Odd behavior of my system, Low Battery Cut-Off is goofy

Organic Farmer · May 2018

We have 4400 watts of solar panels, a 'Four Star' E-panel from wholesalesolar, 'Midnite Classic' 150 Charge-controller, 'Magnum Energy' inverter, a 48VDC / 600AH battery bank

[with twenty-four EXIDE marine deep cycle batteries [27MDCST] in 6 strings with 4 batteries in each string].

My EQ voltage is set to 62.4V
Absorb is 59.2v
Float is 53.2v
Absorb Time is 4 hours
EQ time is 3 hours
BMK is set to 600ah
Charger is set to 30A [I am using grid power]
Battery type is flooded
Charger absorb is 4 hours.
LBCO setting is set at 48.8.

This Sunday I did a 4 hour EQ charge. Today after the sun went behind clouds for a couple hours, the system shut down saying LBCO at 96%, the charge-controller is reading 50.8vdc

So what gives?

Why is it going into LBCO at 50.8vdc when I set LCBO to 48.8vdc?

mcgivor · May 2018

Large loads, especially motors, can momentarily sag the battery voltage which could cause a LBCO, on a 48V nominal system the LBCO setting would normally be below 48V to avoid nuisance cut offs, somewhere around 46V would prevent such issues.

BB. · May 2018

Check the voltage at the DC input terminals for your inverter... Also, try 46.0 volts (11.5 volt @ 12 volt bank) and see what happens (not a bad cutoff voltage for a decently loaded flooded cell lead acid battery bank)--And perfectly OK for testing your LBCO question.

What is the load on your inverter (Watts, motor/pump/etc.)?

As a starting point, roughly 3,000 Watts would be a good maximum load for your battery bank (and even 3,000 Watts for solar array maximum). You have charging set for 30 amps max? 60 Amps (10% rate of charge) should be OK (if charger is capable) for a a flooded cell/AGM type battery.

-Bill

MrM1 · May 2018

My SW Inverter also has a Low Battery Cut Out Delay Setting just for this reason, so that if a large load momentarily drops the voltage it will not cut the inverter off. This setting is set in seconds. You might look for a setting like this in the Magnum. I am set to 23v (24v system) and 55 seconds for Low Battery Cut Out Delay.

Organic Farmer · May 2018

Thank you, everyone.

Organic Farmer · May 2018

I changed the LBCO setting to 48.0vdc and we will see what happens next. Our biggest load is our well pump 240vac 7amps, I do not always hear when it kicks on though. So I have no idea if that is what is causing this issue.

Tech support at Wholesale Solar suggests that I record the gravities from all cells, thinking that a battery may have gone bad. Since I have 24 batteries I have been avoiding doing this. If it turns out that I have one bad battery, I hate to consider what the solution would then be.

mcgivor · May 2018

Remember there is the conversion ratio, 7A at 240V is 35 A at 24V, simply using nominal voltage. The inrush of the pump could be 10 times the run current, or 350A, for a fraction of a second, this is where a time delay on LBCO is essential. Still thinking 48V LBCO is over conservative, but one needs to find the sweet spot where nuisance gives way to what actually works in a particular situation.

Edit. 7A at 240V is 17.5 A at 48V, inrush 175 A possible.

Photowhit · May 2018

How old are the batteries?

The "27MDCST" appear to be Lead Calcium batteries;
Info here includes "Calcium/calcium construction gives accessible maintenance-free performance"

https://www.tractorsupply.com/tsc/product/exide-stowaway-marine-rv-deep-cycle-battery-27mdcst

I didn't see another reference to Calcium in a quick check, but it does say maintenance free design which would indicate Lead calcium.

Lead calcium have a shorter life span in a true deep cycle situations.

mike95490 · June 2018

My XW inverter came stock with a 46v cut off @ 60 seconds

sunpowered · July 2019

My system is cutting out when the batteries still have a lot of charge in them.. Im not that great with understanding my system but im assuming its due to low volts or amps. the batteries are getting on the older side but its a lot of money to replace them. Has anyone heard of this battery reconditioning http://smarts919_5589.gr8.com/ is it legit and is it something i could do to my sealed gel batteries to extend their life. Not really looking forward to the replacement cost

mcgivor · July 2019

Batteries have a life expectancy just as we do, so just like there sellers for the alixir of life for humans, there are sellers of the alixir of life for batteries. That's my take on marketing anyhow, when one is old, or a battery is old, both are old it's a natural phenomenon that can't be reversed.

sunpowered · July 2019

Thanks Mate I guess im just hoping for a way to get more life out of my batteries as they are a huge cost and for $47 I thought maybe give it a go. I was hoping someone else had tried it ?

BB. · July 2019

Some folks use Desulfators to extend battery life (some folks love them, some folks hate them, many folks don't see any good/bad from them).

I know nothing about this company that rejuvenates lead acid batteries. It started as a kickstarter project for the "battery rejuvenator" charger, and turned into a company that uses the charger to buy/receive old batteries and sell rejuvenated batteries:

https://revoltbatteryexchange.com/

The above (and a little desulfator talk) is from a Candlepower Forums thread:

https://www.candlepowerforums.com/vb/showthread.php?384605-Rejuvinator-Lead-Acid-(Gel-Cell-)-on-Kick-starter

-Bill "your mileage may vary" B.

sunpowered · July 2019

Thanks for your advice i might give it a go on some other batteries first and see if it is usefull

Odd behavior of my system, Low Battery Cut-Off is goofy

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