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When not charged by the alternator, the only charger connected to my starter battery is the trickle charge output of the Multiplus.
The voltage of my house and starter is measured by the smartshunt.
In VRM I have noticed that the voltage graph for both starter and house is identical, though the actual voltage is not the same.
Is this a normal artifact of the trickle charging, or is this a symptom of bad wiring somewhere?
The trickle charge follows the internal charger cycle. Usually it is similar or the same voltage. (On the 12v systems)
Your looks like a 0.3v difference. Is there a long run to the battery? What gauge wire is it? Voltage drop usually length and wire gauge. Has it always been like this or is it a new behaviour
Other than a pinch point maybe corrosion at the starter battery? Loosened connection?
The trickle charger function is taken from the main DC input from the house bank and it flows though a diode and current limiter so the starter battery voltage will always be 0.3 to 0.5V lower than the house battery voltage. The diode is there to stop the starter battery trickle charging the house battery if the house battery is flat. My boat does exactly the same as yours, I have a plot on VRM to keep an eye on this.
During this whole period my (lithium) house bank was at 13.5V float. The three voltage-spikes at the end of the graph seem to be a result of the MPPT charger that is connected to the house bank only.
But apart from the voltage difference, does it make sense that the starter voltage automatically increases when the MPPT only charges the house?
The only connection between house and starter is the trickle charge of the Multiplus.
All the battery cables is 70mm2, and less than 2 meters long. This is a new-ish system, so no sudden changes in behavior.
Here are my 2 sets of batteries, the starter battery follows the house battery less 0.35V and the starter battery increases when the solar charger goes to absorption, but this is short today as the batteries were already full.
Trickle charge is at house battery voltage, so yes makes sense.
