current opinion on mixing FLA/AGM

[daveNZ]

My alternator charges the FLA Start battery, which is connected via a VSR to a FLA House battery. If I change the house battery to an AGM, any issues?
Alternator provides 14.5V (at battery), internal, not smart, regulator.
Some say OK , others not!

[Adelie]

AGMs and FLAs don't mix well, they have different preferred charging protocols (voltages mostly).

Do you need to replace the house or just want to?

Assuming you need to replace and are going cruising replace with FLAs and use the money you saved on solar panels and a PWM regulator.

The following are two links to very good discussions of battery issues, one by a technically oriented long term cruising couple and the other by a professional marine electrician who actually tests batteries and related dear.

http://www.bethandevans.com/systems.htm#29.
http://forums.sbo.sailboatowners.com...d.php?t=124973

If you are not cruising and have special needs then maybe the AGMs would be right for you but to install the right so they don't die in a coupe years will cost you significantly to upgrade your whole system, not just to buy better batteries.

[colemj]

You won't have any problem with this at all. Set up your charging systems for the AGM's and let the VSR take care of the FLA starting battery.

The start battery sees such little draw down that it will never have a sulphation issue seeing the slightly lower absorption voltages used with the AGM.

However, I would re-think your decision to use AGM house batteries with your fixed-voltage regulator.

Mark

[daveNZ]

Thanks for these answers. I have seen Maine sails very good notes before, and the other thread is great reading.
But as you see, 2 answers and 2 opinions already.

Yes I do need to replace the house battery, PO has used a start type battery as the house battery (there is a separate 'start' battery for starting) not unusual here for a small launch, many owners believe they can recharge a 'start' battery more quickly??
I'm not interested really in that theory and will buy with a proper deep cycle battery (or 2).

Question re AGM is: is a fixed internally regulated 14.5 v OK for an AGM battery. I guess I should refer to individual battery manufactures specs.?


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[Adelie]

Actually I count 2 posts, and at least 3 answers.
At the end of Mark's post he agrees with me that if you are going to keep the dumb regulator the AGMs aren't the best choice.
As it happens I concur with him that if you have a smart regulator you can charge both without damage to the AGMs.
In this case we are reading different things into the scenario behind our answers.
To give answers more pertinent to your situation we probably should have first asked questions related to budget, how the boat is used (monthly, weekly, daily, and for how long each time, or liveaboard), how it's stored (with or without an external power hookup), size, type (sail or motor).


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[daveNZ]

This is not a quick project.
I'm not fixed on using AGMs but....
I can source some that fit my battery box, most FLA are two wide
Available with 5year warranty
Cheaper than say Trojans
Might charge faster
...so have some positives.

I am still curious about:
1. How accurate is the voltage reading on a victron bvm700? i.e. I can imagine even the small cable and fuse they supply for +ve connection could have voltage drop of .01 or .02 volts.
My multimeter reads different to the victron but my meter is not high quality so just wondering if any one has tested this, or does everyone just accept what it says as gospel?

2. Is alternator output of 14.5V, where battery spec wants 14.7V, going to make a big difference long term? If solar at correct float of 13.8 is going to top up (eventually) when boat left on marina, does the lower alternator absorption voltage really matter?
We do 2 to 5 day trips with occasional 7-10 days. Main user is a 40 watt fridge. All lights are LED so I think daily AH requirements are only about 40AH.

I suspect I'm close to over analysing this. I know FLA are more tolerant of charging 'abuse', but if AGMs would charge faster, even with a small alternator, then that's maybe worth it.

Love the Victron BVM700, at least we now know! Would be interested in people's experience re getting the CE and Peukerts values set so as to obtain consistent SOC readings for either FLA or AGM batteries.



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[ranger58sb]

Dave, our charger manual instructed using the same setting for AGMs as for FLAs.


Our AGM battery manufacturer's instructions agreed those charging voltages were within the acceptable range. (Newer chargers from the same manufacturer include more AGM-oriented profiles, and even user programming.)


We have three banks of batteries (two separate combined engine/house banks in a twin engine boat, one independent genset battery). We switched one big bank from FLA to AGM in Spring 2006, still going strong. We switched the other two banks in Fall (I think) of 2009, still going stronger.


We can recharge easily and often, from either shorepower or genset (latter usually 2x/day). I haven't needed to pay any attention over the years to CE, Peukert, etc., just simple voltage.

I have no clue what kind of alternators we have; after engine warm-up, I see a constant 13.7v read-out on the bridge (i.e., 20' from the batteries) on that bank when the whole (relatively extensive) electronics suite is running.

Haven't ever heard anyone say AGMs are cheaper than Trojans before...

-Chris

[svlamorocha]

Originally Posted by daveNZ

My alternator charges the FLA Start battery, which is connected via a VSR to a FLA House battery. If I change the house battery to an AGM, any issues?
Alternator provides 14.5V (at battery), internal, not smart, regulator.
Some say OK , others not!

There are many such setups in the bareboat fleets. There are obvious problems if you do not have a VSR (hence bateries are set to equal voltage while discharging) AND the FLA batery is actually cycled, but that does not apply in your case. I am yet to see a problem in a setup like yours.

[Adelie]

Originally Posted by daveNZ

T
I am still curious about:
. . .

