Decreasing charge time of FLA house bank

[Dave Lochner]

How old are the batteries? When was the last time they were equalized? Has the water level been checked?

[Stu Jackson]

What kind and size of generator?

[ramblinrod]

Originally Posted by haveaday

Hello,

I have a FLA house bank made up of 8 GC2 batteries. This is a 12v house bank with each battery providing 215ah. So, wired in series and parallel it's a 12v, 860ah bank. Overnight running refrigeration and a few other house loads the bank is usually discharged 230-300ah by the morning. I then fire up the generator and at first the charge rate into the batteries is about 40amps from my 2600w inverter / charger rated for 120amps of charging. If I start the main engine and allow the 12v alternator on it (100amps and dedicated to charging the house bank) to also charge I can increase the charge rate to 60-70 amps. So, my question is... is there something wrong with my inverter? Is there a way to increase the charge rate without running a 12 liter diesel for the purpose of producing about 25amps of 12v?

The inverter is a Charles industries IQC-2600 original to the 2003 boat.

Thanks
Ben

An 860 Ahr bank should easily accept 100A when discharged 300 A-hrs.

The first step is to reduce your energy consumption. 300 A-hrs is excessive. For a typical fridge/freezer arrangement 30-40 A-hr overnight is typical. Where is the other 260 A-hrs going?

Next, do you have a diode-based battery isolator connected?

If so, are you compensating for the voltage drop?

If not, that is the first place to start.

Post Edit: If your running a constant load of 40A and your charger is 100A, that only leaves 60 A to charge the batteries. A 100 A alternator with a dumb regulator rarely exceeds 60 A output.

[haveaday]

Originally Posted by Dave Lochner

How old are the batteries? When was the last time they were equalized? Has the water level been checked?

I checked the water level today and while I added a little bit they were all well over the plates.

It has been a long time since I've equalized. I'll start an equalization cycle now.

Ben

[haveaday]

Originally Posted by Stu Jackson

What kind and size of generator?

A 23kw Kohler 23EOZD

Keep the questions and thougths coming. If I can improve things I'd be thrilled.

[haveaday]

Originally Posted by ramblinrod

An 860 Ahr bank should easily accept 100A when discharged 300 A-hrs.

The first step is to reduce your energy consumption. 300 A-hrs is excessive. For a typical fridge/freezer arrangement 30-40 A-hr overnight is typical. Where is the other 260 A-hrs going?

Next, do you have a diode-based battery isolator connected?

If so, are you compensating for the voltage drop?

If not, that is the first place to start.

Post Edit: If your running a constant load of 40A and your charger is 100A, that only leaves 60 A to charge the batteries. A 100 A alternator with a dumb regulator rarely exceeds 60 A output.

This morning after 9 hours I had discharged 265 ah according to a Victron consumption counting BMS. I have four Fridges, three of them household. I would expect they are drawing at least 50 ah overnight each. That gets me to 150 from the households and maybe about 30 for the other fridge. I run a plotter all night for anchor alarm, an incandescent anchor light (on the list to convert to LED) and a small host of other loads that adds up to about 10ah of sustained load. I realize that by sailboat standards that's a ton. On this particular power boat I've struggled to get that number lower.

When the generator is running and the batteries are being charged the fridges are being powered by 110 coming from the generator and not the inverter. The other loads I mentioned would continue to come off the 12v side and probably add up to about 10-12 amps. So, I should still have 100ish amps available from the inverter and maybe 85 from the alternator.

I don't believe there's a battery isolater in mix. The only thing being charged by the engine alternator is the house bank so I don't think an isolater would be necessary. Though I certainly could be mistaken. I haven't seen one in the mix.

Thanks
Ben

[Captain Bill]

What size are your cables from the charger to the batteries and how long are they. Also are there any battery switches between the charger and the batteries. I have seen corrosion on battery switches cause charging problems as the charger sees a higher voltage than the battery. At the amps you are seeing the switch would get quite hot.

