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Multiplus and smartsolar overcharging with engine on

On my narrowboat, I have a multiplus compact with engine driven Alternator with standard regulator (mobiletron vr lc111) to deliver charge to a bank of 4x105Ah leisure lead/acid batteries. This works fine on its own. This was already there when I bought it.

I've installed 450Pw of solar through a victron mppt 150/45 and that works fine in isolation too. (wired into main battery +/-).

I believe both boxes are set to default settings.

The trouble comes when I switch the engine on there is an immediate bad egg smell from the batteries, indicating overcharging and the mppt appears to get very hot. I am assuming too much current is being delivered to the batteries or voltage is too high if that makes any sense!?

I can get by, by switching off the mppt charging through the app whenever I switch on the engine, but that's not optimal.

Is there a way to change settings to force the Alternator charging to back off, when there is enough solar charge current being delivered? I can't find anything in a manual or searching this forum.

Is possible I need to buy a smarter regulator for my Alternator to allow it to work in tandem with the mppt, happy to receive product suggestions.

Will happily provide more info as directed.

Thank you


MPPT ControllersMultiPlus Quattro Inverter Chargerbattery charging
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An update on the changes suggested by PW. I've now been running for a few days with the solar charger set to 14.1v absorption (when the Alternator kicks in, it shows approx 14.2v at the MPPT). This seems to work well, very soon after I start the engine, the MPPT drops onto absorption, then after a few minutes, into float. I might try tweaking it back up to 14.2v to see if it's still OK but at least it's working well now.

Thank you PW Farnell!

2 Answers
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pwfarnell answered ·

What absorption voltage do you have set on the MPPT, what voltage does your alternator reach when the batteries are full on its own and what voltage is reached when both the MPPT and the alternator are working. These should all preferably be measured using the MPPT to ensure consistency.

What may be happening is that with the MPPT, the alternator regulator is being forced to deliver a lower current and higher voltage, some regulators increase markedly in voltage as the current demand falls. You could reduce the MPPT voltage set point to below the alternator regulator voltage so that it stops providing charge when the engine is on and the batteries are full.

On my narrow boat, the alternator regulator climbs from 14.1V when the batteries are discharged to 14.6V when the batteries are fully charged. I have set my MPPT to 14.5V so for most of the charge the MPPT is supplementing the alternator output, but when the batteries are full, the MPPT shuts down as the alternator drives the voltage above the MPPT set voltage. My system works well like this.I

Before considering an external controller, you should see if there is another regulator with a lower set voltage.

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Thank you, please see my update comment, it seems to be working well using your suggestion.

I really appreciate the help!

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tony-jackson answered ·

Thank you PW, great answer, I understand. My battery is low enough now to accept a good charge and I'm about to set off. Will do some measurements and tweaking. Will update with results.

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