change the house over... With the garage I still wanted the option of mains power as well so I installed two seperate power points... One has the mains supply and the other the solar... I fitted a plug on the garage supply and simply plug into which power I want to use.... This is where I get the problem when I plug into the solar supply... I have not tested it fully but I think plugging a single eletrical device in does not cause the problem....

Very strange indeed. What brand name is the inverter? Can you send a link?

Here are a few pics ... don't know if they will help or not....
In the first one the power is coming from the solar panels through the box on the left... through the voltmetre, and then to the solar socket. The other socket is connected to the mains supply. They grey plug is the power lead to the garage and workshop. The other switches are just lighting for workshop.
Then there is a pic of the controller, the battery bank and then the inverter.

Solar 059.JPGSolar 068.JPGSolar 066.JPGSolar 067.JPGSolar 064.JPG

Is anything getting warm when the inverter is in circuit ? What current do you measure in the leads from the panels, when the voltage drops ?

No...nothing is overheating.... I have a voltmetre in-line from the panels and also get a read-out on the controller....

So there are no amps flowing when its connected, yet the terminal voltage drops ? Is there any open circuit voltage on the INPUT to the inverter, crazy as that sounds.


Sure about your panel polarities ?

I would imagine if the polarities were at fault then I would get a consistant error all of the time...?

I think from your description that your battery is too small compared to the size of your inverter. Sure... the battery is fully charged... but it isn't capable of supplying the AMPERES required by your inverter. Test your inverter to see if it works properly when connected to a good automobile battery (assuming the inverter works on 12 volts of course). It could also be that your battery is defective. Many many things could be the cause. A corroded battery terminal or the inverter may be defective. You need to eliminate each suspected problem one at at time using other tests and voltage measurements. If your wiring is too THIN... or way too long like 100 foot... that can also cause voltage losses especially if dealing with higher amperages. Possibly your battery is GOOD... but isnt charged up. If the battery is charged and will not hold a good 12 or 13 volts under a reasonable amp-load... then the battery is bad.

The battery bank seems ok... They are all brand new 12 volt 134AH batteries.. I have eight of them wired in parrelel.... Apart from the voltage drop the system works fine... I can power all my garage and workshop... I just can't charge the batteries with the inverter plugged in.....?