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evm1024 · 03-09-2017, 10:37

Has anyone ever run (or know about) running 2 MPPT controllers off of a single panel (or bank of panels)?

Imagine a set of (oh say) 3 large panels (parallel or serial) driving a larger MPPT controller to charge your house bank. Assume that all voltage and current specs are well within the limits of the controller. No problem here.

Then imagine taking a smaller MPPT controller and placing it next to your windlass battery up forward and running a cable from your solar panels to that controller in parallel with the house bank controller.

Do the controllers oscillate as they fight for amps or what?

Anyone do this?

I'm thinking along the lines of charging a LiFePO4 bank off the main controller and when the LiFePO4 bank is "full" disconnecting the bank from charging. But, also having a smaller set of MPPT controllers charging an AGM (or other non LiFePO4 battery) start battery and or AGM windless/thruster battery.

Inquiring minds want to know!

john61ct · 03-09-2017, 11:44

No, do not do this.

hellosailor · 03-09-2017, 12:13

So you'd use an MPPT controller at the windlass instead of...doing something conventional and less expensive, like using a boost charger? Or, even simpler, just running adequate size cables?

None of those solutions (except the cables) is going to supply adequate voltage while the windlass is running. But if the windlass is only pulling down its own battery, maybe to 90% SOC after use? Those good-but-not-great cables will still be good enough to bring the battery back up, as the demand goes down and the battery regains full SOC.

Throwing expensive and inappropriate electronics at a job doesn't help much.

evm1024 · 03-09-2017, 17:10

A buck/boost charger with an AGM profile would be near Ideal. I picked on MPPT because I happen to have an MPPT 75/15 sitting around.

I choose to not run heavy cables to the windlass battery. I do have fairly small gauge cable running forward so running higher voltages forward gives an advantage.

I am exploring having a charging bus running at a higher voltage that can be distributed to point of consumption (like the windlass) with smaller cables.

Then using chargers that take the higher voltage in and give specific charge profiles (agm, LiFePO4 etc) at the battery.

This is actually a common practice in other domains.

Also, PWM would be better than MPPT due to the interactions seeking the optimal power transfer that MPPT does.

evm1024 · 03-09-2017, 17:12

Let's do try to keep the thread technical and on topic.

It would be wise to assume that I am technical, competent and smart.

foggysail · 03-09-2017, 18:58

Quote:

Originally Posted by evm1024

Has anyone ever run (or know about) running 2 MPPT controllers off of a single panel (or bank of panels)?

Imagine a set of (oh say) 3 large panels (parallel or serial) driving a larger MPPT controller to charge your house bank. Assume that all voltage and current specs are well within the limits of the controller. No problem here.

Then imagine taking a smaller MPPT controller and placing it next to your windlass battery up forward and running a cable from your solar panels to that controller in parallel with the house bank controller.

Do the controllers oscillate as they fight for amps or what?

Anyone do this?

I'm thinking along the lines of charging a LiFePO4 bank off the main controller and when the LiFePO4 bank is "full" disconnecting the bank from charging. But, also having a smaller set of MPPT controllers charging an AGM (or other non LiFePO4 battery) start battery and or AGM windless/thruster battery.

Inquiring minds want to know!

GOOD POST!

What an interesting question! THANK YOU for posting your question! Must admit, have not thought about paralleling a pair of controllers and after thinking about it, I see no reason why such configurations under limited circumstance would not work.

Consider my particular situation for example. I have 1180 watts of panels, and two each 430AH battery banks that I operate in parallel and use for both house and starting. I also have a 24v bank (2 each 12V group 30s or something in series) that provides some AC power via an inverter for low power basic stuff such as lighting, all LEDs. Its main purpose however is to power my windlass and my davit crane, neither of which get much use.

When on anchor or mooring, the only way I can replenish the consumed 24V AHs is to run my genny. In the mean time my Victron 150-70 controller is loafing because the batteries quickly recharge to float leaving my panels to do nothing but attract gulls and their poop. So adding a second controller for 24V service makes a lot of sense AND I INTEND TO DO SO regardless of the naysayers.

