Low SPG readings when voltage is still above 50%...

Mr Vee · May 2013

Hello there all.

Before I start I shall give the details of my system.

4 x 240w Bosch panels
Outback FLEXmax60 MPPT Charge Controller
Outback VFX 3024 inverter
4 x Rolls s530 6v Batteries run is series at 24v

Panels receive full sun from 9am until 6pm in summer and 10am until 3.30 ish in winter

System was installed in mid July 2012

My loads on the system are as follows.

800w water bore hole pump - runs for 15 minutes a day
150 watt fridge on lowest setting (uses about 90 watts for 10-15 minutes every hour)
2 laptops
5 led lights

On sunny days the water is used more and we have a washing machine that does a cold wash

On cloudy days the fridge goes off

Our energy usage is low. Most of my electrical equipment is in storage until the system can cope with it.

The charge controller claims to input 5 - 6.5 KW Hours on a sunny day and 1.5 - 2.7 KW Hours on a cloudy day on average.

I have recently purchased a hydrometer to monitor specific gravity levels on my battery bank as after a long winter and a very wet spring the system had been somewhat under powered. The readings were around 1.22-1.23. I ran an eq cycle on the charge controller at 31.4v over a couple of sunny days and was able to get this up to 1.25-1.255 before I ran out of sun. The system seemed to be performing better until we had a small run of bad weather and the voltage ran low (23.0v). After this it seemed that the battery bank did not want to charge. A full day of sun with 850-940 watts consistent during peak hours and yet it would not rise above 26.2v.

I took a reading with the hydrometer and it was below the scale (the scale being 1.15-1.30) and not just by a bit but by a lot. The top of the glass tube was bobbing in the water. At this I panicked and ran out and bought gas for the generator ( a rather inefficient 6kva petroleum that pushes out 2000w charge and up to another 2000w for ac loads) and ran an eq cycle at 32.0 volts over the day until the readings were 1.26-1.265 across all cells. This is what rolls recommends.

The low battery cut off on the inverter is set at 24.0 volts and the full charge cycle has been completed several times since this (2 hour absorb at 29.4) and hydrometer reading were showing 1.23 in the morning with a voltage of 24.7 easily rising to 1.25 and above with the absorb cycle.

After another couple of cloudy days the system is down to about 24.0 volts last thing at night but has not gone so low as for the cut off to occur.
Yesterday I took a hydrometer reading while the the voltage was above 24 volts and the sun was not shining and my reading was 1.15-1.16 across all cells.

This has confused me as I thought the system was working better now and yet my SG reading indicate that my batteries are way below 50% SOC even though the voltage is above 24 volt. This SG has remained consistent throughout the day even though levels have gone up to 26volts despite the lack of sun. If it was not for the hydrometer I would not know that I have a problem.

What can I do? Should I run another eq and continue until all cells read 1.26-1.27 (I was only short by a hare's breath). Could I have a faulty cell or are my batteries shot after one winter?

I wish to expand the system in the near future doubling the bank and adding more panels to match. I am worried that if these batteries are now compromised I will not be able to see the full potential of any new batteries that I add.

Sorry to be so long winded but I wanted to answer the obvious questions before they are asked.

Thanks in advance.

Blackcherry04 · May 2013

Re: Low SPG readings when voltage is still above 50%...

The short, is run another EQ and up the daily charge voltage to at least 29 V and increase the time. After you get them stabilized, then you can work on the Voltage and Time settings. You need to get a foot in the sand on the SG's to give you a constant to shoot at. The batteries are good or the SG's wouldn't have came up from the first EQ and if you checked all the SG's you should have noticed a bad cell.

Cariboocoot · May 2013

Re: Low SPG readings when voltage is still above 50%...

Welcome to the forum.

I have a pretty good idea what the problem is, but let's check the numbers first.

Four 240 Watt panels = 960 Watts of array. Typically you could expect about 30 Amps peak charging current from that on a 24 Volt system.

The Surrette S530's are 400 Amp hours, so you should be able to achieve a peak charge rate of 7% on a sunny day with no loads.

It's that "on a sunny day" that's getting you. You've had a lot of not-so-sunny days and the charging will have slipped. If loads are used at the same time as is typical, it's even worse. The longer this goes on, the more sulphated batteries get.

