Hi all, This past week we were sheltering in place on the boat 60 miles from home when entire electrical system crashed. My 4.5 yr old three 4d agm's from west marine batteries would not hold any sort of charge.
First thing to do in a situation like this, when you feel this is not "normal behaviour, is to electrically isolate each battery. Once they are isolated from each other, let them sit for two hours then measure the voltage of each individual battery. If one battery is more than 0.5V lower than the others do not wire it back into the remaining bank electrically.
How are you measuring your Ah usage and SoC? The bottom line is that under normal usage your bank should not dip below 12.1 to 12.2V, under normal house loads. When you see the volts hit 12.2V it is time to start recharging.
With genset running max charge 12.3v attained
It sounds like you may have let the batteries get below 12.1-12.2V.
and the standard issue 20 amp xantrex started overheating.
A 20A charger on a 598Ah bank is grossly undersized. AGM batteries benefit, cycle life wise, from high rate charging. It is one of the puzzle pieces that help get longer life. Even at face value, with no loads on, your effective charge rate is just 3.3% of the battery bank Ah capacity. With vessel loads on, such as fridge etc., lets call this 8A, you're looking at about 0.02C or just 2% of Ah capacity. This really does not even quality as charging more like trickle charging. The bare minimum charger for any boat, even with flooded batteries, is typically 0.1C or 10% of Ah capacity after system dock-side loads are subtracted. A bank like yours really deserves a large inverter/charger or two chargers in parallel of 120A +. This still only gets you to a .2C charge (20% of Ah capacity) but is still much better.
Finally established that I could let engine idle and the alternator produced just enough power to keep house bats above 12.2 without overheating the xantrex.
This is a recipe for also burning up a factory alternator. At low idle speed we also have low RPM which means low fan speed on the alternator. idle speed into large banks is one of the number one causes of heat related failures in marine alternators. You would be best served to add an external regulator that can temp protect that alternator.
As soon as the engine was stoped house batts would rapidly drop to 12v or even less.
There are only two scenarios here:
#1 You have a battery that has failed internally
#2 You grossly over-discharged the bank
Only fridge, freezer and a few lights on.
We have many boats that are pulling 15A +/- between the fridge and freezer alone. Add lighting etc. and you've got quite a draw. Without a battery monitor your essentially shooting darts blindfolded.
We had to live like this for 36 hrs awaiting wind shift. Thankfully I had just replaced the start battery.
Events like this are why you will always hear me suggesting using a large deep-cycle battery as a "start/reserve" bank as opposed to just a starting battery. At some point you may need to rely on that battery as the 12V DC energy source for the entire vessel.
After returning to dock and engaging shore power the xantrex immediately started overheating in spite of batteries reading in the high 13+v because of the 5 hr motor at 2500 rpm.
FDLFBX (Friends don't let friends by Xantrex.) (wink)
Apparently the xantrex 20a is way undersized and we are looking at 50amp now.
Grossly udnersized and not a quality charger either. It should not be overheating putting out its rated charge current. A 50A charger is also very much undersized for a 598Ah bank of AGM batteries. A 60A charger would geet you to 0.1C but for AGM this is still small. AGM batteries benefit from high rate charging.
Also figuring on replacing the three 4.8 yr old agm batteries. I am really disappointed in the short life of these pampered batteries.
If you've been routinely discharging them below 12.1 to 12.2V, before you start recharging, they have not been pampered. Using a 20A charger on 598Ah's of AGM also means they have not been pampered. Using a stock alternator on them, if you still have the factory alternator, also means they have not been pampered.The WM/East Penn AGM's are also not a deep cycle AGM battery. They are a dual purpose battery. We would never install these as house bank batteries when there are far superior AGM choices out there. See the May and August 2015 issues of Practical Sailor for more information on how poorly these batteries perform against premium AGM batteries.
Giving gel's a strong look now.
The East Penn gels are excellent, rated by East Penn at 1000 cycles, but will require all charge sources be temp compensated and custom programmable. They should not be used with a stock alternator. When charged correctly they can easily last 8-10 years or more. When charged incorrectly they can be destroyed in a few months.
Lithium at $10 per ah just seems crazy Gel's at $3 per ah. I would like to here from any of you that have replaced your system. I really really really don't want to have to crawl around the floor watering batteries. Sealed batts please. Lithium has not been entirely dismissed. Thanks
LiFePO4 and GEL batteries are not at all "drop-in" they require a full system approach to make them last. This means new charger, inverter/charge, alternator, regulator, solar controllers etc.. AGM's are not "drop-in" either and they to do best when installed using a system approach.
