2200 watts of solar on the roof?

[MTVR]

Dreadlocks (and/or other smart people), can you recommend some brands and maybe even some specific components? I don't know what brands are good, and which are crap. I'm struggling to figure out Sterling's line of 24VDC-24VDC chargers. I don't think I need waterproof. If the mini-split is drawing 9 amps at 115VAC, that would be just under 45 amps at 24VDC- would a 50 or 60 amp B2B charger be enough to keep up with the mini-split and even have a little left over to recharge the house battery bank? Would it be reasonable to expect to pull 45 amps (or so) from a large-case 150-amp alternator at idle?

I was also looking at a similar B2B charger by Powermax.

 

[MTVR]

Could go the other way, setup a AC only inverter @ 80% size.. wire em up to a AC-ON switch that turns em both on at same time...

I was envisioning one large inverter primarily to run the mini-split, but that inverter would also available to power any other energy hogs, if I turn off the mini-split long enough to run them.

And then another smaller inverter to run any other smaller 120VAC stuff.

But the house lighting, water pump, etc. would be run at house voltage (tentatively 24VDC).

 

[dreadlocks]

Your going to need to limit your DC charging off engine at 0.4C of your LFP size, so for 2 100AH 12v BB's in a series thats 40A charge rate @ 24v.. if you go with 4 batteries, its 80A charge rate @ 24v..

you can parallel most DC chargers just fine if you need more, I know Victron's Orion DC chargers can be horizontally scaled to whatever you need.

Given your AC needs and all that I think 200AH of LFP @ 24V is going to be more appropriate, if you go with less than that you'll have way too much solar and way too much alternator current avilable to your LFP bank, and you need that current so you can run the AC with minimal battery requirements.

 

[MTVR]

I guess another way to do a house battery bank would be four Trojan T105 GC2 6V AGM batteries in series. That would give me 217Ah out of a 24V bank, and if I understand correctly, I would safely be able to use about the same number of Ah from that, as I would from a pair of 12V 100Ah Battleborn lithiums in series.

The weight would be no problem for me.

But then I have to live with how long it takes to charge (especially the final part) non-lithium batteries.

 

[MTVR]

So how do I limit DC charging? By selecting a charger based off of the stated capabilities of the charger, or is it programmable?

 

[Joe917]

I guess another way to do a house battery bank would be four Trojan T105 GC2 6V AGM batteries in series. That would give me 217Ah out of a 24V bank, and if I understand correctly, I would safely be able to use about the same number of Ah from that, as I would from a pair of 12V 100Ah Battleborn lithiums in series.

The weight would be no problem for me.

But then I have to live with how long it takes to charge (especially the final part) non-lithium batteries.

That would not even be remotely close to your battery needs. If you use 6v deep cycle at the charge rates and loads you have, you will roast 4 batteries in no time. 4 Rolls Surette 235ah (the top quality 6v gc ) will max out at 45 amps 24v, anything more will shorten battery life. Trojan 105's will have a lower performance.

 

[dreadlocks]

Either the charger has a fixed current output that needs to be at or under your max desired charge rate, or it needs to be programmable to limit that current.. Victron's SmartSolar's can program the current rate you want them to max output, but the Orion DC-DC chargers you cannot.. you get those sized to your needs

 

[MTVR]

Copy, and copy.

So maybe two Battleborns in series makes the most sense at this point.

...and thank you...

 

[MTVR]

If I had no sun, and was running the engine to power the mini-split off a 40-amp DC to DC charger to stay at that .4 charging point that you mentioned, and the mini-split was drawing about 45 amps at 24VDC through the inverter, then my house battery bank would make up that 5 amp deficit by slowly discharging, right?

What If I exhange the 12K BTU mini-split for the 9K BTU version? It draws about one amp less (8 vs. 9) than the 12K BTU version at 115VAC, which at 24V would get me down from about 43 amps at 24VDC to 38 amps. Do you think that 5 amps less consumption in this scenario be worth giving up 33% more cooling capacity? That would be tough to accept. I don't think I'd be running the engine for hours and hours to do this. By the time we account for inverter losses and incidental interior LED lighting, we're already gonna be back over that 40A threshold and discharging the battery anyway, just not quite as quickly.

