Lithium batteries and new solar charger

Slownsy wrote:
Thinking if I get a Victron 100/75 MPPT controller I can go parallel and series for 24V and have less voltage drop and hopefully better charging, and also maybe adding 2 more panels.

I think you mean connect your panels in series, not parallel, for higher voltage. Yes, the voltage drop would be less of an issue.

600w aimed at a high sun on a nice day will supply 6 x 6.2 amps (you get Isc value worth of amps to battery with PWM) so 37.2 amps. With the panels lying flat you get fewer amps than that. How many amps will depend on your location and time of year.

(I have three 100w and have often seen 18.6 amps to the battery with them aimed. )

So the 30 amp controller is already not enough except the panels are flat so you are under 30 and the controller has not over-heated.

Your length of #8 is not an issue because voltage drop doesn't matter so much with PWM. Panel voltage will be close to battery voltage so you have room for the voltages drop without it bothering anything.

Voltage drop matters greatly with MPPT though. You benefit from the 24v needing thinner wire than 12v, but adding panels will increase the amps and it could be a wash so you could need fatter wire anyway.

Two LFPs will have fewer usable AH than four 6s, but with the solar you will only notice when there is an overcast for a couple of days so you need your battery bank as a "reserve" until the sun comes back out. It "depends" whether your two LFPs will be enough reserve, but it also "depends" whether the four 6s would be enough, so there is no way to be sure. You have to figure the odds on that. Obviously the odds are better in CA than in WA, eg.

Your plan will save a bunch of weight. That’s good!

Series them all for lots more volts and less loss.

If your voltage is adjustable on the PWM I would get the lithium batteries first and see where that takes you.

With 600W wired for 24V nominal it will output 37V max, 15A max.

#10 wire is fine for running 40V*15A input to MPPT. If there is already #8 routed through the roof, - better yet, but the difference will be negligible on 30ft one-way distance from panel to controller. The loss of energy in #10 or #8 will be few amp-hours a day, nothing to worry about.

Post-controller output will be 40-45A max. You don't need 75A MPPT for this, 45A MPPT will do, as long as it can handle 40V input.

Ok thanks so far, the existing batteries has 520A so useable 260A. Lithium 200A so a bit less, normal use about 75A so at least 2 days with no solar at all, and with my Magnum I can charge back up at max 125A. I will get the batteries and se how charger goes, it can also be set for 24V. So maybe have a bit of a play around.
For those who don’t know I am back in Australia and we don’t have many days whiteout any sun.
Frank.

Your two 100 LFP will actually have 80 usable each so 160 not 200 to compare with the 260. (you don't normally go below about 20% DOD)

Your controller is a 12/24 but being PWM that only means 24 if the batteries are also 24. To go 24 panel and 12 battery, you must have an MPPT with its buck converter that PWMs don't have.

Sorry I missed "maybe adding 2 more panels". That would be what - 1,000W total? When wired for nominal 24V, this would be 37V max, 25A max, post-controller about 73A. Then - yes, you need 75A controller. On the Morningstar website there was a calculator to figure out how many panels and in what configurations you may safely wire with MPPT.

Keep in mind that on sunny day in winter (this would be June-September in Australia) your harvest will be 1.5-1.8 times less than in summer. It might be sunny but the sun is low.

BLF13 the batteries are rated at 1.28 KWhr each. Yes thanks for reminder re PWM .
Almot currently 4/150V Renogy panels, and yes maybe will still go for 2 or more and MPPT controller. Yes sun is less in summer, but vi will head op north a bit.
Frank.