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Old 02-15-2011, 12:19 PM   #1
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Genset Battery charging

This is my first time dry camping and I am trying to learn how to properly charge my batteries. For now I am confined to generator charging with a Magnetek 7345 converter. As far as I know it is a single stage charger?
Would love to upgrade to a progressive dynamics 9365 with charge wizard, but will save that money towards a solar install sometime in the future.
When I check my batteries while plugged into shore power after 24 hours the voltage shows 13.2 volts. When I test the batteries after resting they show 12.7 volts. I have not checked them with a hydometer yet.
After the first day of dry camping I soon found out that 2 group 24 batts (fairly new) at 164 amps was not enough. I had room for one more battery, so I added the same model 12 volt deep cycle in series. Now I have a total of 246 amps. Not great, but good enough for now.
My main concern is how long I need to run the generator to charge the battery bank. I began charging when the batts got down to 12.2 volts. With the Magnetek 7345 I could not get the batteries near full after charging for 2 hours, so I came up with an idea. I added my 15 amp Schumacher XCS15 digital charger to the mix. With the Magentek and the added digital charger I increased my charge voltage to 13.4 volts and the batteries seem to charge up in about 1.5 hours.
Question is, am I harming anything by doing this, and when charging off the genrator should my Magnetek be charging at a higher rate then 13.2 volts
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Old 02-15-2011, 01:17 PM   #2
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I think you must have added that third battery in parallel. What you are doing with the charger is fine. The Magnetek is more a converter than a charger. You might try turning the Magnetek off while charging with the Schumacher, the charger may be limiting charging because of the voltage it sees from the Magnetek.
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Old 02-15-2011, 02:22 PM   #3
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If you are not bringing the voltage up to 14.8 V you are not getting any where near a full charge. It takes a long time to do this with a generator and most chargers are not set to do this.
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Old 02-15-2011, 04:15 PM   #4
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re: "Would love to upgrade to a progressive dynamics 9365 with charge wizard, but will save that money towards a solar install sometime in the future." --

do yourself a big benefit and upgrade your converter now and set solar aside until you can afford less critical things. The best thing you can do for your batteries and your system reliability is to upgrade the converter.

Your voltage measures are reasonable. 13.2 volts is a good float voltage. 12.7 is a good full charge battery voltage when there is no charger attached and the surface charge has drained off. Keep you batteries above 12.0v as measured after resting with no significant charging or discharging for at least a half hour for best battery cost efficiency.

As for hydrometry -- don't! That sort of things needs proper hazmat conditions and really doesn't do anything for the typical RV enthusiast. You can learn all you need to know by a proper voltage measure that you interpret properly.

The PD plus chargewizard will not only optimize charging from the genset but it will also maintain your batteries properly when you are at home and plugged in. It will keep a full charge on the batteries, help inhibit sulfation, and significantly reduce electrolyte loss risk.

Keep in mind that it takes 8 to 12 hours to completely charge your batteries. A genset with a good charger (like the PD+CW) will get them up to 85% or so in a few hours. A genset can get you by when off grid but your batteries do need a full and complete charge at least weekly.

in re the 14.8 volts - that is getting a bit high for RV stuff that may be in the circuit. That is why most RV converter chargers usually use 14.4v as the bulk charge voltage. That is high enough to get a good dose of current into the battery (especially when it is down) but not so high as to cause concern about your RV appliances and devices.
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Old 02-15-2011, 05:38 PM   #5
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[QUOTE=Wanabee FTer;790946]This is my first time dry camping and I am trying to learn how to properly charge my batteries.

there are many references on rv systems on the internet. here are some of them. i hope these don't overwhelm you. i think windsun is one of the best.

The 12volt Side of Life (Part 1)

Electrical Tutorial

Batteries -- and Other Electric Stuff by phred

RV Batteries

Deep Cycle Battery FAQ
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Old 03-21-2011, 11:10 AM   #6
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As for hydrometry -- don't! That sort of things needs proper hazmat conditions and really doesn't do anything for the typical RV enthusiast. You can learn all you need to know by a proper voltage measure that you interpret properly.

re the 14.8 volts - that is getting a bit high for RV stuff that may be in the circuit. That is why most RV converter chargers usually use 14.4v as the bulk charge voltage. That is high enough to get a good dose of current into the battery (especially when it is down) but not so high as to cause concern about your RV appliances and devices.
Both of these statements demonstrate very well that what I say about the general consensus being wrong. Then again, if by the "typical RV enthusiast", you mean the the folks parked elbow to elbow in RV parks, then you may be correct. However, this thread was started by somebody who wants to dry camp. The correct answers are different for him.

First, the voltage is a very rough indicator of charge level and is very difficult to interpret. It can be used as a way of verifying that the battery system is healthy, sort of like checking your blood pressure, but it does not tell you the whole story. A hydrometer is the accurate way to test. Of course you need to be careful with acid, but how difficult is that? Go to bogartenginering.com (Trimetric battery monitors). You will find that Ralph, the inventor of the meter, tells you that you need to use a hydrometer, plus the voltage, to verify that the meter is programmed correctly and giving you accurate data. a Trimetric is a wonderful tool, but only if it is set up correctly. If it is set to tell you the batteries are full when they are not, it is just another feel good thing that will help you to ruin your expensive batteries by undercharging them with any converter run from a generator.

