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twistedtree asked

Skylla-i power supply voltage adjustment

What are the conditions needed to adjust the Skylla-i's power supply mode voltage? I'm talking about Mode 9. I understand that you turn the Absorb voltage POT a bit and the unit goes into programming mode, but how do you measure the programmed voltage?

With or without a load connected? You can't adjust it with LFP batteries connected because the batteries will sink all the output current and the voltage won't move. So that makes me think it should be done with the output open circuit. But when I do that, if I overshoot the target voltage, it takes forever for the output voltage to bleed down, and by the time it has, the unit has exited programming mode.

With or without the voltage sense connected?

It looks to me like the only way to do this with any accuracy is using a dummy load of some sort that is within the output range of the Skylla. That's not somegthing I normally carry around with me from boat to boat.

Skylla
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2 Answers
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Kevin Windrem answered ·

First of all, don't use power supply mode when connected to any battery bank. There's no control over charging current in this mode so you could damage your batteries with either too much current or too high a voltage.

With no load, the output voltage will fall slowly because of capacitors on the output. Your best bet for adjusting power supply mode voltage is to connect a small load. This will allow the voltage to fall more rapidly when the voltage is turned down. A couple of automotive 12 volt bulbs connected in series for 24 volt adjustments should be fine.

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twistedtree answered ·

I discovered that you need to disconnect both voltage sense leads. Just disconnecting one so it's open circuit isn't enough.

So the procedure, which hopefully someday will be in the manual, is to disconnect both voltage sense wires, and disconnect the battery output. I'm guessing you probably need to disconnect all the battery outputs, not just the main one, but I haven't tried that. Presumably Victron has and know the answer. Then you can adjust the output voltage, with a note that any decrease in output voltage will take a while to be reflected in the output, so it's best to start low and creep up on the desired voltage, avoiding any overshoot. If you happen to carry around some incandescent 24V light bulbs and clip leads, then they can provide a small load to help with down-adjustment. But those aren't normally in my bag. Can't even think when I last saw or used an incandescent bulk.

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