A Victron 75-15 I believe will work well for this task with my panels outputing voltages in the sixties. The worst thing I can see happen is the panel loads will just lower the input voltage to the controllers forcing them to find a new Vmp and of course this will change as a function of the loading. They will still provide an output but limited to the power provided by the panels.... think watts. If it looks like I might get close the the 75V limit on the contoller, I will just clamp the panel outputs to 70V with zener diodes.

evm1024 · 03-09-2017, 20:12

Foggysail, Do let us know how well it works once you get it wired up.

Your situation is vary much like what I am thinking about. 1) lots of solar (1kw+), LiFePO4 that gets to 80% SOC in a few hours under solar alone and then has its charging shut off, a non-LiFePO4 bank on a second controller that is a small percentage of the total solar capacity and needs to reach 100% SOC (and does not have a good charging scheme like your case).

I'm expecting that the time constant for the MPPT is long enough that the two controllers to dot go wild as they interfere with each others loading. The larger controller should dominate just due to its greater load on the solar panels.

The naysayers might have a point if we were talking about a small solar array.

There are a lot of things to unlearn with LiFePO4 (always keep at 100% SOC for one) and a few to unlearn with a KW of solar (no need to squeeze out every watt when you are fully charged in 4 or 5 hours).

Regards!

foggysail · 03-09-2017, 20:31

Remember, the loads will not be pulsated so my assumption is they... meaning both controllers will settle on a Vmp and work independently. And I agree that the larger loaded MPPT will determine the panel output voltage at any time because of loading, and the lower loaded controller will adjust to it.

I don't expect to see any problems other than my time to get this installed and tested. I do want to get it done before we haul in late October. More later.

evm1024 · 03-09-2017, 23:29

Quote:

Originally Posted by foggysail

Remember, the loads will not be pulsated so my assumption is they... meaning both controllers will settle on a Vmp and work independently. And I agree that the larger loaded MPPT will determine the panel output voltage at any time because of loading, and the lower loaded controller will adjust to it.

I don't expect to see any problems other than my time to get this installed and tested. I do want to get it done before we haul in late October. More later.

Likely you are right. Looking forward to hear what happens.

Catnut · 04-09-2017, 00:08

Great topic. 2 days ago I was on a yacht with a mix of battery technology. LiFePo batteries for the house bank (I was told that these provided power for 5 days before dropping to 20% 'ish SOC). Lead batteries were used for the windlass, bow thruster and engine start.

The boat did not have any solar, but used a large alternator on the main engine, or battery chargers off an Onan generator to charge everything.

I did ask how the charging of the different battery technologies worked with a single charging point, and was told that it was handled by a programmable controller. Unfortunately I don't know who made it. As far as I could see most of the equipment was Victron, with battery monitors for each of the battery groups.

The electrical work was done in Australia, and seemed to be of a high standard.

With Lithium technology moving forward at a rapid pace, in my view this is likely to be a more common mix of technologies in the near future.

Dadrock33 · 05-09-2017, 05:06

Why not just install an ACR in the lines from the solar panels and that will supply power to your battery's needs?

evm1024 · 05-09-2017, 15:48

Quote:

Originally Posted by Dadrock33

Why not just install an ACR in the lines from the solar panels and that will supply power to your battery's needs?

Isolation - an ACR would end up combining the LiFePO4 bank with the windlass AGM bank. The AGM likely would never reach 100%SOC.

john61ct · 05-09-2017, 16:27

Let's look at a more conventional approach, correct me if I misunderstand your goals.

You have lead bank that needs to get to 100%, so should get priority.

LFP is prevented from getting full by BMS relay or something.

So just put the SC output on the lead bank from the beginning.

Put a B2B e.g. like Sterling's BB1260 from there to the LFP. Set its custom voltage output as you like, and to only start charging when lead bank's voltage shows it's past Bulk stage, maybe 75% full and amps accepted starting to decline.

Also possible to trigger starting from a relay, triggered by SoC BM, whatever.

As the lead bank is accepting less and less current, the solar output is going to LFP.

When the LFP is cut off, the lead bank continues to get its low-amps charge, until SC goes to Float.

evm1024 · 05-09-2017, 16:35

Hi John61ct - With all due respect:

You are missing the point of this thread. The point is to see what happens when you place 2 solar controllers on a single panel set.

In the larger context (for me) I'm looking at having a charging bus running 48 volts or so that is wired to point of need chargers.

Nothing conventional about it on a cruising sailboat.