Battery charging amps

Northern_BC

I am worried my batteries are not being charged properly and have been reading lots of posts on this site. 

Being winter, my loads are much greater than summer and I am using my generator lots (short cloudy days also, so very little solar). My concern over the batteries comes from the generator running under an hour when it kicks on, and also can be starting every few hours. There is no way my battery bank should be charging that fast. 

My 3 year old battery bank is 1520 ah. The XW6048 inverter is set to start the generator when the batteries reach 49.5V for 15 minutes. It is set to run the 3 stage charge, where it shuts off after reaching float. I have always had the system set to start charging  at no less than 70 - 80% discharge. Other than a few times I had errors and the gen did not start up. 8 months of the year my solar is enough that the batteries never drop to the pre-set limit that the generator is set to turn on. I follow the manufacturer colt settings for the 3 stage charge. In other words, I have tried to take care of the battery bank.

These posts have me thnking Iam not charging at enough amps.

https://www.solar-electric.com/deep-cycle-battery-faq.html
https://forum.solar-electric.com/discussion/16348/48v-system-charge-settings
https://forum.solar-electric.com/discussion/14613/battery-system-voltages-and-equivalent-power

From these three posts; I think  need to be charging my battery bank upwards of 1520 / 8 = 190 amps. This is not possible with what I have. The max charge rate on the XW 6048 is 100 amps. My generator has a max amps of 54 (108). The inverter shows around 100 amps when the generator kicks on to bulk charge at the max charge rate of 100%. I have two MPPT 60 150 solar charge controllers that I assume would allow for 120 amp charge rate if the 6 kW of panels can produce that.

The XW 6048 has so many safety features built into it that I can not charge my batteries at a high amp rate for a set period of time. The inverter moves from the bulk charge to absorb quickly on the state of my batteries now. So they only charge at 100 amps for a short time before moving to absorb, where the charge drops down to 30 amps, and then to float where the charge drops down to 10 amps. Ican adjust the voltage of the charge only.

Am I under charging my battery bank and wrecking my  battery bank? Do I need to upgrade my system to allow a higher charge rate? I hope there is something I can do to save my expensive batteries.

Thanks.

WaterWheel

From what I understand a sulfated battery will hit absorb voltages much faster.      That would make your 6048 end charging faster than expected.

mcnutt13579

I doubt there is anything wrong with a 3 year old Enersys battery.  It should be a stout battery and you obviously care about it.

I think the "problem" is you are not letting it get low enough before starting the genset.  The old Trace SW (1990s) and Outback Mate2 had voltage set points of 47.2 / 2 hours and 45.2 / 15 minutes.  Those settings always worked well.  Maybe a few tenths higher for such a large battery.  This will be 50-60% discharge.  I see you don't want that.  But you are starting the generator when the batteries are still 70% full from what I can tell.

mike95490

1) you need hydrometer readings to determine what state your batteries are in.

2) With the Combox, SCP or Gateway, you program the battery size into the XW and it then "knows" how to properly charge that size of battery.

Northern_BC

I am basing my depth of discharge from reading this site which I find most people are saying to discharge to 75% on daily use battery banks. Maybe it is too conservative? I had a SW inverter before my XW. It was a good unit with a very good manual from trace.I still use it for reference at times.

I have set my battery type to custom and entered in the ah and factory charge settings. This was done in the inverter, charge controllers, and battery monitor. 

mcgivor

Undercharging would be termination well before float, timed out by the charging source, rather than end amps, the 2% of programed capacity, thus if the battery is satisfied that is how much it can absorb, increasing current will only shorten the charge cycle.The 49.5V for low battery is conservative, if there are loads present the actual open circuit voltage may be significantly higher, this could cause short cycle generator charging. Observation of the open circuit battery voltage when the generator starts charging will reveal if the state of charge is actually higher than perceived, if voltage initially increases rapidly this may indicate the battery is at a higher SOC, baring loss of capacity of course.