[Dave Lochner]

Originally Posted by haveaday

The boat involved is a Carver Voyager 570. I have many datapoints that suggest Carver didn't intend the boat to be used as a true cruising boat the way we are using it. The cost of replacing all the household fridges with proper 12v marine fridges is likely not worth it. We've seen too many other limitations for this boat in a cruising role and will likely look to move to something better suited for the kind of cruising we're doing with it. We're from Chicago and have boated on the great lakes our entire boating careers. We're currently in the Bahamas with the boat and seeing some limitations. A the same time the boat has gotten us here and gives great living space for my wife, two daughters and me.

Ben

This is helpful information. Like Skip, I follow RC's (aka Maine Sail) advice, as well as others.

All batteries when new and fresh take a good charge and should be close to rated capacity. As they go through charge and discharge cycles their capacity drops. You batteries when brand new and fresh were 860Ah, but now after many cycles it is no longer. Without a 20 hour discharge test, you won't know what the actual capacity is. That's the first part.

Next, the more deeply discharged the batteries become, the faster they age. When you started your trip, discharging 200Ah from a fully charged bank was a about a 25% discharge. Now that the battery has maybe 600Ah capacity (due to age and cycling) that same 200Ah discharge is 33%.

Charging rates decline as the state of charge increases, such that the first amp of charge goes in pretty easily and quickly. As the batteries become more charged the internal resistance increases and the rate of charge decreases. The first amp goes in quickly, the last amp takes many minutes. The last 10% of the charge may take 5 to 6 hours and the battery will only take a few amps of current. Even though your charging source may be capable of putting out 100 amps, it won't for a long time, it should taper off and the last few hours will see only a few amps trickling in.

On your way to the Bahamas, you probably spent a lot of nights plugged into shore power and so your batteries were getting a good charge equal to what the refrigerators were drawing. Life was good. When you were traveling, you were traveling for many hours a day with the alternator charging the batteries and providing a good deal of the electrical power being used. The result is that the batteries were not that deeply discharged.

Now you're on the hook. Refrigerators, freezers, lights, stereos, chartplotters and iPads drawing current. But, you're running the generator fewer hours than you were running the engine and you're not tied into shore power. The result is that the batteries are not getting fully charged. If you start with 100% SOC and draw 20% down and put back 10%, you're at 90% SOC. Draw that 200 Ah down again and you're now at ~524Ah, or 60% SOC, put back 100Ah and you are at 84% SOC. Pretty rapidly you are loosing capacity and then you get to the magic 50% SOC.

At 50% SOC, things go south pretty quickly and the batteries get trashed, because it gets harder and harder to get back to 100% SOC and over time and cycles 100% SOC that started at 860Ah, becomes 800Ah, 700Ah, and the spiral continues.

A boat like your Hunter Carver was engineered to travel from marina to marina with batteries charged along the way and charged from shore power. The generator was only there to keep things up for a day or two on the hook, before heading back to the marina or to a longer motor.

I think this is why you find yourself in the position you are in. The battery capacity has declined and they are not being fully recharged in the relatively short time the generator is running.

On the generator, you mentioned that it speeds up when the AC comes on. It does this because the electrical load on the system goes up. When the generator is running the electrical system functions as one source, devices don't distinguish generator electricity from battery electricity. The AC has a higher demand, the generator tries to meet it and anything left over goes into the battery.

[john61ct]

Without shore nor solar power, fossil fuel power will never get the bank to full unless heroic efforts applied and very accurate monitoring gear.

PSOC abuse situation, greatly accelerating their (what used to be slow) murder.

[Pizzazz]

The charging profile for GC2 batteries is simple and we'll understood. When you start charging the batteries the voltage will increase from about 13V (deeply discharged) to 14.4V (around 80% charged) and stay there for the acceptance portion which takes ages. You need:

1) Make sure you are in bulk charging mode (voltage starts below 14.4 and climbs up slowly).

