Bad Idea to Buy Batteries in Two Stages?

[Mic the Vegan YT]

Hey guys,

I am new to the DIY Lifepo4 topic but I am quite sure I want to use them for a 1,400-1,800 watt system for my tiny house on wheels. My problem is the tiny house is going to use a 9,000 BTU mini split and the run time / watt hours per day of this is almost impossible to estimate accurately (similarly sized AC systems burn around 2,600 watts a day but who knows: https://homeguides.sfgate.com/much-cost-run-portable-air-conditioner-102489.html). That's 216 amp hours at 12 volts if my math is right. We have grid as a back up if we run out of power.

So my question is, would it be a bad idea to buy a batch of about 400 ah worth of 12V batteries now and then if I need another 400 ah buy it later if I need it? I understand that these batteries become unbalanced through different use scenarios due to charge cycles. But would 30-40 charge cycles out of thousands really ruin it? I could even run the equivalent amount of charge cycles for the second batch of batteries with the first batch to give them the same amount of wear. The temperature will be constant. Has anyone thought about this? I didn't see it addressed at first glance so sorry if it was.

P.S. If anyone is concerned about such a high wattage 12V system my plan is to use 3 parallel 40+ amp mppt controllers. I would go 24V but I already have a 12V inverter and don't want that 12-24 DC converter energy loss.

Thanks,
Mike / Mic

 

[FilterGuy]

You can definitely add more batteries later. Particularly if the existing batteries have not been worked very hard. It sounds like you will know pretty quickly so I would not worry about it.

Meanwhile, even though your estimates may be off, doing some load calculations would still be worthwhile. Run the numbers with high and low assumptions and see what the range of sizes for the system pops out.

There is a tool here that can help you out. https://diysolarforum.com/threads/energy-audit-and-system-sizing-spreadsheet.3552/

 

[Supervstech]

Hey guys,

I am new to the DIY Lifepo4 topic but I am quite sure I want to use them for a 1,400-1,800 watt system for my tiny house on wheels. My problem is the tiny house is going to use a 9,000 BTU mini split and the run time / watt hours per day of this is almost impossible to estimate accurately (similarly sized AC systems burn around 2,600 watts a day but who knows: https://homeguides.sfgate.com/much-cost-run-portable-air-conditioner-102489.html). That's 216 amp hours at 12 volts if my math is right. We have grid as a back up if we run out of power.

So my question is, would it be a bad idea to buy a batch of about 400 ah worth of 12V batteries now and then if I need another 400 ah buy it later if I need it? I understand that these batteries become unbalanced through different use scenarios due to charge cycles. But would 30-40 charge cycles out of thousands really ruin it? I could even run the equivalent amount of charge cycles for the second batch of batteries with the first batch to give them the same amount of wear. The temperature will be constant. Has anyone thought about this? I didn't see it addressed at first glance so sorry if it was.

P.S. If anyone is concerned about such a high wattage 12V system my plan is to use 3 parallel 40+ amp mppt controllers. I would go 24V but I already have a 12V inverter and don't want that 12-24 DC converter energy loss.

Thanks,
Mike / Mic

What model mini split? What SEER rating? I might be able to estimate loads for you to better source it.

 

[Mic the Vegan YT]

What model mini split? What SEER rating? I might be able to estimate loads for you to better source it.

It's is a 9,000 BTU Pioneer inverter mini split (120V) which apparently has gone up in price.

• Cooling capacity: 9, 000 btu/h with 22.5 seer efficiency
• Heating capacity: 9, 800 btu/h with 10.5 hspf efficiency

Yeah I should just take the time to do the calculations. I have used that software before. It's just hard to want to do that when the house is almost done and I can get a real world measurement very soon. Thanks so much!

 

[ghostwriter66]

It's is a 9,000 BTU Pioneer inverter mini split (120V) which apparently has gone up in price.

• Cooling capacity: 9, 000 btu/h with 22.5 seer efficiency
• Heating capacity: 9, 800 btu/h with 10.5 hspf efficiency

Yeah I should just take the time to do the calculations. I have used that software before. It's just hard to want to do that when the house is almost done and I can get a real world measurement very soon. Thanks so much!

Let me know the numbers you come up with after you do your power-budget ... I have always been the person who thinks SOLAR + AIR CONDITIONING = HOLY GRAIL or maybe UNICORN would be a better word ... ... guess it all depends on what part of the country you are in -- and how cool you actually want to get it ... but once you come up with your Wh requirements please let me know ... i'm curious ...

PS -Cool Name -- mic the vegan -- for over a year before i came out here to South Texas from LA i was a VEGAN -- i later figured out that I was a social VEGAN and was doing it mostly because my boyfriend is a Doctor and all his friends were really into that .... So after I left LA and got to South Texas and started working with the oil hands and discovered this wonderful thing call BBQ !!! Holy Crap - I gained about five pounds - my face cleared up .... I got stronger ... but from a dietary side it has been a downhill slide since then .. i almost feel like I need to go to some BBQ AA meeting .... everytime my boyfriend flies out to visit I have to air out the apartment for several days prior to his arrival so the "meat" smell is gone ... and its getting harder to go back to LA and visit because of the dietary restrictions i am placed under ... sometimes i will sneak off for a "run" and wind up at a Burger Joint ... I think this relationship is doomed (with Him .. not the BBQ) ... anyway ... just wanted to say hi ...LOL

 

[Mic the Vegan YT]

You can definitely add more batteries later. Particularly if the existing batteries have not been worked very hard. It sounds like you will know pretty quickly so I would not worry about it.

Meanwhile, even though your estimates may be off, doing some load calculations would still be worthwhile. Run the numbers with high and low assumptions and see what the range of sizes for the system pops out.