Voltage: Go to trojanbattery.com The correct charge voltage varies with temperature, but their chart shows that 14.8V is correct at 77 degrees F. At cooler temps it should be higher. They also have a chart that is based on charging amps as a percentage of battery capacity that shows you should raise the voltage with lower amps available, such as with most solar systems. You can also go to morningstarcorp.com and look at the instructions for the Tristar. Page 29 has a chart for temperature compensation. My system provides well over 15V during cool conditions and I have been doing this for years. Many people in the RV world still argue with me, but how can you argue with success? There is still no generator behind my rig, I add water to my batteries every three months and this morning on a rainy day the first thing I did was use the coffee grinder and then the Mr Coffee. The only issue in RV electronics is that light bulbs don't last as long when run at higher voltage, but ours are off in the day time when the voltage might be high. Inverters that are designed for solar (not for truckers) will work at up higher voltage inputs and then the output that we use to run our life is regulated 120VAC. The control boards in the fridge and water heater are designed to take over 16V. I have never burned one up. 14.4V is used by the industry because they expect us to be plugged in 24/7 and they are so worried about overcharging that it is just ridiculous. This is about liability worries, not truth.

The biggest reason that you don't see me on these forums very much is because I get very tired of trying to fight the general consensus that is such a hindrance to those of us who want to successfully go off grid. It took me years to figure it out because everywhere I went I found bad advice. I am still the voice in the wilderness when it comes to successful solar power.
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Old 03-21-2011, 04:42 PM   #7
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re: "Both of these statements demonstrate very well that what I say about the general consensus being wrong." -- I think you need to back off a bit and get your facts straight, both about the consensus and what I am saying about batteries. I much prefer not just labeling something wrong but rather explaining why I think it is so and what is more correct and why that is the case.

re: "First, the voltage is a very rough indicator of charge level and is very difficult to interpret" -- voltage is the outcome of the same electrochemical process and is directly correlated to specific gravities, which is why you often find charts with both listed versus state of charge. Both voltage and specific gravity need 'interpretation' in light of battery temperature, recent usage (e.g. electrolyte stratification), and other matters. Both need care to assure a proper measure. The use of voltage as a primary battery state of charge indicator can also be seen in its use in battery gauges and in the automatic cutoff mechanisms on many heavy low voltage loads.

re: "Of course you need to be careful with acid, but how difficult is that?" -- as a matter of fact, quite difficult because it does need attention to detail. Things have changed over the years as people are now a bit more concerned these days about acid burns and eyesight loss and such things. I have my share of acid burned pants and shirts and I have indeed chased mercury globs around the floor and work surface (some say that's the source for my debate points, but I digress ... ;-). I am also acquainted with the fact that many folks don't pay much attention to risk reduction even when they have been carefully trained. That is why I think the best safety is to avoid putting yourself in a spot where special precautions are highly recommended.

re: "You will find that Ralph, the inventor of the meter" -- appeals to authority do not matter as much to me as the validity of what is offered and being able to understand its reasons, rationale, and context. (And don't get me started on the problems with electron counters! -- especially in regards to proper measurement technique, interpretation of measures, and such things as accuracy versus precision.)

What you cite from Ralph about recommended voltages has several important caveats that need to be understood before being taken as is. One is the difference between applied charging voltage and battery voltage during charging. Another is the role of the current capabilities of the charging sources. Battery charging voltage can be an interesting topic because it has a lot of depth.

re: "The correct charge voltage varies with temperature, but their chart shows that 14.8V is correct at 77 degrees F." -- this depends upon the battery and what you are trying to do. There are good reasons why RV converter chargers tend to run 14.4v as their bulk phase voltage maximum and absorption switch point (as described above). Float voltages usually run in the range of 13.2 to 13.8. Resting fully charged battery voltage after the surface charge has been removed runs around 12.6 to 12.8v


re: "I add water to my batteries every three months" -- loss of electrolyte usually indicates overcharging. This might be related to the 14.7v bulk charge voltages or perhaps too high a float voltage. Less common, it might be due to excessive charge or discharge currents (mismatch between bank size and use profile) or heat. Either way, it is something that should be fixed if possible.

re: "if by the "typical RV enthusiast", you mean the the folks parked elbow to elbow in RV parks, then you may be correct. However, this thread was started by somebody who wants to dry camp. The correct answers are different for him." -- I think that context is indeed extremely important and agree with you on this. But the creation of categorizations to dispute what I offer is way off base - a constructed fallacy as it were. That sort of thing doesn't help IMHO.

The context, the use profile, is a very interesting and important topic in its own right as it has significant influence on battery life, battery warranties, and other matters. I find it especially pertinent when folks get into 'deep cycle' myths or the need for equalization charging.

Quote:
The biggest reason that you don't see me on these forums very much is because I get very tired of trying to fight the general consensus that is such a hindrance to those of us who want to successfully go off grid. It took me years to figure it out because everywhere I went I found bad advice.
I can certainly agree with you here (but I don't think the hubris is appropriate as we can all learn). It is why I try to make sure anything I offer has a reason, a 'because', a careful explanation with appropriate context, reference and citation if needed, and good empirical support.

IMHO, we have a responsibility to clarify the errors and misperceptions that exist and are promulgated in these forums, to provide education as we can, and to help folks understand those technologies upon which they depend.
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