One thing to consider is if the inverter charger is programed to reach float, the charge controllers will also transition to float, if the generator runs in the morning it could render the controllers useless for the rest of the day, unless the recharge value is programed higher than the defult of 50V, which is very close to the 49.5V generator restart value, which will repeat the cycle once float is reached, so essentially it would be a generator system rather than a solar system. 

From observations when I had to use a generator, when the charge controllers can no longer compete with the inverter charger, they simply stop, their input, but it has been a while since I needed a generator.

Just a collection of thoughts which may help, naturally SG is the best way to establish SOC.  

Estragon

+1 on measuring SGs.  It's really the only way to get a good handle on the efficacy of your charging regime.

Also, where are the batteries located (eg cold shed)?  Cold batteries can lose a fair bit of apparent capacity.  A 1500ah bank might have an apparent capacity of more like 1000ah or less in freezing temps, for example.  Properly maintained, the capacity comes back when it warms up, but while cold it behaves like a smaller bank.  FWIW.

Estragon

For a sense of the magnitude of temp vs capacity effect:
http://support.rollsbattery.com/support/solutions/articles/5860-temperature-vs-capacity-flooded-lead-acid-batteries

Northern_BC

Thanks mcgivor. The voltage does initially increase rapidly when beginning to charge. I will spend more time today focusing on the voltage to be sure. 

My battery monitor does show around 90% (I'll watch it closer today) when the inverter is showing down around my 49.5 or 75%. I always thought that it was lying to me, and I should trust the reading on the inverter, but maybe not. It must be detecting the open circuit voltage only? Can you or someone explain this to me a bit more? The voltage reading on the monitor is usually with .3 or of the reading on the inverter display,  but still says upwards of 90% charge when based on the chart it would be less.

When the generator starts the charge controllers stop charging. I assume to protect from over current to the batteries. When the gen stops they will begin again from a float charge. But I have observed that they will switch to bulk at end of day or if cloud cover comes up, putting the output less than the load.

Estragon

"Open circuit" voltage in this context would presumably mean the resting bank voltage (no loads or charging for some time, eg several hours).  With a net load, voltage will get pulled down in proportion to the size of load.  This is the purpose of the 15minute dely on gen start (so a periodic load like a pump coming on won't trigger it).  If you have loads(s) pulling voltage down for 15mins though, the genny starts irrespective of actual state of charge.

A 0.3v difference between inverter and meter voltage seems high to me.  Could small wire or loose connection be making the inverter see lower voltage and false starting genny?  Does the difference get bigger with higher net charge/discharge current?

Estragon

IMO, the charge controllers should only stop charging if either they've already completed their bulk/absorb cycle, or the inverter has raised bank voltage to above the controller absorb setting.

Unless it's been a really long spell of gloomy weather, I only use the genny to bulk charge (~85% SOC), and let charge controllers do absorb to the extent possible with available pv current.

Northern_BC

The battery room is heated. Depending on the outside temperature it can be around 10 - 20 degrees celcius inside. Right now my heater is acting up so it is about 7C. 

Is it possible to measure SG on a sealed battery?

mcnutt13579

What battery is this exactly?  1520 Ah had me thinking it was a flooded Solar One battery

mcgivor

Northern_BC said:

Thanks mcgivor. The voltage does initially increase rapidly when beginning to charge. I will spend more time today focusing on the voltage to be sure. 

My battery monitor does show around 90% (I'll watch it closer today) when the inverter is showing down around my 49.5 or 75%. I always thought that it was lying to me, and I should trust the reading on the inverter, but maybe not. It must be detecting the open circuit voltage only? Can you or someone explain this to me a bit more? The voltage reading on the monitor is usually with .3 or of the reading on the inverter display,  but still says upwards of 90% charge when based on the chart it would be less.

When the generator starts the charge controllers stop charging. I assume to protect from over current to the batteries. When the gen stops they will begin again from a float charge. But I have observed that they will switch to bulk at end of day or if cloud cover comes up, putting the output less than the load.

