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  #11  
Old 03-07-2008
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Umm... I think you're a bit confused... I'm not mistaking an MPPT for anything. I'm also aware of the shortcomings of hooking panels in series... it was just a point that most MPPT controllers can take more than 17 VDC as an input, and that by stacking the voltage, you might be able to save a bit more on the MPPT use end of things.
Quote:
Originally Posted by hellosailor View Post
sd-
Don't mistake an MPPT charge controller for being a "solid state" conversion. I mean, it is solid state in the sense that there is no "buzzer" creating an AC voltage, like the old UPSes used to use to make AC from DC batteries.
But an MPPT controller simply takes DC and puts it into a high frequency switch, converting the DC into a 30KHz AC signal, which is fed into a transformer. (Pulsed DC, but that's still more AC than DC to me.)
Then the other side takes the AC power from the transformer, and sucks it back out in an optimized fashion. The fact that they are running around 30KHz allows them to be pretty efficient, this is essentially the same technology that is in every computer's "switching power supply" these days for $20-100.
The MPPT controller goes one better, in theory, by also having a cheap dedicatred CPU on board that looks at the input and output, and tries to get smart about how to deal with the conversion. (An easy task, like winning at poker all the time every time.[g])


SD-
With some panels you an get 48V out, others you can't. If the factory has used three "12"V arrays in one panel, that might get you 48 volts at peaks--if you can rewire the arrays. In order to get better seals and lower costs, more of them are coming hardwired for 12 or 24v operation and you tsake what you've got. The problem is, if you wire up 2x12 or 2x24 to get higher voltage, and EITHER panel gets any shade--you lose output from the whole array. On the other hand, if you have all the strips in each panel set up in parallel (i.e. internal and external, all set for 12V) then any shade on any one part of the array just reduces the output amperage--instead of reducing the voltage of the whole system.
And of course, on a US-market boat, you've still got to get it down to a 12V battery, not a 48V one. Going from 12 to 24 volts give you some extra efficiency, going from 24 to 48 is just gilding the lily. Like calling a four stage charge with an "off" cycle a "five stage" charger. As, ahem, some of the makers are now doing.
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  #12  
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.. so how often per hour is the Maximum Power Point derermined by the Tracker? This determines its efficiency under normal sailing boat conditions. My information is that is very slow, but I might be wrong. There might be better trackers available now. Who knows something definite?
Aage
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aage-

Most MPPT charge controllers track the battery status fairly frequently, if not continuously, to prevent them from frying the battery and to optimize charging efficiency. They're not slow at all.
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Quote:
Originally Posted by sailingdog View Post
aage-

Most MPPT charge controllers track the battery status fairly frequently, if not continuously, to prevent them from frying the battery and to optimize charging efficiency. They're not slow at all.
Hello SD,
do you have a technical reference for me? Aage
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While not a technical reference, this page pretty well describes the technology used in MPPT charge controllers. Most important part for you is the last graf.

Quote:
Most newer models of MPPT controllers available are microprocessor controlled. They know when to adjust the output that it is being sent to the battery, and they actually shut down for a few microseconds and "look" at the solar panel and battery and make any needed adjustments. Although not really new (the Australian company AERL had some as early as 1985), it has been only recently that electronic microprocessors have become cheap enough to be cost effective in smaller systems (less than 1 KW of panel). New units, such as the Blue Sky "solar boost" series, and the Outback Power MX60 have finally broken the cost/benefit barrier.
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Hello SD,
the page you cite is quite informative but it does no tell you how often the optimum point is searched for. I looked around quite a bit, and the only information I found was once per two hours! These units are primarily built for stationary applications, e.g. houses. THe market for our moving "houses" is probaly too small. I would be happy if you could proove me wrong,
Aage
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aage-

You should probably look at the bluesky or outback sites.

Since you appear to be unable to research this yourself... the Outback Charge MX60 user manual says the MPP adjustment interval has a default setting of THREE MINUTES:

Quote:
In the Sweep Interval screen, press the <-MIN> soft key
to adjust the sweep interval from 03 minutes (default)
to 00 minutes. Press the soft key until the MPPT
Mode screen appears.
The Blue Sky 2000E MPPT charge controller manual says the following:

Quote:
Solar Boost 2000 continually recalculates the maximum power voltage as operating conditions change.
This is basically what I said previously, as well as what the page I pointed you to said.
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—Cpt. Mal Reynolds, Serenity (edited)

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  #18  
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Sd, I think aage is still refiring to a solar Tracker not an MPPT.
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  #19  
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If that is the case, I can't help someone that can't tell the difference after what everyone has said here. I'd have to call him Forestt from now on.

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Sd, I think aage is still refiring to a solar Tracker not an MPPT.
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—Cpt. Mal Reynolds, Serenity (edited)

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