Charging acceptance

[All U Get]

Hi all,

I’ve added different charge controllers over the years and have had an observation that many of you may encounter. We are on a mooring ball and like to keep the batteries near full charge so that our refrigerator (DC) can run the next 23 hours. With the generator running, our charger/inverter will supply many amps at 14.2v to bring the batteries to the acceptance level. Then it appears the charging reverts to 13.4v with no amps flowing(acceptance level). I understand that it should continue to charge until the float level is reached. Then drop to the lower amps. Does this seem reasonable?

Part two of the head scratching comes when the solar panels put out some current at 12.8 or 12.9v. The charger/inverter senses a good battery State of Charge and won’t add any energy to charge the batteries. This also can happen when the main engine alternator doesn’t charge the bank even when running all day. (Several cruisers have mentioned this occasionally happens to them). So how does everyone set their charging levels, if you can? Would adding a disconnect switch to the solar controller to take it offline. I can do that with my wind generator by locking the blades to keep it from trickle charging while we power/sail.

 

[dlochner]

I’ve added different charge controllers over the years and have had an observation that many of you may encounter. We are on a mooring ball and like to keep the batteries near full charge so that our refrigerator (DC) can run the next 23 hours. With the generator running, our charger/inverter will supply many amps at 14.2v to bring the batteries to the acceptance level. Then it appears the charging reverts to 13.4v with no amps flowing(acceptance level). I understand that it should continue to charge until the float level is reached. Then drop to the lower amps. Does this seem reasonable?

Tom, need some more information. What kind of batteries? How many? Total Amp hours? Also what kind of charger?

14.2 volts is a little low for charging. AGMs like about 14.4 v and FLAs like 14.8 or even a little higher. The typical charging profile has the charger start with putting out its maximum amperage until the voltage rises to a predetermined level based on the battery type. Once the the voltage is at that level, the charger holds the voltage constant and the amperage will gradually decline as the battery becomes fully charge. Finally it will drop to a float voltage around 13.4 when the battery can only accept 1 or 2 amps. The amperage will continue to very slowly decline to zero. Something similar may be happening on your boat.

When your charger is showing 13.4v with 0 amps there are a couple possibilities. One, the amperage being produced is too small to be shown on the ammeter. Or, there may be a small load on the the system, like a propane monitor that is equal to the load being provided by the charger, so the net current draw is 0. This happens every morning on my boat. The propane monitor will draw about .6 amps. As the solar panels come online the ammeter will show a gradually decreasing draw eventually reaching 0 and then goes into positive numbers.

 

[Tom J]

It can get very confusing when you have different types of batteries being charge by multiple charging sources. Ideally, you want the best source for each type of battery. On my boat, the alternator charges the start battery quickly and keeps it at a float level. My golfcart house batteries are charged by the solar panels and run through bulk, acceptance and float stages with the MPPT controller running things. I have a dual circuit battery switch so that the two circuits are isolated. On shore power, I don't use the onboard battery charger (old, dumb unit) unless the sun doesn't come out. The work around to this system is that I can turn on the ACR when I leave an anchorage on a cloudy day, and charge both circuits with the alternator.

 

[rgranger]

I'm not sure if this applies but when you said...

when the solar panels put out some current at 12.8 or 12.9v. The charger/inverter senses a good battery State of Charge and won’t add any energy to charge the batteries.

... I wonder what you mean by "a good battery state". If you think of water pressure as an analogy to voltage, then a solar panel putting out 12.8 volts cannot put any more "pressure" into the battery since the battery is at a higher voltage (pressure). You have a diod in line with the charging system and you can think of that as a one-way check valve that won't let the battery's "pressure" bleed out to your solar panels. But to push into the battery still requires a pressure greater than what is in the battery. If you want the solar panels to be able to put electrons into your 14.8 volt batteries, then you need a panel voltage that is higher than 14.8 volts. I don't know your system but there are ways to step up (or down) voltage by placing resistors in the lines. (V = IR) where I is current and R is the size of the resistor.

 

[Davidasailor26]

Part two of the head scratching comes when the solar panels put out some current at 12.8 or 12.9v. The charger/inverter senses a good battery State of Charge and won’t add any energy to charge the batteries.

