Battery Voltage verses amps

dsbentley · #1 (**permalink**) 04-29-2008

I have a 12 Volt system and a 24 Volt system each controlled by a Link 2000 battery monitor. I also have a Airx wind generator on each system. When I am at the dock, I have been leaving the Battery chargers off once they show within 10% of full on the amp gauge. The wind generators will keep the batteries full as I am only using the DC lights and fans at the dock. I went out to our local anchorage last night and got a low voltage warning on the Link 2000 and noticed that even though the amps were within 10% of full, the 24 Volt batteries were reading 22 volt and 12 Volt were reading 11 or even 10.5. I have new AGM batteries as of two years ago and they have been working fine. I don't know if the voltage is low because I have not been leaving the battery chargers on while on shore power. I have a Xantrax 2500 on each of the systems with the built in smart chargers. They normally go from a red light Charge, to a Yellow light Accept to a Green light Float when they are charged to 95% but over the past two months the 12V charger will only stay on the Charge mode and I thought this might be "cooking" my batteries so I turned it off once charged to 95%. I have not called Xantrax to see why the 12V Link is doing this.

Any insight on why the batteries are not showing 14 and 28 volts when fully charged? I am a novice when it come to electical and batteries so explanations in laymans terms are appreciated.

camaraderie · #2 (**permalink**) 04-29-2008

The simple answer is that they are NOT fully charged. Stop all use and input to the batteries for several hours and then take a voltage reading at the battery posts with a voltmeter. That will tell you the real state of charge.
AGM's MUST be charged to 100% on a regular basis (at least once every couple of weeks) or they will suflate and lose the ability to be charged.
The Xantrex Link reading within 10% of full means nothing over time and probably needs a re-set. Are your amp hour settings on the Link set for actual amp hour capacities of each bank of batteries? Does the link know that your second bank is a 24 Volt system? (I'm not even sure you can configure two banks at different voltages with the 2000) EDIT: CHECKED MANUAL...You CAN!
Given the fact that your dockside Xantrex charger will not go into float mode, I am of the opinion that you have toasted the batteries somehow. What type of charging regulation do you have on your wind and solar? Are they set for AGM?
You have a very complex system and distance diagnosis is going to be difficult...but the first step is to diagnose the battery condition. If it is really 10.5 volts that is dead flat and the Xantrex charger (can you give the real model number?) may not work with a dead battery. You may need to remove from the boat and use a less smart charger to try to get it to accept a charge. Sounds like the 24V charger DOES go to float stage and is not dead flat...so charge that battery bank to 100%...let sit 10 hours disconnected from everything and do your measurements. You should see a minimum of 25.2 V at the terminals or you have lost capacity. Anything less than 24.5 V indicates a failed battery. On the 12V side...once you are able to fully charge to 100% and wait 10 hours...anything less than 12.2V means the same and you should see 12.6 if all is well.
You may be alble salvage something with an equalizing charge but AGM's must be EQ'd carefully and instructions vary by mfr. so suggest contacting them if you reach this point.
I think that from your description, your charging sources and routine have cooked these batteries but it is certainly worth some effort to try to save them and diagnose what went wrong.

chucklesR · #3 (**permalink**) 04-29-2008

I'd quess your batteries have been overcharged by your wind gen all winter and have cooked off. AGM's are very sensitive to over-voltages and if they were not set properly (every manufacture has a different high end, but most will burn if over 14.1v is applied). Have you ever looked on a windy day to see how much voltage is being put out by your AirX? They can get scary high if not regulated well including having a shunt to dump to if they put out too much. I'm not sure if the Link 2000 has a shunt built in to it, I don't think so.

Altho it seems Cam and I are saying the opposite (I say over charge, he says under charge) it comes down to dead batteries. Wet cells are easy to check, simply look and see if they are dry. You don't have that option.
Cam's checks will tell you the state of your batteries, start there and see what is going on. If they take a charge I'd still consider them suspect as to how many ah's they will hold.

dsbentley · #4 (**permalink**) 04-30-2008

Cam, My solar panel has a charger controller and I am told that each AirX wind generator also has one built in. I know this is the case because when the battery charger is on at the dock and the batteries are charged and in the Float mode, the wind generator will not spin until the batteries are drained down. Just to be clear, I have two totally separate battery systems each with thier own Link 2000 monitor so one is running the two banks of 24V batteries giving 220 Amp hours (Four 6 volt AGM's) and the other is running two bank of 12V (two banks of 6V AGM's )at 440 Amp Hours. I have told the Link 2000 what type of batteries I have and set the total amp hours correctly. Even when the 12V Link is not switching the charge state from Charge, to Accept to Float, I think it may be working properly as the amps in is only showing about 1 to 2 amps in rather than the 20 to 30 in when in the Charge mode. I was told I can not Equalize AGM batteries and that I am better off to simply discharge the batteries to 75% then fully charge them back up. Mt battery guy also said I am much better off leaving the chargers on while at the dock in float mode rather than letting the AirX do the charging.

dsbentley · #5 (**permalink**) 05-01-2008

I checked the batteries today and found a loose cable going to the 12V Positive and a bad connection on the main 24V bank so I changed those and took readings at the posts. On the 4 six volt batt that make up the 24V bank, they were reading 6.8 each and showing over 28 on the Link 2000. The 12V batteries were reading only 5.5 each then I turned on the Freedom 25 130 amp charger and they all read 6.8. I then turned the charger off and they still were reading 6.7 but the Link 2000 only showed when to be at 11.5. I reset both Link 2000 by disconnecting shore power and taking the main fuse our for 30 seconds as per the maunuel then I reset the Amp hour settings to show 220 Amp hours for the two banks of 24V batteries (4 six volt 110 amp batteries each bank 8 total) and 440 Amp Hours ofr the 12V bank (4 six volt 110 amp batteries) and Battery Type to AGM. I am still getting only a charge red led on the 12V so I don't think it will go to float at this point. I will call Xantrex and see what they can tell me.

dsbentley · #6 (**permalink**) 05-01-2008

I just talked to Xantrex and they said they think the batteries are fine but that the tempature sensor may be giving the Freedom 25 a bad reading and causing it to stay in the charge mode. They said to unplug the black wire with the phone connection going into the Freedom 25 charger for an hour while the system is charging and then call them from the boat to tell them what it is doing.

camaraderie · #7 (**permalink**) 05-01-2008

Well...that's a whole lot better than we might have expected! Always start at the beginning is the lesson!
Hope the temp/sense solves the issue for you. Keep us posted!