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Battery Voltage

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Tom Rogers:
[quote author=]I have a chart that shows the percent of charge at the various voltages.  I have always set the auto start at 11.9 volts as the batteries are at 40% of charge at that point (the chart recommends not going below 40%).  12.06 volts is 50%, 12.2 Volts is 60%, 12.32 volts is 70%, 12.43 volts is 80%, 12.5 volts is 90% and 12.6+ is 100%.  10.5 volts is 0% of charge.[/quote]

Great information. Thanks !!!!

Gerald Farris:
Here is the chart from Trojan Battery Company. The voltage readings are open-circuit with no load (any amount of load will reduce voltage). Trojan states that discharging their batteries below 20% will cause damage and shorten its life, although most battery companies recomend a minimum of 40%. As you can see from the chart, the 40% mark is at 11.96V that I round off to 12V. The 11.5V reading is a 10% charge state that shortens battery life.    

Gerald

Table 4
State of Charge as a measure of Specific Gravity and Open-Circuit Voltage
 
                                               Open    Circuit      voltage
 Percentage    Specific
 Charge           Gravity          Cell            6 Volt          12 Volt

100                 1.277            2.122           6.37           12.73
90                   1.258            2.103           6.31           12.62
80                   1.238            2.083           6.25           12.50
70                   1.217            2.062           6.19           12.37
60                   1.195            2.04             6.12           12.24
50                   1.172            2.017           6.05           12.10
40                   1.148            1.993           5.98           11.96
30                   1.124            1.969           5.91           11.81
20                   1.098            1.943           5.83           11.66
10                   1.073            1.918           5.75           11.51

Joel Ashley:
There is every reason to go with the 12v mark, but my experience was not all positive when I tried that, at least when using autogenstart.  11.5v just worked out better.  I've seen no noticeable loss in battery strength, but my coach and chassis batteries normally last at least 6 years anyway, and I'm only half way to that point in this coach using the autostart system, so who knows.  Certainly battery life is affected some way by any discharge, depending on battery type, but the degree of battery life lost may not be significant unless we're talking deep and numerous discharges.

Additionally I should say I rarely have needed the autogenstart anyway, since I am usually around to start the generator manually before it gets near 12v and I run it back to float charge .  If a person does that, I would assume that minimal impact on battery life overall would be the norm.  On the other hand, if you use the autogenstart often, and the other control panel settings such as time-of-day, etc., don't factor in to complicate things, then by all means I'd use the 12v setting.  Jim's question sounds as if he may not be necessarily referring to the autogenstart system, so the 12v mark he's already using is the answer for him.

Jim Shaw:
Thanks to everone for the input. I do not use the autostart on my generator, but manually start it when needed. My batteries are seven years old and still going strong so the 12 volt limit I use seems to be the way to go. I am very careful to never let them get low on water and keep the terminals clean.
Jim

Joel Ashley:
Jim-

If available on your coach, you'd do well to program your autogenstart system.  I have to agree with Tom that it can be confusing, though, and Lord knows I pulled my hair out over the thing a time or two.  Especially when I thought everything was set right, and the generator would come on for no apparent reason;  I'd manually shut it off... and it would kick on again a minute later.  It took awhile to learn to coordinate the black box in the electrical bay with the digital panel inside.  Sounds intimidating I spose, but having the thing there as back up offers some peace of mind to me, since a few years ago coming back late to our old casino dry-camped Pace Arrow after some long hours enjoying ourselves, only to find everything deader than a door nail - coach and chassis.  

A long cold night in pitch black fretting over what had been left on and what to do the next day was no fun.  This after fuel problems earlier that day stopped us on a steep grade in the outside lane of busy Hwy 101, requiring a tow into Coos Bay;  after quick repairs, that scenario weakened batteries that then weren't ready for the long stint in the casino lot with one light left on.  It was a learning experience re. system electrics.  But, hey, the Missus won $50 off a nickle bandit  :o.

To avoid a repeat "stranding" like that, I take advantage of the autogenstart on our Beaver, set it at 11.5v, and have some confidence that if something gets left on inadvertantly, the HydroHot fans run too long, refer ignition, etc., the generator will come on to cover the problem if we're away from the coach longer than planned.  As mentioned in a prior post, that's rare, so I'm not concerned about any significant detriment to the bats.  You also want the refrigerator circuits viable and they inactivate at 10.5v.  The autogenstart gives you some freedom to park and then jump in the toad and do your thing all day, and removes that aspect of worry if some unfortunate occurence keeps you seperated from the coach for some time.

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