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denys avatar image

How to connect 12v DC generator in parralel with Smart Solar controller

How to connect 12v DC generator in parralel with Smart Solar 12v to the battery to avoid conflicts during the charging ? Does anyone have drawing ?

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What "type" of DC generator are you talking about?  Vehicle alternator, a "solar generator", PV panels?  All can be directly connected to battery(s) in a parallel configuration but depending on the type of DC generator may need some "control/safety" devices added to the connection. 


Hi. Thanks for your reply. Im talking about Vehicle alternator, in my case small sailing boat outboard motor with alternator to DC 12v 5A. I would like to connect both PV 40 (60) watt + outboard generator to Li-ION batt 70 Ah. I have smart solar 75/15 for PV module and if I understand correctly will require BMS controller or so in between the battery and DC GEN which will protect the battery...

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Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

@Denys, multiple charge sources can be parallel-connected to a single battery without any problem, no need for a diagram. Just make certain that under no circumstance do you exceed your battery's recommended maximum charge rate, and make certain that all circuits are fused or breakered as appropriate to wire gauge and expected current.

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Hi. Thanks for your reply. Im talking about Vehicle alternator, in my case small sailing boat outboard motor with alternator to DC 12v 5A. I would like to connect both PV 40 (60) watt + outboard generator to Li-ION batt 70 Ah. I have smart solar 75/15 for PV module and if I understand correctly will require BMS controller or so in between the battery and DC GEN which will protect the battery...

@Denys, you will require a BMS for an LFP or Li-Ion battery and it must be the first thing connected to the battery. Please refer to your BMS user manual and/or your battery user manual for the correct connection methods.

denys avatar image denys Justin Cook - Bay Marine Supply USA ♦ ·

Hi, Is it possible to use Smart Solar charge controllers solar power input port as a parallel input for DC generator ? If the current will be in range of the controller capabilities and diod schottky installed on PV module to lock revert current flows ???

No - the MPPT chargers require that PV input voltage is +5v higher than the Battery voltage. AS such if your DC batteries were sitting nominallly at lets say 12.5v - it would mean the input to the MPPT would need to be 17.5v - Most DC Alternators do not exceed somewhere between 14 and 15v. so it would never be any good to an MPPT for output of any more than 9-10v

Also although you have the right idea with the schottky to remove current reversal, you will also suffer forward voltage drop, so that reduces it even more.

Typically what will happen is all determined by the Batteries internal resistance, as one source starts charging it will put a certain amount of Voltage at a certain current into the batteries. As a 2nd is applied Both sources will put as much into the battery as it is willing to take, and that they are able to give. The voltage delivered will not change based on the value of Voltage that the MPPT or Alternator are seeing, but rather the Internal Resistance, which in itself will of course change as the battery becomes more charged, at which point Each of the Charge sources will adjust what is being delivered. the MPPT will do it smartly, the alternator, not quite as smart...but typically they have a circuit which will step down the supply.

As you mentioned - The best way to get the most out of the setup is to make sure that in between all your sources and your Li-IONs that you have a BMS - whether that is part of the Li-ION or seperate, but something that can be programmed to make sure you do NOT exceed the specs - the MPPT can be programmed, but most likely the Alternator will be suited more to a typical PB/SLA which has different charge characteristics to Li-ION