Voltage is a poor method of determining SOC, it should only be considered a rough guide at best, there are differing values depending on electrolyte concentration and or manufacturer. Sadly with sealed cells it's practically impossible to measure SG, so voltage is about the only practical method other than a load test where the battery is discharged to a terminal voltage 10.5V.

With regards to differences in values of the battery monitor, the point of reference could play a part, if the monitor reads close to the battery with the inverter measuring internal voltage, there would be a voltage drop in the conductors feeding the inverter. This voltage drop will be dependent on load, as load increases so dose voltage drop, this is simple to measure by using a digital voltmeter, one probe on the inverter input the other on the battery terminal. Even the best meter will have tollerance +/- 5% for example, even 1% of 50V is 0.5V, temperature of the measuring equipment will offset readings to some degree.

The controllers don't shut down to protect themselves, they simply can't match the voltage and current supplied by the inverter charger. If the current is reduced to a value which matches the charge controllers, they will work together, most users only use bulk to mid absorption  charging as charging to float is an inefficient use of fuel. The other problem is that as mentioned before, the charge controllers will remain in float until recharge voltage is met. 

Perhaps adjustments to settings will solve the mystery, programming is simple so I would experiment with different settings keep records of how it performs then select the best, this could be a seasonal adjustment, every system is different. Winter is especially challenging in Northern BC, work would take me there to service HVAC equipment, near the coast was the worst Kittamat, Prince Rupert in particular, Ft. Nelson was colder but at least there is sun, where are you?

Northern_BC

The batteries are enersys powerssafe SBS 190F. 

The night before last I set the system to start at 49.2. The SCP light was flashing at 7:30am with the low voltage. So the gen was going to be triggered to start soon. 

This morning I checked around 7:30 am and see that I left the generator on manual off by mistake. The battery monitor was reading 48.9 volts, 91% charged, 22 hrs remaining to the 75% depth of discharge I have input. I had run the gen the previous morning, and only got a few hours of mixed cloud and sun during day.

Performing a load test is difficult with my setup and over the winter. If I can be confident that 49 to 49.2 is not actually 60 to 70% discharge then I'll probably set the system to start the generator around those values. Interesting that 49.5, just 0.3 volts more was triggering my gen to start every few hours, vs the 49.2 that was around 16 hrs from charge to triggering a start. 

I don't mind running my generator in the winter. It is built to run, 1800rpm, and is relatively easy to service and maintain.  The batteries are a different story. I got a much shortened life from my previous bank and am paranoid about my current bank to keep it safe. I didn't have the system I have now before.

I live 30 mins east of Fort St John, BC. Mid November through mid January are tough solar months. Fair bit of overcast mixed with short days. 

mcgivor

To get a more accurate indication of state of charge try disconnecting all loads and charging sources when the voltage is at 49.5V. Let them stand that way for some time ~2 hours, the voltage will increase, let's say the voltage increases to 50.4V, use that as a rough estimate for SOC, subtract the difference, 0.9V in this example, subtract that from the 49.5V to give a low battery voltage of 48.6V.

With my second lead acid system 400Ah , which is very lightly used, mostly the inverter 18W with occasional 100W on demand pump, 12W led light and 4 hours refrigerator via transfer switch to relieve my main system of shading issues at this time of year. The daily minimum voltage connected,  is constantly 24.8V which equates to 49.6V, on a clear day the controller is already in low current PWM by 8:30 in the morning even with refrigerator load. Since the actual SOC by loaded voltage is probably higher than apparent, reducing low battery setpoint  slightly will prevent short cycle generator run, if that is a problem, from a noise standpoint, doubt it will have any effect on battery life expectancy, but I do understand paranoia after nearly loosing my first bank.

Fort. St. John is nice in the summer, did a canoe trip down the Peace river,10 days of beautiful scenery camping along the way, winters are not my thing however.

mcnutt13579

Forget my comments about lower start voltage above.  These AGMs have a very short life span if you run them that way.  Carry on charging them the way you have been doing.