Battery Question

[BWagner]

So I have a house battery bank consisting of 10 six volt golf cart batteries which is separate from my starting battery. The only thing the two have in common is they both receive charge from the alternator when the main engine is running. My question is, can I use a sealed AGM or gel battery as my starting battery? The alternator is the 80 amp stock alt that came with the boat. Obviously you can't use different type batteries in the same bank but I'm not sure if it would make any difference here. Any thoughts would be appreciated.

 

[Don S/V ILLusion]

The only problem would be when recharging off your charger, not the alternator. A properly functioning alternator of the conventional OEM variety won't sense the single start battery separately from a severely low bank thereby sending a higher charge rate than your start battery needs. But in that scenario, the interval during which the alternator is pouring current out will typically be short.

The problem comes from using a shore powered charger not designed to sense multiple banks. If yours does not, and the house bank is low, you could easily cook your start battery.

The punch line here being it depends on your battery charger.

 

[Rick D]

I Did

So I have a house battery bank consisting of 10 six volt golf cart batteries which is separate from my starting battery. The only thing the two have in common is they both receive charge from the alternator when the main engine is running. My question is, can I use a sealed AGM or gel battery as my starting battery? The alternator is the 80 amp stock alt that came with the boat. Obviously you can't use different type batteries in the same bank but I'm not sure if it would make any difference here. Any thoughts would be appreciated.

I put an Optima start battery in about seven years ago, It is AGM but has a charge profile the same as wet cell. The batteries are isolated by an isolator. The AGM, I believe, does not get a trickle charge from the AC charger. It just sits and gets it's charge from the engine when I run it. Anyhow, no problems.

 

[Stu Jackson]

http://forums.catalina.sailboatowners.com/showthread.php?p=1034291&highlight=balmar.net

 

[Bill Roosa]

Just for the record 10 six volt batteries in a house bank will start your motor....... sooooo why even have a start battery that is a different chemistry? Stick with wet cell and eliminate the problem. The AGM is probably more expensive also!!!
IMHO you really don't need a start battery if you monitor your house bank with a simple volt and ammeter and then manage your loads and production.
try this:
http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

Had a situation Friday night. bunch of crew sailing after dark. glanced at the voltmeter and saw 11.9!!!! warning, warning Will Robinson! Quickly checked the ammeter and sure enough drawing 15 amps. My common consumption is 5amps +- .5 amps and my brain has memorized the voltage of the battery when it is supplying that C level. Checked the breakers and sure enough the freezer (adds 5 amps) and running lights (adds 3 more), plus a few cabin lights. turned off the freezer and reefer (unload 10 amps) and dropped the amps to 5 and sure enough the volts IMMEDIATLY came up to 12.7 which is above 90% SOC which made much more since to me as we had only been under sail for about an hour. Consulting the link (I have it printed out) above for the 15 amp C rating and sure enough 11.9 volts above 90% charged.
I know some of you think it takes a Phd to read a voltmeter to the 0.1th of a volt but it is really not that hard and you don't have to wonder if my battery monitor is calibrated or something got "goofed up" and it is reading wrong. And you probably already have the instruments.
Think of how salty you will look when you glance at the voltmeter and ammeter and proclaim the batteries are at xx SOC so we should be OK till morning. Not punching of buttons to get a readout, just a glance at the panel.

 

[Maine Sail]

Just for the record 10 six volt batteries in a house bank will start your motor....... sooooo why even have a start battery that is a different chemistry? Stick with wet cell and eliminate the problem. The AGM is probably more expensive also!!!
IMHO you really don't need a start battery if you monitor your house bank with a simple volt and ammeter and then manage your loads and production.
try this:
http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

