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Float losses are roughly the same as charge losses. LFP round trip efficiency is ~99%.

Converting AC to DC is $x efficient and converting DC to AC is $y efficient. The values for $x and $y depend on the hardware used. A good quality inverter charger in bypass mode is nearly 100% efficient. Are the losses significant because you will be paying for the AC power from the mains?

I don't trust any FET based BMS to protect against a dead short as I've said repeatedly in this thread. Since I've seen some evidence that the breaker is dc rated with sufficient breaking capacity at sufficient voltage I will trust the breaker. I have suggested that Signature solar should reword...

I disagree.

What mess? Please be specific.

"The included breaker is not a guarantee of battery protection. Size and install the correct over current protection for conductors and battery if not included with the product." -- https://signaturesolar.com/content/documents/EG4/EG4-LL 48V-24V Manual-1.2.0.pdf

@SignatureSolarJames @Will Prowse ^

For reference this is the manual bit that I'm referring to. https://diysolarforum.com/threads/single-vs-multiple-class-t-fuses.57889/post-731057

"Rated Working voltage Ue:DC60V/110V（1P） Service short-circuit breaking capacity Ics:15kA/7.5kA. Ultimate short-circuit breaking capacity Icu:20kA/10kA." That is good. Please update the manual to get rid of the weasel words.

Cool, as soon as they update the manual I will be satisfied.

If you trust the BMS then you don't need high aic over-current protection for the feeders. its nice to have but not necessary. The feeder does need to be protected but a fuse of lesser breaking capacity would be fine. Of course the fuse should ideally be as close to the start of the wire as...

That is where we differ. I don't trust any fet based bms and since Signature solar doesn't stand behind their breaker, I don't trust the breaker either.

Does that mean you trust the server rack battery breakers to protect the individual batteries?

Do you mean 6 inches? If you mean 6 feet, isn't that a bit arbitrary?

Bottom line is I don't trust BMSs, and I see any un-protected wire as a danger that can and should be avoided. The feeder/branch design pattern is to the best of my knowledge a time tested best known method. In a dead short scenario, if the BMS fails I think its between possible and probable...

@AHTrimble what does you being a firefighter have to do with anything?

@AHTrimble are your batteries made by trophy? They have a different breaker in them. If yes, I suggest you talk to the owner of trophy and finding out breaking capacity of those breakers. Remember breaking capacity is voltage specific. We are looking for > 4000 amps at > 60 volts. Ideally >...

The batteries have smart BMSs which you can use for administrative disconnect. The circuit breakers add significant resistance, significant expense and just add clutter. This guy said it best https://www.goodreads.com/quotes/19905-perfection-is-achieved-not-when-there-is-nothing-more-to It...

@the overall topology concept is called feeder and branch. The lynx components are made to work with this topology. The batteries connect to the power-in, which doesn't have fuses because the batteries are supposed to be fused at source. The optional shunt tracks all current in and out of the...

https://en.wikipedia.org/wiki/Kirchhoff%27s_circuit_laws The summary of this article is, current in = current out. Nope I can't. Just assume I'm not from this planet. Use a small wire try for <8 inches. I already told you to get rid of them. I don't care what you have seen. Its been...

Get rid of the circuit breaker box between the lynx power-in and the batteries. Use a 250 amp class t fuse as close as possible to each battery positive terminal Get rid of the class t fuse between the power in and the shunt Connect the the backplane of the lynx power-in to the lynx_shunt Use...

@AHTrimble please post your updated topology and I will critique it. As I said before the whole topology has to be considered.

The class t fuse between the busbars. Just join the backplanes of the lynx components.

IMO that is a waste of a class t fuse. It seems to me, this whole thread and many others like it is about people trying to save money. IMO over-current protection is the last place to try and save money.

That is only part of the mission. The other mission is to protect the wire which means the fuse must be at the battery. The most important mission is protect the battery from a dead short. Nobody wants an electrolyte volcano. Should be fine. Requires 1/0 awg wire or better for ABYC rules.

Also I'm guessing that the breaking capacity is ~5000 amps at 60VDC.

The lynx power in has to be modified to accept fuses. Also, batteries should be fused as close to the positive terminal. This minimizes the chance of an un-protected short.

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Are the 3 way switch positions... off one on one and two on ?

The drawing is hard to follow but it appears that the house and starter battery are in parallel, which moots the delineation. Am I interpreting that correctly?

Something doesn't smell right and I don't mean the electrolyte in the container.

I think its safe to say that the Victron lynx system is the most popular distribution system for experience people. I just found these. https://www.littelfuse.com/media?resourcetype=datasheets&itemid=3511fb09-2c05-43b4-a093-f9f22b9f3cdd&filename=mega120v-sf56-datasheet-v16.2 AIC of 2500 amp at...

Also the further away from the battery, the higher the path resistance.

High AIC fuses are only required on the battery(feeder) circuits. The branch circuits can get away with lesser fuses. The branch fuses can break on over-current, but are not guaranteed to break a dead short. In a dead short on a branch the BMSs will likely cascade trip if the branch fuse...

Its got electrolytes!