QUOTE(Lindsay Richards @ Nov 23 2009, 11:42 AM) [snapback]20109[/snapback] We have a small solar charger that came with our Itasca to keep the batteries topped off. I do also but it apparently isn't enough or never has worked. If I don't exercise my MH at least once a month, my engine battery will be so low I have to use the auxilliary boost to start it. I've never had a problem with the two house batteries other than having to replace them after five years.
QUOTE(pianotuna @ Nov 23 2009, 09:26 PM) [snapback]20114[/snapback] Hi abbygolden, Yes it will make a nice difference. Depending on the battery chemistry and the charger. If the charger is one of the new "smart" chargers and the battery is down to 80% state of charge an hour may bring it back to say 90% (again depending on chemistry). If I were you, I'd: -start the generator, so the converter can work its magic on the "house" battery bank -start the engine for that 15 minute warm up -get the charger "ready to roll" on the chassis battery bank -turn off the engine -turn on the charger powering it from the generator. But then, if I were you, I'd already have a solar system in place to take good care of the "house" battery bank. Thanks for the info, but I'm still confused (despite having read the links you sent to me, thanks incidentally). If I read your suggestion correctly, are you recommending that after I shut off the engine that I charge the engine battery while the generator is running or the house batteries (I'm not sure if "chassis" batteries are the same as engine batteries, but I don't think so)? It's the engine battery that I want to charge. Also, can I charge the engine battery while it is running or do I need to wait until I turn off the engine? Also, as I wrote to Lindsay, I have a 5w solar panel that came with my Itasca that I thought was supposed to keep the engine battery topped off. If that is the purpose, it hasn't worked. I also have a 5w plug in to the cigarette lighter panel but if I use the battery disconnect switch, it won't work. Sorry I can't get this stuff into my pea brain so I can comprehend it. I guess my brfain has been clogged with golf thoughts for so many years that there is little room for anything else!
Don, All batteries have internal resistance and the low cells (resistance) will past more current than the higher ones. So they will charge up faster. This is call impedance if I remember right. In the telephone offices we used 23 large flood cells to make up 50.6 volts. Each cell should read out at 2.20 volts but some would read at 2.10 or 2.05. Then others would go high like 2.25 or 2.27. Bottom line, each month the reading would change around. High cells will drop and low cells will go up. You can never get it on the money. We changed over to Gel cells later and found close to the same problem. Each Gel cell had a weight of 250 lbs. and a 20 year life same as flood cells.
Hi abbygolden, Yes chassis battery = engine battery. 15 minutes of run time is not enough for the alternator to do much charging. That's why I suggested using the generator and a battery charger on the engine battery for another 45 minutes. 5 watts won't keep up with the parasitic loads on a modern engine. 15 watts might. QUOTE(abbygolden @ Nov 24 2009, 08:55 AM) [snapback]20120[/snapback] Thanks for the info, but I'm still confused (despite having read the links you sent to me, thanks incidentally). If I read your suggestion correctly, are you recommending that after I shut off the engine that I charge the engine battery while the generator is running or the house batteries (I'm not sure if "chassis" batteries are the same as engine batteries, but I don't think so)? It's the engine battery that I want to charge. Also, can I charge the engine battery while it is running or do I need to wait until I turn off the engine? Also, as I wrote to Lindsay, I have a 5w solar panel that came with my Itasca that I thought was supposed to keep the engine battery topped off. If that is the purpose, it hasn't worked. I also have a 5w plug in to the cigarette lighter panel but if I use the battery disconnect switch, it won't work. Sorry I can't get this stuff into my pea brain so I can comprehend it. I guess my brfain has been clogged with golf thoughts for so many years that there is little room for anything else!
Hi John, I was aware it is impossible to get all cells equally charged--and that "equalization" charging was an attempt to help "weak" cells catch up. Are you saying (trying to learn) that a battery that is at 50% state of charge has lower internal resistance than one that is at 80% state of charge? And therefore it will charge faster? I thought that the acid turned to water--which is a poorer conductor and increases resistance? And what about the connection resistance? How does that "play out"? QUOTE(John Blue @ Nov 24 2009, 09:12 AM) [snapback]20121[/snapback] Don, All batteries have internal resistance and the low cells (resistance) will past more current than the higher ones. So they will charge up faster. This is call impedance if I remember right. In the telephone offices we used 23 large flood cells to make up 50.6 volts. Each cell should read out at 2.20 volts but some would read at 2.10 or 2.05. Then others would go high like 2.25 or 2.27. Bottom line, each month the reading would change around. High cells will drop and low cells will go up. You can never get it on the money. We changed over to Gel cells later and found close to the same problem. Each Gel cell had a weight of 250 lbs. and a 20 year life same as flood cells.
