How to avoid overcharging my battery bank

[Hinchebyinch]

Hi. Thanks in advance for your help

I am in Haiti. My system is as follows

• 6 x Trojan t-105's (675ah 12v bank)
• Magnum 1500w inverter/charger
• Flexmax 80 mttp
• about 1000w solar on the roof
• I consume about 6 kwh per day of electricity

After about 5 months just got reconnected to the grid. At the moment we are getting about 6-8 hours of grid electricity per day, and it always comes at night (around 10pm-6am). It will charge my batteries nicely overnight. Then it goes off at 6 and sunrise is at about 7, start getting some decent watts at about 8:30. In that time the "under-load" voltage of my batteries has dropped below 12.5, so the flexmax goes into Bulk charge when it wakes up. It will wont normally reach the absorbtion stage as basically i take out almost what i am putting into it all day long, so it can be charging for hours at 13.8-14v and my batteries seem to get warm.

What would be the best settings for my voltage? Bear in mind that sometimes without warning (though rare at the moment) they will give an entire day of grid power, and sometimes they will not give any for a week or so

I am thinking............

Charge overnight with grid power
Set rebulk on the flexmax to a lower voltage, i.e. 12.1v, so if the batteries have had a charge overnight it will not bulk charge them again, and set the float at 13.2? (Trojan website says float at 13.5 but it seems high to be at that all day long?)
And then my panels should just produce enought to keep it at that voltage, thereby replacing what is taken out in near enough real time? That way there should only be an hour or two in the morning, and five or six in the evening where everything is powered just by batteries?

Also thinking maybe i can set the magnum inverter to charge at 30%? then it wont matter if they give grid power at the same time as im solar charging?

Really appreciate your help - Sam

 

[snoobler]

So basically, you want to charge your batteries with grid and not over charge them with solar?

https://www.trojanbattery.com/pdf/datasheets/T105_Trojan_Data_Sheets.pdf

Set FM80 bulk/absorp/float to 13.5V. The only consequence of that is 13.5V may have a slightly higher risk of venting/fluid loss over long periods of floating. Given that you'll be "floating" at less than 100% SoC, the risk is minimal. Simply check regularly and add distilled water when needed.

Set Magnum to charge as high as it can, 67.5A max (10% of capacity, Trojan allows up to 13%). Note that charging at less than 40A is unhealthy for your batteries. If tail current can be specified (absorption termination current), it should be 13A (2% of capacity, Trojan allows 1-3%). You should be using temperature compensation as well via a temp probe attached to the battery (usually (-) terminal) feeding temp data to the Magnum.

Thusly configured, early morning load will pull the bank down a little, then bulk/absorp/float at 13.5V will maintain the battery at that slightly reduced state of charge during use all day, a little more reduction in the evening, then fully charged with the Magnum using a normal charge profile at night.

This should result in a very shallow depth of discharge every day and maximize the cycle life of your battery.

Get yourself on a battery maintenance schedule to include individual 6V battery voltage and SG monitoring.

Trojan Battery | Battery Maintenance

The key to achieving optimum performance and long battery life is to follow a regular care and maintenance program. Read our tips for high performance battery maintenance.

www.trojanbattery.com

Equalize when SG criteria dictate it is needed.

 

[Hinchebyinch]

Thanks, that is really helpful.

So to confirm, i can just set the bulk voltage to 13.5 too? that would mean that i could never bulk charge off solar, however if we have a couple of days or a week when they dont give grid power i just manually change bulk voltage back up? what about the idea of setting the rebulk voltage low so it would detect if i go a night without power? That said i dont want the power to come on in the morning (it isnt fixed times) and then charge at over 110a. Im trying to figure out the settings where it will run with the least input from me

 

[snoobler]

Isn't the default re-bulk at 12.0V anyway?

http://www.outbackpower.com/downloads/documents/charge_controllers/flexmax_6080/owner_manual.pdf

Page 96



Also indicates the absorp can be set to anything between float and 80VDC.

Once the charger shuts down at the end of solar day, it's always going to start the next day in bulk mode even if re-bulk isn't hit.

With nighttime grid charging, you would briefly bulk off solar, but only to 13.5, quickly absorp, then drop to float. FM80 would vary charge current to maintain 13.5V under loads.

I didn't pick up on the variability of the grid power.

If you didn't get grid for one night, you would again bulk/absorp at 13.5V. This would put you at a lower state of charge, but it would probably be fine for a single night. Since you don't seem to have enough solar to fully charge AND run your loads, I don't know that it matters. You can't charge your batteries anyway if you don't get grid power at night.

The single setting at 13.5V absorp should also handle the dual charging situation as well. While higher currents aren't recommended, they are often tolerated better at lower voltages. With BOTH charging at only BELOW 13.5V, there is little risk.