Had a situation Friday night. bunch of crew sailing after dark. glanced at the voltmeter and saw 11.9!!!! warning, warning Will Robinson! Quickly checked the ammeter and sure enough drawing 15 amps. My common consumption is 5amps +- .5 amps and my brain has memorized the voltage of the battery when it is supplying that C level. Checked the breakers and sure enough the freezer (adds 5 amps) and running lights (adds 3 more), plus a few cabin lights. turned off the freezer and reefer (unload 10 amps) and dropped the amps to 5 and sure enough the volts IMMEDIATLY came up to 12.7 which is above 90% SOC which made much more since to me as we had only been under sail for about an hour. Consulting the link (I have it printed out) above for the 15 amp C rating and sure enough 11.9 volts above 90% charged.
I know some of you think it takes a Phd to read a voltmeter to the 0.1th of a volt but it is really not that hard and you don't have to wonder if my battery monitor is calibrated or something got "goofed up" and it is reading wrong. And you probably already have the instruments.
Think of how salty you will look when you glance at the voltmeter and ammeter and proclaim the batteries are at xx SOC so we should be OK till morning. Not punching of buttons to get a readout, just a glance at the panel.

15A load on a house bank at 90% SOC and only 11.9V? Is this a small bank or is it perhaps getting long in the tooth? A 15A load on a 300Ah bank is only a C/20 load.....?

 

[Bill Roosa]

420 AH and yes it is long in the tooth. Going on 7 years now.
Which brings up a great point, you can predict battery failure with this technique also.
But you have to start seeing the patterns and not just looking at the numbers

 

[Maine Sail]

11.9V@ 90% SOC at a C/28 load I'd say that bank is beyond dead....

BTW been running a 12A to 16A load since about 1:00 today Espar, 12V refridge and various other loads. Solar reduced the load some when it was brighter but it was still between 12A -16A.. Battery terminal voltage is still 13.29V......

Using voltage on LiFePO4 is not feasible...

 

[Maine Sail]

So I have a house battery bank consisting of 10 six volt golf cart batteries which is separate from my starting battery.

That is a bank of approx 1125Ah's and is massive. It will require all charging systems to be addressed to appropriately match that capacity with current.

The only thing the two have in common is they both receive charge from the alternator when the main engine is running.

How are they getting this charge? By using BOTH on the battery switch, a diode based isolator, an ACR type relay or an Echo type battery to battery charger??

My question is, can I use a sealed AGM or gel battery as my starting battery?

The simple answer is yes but how to do this is where it goes awry. An AGM would be fine as the charge voltages are similar but a GEL battery poses issues as it can not be charged at more than about 14.1V and the wets should see 14.4V - 14.8V in absorption.. There are ways to make this work but the real question is why do you want a GEL or AGM battery for starting when you already have 10 flooded batteries? You can easily start off the house bank if you want to..

The alternator is the 80 amp stock alt that came with the boat.

With that alternator your charging capabilities are grossly under sized and the alt will be over worked. When Hitachi's over work they cool themselves by reducing the output voltage. This, on top of the low amperage for your bank, will only lead to chronic under charging and greatly extend your "time to full". As it is if you drew your bank to 50% state of charge then it would take you 10 - 15 hours of engine run time to recharge most of that capacity, and that is at a good voltage when the alt eventually gets there..

Obviously you can't use different type batteries in the same bank but I'm not sure if it would make any difference here. Any thoughts would be appreciated.

An AGM would be fine but your first priority should be to:

*Address your alternator and belts

*Check water levels and specific gravity of the bank

*Fully equalize your existing bank as they have likely been chronically undercharged.

An alternator in the 200-225A range (hot performance would be 170 - 195 or so) would be a good fit but you will also need a serpentine pulley kit to drive that HP.....

 

[Stu Jackson]

A parallel question might be: What is the energy budget that would require such a massive house bank? If answered, one could perhaps make the point that it is oversized and that the work required to support it, as Maine Sail points out, may well be unnecessary.

 

[Chief RA]

If 10 ea. 6 volt batteries are set up in a series parallel 12v configuration: total amp/hrs are one half the total of all the amp/hrs of the 10 batteries! (example/10 x 100ah=1000ah divided by 2 = 500ah total) Use 2 of your 6v batteries as a starter bank and eliminate the AGM.
Chief

 

[Maine Sail]

If 10 ea. 6 volt batteries are set up in a series parallel 12v configuration: total amp/hrs are one half the total of all the amp/hrs of the 10 batteries! (example/10 x 100ah=1000ah divided by 2 = 500ah total) Use 2 of your 6v batteries as a starter bank and eliminate the AGM.
Chief

Right..... 10 X 225AH = 2250Ah / 2 = 1125Ah bank

Or 5 series pairs at 225Ah = 1125Ah...