2. Is alternator output of 14.5V, where battery spec wants 14.7V, going to make a big difference long term? If solar at correct float of 13.8 is going to top up (eventually) when boat left on marina, does the lower alternator absorption voltage really matter?
We do 2 to 5 day trips with occasional 7-10 days. Main user is a 40 watt fridge. All lights are LED so I think daily AH requirements are only about 40AH.

I suspect I'm close to over analysing this. I know FLA are more tolerant of charging 'abuse', but if AGMs would charge faster, even with a small alternator, then that's maybe worth it.
m

The slightly low voltage should no be a problem, the battery will charge slightly slower, lets say 5% or so longer and will need to be equalized a little more often maybe.

The AGMs will not charge faster unless you get a big alternator, 100amp or larger, or a big charger. Even then the faster charging will only occur during the bulk phase from 50-75% SoC. Let's say you can get thru bulk in 60min instead of 90min. There's still 3hr to go to get thru absorbtion. And if you get sick of charging before the cycle is done then you are leaving the battery in a state of partial charge. AGMs like to be fully charged before discharge starts again or they start losing life and capacity.

Since the point of this thread is to figure out the best battery to go with your existing charging system, FLAs look to be better.

[Maine Sail]

Originally Posted by daveNZ

Question re AGM is: is a fixed internally regulated 14.5 v OK for an AGM battery. I guess I should refer to individual battery manufactures specs.?

Odyssey/EnerSys has actually studied the differences between "optimal" charging voltage and sub optimal.

In Odyssey/EnerSys testing the cycle life difference between charging their TPPL AGM's at 14.2V and 14.7V is roughly 260 cycles at 80% DOD. This 260 cycle difference is for a battery rated at 400 cycles to 80% DOD in the lab. This means that by charging the Odyssey, temp compensated, at 14.7V you can realize a 186% increase in cycle life over charging at 14.2V (140 cycles @ 14.2V vs. 400 cycles @ 14.7V to 80% DOD)... Yes the optimal charge voltages can & do make a difference.

This 0.5V voltage difference creates a MAJOR hit to the lifetime performance of the battery if your charger can't charge the batteries correctly. While 0.2V does not sound like much, it will be sub optimal, and is just one more piece of the puzzle that can lead to sub-optimal performance.

During the recent Practical Sailor PSOC testing (May 2015 issue) the AGM batteries that were non sulfation resistant types did better with higher charge voltages.

Also not all AGM batteries are created equal and some are very, very poor performers in a PSOC environment. Firefly, Odyssey, Northstar & Lifeline and were the top premium AGM batteries in order of sulfation resistant performance.

You are also not temp compensating the charging, which can also harm AGM batteries. If you run the motor too long, without float, you also run a risk of drying out the battery, though this rarely happens on sailboats but certainly can.

[daveNZ]

Many thanks folks for those comments. FLAs look to be a sensible choice; unless I bite the bullet with an external regulator as well.

[sailinglegend]

Originally Posted by Adelie

....The AGMs will not charge faster unless you get a big alternator, 100amp or larger, or a big charger....

This is incorrect. Most good AGMs will charge faster because they have a much higher Charge Efficiency, but not all brands make these claims, so potential new buyers are often confused.

Wet cells may be as low as 70% efficient which means about 140Ah must be put in to actually raise the capacity of a battery by 100Ah.(70% of 140Ah is 100Ah) AGMs like Lifeline may be up to 98% efficient so only 102 Ah needs to be put in. That’s nearly 40% faster charging and it doesn’t take a large alternator to do it.

[colemj]

This may be true in theory, but a small, internally regulated alternator will not charge AGM's any faster than FLA's in practice. This type of alternator is inherently limiting and to gain any practical charging advantage from AGM's requires a larger charging source - as Adelie pointed out.

Mark

[daveNZ]

Does the same 45A Marelli alternator, with an external regulator, count as a better charging source?

If I can get 40-45A out if it, I should be able to charge a 200-220 bank, correct? (20% of Cap)

So no one yet can offer a measured voltage versus what a Victron BMV700 shows? I'm curious as I know voltage drops are very real; my Furuno GPSNav unit shows 13.1V where Victron BM shows 14..45V ! The GPS is about 4M of wiring from the battery, via the distribution bus, so obviously not ideal wiring. Surprising as rest of boat, e.g. battery/switches are probably over sized.


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[svlamorocha]

Originally Posted by daveNZ

I'm curious as I know voltage drops are very real; my Furuno GPSNav unit shows 13.1V where Victron BM shows 14..45V ! The GPS is about 4M of wiring from the battery, via the distribution bus, so obviously not ideal wiring. Surprising as rest of boat, e.g. battery/switches are probably over sized.

Good point. In my opinion the voltage displays in instruments are worthless for the purpose of estimating battery voltage, because the instruments are usually fed by a 16 or 14-gauge wire that also feeds a plotter that draws several amps, and then there is a length of very thin bus power wire. In my own boat when I turn the plotter the voltage display of the Raymarine multiple display drops by 0.3V, which makes it useless as a proxy for battery voltage.

In my opinion the voltage display in the instruments is only useful when you are trying to find out if a certain instrument problem is due to low voltage.

All that case, your .35 drop is a bit extreme. Is it evenly balanced across positive and negative? Have you checked if there isn´t a big drop around the infamous "common ground point" in the engine, if any?