How long should my house batteries hold their charges before generat

September 22, 2012, 11:11:48 pm

Questions for all you folks with an electric or near electric motoromes. How long do your batteries last while dry camping before the autogen kicks in? I have 4 brand new Lifeline 8dl 12v house batteries. It seems it only take a day before the generator is kicked on to recharge the batteries. My coach is all electric, except for the propane cook top. I have turned off the electronics that I can. The weather is mid and no call for heating of any type. The electric hot water heating is also off. Any comments or insight would be appreciated.

Gary 2005 Magma 42'

Re: How long should my house batteries hold their charges before gen

Reply #1 – September 23, 2012, 11:33:46 am

Yahoo Message Number: 82563

Gary - This is a tough question to answer with any degree of accuracy. There is a "soak in" time with Lifeline batteries so brand new units might not be delivering full capacity yet. Not sure of all the details on this but that might be a factor. Once the batteries have broken in, their available energy output can be calculated from discharge tables. Also keep in mind that a 20 hour discharge at 10A (200 amp hours) isn't the same as a 50A discharge for 4 hours (also 200 amp hours). The chemistry isn't linear.
You need to be able to monitor (accurately) how much current is being drawn from the house bank. In my case, I made a monitor based on hall effect sensors. It's here: http://muniac.smugmug.com/Travel/Country-Coach-2006-430-Allure/IMG3354/749383635_XePRS-M.jpg This allows me to know exactly what's going in and what's coming out. This is very important when evaluating and predicting your battery's performance. Lifeline batteries are AGM chemistry which means you can't take a hydrometer reading on the electrolyte (the only accurate way to determine state of charge SOC). Open circuit voltage VOC is thus substituted. But that is only accurate at no load after a long settling time. Something that isn't practical if you are constantly drawing current from the batteries. So you approximate it and/or anticipate it knowing your load and how long the battery bank has been supplying power to that load at a given discharge rate. The risk here is applying an inappropriate recharge which ultimately shortens battery life. Sometimes it just can't be helped owing to the need for maintaining some degree of practicality. It's the cost of doing business as they say.
The depth of your discharge cycle will influence battery life. The deeper the discharge the more strain it places on battery chemistry. As a rule of thumb, discharging batteries to 50% SOC is conservative with a deeper cycle perhaps every 5th discharge. Lifeline has suggestions about this which are good to follow. BTW I have 4 8D Lifeline batteries as well. See here: http://muniac.smugmug.com/Travel/Country-Coach-2006-430-Allure/IMG3270/738717472_Ff4BF-M.jpg These are excellent batteries and perhaps the best money can buy.
As for conserving power, there are phantom loads to include solenoid coils, wall warts and small DC loads that you'll need to track down. Our bus is a pig and will draw 250 watts of DC just to power the goodies. And that figure means everything appears to be turned off. I could probably cut this in half but we rarely boondock so it isn't a big deal. That said, I can run for months without charging the house bank from AC. The solar takes care of it (about 2kW per day collected) and the batteries can easily provide power during the dark period. Microwave, TV, frig and A/C units run off of commercial power, however. Hope this brief ramble helps you in a few areas.

At 08:11 PM 9/22/2012, you wrote:

Re: How long should my house batteries hold their charges before gen

Reply #2 – September 23, 2012, 04:33:29 pm

Yahoo Message Number: 82579

Gary,

Just on the facts that you have given I think you are okay.
Assuming that your generator is set to start at 50% state of charge, you have about 500 Amp hours usage in 24 hours. That is a constant discharge rate of 20 Amps. Considering that your coach is running a household refrigerator, water pump, lights and is supporting a complex coach like a Magna your performance seems perfectly fine to me.

George in Birmingham
'03 Magna 6298

Re: How long should my house batteries hold their charges before gen

Reply #3 – September 24, 2012, 01:37:37 am

Yahoo Message Number: 82593

Thanks to everyone that has responded to my question.
Gary C

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