 

[Chief RA]

BWagner just needs to eliminate some of his bank if he has batteries of such size! Even with a 42' boat he only needs maybe 6 of his 6v batteries and still use 2 of those for starting!
Chief

 

[Maine Sail]

BWagner just needs to eliminate some of his bank if he has batteries of such size! Even with a 42' boat he only needs maybe 6 of his 6v batteries and still use 2 of those for starting!
Chief

It all depends upon what his use/loads are... An 1125 Ah bank goes pretty fast when you are only cycling between 50% and 80% SOC when off cruising. That means his usable capacity from an 1125Ah bank is really only about 340Ah. If he used 125Ah per day that is only about three days on the hook with silence.....

 

[artboas]

Mismatch

So I have a house battery bank consisting of 10 six volt golf cart batteries which is separate from my starting battery. The only thing the two have in common is they both receive charge from the alternator when the main engine is running. My question is, can I use a sealed AGM or gel battery as my starting battery? The alternator is the 80 amp stock alt that came with the boat. Obviously you can't use different type batteries in the same bank but I'm not sure if it would make any difference here. Any thoughts would be appreciated.

Just read your post.
I like the golf cart batteries, as I find them to have the most economical solution
Plus, they are easy to lift, etc.
But, the stock 80 amp alternator is just plain wrong. You'll be running your engine for hours on end to keep these topped up. Plus. The stock alternator doesn't have bulk, absorb, float modes.
You need a high capacity alternator with an external regulator.
Minimum 150 amp.
You will need to address how you will drive this from the engine. Your best bet is a serpentine belt.
The belt that drives the stock 80amp is too small

Good luck.

 

[Chief RA]

Nobody needs that much power at sea without one really long extention cord! I am done, I have made my evaluation regarding his situation! Hope we helped as we received no feedback from him. Chief

 

[Rick D]

There can be reasons...

Nobody needs that much power at sea without one really long extention cord! I am done, I have made my evaluation regarding his situation! Hope we helped as we received no feedback from him. Chief

Friend of mine sailed for a while with an ailing wife and needed all of that for her equipment and then some. At least she got to enjoy some of her favorite time on the boat while she could.

 

[H45DS]

An AGM would be fine but your first priority should be to:

*Address your alternator and belts

*Check water levels and specific gravity of the bank

*Fully equalize your existing bank as they have likely been chronically undercharged.

An alternator in the 200-225A range (hot performance would be 170 - 195 or so) would be a good fit but you will also need a serpentine pulley kit to drive that HP.....

All this PLUS... ensure that you have adequate cooling for your alternator. I learned this the hard way in my boat (Hunter 45DS) when I replaced my three stock 4D wet cell house bank batteries plus the starting battery with larger capacity Lifeline AGMs. My stock alternator would overheat in even cooler (70's) temperatures due to the greater charging current requirements of AGM batteries (really a sign that I was overly taxing my alternator). I put in a cooling fan to pull more ambient air through the engine compartment as well as a serpentine belt system, which helped, and this year finally $olved my problem for the long-haul by installing a Balmar 94-series 210A alternator - a lot beefier and 90+ percent of the time I'm using a very small percentage of its current output capacity.

 

[Bowedtoothdoc]

I would assume that the OP has a genset with a dedicated charger/inverter for charging the house bank. That is how the setup on my boat works. I have 6 of the golf cart batteries for my house bank.

 

[Benny17441]

You do indeed have a massive battery bank. I do feel a little curious but will not inquire about the choices that led to such a massive installation wether by yourself or a PO. Let's just say it is what it is. I would think that an appropiate battery charger to handle that size bank will have the capability of being adjustable to run different chemistry banks simultaneously but why constrain the charger output by having to have a specific setting for a one battery (or small) bank when it is simpler to maintain the same chemistry and make better use of its output capacity. You may also gain redundancy by being able to shift batteries around and reconfigure the Home and Starting banks. Do conduct an electrical survey according to your usage between recharges and that may help you in the future to reduce or maintain the size of the bank and its efficieny.