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djsmiley asked

Multiplus II - AC input ramp up time

Recently installed a Multiplus 3000 at a RV of a customer. He had a (small) petrol generator already available. (2800W). However, since this is a rather old unit, it struggles with sudden high loads.

From idle (no load) to a load takes some time to stabilize. The MP however detects it as a instable grid, and shuts down and the process repeats.
(Customer has an auto transfer switch so the AC input of the MP is either grid OR generator)

I have to reduce the DC charger to 20A in order for the MP not to shutdown.

By adding a base load of 300W (Halogen bulb) I was able to get 40A (common trick to stabilize small generators). However, I think it would be able to provide more charging if the charger ramp-up was slower (so the generator has more time to adjust for the load).

On some of our bigger UPSses we have an adjustable ramp-up time: The time which it takes to slowly switchover the load (and not a big drop of the load on the generator).

Is it possible to configure this setting? (Either a configurable timer, of just a toggle box 'enable slow ramp-up' which is like 60sec or so (so smaller generators have sufficient time to stabilize)

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1 Answer
JohnC avatar image
JohnC answered ·

Hi @DJSmiley

Yes, it's called Dynamic Current Limiter. A 'soft-start' of sorts, designed for gensets..

1669433993496.pngTrouble is, the Multi doesn't know of the external ATS. So if it were already running on highish grid power and the genset was switched in then the genset would still gag and likely cause the Multi to reject. Once anyway, when it attempts a reconnection the DCL should bring it back on ok. (Providing the grid hasn't switched back in too at the ATS).

1669433993496.png (51.7 KiB)
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Kevin Windrem avatar image Kevin Windrem commented ·
Wouldn't the Multi immediately drop the AC input when the external transfer switch changes sources? The phase would be different unless you get really lucky/unlucky. Voltage and frequency might also be different by a little bit.
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JohnC avatar image JohnC ♦ Kevin Windrem commented ·

@Kevin Windrem

I don't know Kev. Legit standalone ATS's are expensive and spruik <20mS transfer time (1 cycle). Is a Multi that picky? In this particular case it may not be important anyway, as the 'customer' here may well be using the ATS as a selector switch for two sources which are manually started. So the sources don't arrive together.

But this guy wants to know..

And I posted a link there back to this one. This is something I don't recall being discussed before. And I'd be interested in the answer too..

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