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Simon Churchill avatar image
Simon Churchill asked

Multiplus Maximum AC Input Current

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


MultiPlus Quattro Inverter Charger
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2 Answers
jwfrary avatar image
jwfrary answered ·

You need to leave the unit in charger only mode when leaving the vessel. You can do this with the switch on the front of the unit, from a GX device in the software menu or a Multi Control Panel. (you can also wire a remote switch to the Multi)

The result will be that the trip will likely go as your running more devices on the vessel than the incoming supply can support, but when It does trip then at least the batteries will remain full aside from the DC loads of course.

At the end of the day you can't take more out than you put in.

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Simon Churchill avatar image Simon Churchill commented ·
Hi thank you,

I had thought about leaving in charger mode but as you say the DC loads will drag battery down anyway. The problem in this case should go away now as the shore power has been upgraded to 63A. My post was mainly investigating if now or in future there where other ways to operate.

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jwfrary avatar image
jwfrary answered ·

As a more complex alternative, you could use SOC or other appropriate value to switch a relay on the Multi which could switch a contactor for cutting off high load ac devices.

But you will still end up with flat batteries if the unit is set to on!

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Simon Churchill avatar image Simon Churchill commented ·
If external AC loads were switched off the current would fall back to under the set limit. Thus the battery charger would be restored. So a way of monitoring the load and then shedding it would be aq good idea, but I hope not needed now.
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