Now it's anecdote time: I need to replace the battery in my mower. Charge it up, and it gets to 12.7 Volts. It will drop to 12.6 overnight. But if I try to start the mower the Voltage drops to 10 in an instant, and does not 'rebound' back up over 12 Volts when I leave off the starter. The battery is sulphated: it will charge to the "right" Voltage but it no longer has sufficient capacity to deliver the current demand. Like finding your 'D' cell as become an 'AAA'.

I fear this is what has happened to you, but on a more expensive scale.

What to do about it:
1). Bulk charge the batteries using the generator early in the morning. Let the panels do the Absorb and then run EQ cycle if possible. Do it again and again until you can see no further improvement in SG levels.

2). Check the Absorb Voltage and time. Expand the Absorb time to 4 hours, set the FM60's End Amps function (don't tell me; they deleted that from the MX model?) to about 6 (1% plus some compensation for loads). Make sure you have a remote temperature sensor on the charge controller. You may want to push the Absorb Voltage to 30-30.5. Surrettes can be the very devil to work with.

3). Set the LVD on the inverter to 24. Under load that will ensure the batteries are not taken below 50% SOC; when the load is released they will rebound above that Voltage.

4). Increase panel capacity if at all possible. 1250 Watts would be good for consistent sunny operation. If you have bad weather, bulk up with the generator first thing. Do it again at night if the batteries haven't got a full charge from the sun. The alternative is adding even more panels.

First lets see if those expensive batteries can be saved. Charge, EQ, get the SG up. if it won't rise any more, you're done. If the cells are fairly consistent in SG then there's no one damaged cell. If after getting the SG up to 1.270-ish they still fall off before nightfall they are sulphated.

As always, check your loads. You should have enough capacity there for 4kW hours AC per day.

Mr Vee · May 2013

Re: Low SPG readings when voltage is still above 50%...

Hi there. Thanks for your reply.

After the last eq which finished at 7 pm at 1.255-1.265 across all cells. At midnight this was relatively unchanged. 1.25 more or less across all cells. The next morning the reading was 1.24 across all cells more or less. The variation between cells has always been no more than .02.

The problem is the fact that the batteries are able to drain down to such a low SOC and yet the low voltage cutoff is set at 24.0 volts and can be set no higher. We rae on our fourth cloudy day, the voltage has not dropped low enough to cut off and we have had about 2.5 kwh per day and still the SPG is 1.16-1.17.

I'll try another eq cycle when the sun returns, hopefully tomorrow according to the weather report. I will also run the generator to complete this.

westbranch · May 2013

Re: Low SPG readings when voltage is still above 50%...

for the best bang for $$ expended running your gen you want to use the gen for Bulk charging, not for finishing a charge. As 'Coot said let the PV finish the charge.

YehoshuaAgapao · May 2013

Re: Low SPG readings when voltage is still above 50%...

Smells like sulfation to me.

When you upgrade and double your battery bank, I'd triple the solar panels. At 24V, you will need to get another charge controller, or convert to 48V (which would need a new inverter, and convert to a string size of 3 if you current string size is 2). 240W solar panels are $200-250. One of those surretes is $300-350.

If you replace your battery bank and stay with Surrette, see if you can get S-500EX. They are the quarter-inch series 5000 plates in a series 4000 L-16 container (they call them series 4500). Wonder how well they will actually do. They have a slightly less capacity.

Cariboocoot · May 2013

Re: Low SPG readings when voltage is still above 50%...

Not necessarily sulphation; it could be the battery bank is not sufficient to handle the overnight loads without being drawn too low. That is an issue I mentioned before, and it does need to be examined otherwise all is for nowt; the problem will simply reoccur.

Mr Vee · May 2013

Re: Low SPG readings when voltage is still above 50%...

YehoshuaAgapao wrote: »

Smells like sulfation to me.
240W solar panels are $200-250. One of those surretes is $300-350.

Ha ha. you guys have it good over there. For me here in Portugal we get fleeced because the country is poor. We pay €450 ($585) for a panel and around €375 ($487) for a surrette!

I ran the genny this morning (beautiful sunny day) to get it up to absorb voltage but as soon as I switched off, battery voltage backed right off again and has taken all day for the panels to bring it back up to 29 volts, SPG reading at 1.17-1.18. A long way from 80% charge no? It seems the voltage figures do not equate with the SPG readings until it has had a long charge over a few consistently sunny days or been given some eq time.

