question

hanst avatar image

Can I connect a MPPT solar charger to the loss-free diode pair which are connected to the altenator?

Hi,

I have 2 loss-free diode bridges between the alternator and my 4 (1x start, 1x bow thruster, 1x winch, 2x service) batteries. The specific type is this one:

https://www.studer-innotec.com/media/document/0/mbi_series_user_manual_en.pdf

Can I connect an MTTP solar charger to the same + as the where the alternator is connected to?

I'd like to do so, so that all batteries get charged and not just the service battery.

All batteries are 'deep cycle 12v' batteries.

charging batterychargercharge controller compatibility
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1 Answer
Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

Hello @hanst,

Technically this might work, but there's a few things to note:

First, it is not a Victron-supported connection method, so if you connect it this way, you'll lose a lot of the technical support capability of Victron's distributor network; we can't diagnose any possible aberrations in behavior of the MPPT because it's been connected in a manner that has not been tested and is not supported.

Second, the charger will function in unexpected ways, since all of its internal algorithms are based on the assumption that it will be connected as designed - that is, connected directly to a single battery bank. Will it still turn on and start charging? Almost assuredly... but we can only guess as to how it will determine its absorption timer and a number of other variables, given that each battery will likely be at different voltages at any given time and battery voltage is a key aspect of how the MPPT determines its behavior.

Finally, just note that your listed diode pair are also not Victron-supported, so there's simply no way to tell for certain how this is going to behave. I know, for example, that a similar setup does technically work when using Victron's ArgoFET battery isolator (although still not a supported connection) and I also know that it results in aberrant behavior in the MPPT (including history loss and excessively long absorption timers), but since your diode pair is not a Victron product, we can't begin to tell how the combination might or might not function.

Bottom line: This might work, but it is not recommended and is not supported.

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Hi Justin,

thanks for the answer. I've googled more since my post and noticed another solution using a https://www.victronenergy.com/battery-isolators-and-combiners/cyrix-battery-combiners

The diagram is in dutch, but I think it's clear enough.

This is a Victron product and it will allow the MPPT to 'see' the battery.

Any thoughts on this?