Marine starting batteries
- Thread starter Mosiah30
- Start date
MichaelK
Solar Wizard
Well yes, but they are not the optimal choice. You could use plain old automotive starter batteries if you really had nothing else, but they're an even poorer choice.
Marine starting batteries are a compromise; Their plates are thicker than a starting battery, but thinner than a true deep-cycle battery. They are better than nothing, but they will NOT last a long as a real deep cycle battery.
Don't buy them just because your local store has them in stock. Spend a bit more effort to find someone marketing real off-grid batteries in your area.
To answer the refrigerator question, assuming a frig uses ~1200WH per day, and you don't want to use more than 20% of your battery capacity, you need (1200W/system voltage) x 5 = battery size. Let's assume you design a 24V system. Your battery size should be (1200/24) X 5 =250AH. Four 6V golf-cart batteries would supply about that much capacity. Plug in whatever alternative numbers if you chose to make design changes.
To expand on this a bit more, to keep these batteries charged, you'll want to charge at about 1/10C, or 25A. To get 25A at a charging voltage of about 26V use 25A X 26V X 1.25FF = 812W. Three 260 to 275W grid-tie panels wired in series would produce this much power.
Marine starting batteries are a compromise; Their plates are thicker than a starting battery, but thinner than a true deep-cycle battery. They are better than nothing, but they will NOT last a long as a real deep cycle battery.
Don't buy them just because your local store has them in stock. Spend a bit more effort to find someone marketing real off-grid batteries in your area.
To answer the refrigerator question, assuming a frig uses ~1200WH per day, and you don't want to use more than 20% of your battery capacity, you need (1200W/system voltage) x 5 = battery size. Let's assume you design a 24V system. Your battery size should be (1200/24) X 5 =250AH. Four 6V golf-cart batteries would supply about that much capacity. Plug in whatever alternative numbers if you chose to make design changes.
To expand on this a bit more, to keep these batteries charged, you'll want to charge at about 1/10C, or 25A. To get 25A at a charging voltage of about 26V use 25A X 26V X 1.25FF = 812W. Three 260 to 275W grid-tie panels wired in series would produce this much power.
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I still like them and have used them in all kinds of applications, just like anything else some are better than others, AH rating is not to high on them so don't discharge them to deep and don't let them go dead from sitting to long and they usually last
For a limited use, they can work ok, but you won’t get much time with them, and they won’t recharge easily, and they will die soon if discharged deep and left low.
Hedges
I See Electromagnetic Fields!
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Starting batteries are good for high surge current. Automotive deep-cycle can handle more cycles than starting-only batteries.
If you run heavy loads only during the day, with enough PV to keep the batteries at float voltage, then draw no more than a few percent of capacity at night (e.g. a small LED lamp), then they could work well.
So this kind of setup could be good to run a refrigerator during the day (battery supplies surge current to start it), if you shut off the inverter as soon as PV production drops below consumption and battery starts to deliver current. (shut off inverter, not just load, because they draw significant current at idle.)
So I think a single automotive starting battery and a sine-wave inverter capable of supplying starting current (about 5x the label on the fridge) would work great for a refrigerator, if you came up with a suitable way to turn inverter off and on at the right time.
PV panels are cheaper than batteries, so "over panelling" to provide enough for the fridge all day long is practical. Ice is even cheaper, so a top-freezer will coast through the night economically.
If you run heavy loads only during the day, with enough PV to keep the batteries at float voltage, then draw no more than a few percent of capacity at night (e.g. a small LED lamp), then they could work well.
So this kind of setup could be good to run a refrigerator during the day (battery supplies surge current to start it), if you shut off the inverter as soon as PV production drops below consumption and battery starts to deliver current. (shut off inverter, not just load, because they draw significant current at idle.)
So I think a single automotive starting battery and a sine-wave inverter capable of supplying starting current (about 5x the label on the fridge) would work great for a refrigerator, if you came up with a suitable way to turn inverter off and on at the right time.
PV panels are cheaper than batteries, so "over panelling" to provide enough for the fridge all day long is practical. Ice is even cheaper, so a top-freezer will coast through the night economically.
Pretty much.
There are variables that make one chemistry better than another, but in general, LFP is hard to beat overall... by a large margin.
Hedges
I See Electromagnetic Fields!
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Probably. And those were the traditional batteries for off-grid solar homes.
But start with your application. How often do you expect to cycle them? How many watt hours to be supplied before recharging? What is the peak load (including starting motors)?
When in use
Well, you have mentioned several different types...
LFP isn’t a concern, most lead acid types off gas, and need containment...
Answer depends on what you will power, not the type of battery.
but, yes.
Pure sign wave is more efficient, and better on nearly anything.
Hedges
I See Electromagnetic Fields!
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If AGM, should be OK inside the house.
Batteries prefer moderate temperatures.
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