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farmer ted could you quote some sources for this info you present as it goes against most every thing i have learned dealing with battery banks on ocean going boats


1 we have always strived to charge our banks with a charge equal to 20% of the ah rateing of the bank for example a 200 amphour bank we would use a 40amp charge give or take

supporting quote from  http://www.ibsa.com/www/faqs/tech_talk/maintenance/charging.htm

What's the best way to charge deep cycle batteries? The maximum charger rate in amps should be 20% of the amp hour rating of the battery.


Normally, deep cycle batteries do not require special charging procedures. However, we recommended that you use a charger designed specifically for deep cycle batteries. It is best to slow charge all batteries, especially deep cycle. The 20% rule should be used when charging a deep cycle battery. That means to choose a charger where the maximum current (in amps) is less than 20% of the Ah rating. For example, an Interstate SRM-27 is rated at approximately 100 Ah, so a 20-amp charger should be the maximum. Also, it is best to use a charger that is adequate to recharge the battery within 10-12 hours
more important is voltage finding a charger with adjustable voltage allows you to set the proper voltage for the different stages of charging

here is a voltage table from the trojan battery website

Table 2. Charger Voltage Settings for Flooded Batteries

System Voltage 12V
Daily Charge 14.8
Float 13.2
Equalize 15.5


and as far as burning up auto alternators i have run a 35 amp auto alternator on a 5hp briggs full feilded (full output) as a portable charging station for my cabin for years running 8hours per day attleast 100 days a year and i have reringed the motor twice and had no probs from the alternator and on my old fishing boat (36ft twin diesle) i had a pair of 200 amp alternators (1 on each engine) using 3 stage regulators and when we were away from shore the average amp load was over 200 amps running all the lights pumps inverters dc ice maker inverter and other cant live with out goodies and never had any probs with the alternators

so before you guys change the way you charge your batteries dont take my word for it or anyone elses do some searches on the net about charging batteries and make sure you learn how to charge the batteries you have since leadacid batteries wheather auto, marine or tru deep cycle require different settings even different maufactures sugest different settings for there batteries they also use different terms like "amp hour" vs "20 hour amp hour" do you know the difference or is there? and if you have a tru sealed battery like the gell cells then there are a whole different range of settings youll notice in 1 quote above they suggest full charge be completed in 10-12 hours max it wouldnt take a very large battery and a 2 amp charger could not finish up in that amount of time

its been a few years since i was on the sea but if anyone would like i would be happy to dig out my sources and elaborate further
 

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farmer ted said:
the only point I was trying to make was that as a general rule: the lower of a rate you charge ANY battery, the better it is for the battery.
this "general rule" is way inaccurate charging a battery to slow is just as bad as to fast

you are correct in saying automotive type chargers are not the best for recharging deep cycle batteries they work ok in cars to keep the battery charged and provide extra power for accesories

you have to be carefull if you use automotive type chargers as they will hurt batteries due to high voltage if left on to long regardless of the amps

i checked out the stay n charge web site and they dont give much info but it sounds like it will use not only the tow vehicals charging system but also the main boat engine also

you could do the same thing with some wiring and battery isolators just like what you would use for setting up dual batteries in your truck only the second battery is in the boat
 

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im always up for learning new thing so point me in the direction of some supporting documentaion for your ideas
 

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here is a response an email i sent to trojan battery company

Hello,

We generally recommend a charging rate of about 10 to 13% of the system's amp-hr capacity.  This means that for a pair of T-105 (225 amp-hr), a good charging rate is about 20 to 30 amps (22.5 to 29.3 amps to be exact).  For deep cycle batteries, low and slow is good.  You can, if you wish, go higher in the current, up to 50% of the capacity.  Be aware that the higher you go in the charging rate, the more accurate your controller must be in order to prevent overcharging your batteries.

Please contact me if you need further assistance.

Best regards,

Jim Le
Technical Support Engineer
Trojan Battery Company
800-423-6569  Ext. 3045
it is funny they use the term "low and slow" yet recomend 20-30 amps also noted was that you can go as high as 50% charge rate as long as your controller was up to the task and at 10-13% that fall in with the finish charging in 10-12 hours

seems the important thing is to keep them full of water and dont let them over charge (voltage) and dont charge a frozen battery then they will last a long time
 
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