Hi Prof, Hello Don, You have not allowed for the internal resistance for the batteries, nor the resistance for each connection. These amount to more than the resistance in the wire. The internal resistance of the batteries has nothing to do with the resistance in the interconnect cables. Clean, properly torqued connections with a surface contact area comparable to the circumference of the interconnect cable should introduce negligible resistance. With only two batteries balanced wiring need not cost a dime extra. In my case it cost nothing extra for the buss bar system--and about $20.00 for the wiring the triple battery bank. The method your referenced material shows for balancing four or more batteries requires extra lengths of cable. This is counter intuitive to what you are trying to accomplish by reducing cable resistance. All of this needs to be evaluated and the added resistances computed before making a decision to implement wiring in this manner. I do not have your expertize, nor do I have a spreadsheet to "crunch the numbers" so I can only quote from the smart gauge web site. A spreadsheet is not required. All that is necessary are basic math skills and Ohms Law. A reference text or some checking on-line will give you the resistance for particular metals, lengths, AWG sizes and CMC. Without an understand of these mathematical concepts or the ability to perform the computations one will not have a clue as to what is going on in a circuit. "Now in all fairness, many people say 'but the difference is negligible, the resistances are so small, so the effect will also be small'. The problem is that in very low resistance circuits (as we have here) huge differences in current can be produced by tiny variations in battery voltage." I am not sure where you are getting this information. Comparisons using the terms huge, current, tiny and battery voltage do not exist in the typical parallel battery connection found in a RV. But, if you are wiring a battery bank for a Tesla Motors vehicle we may indeed need to factor in variations in current and voltage from individual batteries because the sum of variations in hundreds of batteries can become significant. I'm always interested in learning more. May I ask you to elaborate on "other uncontrollable variables in the system that will have a greater impact." Are there solutions to these variables? Temperature is, of course, the major "uncontrollable" we encounter. How can the charging current "go to the lowest charged battery first"? This seems counter intuitive to me. In an unbalanced wiring scheme the resistance will be highest to the last battery in the chain. It seems logical to me that this battery would receive the least amount of charge--and get it last as well. A completely dead or "flat" battery will have an extremely high resistance. In fact, it may never recharge. What we are looking at are good batteries with a normal state of discharge (up to about 75%). The battery in a parallel bank that has the lowest state of discharge will also have the lowest internal resistance. Thus, it will take the largest share of current available. Again, this is a principle of basic electrical circuit understanding. Current in series circuits will be equal at all points. In parallel circuits it will divide between the resistances. Since you stated that you were unable to complete the calculations without a spreadsheet, you may find the following link beneficial. All you need to do is enter the values in the appropriate boxes. http://www.csgnetwork.com/parallelresistcalc.html Folks here hate polls--but I think I'll do one now on inverter size, just to "put a finger in the wind" to see which way it is blowing. Any poll conducted on this thread would be statistically insignificant. Since this is a battery thread and is of interest to those with a desire to expand their battery capacity it would give extremely one sided results. If you want to run a poll that provides statistically significant results I would suggest a broader sampling of all RV owners. Maybe you could knock on camper doors the next time you visit a large campground and see what type of responses you receive? Gentlemen, I stopped here as a result of our host pointing me in this direction after I posted a campground review. My sole intent was to share a source for perfectly usable AGM batteries at an extremely low price or even free. My old fingers are badly swollen by arthritis and extensive typing causes me great pain and discomfort. As much as I would like to hang around and debate the validity of information posted on other web sites, I simply cannot. I wish you all well... and I am impressed with the work and accomplishments you have apparently achieved in expanding battery capacity in your personal RVs. Your work should be shared as it serves as an example of what can be accomplished when one wants to expand beyond the largely inadequate OEM battery set-up. Randy
Hi all, As Prof has indicated he doesn't wish to continue the discussion I'll not reply to his comments. I do appreciate his efforts. Thanks Prof for the suggestions about cheap source of very good batteries. It has been food for thought and one of those thoughts is that unbalanced 12 volt batteries, if there are only two 12 volt batteries, cause the first battery in the chain to work approximately 15% harder. I've also learned that lead acid batteries *do* increase in resistant as they discharge. changing resistance with state of charge Scroll right to the bottom for a graph for lead acid cells. I've also learned that the resistance rises as temperatures become lower. internal resistance vs temperature Scroll down five screens.
I found these guys particularly useful on sealed lead acid battery advice Sealed Lead Acid Battery Advice
Hi, I found a nice page about batteries and freezing here: http://www.cdtechno.com/custserv/pdf/7953.pdf
