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Battery power
Well first day of clinic left coach no power here so gen on auto start fridge on no other things on except loads you can’t turn off , new batteries where put in at liberty 14 hours on battery before gen started that’s sweet
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45 Replies
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Does anybody no what liberty sets the gen auto start at for the batteries ???
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Peter,
It is pretty low. I don’t know the exact value but it is around 23 volts. I am sure Jack Finch can give you the exact value because he has made some mods to get an earlier auto-start.
When I bought my coach I wanted the auto-start to be somewhere around 50% of discharge and it was refused. Odinarily I would have made an issue of it, but over the years I have found Liberty has very good reasons for doing what they do so I chose to not ask for or modify my auto-start voltage.
As a full disclosure however I need to explain when we dry camp, such as an overnight when on the road, I run the generator until we go to bed, and I turn it off unless we need heat or AC. When I wake in the morning I either re-start the generator or hop in the driver’s seat so my batteries aren’t beeing deeply discharged enough to even require the auto-start.
I believe in running the generator so we rarely rely on the inverters as our source of 120V.
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Thanks Jon that’s what I do is at night just as I go to bed shut it off if I don’t need heat or ac then in morning start it for about 3 hours then at night about 3 hours I don’t use much power during day I am not in it just small loads charger for creston , if I did need power I would run gen , auto just on for the first clinic just in case I am doing clinic and batteries went low , until I see how much power is used but if I need heat or ac or hot water I run gen , just need couple days at first clinic to see how much batteries go down I do not rely on the auto start I do it start it myself that way I know when to and batteries are not getting to low.
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Peter, One thing to be aware of is the Webasto works great without shore or generator power, but it is an energy hog in the respect the circulating pump, the Webasto itself, plus all the individual heat exchange fans pull a lot of juice.
That is one reason why if I need heat, even with my 24 volt Webasto system, I run the genset all night.
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auto start at 22.3v
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Yikes, Jeff just reminded us how low the autostart is set on the Watch Dog.
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Jeff why is it set so low and not at 24.5 or 50%
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My guess is that is not the resting voltage, but that the batteries will be under load.
If we subscribe to the information available on a number of sites about the charge / discharge cycles let’s assume a deep discharge causes the battery life to be 1000 cycles. Then let’s assume we use a 50% discharge by manually starting the generator and we extend the life to 5000 charge / discharge cycles.
Let’s make another assumption. Let’s assume if we never are connected to shore power or never manually start the generator we need to charge the batteries 2 times per day. That means relying on autostart we get only 500 days of use out of our batteries. That’s a problem if you dry camp in Quartzite for 500 days because in a year and a half you need to replace batteries.
But how many of us use our coaches as much as 100 days per year, and during that time we are always dry camping? If we are running our generators or are on shore power we have little or no charge / discharge cycles so it is unlikely a deep discharge as expressed above is going to have a measurable affect on our battery life if you opt to replace batteries before they have problems. If I stay with my 5 year schedule no matter how I decide to determine at which point I will recharge it is unlikely I will not reach 5 years of use.
I see the 5000 cycles as a theoretical value because our batteries are unlikely to ever see that number based on how we use our coaches. I suspect our batteries will just age out before we ever get to that point.
I think I just talked myself into considering the use of auto-start.
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The Lifeline AGM batteries have a rated cycle life of 1000 discharge/recharge cycles at a 50% depth of discharge. Decreasing the depth of discharge to 10% will extend the cycle life to 5000 discharge/recharge cycles. The cycle life drops to 500 cycles at about 84% depth of discharge.
Ideally, the battery plant should be sized to limit the daily depth of discharge to 10%. Unfortunately, this substantially increases the size, cost, and weight of the battery plant. Like everything else in coaches or RV’s, compromise is the name of the game.
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I use mine 280 days a year and maybe 15 weeks with power mostly dry camping no power just use gen
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I think Jeff is correct on the voltage of 22.3,the converters were trying to beat each other in how long their system would run overnite without starting the gen.Unfortunately the watchdog is not progrogramable and the voltage is fixed.
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I think the low setting is to prevent the generator from starting every time you get a downward spike in the voltage usage. Which will probably happen frequently and a low resting voltage will happen very infrequently.
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like everything on the coach there is a compromise maybe the perfect auto start would sense amp draw as well with a time value built in. Most people don’t want the auto start to fire up too frequently. So I believe the value is set with not only battery voltage mixed into the equation but potential load as well. This is why a lot of coaches have low hours on the generators for the age of the coach. The generator is another Diesel engine that needs to be exercised. For Peter this is not a issue, but it is for many.
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To add to what Jeff says, exercising the generator is not just running it, but loading it up as much as possible. It does the generator no good to have it runnning with barely any load. In fact every diesel likes to be worked hard.
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Jack is probably right. The setting may have been driven by the marketing department.
If the watchdog has a dedicated input for battery bank voltage sensing then it could be easy to set the start voltage to a higher voltage. Adding an appropriately sized resistor in series with the sense lead will fake out the watchdog into thinking the voltage is lower than it is. This ONLY works if the watchdog has a dedicated voltage sense input.
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