Hopefully tomorrow we can complete the absorb cycle and get up to 1.25 or more SPG. I shall take a reading last thing tonight and first thing tomorrow morning to see what difference has happened over night.

Thanks again for all your help.

Mr Vee · May 2013

Re: Low SPG readings when voltage is still above 50%...

OK I have followed your advice and have made some great improvements!

I put the absorb up to 30.0 volts and have extended it to 4 hours which has run for a few days. LVD has been on 24 anyway and so it remains.

I have been shutting the fridge off overnight and only starting it when the sun is shining, if the day is cloudy the fridge stays off. Extra circuits are turned off overnight in case of phantom loads.

After a few days of this my SPG is at 1.26 across all cells once float is reached. 1st thing in the morning it has been no lower than 1.23 and normally is 1.24 to 1.25.

One thing here is vexing me slightly: When I take a reading with the hydrometer I find that depending on how i take the reading I get different results. For example, once the system is in float I pick my pilot cell. If I draw the fluid into the hydrometer quickly the glass bulb bobs up to the surface very quickly and I get a reading of 1.24. If I draw it in slowly I get a reading of 1.25 and if I draw it in v-e-r-y s-l-o-w-l-y I get a reading of 1.26. If I draw fluid into the hydrometer and then squirt it back deep into the cell a few times effectively mixing the electrolyte I can get a reading of 1.27 if I draw the fluid in very slowly again. Through all these readings 1.26 seems to be the average so this is what I quote. Which reading should I trust?

If my estimation is right (1.26) should I further equalise to bring this up to 1.27? I have a week of good weather coming up now so the timing seems perfect to nail this problem.

Blackcherry04 · May 2013

Re: Low SPG readings when voltage is still above 50%...

Mr Vee wrote: »

OK I have followed your advice and have made some great improvements!

I put the absorb up to 30.0 volts and have extended it to 4 hours which has run for a few days. LVD has been on 24 anyway and so it remains.

I have been shutting the fridge off overnight and only starting it when the sun is shining, if the day is cloudy the fridge stays off. Extra circuits are turned off overnight in case of phantom loads.

After a few days of this my SPG is at 1.26 across all cells once float is reached. 1st thing in the morning it has been no lower than 1.23 and normally is 1.24 to 1.25.

One thing here is vexing me slightly: When I take a reading with the hydrometer I find that depending on how i take the reading I get different results. For example, once the system is in float I pick my pilot cell. If I draw the fluid into the hydrometer quickly the glass bulb bobs up to the surface very quickly and I get a reading of 1.24. If I draw it in slowly I get a reading of 1.25 and if I draw it in v-e-r-y s-l-o-w-l-y I get a reading of 1.26. If I draw fluid into the hydrometer and then squirt it back deep into the cell a few times effectively mixing the electrolyte I can get a reading of 1.27 if I draw the fluid in very slowly again. Through all these readings 1.26 seems to be the average so this is what I quote. Which reading should I trust?

If my estimation is right (1.26) should I further equalise to bring this up to 1.27? I have a week of good weather coming up now so the timing seems perfect to nail this problem.

Sounds like your there, I'd go forward with Time & Voltage and keep the EQ for when you really need it, It's hard on the batteries. If you sliding backwards, up the voltage .05 volts for a couple days or up the time for 30 minutes or so. Then use the EQ charge to make big changes once a month or so.

The readings are effected by the Temperature of the Electrolyte and the Mixing during gassing. The warmer the electrolyte, the lower the density so the float will read lower as the float will be lower. For instance, my boat sits 1 " higher in the water in the winter than it does in the summer. There is also a degree of error and repeatability that you should consider.
.

Mr Vee · May 2013

Re: Low SPG readings when voltage is still above 50%...

1 " being one inch? Thats a lot of difference. Currently temp is around 10-16 degrees C. The batteries are in a concrete room underground so are not affected majorly by outside weather at the moment. Should I be adding on top of my reading to get a true result.

Ideally I would like to get off of the 30 volt 4 hour absorb down to a more reasonable 29.4volt 2.5 hour charge. Is this feasible?

Blackcherry04 · May 2013

Re: Low SPG readings when voltage is still above 50%...

Mr Vee wrote: »

1 " being one inch? Thats a lot of difference. Currently temp is around 10-16 degrees C. The batteries are in a concrete room underground so are not affected majorly by outside weather at the moment. Should I be adding on top of my reading to get a true result.

