When setting up a Multiplus for AC1 and AC2 inputs maximum current we had been made to believe that this helped stop over loading a restricted supply such as a 16A shore power hook up. What we never considered was the actual implications of this setting. As follows:
We have a clients vessel that is left over night and weekends on a berth and unattended. The vessel has to be kept alive 24/7 with DC monitoring systems, AC heaters and CCTV. If we lose shore power the risk is batteries going flat and losing all the monitoring.
We thought the idea of being able to restrict the input current to both 16A and 32A was a good idea as these were the normal supplies available, where 32A was the norm when on own berth, 16A setting is only required if away in a marina with only 16A available.
However what we had not understood was that the only actual load shedding that can be seen to be available is that the battery charger shuts down and lets AC pass through with no restrictions. Thus if the total current of AC loads is over 16A or 32A, the battery chargers load being shed is not going to reduce the load on the input to less than that is set but only stop battery charging, and could trip the shore connection leaving a completly dead AC and DC system.
If this is true it appears a Multiplus is perhaps targeted at the maintenance of AC systems where the batteries are not used for loads other than the inverter function? This point has truly been missed.
It would be nice if a multiplus could be put in a mode where its priority is maintaining battery loads by maybe dumping AC2 out and then Dumping AC1, so battery charging is maintained and AC1 is last AC load output to be dumped. Is this by any chance possible?
This realisation had come to a head now as a result of using engine heaters that have caused battery charger to shut down and battery to go flat as a result of having 24/7 DC loads. It would be better to lose the engine heaters as these are not critical and are already wired via AC2 out, so that they cant function in Inverter mode.
The main reason for using Multiplus was the conveniance of having auto switching from Generator to shore power and the UPS function for short duration if generator was down. But also to a limited degree ability to provide AC via engine 24V alternators and battery.
Any thoughts on idea of AC load shedding rather than battery charger shutting down?
Simon
