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Old 26-11-2018, 09:59   #1
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Using mppt controller to regulate old chargers

Finally purchased a new to me Bénéteau 393.
I have been reading this forum for over 2 years helping me decide on the right boat hope I chose a boat I will enjoy for a long time.
Boat is on the hard for the winter doing the basics necessities. The only new project for this winter is solar.
Will install 4 flex 100w panels on Bimini with Victron smartsolar 100-30.
Present batteries 2 * 110 amp each were installed by previous owner as part of the closing of sale to me.They are the so-called dual purpose flood acid sealed batteries. I just want them for 1 season then I will be going to lithium the year after.
My question is I have a very high end and very efficient 24v 50 amp power supply that I was thinking of using next year for the lithium’s and would like to use a mppt controller to take care of the charging algorithms when plugged into shore power. Anyone see any reason this can’t be done?
The only thing that pops up in my mind is that maybe the mppt controller works on a floating ground input? Anyone know if this is so or can the negative of mppt controller be common ground.
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Old 26-11-2018, 10:56   #2
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Re: Using mppt controller to regulate old chargers

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Originally Posted by zavman View Post
My question is I have a very high end and very efficient 24v 50 amp power supply
That is its output, what is its input?

Link to the model?

> use a mppt controller to take care of the charging algorithms when plugged into shore power

those are usually driven by solar panels, never seen one takes shore power as input

> can the negative of mppt controller be common ground

Yes usually all DC circuites' negatives are tied together, and suitably sea-grounded at a single common point, e.g. the engine or its main bus

That is not the case for anything AC however, usually best to use a pro for that.
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Old 26-11-2018, 12:15   #3
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Re: Using mppt controller to regulate old chargers

Power supply is 90 to 240 v ac input and 24 v dc 50 amps output want to use it to charge lithium off shore power. Asking if mppt controller will take the 24v dc from power supply to charge lithium’s properly.
Sorry for not explaining myself properly
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Old 26-11-2018, 12:49   #4
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Re: Using mppt controller to regulate old chargers

Do you have a 24V DC system?
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Old 26-11-2018, 12:51   #5
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Re: Using mppt controller to regulate old chargers

12 volt system
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Old 26-11-2018, 13:07   #6
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Re: Using mppt controller to regulate old chargers

OK, I think I finally understand what you are asking/thinking of doing.


You want to use the 24V charger to create 24VDC from mains power, then use an MPPT controller to convert 24VDC to 12VDC to charge you batteries.


Is that correct?
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Old 26-11-2018, 13:36   #7
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Re: Using mppt controller to regulate old chargers

It’s a power supply not charger, but yes that’s what I would like to do instead of buying new high current charger with lithium algorithms
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Old 26-11-2018, 14:00   #8
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Re: Using mppt controller to regulate old chargers

Can an old lead acid charger plugged into a mppt controller could properly charge a new lithium installation ?
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Old 26-11-2018, 14:23   #9
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Re: Using mppt controller to regulate old chargers

Short answer: "Flooded sealed" aka maintenance free batteries are the worst possible choice and "dual purpose" just means they're not deep cycle, so they're really disposable. For one year as a cheap way to get through, that works.

But lithium batteries of ANY sort require special lithium charging protocols. They require a BMS (Battery management system) or other charge controller which will fondle them in ways that no conventional charger, including MPPT controllers, will.

Since you've got time, I'd suggest reading up some of the many web and forum discussions that go into extensive detail (and debate) over these issues, and plan to double or quadruple whatever you had been planning to spend, if you go lithium.
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Old 26-11-2018, 15:13   #10
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Re: Using mppt controller to regulate old chargers

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It’s a power supply not charger, but yes that’s what I would like to do instead of buying new high current charger with lithium algorithms
Short answer: NO!

An mppt controller works by scanning the voltage/power curve to fine the peak power point. How often they do this depends on the design, but they are NOT designed to work with a constant voltage supply.

Of course someone here will say "Sure, go ahead"

I'd suggest if you want a better answer than you might get from random strangers just call the tech support line of the brand mppt controller you are going to use.

You can get a cheap 3 stage battery charger for, well, cheap.
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Old 26-11-2018, 21:15   #11
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Re: Using mppt controller to regulate old chargers

some solar controllers will accept input from a power supply just fine.

PWM type more likely.

But all you need for daily charging of LFP is a steady 3.45Vpc - 13.8V for 4S "12V"

No "stages" required, all Bulk is fine, will start out lower, when you hit the 13.8, just stop and call it Full.

and no need even to get all the way there, long as you put in a bit more than you take out each day, don 't let it go below 12V, will have a very nice long life.

there are dozens of previous threads discussing the various beliefs about BMS and balancing etc, please read them so all the same arguments don't need to be repeated.
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