What kind of charger, and is it in some kind of California Power Save mode? A 3 stage charger should at least try to bring the batteries up to the mid-13’s to float, even if they’re 12.8 at the start.

 

[JohnShannon]

The traditional 3 stage charge
STage 1 Constant current battery voltage increases until
Stage 2 Constant voltage ( 14.4V or so ideally temperature dependant) charge current decreases until
Stage 3 Constant voltage point is shifted down to 13.6 volts or so this is called float

This all gets super complicated with loads subtracting current, multiple charge sources, fancy alternative algorithms.

 

[Terry Cox]

Hi Tom, our boat has two 8D AGMs for a total of about 450 AH. While normally connected to shore power the Xantrex Freedom 25 will keep the AGMs in a float state (-0 AH) until disconnected. While out cruising, we use our 8KW Genset to recharge the house bank every other day. No solar panels here. The Link 1000 provides good information about battery state while away from shore power.

I keep an eye on both volts and amps consumed. Normally when amps drop to about -190/-200 (12.2 vdc) I run the Genset for about 1.5 - 2 hours, which brings the amps state to about a -20 (12.8 vdc). That amount of time brings the charge state through accept, but not into float. In order to reduce the -20 amp state to -0 would mean running the Genset for another two to three hours during the float state, which I never do. I aways wait until shore power becomes available in order to complete the float state rather running the Genset for an extended time frame, which gives no real benefit other than fuel consumed.

Over the years we have completed several extended two month plus cruises and what I have described above has worked quite well. The AGMs seem to handle the process and as long as they receive a completed float state charge periodically, no harm no foul, IMHO.

 

[All U Get]

Tom, need some more information. What kind of batteries? How many? Total Amp hours? Also what kind of charger?

14.2 volts is a little low for charging. AGMs like about 14.4 v and FLAs like 14.8 or even a little higher. The typical charging profile has the charger start with putting out its maximum amperage until the voltage rises to a predetermined level based on the battery type. Once the the voltage is at that level, the charger holds the voltage constant and the amperage will gradually decline as the battery becomes fully charge. Finally it will drop to a float voltage around 13.4 when the battery can only accept 1 or 2 amps. The amperage will continue to very slowly decline to zero. Something similar may be happening on your boat.

When your charger is showing 13.4v with 0 amps there are a couple possibilities. One, the amperage being produced is too small to be shown on the ammeter. Or, there may be a small load on the the system, like a propane monitor that is equal to the load being provided by the charger, so the net current draw is 0. This happens every morning on my boat. The propane monitor will draw about .6 amps. As the solar panels come online the ammeter will show a gradually decreasing draw eventually reaching 0 and then goes into positive numbers.

I have 8D gels with 900 amp hours and a 4D gel starter battery.

It can get very confusing when you have different types of batteries being charge by multiple charging sources. Ideally, you want the best source for each type of battery. On my boat, the alternator charges the start battery quickly and keeps it at a float level. My golfcart house batteries are charged by the solar panels and run through bulk, acceptance and float stages with the MPPT controller running things. I have a dual circuit battery switch so that the two circuits are isolated. On shore power, I don't use the onboard battery charger (old, dumb unit) unless the sun doesn't come out. The work around to this system is that I can turn on the ACR when I leave an anchorage on a cloudy day, and charge both circuits with the alternator.

The solar controllers and wind controler are new and want to give me ’free’ energy charging the batteries at a low rate especially with the low sun angle.

I'm not sure if this applies but when you said...


... I wonder what you mean by "a good battery state". If you think of water pressure as an analogy to voltage, then a solar panel putting out 12.8 volts cannot put any more "pressure" into the battery since the battery is at a higher voltage (pressure). You have a diod in line with the charging system and you can think of that as a one-way check valve that won't let the battery's "pressure" bleed out to your solar panels. But to push into the battery still requires a pressure greater than what is in the battery. If you want the solar panels to be able to put electrons into your 14.8 volt batteries, then you need a panel voltage that is higher than 14.8 volts. I don't know your system but there are ways to step up (or down) voltage by placing resistors in the lines. (V = IR) where I is current and R is the size of the resistor.

Yesterday I had the panels complete the charge because of the clear sky and we’re getting a better angle to the sun.

