Hi Chris,
Yep, this conversation has mixed two different charging technologies. MPPT is a variation on a buck/boost charger that converts low voltage input to a higher set voltage output, i.e. taking 3A at 12.0V and turning it into 2.4A at 13.8V (with various losses related to the conversion). Since solar panels spend part of the day at voltages that are too low to charge batteries, the MPPT controller makes that low voltage output useful, providing the battery with more total charging current over the course of the day.
Diversion load controllers take excess current (MPPT adjusted or not) that the battery can't use because it's fully charged, and route it somewhere else. That somewhere else can be a water heater, a de-humidifier, a ventilation fan or some other load that would be useful while the sun is shining. I guess that one could even run some sort of motorized bird deterrent. If the boat is using a wind generator, the load could be diverted to lights since the power could be available while it's dark. I don't know if any of the existing diversion load controllers use sophisticated multi-stage charging profiles, certainly the simple version that you described does not.
There's no technical reason that both devices can't be built into the same unit. I would think that the buck side of an MPPT controller is already a different circuit that the charging profile controller, they're just in the same box or on the same IC (kind of like the GPS circuit in your smart phone).
Obviously, the super-cool device would use MPPT to convert every last watt into usable charging current, a sophisticated charge controller to extend the overall life of your batteries and a diversion controller that would take any excess current that the charge controller decided it didn't need and send it to another useful load. When I say it like that, it sounds so simple. It makes me wonder why it hasn't been done already. I'm sure that a device like this would be useful beyond the marine environment, it sounds perfect for any off-the-grid application.
Fair winds,
Eric
Marina del Rey, CA
PS. Now that I think about it, I'm guessing that the Mars Rovers had charging controls even better than that.
--- In electricboats@yahoogroups.com, chris Baker <chris@...> wrote:
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> Hi guys
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> I just took a look at this site and what he's offering is the same principle as the Xantrex and Morningstar diversion controllers except that its switching will be relatively slow.
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> It dumps the load into a water heater or some other resistance load when the voltage reaches 13.9v (for 12v system) and then switches off again on the way down at 12.9v. This cycle might take a few seconds and then the voltage will start to rise again as the charging sources again feed into the battery, bringing its charge back up to the dump voltage, at which time it switches the diversion load on again.
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> And so it goes on switching the diversion load on again off again and keeping the battery voltage between 13.9 and 12.9. This is exactly what is done by a switch mode controller, or pulse width modulation controller, except that these do the switching at thousands of times per second. And with the solid state PWM controllers the voltage of the battery is kept pretty much exactly at the target voltage, rather than fluctuating between the limits.
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> The names of these devices describe well what is happening. Switch mode is switching on and off quickly, and pulse width modulation is a fancy way of saying the same thing. The width of the pulse is really the length of time the pulse of load dumping is taking. And this width, or time connected to the load, is modulated by the voltage sensor. And whether with width of the pulse is 2 or 3 seconds, or just 2 or 3 thousandths of a second, its still pulse width modulation, just a difference in timing.
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> You can achieve the same result by using a dual battery switch that is offered at 4WD or offroad accessories car shops. You know the kind of switch that watches the voltage of the main battery and when it rises to say 13.5v it closes a relay which connects the second battery. The idea of this switch is that when the main battery has a good charge level it connects the second battery into the circuit so it can be charged as well. If instead of connecting a second battery, you connected a load, it would act as a diversion mode regulator. It will switch the load off again at around 12.7v and allow the battery to begin charging again.
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> And so back to this charge controller in the link... its really a pretty simple device and nothing modern or groundbreaking in what he's proposing. He just added a generous mix of hypebole to make it sound more than it is.
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> I'm thinking that the only way to get MPPT as well as diversion load is to have two devices, a MPPT device in series, but without voltage regulation, and the diversion load controller in parallel so that we can harvest the power that is excess to battery charging needs.
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> Cheers
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> Chris
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