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AGM batteries in good condition but voltages drops too fast.


SunnyParys
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We have a strange problem. When the system works through batteries, the voltages drops like if the batteries are damaged. But tests shown they are still as good as new.

 

The 230a string of 4 batteries are supposed to deliver around 5500w to 50% capacity according to my calculations. However, with a load of around 300w they would drop to 48v in around 3 hours.

A bigger load like a kettle would drop the volts from 52v to 48v with-in a minute.

The energy consumption is low at night. So, the first few nights they gone through till the next morning. A cloudy day, and the inverter switched to Eskom around 12am. The next night, 10am. The night after that, like they are now, lasted for 3 hours. That 3rd night, had a sunny day. So I got worried.

I didn’t know about voltages at that stage so wasn’t monitoring it. However, I did some reading after the problem got to lasting 3 hours and noticed the batteries are not supposed to go below 48v. It’s been set on 47v back to utility. That’s why my first thought been they are damaged. Since I set it up to 48v, the volts dropping never got worse.

The battery test results as follow (All 4 batteries shown around the same results):

Voltage: 13.23v.

Measured: 1308 SAE (A).

Rating: 1260 SAE (A).

 

Currently the Growatt is set on SOL to switch to eskom after dark. The last hour of sunshine the panels don’t give much support, so mostly the volts are on around 50v before switching over to utility. The loads during that hour average at around 300w.

There’s 9 panels to recharge the batteries in the morning before going back to solar at 55v. I don’t think the problem is with charging, the batteries appear to be fully charged according to the person whom done the test on them.

 

Is it possible that something in the inverter got damaged? Growatt 5KVA off grid inverter. The system is around 6 months old, I’ve been looking for answers for more than 5 months.

I’m not getting support from the installer and would really appreciate some words of wisdom.

 

Thank you.

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16 hours ago, SunnyParys said:

A bigger load like a kettle would drop the volts from 52v to 48v with-in a minute.

This could be normal for the voltage to drop while under the load of a kettle and then when the kettle has boiled the voltage should bounce back to the 52V

16 hours ago, SunnyParys said:

The battery test results as follow (All 4 batteries shown around the same results):

Voltage: 13.23v.

You could do a load test on the batteries if you have a dc multimeter, It will be a good indication to measure the voltage across each battery when a load like a kettle is on, that should indicate what battery is the weakest or even pick up the faulty battery, normally one or two batteries will have a significant lower voltage in the bank of four, doing this test with batteries charged at 100% and do the test again with batteries at say 70%. that is how I picked up my faulty batteries. I then took them for a proper battery test and they just confirmed the same faulty batteries. Just my bit of experience.

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On 2020/11/04 at 12:02 AM, SunnyParys said:

the batteries are not supposed to go below 48v. It’s been set on 47v back to utility. That’s why my first thought been they are damaged. Since I set it up to 48v, the volts dropping never got worse.

I think that's the problem. I would have set the "back to utility" voltage setting even higher, say 50 V.

Your symptoms are compatible with a battery that has good power delivery, but poor energy capacity. That happens to lead acid batteries that are discharged regularly well below 50% SOC. 48 V is nearly empty, depending on the load and many other factors.

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Appreciated Gerrie and Coulomb. Wish I found this site earlier then I wouldn't have had to just go on "trusting the installer".

I've found a better installer since and would pass the recommend test on to them. I truly believe you two are correct, the batteries are faulty. But, I didn't want to buy Pylon just to find there's a problem with the inverter. New at this, so just took guesses at what can be wrong. It took me by surprise to see the good battery test results since they're behaving oddly. 

I do however have two concerns on Pylon Tech. Our routine, after dark the only higher load we use is a microwave, for around 3 times 1 minute. Can a Pylon handle that kind of load? Secondly, if Pylon is just used as back up for if Eskom fails, how tough is a cold start really on them? Lets say, winter time and the Utility fail at 6am and the 'back up battery' wakes. It gets pretty cold in the garage where they would be.

