I have installed a Multiplus 12V 800VA in my van that is connected to a 300Ah LiFePO4 battery (Li-ion), via a Smart Shunt. During long stay in garage, the starter battery is getting low. I’d like to be able to use the trickle charger of the Multiplus to keep it at sufficient voltage when connected to 230V garage supply. Would there be any problem if I am connecting the trickle charger to the vehicle starter battery which is a 92Ah Lead-acid AGM battery ?
Note the elements and connexions in my system:
4x MPPT75-10 ensure solar charging from 4 x 110 W panels - all MPPT connected to Smart Shunt Load side and to Cerbo via VE-direct
A DC-DC charger Orion XS 12/12 50A ensure charging of LiFePO4 while driving - connected to Cerbo with VE-direct
Multiplus DC is connected to Load side of Smart Shunt (-) and to positive busbar. Multiplus is also connected to Cerbo GX through Ve-bus cable - All the dip switches (1-6) of Multiplus are on OFF.
Positive of starter battery is NOT connected to the Smart Shunt (System/Load side), but it is connected to the IN connector of Orion XS 12/12 charger, which GND is then connected to the Systeml/Load side of the Smart Shunt
Positive of starter battery is also connected to “Aux- bat. starter “ of Smart Shunt, for battery monitoring
Smart Shunt connected to Cerbo by Ve-direct
A Battery Protect 12/24-65 is also present between domestic battery and Loads (GND connected to Smart Shunt Load side)
I have seen a very interesting post (How does the Multiplus trickle charger work) suggesting that this should not be done , but I wonder if the presence of the Smart Shunt, Battery Protect and Orion XS 12/12 in my system and the wiring described above are changing something to this recommendation of NOT doing this.
The underlying issue is essentially, that the LFPs resting voltage can be high enough to allow a small current to flow to the starter battery even when no chargers are actively charging the LFP battery. So it is possible that the LFP could get over-discharged by the trickle charger. Neither the shunt nor the batteryProtect can stop this. Its even possible that the trickle charge current is small enough for the shunt to not detect it, so not even the SOC would go down.
Ive tackled this issue by using a relay in line with the trickle charger. Its coil is supplied by the ACin that also supplies a MultiPlus. So only if i have mains voltage supplied to the MP the starter battery gets trickle charged. You can of course use some other source for the relay coil, like a load output of one of the MPPTs or a cerbo relay.
Another possibility is to use an additional diode in series. This will drop the trickle charger voltage an additional 0.4-0.8V depending on the diode type used. So the voltage level of the LFP needs to be that amount higher in order for a current to flow.
Theres also this thread that holds valuable information i think, although its in german
If I understand you correctly, I could wire the trickle charger to the starter battery via one relay of Cerbo . I could use the “manual” relay (1 or 2, in mode NO) and would get a manual switch in my control panel that I could activate only when I connect the 220V from the network (Multiplus charging LFP) . The risk is to forget to switch it off when the Multiplus has completely charged my LiFePO4 battery and stops (it would then start to drain the LFP battery if the LA battery still needs some charging via the trickle charger cable). A better solution would be to use Relay 1 with a condition … but what type of relay config should I use in the Cerbo (I only see Manual, Alarm ? , Generator ? , Pump ?) and what condition could I use to get it linked to the fact a charger is active (either Multiplus or solar MPPT chargers) ? I don’t see easy options in Cerbo …
Your idea of using a separate relay on the trickle charger cable is attractive, the relay being activated by the 220V from the P17 plug (or AC in of MP). That would cover the case when connected to 220V. Could you share some more details of the relay type and characteristics that are needed (I am not proficient at all …) as well as wiring scheme to make sure I get it right
When charging by solar, what should be the wiring to the relay ? (you are suggesting using a load output of one MPPT …) - what if I have 4 MPPT’s generally all working simultaneously , would only one be sufficient to trigger the relay closing ? Could you also share some details / specs of the relay that would work for that ? and again wiring scheme ? …
Assuming I go for the relay solutions, if I want to ‘cover” both cases of solar charging and 220V charging via Multiplus, is it all-right to simply wire the trickle charger output to LA battery by 2 parallel circuits each with its relay, one activated by the Multiplus AC in and the other one by the MPPT load output ?
Finally if I would go for the additional diode in the trickle charger line to starter LA battery, it would cover all situations in once and be simpler isn’t it ? in that case, no need to worry about what is charging the LFP (solar or MP), because as soon as the LFP will be charged enough, a current would flow to LA battery in the limits imposed by the diode(s). This would then direct excess of charging voltage to the LA battery and contribute to recharging it . Could you also share the model, type and characteristics of the diode to be used ?
I made a fancy intelligent controller for this, using Node-RED and one of the available relays in my GX device. This solution requires adding software but requires adding almost no new hardware other than an external relay. Node-RED Multiplus Starter Trickle Charge