MPPT/DC to DC Charger for Trailer Build

Grit dog wrote:

halhawkins wrote:


No the generator is what is going into the shore power.

Why couldn't two batteries with 115ah each handle 90a load?

Gotcha, genny = shore power.
Batteries 2 115ah 12V FLA, SLA or AGM batteries have theoretically 230ah total at brand new 100% charged.
So at 90ah of draw, no charging, they are in need of being recharged in less than an hour (keeping with the 70-80% min charge for max service life) or in just over an hour they are dead as doornails at 50% SOC.

Rough numbers, you need to be feeding the 2 batteries, idk, around 50-60amps of charging just to barely hold your own in a perfect world scenario. Happens to also be that around a 25A rate is about the max you can charge a typical 12V deep cycle like you're proposing.

So if you had a 60A converter charging full tilt the whole time, theoretically you have "just enough" charging and capacity to maintain that load and not kill or shorten the battery life significantly.

Say you're pulling about 10A AC from the genny to run the converter, you're still looking for another 25A AC (per your calcs) for the A/C and AC outlets. 15A is LOW for the A/C when it cycles.
So all in, you have marginal battery reserve power ("marginal" being generous), full max charging out of a BIG converter that basically will try to charge the batteries too fast (it actually won't, it'll be putting all its power straight to the load basically) and it will all require a 4kw + generator, basically putting you out of the "quiet" generator market without spending big bucks there.

So yes with a big generator and a big converter, you can make the milquetoast battery capacity work, but everything will be running full throttle at basically 100% load and duty cycle.

All this without also considering inefficiency losses due to converting and inverting power.

Simple solution is to provide more DC power storage capability since you're already spending a bunch of money and give the batteries and the rest of the hardware a break.

This assuming your power draw calcs are right and not low, which makes the situation worse, or considerably high which lessens the issue.

There's a reason there's a sort of "practical limit" on what your proposing which is pulling more juice than most all RVs and many homes and why "houses" don't use DC power and why solar power arrangements have huge battery banks when they're providing significant power.

Youd be better off figuring out how to NOT pull most of your power DC and get it most/all to AC and find a nice big generator setup like a diesel Onan to run the whole show and keep the batteries for what they were intended for.

Thanks. FYI the rooftop A/C (15k Recpro unit) I have is specced for a 15a breaker.

Would adding 2 more batteries suffice then? I already have the 30A generator, so I'd rather not have to switch to a 50A generator. That's a big part of the issue.