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Battery power
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The Watchdog does have a dedicated input.
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Gil,I added a resistor as you stated and actually made up several sets that I soldered to glass fused that we’re open,then determined when the ohm value would start the generator,now I can adjust the generator start voltage.
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the question is why are we screwing with this? the RV industry has probably put more time in on this subject than all of us combined and these are the setting they recommend and there are millions of RV out there. How many people on this forum can say they lost a set of batteries because of a low auto generator start setting?
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Jack,
You could use a potentiometer with calibrated marks for the voltages you want.
Greg,
One size does not fit all. There are always trade-offs.
If you want maximum battery use time and don’t care about how long your batteries last then set your generator start for just above the inverter cut-out voltage or lowest volatge that will start the generator if you start your generator from the house bank. This should be about 10.5/21V.
If you want maximum battery life and have the ability to set quiet hours or can remember to turn off your AGS controls when you go to sleep or you don’t care if the generator starts when you are sleeping then set the AGS voltage to no less than 50% discharge voltage for your batteries. Generally, that would be about 12.1/24.2V. However, this is unrealistic unless the batteries aren’t powering anything. A more realistic setting would be 11.5/23V or so.
Load is a major driver in your decision. A large load will, at least momentarily, drop the voltage. It doesn’t have to be a large load as any load will draw the voltage down. That’s why your AGS should employ a delay circuit that requires the threshold voltage to have been met and maintained for some period of time.
FWIW, the only AGS systems I’ve ever seen that have a fixed start voltage are those that were custom made, like the one described here. Here’s a link to an example of one commercially available AGS, Magnum AGS, commonly found today. You will see that the default start voltage is 11/22V but is user adjustable 10-12/20-24V and it does have a 2 minute threshold timer.
Anyone that would like to have better control of their auto start and doesn’t have newer inverter/chargers, the AGS I referenced should be cabale of supporting the generators used by most, if not all, converters and it’s less than $300. These haven’t been around for a long time, that’s why converters had to use their own home brewed solutions. BTW, early controllers were for solar systems and I’ve seen at least one installed by a converter. These will not function properly for our application without modification.
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On my last Liberty I used a potentiometer adjusted it at 24.8 volts worked great. For as I know it is still on there and working fine
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I have a new Marathon H3 with Lithium Ion batteries. Reading this string of comments leaves me wondering how my generator strategy might be influenced with these batteries. Any thoughts?
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Did we meet at Marathon-Dallas ? Marathon techs were adding a bay Refrig-Freezer.
I Know Marathon has a pre-set program from the factory. Confirm auto start is engaged, let the electric waves do there thing starting generator at called for cut – in.
Probably a good conversation with Leon at Coberg, OR.
Welcome to PC Ed and Sharon. Congratulations…. owning a brand new Marathon.
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Welcome Ed & Sharon,
A new Marathon will LI batteries is going to be a very interesting learning session. How they setup the charging and auto-start utilizing LI batteries with a constant 12v would be great information. Looking forward to hearing how it’s all working out for you.
Thanks for joining PC, you found the right place….
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Ed and Sharon,
Welcome aboard. I have zero knowledge of how Marathon has set up your electrical system using Li batteries, but I would guess an extensive amount of engineering has gone into its design.
If I were the owner of such a coach I would change my ways of manually trying to charge the batteries and would rely instead on the technology Marathon has built into the coach.
Unlike conventional batteries which exhibit a lowering of voltage as the charge is depleted your Li batteries are going to deliver a constant voltage up until the point at which they will shut down. Marathon has undoubtedly set up the system to be recharged prior to that point and that is how it is intended to be used.
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Al, no we haven’t been there. We were at Marathon Florida recently getting a few items handled.
Tom, so far the batteries have performed without issues. However, I don’t have prior experience with which to compare. To date, I have relied on the Auto Gen function to decide when to fire up the generator, and it has worked without problems.
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Ed,
If not in your owner’s manual you should ask Marathon what they set the AGS voltage theshold to. I assume they too are using the MasterVolt batteries. If they are using one of the common inverter/chargers the AGS should be linked to and configured through the inverter/chargers. If so, it should be easy to see what it is set to. I would hope Marathon set the start voltage per the battery manufacture’s recommendation without marketing influence.
For all that use the quiet hours function on their AGS I highly recommend running your generator for a few hours just before quiet hours. The reasoning is that you don’t what to draw your batteries, regardless of chemistry, down too low or get to the point where your inverter kicks out. As far as I know, none of the AGS systems predict future load demands so they will charge the batteries before quiet hours.
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Gil,
It is my understanding that Li batteries do not have a voltage drop off as the charge is depleted so there is no way an owner can know when it is time to re-charge. All that information has to come from the battery “brain” which is communicating with the auto-start.
My guess is the only time the decision when to charge becomes an issue is when dry camping since driving or connecting to shore power automatically is keeping the batteries charged. The use of Li batteries increases the complexity of the system and I have to presume Marathon has considered all the “what if” situations to avoid full discharge of the batteries and to insure proper charging.
Even if an owner knew the means by which the start system is engaged I think it would be difficult to manually control charging as efficiently as allowing the system to control charging because on the Li batteries voltage is a constant right up until the point at which they shut down. That means the system is designed to anticipate that shut down point and initiate charging. I have no clue how that can be compatible with locations that have a “quiet time”. It might be that the generator is as quiet or quieter than the typical coach AC system so nobody is affected.
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Jon is correct.. The LI provides a constant voltage, example 12v, until such time the battery is nearing is discharge point and then shuts off. When it shuts off, there is a small almount of reserve power for a very short period if needed. What’s interesting, is the voltage on a 12v is exactly 12v through the entire cycle with no variations in voltage until it switches off.
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Jon & Tom…
Don’t a lot of Liberty’s have gel batteries… how do they do and how do they compare to the AGMs?
Diane
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Yep, Li-ion batteries do have a relatively flat voltage curve through most of discharge cycle with a fairly rapid waterfall drop off near the end of their discharge cycle. This doesn’t preclude the use of voltage as an indicator of useful remaining cycle life. However, it would be more difficult.
Li-ion batteries do require per cell monitoring for protection; the MasterVolt battery is no different. I pulled up their manual and they have over/under voltage and state of charge signalling using their communication bus and processor. Given the SoC output parameter is configurable, I would suspect this is used to signal the AGS function. They have both a high and low SoC signals, so the high SoC signal could be used to turn off the generator rather than running it for some some set run time.
The quiet time restrictions can still be an issue. Take for example the Balloon Fiesta, no generators allowed to run from 10pm to 7am. This is not just because of noise, but for exhaust fumes. So, it doesn’t matter how quiet your generator is, you can’t run them. On 12V systems inverters typically cut off at 10.5V and the low voltage threshold for the MV Li-ion is 10V. The good news is that your inverter should cut out before the batteries hit their low voltage threshold. The bad news is that a Li-ion battery will drop from 10.5V to 10V very quickly; maybe too quickly for the inverters to shut down first. On a per battery basis, all cells will be commanded to turn off if any one cell hits a low voltage threshold, so the battery will protect itself; at least in therory. I would still recommend running the generator a few hours before quiet hours regardless of battery chemistry.
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