Currently my boat’s starter and aux battery are charged by the alternator through a bridge rectifier.
My aux battery (actually: 2 batteries in parallel) is charged by solar and a shore powered charger/inverter.
My starter battery is only charged by the alternator and I would like to be able to charge it from shore/solar power if needed, but also start from the aux battery, just in case.
Hence the Cyrix.
All Victron schematics that I found show a direct connection between alternator and starter battery.
However, in my case, it seems the wire to the bridge rectifier, carrying the alternator’s current, is coming from my dashboard, presumably the ignition. It’s still a mess down there that I am cleaning up, so I can’t be 100% sure, but the ignition is the only thing that makes sense.
So my first question is: why would the alternator’s current go all the way from aternator to ignition and back (alternator and bridge rectifier are very close in the engine room), using a relatively thin wire (16mm2 it seems)?
And my second question is: should I keep it this way when I install the Cyrix or should I change it according to what Victron shows?
Ive seen charge current gauges fitted to dashboards, which worked by passing the actual current through the gauge rather than using a shunt or similar.
The charge current passing through a gauge isnt directly an issue, as long as you remove the rectifier and instead connect the wire from the alternator to the starter battery.
But by removing that loop into the dashboard you would lower the voltage loss. In general wiring should be kept as short as possible.
Ah! That is also a possibity, of course. It could be used to show the amps on my dash!
By the way, I did not explain the situation 100% correct, as the wire from the alternator is going directly to the bridge rectifier and the starter battery side is going to the dashboard and from there back to the starter (and therefore battery). Doesn’t affect my questions though.
Firstly from a technical aspect, the Bridge rectifier converts AC to DC, and is built into the Alternator.
As mentioned above, if the main alternator current goes to and from the Dashboard, then this would be for current measurement.
This is needed to protect the alternator output. Should the alternator suddenly become disconnected from any battery at high load/rpm, then there will be a destructive voltage spike generated.
Using a shunt (in the negative) to measure alternator current is very difficult, as the alternator negative is usually through the frame, and electrically connected to the engine block.
Not necessarely. Bridge rectifier modules get also used a lot to combine two DC sources, or like in this case, as a diode splitter. In both cases, only two diodes of the module are actually being used. But the form factor, cheap price and wide variety makes then viable options compared to single diode modules.
Besides that, i would bet any alternator out there uses single diode modules in a bridge configuration, not a single package rectifier module.
Whether you use a pre packaged brige rectifier, or build it out of individual diodes, it it still a bridge rectifier.
However, your point about using bridge rectifiers as diode splitters or combiners is noted, and you also need to be aware of the voltage drop associated with these.
Victron have several solutions for eliminating this volt drop, and the Cyrix is a valid solution.
I think I have created som confusion by using the word rectifier here, excuse me. What I meant by this is the ‘splitter’ between starter and aux battery, I used the wrong term here (and not sure what it is called in English)
In the meantime, I created better access to my dashboard and concluded that indeed, the wire from the battery-splitter is going into an Amperage gauge and from there, back to the starter battery…
I am not sure, but it looks like the gauge isn’t even functioning, so I am considering totally removing it, thereby creating a much shorter path from splitter to battery and hopefully some higher charging effiency.
When I want, I can check my smartshunt status to see how the starter battery is doing anyway.