FWIW, We're planning 3.5" polyiso insulation all around (with some thermal bridging), as well as the most efficient windows and doors that we can afford...

 

[MTVR]

Oops- and I forgot to mention the "R" word. We have a dorm fridge. The only spec I can find so far, is 54 watts...

 

[MTVR]

We absolutely do not plan on spending time in traditional campgrounds.

But as a last-ditch charging option, if we are able to "access" a standard electrical outlet, I was thinking of including an external 15A shore power connection, to feed a 24V charger for our house battery bank. A 15A connection would be plenty to power a 40A 24VDC charger. That charger could even be temporarily repurposed to recharge the truck's batterys in an emergency. Given our scenario, is there any point to using a standard 30A RV-type external connection point, supplemented by a 15A adapter?

 

[dreadlocks]

more or less, there's gonna be the conversion losses of the inverter, ~10% is +4.5A all on its own.. plus other potential areas for losses, your pushing it.. you could perhaps have a couple DC chargers inline and only turn on the parallel ones when you need the amp boost because of AC? hrmm, would have to think how to make that idiot proof tho.. mebe have a DC charger that only kicks on when the AC is turned on or something, if engine's not running it wont do anything.

If you wanna run your air con off opportunistic power sources you should do a 30A external feed... I avoid campsites too but sometimes ******** happens, my very first site w/my trailer was in a f'n KOA.. but I had just driven across the midwest for 12h to buy it, and was in the middle of a large metro with another +4-5h drive to nice camping country.. so tired and done driving for the day I towed it 10 miles to the Koa camp and thats where I broke her in at, we were gone before the sun came up... sometimes yeh just need to take whatever you can get even if yeh dont wanna.

 

[Alloy]

That would not even be remotely close to your battery needs. If you use 6v deep cycle at the charge rates and loads you have, you will roast 4 batteries in no time. 4 Rolls Surette 235ah (the top quality 6v gc ) will max out at 45 amps 24v, anything more will shorten battery life. Trojan 105's will have a lower performance.

My $0.002..... I'd go with Lithium before spending the $$$ on Rolls.

 

[Alloy]

I guess another way to do a house battery bank would be four Trojan T105 GC2 6V AGM batteries in series. That would give me 217Ah out of a 24V bank, and if I understand correctly, I would safely be able to use about the same number of Ah from that, as I would from a pair of 12V 100Ah Battleborn lithiums in series.

The weight would be no problem for me.

But then I have to live with how long it takes to charge (especially the final part) non-lithium batteries.

To achieve the same usable amp hours a FLA bank would need to be 400A to be the same as 200Ah of BB Lithium

A FLA bank would need to be 1600Ah to put the same 200A load as BB Lithium without affecting life of the FLA batteries. Our FLA bank is 900Ah so each time I run the microwave (140A) I'm shortening the life of the bank.

 

[Alloy]

If I had no sun, and was running the engine to power the mini-split off a 40-amp DC to DC charger to stay at that .4 charging point that you mentioned, and the mini-split was drawing about 45 amps at 24VDC through the inverter, then my house battery bank would make up that 5 amp deficit by slowly discharging, right?

What If I exhange the 12K BTU mini-split for the 9K BTU version? It draws about one amp less (8 vs. 9) than the 12K BTU version at 115VAC, which at 24V would get me down from about 43 amps at 24VDC to 38 amps. Do you think that 5 amps less consumption in this scenario be worth giving up 33% more cooling capacity? That would be tough to accept. I don't think I'd be running the engine for hours and hours to do this. By the time we account for inverter losses and incidental interior LED lighting, we're already gonna be back over that 40A threshold and discharging the battery anyway, just not quite as quickly.

FWIW, We're planning 3.5" polyiso insulation all around (with some thermal bridging), as well as the most efficient windows and doors that we can afford...

Here's some info on polyiso

Cold-Weather Performance of Polyisocyanurate - GreenBuildingAdvisor

The ability of insulation products to resist the flow of heat changes with temperature. Most insulation products — including fiberglass batts, extruded polystyrene (XPS), and expanded polystyrene (EPS) — perform better at low temperatures than high temperatures. At lower temperatures, there is...

www.greenbuildingadvisor.com