I like the "lazy" way, i.e., least effort. IMHO, absorp to 13.5V requires no further input unless there are multiple nights of no grid, and then you need to reset absorp and cut your loads way back to make sure you can charge your batteries.

You can always try it both ways.

 

[Hinchebyinch]

Thanks so much for all of your help. By the look sof it my batteries are on the way out, they will not get up to over 14v after a lot of charging on grid power and are getting very smelly.

In a hot country where the ambient temperature is always over 25 degrees, should that change the charging voltages? I'm just wanting to check that if i buy new batteries i can look after them

 

[Hinchebyinch]

And in follow up to this....

This morning we had grid power so there was no load on the batteries that had been charging all night. I had set to float at 13.5 and for hours the fm80 was putting in 700w to kep them at 13.5 and never getting lower. That is what makes me think the batteries are getting finished. Because if i have grid power, the voltage should stay at 13.5 with a small amount of amps to keep it there - am i correct?


Thanks again you have been so useful

 

[snoobler]

If you're getting venting and stink at 14V, it's possible they're worn out or damaged.

At this point, I would check specific gravity of all your cells after they are fully charged an unused for an hour if possible.

temperature compensation should always be active for FLA/AGM batteries. As temperature in creases, voltage should be decreased. if you haven't been doing this, you've likely damaged them a little tiny bit every day it's over 25°C during charge. Inversely, if you've been charging at night where it's notably lower than 25°C, then voltage should be INCREASED.

IIRC, it should be -0.03V/°C for Trojan 12V.

 

[Zil]

My lead acid battery had a bad time in the heat while charging with solar. Even though the CC has temperature probe.

 

[snoobler]

Mine are in a storage container with 30°F swings per day. They'll hit just over 100°F pretty regularly. Fortunately, I'm usually in float well before that.

This morning was pretty cool, but during the absorption phase, it dropped voltage by 0.9V over a 11°F increase:

 

[Hinchebyinch]

Mine are 2 1/2 years old and have had a hard life. They were frequently deeply discharged from when we would go for a week without grid power (before solar) and we didn't have the gas to run the generator to charge them. In April the transformer fell off the pole in the street and we were without grid power from april - last week. We used the generator for a while but it was hard to run the generator for 7 hours every day so the batteries often didnt get a complete charge, and then we bought solar panels in May but as we are on 12v it was never enough to fully charge the batteries and be used through the day. They would sit for a long time at just below 13.8 or 13.9 volts with about 25 amps going out of the batteries and 50 going in (so only 25a surplus).

Last week we got reconnected to the grid which sometimes works, but the batteries will no longer get above 14v and never reach the end of a charge cycle. I also bought another panel so now its an oversized array (approx 1600w) to give me the extra power in the morning and evening and because its so hot here all year round the efficiency is low.

Right now i am hoping that they will continue to give electricity most nights and during the day we can basically get what we need from the solar panels, and i can just squeeze another 6 months out of the batteries while they die. Im tempted to set the inverter charger to just charge to float voltage (or just above) too so that it isnt just overheating the batteries...... When we get the money will replace the stupid 6 battery bank with 8, and then when we get a bit more money i can put on a 24 or 48v inverter, and then when we get more money add on more panels, and then one day live the dream of powering air con from solar and never sweat again!!!

 

[snoobler]

Based on your description, I would conclude the batteries are severely deteriorated.

"frequently deeply discharged" and "go for a week without grid" - even a SINGLE event like this causes MASSIVE damage to a lead-acid battery. With very deliberate effort that may take the batteries offline for several days while you treat each one individually, it's possible to reverse a lot of the damage via SG measurements and equalization charges to match, but if it's not done ASAP, the damage becomes permanent.

99% sure your batteries are dead or nearly so.

Are you properly maintaining fluid levels?

Consider that if you're not properly maintaining your batteries, your next purchase will likely not last very long either.

Trojan Battery | Battery Maintenance

The key to achieving optimum performance and long battery life is to follow a regular care and maintenance program. Read our tips for high performance battery maintenance.

www.trojanbattery.com

https://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf

 

[Hinchebyinch]

I agree completely.

When we arrived here I knew almost nothing about all of this and just bought what other people picked out for us.

I have always done my best on the fluid levels, but, for example, last year there were three months of protests that blocked supplies getting to the town and there was no battery water available to buy. Most things are not readily available and are a 3 hour drive to find, and when found its often double the price.

One of the big problems here is theft, so it is often cheaper to buy new batteries every few years then invest in a system able to maintain everything well and it draw attention and get stolen.

When we buy flooded batteries here we hope for 3 years. Power is so poor and it's so difficult to buy anything we are happy just to have something.

Your help is saving me loads of money