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alaskannoob asked

Hooking 48V Multiplus II 8000VA to batteries for first time...will this pre-charge the caps?

Before taking the 2 x Multiplus II 8000VAs and our 2 x Smart Solar 450/200-tr units up to the off grid homestead and hooking them up to our 8 x US5000 batteries, I figured I'd use on-grid life to try to program them in advance.

So I bought 4 x 12V 50AH lithium batteries and wired them in series to make a small battery bank. I'm thinking that should be enough power to run the MP since it won't be inverting and won't have any loads, enough for me to program it.

But I'm nervous about this pre-charging the caps thing. I couldn't find a resistor where I'm at, and I like the idea of hopefully seeing the caps get charged, so I bought 2 x 24V 70W incandescent bulbs that I'm going to wire into series for a 48V 140W pseudo-resistor.

I expect that when I touch the negative terminal with those bulbs acting as resistors, they will light up and eventually or maybe quickly extinguish which will tell me the caps are charged, so that I can hook up the negative terminal and switch the MP on without all the sparks others talk about.

Is this a bad plan? Many thanks for any help!

Multiplus-II
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Rob Duthie avatar image
Rob Duthie answered ·

Hi

Dont worry about that to much, once you turn on the breaker it over in a split second no bangs cracks nothing.

When the power is turned off you have to re power at some stage anyway.

Never had a issue with the installs i have done to date on Victron Multiplus2 etc.

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nickdb avatar image
nickdb answered ·

If you have mppts, just configure those first, and power them first, they Will precharge from solar then the battery can be enabled with no issues.

Just don’t do it via AC in, that is unsupported and puts a lot of stress on the input relays.

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alaskannoob avatar image
alaskannoob answered ·

Got er done. Used a 100W 120V light bulb on the negative. It turned on for a half second and went right out. Hooked it up, no sparks, everything worked fine. Thanks for the advice!

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Fideri avatar image Fideri commented ·

@AlaskanNoob Great. But I have 2 questions:

1. Why did you choose to use 1 bulb of 100w 120v (I'm guessing AC) instead of the initial plan of 2 DC bulbs of 24v each wired in series to give you 48v? This makes more sense to me but you obviously did it right.

2. Could you outline the steps you followed step by step? Specifically, I was planning to put the bulb in the positive line but I see you put it in the negative line.

Thanks

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alaskannoob avatar image alaskannoob Fideri commented ·

Couldn't find DC bulb. Not sue why I put it on the negative, probably just saw somebody else do it online. I did not put much thought into any of this.

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alaskannoob answered ·

I have an EG4 chargeverter hooked up to my bus bar, so I think I'm going to try to use that to avoid this issue. I'll fire it up at 52V and 100A output, then flip the switch to the bus bar with the batteries off. That should fill up the caps and hopefully I'm not transferring the inrush issue to the EG4 (if I am, that's just one set of cables to the bus so I'll wire in one of those switches and a resistor for its connection). Then I'll dial the EG4 back to 52V and 10A to make sure the caps aren't depleting and turn the batteries on. We'll see if that works...

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