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Old 11-02-2010, 12:59 AM   #15
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Originally Posted by az bound View Post
A fully charged 12v battery puts out 13.4 v. Minus 20% is 2.68v, which equates to 10.72v. So the 11v restart is within a safe range.
Doesnt work that way..The state of discharge vs voltage is not linear...By the time you get down to 10.7 vdc, your dead.. Battery manufacturers recommend you only discharge 50% before recharging. 50% discharge equal ~12.2 vdc.

Luv2go's chart is a good thing to keep handy.
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Old 11-02-2010, 06:06 AM   #16
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Originally Posted by Midniteoyl View Post
Doesnt work that way..The state of discharge vs voltage is not linear...By the time you get down to 10.7 vdc, your dead.. Battery manufacturers recommend you only discharge 50% before recharging. 50% discharge equal ~12.2 vdc.

Luv2go's chart is a good thing to keep handy.
I am trying to get a handle on this. My AGS is set to start the genset at 11.v. I have the exact same system as my previous coach in which the AGMs lasted 7years. We do mostly boondocking so the batteries are cycled quite often.
If the batteries are dead why would all the lights and residential refer still be operating when the genset starts?
If the batteries are being that deeply discharged that often I should not be able to get 7 years of useful life out of them.
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Old 11-02-2010, 09:33 AM   #17
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I hear a lot of talk lately about AGS at 11volts, I've never used mine, but I'm wondering if on my Diesel Onan and the preheater being used before start, WILL the gen start at 11 volts?
nor have I used the thing that starts the Ac's with high temp inside the coach
another toy never used.
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Old 11-02-2010, 10:37 AM   #18
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I am trying to get a handle on this. My AGS is set to start the genset at 11.v. I have the exact same system as my previous coach in which the AGMs lasted 7years. We do mostly boondocking so the batteries are cycled quite often.
Possibly part of your experience is due to they way your AGS works versus the way the battery depth of discharge levels is specified.

In real-world applications there is always a load on the battery (especially with your residential refrigerator), so the battery voltage is less than the voltage you would read if you disconnected the batteries and let them set for 6 hours, which is what the above chart is based on. Actual battery voltage is less because of internal battery resistance and resistance of external wiring, among other things. This may help account for your experience with your old batteries.


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If the batteries are dead why would all the lights and residential refer still be operating when the genset starts?
As above, I believe your AGS is actually starting the generator before your batteries get to 0% charge, otherwise they would not run your lights and residential fridge.

For example, the Magnum standalone AGS will start when the voltage reaches 11.0V for two minutes. Depending on wiring, and loads, the AGS module could sense 11V for two minutes when the batteries have much higher "resting" voltage. For example, if your fridge is running and you have a couple other loads or maybe you are microwaving or using a hair dryer for a couple of minutes.

BTW, this voltage is adjustable for this particular Magnum AGS, also the Onan EC30. Your coach mfr or installer may have set it differently from the default setting.

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If the batteries are being that deeply discharged that often I should not be able to get 7 years of useful life out of them.
Here is a chart made from a table my battery manufacturer provides that shows that cycle life is adversely affected by depth of discharge:



Other manufacturers have similar charts, as all lead acid batteries behave in a similar manner.

To get 7 years (approx 2555 days) out of the chart above, your could do an 80% depth of discharge about every 4.3 days. I suspect your daily average depth of discharge is much less, more like 10 to 15% (over the 7 year life of your batteries).
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Old 11-02-2010, 04:13 PM   #19
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Luv2go; Thank you ! That sounds a lot more resaonable to me than anything I've ever heard. If I get 7 years of service on these batteries i'll be a happy camper.
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Old 11-02-2010, 07:55 PM   #20
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Boondocking is an exiting experiance;; It can be done 12/14 days with no problem;; However;;; To run a refrigerator on An inverter or on 12 volts is not in the best interest when boondocking;; It needs to be switched over to gas/propanewhie booning; Also a shower is a washcloth and a pint of water in the sink;; you will have some sailer boy tell you how to take a shower with 1 gallon of water;;; Been there done that;; Use the washcloth.. It's afful hard to get water. so we conserve. It's more Enjoyably . And we don't need so much Deoderizing spray.. LIfe is good..
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Old 11-02-2010, 09:41 PM   #21
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Boondocking is an exiting experiance;; It can be done 12/14 days with no problem;; However;;; To run a refrigerator on An inverter or on 12 volts is not in the best interest when boondocking;; It needs to be switched over to gas/propanewhie booning; Also a shower is a washcloth and a pint of water in the sink;; you will have some sailer boy tell you how to take a shower with 1 gallon of water;;; Been there done that;; Use the washcloth.. It's afful hard to get water. so we conserve. It's more Enjoyably . And we don't need so much Deoderizing spray.. LIfe is good..
Be sure to stay upwind of this guy too!

We do most of this but have purchased the 6 gallon water containers (3 of 'em) if needed. Our class A has a pour spout in the event we need to top off. Truth is we can run 4-5 days washing dishes, using the toilet and taking showers with 2 people. Definitely not 2 weeks, but works for us.