These questions had me wondering, should I get enough batteries to carry through the night to avoid cold start? If they can't handle heavier loads, that would not be a good idea since there's an early morning kettle too. Then I'll rather just get one 3.5kwh for back up at night and support during the day when a cloud blows over. But, then that one battery is exposed to a cold start.

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3 hours ago, SunnyParys said:

I do however have two concerns on Pylon Tech. Our routine, after dark the only higher load we use is a microwave, for around 3 times 1 minute.

The pylontech 3.5Kwh can deliver 74A max but recommended discharge is 37A, with the microwave on for such short duration shouldn’t be a problem,   but something to consider is what other loads you might already draw during the night when you want to use the microwave, that might push your battery Amps much higher than the recommended 37A (I tested my microwave’s battery current before and it has a start spike of 49A and than drop to about 32A afterwards) I removed my microwave and even my kettle from the inverter because I wasn't comfortable with that higher load on a single 3.5Kwh pylontech, I will feel more comfortable to use the microwave and kettle once I installed a second pylon, so for now I just nurse my pylontech battery although I do maximize the use by using it for long  periods but with loads that don’t have high currents.

 

3 hours ago, SunnyParys said:

if Pylon is just used as back up for if Eskom fails, how tough is a cold start really on them? Lets say, winter time and the Utility fail at 6am and the 'back up battery' wakes. It gets pretty cold in the garage where they would be.

 The specs say working temperature -10 to 50 degrees, mine is also in the garage and it is pretty cold there in winter, so I’m also a bit concerned and think maybe to put a blanket over it in winter. 😃

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Gerrie, 2 Pylons and a 74a for a short duration of a kettle or microwave should be okay? I ventured into solar on a terrible time, right before the lockdown. Pylons been hard to find and expensive if found so I trusted the installer after he said AGM is better. Since then, I found he's been the only person to think so.... For our loads, 2 pylons  would take us through the night even on 60%, since our load is less than 4kw from dust till dawn. My thinking is, get 2 pylons, then put the inverter on "Charge with utility only if solar isn't available".  Put the Utility charging to low amps to safe electricity, for if the batteries don't see it through the night. That way, the batteries are either supplying, or charging, so no cold start. But, I want to be sure I won't damage the batteries with a load of a kettle or microwave. The cost on the AGM's, that's about as far as I'm willing to go with school fees. 

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13 hours ago, SunnyParys said:

he said AGM is better. Since then, I found he's been the only person to think so....

Believe me, since I installed my system, I've been to many solar suppliers/installers. As this is corruptus maximus South Africa, if you walk into a store and agm is all they have, that will be the best battery ever, just to get rid of his stock. Had one guy tell me truck batteries are the best... (because they are big). Rather listen carefully to the guys on the forum. They offer their knowledge for free and that is priceless.

You could put the big loads (Hair dryer, kettle, microwave etc... on eskom (or gas for kettle) It will cost less to pay eskom for that than the damage to your batteries.

You didn't mention the geyser. Again, go for a gas geyser. (if not already) I'm not sure if I can link a website to the forum, but here goes...

https://www.takealot.com/all?_sb=1&_r=1&_si=38ae2bbb4ff87715e5c2d2b5d9d795cb&qsearch=gas geyser

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  • 2 weeks later...

Thank you for the replies all! Just felt like an update on my original post, for if someone with a similar problem browse by.

I'm currently typing on a PC, that's powered by the AGM's that's been faulty. Found a really reliable installer in Parys, they showed up to test the batteries on a load test. I stood there waiting for bad news, but instead, they fixed them. I can't go technical with my knowledge, but in short, it's been incorrect charge settings. From what I understood, the settings caused something like "more volts than amps" in the batteries.

Still some work to do to get them back to working 100%, HUGE improvement within a week though. I would be discussing the next step with them when they come to install the Geyserwise system with panels for the geyser (Wanted to venture into geyser savings ages ago, but had to wait to see if we need new batteries first. Messed up to be on a budget :-) ). Gas won't work here, water pressure in Parys can't always keep those going.

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