Mercruiser
New Member
What I describe here are not big issues. But I thought some of you might want to know.
I am bench testing my shiny new Multiplus II 12V 3000VA. I made a pre-charge circuit using a 12V incandescent automotive bulb (Type 1003, 1A at 13V) and a momentary switch. It works great. One thing I really like about using an incandescent bulb is that it provides visual indication of current flow magnitude, whereas a 25W power resistor (or similar) does not provide any indication if it is conducting current or not.
Here are two surprising things I noticed:
1) Connecting the V-Sense input (to 13V) pre-charges the capacitor at a nice slow rate. I discovered this accidentally when I pushed my pre-charge momentary switch. The incandescent bulb didn't light up. Then I measured the Victron MP battery terminal voltage. It was 13 V. I expected it to be zero because I had not yet connected the battery. Turns out, I connected the V-Sense input first, and that pre-charged the capacitors. To verify, I disconnected the V-Sense and discharged the capacitors with another bulb. I then connected the volt meter to the MP battery terminals and connected the V-Sense input again. It took about 10 seconds to charge the capacitors up to 13V through the V-Sense input. For comparison, my type 1003 incandescent bulb charges the capacitors in about 3 seconds.
I was a bit surprised that the V-Sense input is not electrically isolated from the Victron battery terminals. But at least they put a decent resistance in the circuit. If this was a documented feature of V-Sense, I would have just used that instead of building a pre-charge circuit. Oh well. It's already done.
Note: The MP rocker switch has to be in the O position (completely off) for this to work. If the rocker switch is in the I or II position, the capacitors do not charge.
One more ramification of this V-Sense behavior, when putting a seasonal MP II in long-term storage (RV, boat, summer cabin), you probably need to disconnect the battery terminals AND the V-Sense. You would not want to slowly drain the battery through the current path from V-Sense input to loads connected to the MP battery terminals.
In case you are not familiar with the term, V-Sense is an optional connection for the MP II, as described here: https://www.victronenergy.com/media...tml#UUID-fcc597e4-d20d-e11e-76a3-827a6b984e44
2) You cannot pre-charge the capacitor if the MP rocker switch is in the I or II position AND the MP mode is set to OFF in the Victron Connect app. In this configuration, the MP is trying to draw power from the battery terminals and this prevents the capacitors from charging with my type 1003 incandescent bulb. This behavior is the same, regardless of whether the AC-IN is powered or not. To charge the capacitors, I had to first put the rocker switch in the O position (completely off).
I discovered this when I pushed my momentary pre-charge button and the incandescent bulb stayed lit as long as I pressed the button. The expected behavior is for the bulb to turn on bright at first, then dim over a couple of seconds as the capacitors are charged to 13V.
I think these two examples show some of the advantages of using an incandescent bulb in a pre-charge circuit, instead of a power resistor. I would not likely have noticed either of these behaviors if I had been using a power resistor.
I am bench testing my shiny new Multiplus II 12V 3000VA. I made a pre-charge circuit using a 12V incandescent automotive bulb (Type 1003, 1A at 13V) and a momentary switch. It works great. One thing I really like about using an incandescent bulb is that it provides visual indication of current flow magnitude, whereas a 25W power resistor (or similar) does not provide any indication if it is conducting current or not.
Here are two surprising things I noticed:
1) Connecting the V-Sense input (to 13V) pre-charges the capacitor at a nice slow rate. I discovered this accidentally when I pushed my pre-charge momentary switch. The incandescent bulb didn't light up. Then I measured the Victron MP battery terminal voltage. It was 13 V. I expected it to be zero because I had not yet connected the battery. Turns out, I connected the V-Sense input first, and that pre-charged the capacitors. To verify, I disconnected the V-Sense and discharged the capacitors with another bulb. I then connected the volt meter to the MP battery terminals and connected the V-Sense input again. It took about 10 seconds to charge the capacitors up to 13V through the V-Sense input. For comparison, my type 1003 incandescent bulb charges the capacitors in about 3 seconds.
I was a bit surprised that the V-Sense input is not electrically isolated from the Victron battery terminals. But at least they put a decent resistance in the circuit. If this was a documented feature of V-Sense, I would have just used that instead of building a pre-charge circuit. Oh well. It's already done.
Note: The MP rocker switch has to be in the O position (completely off) for this to work. If the rocker switch is in the I or II position, the capacitors do not charge.
One more ramification of this V-Sense behavior, when putting a seasonal MP II in long-term storage (RV, boat, summer cabin), you probably need to disconnect the battery terminals AND the V-Sense. You would not want to slowly drain the battery through the current path from V-Sense input to loads connected to the MP battery terminals.
In case you are not familiar with the term, V-Sense is an optional connection for the MP II, as described here: https://www.victronenergy.com/media...tml#UUID-fcc597e4-d20d-e11e-76a3-827a6b984e44
2) You cannot pre-charge the capacitor if the MP rocker switch is in the I or II position AND the MP mode is set to OFF in the Victron Connect app. In this configuration, the MP is trying to draw power from the battery terminals and this prevents the capacitors from charging with my type 1003 incandescent bulb. This behavior is the same, regardless of whether the AC-IN is powered or not. To charge the capacitors, I had to first put the rocker switch in the O position (completely off).
I discovered this when I pushed my momentary pre-charge button and the incandescent bulb stayed lit as long as I pressed the button. The expected behavior is for the bulb to turn on bright at first, then dim over a couple of seconds as the capacitors are charged to 13V.
I think these two examples show some of the advantages of using an incandescent bulb in a pre-charge circuit, instead of a power resistor. I would not likely have noticed either of these behaviors if I had been using a power resistor.
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