Monitoring and Controlling Battery Charge

[Olegna]

Hi! This is my first post on any board ever believe it or not. I am also brand new of this year to off grid. Thanks for patience in advance for my ignorance.

I have a cabin. Solar:4- 460w Jinko, Renogy 100A CC, Cotek 12V 2000w Inverter/Charger

Batteries: 8- 6V 230 ah Carbon Lead Acid AGM in 12V configuration to produce a total capacity of 920ah. All equipment less than a year old.

I am in Canada and to make things worse I am in the forest so this time of year, solar is extremely limited. I am relying on generator charging via inverter. I try to bulk charge in the morning and hope solar can top up during the day.

This has been unsuccessful due to a faulty inverter that was recently replaced. The new inverter works better but has trouble determining state of charge and never ever seems to run long enough at high amperage to actually charge the bank fully.

To illustrate, the battery voltage at 12.2 in morning after everything turned off for the night tells me I am somewhat low. I turn the generator on and the inverter starts charging. It charges at 100amps for about 10 mins, then in about half hour is below 40amps. Seeing as I have 920 ah capacity, it should charge at high amperage for much longer to replenish the capacity lost. By nightfall, I have to run the generator again, but I can't seem to get the voltage to read above 12.4 by morning.

My only real load is the inverter itself, 35w and Starlink which I turn off at night.

If I was starting again, I would probably get a Victron CerboGX, Smartshunt, and victron cc and inverter to solve this and may do so in future when I can afford to.

I have researched battery monitors and the Smart Guage seems to be the winner for SoC for batteries that may have lost capacity over time.

My main question is how can I not just monitor but actually CONTROL charging of this bank. I would like to purchase a Smart Guage but I am not sure how to get my charge controller and inverter charger to work with it.

As a second question, I am wondering if configuring the batteries the way I have is creating small variances in voltage due to resistance in wiring. I have the leads for charging at either end of the battery bank (Positive at one end and negative at the other), both for inverter and charge controller.

Thank you for any help

 

[chrisski]

generator on and the inverter starts charging. It charges at 100amps for about 10 mins, then in about half hour is below 40amps.

That seems like you have a close to full battery, 90%.

Is the charge voltage the bulk/absorption voltage while the amperage tapers down?

A good shunt will help you track.

Also, 100 amps may exceed the charge limit for the AGM batteries. The spec sheet will say 10% (96 amps) to 30% i288 amps).

As a second question, I am wondering if configuring the batteries the way I have is creating small variances in voltage due to resistance in wiring.

Please look at the link in my signature for paralleling batteries. 4 batteries in parallel can die quickly if not wired right.

 

[seneysolar]

How long do you run the generator? You need absorb time, min 4 hours

 

[Olegna]

That seems like you have a close to full battery, 90%.

Is the charge voltage the bulk/absorption voltage while the amperage tapers down?

A good shunt will help you track.

Also, 100 amps may exceed the charge limit for the AGM batteries. The spec sheet will say 10% (96 amps) to 30% i288 amps).


Please look at the link in my signature for paralleling batteries. 4 batteries in parallel can die quickly if not wired right.

Sometimes it charges at bulk at first like it should and sometimes it skips and goes right to Absorb. Also, I should mention that the voltage comes down quite fast. Hour or 2 after I turn off the generator, voltage drops to 12.4 again. It is under load from Inverter/Starlink however, that brings it down but even at rest overnight it rarely reads higher than 12.5. Usually reads 12.2 in the morning without any load overnight after being charged in the evening. Hard to think it is ever at 90% but a monitor will help with that I guess. At this point I am leaning toward a shuntless like Smartguage because it doesnt need calibration according to most. I just feel it is of no use if I can't use the information to control charging.

 

[Olegna]

How long do you run the generator? You need absorb time, min 4 hours

I do run it until the amperage drops under 10 amps but sometimes this happens relatively fast Iike an hour or less. I feel it a waste to run the generator under 10 amps. I hope the solar will do the top up. I have set the solar charge controller to the recommended absorb voltage so it will give it the extra time during the day. Unfortunately, the days are very short and my window of sun is only a few hours at best.

 

[seneysolar]

Measure the voltage when it drops to 10A. Settings may be wrong on your charger. Im not familiar with cotek. A battery monitor system is good but can be difficult to add during a battery problem. Most require the user to tell the monitor when the batteries are full. So bad information in, gives you bad information later. For right now your dc volt meter is your friend.

Personally i would want to see at least 14.4 for at least 2 hours , then 13.8 for an additional 4 hrs. Theres probably no way to control the charge rate on the charge controller other than by selecting battery type for the pre set algorithms. If it doesn't hold that higher voltage long enough, charging is doomed.

Iota makes a decent stand alone charger, and opt for the "turbo" controller that plugs into it. They are simple and work great.

At this point you will need to start with an equalization charge to help get your batteries back in line.

Theres a thread on here called "charging with a suitcase generator". Might be worth a look for you. Lead acids like slow charging. You will need hours of charging so youll want the most efficient generator while doing it.

 

[Olegna]

That's very helpful, thank you. I have been looking at smaller generators. I think I am spending close to $8 cad just for a 4 hr charge. Not sustainable which is why I'm here.

I will look into the Iota too. I still think it is necessary to have a control /monitoring system for battery banks. The built in charging based on voltage is easily messed up when there are loads and several chargers connected. I wonder if anyone is using Smartguage with Smart bank. It claims to allow you to connect chargers of several types to it. Also claims to never need adjustment like most do, as you have said.

 

[seneysolar]

Looks like you can adjust settings on that cotek but you need the controller.

It appears that you might be experiencing this function mentioned in the manual where it skips absorb and goes to float.

First double check your dip switch settings for battery type. If no luck, id buy the controller and customize the bulk and absorb times.

 

[Olegna]

Yes. I have the CR-20. I did also enter the custom voltages according to the battery manufacturer's specs precisely. I have the absorbe time at 4 hrs at the moment. Unfortunately, the manufacturer doesn't recommend equalizing AGM batteries. I have no idea what it means when it says it skips bulk and absorb but I assume it means if the batteries are already charged up enough to skip the first stages.

Thanks for the research. I appreciate the help.

I have looked into DC to DC chargers, don't seem to be too common. I thought maybe one of those lithium power stations I could charge on grid and use that just to top up the batteries for the last hours. Won't use much power to trickle charge. Give the generator a break. Probably a dumb idea but getting desperate.

 

[seneysolar]

Yes. I have the CR-20. I did also enter the custom voltages according to the battery manufacturer's specs precisely. I have the absorbe time at 4 hrs at the moment. Unfortunately, the manufacturer doesn't recommend equalizing AGM batteries. I have no idea what it means when it says it skips bulk and absorb but I assume it means if the batteries are already charged up enough to skip the first stages.

Thanks for the research. I appreciate the help.

I have looked into DC to DC chargers, don't seem to be too common. I thought maybe one of those lithium power stations I could charge on grid and use that just to top up the batteries for the last hours. Won't use much power to trickle charge. Give the generator a break. Probably a dumb idea but getting desperate.

Shoot if that scenario where it skips charge stages cant be programmed out, id bail on it. Id verify it first with volt meter but probably worth a phone call to tech support at cotek.

IOTA DLS-75 with Turbo control and a 2000-2500 suitcase generator would be my next move. 75Amps for 6-8 hours on 1 gallon of gas = best bang for the buck

No experience with the lithium power stations but i haven't seen one big enough to do what you need to.