What kind of charger, and is it in some kind of California Power Save mode? A 3 stage charger should at least try to bring the batteries up to the mid-13’s to float, even if they’re 12.8 at the start.

Trace charger/inverter which is somewhat adjustable, but if it’s reading a charged battery, it won’t add more energy so it returns to idle.

The traditional 3 stage charge
STage 1 Constant current battery voltage increases until
Stage 2 Constant voltage ( 14.4V or so ideally temperature dependant) charge current decreases until
Stage 3 Constant voltage point is shifted down to 13.6 volts or so this is called float

This all gets super complicated with loads subtracting current, multiple charge sources, fancy alternative algorithms.

That’s about what I follow with the house charger when I start it before the sun is on the solar panels.

Hi Tom, our boat has two 8D AGMs for a total of about 450 AH. While normally connected to shore power the Xantrex Freedom 25 will keep the AGMs in a float state (-0 AH) until disconnected. While out cruising, we use our 8KW Genset to recharge the house bank every other day. No solar panels here. The Link 1000 provides good information about battery state while away from shore power.

I keep an eye on both volts and amps consumed. Normally when amps drop to about -190/-200 (12.2 vdc) I run the Genset for about 1.5 - 2 hours, which brings the amps state to about a -20 (12.8 vdc). That amount of time brings the charge state through accept, but not into float. In order to reduce the -20 amp state to -0 would mean running the Genset for another two to three hours during the float state, which I never do. I aways wait until shore power becomes available in order to complete the float state rather running the Genset for an extended time frame, which gives no real benefit other than fuel consumed.

Over the years we have completed several extended two month plus cruises and what I have described above has worked quite well. The AGMs seem to handle the process and as long as they receive a completed float state charge periodically, no harm no foul, IMHO.

I think the same way about using the genset as little possible, but when I do it would be better during the mid-morning instead of dawn. Has anyone added a switch between their solar controller and batteries to interrupt the charging?

 

[dlochner]

I think the same way about using the genset as little possible, but when I do it would be better during the mid-morning instead of dawn. Has anyone added a switch between their solar controller and batteries to interrupt the charging?

I don't think this is necessary. The solar controller should come on and provide an appropriate level of charge and/or as much as it can when ever the battery can accept it. The amount of current delivered to the battery is determined by the battery not the controller, either the charger or solar controller. Either device should put out the maximum it can.

If you do want to prevent the charger from overriding the solar, just turn the charger off. That's what I do. I have Firefly batteries which want to be deeply discharged to ~40% SOC and rapidly recharged. I turn the charger off, let the solar meet the daily needs until the SOC drops and then turn the battery charger on for 24 hours or so.

Edit: Providing the bulk charge (constant current) early in the day and then letting the solar finish off the charge during the day is an energy efficient way of charging.

 

[dLj]

Hi all,

I’ve added different charge controllers over the years and have had an observation that many of you may encounter. We are on a mooring ball and like to keep the batteries near full charge so that our refrigerator (DC) can run the next 23 hours. With the generator running, our charger/inverter will supply many amps at 14.2v to bring the batteries to the acceptance level. Then it appears the charging reverts to 13.4v with no amps flowing(acceptance level). I understand that it should continue to charge until the float level is reached. Then drop to the lower amps. Does this seem reasonable?

Part two of the head scratching comes when the solar panels put out some current at 12.8 or 12.9v. The charger/inverter senses a good battery State of Charge and won’t add any energy to charge the batteries. This also can happen when the main engine alternator doesn’t charge the bank even when running all day. (Several cruisers have mentioned this occasionally happens to them). So how does everyone set their charging levels, if you can? Would adding a disconnect switch to the solar controller to take it offline. I can do that with my wind generator by locking the blades to keep it from trickle charging while we power/sail.

Is there a way to have a single controller monitor and control the charging current going into your batteries that accepts all incoming sources and allows each to give what they can, turn on others to add what is needed, in order to produce the correct current and voltage flow to correctly charge your batteries? It sounds like that is what you asking for...

dj

 

[Davidasailor26]

It really shouldn't be necessary to turn off any charging source for the others to work. The controllers should each try to bring the batteries up to their bulk voltage set points by pushing as much current as they can. Once they hit those setpoints they should keep that voltage while the battery's resistance increases, reducing the current until that falls below a threshold where the controller drops to the float voltage.

