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Old 12-05-2010, 23:22   #1
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MPPT Solar Controller as AC Charger

I've just replaced my totally dead wet cells with larger AGM batteries, and with all such projects the feature creep has really hit the pocketbook hard. The last joy was to discover that my older charger, while having the exact same model number as the currently sold version, does not have the mode for AGM, nor is it upgradable. Unfortunately, it has this crazy auto-equalize routine that cannot be shut off, which would lay waste to the AGMs (it came with the boat, what can I say?)

So I have been kicking around the idea of getting two 130W solar panels and a good MPPT controller instead of an AC charger. I live in sunny California, and to be honest the boat does spend the larger share of time in the marina (for now).

So, the real question is... can the MPPT controller function as an AC charger if I feed it with a DC power supply? To my untrained mind, it would seem logical that the controller wouldn't care where the power source originated, solar or rectified AC. As a ham, I have a plethora of DC power supplies laying about the house, several of which have adjustable voltage. I was thinking if I supplied the controller with around 14v at 30 amps (max) it would be able act like a fixed AC charger.

Like was said over in the open array radar thread... you don't see this on many sailboats, which gives one pause to wonder why...

JRM
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Old 12-05-2010, 23:30   #2
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So, the real question is... can the MPPT controller function as an AC charger if I feed it with a DC power supply?
I don't see how this would work. The controller would not be able to discern between the two power sources. With separate systems, you can set the float voltages at a different level so that the shore-power charger would not come on while the solar controller was doing its work. But you won't be able to do that with a single controller.

Besides, it's a good thing to have multiple charging options. System redundancy is a cruiser's best friend.
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Old 13-05-2010, 00:05   #3
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With our 2 solar panels we never need to plug into shore power!!

The other day we were at some public dock and the harbour master seemed quite miffed that we didnt want electricty! I think his power charges must have been high


With solar you do not ever need an AC charger.

Our wiring goes direct into the batteries without a solar regulator - I regulkate mnanually by dropping the panneal. But I will be putting a solar regulator on as the panels make too much power! What a great problem to have
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Old 13-05-2010, 08:04   #4
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It probably would work. You would need blocking diodes so that your AC power supply does not back feed the solar panels. And set the power supply for about 16 V. It needs at least a volt drop to work. So in order to supply the 14.5 V you will need for decent charging you will need to supply the controller 16 V.

Also make absolutely sure that you rcontroller has a multistage charging algorithm so it drops to about 13.5 V when fully charged.

David

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Old 13-05-2010, 08:13   #5
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I am confused. Do you want to use a solar controller to supply AC power to your AC panel?
MarkJ is right - we have 2, 120w panels and an MPPT controller, and I almost never have to use the shorepower charger - I just use it to provide an equalization, but if I understand the MPPT thing, that too might be not needed. I leave the shorepower cord at the marina in place, but I don't often turn on the charger. Once I get our inverter wired up to the outlets, the cord will go into storeage.
Chris

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Old 13-05-2010, 11:11   #6
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So, the real question is... can the MPPT controller function as an AC charger if I feed it with a DC power supply?
Yes it will, except that you will be wating the whole point of a MPPT controller as there is no MPP to track. What you are using is the battery charging circuits of the MPPT controller to do the job.

Its doable but unusal and wasteful.
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Old 13-05-2010, 12:08   #7
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It will work. I believe his point was to avoid having to buy a new ac battery charger.

I don't however think it would be very efficient. I think the MPPT controller is about 90% efficient. I think the ac-dc converter will be no were near 75% efficient. Combine the two, just get's worse. I think you'd find if you didn't already have the components, a purpose built charger would be less expensive. Do you have the enclosure for this project?
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Old 13-05-2010, 20:47   #8
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I agree it should work in theory, but my only concern is if there is any AC ripple component to the DC output, it might confuse the MPPT controller. You couldn't hurt anything by trying it as long as you keep an eye on the battery voltage until you're confident with it.
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Old 13-05-2010, 21:08   #9
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No need to get cute. If you want an AC-powered battery charger, just get an Iota w/the IC-4 smart charge function. Inexpensive, reliable, great battery chargers with models from 15A to 90A. Arizona Wind and Sun is a good source for them.

IMHO,

Bill
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Old 13-05-2010, 23:31   #10
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With my old boat I used a large transformer and hooked it up to the solar regulator(Non MPPT). It was a very cheap large battery charger with more features and control options than any of the marine battery chargers. When I used the boat I switched it back to a normal solar regulator.
The batteries lasted 18 years ! and the regulator is still going strong on my current boat.
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Old 15-05-2010, 13:27   #11
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No bridging rectifier!? Hmmm. Wouldn't have the nerve, but, hey what do I know. Where is Rick when you need him!?
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Old 15-05-2010, 14:35   #12
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No bridging rectifier!? Hmmm. Wouldn't have the nerve, but, hey what do I know. Where is Rick when you need him!?
Most batteries prefer DC so yep you need a bridge rectifier. Google dc power supplies and you will find loads of simple circuits that can be built for a few dollars. Alternatively cannibalize the transformer from another application and it is likely to have the relevant rectifing and smoothing components. An old "dumb" charger is ideal.
If you have no knowledge of electronics don’t attempt this sort of hook up. Mains voltage can be lethal especially on a boat.
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Old 15-05-2010, 15:06   #13
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You neglect to say how big your battery bank is and how big a charger you want. I have a 660 amp AGM bank and 4 130 watt solar panels mounted on top of my bimini. With 30 amp Blue Sky controller it almost always takes care of my electrical needs. I have a 7 cu ft fridge and a small portable freezer. Only once in the last 2 years have I had to run the engine for battery charging.

This is not cheap. The solar panel rig and charger cost me over $4000.00 and I did a lot of the installation myself. however I am free of marinas and the tyranny of daily running the engine or a generator. It is well worth the price.

If you are based in a marina, I would have a good quality battery charger with 3 stage regulation. Since you have AGM batteries it should be 25 to 40 % of the battery capacity. It is a heck of a lot cheaper then going with a solar system with a large dc power supply that would not be off the shelf and expensive itself
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Old 15-05-2010, 15:36   #14
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If you are based in a marina, I would have a good quality battery charger with 3 stage regulation. Since you have AGM batteries it should be 25 to 40 % of the battery capacity.
Your solar system will only supply about 6% of the battery capacity. The batteries don’t know if the power is from solar or a battery charger.
Why manufactures of AGM batteries insist on a large capacity battery charger is a mystery to me. They do need to fully charged reasonably often, but this could be done with a 50A battery charger, just as you do with your 520W of solar
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Old 15-05-2010, 20:11   #15
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You can use the solar regulator with an unregulated DC supply--when I first got to Australia my 220v dock power system was a cheap 6 amp automotive charger, hooked to my solar regulator.
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