There is a tool here that can help you out. https://diysolarforum.com/threads/energy-audit-and-system-sizing-spreadsheet.3552/

Cool, good to know. I'll have to get less lazy and just do the calculation it seems. My really sketch calculations put our total summer use 437 amp hours a day so with 2 or 3 days of no sun plus inverter loss it's obvious that I need a way bigger bank than 400 amps: https://docs.google.com/spreadsheets/d/1yDhEhGvj2TDpTrtyLaGHaQGB6UW224TWbvDD_brpYXM/edit?usp=sharing

Either way, even if I know I am under sizing the battery bank initially for cost purposes I'm happy that I can add more batteries. I can but $1,300 of batteries to start and another $1,300 in a couple months instead of slamming it all at once.

 

[Mic the Vegan YT]

Let me know the numbers you come up with after you do your power-budget ... I have always been the person who thinks SOLAR + AIR CONDITIONING = HOLY GRAIL or maybe UNICORN would be a better word ... ... guess it all depends on what part of the country you are in -- and how cool you actually want to get it ... but once you come up with your Wh requirements please let me know ... i'm curious ...

For sure, let me add that the tiny house is extremely well sealed, has a energy recovery ventilator and pretty good spray foam insulation. It is in the Midwest where we can get really hot summers so it is going to be interesting. I might have to open up the old HEED software (Home Energy Efficient Design).

 

[Supervstech]

Cool, good to know. I'll have to get less lazy and just do the calculation it seems. My really sketch calculations put our total summer use 437 amp hours a day so with 2 or 3 days of no sun plus inverter loss it's obvious that I need a way bigger bank than 400 amps: https://docs.google.com/spreadsheets/d/1yDhEhGvj2TDpTrtyLaGHaQGB6UW224TWbvDD_brpYXM/edit?usp=sharing

Either way, even if I know I am under sizing the battery bank initially for cost purposes I'm happy that I can add more batteries. I can but $1,300 of batteries to start and another $1,300 in a couple months instead of slamming it all at once.

I do not think you will need anywhere close to 437Ah...
That would be 6KWh a day.
My condo in Charlotte with all electric and a crappy 14seer heat pump eats about 11KWh a day...

A 9K 22seer mini should have your needs dialed in around 2.8KWh a fay... less if you are frugal.

 

[FilterGuy]

PS -Cool Name -- mic the vegan -- for over a year before i came out here to South Texas from LA i was a VEGAN -- i later figured out that I was a social VEGAN and was doing it mostly because my boyfriend is a Doctor and all his friends were really into that .... So after I left LA and got to South Texas and started working with the oil hands and discovered this wonderful thing call BBQ !!!

I was on a business trip to Houston once and one of my colleges asked the desk clerk at the hotel where we could go for vegetarian. The guy looked at her and in all seriousness said. "Lady! Your in Texas!!!"

 

[Mic the Vegan YT]

I do not think you will need anywhere close to 437Ah...
That would be 6KWh a day.
My condo in Charlotte with all electric and a crappy 14seer heat pump eats about 11KWh a day...

A 9K 22seer mini should have your needs dialed in around 2.8KWh a fay... less if you are frugal.

Sorry, I should have specified that my entire house requirements were 437 Ah and actually my AC estimate was 2.6 kwh a day as you can see here so we are right around the same place! https://docs.google.com/spreadsheets/d/1yDhEhGvj2TDpTrtyLaGHaQGB6UW224TWbvDD_brpYXM/edit?usp=sharing

So 233 Ah a day on cooling. Thanks!

 

[Mic the Vegan YT]

Let me know the numbers you come up with after you do your power-budget ... I have always been the person who thinks SOLAR + AIR CONDITIONING = HOLY GRAIL or maybe UNICORN would be a better word ... ... guess it all depends on what part of the country you are in -- and how cool you actually want to get it ... but once you come up with your Wh requirements please let me know ... i'm curious ...

PS -Cool Name -- mic the vegan -- for over a year before i came out here to South Texas from LA i was a VEGAN -- i later figured out that I was a social VEGAN and was doing it mostly because my boyfriend is a Doctor and all his friends were really into that .... So after I left LA and got to South Texas and started working with the oil hands and discovered this wonderful thing call BBQ !!! Holy Crap - I gained about five pounds - my face cleared up .... I got stronger ... but from a dietary side it has been a downhill slide since then .. i almost feel like I need to go to some BBQ AA meeting .... everytime my boyfriend flies out to visit I have to air out the apartment for several days prior to his arrival so the "meat" smell is gone ... and its getting harder to go back to LA and visit because of the dietary restrictions i am placed under ... sometimes i will sneak off for a "run" and wind up at a Burger Joint ... I think this relationship is doomed (with Him .. not the BBQ) ... anyway ... just wanted to say hi ...LOL

RE the vegan part. I have a whole channel vegan health stuff. My guess is that you weren't getting enough calories as a vegan which would have anyway diving for high calorie animal products. Anyway, that's a totally different topic. https://www.youtube.com/channel/UCGJq0eQZoFSwgcqgxIE9MHw

 

[Stephen Shreds]

RE the vegan part. I have a whole channel vegan health stuff. My guess is that you weren't getting enough calories as a vegan which would have anyway diving for high calorie animal products. Anyway, that's a totally different topic. https://www.youtube.com/channel/UCGJq0eQZoFSwgcqgxIE9MHw

First I thought it was the silicone valley dude but remembered the your channel. This is a really random place to find you.

 

[Mic the Vegan YT]

First I thought it was the silicone valley dude but remembered the your channel. This is a really random place to find you.

Ha yup. Well I also have a tiny house channel called TIY (tiny it yourself) so this stuff is right up my alley

Stoked to get this solar going.