I found a couple different manuals for Trace Inverter / Chargers depending on the model - http://www.xantrex.com/documents/Discontinued-Products/830-1M1512.pdf and https://www.altestore.com/static/datafiles/Others/Xantrex_TR_Operation_Manual.pdf. Not sure which model you have, but the second manual has some interesting conditions -

"When the current equals the programmed return amps value (5% of the battery capacity setting) set with the Battery Bank Capacity potentiometer, the charger switches to the third stage–float."

Second: "The Trace Series will transition to the Standby (charger OFF) Mode after 1 hour in the float stage... You can manually initiate a new charge cycle while in Standby Mode by pressing the ON/STANDBY switch once, to transition the Trace Series to OFF, then pressing the ON/STANDBY switch again." Can you try that ON/STANDBY button to see if you can start a new charge cycle? The charger really should go to the bulk voltage first, not just sit at 12.8 when it first turns on.

 

[All U Get]

My charger doesn’t go into bulk charge until the batteries are below 12.8v, I believe. I also believe my solar controllers are the same so if I sleep in, they begin charging with the rising sun. It might only be 2 or 3 amps but it raises the battery volts enough so the big charger doesn’t want to help. It will charge at 70-80 amps and slowly lower as the battery level gets near acceptance.

Today I was up early and started the genset and charger. After 2 hours it completed the bulk charge and indicated it was no longer charging. My battery monitor had 14.2v and slowly dropping to 13.6v. I left the charger on thinking as suggested there was some charging going on but to small an amount to be measured. The monitor did show 5-8 amps flowing. I let it run for about 10 minutes and noticed that maybe the voltage was a little higher, not too much.

The solar controllers at that time still had the batteries in bulk charge. So maybe their charging levels are set for different battery types. I’ll have to check when I’m on the boat after laundry .

 

[JohnShannon]

I think the issue here is, what are the requirements for the charger to exit "float mode" ? Float is when the battery has completed a charge cycle and is sitting at 13.6V. The charging is complete. Next the battery is put under load and its voltage falls to some level, the charger realizes that the battery has been discharged and initiates another cycle.

If there is some other source of power charging the batteries then maybe the battery voltage doesn't fall enough to reset the charger

 

[Tom J]

My charger doesn’t go into bulk charge until the batteries are below 12.8v, I believe. I also believe my solar controllers are the same so if I sleep in, they begin charging with the rising sun. It might only be 2 or 3 amps but it raises the battery volts enough so the big charger doesn’t want to help. It will charge at 70-80 amps and slowly lower as the battery level gets near acceptance.

Today I was up early and started the genset and charger. After 2 hours it completed the bulk charge and indicated it was no longer charging. My battery monitor had 14.2v and slowly dropping to 13.6v. I left the charger on thinking as suggested there was some charging going on but to small an amount to be measured. The monitor did show 5-8 amps flowing. I let it run for about 10 minutes and noticed that maybe the voltage was a little higher, not too much.

The solar controllers at that time still had the batteries in bulk charge. So maybe their charging levels are set for different battery types. I’ll have to check when I’m on the boat after laundry .

While there is nothing wrong with multiple charging sources, there can be unintended consequences. I noticed one day while motoring on a sunny, calm day, that my tach was reading zero. Since my tach is reading off the alternator, I realized the alternator had quit. The voltmeter indicated a good charge on the batteries, so I continued motoring, thinking I would troubleshoot the system when we docked for the day. It was almost funny when we were tying up at the dock, and the gentleman helping us asked how we were doing. I explained the alternator situation, and that I might need to get a new one. He took a look at my solar panels and told me most likely the batteries had a full charge and the alternator had shut down. I started the engine, and sure enough, the tach read fine, all was well. Duh!

 

[b.needalman]

The behavior you are seeing is normal. Batteries take a high rate of charge for a very short time. See three stage charger noted above. The last 10% take almost as long as it does to bring the batteries from half discharged to 10%. Since you have wind and solar, it is never worth using a diesel generator for the last 10%. Just turn it off.

If the solar/wind can't keep up the fridge, then it will be hard to get to fully charged without running the generator for hours which is both noisy and expensive.