Battery Charger - Leave it on or off?

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timjet

timjet

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I have 3 battery banks. Two house, *selectable from a battery selector switch (1- Both - 2 - Off). The third bank powers the generator start circuit exclusively. My battery charger has 3 outputs which of course change each bank as necessary. All batteries are AGM and the charger is setup to charge AGM batteries.

Question: With fully charged batteries should I leave the charger on when I'm not at the boat?
 
IF it is a modern 3 or 4 stage unit with an operating brain, leave it on.


The unit may hold the boat up if the leak is within the minor capacity of most electrical bilge pumps.
 
The very fact that it allows charging of three seperate banks and is switchable for battery types means it has a brain ie: multistage charging. Leave it on that's what's there for.
 
I leave the charger on 100% of the time ever since we bought the boat 16 years ago*as we have a constant draw on the batteries especially in the winter with the Webasto, 25 amps 12 volt DC.***

It would depend on the amp draw on the battery, how long you leave the boat and how big the battery bank.*
 
I have a "smart" charger w all AGM batts. I turn it on about once a week (or so) or whenever the batts fall to 12.55 volts. My charger charges at 14.35 volts. I decided it may not be good to have the voltage constantly above 14 volts so I have been draining down to 12.5 to 12.55 volts * * ...then charge for about 8 hrs *and repeat. It's handy for me to do as I live about 1/2 mi from the boat.
 
nomadwilly wrote:

I have a "smart" charger w all AGM batts. I turn it on about once a week (or so) or whenever the batts fall to 12.55 volts. My charger charges at 14.35 volts. I decided it may not be good to have the voltage constantly above 14 volts so I have been draining down to 12.5 to 12.55 volts * * ...then charge for about 8 hrs *and repeat. It's handy for me to do as I live about 1/2 mi from the boat.


No offense but I'm not so sure how "smart" your AGM charger is unless it is a single stage charger that only has bulk charging rate at 14.2-14.4 volts.* If that is the case, you do want to to remove it.* If you have*a 2 or 3 stage charger, they will have 'float" stage of 13.2-13.3 for AGM's.*
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timjet wrote: Question: With fully charged batteries should I leave the charger on when I'm not at the boat?

When we had our electrical shop install an inverter/smart charger a number of years ago, on their advice we have left the charger on all the time in the slip*since then.* We were told that sending a float charge to the batteries all the time will extend their life and enhance the performance of the batteries.

Our charger/inverter sends its three-stage signal to the house batteries.* The start and generator batteries get an echo charge, which is a float charge only.

We also equalize our house and start batteries annually.

If one does not have a "smart" charger it's probably not wise to leave the charger on all the time as this could overcharge*(boil) them.* Something to consider is if one is away from the boat and a leak develops, what happens when the bilge pump exhausts the batteries and the charger is off?

A charge rate will vary with the ambient temperature.* The colder it is, the higher the charge rate will be.* Our inverter/charger is fitted with the optional temperature sensor that will have the charger compensate for the ambient air temperature.
Click to expand...

*


-- Edited by Marin on Thursday 13th of January 2011 08:18:57 PM
 
On a Smart charger the final , float voltage is settable.

This setting will be low for dockside use .

IF you can not keep the float voltage low it will cost some distilled water every so often.
 
You may decide to rethink this.

AGM's are expensive.

AGM's will hold a charge for many months if completely isolated.

Short cycle charging is not healthy for batteries

AGM's cannot recover lost electrolyte.


All batteries, AGM's included have a finite number of charge cycles.

Most "smart" chargers will change from float to a charge cycle when there is a load placed on the bank - for example, if your bilge pump comes on, if you visit the boat and turn on lights, tv etc for even a few minutes, the charger will notice the load and begin a charging cycle - Even though your battery is at 99.9% SOC, this effectivly counts as a recharge cycle - albiet it is less harsh on the battery than a charge cycle that begins with a 50% discharge.

Since a 'smart' charger runs through a program of a minimum time setting for bulk, absorb, before float voltage, you are applying the bulk voltage - as high as 14.8v depending - to a bank with a 99% SOC - this may potentially cause some boil off

One solution is to charge your bank to 100%, then isolate the bank. And use the charger as a powersupply for dockside loads (assuming it can handle the loads). When you are cruising you reconnect the bank and recharge via your normal charging system - alternator etc.

This effectively limits the number of charge/discharge cylces of your expensive battery and will lead to a longer bank life.
 