2) Make sure the charger configured to supply max current at 14.4V. If in bulk charging mode GC2s can take up to 1/3C which means in excess of 200A in your case. Older or worn out batteries typically do not retain charge well but they accept the rated current.

Note that if you oversize your battery bank you will spend a lot more time in the acceptance range (80%-99% charge) which means long and inefficient charging times. My firm conviction is that you are better off undersizing your bank, abusing the batteries in the bulk charging range (20-80% charged) and replacing them often. There was another thread on this subject a few months ago.

[smac999]

you should be able to get 200a with both going...

or the full 100 from either.

you need to check all the voltages. both at battery itself and charger output. if you battery is going from say 12.5v to 13.5v and the charger is only putting out 40a. the charger is having issues. or the charger wiring.

if the battery is going from 12.5v to 14.6v and the charger is putting out 40a. then the batteries have issues. as that is the most they will take. which should be higher if you are 300ah down.


the other issue you may have is if you are running too much AC through the inverter charger IE all your friges. the charger will cut back as it will likly only allow 30a total through it. so if you are running 20a of AC you only have 10 left for charging. and you need probably 18a ac to get 120a dc out of the charger.

so make sure you shore setting is to 30a. and try turning off all AC loads for a few mins and see if the charger goes up.

[haveaday]

According to the current reading on the Victron BMS I am seeing 13.56v at the batteries right now. When the alternator is running the voltage is higher but not over 14v. It is also worth mentioning that there is basically no time when the 12v system isn't under some load. So currently I believe there's about 30a of 12v load being consumed while the charger is also supplying charge current. Not sure if this would reduce the voltage to that level or if this is still pointing towards an issue with the charging function of the inverter.

Ben

[darylat8750]

+ another one for modifying the electrical system to Rod's (Maine Sail's) advice. With your huge genset you may also want to consider adding another battery charger with a high quality controller.

If you are considering changing boats all this advice may be a waste of money. You are not likely to get a reasonable return on investment on these type of modifications to this boat. Don't make your wife and kids feel like they are camping in a tent. Run the genset as required and move to a real cruising type trawler when you can. Keep Momma Happy!

[smac999]

Originally Posted by haveaday

When the alternator is running the voltage is higher but not over 14v.

you need to measure both sides. if the alt post is 14.5v and the battery is 13.5 then it's a cable issue too small, lose, or going through diodes or other junk. and you will have limited charging

[wayne.b]

Originally Posted by haveaday

According to the current reading on the Victron BMS I am seeing 13.56v at the batteries right now. When the alternator is running the voltage is higher but not over 14v. It is also worth mentioning that there is basically no time when the 12v system isn't under some load. So currently I believe there's about 30a of 12v load being consumed while the charger is also supplying charge current. Not sure if this would reduce the voltage to that level or if this is still pointing towards an issue with the charging function of the inverter.

Ben

===

You appear to have a similar configuration to our Grand Banks 49: Magnum 120 amp inverter/charger, 8 Trojan T-145 golf cart batteries, 3 fridges, 1 freezer, lots of electronic toys, Kohler 20 KW generator, etc. We run the generator in the morning until the charger drops well into the acceptance range of about 50 to 60 amps. The starting rate in the bulk phase is about 110 amps which lasts for about an hour. Total run time in the morning is usually about 1 1/2 hours. We'll run the generator again while cooking dinner for maybe an hour or so, and again before bedtime until the charge rate drops well into the acceptance phase. That seems to work fairly well for us with the batteries lasting 5 years or so even with a lot of time at anchor. When underway we have a 300 amp firetruck alternator on the port engine which will fully recharge the house bank on a normal full day run. They also get fully charged if we're on a dock, maybe once a week on average.

I think you need to focus on getting more charging amps during the bulk phase, whatever that takes. It could be charger settings, cables that are too small, bad connections or what ever. You should be able to recharge at over 100 amps in the morning just like we do. It's also possible that you may need a new inverter/charger.