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Go Back   SailNet Community > On Board > Gear & Maintenance > Electrical Systems > Charging two batteries on one charger
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Thread: Charging two batteries on one charger Reply to Thread
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Topic Review (Newest First)
12-25-2011 12:56 PM
mitiempo With some chargers like the Xantrex (not the best but the most prolific I think) you can switch from 3 stage to 2 stage charging. After a full charge is reached the charger sleeps until the voltage drops to 12.5 and it then comes on to fully charge before sleeping again. It refreshes the batteries each 21 days automatically in this mode. This is better for the batteries than a constant float and takes care of any self discharge issues.
12-25-2011 12:54 PM
Maine Sail
Quote:
Originally Posted by Stu Jackson View Post
Drivel and quite unnecessary.

Charge the batteries up, disconnect them and store them in a cool place. Do what Maine Sail suggests.

You could also thumb around the Ample Power Primer, download from the tech tab at Ample Power Company Home Page
Unfortunately for those in hotter/warmer climates the use of a float charger can be necessary, but, I'd still prefer a timer connected to it so they would see absorption ever two or three weeks or so..

Unfortunately many "float currents" do not always prevent electrolyte stratification and with these chargers/maintainers, despite being "floated", the batteries. if wets, can still develop stratification. This is why in colder climates I much prefer to hit them a few times over the winter with a good absorption charge to get the electrolyte moving.

I have a customers battery on the bench right now, that I just finished equalizing, checking cell balance and charging to full. It is sitting at 13.5 volts and is seeing just 0.025A +/- to maintain the 13.5V. 0.025A does not and will not always prevent electrolyte stratification. A better quality marine charger will have a program that reverts back to absorption voltages every now and then to get the electrolyte moving.

I have a very nice charger, the boat is in our yard, and I still will not leave it on constantly. I them it yesterday for about 6 hours for the first time in about three to four weeks.

Some folks are comfortable with float chargers. I've seen too many failures, of all types of chargers, to trust them implicitly when I am not there.....
12-25-2011 12:43 PM
Stu Jackson
Quote:
Originally Posted by LakeSuperiorGeezer View Post
I always float my lead acid batteries, whether deep cycle of starter batteries when there is infrequent use. Here is a web site that explains: How Does A Float Charger Work?
Drivel and quite unnecessary.

Charge the batteries up, disconnect them and store them in a cool place. Do what Maine Sail suggests.

Bill's right, too, but if the boat is in a "warmer" environment, most likely the folks are using the boat. Warmer weather = higher self discharge. Pretty easy to figure out: charge once a month, but don't leave 'em on float, because of what Bill said.

You could also thumb around the Ample Power Primer, download from the tech tab at Ample Power Company Home Page
12-23-2011 09:40 PM
mitiempo Or an Echo Charge.
12-23-2011 08:40 PM
Waltthesalt Look into an ACR relay. There's also the Duo-charge type regualtor units made for this. This cuts out the smaller battery when it's charged. Agree it's problematic to charge different types of batteries e.g. lead acid and gel.
12-05-2011 12:55 PM
btrayfors The above discussion worries me a bit. Not because some of the statements made are wrong, but because of the danger of their being misinterpreted.

I hope that no one takes away from this discussion the thought that it is always OK to charge your batteries before leaving them to themselves for the winter. While that might be a viable strategy in the cold frozen north, it is most definitely NOT a good idea for those habiting more temperate latitudes, i.e., those in which the temperatures during "winter" vary widely and/or stay relatively warm.

Keep in mind that all batteries have a self-discharge rate. Flooded batteries lose more each day/week/month from self-discharge than do, e.g., AGMs or gels, and this rate depends both on temperature and on age/condition of the battery.

If the ambient temp is very low, like near freezing, the self-discharge rate will be quite low. This is the condition which I believe MaineSail was referring to.

However, in areas like the Chesapeake daily temps during winter can vary widely....we even get some 70-degree days during December and January....and we can get some very cold (under zero degrees F) days and nights. If your boat is unheated the ambient temp will be affected by the outside temp and the amount of sunlight, as well as the degree of insulation.

What's the danger of leaving a battery less than fully charged? It can and will sulfate, and it will suffer from stratification (i.e., differing electrolyte concentration at various levels). These are the big killers of batteries which, unchecked, will result in loss of capacity and reduced overall life.

Remember, too, that even at a float voltage of 13.2-13.6, a flooded battery will sulfate and stratify somewhat. To avoid these conditions it is necessary to periodically increase the charge voltage to 14.4-14.8 or so.

If you're living in southern latitudes, say South Carolina to Florida or the Caribbean, don't even think about leaving your flooded batteries without at least some means to charge them periodically. In these climates, unattended flooded batteries can be killed by neglect in very short order.

Bill
12-05-2011 12:30 PM
Barquito Thanks for the replies everyone.

Wow, the cold Wisconsin winter could actually save me some work? Cool. Next year, I will just make sure the batts are topped off, and leave them on the boat.

I have a pretty simple electrical system, with a house battery and a starter battery. Where would I look to see if there is a diode protecting back current?
12-04-2011 10:07 AM
Maine Sail
Quote:
Originally Posted by LakeSuperiorGeezer View Post
I always float my lead acid batteries, whether deep cycle of starter batteries when there is infrequent use. Here is a web site that explains: How Does A Float Charger Work?
If you like that and are comfortable, then it is fine, but PLEASE do check on them frequently! I have seen far to many failures of chargers, all types and brands, to leave batteries unattended and on smart of "float" chargers. I simply won't do it to my own batteries and don't and still get above average life out of them. In the cold North we simply don't need to leave them constantly plugged in if topped up and disconnected.

In hot climates it can be a necessity due to self discharge as this accelerates in warmer temps and drastically slows in cold temps..

Most all boat yards up here specifically ban this practice in the winter, if batts are left on-board, and also stipulate that the batts must be left 100% disconnected from the vessel.

Some battery manufacturers also specifically advise against it, such as Lifeline.

Not all chargers behave the same or charge the same way. Some that claim float or smart provide a constant current and some pulse it ON/OFF based on voltage. The higher the float voltage setting the more often the current will be flowing in a pulsed charger..

If battery chargers were more reliable I may not have such an issue with it but I just see far to many failures and the resulting destroyed battery banks. With cold stored batteries I see leaving them plugged in and unattended akin to fogging your cars engine every time you shut it off. Not really necessary..

The other side is we have many unscrupulous manufacturers claiming "smart charging" selling pure unadulterated JUNK that is nothing of the "smart" sort...

This charger ruined a customers $1400.00 bank of NEW gel batteries charging them at over 16V on the GEL setting.... Smart? Hardly.??

Schumacher Ship n Shore Over Charging - YouTube



In a perfect world a proper float algorithm is fine but we just don't live in a perfect world. Battery chargers remain one of the most unreliable devices I see on boats. Please use them carefully...
12-04-2011 09:33 AM
skygazer
Quote:
Originally Posted by LakeSuperiorGeezer View Post
I always float my lead acid batteries, whether deep cycle of starter batteries when there is infrequent use. Here is a web site that explains: How Does A Float Charger Work?
Thanks, good explanations.
12-03-2011 10:21 PM
LakeSuperiorGeezer I always float my lead acid batteries, whether deep cycle of starter batteries when there is infrequent use. Here is a web site that explains: How Does A Float Charger Work?
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