And what's wrong with a Navy shower? Took 'em for 6 years.
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Old 11-02-2010, 11:41 PM   #22
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For example, the Magnum standalone AGS will start when the voltage reaches 11.0V for two minutes. Depending on wiring, and loads, the AGS module could sense 11V for two minutes when the batteries have much higher "resting" voltage.
I've had this condition happen on several occasions where my batteries were doing a slow, steady discharge (near "resting") at say 12.4V when my wife flips on the microwave and immediately steps into the bathroom and fires up the hair dryer. In that condition, I've been thankful to have the AGS fire up as a protective backstop from potential "meltdown".

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Because that inverter company thinks all batteries can be discharged to about 15-20% without harming them, which of course is wrong according to the battery manufacturers themselves. So no, they don't know the 'ins and outs'.
If you understand just how much finesse and how complex this sine wave Magnum bad boy undertakes in managing shore/genset/charging/multiple legs/etc. etc., I just can't believe the company (probably graced with fairly brilliant EE designers) failed not look at these same charts like us advanced, techie RV owners have.

So I guess I'm still concerned about the unpredictable slow drain overnight to the 11V low state and still looking for a good reason as to why they only offer an 11V gen start fire-up voltage. Maybe I will try to ping their tech support and see what they have to say in defense of what seems to be the safe stance of "don't let your batteries drop below 12.1V."
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Old 11-03-2010, 01:05 AM   #23
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.... still looking for a good reason as to why they only offer an 11V gen start fire-up voltage.
My bad! Crawled in the basement and realized that my unit has the exact same controller as the one Luv2Go listed. I was only reading the remote controller inside the coach which is only showing the setting on the actual controller underneath the coach adjacent with the Inverter. Thanks a bunch- have now set it to 12V (and can sleep in peace now).
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Old 01-23-2011, 08:58 PM   #24
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1.75 VPC is dead

The actual minimum voltage for a lead acid battery is 1.75 volts per cell, 12 volt battery or 2 6 volt batteries in series, no different, total 6 cells to 12 volts, 6*1.75 is 10.5 volts.

We set our Low Voltage Disconnect at 1.8 VPC to give some room, this is 10.8 volts.

Either way, this is the point that the battery is concidered DEAD, you still can discharge more from the battery but at this point you can damage the battery.

The next issue is "wear", the battery is a chemical reactor, energy in caused one reaction, energy out causes another.

The deeper the cycle the more wear takes place, a deep cycle battery will weigh more per volt/ah than a normal battery.

Starting batteries have higher CCA than a deep cycle battery as they are designed for short periods of high current while the deep cycle is designed for long periods of low current.

11 volts is ok for an automatic start of a generator to recharge the batteries, 11.5 would be better on the batteries as it is less discharged and the charge current would be less.

Depending on the fuel consumption of the generator, the time restrictions on generator running and a few other options the optimum voltage could be different.

If set too high the generator may run too short of time, it needs to run at least 20 to 30 minutes to insure everything gets hot, and if it starts at too high a voltage then it may be running needlessly while its run timer waits until the engine has met the minimum run time.

Set too low of voltage then the generator may run harder than needed and the charge rate may be higher than the batteries would like.

The correct voltage would have the generator start and meet minimum running requirements while keeping the rate of recharge within the requirements of the battery.

Granted the generator should not be running 10 times a day, but it could be configured to run during times of the day where it is not a noise or odor problem.
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Old 01-23-2011, 09:30 PM   #25
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The furnace fan is a battery killer - in chilly weather it will run the batteries down overnight for sure
Really? are you sure? What if the therm is set at only 55? I have two 6 volt golf cart batteries that I thought should easily handle a cold night of furnace use.
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Old 01-23-2011, 10:03 PM   #26
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"....11 volts is ok for an automatic start of a generator to recharge the batteries, 11.5 would be better on the batteries as it is less discharged and the charge current would be less."
I see this same chart on numerous battery advice websites, where the recommendation says not to discharge below 50% for the optimum life of the batteries (or 12.06 discharge).


Can you provide some solid, reputable sources that reinforce and validate that 11 to 11.5 volt discharge is acceptable? The difference in my coach between 12.2 and 11 is huge in terms of additional battery power. But I'd hate to trash my newly replaced batteries when the charts say you have discharged your 6v batteries a full 80% when they reach 11.5v....let alone discharging all the way down to 11v which appears to be only a 5% state of charge remaining.
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Old 01-23-2011, 11:34 PM   #27
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I think you need to find out if the voltage shown on that chart is while the battery is under load or not. I would think its 'not under load', or 'standing' voltage. Standing voltage for any given state of charge will be higher than that while under load... Soooo, if you have it set to 12v, are using the batteries and the genset kicks in, you are in reality at less than 50% discharge... how much depends on a couple of factors such as battery condition, wire size and condition, temps, load, etc, but you could have as much as 70% capacity left (rare though). What you need to do is do some tests where you discharge the batts to 12v as shown under load, then let them stand with NO load (disconnected) for 24 hours and check again.. this'll get you closer to your 'real' state of discharge.. you might find you can set the kick in point to 11.75 or so...
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Old 01-24-2011, 12:25 AM   #28
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Good primer and a more accurate way to test if you have a hydrometer.. : Voltages, Specific Gravity and State of Charge (609) | Rolls Battery
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