Ideally I would like to get off of the 30 volt 4 hour absorb down to a more reasonable 29.4volt 2.5 hour charge. Is this feasible?

Well, the SG is dependent on your usage and the capacity of your bank and the size of your array. You only have two variables, Time and Voltage in the charge cycle you can change. The temperature of your batteries are not only effected from the ambient, they are effected by the charge cycle. You always correct the temperatures of your readings somewhat. I have a digital temperature prob in a cell, that said, I look for trends and don't focus on a day to day readings.

It's a big boat and has a aluminum hull , 18 x 78 feet. It's funny, it can sit in a frozen lake and never completely freeze in, you can always slip a piece of cardboard between the ice and the hull, so it's always floating. I guess there is always enough heat above or below the ice and the aluminum transmits it..

Here is a interesting Hydrometer, I have two of them. They are automatic.

http://forum.solar-electric.com/showthread.php?18498-Calibrate-your-Hydrometer&highlight=hella

If you want one really bad, it's $11.30 Euro and $29,00 Euro Shipping !!! by DHL. I have 2 of them and it takes about 30 days shipping. They will only ship with DHL, it's a shipping rip-off.

So the cost is about $44.00 USD

http://seekpart24.com/hp/battery-aci...t-tester-18115

There is also a Blue one, but it costs a little More for the " Hella " branding.

http://seekpart24.com/search?q=8PD006541001

I have tried to contact the Manufacturer a couple times and offered to buy 100 of them , no reply. They might be out of business or someone else may have bought the company.

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Mr Vee · May 2013

Re: Low SPG readings when voltage is still above 50%...

OK so this all sounds positive although the rolls manual states the optimum voltage for absorb to be 28.8-29.6 so surely operating in this range is preferable no?

Blackcherry04 · May 2013

Re: Low SPG readings when voltage is still above 50%...

Mr Vee wrote: »

OK so this all sounds positive although the rolls manual states the optimum voltage for absorb to be 28.8-29.6 so surely operating in this range is preferable no?

Generally , yes. You have to understand it hard to write a manual to cover every situation and charging source. If you call there tech line and they would tell you to increase your charging ( Voltage & Time ) if your falling behind and deficit charging or do a EQ to catch up.

NorthGuy · May 2013

Re: Low SPG readings when voltage is still above 50%...

Mr Vee wrote: »

OK so this all sounds positive although the rolls manual states the optimum voltage for absorb to be 28.8-29.6 so surely operating in this range is preferable no?

Since your battery are in a cold place, there must be a temperature compensation for charging voltage. So, you need about 1 degree C higher than they recommend. Many chargers will have a temperature sensor to automatically compensate. If yours doesn't have one, you need to adjust manually.

If you need to increase charging voltage a bit over manual that's Ok. My batteries were so stubborn that I had to add 5.2V (on 48V, same as 2.6V for you). So, extra 0.5-1V will not hurt if you really need it to keep your batteries charged.

Mr Vee · May 2013

Re: Low SPG readings when voltage is still above 50%...

I have temperature compensation installed. This system is under a year old and only suffered punishment during the winter and an extended wet period in the winter. I think I panicked somewhat as to the severity of this situation upon taking some very low SPG readings. With the summer here now and longer daylight hours with plenty of sunny days there is no danger of deficit charging, and now, armed with a truer knowledge of what my system can put out I am able to tailor my energy usage so the batteries are topped up fully almost every day. By autumn I hope to install at least 2 new panels to help with the winter deficit problem and I will have to use the generator more to keep things running smoothly.

With this in mind my system is not one that is suffering with deficit charging as a constant. I hit absorb every day unless it's REALLY cloudy and most days reach float. I am trying to recover the batteries from 2-3 months of bad charging that I will ensure NEVER happens again.

I just want to try and keep the batteries as close to peak performance as possible so when I expand in the near future these batteries don't drag down the new ones.

I guess experimentation is the key as each system is different and each user has different energy requirements.

I will try gradually backing off the voltage and the time and see if the SPG readings are the same at float. As soon as they drop I'll increase again. In a few weeks I guess I'll have it right.

Thanks loads to all who got involved here for all of your help, your advice has been extremely helpful and you have helped me to (hopefully) bring my system back to its peak and at the same time arming me with a sounder knowledge of my system and batteries in general.

Low SPG readings when voltage is still above 50%...

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