Well guys I think it's me that's not so smart. I just forgot how the charger works * ..I think.I'll go down to the boat and turn it on and look at it tomorrow. By then it should be in "float" mode. It's so cold and it's blow'in so hard I really don't want to go down there again today * *.....tomorrow.
I don't think my AGM batts are 100% good either. Had the same batts in my previous boat and I think they held their voltage better. The boat yard we had working on our boat while we were in Alaska ordered the batts at least 6 mos before they were needed so they sat on the floor all that time.


-- Edited by nomadwilly on Friday 14th of January 2011 05:48:48 PM
 
"All batteries, AGM's included have a finite number of charge cycles."

True but,

A charge cycle is not switching from float to charge.

It is bringing a depleated batt (down 70%, 50% or only 10% back to fully charged)

The depth of discharge will control the number of cycles the battery can deliver , as well as how long the batt was left discharged.Most mfg have graphs.
 
Leave it on. As usualy, y'all are overthinking this deal. Healthy batteries with a good smart charger will last you MANY years of use.

I had a malfunctioning smart charger that would never go to FLOAT so I had to turn it on and turn it off as necessary...just like Eric is doing. My batteries lasted a whopping 2 years doing that. Batteries DO NOT like being left in a stage of unchargedness. ANd if you leave your charger off, they will drain over time. ANd when you go back down to the boat and turn them on, they will top up....using one of those valuable cycles that we are talking about. Keeping batteries topped up with a float charge is not a charging cycle. Allowing batteries to "leak down" and then recharging is a charging cycle and takes a chip out of the life of your batteries. I put a brand new charger and brand new batteries on my boat and they lasted 4 years and were still working well when she was sold.
 
Yes, if its a relatively new unit it will sense the battery charge and go to trickle; I leave both my 20 and 50 amp chargers on 100% of the time.
 
Baker wrote:
Leave it on. As usualy, y'all are overthinking this deal. Healthy batteries with a good smart charger will last you MANY years of use.

I had a malfunctioning smart charger that would never go to FLOAT so I had to turn it on and turn it off as necessary...just like Eric is doing. My batteries lasted a whopping 2 years doing that. Batteries DO NOT like being left in a stage of unchargedness. ANd if you leave your charger off, they will drain over time. ANd when you go back down to the boat and turn them on, they will top up....using one of those valuable cycles that we are talking about. Keeping batteries topped up with a float charge is not a charging cycle. Allowing batteries to "leak down" and then recharging is a charging cycle and takes a chip out of the life of your batteries. I put a brand new charger and brand new batteries on my boat and they lasted 4 years and were still working well when she was sold.
Click to expand...
I have to agree with you John. I have a Freedom 10 Inverter/Charger that I leave on twenty four/seven, and my batteries are lasting seven years with consistency.

*
 
Well, I finally ran the batts through a charge cycle and the float voltage was 13.75. I'll look up my charger manual and learn how to set the float voltage down to 13.2. Thank you Larry and FF.
 
Eric--- The float voltage will vary with the ambient temperature. If it's very cold, the float voltage can be as high as 14 volts according to our Heart Freedom 25 manual. In "normal" temperatures like we get in the spring, summer, and fall, the float voltage is typically 13.5 volts. We observed this on our remote panel for the Freedom 25. In the winter the float charge would typcially be 14 volts. In the summer it was usually 13.5. This was with lead-acid 8Ds. I notice that now that we've recently switched to 6vdc golf cart batteries wired in pairs the float voltage is 13.5 in the winter and 13 to 13.5 in the summer.
 
float voltage is 13.5 in the winter and 13 to 13.5 in the summer.

That is a bit high for a float voltage , and will cause watering to be needed.

Can you bring it down?
 
FF wrote:

float voltage is 13.5 in the winter and 13 to 13.5 in the summer.

That is a bit high for a float voltage , and will cause watering to be needed.

Can you bring it down?
Click to expand...
That's what the manual says it should be and also what our electrical shop says it should be.* There is never any liquid on top of the batteries.

*
 
My float voltage varies* between 13;1 and 13.2.* Guess it is because of the boring temperatures we endure.* Ho hum!
 
Moonstruck wrote:
My float voltage varies* between 13;1 and 13.2.* Guess it is because of the boring temperatures we endure.* Ho hum!
Click to expand...
As does mine, Don.

*
 
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