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Old 03-06-2024, 09:44   #1
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New owner questions about 48v, solar and battery problem

I have a 33ft sailboat that was converted to all solar and electric by the previous owners. A 48v Thunderstruck electric motor, 800w of Solar, 4 lifepo batteries connected in serial. The batteries are intended to be the drive energy and the house bank, with a DC converter in the system as well, and a small 1200w inverter. I realize there might be additional problems with the way it is currently configured, but I have one main question.

It seems that right now, the mppt is energizing the DC system, even when the battery switch is off, and no power is coming form the batteries. I'm definitely new to marine and solar electric systems, but pretty familiar with the terrestrial version. Is this normal, that when I want to work on any of the dc components, I have to shut down both the mppt controller, and the batteries? That doesn't seem right, and an electrician I hired and paid too much for, wasn't any help. The wiring seems to follow all of the guidelines I find from Victron, so maybe that really is just the normal way things are supposed to work. If not, where do I start the troubleshooting? I'm including a couple of pics. Thanks in advance.
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Old 03-06-2024, 10:31   #2
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Re: New owner questions about 48v, solar and battery problem

Victrons advice is to connect the batteries first then solar panels and reverse when disconnecting. So whilst your system works it's not right. Risk, suppose the MPPT decides you have 24v system and you connect your 48v batteries to it when next on board. How long before you realise something is wrong and solar isn't charging.

How about a sign on the battery master switch saying shut down MPPT first?

We have a hybrid LFP/FLA system and just leave the FLA battery on charge when not on board only disconnecting the LFP. It could run the bilge pump if needed but we seem to only have dusty bilges needing a polish every year.

How big are those LFP batteries? a 1200w inverter presumably Victron is neither fish or fowl. Given the 48v battery bank, a decent sized inverter offers some real advantages for larger loads like electric cooking.

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Old 03-06-2024, 10:40   #3
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Re: New owner questions about 48v, solar and battery problem

There doesn't seem to be a "standard" way, as many boats connect many things differently. The most thorough would be to have a buss bar, and every item on the bus bar has it's own disconnect switch. So, you could disconnect the battery, but still have solar power the vessel loads. Or, disconnect the vessel loads, and still have solar charge the battery. Or any combination of what you want to do.
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Old 03-06-2024, 11:06   #4
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Re: New owner questions about 48v, solar and battery problem

Yes that is typical although there is no universal standard. The battery isolation switch isolates the battery from the rest of the system nothing else.

You may wish to install a PV disconnect switch. Note that MPPT should never be disconnected on the output side while under load. So ay switch should be on the input side between the panels and the MPPT.

Quote:
Is this normal, that when I want to work on any of the dc components, I have to shut down both the mppt controller, and the batteries?
Yes and possibly AC charger as well.

There is no way for one switch to handle everything certainly not in any way that would be obvious. If the AC charger and MPPT were connect to the battery on the battery side of the isolation switch the isolation switch would disonnect that circuir from the rest of the boat but the batteries really wouldn't be isolated. You would have a complete energized system. Someone not understanding that atypical use could make disastrous assumptions.

So ideally every power source (battery, MPPT, DC to DC charger, AC charger, etc) has its own isolation switch and disconnects it from everything else.
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Old 03-06-2024, 13:24   #5
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Re: New owner questions about 48v, solar and battery problem

Thanks for the info. I guess it just seems like the solar should be charging the batteries, and the batteries supplying power. So that severing the battery to DC panel and isolating the battery output, would cut dc power entirely.
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Old 04-06-2024, 10:46   #6
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Re: New owner questions about 48v, solar and battery problem

The solar should be direct to the battery. (Wirh fuse / breaker ) The battery switch shuts off loads. The solar will keep charging batteries if the battery switch is off. Which means you can shut the switch off and leave the boat. Abd it will still charge. If the solar was after the switch. The loads would be directly powered by the solar if the battery switch was shut off. So loads would be still be trying to work. Which you don’t want.
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Old 14-06-2024, 06:47   #7
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Re: New owner questions about 48v, solar and battery problem

Quote:
Originally Posted by smac999 View Post
The solar should be direct to the battery. (Wirh fuse / breaker ) The battery switch shuts off loads. The solar will keep charging batteries if the battery switch is off. Which means you can shut the switch off and leave the boat. Abd it will still charge. If the solar was after the switch. The loads would be directly powered by the solar if the battery switch was shut off. So loads would be still be trying to work. Which you donít want.
That's what I thought, but it's wired just like victron recommends, and one of the other comments above indicates that's how it should work. I am pretty confused.
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Old 14-06-2024, 07:10   #8
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Re: New owner questions about 48v, solar and battery problem

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Originally Posted by Enkiboat View Post
That's what I thought, but it's wired just like victron recommends, and one of the other comments above indicates that's how it should work. I am pretty confused.
There is no right answer. It is just a switch it doesn't care. The question is what do you want the switch to do.

Most people would assume a battery disconnect switch to do exactly what the name says and that is disconnect the battery from everything. Effectively being the same as disconnecting the battery cables just with less work. Most people would be surprised to have the battery isolation switch off and seeing current flowing into the battery.

Technically could you have a switch that does something else and it work? Sure. It is just a switch.

Now ABYC says you should have a means to disconnect the battery from the electrical system however battery charger to include PV charging can be on the battery side of the switch so it is compliant either way.

Quote:
11.6.1.2 BATTERY SWITCH
11.6.1.2.1 A battery switch shall be installed in the positive conductor(s) from each battery or battery bank with a CCA rating greater than 800 amperes, or 100 Ah if CCA is unavailable.
EXCEPTION: Trolling motor conductors connected to dedicated trolling motor batteries provided with overcurrent protection at the battery and a manual means of electrical disconnect separate from the trolling motor controls.

NOTE: Conductors supplying the following may be connected to the battery side of the switch:
1. electronic equipment with continuously powered memory;
2. safety equipment such as bilge pumps, alarms, CO detectors, and bilge blowers;
3. battery charging equipment;
4. impressed current systems; and
5. propulsion ECU battery constant power.

11.6.1.2.2 A battery switch shall be mounted in a readily accessible location as close as practicable to the battery.

11.6.1.2.3 Battery Switch Ratings - The 30 sec rating of a battery switch shall not be less than the maximum cranking current of the largest engine cranking motor that it serves. The minimum continuous rating of a battery switch shall be the total of the ampacities of the main overcurrent protection devices connected to the battery switch, or the
ampacity of the feeder cable to the switch, whichever is less.
I like to keep things obvious. If I turned the battery disconnect switch on a boat in preparation of removing, checking, or servicing a battery I would expect to see no current across the battery but I would check first because on boats the only standard is there is no standard.
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