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cfdlighthouse avatar image

How to use lynx distributor for parallel wiring?

I am building a 4 - 12v 100ah lithium battery bank for my boat. I want to use the lynx distributor and shunt for the battery in. Does wiring and fusing each battery individually to the terminals of the distributor serve the same function as wiring the batteries in parallel and just bringing in one positive and one negative? meaning the bank remains 12v with a 400ah capacity with the added protection of fusing each battery?


Thanks

Lithium Batterybattery
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5 Answers
blutow avatar image
blutow answered ·

You can use the Lynx distributer as you describe, but keep in mind that the fuses in the Lynx are not completely protecting your battery wiring. You need a fuse at the battery if you want to protect the wire run to the lynx. My understanding is that it's not required by code (check for your region/application) to fuse at the battery depending on length of the wire run, but I think it's a good idea. The fuses at the lynx offer some protection going the other way since charge current can be flowing from the lynx to the batteries.

There is also a lynx "power in" module that is less expensive than the lynx distributer and designed to do exactly what you describe, but without the fuses and electronics. It appears that the intended design of the system is to use the "power in" to connect to batteries, then through the shunt, and then using the distributer to consolidate loads and charge sources. It's a pretty slick system. I decided to only use the distributer with a smart shunt and my batteries are consolidated at the switch and a traditional negative bus bar. I might have done with all the components, but I was tight on space. I wish they could incorporate a battery disconnect switch into the lynx power in some how, otherwise, you are stuck doing a switch for each individual battery feed.

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@blutow,

thanks, that makes sense. the batteries are rated at 150amps continuous out put, do you think if i use 2/0 cable for a less than three meter round trip, battery to lynx, back to battery, with a 175 amp mega fuse on each battery i would think that would protect the cable from both a charge and discharge current draw? i dont mind spending the extra money on a distributor for both the DC in and one for the DC loads if it makes it safer. i would rather over protect than have a fire.

blutow avatar image blutow cfdlighthouse ·

Yeah, 2/0 is more than you need, 0 would do it with margin to spare. Keep in mind that your batteries might be rated for 150a, but they will only be pulling 1/4 of the DC load on your system if you are running 4 batteries. I don't know what you are planning, but most people are never going to pull more than 250-300a continuous across the system, so less than 100a per battery. That said, It's not a terrible idea to size for worst case in the rare situation you might need to run on 1 or 2 batteries, particularly with such short wire runs. 175a mega fuses at the lynx are probably good, but I see a lot of folks go bigger on batteries runs. I'll defer others on that. I'd recommend going with something similar or bigger MRBF terminal fuses at the batteries.

@blutow,


right on thanks. As far as the loads go, i am trying to run my entire boat off the dc side either switched dc or inverter loads on the ac side, so all the normal dc loads, nav lights, cabin lights, cabin fans, vhfs, ais, charplotters, radar, auto pilot, etc,

I am also running two dc isotherm fridges, a isotherm freezer, four bilge pumps, water pump, saltwater wash down, and a hydronic heating system.


i have a seperate golf cart battery bank for the windlass

Ac inverter loads would be outlets, two burner induction stove, recirculating pump for the hydronic system, a 6000btu ac for the master cabin.


ill have 1400w of solar on the roof also running through two charge controllers back to the dc side

seb71 avatar image seb71 cfdlighthouse ·

You have a lot of loads for a 12V system.

@Seb71,

Yes, the boats 48 feet long, twin diesel engines, so lots of systems, not everything runs at once though so there are alot of intermittent loads based on whats happening, the only true constants are the refrigeration and the iso therms are really efficient, starting and windless batteries all charged off alternators, ill be using a multiplus so ill get passthrough when connected to shore power at the dock

seb71 avatar image seb71 cfdlighthouse ·

How do you plan to charge these batteries? Only from the PV?


Have you purchased anything yet? If not, look if a 24V or a 48V system could work for you.

The multiplus inverter charger will charge the batteries when connected to shore power, other than that yes the pv system, and yes i have thought about 24v, the issue then becomes the actual appliances if something were to break are hard to get if we are crusing, where 12v stuff is readily available at most marine stores, for 24 volt we would also need a dc to dc converter to power the 12v loads that are not available in 24v. It honestly just adds a layer of complexity to the boat where the benefit of lower amp draw, smaller wire size and some efficiencies of a 24v system are seemingly outweighed by the ability to source replacements

seb71 avatar image seb71 cfdlighthouse ·

In that case, I would say to go for a 48V system.

Have some spare DC-DC (48V-12V) converters on board (just in case) and you are set.

@Seb71,

Thanks for all the comments, I have never looked at 48v systems, just for the sake of redundancy and like i have said before sourcing non 12v parts/systems, etc especially outside of the us. what would be the benefit of a 48v system? since my boat is wired as a 12v boat how would I integrate 48v DC into it from a DC distribution standpoint?

Thanks

seb71 avatar image seb71 cfdlighthouse ·

You already mentioned lower current, smaller wire gauge (for DC wires). So smaller loses and cheaper and easier to manage wires.

Because of the huge currents involved, there is also a (quite low) limit on how powerful the 12V inverters can be. Probably this is the reason Victron does not even make a 12V inverter in the new Multiplus II series.

makes sense - thanks again for the feedback! I will go back and revisit the design to make sure i can optimize things

seb71 avatar image
seb71 answered ·

Make sure that all 4 positive wires (battery-lynx) are the same length and all 4 negative wires are the same length.

Also select the cross section of those wires based on expected current and with greater current carrying capacity than the battery fuses you will have there.

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Stefanie avatar image
Stefanie answered ·

Hi @Cfdlighthouse,

yes it does. Having them individually wired is the safer (and recommend) option because each battery is fused properly and in case a battery fails for whatever reason, you can simply disconnect the faulty battery from the Distributor and still have the other 3 working.

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cfdlighthouse avatar image
cfdlighthouse answered ·

Stephanie thanks thats what i thought i just want to confirm

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cfdlighthouse avatar image
cfdlighthouse answered ·

Excellent, that was going to be my next question about wire sizing and if the same lengths were important. The batteries will only be about 3 feet from the distributor. I am building an electrical room where one of the super small not useful showers was, where everything will be located, isolation transformers, multiplus, batteries, solar charge controllers etc.

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