Voltage drop

[Pipsail]

Hi, I seem to have a problem with my system. I have 340w panel, 20a mppt controller, 1500w pure sine wave inverter and 2x130ah batteries. While being solar charged there is no problem but after dark, with all loads turned off (<2a draw with inverter and pir security) the voltage drops to 71% within 3 hours. Is this normal? Batteries are less than 3 months old and of the same batch. Confused.
Any ideas?? TIA.

 

[solar_mike]

Yes. Very odd. Anyway to measure AH"s being used ? I am a fan of the victron bmv. That is the best way to measure battery usgae and draw down. Also, maybe try isolating one of the batteries to see if you have a bad battery.

 

[Dzl]

Hi, I seem to have a problem with my system. I have 340w panel, 20a mppt controller, 1500w pure sine wave inverter and 2x130ah batteries. While being solar charged there is no problem but after dark, with all loads turned off (<2a draw with inverter and pir security) the voltage drops to 71% within 3 hours. Is this normal? Batteries are less than 3 months old and of the same batch. Confused.
Any ideas?? TIA.

Not sure what type of batteries you are using or how you are measuring voltage, but if Lifepo4, voltage is not a good indicator of SOC.

 

[solar_mike]

Very true. I just checked my batteries and based on my battery monitor ( monitors ah's used), i am at 56% capacity. But going on voltage, i am at 13.09v , for my Lifepo4 batteries and that means i am close to 39% huge difference..

 

[Rod64]

I experience the same phenomenon with FLA with only a couple of LED lights on. It goes from 100% to 70% and below in no time once inverter is on. The inverter voltage reading is higher than the CC by 10-20%. I think that CC readings with any type of load are underestimating the SoC.

 

[cypher2001]

While voltage on LIFEPO4 is difficult to use to calculate an accurate SOC, it can be used to determine at the edges. 13.09V is pretty low. Is the battery bank ever getting charged fully? If you fully drain those batteries, I don't think the solar will recharge them in a single day. Can you tell how much solar you are getting from the charge controller?

 

[Zil]

Hi, I seem to have a problem with my system. I have 340w panel, 20a mppt controller, 1500w pure sine wave inverter and 2x130ah batteries.

If you have one of the lead acid chemistries, you are not getting to 100% state of charge. If so, your battery will soon be a lead brick. Don't trust the controller to tell you.

 

[cypher2001]

If you have one of the lead acid chemistries, you are not getting to 100% state of charge. If so, your battery will soon be a lead brick. Don't trust the controller to tell you.

You are correct... the OP doesnt indicate battery chem. Should have started there.

 

[Pipsail]

Hi all, thanks for your replies. I am monitoring the bank with a monitor with a 100a shunt. The system was working fine until the Renogy charge controller went into the periodic ‘equaliser’ mode. The monitor shows .5A going out but the battery voltage drops alarmingly quickly. I wii try isolating one of the batteries and see what happens. They are brand new and matched.

 

[Pipsail]

Sorry, using 2x130Ah SLA batteries.

 

[gnubie]

Can you post a link to the web page for the batteries, or even the manufacturer's web site if there is one.

 

[Pipsail]

These are the ones.

Hankook DC31 Deep Cycle Leisure Battery

This heavy duty deep cycle battery is designed to meet the needs of leisure and marine vehicles. With its sealed calcium construction which makes it 100% maintenance free this battery is fast becoming a favourite within the industry. This range is suited to seasonal use such as Caravans...

www.batterymegastore.co.uk

 

[mopat]

Battery link seems to say 100Ah. Calcium batteries require a higher charge voltage than conventional batteries. If used in a deep cycle situation it is advisable to use a charger designed for calcium batteries of has a calcium charging mode to get the maximum life out of the battery.

"working fine until the Renogy charge controller went into the periodic ‘equaliser’ mode": Sealed batteries do not tolerate equalization,

Not sure what renogy controller you have; ROV-20? can you make it NOT equalize?

 

[Zil]

I think your battery is not being fully charged.

 

[Pipsail]

Hankook XL31S Dual Purpose Leisure Battery

Hankook XL31S Dual Purpose Leisure Battery product brought to you by BMS Technologies LTD Offering free next working day delivery.

www.batterymegastore.co.uk

Sorry wrong link.
will have to look into disabling the equalisation mode. Didn’t realise that sealed batteries were damaged. Thought the CC would have sensed that.

 

[Pipsail]

Am away from home at the moment. Pretty sure I’ve got a renogy rov 20.

 

[mopat]

Hankook seems to recommend constant current charging at 6.5 Amps for their 130Ah battery:

 

[gnubie]

Hankook XL31S Dual Purpose Leisure Battery

Hankook XL31S Dual Purpose Leisure Battery product brought to you by BMS Technologies LTD Offering free next working day delivery.

www.batterymegastore.co.uk

Sorry wrong link.
will have to look into disabling the equalisation mode. Didn’t realise that sealed batteries were damaged. Thought the CC would have sensed that.

It won't be immediately damaged so that isn't the problem being seen here.

The issue with equalisation of a wet sealed battery is that over time the water in the battery will be driven off as the chemical processes in the battery don't recombine 100% of the hydrogen and oxygen gas produced during charging. The higher the rate of production of those gases the worse the recombining rate and the rate of production is related to the voltage you put on the battery's terminals. If you aren't trying to get maximum possible life out of the battery, ie you are happy with the typical about 400 cycles at full charge / discharge and expected years which might be 5 (not checked this battery's spec), equalisation isn't going to cause you problems.

Usually people that are running solar are trying to wring all the life out of a battery they can so then equalisation is not a good idea unless the battery is showing signs of noticable capacity drop after a year or more of use.

Flooded, usually spec'd for equalisation
AGM, usually not spec'd for equalisation but won't be outright killed if done occasionally
GEL, never equalise charge a gel.

 

[Pipsail]

Thanks gnubie, it’s not an immediate problem then. I can’t think what’s gone wrong. Watched all the YouTube tutorials regarding the wiring up of the system and can’t see where I’m getting the voltage drop from with very little load.

 

[gnubie]

Fully charge them separately as 12V batteries, I'm assuming they are in series for 24V. Make sure your charger is configured for the right voltages for your calcium batteries. They do have different voltages compared to a regular lead acid, as pointed out by mopat. Then check their resting voltages. They should stay pretty much the same. If they do, do a load test on each one separately to see how many amp hours you can get out of them. If one is OK in terms of amp hours and the other not, do an equalisation charge cycle on the one that isn't and see if that helps.

If the resting voltage of one battery does collapse, sinks down below 12.4V it's probably toast unfortunately. Do an equalisation charge on it and cross your fingers.

It's really important that the charging voltages are in the window recommended by the manufacturer when not doing equalisation charging as if they are not a full absorption charge will not be done and the battery not fully charged. That's not good for a lead acid and can lead to where you are in the sort of time frame you have noticed.