SOLAR

We have 420 Watts of solar panels and 480 AH of battery--4 GCs and a 2000 Watt PSW inverter. Our microwave draws 160 amps from the batteries when running through the inverter. We ONLY use it at most 2 minutes at a time and let the batteries recover a little. I would not use an electric toaster--cheap stovetop ones do a great job.

Many have told you that 2 group 27 batteries are inadequate an I agree. We used to have 4 group 24s and they were marginal. If there is room for 2 GSs it would work, but watch battery voltage as the microwave runs. 3 group 31 true deep cycle might be your best option if you have room.

As far as balanced wiring of 3 12 v batteries is concerned, positive at one end and negative at the other is pretty close and when you do you battery maintenance you could swap them around every three to six months. Balanced wiring is only of concern if high current present either in use or charging.

To wire 3*12 requires 4 short interconnect cables. If you connect both load and the charger at opposite Pos/Neg, it will be a "proper" charging, i.e. balanced. (Well, almost balanced). 100A current of MW will split into more manageable 33A per battery.

AGM can support higher current than flooded before the voltage under high load drops too much. And - yes, they can be charged a little faster than flooded, even "normal" AGM like Deka. Lifeline AGM can be charged MUCH faster but with mere 500W solar this is not important, IMO.

And here I have three rather large 8-D's wired like that.

scrubjaysnest wrote:

Almot wrote:

scrubjaysnest wrote:

4 GC-2's or a 450Ah battery bank ...

3*100AH AGM might work too, if there is no room for 4*GC.

Wiring 3 12 volt batteries to properly charge is going to be ugly. With the cost of AGM's this will be a key point.

I really don't think it's that big of a deal to charge three. The resistance of AGM's are low and charge acceptance is high. I have three smaller AGM's paralleled in one bank. The (-) charge wire is on one battery and the (+) wire is on another, last in line. I haven't measured exactly the health of all three but they seem to be hanging in there well.

Is there something I'm missing?

Almot wrote:

scrubjaysnest wrote:

4 GC-2's or a 450Ah battery bank ...

3*100AH AGM might work too, if there is no room for 4*GC.

Wiring 3 12 volt batteries to properly charge is going to be ugly. With the cost of AGM's this will be a key point.

scrubjaysnest wrote:

4 GC-2's or a 450Ah battery bank ...

3*100AH AGM might work too, if there is no room for 4*GC.

I guess I should have said the MW is 900W so a little less toaster 1200w. really don't want to run anything else just warm up food or toast a frozen waffle.

Lets look at a little math here from your figures: MW, 900 watts,120 vac equals 7.5 amps times 10 to get it to dc amps is 75 amps. It ignores inverter losses.
Two 12 volt 80 Ah batteries in parallel is 160 Ah. We don't want to go below 50% SOC, or use over 80 Ah. If the inverter is 85% efficient then your current draw is ~86 amps.
Now the good side is we don't usually run the MW for an hour but there are battery factors that may not let you get that kind of current even for a short time. A high current like that may cause the inverter to exceed it's low voltage cut off point for one.

The math indicates 2 100 watt panels at a 5% ROC are sufficient for a 106 Ah battery bank. 5% is the very lowest you want to recharge the batteries at per most manufacturers.

Bottom line is like others said you will need more solar and a much larger battery bank.
4 GC-2's or a 450Ah battery bank wants 424 watts of solar for the 5% ROC. My suggestion would be 2 250 watt panels @24 volts Vmp feeding a MPPT controller and you might be ok.

Colo Native wrote:
I guess I should have said the MW is 900W so a little less toaster 1200w. really don't want to run anything else just warm up food or toast a frozen waffle.

You need a bigger battery bank, to run MW or toaster. 900W MW draws 1200-1300W, if not more.

Solar-wise your 5x6 ft space is (almost) enough for 2*250W panels. Each panel is 65"x39". They would require 35-40A MPPT controller (this is the only thing that your solar shop got right). Panel surface will be 3"-4" above the roof, so if you stay 14-16" from A/C and 8-10" from other structures, there will be none or very little shading.

Again - others said this already - solar of this size will NOT run MW or toaster. It will charge the battery, and the battery will run inverter. 500W solar should be enough to recharge the battery after careful use of MW and toaster, but you need a bigger battery bank. Your 2*80 AH bank is too small.

And, please don't tell that you "don't want to run anything else" :) - your other loads will consume another 40-50 AH a day, in addition to 40-50 AH consumed by MW and toaster.

If you are not in a hurry, you can reheat leftovers in a double-wall pot on propane stove. It's slow but it works.

Your plan is fine. Yes it will work even if a bit marginal.
With a microwave or any electronic controls on the toaster I recommend sine wave inverter only.
I recommend Go Power inverter although you can find others for less if needed.

You need big batteries and the inverter. And a charge wire (large) from your alternator. Not solar.

Charge while you drive.